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June 29

Physics in different engine designs

2 engines have the same number of cylinders, engine displacement, stroke ratio (etc). One is shaped like a V with 2 cylinder heads while the other is shaped like an I with one cylinder head. Why is it that the I shaped engine has more power output in the same measured timeframe as the power output of the V shaped engine? 64.170.21.194 (talk) 02:22, 29 June 2017 (UTC)[reply]

More cylinder heads implies more mass to accelerate and decelerate with each stroke, wasting power. (Even if the design allows most of the kinetic energy to be reused, there's still going to be losses in the process, due to friction, etc.) StuRat (talk) 02:26, 29 June 2017 (UTC)[reply]

The cylinder head is bolted to the engine block and does not accelerate. Please ignore the incompetent advice of the above editor. As to the Op's question, it is far too hard to explain in a short thread, and plenty of counter examples can be found. Greglocock (talk) 03:59, 29 June 2017 (UTC)[reply]

I believe sturat may have been talking about the moving components in the cylinder head (such as the valve train). "Please ignore the incompetent advice of the above editor" that's rather rude and hypocritical. You claim it's too hard to explain and that there are plenty of counter examples yet you fail to post a single reference. I'd say greglocock's advice is more incompetent.. at least sturat was contemplative. 64.170.21.194 (talk) 04:35, 29 June 2017 (UTC)[reply]

Well i'll let the unicorn and rainbow specialists sort this out, as an engineer I don't do much with either. However, I'll give you two bits of actual help. In the example you have specified the BMEP of the V engine is less than that of the I engine. The reasons why BMEP varies are many, far too many for an answer like this, but include friction, pumping losses, volumetric efficiency, valve timing, exhaust back pressure, ignition timing, and mixture. John B Heywood wrote a book that is both readable and useful "Internal Combustion Engine Fundamentals". Greglocock (talk) 06:20, 29 June 2017 (UTC)[reply]

There is credence to the inertia of the number of valves in the cylinder head. Hemi engines have two valves per cylinder. They have a reputation for high horsepower, but they aren't the best out there. There are cylinder heads with many smaller valves. The valves barely open, allowing them to open and close faster than the two-valve Hemi engines. Because the valves can open and close faster, the engine can run faster and more efficiently. It doesn't make a difference for a consumer vehicle, but if you are trying to maximize HP per cylinder, you will want to go for 32-valve cylinders like the AMG (and double the HP of a HemiV8 with a little inline 4). 209.149.113.5 (talk) 15:04, 29 June 2017 (UTC)[reply]

Hemi engines can have any number of valves they like. Four is just as common as two, and has been for decades. Five and six aren't that unusual either. Andy Dingley (talk) 15:52, 29 June 2017 (UTC)[reply]

I have seen 4-valve hemi (all lower case) engines from Europe, but I've never seen a 4-valve Hemi (upper case Dodge TM) engine. I did see a 4-valve mod for the 5.7L Hemi, but the heads weren't hemispherical. You were basically modding a hemispherical head into a wedge head. 209.149.113.5 (talk) 12:13, 30 June 2017 (UTC)[reply]

see Single-cylinder engine: it only says that it "will often deliver the maximum power possible within a given envelope", not that "the I shaped engine has more power output than as the V shaped engine"

The latter may be true for some ideal engine, but for a number practical reasons multicylinders are still the common real thing.

Now simple geometry (ratio of volume against surface) says that for the same displacement the 2-cylinders (and even more so with more cylinders) has

more surface of the cylinder, meaning
- more leaking heat, needing to be cooled instead of contributing to gas pressure and work
- more cylinder mass to stand the same pressure
- more piston mass
more piston friction perimeter
twice as much valvetrain to move, twice as much pipes in and out etc. each being smaller but MORE than half those of the 1-cylinder, the combine volume and mass are bigger

It seems to me that this explains the claim

Gem fr (talk) 10:41, 29 June 2017 (UTC)[reply]

What do you mean by "an engine" here? A conceptual engine, differing only in one detail? Or a particular model of engine, built and running?

In the first case, there is no difference. Certainly no fixed saying that V engines are more or less powerful, as a law of nature. In the other case, there are a great many other factors that will differ between the two, and we've no information on those.

Otherwise, what Greglocock said. Andy Dingley (talk) 11:09, 29 June 2017 (UTC)[reply]

How can two engines have the same number of cylinders if one has two cylinder heads (two cylinders) and one has one cylinder head (one cylinder)? 209.149.113.5 (talk) 14:38, 29 June 2017 (UTC)[reply]

The first clause says, "same number of cylinders", although isn't clear how many this is. It's common for V engines to have two cylinder heads, inline engines to have one head, and for this head to serve as many cylinders as needed. Andy Dingley (talk) 15:01, 29 June 2017 (UTC)[reply]

I think this is just blurring the definition of the "cylinder head." I have a V8. So, I can take the long block with four big bumps on it and call it a cylinder head, but I can also take that off. Under it is a valve cover, coil, and spark plug mount for each cylinder on that side of the engine. I can call each of those a cylinder head. So, I could say that my V8 has two cylinder heads - one on each side, or I could say that it has 8 cylinder heads - one for each cylinder. Because the number of valves per cylinder, which you'd expect to find in the cylinder head assembly, is pertinent to this discussion, I immediately think of the cylinder head as being the assembly independently mounted to each cylinder, not the cover that goes over all the cylinders. But, I can easily see why someone would use a different definition, which is perfectly valid, especially on engines where you can't separate the cover and independent assemblies. 209.149.113.5 (talk) 15:09, 29 June 2017 (UTC)[reply]

There is a surprising number of Engine configuration. A cylinder can have no head (Opposed-piston engine ). 2 cylinders can share the same cylinder head, as Blooteuth illustrated above. And, while it seems pointless to use several cylinder heads on a single cylinder, it doesn't seem impossible (as per the joke :"according to feasibility test, it can done; according to idiotability test, it would be stupid"). So the number of cylinders and the number of cylinder heads are not necessary the same (plus the pertinent point raised by 209.149.113.5 above). Gem fr (talk) 15:17, 29 June 2017 (UTC)[reply]

Yes, it is a blurring of what is meant by the word "head". It can mean anything from "the part of the cylinder where the valve(s) and spark plug(s) are" to "the entire assembly of wires and hoses bolted to the top of the cylinder block." I personally shouldn't have jumped in with what I was thinking of by "head." 209.149.113.5 (talk) 15:36, 29 June 2017 (UTC)[reply]

Monobloc engine and junk head might both be of interest. We don't have an article on narrow-angle V engine, but there are some on Lancia V4 engine (a series of barely related engines, thrown into one WP article) and also VR6 engine.

For an engine of n cylinders, there are usually either 1, n/2 and n cylinder heads used, depending on design. These days it is usual to have one head per cylinder bank, i.e. one for an inline engine, two for a V and almost never any more than this. Large diesels (ships and railway locos) still often use a single head per cylinder. Pre-war engines (and US fire engines) with non-monobloc cylinder blocks used to use n/2 or n/3 heads (one head to two or three cylinders), but that's pretty rare nowadays.

"Cylinder head" does have a clear definition, albeit a broad one. You can't have two per cylinder. Andy Dingley (talk) 15:52, 29 June 2017 (UTC)[reply]

Again: Cylinder head. Blooteuth (talk) 15:58, 29 June 2017 (UTC)[reply]

There is a design (that I don't think is used) in which the piston slides back and forth in a cylinder with spark plugs on each end (with associated valves). Depending on your definition of "head", you could call that a two-head cylinder. I believe we've beat the vagueness of "cylinder head" to death by now. Some people have their own definition and violently disagree with any other definition. Some people (like me) prematurely jump to the conclusion that others are using the same definition, but agree that there are other definitions. Others smartly ask exactly what meaning is being used before continuing the discussion. 209.149.113.5 (talk) 12:13, 30 June 2017 (UTC)[reply]

Sorry, yes, you can have a double-acting cylinder, although these are unsuccessful in medium- or high-speed internal combustion engines. I should have stated "you can't have two heads per combustion chamber". Andy Dingley (talk) 14:55, 30 June 2017 (UTC)[reply]

What hasn’t be pointed out here clearly, is that V engines have a greater 'power to weight ratio' because they are more compact than a straight inline, thus weigh less for the equivalent horsepower. So the engines don't produce more power per displacement (whether it be cubic centimeters or cubic inches) but more power per unit mass of the engine. Aspro (talk) 16:02, 29 June 2017 (UTC)[reply]

Why do V engines implicitly have lower mass? There is no evidence for this. For water-cooled engines, it's more likely the opposite. Andy Dingley (talk) 17:41, 29 June 2017 (UTC)[reply]

It must be clear from the illustration that the "compactness" of the V engine is the reduced length of a line of cylinders at the cost of increased width. The duplication of surrounding hardware (manifolds, valve gear, cooling fins or channels, etc.) inevitably decreases 'power to weight ratio' but the squarer engine shape enables a more compact vehicle design than an inline engine with the same cylinders. Blooteuth (talk) 12:32, 30 June 2017 (UTC)[reply]

The OP specifically stated the following condition: "One is shaped like a V with 2 cylinder heads while the other is shaped like an I with one cylinder head." Therefore all of the nonsense above about a separate cylinder head for each piston and multiple heads per piston is irrelevant.
The OP asked the following question: "Why is it that the I shaped engine has more power output in the same measured timeframe as the power output of the V shaped engine?" All of the nonsense above about the weights and dimensions of the engines is irrelevant. He doesn't care about that. His comparison is simply on the basis of two different engines, of which one may be several times the weight of the other but the displacement is the same. He is not making the comparison on the basis of power to weight ratio.
Now, what do we make of the comparison that he did actually state, "more power output in the same measured timeframe"? I don't know what it means, since power is the rate of doing work. Is he asking why the I has better acceleration?
If we assume that he might mean simply "more power output", is it really a fact that an I-engine always has more power output than a V for "the same number of cylinders, engine displacement, stroke ratio (etc).", or has he posed a question that's based on a fallacy? This is the question that must be answered first. If it can be shown that even one production V-type engine develops more power than an I-type of the same number of cylinders, displacement, stroke etc, then the premise for his question breaks down and we need proceed no further. Akld guy (talk) 01:51, 1 July 2017 (UTC)[reply]

Blooteuth already, far as i know correctly, pointed out that "there is no fundamental difference in Engine efficiency" between the different design layouts. That is true with one exeption! Opposed-piston engines can be more effective because they are ideally suited to reach a much higher Compression ratio and thereby a higher combustion efficiency. However they are also in general more difficult to design and operate and that is why other common combustion engine concepts, even the likely exotic Wankel engine, are more commonly build and used. --Kharon (talk) 05:25, 1 July 2017 (UTC)[reply]

Resolved

Changing the refractive index of air (without heating it).

Hello, again!

I've recently been studying optics as it relates to the translucency of various materials (water, air, etc.), and something has now crossed my mind, namely, how the visible spectrum reacts to changes in the state of said material. Permit me to elaborate.

Distilled water, for instance, remains perfectly clear when still. But when agitated, its optical properties distort, and it becomes considerably less transparent. Also, when air is heated considerably (say, in the vicinity of a pizza oven) it also tends to appear `blurry` from a distance.

I cannot help but wonder, though, does there exist any known method for changing the refractive index of air without heating it? Sc., can one—somehow—make otherwise regular air distort light rays between 400 nm and 700 nm in wavelength, and make whatever stands behind it appear `blurry` to an observer.

Thank You. Pine (talk) 08:41, 29 June 2017 (UTC)[reply]

You could add water vapour, or some other gas to air. Another way is to vary the pressure with sound waves. Turbulence due to strong wind would also cause variations in refractive index. see Schlieren photography and Astronomical seeing. Graeme Bartlett (talk) 09:56, 29 June 2017 (UTC)[reply]

———Another way is to vary the pressure with sound waves.———

Now that really intrigues me! What kind of device, in your expert opinion, would most adequately do such (in a space approximately 30 cm X 15 cm X 10 cm), would said sound waves be audible/infrasonic/ultrasonic, and—lastly—would this in any way harm people physiologically?

Please forgive my impetuosity, but this has been gnawing at me for a good long while, now. :)

Pine (talk) 10:19, 29 June 2017 (UTC)[reply]

look at Acoustic resonance#Resonance of a tube of air, i think it will answer your questions since it give you the formulas you need. Ordinary audible sound device can do the trick, however i don't know how much power is needed for the effect to be seen without special apparatus. May be it requires harmful power, or even too much power. Gem fr (talk) 13:31, 29 June 2017 (UTC)[reply]

Given the speed of sound in air 345 m/sec, I speculate the possibility that a strong longitudinal ultrasonic emission over 200 kHz (inaudible) could by modulating the air's refractive index create a virtual Diffraction grating with 1.5mm spacing that when illuminated with very far Infrared light (invisible, equivalent to millimeter radio wavelengths or EHF near 300 GHz) could bend the unseen light into a diffraction pattern. Blooteuth (talk) 22:18, 29 June 2017 (UTC)[reply]

Heat in itself induce very small change in the refractive index of air. Main effect of heat is changing the density of air.

You want to produce a mirage, you should look at the article. It has an artificial mirage example, much easier to do with water than with air. Gem fr (talk) 13:31, 29 June 2017 (UTC)[reply]

I also omitted to mention that changing wavelength changes refractive index a bit. This explains the green flash. Graeme Bartlett (talk) 21:45, 29 June 2017 (UTC)[reply]

Dual SIM

I'm thinking of getting a dual sim Android phone to avoid having to swap SIMs at the border. I only ever need one SIM active at any given time. I don't need the "dual standby" feature.

1. Is this even possible on Android?

2. Does the phone consume extra power if I do it this way?

3. Can I switch the SIMs in software? As in, at the border can I just go through the menus and choose "change primary SIM" and the active SIM will switch? If I had to pop the SIM tray out and physically swap the SIMs then it's no better than my current routine. Scala Cats (talk) 17:24, 29 June 2017 (UTC)[reply]

If you don't get an answer here, try: Computing desk. —2606:A000:4C0C:E200:0:0:0:3 (talk) 20:30, 29 June 2017 (UTC)[reply]

1 Yes - many Android phones have this feature.

2 Yes - it will need to power the extra SIM and use some radio power to contact the cell sites to see if the sim can connect to any network or not.

3 yes go to the configuration section and select the SIM for making calls, texting, and data. You should be able to take calls on either SIM if the network allows it. Graeme Bartlett (talk) 21:42, 29 June 2017 (UTC)[reply]

For point 1, a lot depends on whether the OP is just saying they don't need but don't mind having dual standby, or they refuse to use a phone with dual standby. If it's the later, I don't think it's accurate to say "many" have the feature. The vast majority of dual SIM phones for Android are dual standby as that's in much more demand than switchable only/single standby dual SIM. Switchable only/single standby dual SIM Android phones do exist, but your selection will be a lot more limited.

As for 2, if it's not a dual standby phone I'm not convinced it does consume more power, or at least not more in a measurable way. (The actual chips used for such phones may make a different but that's a lot more complicated. Not that a single standby phone really needs a special chip other than some part to enable SIM switching but different phones have difference chips.) If you are using a dual standby phone then yes it will use more power when both networks are enabled, although for most use cases on Android the extra power usage isn't really that significant. I'd also note that per my earlier point, comparing a dual SIM dual standby phone to one without is actually complicated by the fact that at a minimum, the chips used tend to differ. In reality many phones don't have single and dual SIM options so the differences are likely to be more than just the chops. Power usage differences will probably often depend on these other factors much more than having two networks. (You can of course simply not put in a 2nd SIM, or disable it to compare power usage from having dual standby and single standby on a specific dual standby phone.)

Note that in any case, probably most dual standby phones will also allow you to selectively disable the either SIM or network. However this may not change the preferred network for various features, you may have to do that separetely. I just tried and that's how my Alcatel Flash 2 functions, and I believe. (By comparison if you actually take out the SIM it's generally smart enough to only try and use the SIM that's in the phone.) This is most significant for the data since it's simply not available which you may not appreciate especially if you aren't actively using the internet or you're using an app with some offline features. (Of course if you actively use a lot of data, you also should consider the difference between dual standby as are most phones, and dual active. Same too if you're calling a lot. But if you're not interested even in dual standby then this wouldn't matter.) By comparison at least on my phone, I get a specific warning I need to enable the SIM if I try to SMS or call with a disabled SIM.

While disabling one SIM or network may save power, as I said above it's not likely to be that significant. In fact depending on how often and how long you take to switch I wouldn't be surprised if you could easily end up using more power by disabling one SIM given LCD screen power usage. So unless you have some good reason why you don't want dual standby other than power, I'm not convinced there's a good reason to go around disabling the other SIM.

Also it may not be necessary to choose a preferred SIM for calls or SMS, with both phones I've owned you have the option to be asked everytime. There may also be some smarts where it tries to call back via the same number for a missed call and likewise for a SMS.

One final point note that many dual standby phones with 4G/3G especially those using the various cheap MTK chipsets only have one radio for the 4G/3G part. For obvious reasons, this is generally tied to the SIM used for data. This is fine and likely reduces power usage slightly if the both of network supports 2G with equal coverage but if at least one either doesn't have 2G at all or has poorer or no coverage in some areas then the dual standby can be a lot more limited for obvious reasons. Since the OP isn't interested in dual standby this doesn't seem that important.

Nil Einne (talk) 03:04, 30 June 2017 (UTC)[reply]

On what size and time scale can undisturbed air's refraction index appreciably vary?

A specific tiny region of air can have x molecules now and x+1 molecules the next picosecond, no xenon atoms now and 1 the next picosecond.. Sagittarian Milky Way (talk) 17:42, 29 June 2017 (UTC)[reply]

If the volume dV is small the number of particles in it will obey Poisson distribution with its parameter

\lambda =ndV

, where n is the average particle number density. The root-mean-square deviation will be

{\sqrt {\lambda }}

. The characteristic time will be

\sim {\sqrt[{3}]{dV}}/v

, where v is the average particle velocity. Ruslik_Zero 20:21, 29 June 2017 (UTC)[reply]

Air at STP contains approximately 2.5 x 10²² molecules[1] per liter. Air's refractive index for visible light of wavelength of, say, 430 nm is largely determined by the cubical wavelength volume (430 nm)³ = 8 x 10^-17 liter containing about 2 million molecules. Blooteuth (talk) 21:40, 29 June 2017 (UTC) edited Blooteuth (talk) 12:15, 1 July 2017 (UTC)[reply]

The density of air is 2.5 x 10²² molecules per liter, not 2.5²². (430 nm)³ is 8 x 10^-17 liter, not 8^-20 liter, and that volume contains about 2 million molecules at STP, not 2000. CodeTalker (talk) 22:51, 29 June 2017 (UTC)[reply]

Bioluminescent fungus

What is the biological/evolutionary advantage for bioluminescence in fungi? They certainly don't need to "find each other" in the dark, and don't rely on insects to spread their spores (or do they?). 2606:A000:4C0C:E200:0:0:0:3 (talk) 20:26, 29 June 2017 (UTC)[reply]

I'm not sure if there are advantages, although there may be (possibly someone who knows more about fungi can expand). As long as this trait is not harmful enough to prevent enough organisms from reaching maturity and reproducing to keep the species alive, it can persist. —Paleo Neonate - 21:54, 29 June 2017 (UTC)[reply]

It is a rather expensive evolutionary advancement, and shouldn't have happened without an appreciable benefit. 2606:A000:4C0C:E200:0:0:0:3 (talk) 22:27, 29 June 2017 (UTC)[reply]

From the article: "The physiological and ecological function of fungal bioluminescence has not been established with certainty. It has been suggested that in the dark beneath closed tropical forest canopies, bioluminescent fruit bodies may be at an advantage by attracting grazing animals (including insects and other arthropods) that could help disperse their spores. Conversely, where mycelium (and vegetative structures like rhizomorphs and sclerotia) are the bioluminescent tissues, the argument has been made that light emission could deter grazing." Dragons flight (talk) 22:51, 29 June 2017 (UTC)[reply]

Thanks. (Don't know how I missed that -- skimmed too fast, I guess). 2606:A000:4C0C:E200:0:0:0:3 (talk) 23:20, 29 June 2017 (UTC)[reply]

If a pigment can absorb light at a certain frequency, it can also transmit light at the same frequency. I only just read that in certain cases bioluminescence may be an accidental byproduct of metabolic "leakage" where pigments that absorb light during the day leak light at night when enough free energy is present. I'll see if I can find the source. Basically, the pigment is useful enough during the day that its radiating a little cool light at night does not harm the organism sufficiently to select against the trait. μηδείς (talk) 01:44, 30 June 2017 (UTC)[reply]
The source is Raven, Biology of Plants 6th Ed. p 122.

μηδείς (talk) 14:16, 30 June 2017 (UTC)[reply]

As an aside: For those living in the northern hemisphere. This is a good time of year to go looking for bioluminescents. Tip. Pick a very hot day and for two hours before sunset, sit in total darkness; in order that ones eyes can become fully dark adapted... (OK, if one has red-goggles to hand you can you use them to preserve your night vision but who carries around a pair of red googles?). For the first time one witness it -it is is awesome. It is just like walking into Santa’s grotto (but without the the little elves). The other bioluminescent phenomena that is easy to witness is shell-fish et. al. on a hot night. The bacteria on prawns and such like, can glow surprisingly brightly. The bacteria producing this bioluminescent is not pathogenic, so don't panic - as I am still here to tell the tale. Aspro (talk) 19:09, 30 June 2017 (UTC)[reply]

out of place comment to non-native English speaker
The following discussion has been closed. Please do not modify it.
Yes but look what it's done to your ability to construct sentences with proper grammar, punctuation and proofreading. Akld guy (talk) 21:17, 1 July 2017 (UTC)[reply]

We used to camp in the early fall regularly in Atlantic County NJ, and the firewood that was left over from the previous year (i.e., rotten logs) always had bioluminescent bracket fungi. You could even see it when the fire was down to embers in the cabin. μηδείς (talk) 03:16, 1 July 2017 (UTC)[reply]

Study that measures response time and cognitive perception

I remember a specific study that measures the response time of participants. Basically, the conclusion of the study is that, when the delay between the participant's pushing-on-the-button and the light (signal?) giving off is very short, then the participant will perceive that he/she is not causing the light to turn on. In other words, there must be some time between the action and response to be perceived as the effect of a cause. What is this study? 50.4.236.254 (talk) 22:50, 29 June 2017 (UTC)[reply]

The relevant Wikipedia article is: Mental chronometry. A Google Scholar search of your title finds several such studies. 2606:A000:4C0C:E200:0:0:0:3 (talk) 23:25, 29 June 2017 (UTC)[reply]

Just so you know, mental chronometry is too broad to be a relevant answer to the question. And I don't see how a Google scholar search of the title will lead to a precise result. You have to read the description in the OP to understand fully the question. I'm afraid that I may have misused some words in the title, so I don't even trust my own writing. However, I try to describe my recollection in the description, which is more important. 50.4.236.254 (talk) 00:49, 30 June 2017 (UTC)[reply]

I don't think you are describing the findings correctly, but I think you may be referring to PMID 15702960. That paper is not freely accessible, but you can read an account of the methods and findings in https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4614377/. Our article on the illusion of control also discusses these studies to some degree. Looie496 (talk) 17:31, 30 June 2017 (UTC)[reply]

I believe you are probably thinking of Benjamin Libet's immensely influential work on voluntary action; although your description does not perfectly match the methodology of his most famous iteration of the test for volition, nor the conclusions taken from it, the description is close enough to suggest these are probably the experiments you are remembering. Snow ^{let's rap} 01:31, 2 July 2017 (UTC)[reply]

Here's an additional description of the experiment, from a talk by Susan Blackmore: [2] (and with the greatest possible irony, the video is going to lag a little bit before taking you to the right moment in the presentation, despite my adding the time code!). Does that sound like what you were looking for? Snow ^{let's rap} 01:56, 2 July 2017 (UTC)[reply]

That video is about an experiment that measures the time it takes for someone's will to become movement, or something like that. No, I swear my memory was about clicking on a button. If the button is clicked, then it will light on. If it's not clicked, then it's not on. The experiment tests the length of time on perceived cause, meaning that if the length of time between the action and response is short enough, then the person will think that she/he is not causing the response. But your video sounds equally interesting, though. 50.4.236.254 (talk) 16:37, 2 July 2017 (UTC)[reply]

Longevity of fluorsecent lights

Does turning a fluorsecent light off once a day for a few minutes and then on again shorten its life compared with leaving it on all the time? Thank you bunnies!!! Anna Frodesiak (talk) 23:15, 29 June 2017 (UTC)[reply]

Yes, it incurs wear on the filaments and the ballast. Turning it off if you know you're going to turn it on again in a few minutes is best avoided. --47.138.161.183 (talk) 00:20, 30 June 2017 (UTC)[reply]

Thank you! :) :) :) Anna Frodesiak (talk) 00:31, 30 June 2017 (UTC)[reply]

Now you are entitled to say: "See, I told you so!"

- 2606:A000:4C0C:E200:A975:997:5261:F444 (talk) 20:14, 30 June 2017 (UTC)[reply]

June 30

Unfertilized ovary and ripened ovary in angiosperms

What is the difference between a womb and an ovary? Can an ovary transform into a womb if it is fertilized and bears seeds? If sperm means seed, then what is a seed inside a sweet fruit? Maybe angiosperms have two kinds of seeds? 2600:387:0:80F:0:0:0:83 (talk) 12:58, 30 June 2017 (UTC)[reply]

Maybe the "seed" is really the offspring. But the sperm is the true seed? 2600:387:0:80F:0:0:0:83 (talk) 13:52, 30 June 2017 (UTC)[reply]

Angiosperms are flowering plants - they do not have wombs or produce sperm. The female part of a flower called an ovary, containing the ovules in which the female egg cells are produced. The male part of a flower is the stamen, which produces pollen. When the egg call is fertilised by pollen, the ovule develops into a seed, while the ovary becomes the fruit which contains the seeds. That is the basic pattern - though there are many variations - see Plant reproductive morphology. Wymspen (talk) 18:00, 30 June 2017 (UTC)[reply]

Rh factor in other animals

Apart from humans and macaques, does rhesus factor exist in other animals too? Our article doesn't clarify that. Also, interesting know which species evolved it first (maybe monkeys, maybe not). --212.180.235.46 (talk) 14:20, 30 June 2017 (UTC)[reply]

The Rh blood group system is actually very complicated having 50 distinct defined antigens in humans. In common parlance, Rh⁺ often means only the presence of Rh antigen D. The D antigen only has close analogs in gorillas and chimpanzees but the representatives of the broader family of Rh proteins can be found in essentially all animals. [3] Dragons flight (talk) 16:01, 30 June 2017 (UTC)[reply]

Until what level - genus ? family ? order ? class ? בנצי (talk) 19:35, 30 June 2017 (UTC)[reply]

All animals generally means all parts of the kingdom Animalia Nil Einne (talk) 03:35, 1 July 2017 (UTC)[reply]

This fact is amazing, if it's true (did Dragons flight mean alike ?), since it means that the corresponding part of the genome is extremely preserved in evolution. In other, more practical words, it's highly & fundamentally crucial to survival. בנצי (talk) 08:47, 1 July 2017 (UTC)[reply]

Not necessarily. It just has to not be harmful. Since blood transfusions don't happen in nature, and the placental barrier (and similar barriers in non-placental mammals and other animals) protects offspring of other blood types, it doesn't seem to be very dangerous to have different blood types. Therefore, natural variation produces many varieties. StuRat (talk) 13:35, 1 July 2017 (UTC)[reply]

Didn't either of you at least glance at the source? It says RHAG homologs are found in non-erythroid tissues, which shouldn't be surprising since not all animals have circulatory systems or erythroid cells. It does appear there is some not yet well understood (at least per that source which was last update in 2005 so possibly not very reliable on this) functionally related selective pressure. Again this makes sense since in the absence of a selective pressure, random chance would suggest they would have been lost in at least some lineages. RH orthologs and paralogs are also found in slime mold further supporting this idea. (So actually it probably goes beyond animals.) Nil Einne (talk) 16:25, 1 July 2017 (UTC)[reply]

You can see some of the homologues by looking at HomoloGene link in the article. The protein is basically a big ammonium transporter domain, though some other functions are noted in the MGI data. (Causing blood transfusion incompatibility is not actually a function, just something people discovered when they started fooling with Mother Nature!) Functionally MGI (I think) mentions that red blood cell ghosts (the membranes, in other words) don't transport ammonia as well in knockouts. There is an Rh deficiency syndrome associated with RHAG or RH mutants [4]. I suspect, but did not check, that the cell fragility has to do with the hindrance to transporting ammonium ions. Since ammonium is a basic nitrogenous waste its transport is a universal issue of animals. (Plants have an opposite reason to transport it) Wnt (talk) 11:34, 2 July 2017 (UTC)[reply]

Thanks. Ammonium transporter was mentioned in the other source although I didn't explore it very well. As you said, blood transfusion incompability is an irrelevant "bug" in nearly all circumstance so isn't likely to result in a selective pressure although Rh disease probably could do so. (So that part of StuRat's answer was mostly correct.) But there's clearly some positive selection pressure which preserved and expanded the range of Rh proteins. Nil Einne (talk) 13:51, 2 July 2017 (UTC)[reply]

July 1

Hydrogen versus acetylene as illuminating gas

If a residential light fixture was designed to burn acetylene gas with a mantle and globe, would it also provide light burning hydrogen? Would a different flow rate be needed to provide the same light? If no mantle were used and it just had a flame, would the color and brightness at the same flow rate be similar to acetylene? I realize that either gas would pose a hazard of explosion or asphyxiation and the question is a basic science question rather than a search for advice on practical lighting methods. Edison (talk) 20:51, 1 July 2017 (UTC)[reply]

Neither of these are suitable for use with gas mantles. They, especially hydrogen, work better with the older limelight method, of a bulk incandescent element.

Acetylene produces significant soot on burning. This makes its combustion inefficient, but also makes for a bright flame, as the soot is incandescent. It has long been used in simple fishtail burners for caving and some mining (but not usually coal mining). Hydrogen is generally dreadful as an illuminating gas. It usually needs to be burned with an oxygen supply, but this is often available anyway, when the hydrogen is produced electrolytically from water (see Brown's gas too). Andy Dingley (talk) 21:13, 1 July 2017 (UTC)[reply]

Note that hydrogen gas burned with excess oxygen and nothing else is almost invisible. See illustration. As such, you would need to add something, or reduce the oxygen ratio, to use it for illumination. StuRat (talk) 21:29, 1 July 2017 (UTC)[reply]

The Hindeneburg flames, reportedly orange, also involved the doping compound used on the skin. StuRat (talk) 23:30, 1 July 2017 (UTC)[reply]

Yes a mantle will produce light from hydrogen because it is making the mantle incandescent. The flow rate for hydrogen though, would need to be higher as it has a lower calorific value than acetylene. Any flammable gas will heat the mantle to incandescence. Mostly used today is butane, propane and methane. In past time it was often petrol/gasoline vapour, paraffin/kerosene vapour, coal gas, and of course acetylene. As anyone knows, who have done any acetylene welding, acetylene only produces soot when it is too rich ( i.e., not mixed with enough air. Turn up the regulator on the acetylene welding bottle and the tadpoles of soot stop being produced -even though no oxygen from the oxidiser bottle is beind suplied. An acetylene lamp therefore, is designed to produce a jet which courses vortexes in its flow to mix in enough air to mix and proving a bright flame with no smoke. Limelight came before mantles were develop. Hydrogen burning with oxygen contains no carbon (the incandescence of which provided the bright yellow light) so will only glow blue when the heated oxygen lases down to a lower energy state. One can see this when one looks close at the wick of a candle. The inner shell of the flame is blue. The blue light is also being emitted up further up in the yellow flame but is swamped from human eyes by the brightness of the incandescent carbon. The airship skin was painted with aluminum and iron oxide. Very similar to Thermite and very flammable. Aspro (talk) 23:48, 1 July 2017 (UTC)[reply]

Is polynosic rayon particularly sensitive to chlorine bleach ?

Virtually all my clothes say not to use bleach. Advice which I completely ignore, as most (typically cotton/polyester blends) seem to be able to handle chlorine bleach just fine, giving me sterile, odor-free clothes at minimal cost. However, I have one shirt which is 70% polynosic rayon/30% polyester, and it virtually dissolved in bleach. So, I seem to have discovered that, for this one fabric, the advice to avoid chlorine bleach is legit. Is this known to be the case ? Is it all rayon or only the "polynosic" variety ? Do we have a list of which fabrics REALLY can't be bleached ? (If it includes cotton/poly blends then I know they are lying.) StuRat (talk) 21:14, 1 July 2017 (UTC)[reply]

To "lose one's shirt" is a common expression for making a bad bet. Polynosic is the trademark[5] for a type of microfiber that is a blend of advanced polyester and rayon fibers. Characteristics include luxurious soft touch with a drapeable hand.[6]. Karin Fjellman advises that bleach only works successfully with natural fabrics such as cotton, rayon or linen, (it's also ok with polypropylene fabric) while bleach affects polyester in such a way that cannot be undone or repaired. If you absolutely must whiten polyester, the best alternative to bleach is a good fabric paint. Blooteuth (talk) 23:13, 1 July 2017 (UTC)[reply]

Are you sure you don't have rayon and polyester confused ? My observations are the exact opposite of what you describe. The only other explanation is that the labels on most of my clothes list the wrong materials. StuRat (talk) 23:50, 1 July 2017 (UTC)[reply]

You may check my sources and you would still have a shirt if you had obeyed this: "Machine wash cold with like colors. Tumble dry low. Do not bleach." Blooteuth (talk) 14:24, 2 July 2017 (UTC)[reply]

Rayon is a sort of reassembled cellulose where the individual sugar units have been split up with carbon disulfide, then put back together again in new fibers. Online sources [7] suggest that it can be bleached, though direct exposure to bleach can "weaken" the fibers. Given that just about any organic compound seems prone to free radical reactions (this is much of the basis of macrophages killing stray bacteria or liver cells detoxifying chemicals) I don't expect many things to totally laugh at bleach. The site above also mentions that many rayon fibers are not washable because they shrink and have to be dry cleaned, with "modal" being one of the exceptions; our article says Modal is a brand name for a kind of polynosic rayon, where polynosic rayon is a high wet modulus rayon. I have not sorted out contradictions with the above yet.

Now polyester is harder to sort out. Polyester is a fabric with ... a lot of ester bonds. All sorts of different things can be between those bonds, though there are a few common types. So even though I read quite a few people saying they successfully bleached a polyester garment online, I don't know that there isn't some specific kind out there that disintegrates on contact. Wnt (talk) 11:19, 2 July 2017 (UTC)[reply]

Why not use Hydrogen Peroxide instead. Work out the cost/befit ratio. If you are a high paid company executive or salesman and must always have pristine presentability, then you are only going to get 20 washes out of a shirt anyway -before it starts looking shabby. Trump probably follows suit from other presidents that don't wear washed shits and if you look closely at interviews with Russian government officials they always appear to be wearing brand new out of the box silk shirts. Hydrogen Peroxide is only a 'little' more expensive and over 20 washes costs less than that of a new shirt. The labels 'not to use bleach' is just the same legal disclaimer that manufactures use like 'only dry-clean'. When in fact, washed properly, some labeled 'only dry-clean' cloths come out OK. The secret is often no more, than using good old fashioned soaps rather than modern detergents. But that has to make the housewife think and understand, that the (heavily advertised) stuff she normally buys from the Mall is not actually suitable for everything -as is often claimed on TV. Same for shirts. Aspro (talk) 13:31, 2 July 2017 (UTC)[reply]

Bleach and hydrogen peroxide are pretty similar chemically. Sodium hypochlorite is the salt of HO-Cl, chlorine gas is Cl-Cl, and hydrogen peroxide is HO-OH. These are all isoelectronic (if you count the hydrogen as an "H+"; I'm not sure that term strictly applies). The two halves of each one have the potential to become leaving groups if negatively charged, while homolytic cleavage produces free radicals. There are, of course, real chemical differences, but at a first approximation, I wouldn't assume that peroxide is safe for a fabric when bleach isn't. Wnt (talk) 00:45, 3 July 2017 (UTC)[reply]

Actually, I have considered that, and would use hydrogen peroxide, if it was less expensive. It costs me about US$4 for a 3% solution gallon vs US$1 for a 3% solution gallon of bleach, but I don't believe it has an equal cleaning ability. I'd estimate I would need to use maybe 10x as much, bringing the cost differential to 40x. The main advantage of the switch would be avoiding the more toxic bleach fumes. StuRat (talk) 06:35, 3 July 2017 (UTC)[reply]

Not surprised that 3% cost so much - as your paying for the transportation of mostly water. 35% would make it cheaper than Mall bought household chlorinated bleaches (which also have a premium added to the cost price of manufacture, to pay for advertising of these branded products), And what is the chlorinated bleach strength (probably not more that 18%). You can do the maths in your head to dilute down before adding to your whites. Also think, the cleavage of bonds in synthetic fibers may be greater for chlorine (can't off the top of my head give an immediate reference). After all, the production of PVC (Polyvinyl chloride) depends on this. PVC fibres would be useless for clothing fibres. It has flexibility in large cross section ( i.e. cable insulation) but not the necessary tensional strength that clothing fibres need. Clothes made from for chlorinated fibres would just fall apart – which may be the very phenomena that you may be describing. The shirt manufactures don't care – it causes you to buy more of their shirts. The bleaching companies don’t care because you continue to buy their products as their advertising suggest that only you have a limited choice. Yet, the choice really is yours. Red pill or blue pill. Personally, I like the tertiary purple pill (half way between the two (wouldn’t have made such a good movie if they had included that one). Thus, leaving the extremists to pout, pontificated and ague until the cows come home. Whilst purple people take full advantage of both marketing ideologies so as to choose the best practical stuff for their own use at a cost that suits them. As an aside: Does anybody remember Sheb Wooley's hit - 'Purple People Eater' in the late 1950's. Aspro (talk) 12:46, 3 July 2017 (UTC)[reply]

I added a / to the second small tag to ensure it was closed. Nil Einne (talk) 14:17, 3 July 2017 (UTC)[reply]

July 2

Odds of AIDA mission ending humanity?

The AIDA (mission) proposes to smash a "refrigerator-sized" spacecraft into "Didymoon", the 170-meter satellite of 65803 Didymos. Didymos will pass 6 million km from Earth in November 2023.

As I understand it, the mission is expected to cause a noticeable change in the asteroid's orbit: "The impact of the 300 kg (660 lb) DART spacecraft at 6.25 km/s will produce a velocity change on the order of 0.4 mm/s, which leads to a significant change in the mutual orbit of these two objects, but only a minimal change in the heliocentric orbit of the system"

What I'm wondering is, first: what are the chances they break it? A 170-meter asteroid has very little self-gravitation, and this one passes near to Earth and Mars fairly often, though I'm not sure how often. So could an impact like this lead to Didymoon cracking apart, whether directly or under tidal stress during a future flyby?

And second: if Didymoon comes apart in two pieces, I assume there will be some complicated three-body interaction. I would think that eventually one of the two pieces would get "ejected" (albeit slowly) from the system. How much of a difference does that make in the asteroids' long-term trajectory?

And third: Does any disruption of Didymos, however small, increase its odds of actually hitting Earth rather than skimming past in hundreds or thousands of years? (This assumes a pessimistic scenario for human civilization in which future adjustments don't happen)

Oh, last but not least: Didymos is 0.75 km wide, versus 15 km for the K-T impactor. So... what's the damage like? Wnt (talk) 12:27, 2 July 2017 (UTC)[reply]

One of the sources cited [8] "there is no possibility that the DART deflection experiment would create an impact hazard." I don't know what "no possibility" means here but I don't see any intrisic reason to think hitting it will definitely result in an increase of the the chance it will hit earth in hundreds of thousands of years as opposed to decreasing it. I.E. for such a long time frame, it would seem likely our predictions are too limited such that you might as well think of any hit as having neutral odds. Nil Einne (talk) 13:28, 2 July 2017 (UTC)[reply]

[9] says

Large-scale restructuring is unlikely to occur given the energy regime of the impact event, which is orders of magnitude below the catastrophic disruption impact energy threshold at Didymoon’ size, despite its rather low gravitational binding energy. On the other hand, regolith displacement may occur in the vicinity of the impact point and crater, due to the very low gravity of the asteroid. Even small seismic waves may cause displacement or lift-off of loose material. However, there are no reliable existing tools and knowledge to quantify these effects.

Nil Einne (talk) 13:39, 2 July 2017 (UTC)[reply]

Scale model of the Earth–Moon system: Sizes and distances in real scale.

Even with their low gravity these objects are very sturdy backed together over the Billions of years. Also this "asteroide twin" seems to far away even in its closest visites. Its projected to come nearest earth in 2123 and nearest meaning 5.900.000 km. In real perspective even our own moon at a distance of only 360.000 km is infact much further away from earth then common pictures and our view from earth suggests. There is a tremendous amount of space inbetween all of these distances for objects to pass savely a million times and in all that our beloved homeplanet is infact a very, very tiny spot. So even if we would cause some new objects on new trajectories with this mission, its more likely that you win 20 million $ in next weeks lottery then any of these objects hitting earth in the next 20 million years. --Kharon (talk) 15:30, 2 July 2017 (UTC)[reply]

"Its more likely that you win 20 million $ in next weeks lottery then any of these objects hitting earth in the next 20 million years". Actually that's not true. The Earth impact rate for ~1 km objects is estimated at a few per million years. Objects at that size have an impact energy of approximately 10 gigatons of TNT (somewhat less than the biggest nuclear bombs), enough to destroy cities and cause regional devastation but not enough to trigger widespread or global disasters. Pick a near earth asteroid at random and the odds of a collision within 20 million years is roughly 1%, far higher than the odds of winning the lottery next week. Basically, 20 million years is a really long time when it comes to the orbital interactions of objects that circle the sun every few years. Dragons flight (talk) 16:52, 2 July 2017 (UTC)[reply]

10 gigatons is 100x the largest nuclear bomb ever made. Sagittarian Milky Way (talk) 22:37, 2 July 2017 (UTC)[reply]

You're right, I was misremembering the size of historical nuclear bombs. For scale though, the impact event that killed the dinosaurs and caused planet-wide devastation is estimated at around 130,000 gigatons of TNT, which is still much larger and much rarer. Dragons flight (talk) 04:41, 3 July 2017 (UTC)[reply]

I have to confess i completely made these "20 million" up however the odds you cite refer to all the asteroids out there while i was only referring to probability this twin one will hit earth. Given that our Planet is over 4 Billion years old and this asteroid twin has obviously not seen a chance to "join us" in all that time, we are probably both millions of km and billions of years off with our madeup or cited estimations. --Kharon (talk) 17:49, 2 July 2017 (UTC)[reply]

I would take issue with Kharon's statement that "Even with their low gravity these objects are very sturdy backed together over the Billions of years." From Asteroid#Composition:

Most of the smaller asteroids are thought to be piles of rubble held together loosely by gravity, though the largest are probably solid.

Loraof (talk) 22:10, 2 July 2017 (UTC)[reply]

Thinking about it, a simple scenario: consider a "peanut-shaped asteroid" made from two pieces. A quick search turned up this link - I didn't find a Wikipedia article for a July 25, 2015 flyby; obviously a better link is possible. But the picture says a thousand words: you can have two asteroids stuck together fairly lightly. Now suppose the impactor, expected to cause a 0.4 mm/s velocity change in the Didymoon, causes a 0.8 mm/s velocity change in half of it instead. Then they would get 170000 mm apart - i.e. the diameter of Didymoon, with a 25-fold reduction in gravity between the halves - in roughly 200000 seconds. It would take on the order of a (0.8 mm/s)/200000 s gravity field, i.e. 4 x 10^-9 m/s^2, to stop that separation in that time. And ..... whoah. I just looked up asteroid gravity as a function of size and came up with this figure that claims a 100-meter asteroid pulls 0.0001 g = 0.001 m/s^2, which seems like an incredible amount of force for such a puny thing! So now I gotta actually do the math! That's 1 mm/s^2 velocity change, which ... seems to mean to me that the two halves would come crashing back against each other (with modified overall velocity) in just two seconds!

Unless I fouled up here, my overall impression of asteroid gravity was completely wrong. Yet thinking about it, the math isn't wrong - the Earth is 6000 km, divide by m^3/r^2 assuming constant composition means r, so ~~170~~85 m/6000 km = 31 x 10^-4, write the rest off as density difference. I just never realized that little rocks could have a meaningful pull to them. Wnt (talk) 00:34, 3 July 2017 (UTC)[reply]

Shouldn't it be 85 m and 6371 km? Sagittarian Milky Way (talk) 00:55, 3 July 2017 (UTC)[reply]

You're right. That said, this is an order of magnitude argument - the two would be no where near getting pried apart this way. Wnt (talk) 11:05, 3 July 2017 (UTC)[reply]

what are the chances they break it?

For sure, there will be some dust that will break away, so i guess the answer is: 100%. The questions are rather : "which size?" and "what direction?"

Obviously the ejecta will have energy from the impactor, and less than the latter does (1/2 300 6250² = 5.86 GJ ; 1kg TNT is 4184 kJ, so the impactor bring as much as ~1.4 t TNT).

Now, considering the effect of artillery shells (quite big but lighter than 1.4 t TNT) on Earth, or the impact of objects making impact crater, I guess the impact is expected to produce

- A thrust to the bigger part , keeping most of the momentum and kinetic energy from the impactor

- a cone of things expulsed away from the point of impact, none of them big enough to matter as far as Earth collision is considered (even-though some may be pretty big, from a human perspective: the size of a car or even a tree as evidenced by BLU-82 for instance could move trees)

Does any disruption of Didymos, however small, increase its odds of actually hitting Earth?

It does, in the very same proportion that it decreases its odds of hitting Earth if it were to happen. Chance for Earth to be hit just do not depends on whether didymos is hit by something launched by humans, it only depend on the size of Earth as a target and the density of potentially hazardous object in space (which 65803 Didymos already is, one of the reason it was chosen as target, i guess). Obviously disrupting the target would produce more objects of a smaller size, each having it's own chance to hit Earth, but with smaller chance to do significant damage. Since there are already so many PHO, one more or less do not make a difference.

Gem fr (talk) 14:07, 3 July 2017 (UTC)[reply]

Mechanical clearance of the nasal passage

I noticed that some people suggest that picking a nose is unacceptable behaviour and introduces the risk of abrasion and infection of mucous membranes. It certainly does seem antisocial in my opinion. If a person was to refrain from mechanical clearance of their nasal passage, would the lumen become occluded at some point in infancy and remain that way for the rest of their life or does there exist a natural mechanism for preventing occlusion? --145.255.244.249 (talk) 14:08, 2 July 2017 (UTC)[reply]

Digging in your Nose is no real danger to health but a serious "Blasphemy" of the common concept of Hygiene because the resulting "mining products" are usually, discreetly spread everywhere. Nevertheless, like peeing in Public Baths, infact everyone does it and there are even scientific studies, not about "if" but "how much". --Kharon (talk) 14:34, 2 July 2017 (UTC)[reply]

Do people take showers in Rotherham? I won't give medical advice, but you can draw your own conclusion. μηδείς (talk) 01:08, 3 July 2017 (UTC)[reply]

Chemistry questions.

What's more dangerous, 2 hot gases combine to form a cold gas, or 2 cold gases combine to form a hot gas?

What's a chemical I can use to remove oil off of keyboards? (I've tried monitor wipes, isopropanol, hexane, and wipes to kill bacteria/viruses off of keyboards). According to a biochemistry professor, the oil released from our fingertips is a fatty acid, and so ask a organic chemistry professor to remove fatty acids, dichloromethane.

Who kills bacteria and viruses better, 70% isopropanol or 70% ethanol? As well as, 3% hydrogen peroxide and bleach (5.25%, 8.25%, and 10%).

Strongest known covalent bond is C triple bond O in carbon monoxide and does anyone have any values for how the strongest metallic bonds compare? Stongest metallic bonds likely tungsten-tungsten bonds.

Most dangerous endothermic reactions? (Chain reactions can be endothermic.). Endothermic reactions can cause implosions - the opposite of an explosion - where you get sucked in.

Biology: what happens when plants breathe in carbon monoxide? (Are plants capable of breaking the triple bond, or does the molecule bind somewhere.).

Thanks. 12.130.157.65 (talk) 14:13, 2 July 2017 (UTC).[reply]

Regarding your statement about strong metallic bonds, I would note that the 5d metals like W have such high melting points because the bonding is not only metallic, but has a partial covalent component. Double sharp (talk) 14:21, 2 July 2017 (UTC)[reply]

Regarding plants and CO, according to this article abstract [10], in light bean plants photosynthesize CO into sucrose, and in darkness they oxidize it into CO2 and release the CO2.--Wikimedes (talk) 16:19, 2 July 2017 (UTC)[reply]

I can't think of any really strongly endothermic gas reactions off the top of my head, but I should note that there is a minimum pressure (zero, a vacuum). Of course, a large evacuated chamber can produce a dangerous explosion but it is typically limited in impact. By contrast, a heated gas could develop any amount of heat and hence pressure in theory - hydrogen plus oxygen is a typical example. Also note that an endothermic reaction would get colder as it progressed, reducing reaction rate under nearly all circumstances, whereas an exothermic reaction does the opposite. Wnt (talk) 00:50, 3 July 2017 (UTC)[reply]

Danger has just nothing to do with whether the combined gas are cold or hot. Whether the produce is hot or cold just matter as far it is from tolerable range of humans (or other living things), but for sure you have rather breath 50°C or -20°C air than 20°C Chlorine, don't you?

There many ways to remove fat, but if you use a dissolvent of any sort (as opposed to : just destroy/burn/vaporize them) you obviously need something (a cloth most of the time) to wash them away. dichloromethane is just a solvent, in the matter.

You may want to produce saponification, an everyday way to get rid of fat.

Look at Hand sanitizer for isopropanol and ethanol efficiency for that matter. they are not significantly different, it seems.

hydrogen peroxide and bleach are too dangerous as hand sanitizers of regular use.

implosion has nothing to do with whether the reaction is endo- or exo- thermic, or if it is a chain reaction or not. It is just a matter of consuming significantly more gas (preferably: all of it) than it produce (preferably: none). If you start with air, consuming N2 is very hard (see Haber process), and consuming O2 is easy but always exothermic and reduce pressure by only 1/4 at most. Everyday way to produce implosion is to fill the vessel with steam and cool it brutally with cold water injection (a physical, not chemical, process).

Gem fr (talk) 15:09, 3 July 2017 (UTC)[reply]

Drugs

What portion of patients are prescribed psychoactive drugs to treat mental illness without fully understanding the potential side effects? Benjamin (talk) 16:32, 2 July 2017 (UTC)[reply]

Especially for psychoactive drugs, not even the physicians fully understand the effects, and there is little hope that the patients understand them better. Icek~enwiki (talk) 19:28, 2 July 2017 (UTC)[reply]

Perhaps not fully, but to a reasonable degree? Benjamin (talk) 23:32, 2 July 2017 (UTC)[reply]

You've been given the correct answer, and "to a reasonable degree" is not an objective standard that we can answer without mind reading and speculation. μηδείς (talk) 01:06, 3 July 2017 (UTC)[reply]

My pharmacy gives out lengthy bits of literature for each prescribed drug, with lists of potential side effects and the like. ←Baseball Bugs ^{What's up, Doc?} carrots→ 04:20, 3 July 2017 (UTC)[reply]

Due to the FDA reform bill of 1996 (?) it became mandatory for drug companies to list the most commonly reported side effects, which ended up being things like headache for ibuprofen, runny nose for benadryl, and "delayed back ache" for viagra. Obviously these are not actual side effects of the drug. Very few psychiatric medicines have had long term studies. Look at the problem of sleepwalking on Ambien. I laaughed when a certain congressman claimed he didn't remember driving to a bar at 2am. But I discontinued ambien myself when I started waking up with meals cooked from scratch on my bedstand. I actually boiled spaghetti and made meatballs from ground beef in my sleep. Basically, due to lack of research, poor instruction by doctors and pharmacists, and failure of the patient to read the 4pt small print inserts, the OP's answer is close to 100%. μηδείς (talk) 16:46, 3 July 2017 (UTC)[reply]

Can a carbon triangle molecule exist, at least for a short time?

I mean -C-C-C, or (say) =C=C=C, etc, where the third carbon reaches around and bonds with the first carbon. My chemistry teacher told me no, there's too much strain, which I'm sure is true. But I wonder if it could exist briefly, just like the subatomic particles in particle physics that famously exist for only a picosecond, say. More generally, since physicists find briefly existing subatomic particles of interest, do chemists or chemical physicists find briefly exsting chemical particles of interest?--I'm not sure whether or not the logic holds that chemistry people should therefor find them of interest, because the physicists are trying to look at something going on at the underpinnings of reality, where as briefly existing molecules probably wouldn't help with that, except by analogy.-- Thanks.64.134.228.64 (talk) 19:03, 2 July 2017 (UTC)[reply]

Cyclopropane is a stable molecule. If you mean a cyclic tricarbon, it surely exists as a very short-lived molecule. Femtochemistry might be of interest. Icek~enwiki (talk) 19:20, 2 July 2017

If your chemistry teacher doesn't even know about cyclopropane and strained banana bonds, I'd be very worried. Time to hire a new teacher! Cyclopropene is even more strained, and, although not particularly stable, occurs in natural products. As far as tricarbon goes, as our article states, it's a linear molecule. Fgf10 (talk) 19:29, 2 July 2017 (UTC)[reply]

I don't know what you'd call =C=C=C ... cyclocumulene pulls up some hits, but those are structures -C=C=C=C ... tetradehydrocyclopropene? I'm not sure if I can figure this out with the IUPAC guidelines... Wnt (talk) 01:00, 3 July 2017 (UTC)[reply]

For laughs I went to a PubChem structure search just now, and entered C1=C=C=1 for a SMILES search. It pulled up a bunch of compounds, a surprising number of which have the rudest thing done to a benzene ring - the simplest is called Bicyclo[3.1.0]hexa-1,3,5-triene. [11] Now as far as I know ... Hueckel's rule still applies, and so those bonds are not single and double but roughly order 1.5 ... at least, all the ones around the edge of the ring should be. That other one in the middle, hmmm... you can't really draw a resonance structure for it as a double bond that doesn't have a + or a - at the apex of the triangle, but this probably needs to be looked at with some kind of molecular orbital theory... what kind, I'm not sure. ;) Searching (I was hoping to stumble across a crystal structure, but I don't really know the right way to check for non-protein crystal structures) I ran into part of a paper saying that this is the real structure of what is normally called m-benzyne [12] - given that I had not heard of "m"-benzyne before I should probably avoid weighing in on whether the different structure that article gives for one (with two unpaired electrons) is right or not. Wnt (talk) 23:29, 3 July 2017 (UTC)[reply]

Can dogs control their appetites?

Can dogs control their appetites, or do they depend on their human owners to feed them a specific portion? Is it possible to overfeed a dog, or will they just refuse to eat when they are full? Speaking of dog treats, I have seen one of those doggy treats before. They look like dried-up pig ears and chicken feet. Are they safe for human consumption too? Pig ears and chicken feet are sold in Asian supermarkets, so they are definitely made for human consumption. Plus, they still retain moisture. But what about the dried-up variety that is intended to be sold as "dog treats"? And what is "crude protein/fat/carbohydrates"? 50.4.236.254 (talk) 19:46, 2 July 2017 (UTC)[reply]

Obviously not all dogs can control their appetite. See Commons:Category:Fat_dogs :). From the evolutionary perspective such an ability is redundant and even harmful as wild animals rarely have food overabundance. Ruslik_Zero 19:54, 2 July 2017 (UTC)[reply]

So, if you feed a dog more and more and more, then it will eat everything you give indiscriminately? I think the amount of money you spend on the food is one limiting factor. If you budget $20 for home-made dog food, then the dog is only going to eat $20 worth of food. Budget less, and you provide less, and the dog will eat less. Meanwhile, when I am full, I can't take in any more food. Tried that, didn't work. I just felt very sick and vomited. 50.4.236.254 (talk) 20:15, 2 July 2017 (UTC)[reply]

If you want to chew on dog treats, go right ahead. They're designed to be palatable for dogs, not for humans, so you may not particularly enjoy chewing on a pizzle, but then, you might. Dogs are quite capable of overeating and puking too. --jpgordon^{𝄢𝄆 𝄐𝄇} 21:02, 2 July 2017 (UTC)[reply]

Careful, though dog food should generally be free from harmful bacteria and toxins, it may not be manufactured to human standards. In addition, animal food may contain ingredients (such as bone meal) that the animals are able to digest but that will cause problems for humans. In particular, I've heard of people eating food that cats enjoy and getting severe vomiting or diarrhea. Dragons flight (talk) 21:38, 2 July 2017 (UTC)[reply]

Depends on the dog. Our golden retriever often decides not to eat her whole portion of dog food, leaving 10-50% of the meal behind. I interpret this as her being full. However, just like how people make room for "dessert", even when she is done with her dog food, she will still gladly eat her dog treats. Based on what we have heard from other dog owners, this behavior is rather unusual as many dogs will rarely, if ever, leave food behind in their bowl. Dragons flight (talk) 21:30, 2 July 2017 (UTC)[reply]

Overfeeding in the sense that you'll eat a lot more than you should be eating if you only stop eating when you feel full, doesn't work with natural foods. If you eat your stomach full with healthy whole foods you'll probably not get enough calories, because your stomach hasn't adapted to eating such foods. If you get used to eating like this, then your stomach will expand, your intestines will start to make more enzymes, your microbiome will adjust itself. If you then eat your stomach full you may end up eating more calories than you are used to now, but your metabolic rate will have increased too, so you won't get obese. E.g. I weigh 55 kg but I eat 4000 Kcal a day, most of that come from whole grain carbs. I eat more than 1 kg of fruits and vegetables combined. A friend of mine is obese, he eats just 2000 Kcal a day but that's in the form of high fat, low fiber diet. Count Iblis (talk) 00:35, 3 July 2017 (UTC)[reply]

The topic is about dogs, not humans. I almost thought you were a talking dog. 50.4.236.254 (talk) 22:54, 3 July 2017 (UTC)[reply]

Many dogs do have the ability to stop eating when full, and save the rest for later. Burying food is a natural way for them to save it for later. Since dogs evolved from wolves, which tend to kill large animals, presumably these behaviors developed as a way to handle rare, but large, kills. StuRat (talk) 06:27, 3 July 2017 (UTC)[reply]

How can dogs eat white rice?

I watched on YouTube that humans could feed their dogs white rice with chicken, various vegetables, and assorted fruits. But white rice was also used. Hmmm... if dogs can eat white rice, then how can white rice be unhealthy for humans? And why do humans never cook a family meal that is dog-friendly (no garlic, onion, pepper, avocado, eggplant, or chocolate)? Why should humans eat whole grain but dogs can eat white rice? 50.4.236.254 (talk) 23:44, 2 July 2017 (UTC)[reply]

White rice is not toxic, it simply lacks micronutrients found in brown rice. Whole grain is, on the balance, better to eat not because processed grains are toxic, but because unprocessed grains retain more micronutrient content, what is known as nutrient density. White rice doesn't kill you. Neither does it kill dogs.--Jayron 32 00:12, 3 July 2017 (UTC)[reply]

If whole grain has more micronutrients, then why not just feed the dog whole grain rice with vegetables and some meat chunks? 50.4.236.254 (talk) 00:28, 3 July 2017 (UTC)[reply]

That is not a question that can be answered here without resorting to speculation and debate. You will have to go an ask each pet owner in person. MarnetteD|Talk 00:45, 3 July 2017 (UTC)[reply]

So, you are saying that the answer is subjective, and that the answer varies from dog to dog? 50.4.236.254 (talk) 00:57, 3 July 2017 (UTC)[reply]

He's saying that questions of a "why" nature that seek to explain individual choices are not the purview of this desk. --Jayron 32 01:05, 3 July 2017 (UTC)[reply]

I think some questions are exceptional. Why do humans walk on two legs? is a why question, and humans do choose to walk on two legs. They can, if they want to, walk on all fours. 50.4.236.254 (talk) 01:08, 3 July 2017 (UTC)[reply]

Not very easily. Humans' legs tend to be significantly longer than their arms, making literally walking on all fours kind of awkward. ←Baseball Bugs ^{What's up, Doc?} carrots→ 04:18, 3 July 2017 (UTC)[reply]

There is a matter of value judgment involved - pet owners do make trade offs of various sorts, expense vs. lifespan vs. "quality of life" and so on. A quick web search turns up leading brands of dog food that contain rice, though some are snooty about using brown rice. There are lots of references about it [13]. Bottom line: it doesn't kill them, they eat it, so it's up to the owners to decide when and how much. Wnt (talk) 01:32, 3 July 2017 (UTC)[reply]

White rice is considered easy to digest. When our dog is sick, we feed her white rice with chicken and carrots. It is a simple meal that she likes very much and tolerates well even when she has been sick. However, that is not a complete diet which is why we give her more complete meals most of the time. Her normal pet food does not include any rice, though many pet foods do. As with most foods, white rice by itself is not harmful. It is more a question of how much is consumed and whether it is mixed with a sufficient variety of other foods to ensure that the overall diet meets one's complete nutritional needs. Dragons flight (talk) 04:35, 3 July 2017 (UTC)[reply]

Sounds a bit like people eating saltines when they have upset stomachs. Certainly not a complete food, but better than nothing, if that's all you can keep down. StuRat (talk) 06:21, 3 July 2017 (UTC)[reply]

"how can white rice be unhealthy for humans?"

Sorry to say to the OP, you are assuming something completely incorrect here, a couple of billion people eat white rice every single day, and are fine, so clearly is not unhealthy for humans. There may be more healthy things to eat, but it is not unhealthy, unless abused in large quantities, like anything else (even water). Jayron tried to correct this assumption, but I think he was a little weak on this.--Lgriot (talk) 15:16, 3 July 2017 (UTC)[reply]

I agree. I think the whole question about brown rice vs white rice is arbitrary and based on context. For some people, eating white rice is healthy, and they get dietary fiber and micronutrients from the vegetables that go along with the rice. They don't eat the rice alone. 50.4.236.254 (talk) 23:00, 3 July 2017 (UTC)[reply]

Well I have taken to soaking rice before using it to reduce any arsenic level in it. I think it helps the texture too. I quite like wild rice. Dmcq (talk) 18:30, 3 July 2017 (UTC)[reply]

July 3

How are microbial toxins broken down?

The advice for dealing with spoiled food is to throw it away, because the microbial toxins won't be destroyed by cooking it. The temperatures needed are so high that your food would be carbonized. But since microbes in Nature are constantly busy breaking down biological materials and producing the same sort of toxins, these toxins would accumulate without limit in Nature unless they do get broken down at room temperature by interacting with other chemicals. So, why can't we use such processes to deal with spoiled food or to slow down food spoilage? Count Iblis (talk) 00:42, 3 July 2017 (UTC)[reply]

Basically, you are looking at using a fungus to decompose another fungus or bacterium. That may not be all that appetizing. There is no universal solvent that can break down all toxins. Indeed, part of being a good toxin is not to be easily degradable. There's also the option of feeding slop to pigs, and eating the pigs, or fermenting the mash with yeast or bacteria, and using the ethanol for the usual purposes and solid wastes as compost or food, depending on the end products. The issue is too complicated to say that everything can be made into Soylent Green.

μηδείς (talk) 16:37, 3 July 2017 (UTC)[reply]

Microbial toxin is not all toxic or deadly. In yeast cells, ethanol is produced through fermentation when the oxygen is exhausted. This kills yeast cells, but it surely makes wine tastes like wine! 50.4.236.254 (talk) 01:05, 3 July 2017 (UTC)[reply]

There are several things to discuss here. First, there's no "universal toxin". Chemicals that are toxic to one organism can be completely harmless to another. Indeed, that's pretty much what antibiotics are; they're toxic to bacteria (and sometimes other microbes) but not to you. Caffeine and nicotine are deadly poisons to insects; to humans they're stimulants. Also, not all decomposition is done by organisms. Complex organic molecules left alone will slowly degrade over time from heat, light, oxidation, etc. For instance, fats rancidify. So yes, you could leave spoiled food alone to slowly let toxins degrade, but everything else in the food will degrade as well, and you'll have a disgusting soup of organic molecules. We slow down food spoilage by preventing or inhibiting the aforementioned processes. --47.138.161.183 (talk) 19:34, 3 July 2017 (UTC)[reply]

Social norms and Asperger's

Is willfully breaking written social rules ("Say excuse me after you burp", "Don't chew with your mouth open", "Use your inside voice", "Take your hat off inside a building", "Don't go naked in public", "Don't talk about sex/feces/genitalia in public", "Don't cross-dress", "Don't use the wrong gender restroom", etc.) symptomatic of Asperger's syndrome? Barney the Dinah Shore (talk) 03:16, 3 July 2017 (UTC)[reply]

Not necessarily. Some of those things can be symptoms of mental illness. ←Baseball Bugs ^{What's up, Doc?} carrots→ 04:16, 3 July 2017 (UTC)[reply]

Hmmm. I could believe that a perceived need to say something after burping or to take a hat off when entering a building could be viewed as a form of obsessive-compulsive disorder... Wnt (talk) 11:08, 3 July 2017 (UTC)[reply]

By the way... which one is the 'wrong' gender? - Nunh-huh 04:46, 3 July 2017 (UTC)[reply]

One other than the one you routinely use. — Preceding unsigned comment added by Baseball Bugs (talk • contribs) 07:34, 3 July 2017 (UTC)[reply]

Symptoms are felt or experienced by the patient, signs are noted by the clinician or other person. The activities in the question may also be present in someone who is confused or disinhibited by intoxication from alcohol or other substance. Richard Avery (talk) 07:16, 3 July 2017 (UTC)[reply]

Sure, and it's situational too. Going nude in public is not only OK but is encouraged... on a clothing-optional beach. ←Baseball Bugs ^{What's up, Doc?} carrots→ 07:39, 3 July 2017 (UTC)[reply]

What does "inside voice" mean? ←Baseball Bugs ^{What's up, Doc?} carrots→ 07:36, 3 July 2017 (UTC)[reply]

Volume (and perhaps pitch) appropriate in a confined space. —Tamfang (talk) 08:24, 3 July 2017 (UTC)[reply]

Also, there is a school of thought that you should not apologize after burping, because that merely draws further attention to it, and hence is more rude. ←Baseball Bugs ^{What's up, Doc?} carrots→ 07:38, 3 July 2017 (UTC)[reply]

Id say in most cases its primarily symptomatic for being a Punk. --Kharon (talk) 19:53, 3 July 2017 (UTC)[reply]

BJT voltage divider bias

I made an small experiment (in a simulator) with different combinations of resistors. In particular, the combination of 10k/5.49k, 100k/59k and 330k/240k resistors (the collector resistor and the emitter resistor were 2.2k and 1k respectively in all 3 cases) all biased the transistor to a collector voltage of 2.5V (5Vcc supply.) The base current, too, was roughly the same at 2.48uA, so was the collector current (roughly 1.18mA-1.36mA.) What, then, is the principal difference and is there a rule how to choose bias resistors? I know voltage divider bias calculations are done using equivalent voltage (the actual voltage at the junction between the two resistors and disconnected base) and equivalent resistance (R1||R2), but these are all different (1.77V/3.54k, 1.8V/37k, 2.1V/138k respectively) 78.53.24.21 (talk) 10:09, 3 July 2017 (UTC)[reply]

PS BJTs are capital-W weird. Actual EEs, as opposed to hobbyists like myself, I wonder, what is their ratio of intutive understanding vs "shut up and do the math"? And what is the math? 78.53.24.21 (talk) 10:30, 3 July 2017 (UTC)[reply]

The base current is I_collector/h_FE and very small, just a few µA (microamps). So when the current in the base bias resistors is much larger (in your examples 323, 31, 8.8 µA respectively) the voltage drop in the equivalent resistance (0.009, 0.09, 0.34 V) is negligible. The conclusion is that using low value resistors in the divider gives no advantage. Using higher value resistors saves wasted current, which could translate into slightly longer battery life in portable equipment. However using extremely high resistances would make the biasing more dependant on h_FE which varies with temperature and is not exactly specified in ordinary transistors. See the article Bipolar junction transistor, particularly Bipolar junction transistor#h-parameter model. Blooteuth (talk) 12:17, 3 July 2017 (UTC)[reply]

Thorns on opium poppy engineered or natural?

I can understand why man would have bred or engineered the thorns on an opium poppy plant. Is their evidence for this? thank you — Preceding unsigned comment added by Rextrent2 (talk • contribs) 11:27, 3 July 2017 (UTC)[reply]

Use of Papaver somniferum, the opium poppy was known as far back as Sumer 4000 BC and the ancient Minoans. The stem and leaves are sparsely covered with coarse hairs. I can't understand why any poppy farmer would want to breed thorns on his crop. Blooteuth (talk) 12:28, 3 July 2017 (UTC)[reply]

There are poppies with thorns but not the opium poppy. Dmcq (talk) 12:35, 3 July 2017 (UTC)[reply]

The Sacramento prickly poppy for example. Alansplodge (talk) 19:18, 3 July 2017 (UTC)[reply]

Big cylinder in the gravity well of a black hole

Suppose one had a magically strong 400 mile long cylinder, made up of over 1000 decks each 600 metres high, just outside the event horizon of a black hole, trying to reverse its way out, but making only very very slow progress, so effectively almost stationary.

(Any resemblence to events in the most recent two episodes of a major television franchise entirely non-coincidental).

For those not in the UK, this question was almost certainly triggered by a recently broadcast Doctor Who episode. Bazza (talk) 14:40, 3 July 2017 (UTC)[reply]

Events on the flight deck (level 0, nearest the black hole) appear time-dilated by a factor of 150,000 when viewed on closed-circuit tv from floor 1056, four hundred miles away.

(i) is it possible to calculate (or guesstimate) the relative time dilation between floor 507 and floor 1056 ? I'm guessing the relationship is not linear with distance, so rather a lot less ?

(ii) how would signals from floor 1056 (eg transmitted by a remote life-signs monitor on that floor) appear when viewed at floor 0 ? Would they appear sped-up by a factor of 150,000 ? (Related question: if an observer in free fall crosses the event-horizon, do they see the universe behind them become incredibly blue-shifted -- or is the transition for them apparently imperceptible, with clock-signals from outside still reaching them at a steady rate; since it is only for the outside observer that they will have appeared to have become red-shifted to eternity as they approach the horizon?)

ALSO: What other bodies are buried in this scenario?

-- eg: What is the local gravitational acceleration that the ship is resisting, and that any bodies on its decks would be subjected to if it wasn't for magical artificial gravity ?

-- if our cylindrical object were rotating (a primitive way to make artificial gravity, here replaced by the more advanced magical method), would the difference in time dilation mean enormous twisting forces on the structure -- one end having rotated appropriately for 2 1/2 days, the other for 10,000 years?

-- lifts can be operated between floors. If they run at a steady local velocity, how much more quickly than usual does the journey from 400 miles away appear to take, when viewed from floor 0 ? How magical do they have to be, to extract mass from so close to the event horizon to 400 miles away?

Thanks for any thoughts, Jheald (talk) 11:34, 3 July 2017 (UTC)[reply]

From Gravitational time dilation there is this simplified formula:

t_{0}=t_{f}{\sqrt {1-{\frac {r_{s}}{r}}}}

where

$t_{0}$ is the proper time between events A and B for a slow-ticking observer within the gravitational field,
$t_{f}$ is the coordinate time between events A and B for a fast-ticking observer at an arbitrarily large distance from the massive object (this assumes the fast-ticking observer is using Schwarzschild coordinates, a coordinate system where a clock at infinite distance from the massive sphere would tick at one second per second of coordinate time, while closer clocks would tick at less than that rate),
$r$ is the radial coordinate of the observer (which is analogous to the classical distance from the center of the object, but is actually a Schwarzschild coordinate),
$c$ is the speed of light, and
$r_{s}=2GM/c^{2}$ is the Schwarzschild radius of $M$ .

So you can calculate different t0 values for the different r values. With such a big time dilation, the level 0 is really close to the event horizon, and the energy to lift anything from that up is close to the rest mass of the object*c². Graeme Bartlett (talk) 11:52, 3 July 2017 (UTC)[reply]

@Graeme Bartlett: Thanks.

So, to plug in some numbers:

If we approximate time on floor 1056 as approximately undilated, then r₀ ≈ r_s (1 + 1 / 2.25 x 10¹⁰) -- so, as you say, very very close to the event horizon; with the slower that time is running on floor 1056, the even nearer that floor zero must be.

From Schwarzschild radius, r_s for a one solar-mass black hole is about 3km, and floor zero would be within about one tenth of a micron of the event horizon (which would be a bit tight), with time running at 99.7% of normal on floor 1056, and 99.5% of normal on floor 507.

At the other end of the spectrum, from the same article, the supermassive black hole at galactic centre has r_s = 13.3 million km. 640 km beyond this, time would be running at 0.7% of its speed in free space, while on floor 507 it would be about 0.5% -- the most you can achieve in halving the distance to the event horizon is a reduction of about 70% (ie 1/√2) in the rate of time.

For this mass, for a time dilation of 0.007 / 150000, floor zero needs to be within a fraction of 2 x 10¹⁵ of the event horizon -- about 7 microns.

So the maths doesn't entirely work out.

A couple more numbers: a time dilation of γ = 150,000 corresponds to an escape velocity β = 0.99999999998 of the speed of light; any free photons would have to be aimed very directly away from the black hole to get out.

I'm not sure whether the formula for gravitational acceleration g = 0.5 r_s (c / r)² still applies in such a strongly relativisitic environment; but plugging numbers into it gives 1.5 x 10¹² earth gravity for the event horizon of the one solar-mass black hole; and still 3 million g for the super-massive black hole -- so the magic cylinder (and magic artificial gravity system) do indeed have to be quite strong. Jheald (talk) 15:32, 3 July 2017 (UTC)[reply]

Event horizon says that the local gravitational acceleration for an object in fact tends to infinity (presumably as a consequence of now including relativistic corrections), the nearer an apparently stationary object is to the horizon. My thanks to User:Gem fr for the pointer. Jheald (talk) 15:52, 3 July 2017 (UTC)[reply]

I am still curious as to what the rest of the universe looks like to a free-fall observer crossing the event horizon. From the outside it seems the observer never crosses the horizon -- their time slows down to nothing, and they appear to remain there forever (though red-shifted to oblivion), along with every clock-pulse sent in from outside. But from their own perspective, this is surely not right. They (classically) would continue to fall on the far side of the horizon, and clock-pulses from outside would continue to reach them at a steady (finite) rate. Jheald (talk) 13:11, 3 July 2017 (UTC)[reply]

When I crunched some numbers I got 0.01mm from a 1000 km radius black hole. So just consider this a work of fiction, as the acceleration would vary too much over level 0. Most of the dilation variation would just be close to level 0. You may be interested in Ehrenfest paradox involving rotation in relativity. I can assure you that no material will support the strength required of your cylinder. No need to worry about it twisting either! Graeme Bartlett (talk) 13:26, 3 July 2017 (UTC)[reply]

event horizon is a so tricky thing, i confess not understanding it. So I just read event horizon#Interacting with an event horizon, which may be not perfect, but clear enough. Gem fr (talk) 15:29, 3 July 2017 (UTC)[reply]

The way you put things, you suppose some sort of fixed, absolute event horizon of the black hole, and some way to measure some absolute distance from this fixed boundary. This is not the way relativity works. There is no such thing as a single "event horizon of the black hole", it is all relative to the observer, and is not the same for a man A on the deck 0 as it is for a man B on deck 1. When vertically aligned, man A and man B won't find each other at the same distance and their clocks won't run at the same speed. They are engaged in some sort of twin paradox experiment

redshift is not absolute, either, and its' reverse is not a "blue shift", but ... another red shift ! Objects appear redshifted when they seem accelerated away, so if A see B redshifted, so does B see A redshifted, too. (I am not 100% sure, i confess)

Gem fr (talk) 15:55, 3 July 2017 (UTC)[reply]

See Schwarzschild radius. It is not dependent on the speed or location of the observer. It is dependent on the mass of the object. 209.149.113.5 (talk) 16:47, 3 July 2017 (UTC)[reply]

except that, Mass in relativity depends on speed Gem fr (talk) 08:30, 4 July 2017 (UTC)[reply]

Suppose the black hole is moving at 0.5c relative to you. Everything around the black hole seems flattened in the direction of motion by Lorentz contraction. Does the Schwarzschild radius also seem flattened? If so, then there are probably some details that article glosses over ... if not, double. Wnt (talk) 18:05, 3 July 2017 (UTC)[reply]

Thanks @Gem fr:, anon, and @Wnt:. Like Gem, my instincts -- very much formed from Special Relativity and the twin paradox -- were to feel that the opposite of redshift would not be straightforward blueshift, but something else. However, SR is very different from GR, so I'm not sure how much I trust those first instincts any more; I'm certainly more aware now that I don't have much feel (yet) for GR.

There's also a clear difference between the twin paradox, which is symmetric between the two observers; and the gravitational time dilation, which arises from their having very different proper accelerations (i.e. accelerations with respect to free fall). The gravitational case also differs because it (might) be symmetric with respect to time-reversal, which the SR one isn't -- the signals the twins see moving away aren't the same as what they see re-approaching each other.

But I think the link event horizon#Interacting with an event horizon, that you gave above, is very useful, and it smells right to me, at least so far as it goes.

It says that "observers stationary with respect to a distant object will all agree on where the horizon is"; and that the proper distance to the horizon is finite. (The proper distance might even be the distance between r and r_s -- though I suspect the definitions of the radiuses r may be a bit more subtle than that).

On the other hand, if there's time dilation, then the apparent distance to somewhere near the horizon (eg measured by the time taken for a photon to get there and come back) will appear to tend to infinity. This is not a contradiction, but does appear to indicate that the apparent height of each level (as observed from eg level 1056 -- but not as observed from a lift going slowly up the ship) will appear to get higher and higher.

I *think* photons going down the gravity well get increasingly blue-shifted, as seen by stationary observers on each deck they pass, corresponding to energy they have gained, falling down the gravity well. The rate of them also increases, as more seconds from emissions from a lower deck are being mapped to a single second on the higher deck. So there's a twofold effect, subjecting the higher decks nearer the horizon to an increasing number of increasingly hard X-ray particles. As seen from the lower deck, I think the wavelength appears the same, but in this perspective an increased number of particles fit into the apparently distended space between each deck. The two perspectives would be equivalent.

This, as I understand it, is ~~what leads to the controversial idea that there should be a "black hole firewall"~~ - a very very high temperature region adjacent to the event horizon.

No: BH firewall is something else, (and, on the face of it, very very ad-hoc). Jheald (talk) 20:22, 3 July 2017 (UTC)[reply]

But this would only be perceived by an apparently static observer, hovering close to the event horizon. As I now understand it, the perception of an observer in free-fall, not experiencing the enormous proper acceleration of the static observer, would be very very different -- and so this is how, per my original post above, they continue to hear clock pulses from outside reaching them at a steady rate, with no essential difference made by crossing the horizon. Jheald (talk) 19:32, 3 July 2017 (UTC)[reply]

Twin_paradox#What_it_looks_like:_the_relativistic_Doppler_shift is of interest here; of course there is no "return trip", but the difference of pattern seen from the static to the traveling, and from the traveling to the static, illustrate how tricky things are. Also, observe how long it take to explains just a part of it.

Bottom line: i think we should close the question, we already gave the most relevant links, going further is above what can be expected of reference desk (and, my own expertise, AFAIAC)

Gem fr (talk) 10:15, 4 July 2017 (UTC)[reply]

Recent weather trend

This indicates that the recent hot weather pattern in southern Europe is also man-made. Does this mean that the recent thunderstorm/hail and cloudburst pattern in Europe was caused by heavy evaporation from that heat which formed rain clouds that traveled north? This trend covers a vast area roughly from Germany to Russia. In this month snow also reportedly fell in Murmansk and some other Russian cities. Brandmeister^talk 12:14, 3 July 2017 (UTC)[reply]

Weather is to complex or chaotic to prove a direct correlation between longterm influence and specific local events but its trivial to conclude in general that more heat implies more energy, which implies more extreme weather events. --Kharon (talk) 19:39, 3 July 2017 (UTC)[reply]

it's trivial but it is ... utterly wrong xD

heat and temperature are very different things. Actually, in real life more air temperature usually means LESS atmosphere energy: The air above Sahara as less energy than the air above London, even though it is at quite higher temperature (London air as much higher latent energy of water condensation, than more than make up for the minute energy difference caused by difference in temperature). Foehn wind increase temperature while losing energy. A storm is always much lower temperature than calm region around it. Energy is also a function of pressure, so, for a same temperature and water content, anticyclone have more energy than cyclone, however anticyclone are not associated with extreme weather event, cyclone are. Etc.

and of course, we are talking about an average 1% energy change of every day energy change. That is to say, if everyday change is 0 to 1 and back to 0 again, instead of averaging 0.5, it would average 0.51. No statistical tool is able to link a so minute change to rare events in a so badly known, so naturally noisy, so chaotic, process as weather.

Hence the cautious formulation of IPCC, that can be sum up as "we think it is probably/likely/verylikely so and so (but we cannot prove it)"

Gem fr (talk) 09:47, 4 July 2017 (UTC)[reply]

The same trend of bad things can be observed in media about just anything: economics, terror and war, disease, etc. This is called sensationalism. I don't see anything notable in snow in Murmansk#climate, i guess the average 0.5 snow day in June is like some year without any and a few days of snow a year in a while ; this happened this year, not previous year and probably not the next (but media won't talk about it, will they?).

Humans always need scapegoat for bad things, they just don't accept that Nature/gods are lunatics, when something bad happens someone must have offended them. That's specially true of weather. Plagues of Egypt includes meteorologic events, caused by Pharaoh's unwillingness to obey God. You'll find many instance of human sacrifice such like Iphigenia's to appease gods and get back "normal" weather.

Death dreams (an experience of the dying brain not a normal dream about death)

I watched Jacob's Ladder a long time ago and became aware of the concept of a 'death dream' wherein a dying brain depolarises in a less-controlled way than usual, resulting in a surreal and possibly unpleasant experience for the person dying. It seems like Wikipedia doesn't have an article on the concept of a death dream. Is there any credible information about the concept or is it just a vague idea referred to in some movies? --145.255.244.249 (talk) 12:48, 3 July 2017 (UTC)[reply]

A possibly related concept might be effects experienced by those who lived a near death experience, but that may not be enough damage to really be equivalent... There's of course also "meat's dream"

. —Paleo Neonate - 12:56, 3 July 2017 (UTC)[reply]

I wouldn't call it a "concept." I would call it an 80s movie trope. 209.149.113.5 (talk) 14:32, 3 July 2017 (UTC)[reply]

the concept is much older. See An Occurrence at Owl Creek Bridge. -Arch dude (talk) 18:49, 3 July 2017 (UTC)[reply]

Since there is never recovery from brain death, there can't really be any credible information. As PaleoNeonate said, the closest thing you get is a near death experience. Looie496 (talk) 16:04, 3 July 2017 (UTC)[reply]

That article actually claims you can have a flat EEG from deep anaesthesia or cardiac arrest. I should look into this... obviously there is no logically essential reason why all the neurons couldn't just stop at once for a bit without dying, so it's just a matter of when and to what degree it can be observed in practice. Wnt (talk) 18:10, 3 July 2017 (UTC)[reply]

Which reminds me of Flatliners... —Paleo Neonate - 07:01, 4 July 2017 (UTC)[reply]

Do elephants get boogers in their trunks?

Topic says it all. ScienceApe (talk) 17:30, 3 July 2017 (UTC)[reply]

I would suspect that when elephants are dehydrated the mucus in their trunks would thicken, yes. Note that when they find a body of water, they suck water up through their trunks and spray it back out, and this may serve to clean it out. StuRat (talk) 17:44, 3 July 2017 (UTC)[reply]

But they are probably very, very thin, given the length. --Kharon (talk) 19:26, 3 July 2017 (UTC)[reply]

An example. 209.149.113.5 (talk) 19:31, 3 July 2017 (UTC)[reply]

Pressure on the ground, speed of vehicle

How does the speed of a vehicle correlates to the pressure of its tires on the ground? --Hofhof (talk) 17:46, 3 July 2017 (UTC)[reply]

No direct correlation. See Friction#Dry_friction. The normal force, which is approximately the same as the weight of the vehicle on level ground, under most conditions, does relate to the frictional force, which limits the acceleration of a wheel-driven vehicle and also can limit the max speed, as the normal force needs to be sufficient for the wheels to exert enough frictional force to overcome the aerodynamic drag of wind resistance. The pressure on the area of tires in contact with the ground is roughly the normal force divided by the contact area. So, there is distant relationship between the two, but nothing direct. StuRat (talk) 17:57, 3 July 2017 (UTC)[reply]

As above, no direct correlation in most situations and under most reasonable assumptions. However, some vehicles (including cars with a functional spoiler instead of a decorative spoiler) have an aerodynamic shape that uses airflow to push the vehicle toward the ground, resulting in more pressure as the speed increases. Also, a vehicle going over a hill will see increases and decreases in the vertical component of acceleration, These vary with speed and result in varying pressure. At the extreme, if you pop over a hill you will leave the ground completely, resulting in no pressure. -Arch dude (talk) 18:38, 3 July 2017 (UTC)[reply]
In theory, if your speed is high enough and you are on an astronomical body with a small enough radius and low enough gravity, an increase in speed will reduce your effective weight and therefore the pressure as centripetal acceleration counteracts gravity. This effect is probably not observable on Earth or even on the Moon, but would be appreciable on small bodies such as the moons of Mars or small asteroids. -Arch dude (talk) 18:44, 3 July 2017 (UTC)[reply]

Short: The answer depends on how the car is build. If it has wings the pressure will fall as the vehicle gains speed. If it has spoilers pressure will rise with speed. --Kharon (talk) 19:23, 3 July 2017 (UTC)[reply]

I beg to differ. Above considerations only apply to a perfect road, where ... no tire would be needed! In real life, you need tires, with a correct pressure, and you need them all the more than you speedy drive. When you drive on a speed bump slowly, the pressure barely change in the tire; if you do it with speed, a dramatic spike in pressure will occur.

since pressure is a direct measure of energy, and energy correlates with square of speed, i think that pressure variation in tires correlates with square of the speed of the vehicle. Variation, of course

Also, it is well known that pressure is increased by heat, and that heat is increased by speed. I.e., pressure is greater when you drove for a length of time at, says, 30m/s (108km/h), than if you did at 10m/s (36km/h)

I also expect this effect to be of the square kind (but different)

Now, a proper answer would need to be a tire designer

Gem fr (talk) 10:55, 4 July 2017 (UTC)[reply]

July 4

Is this still co-evolution?

If one species uses fancy tools to manipulate the genes of another species and the latter species is made to benefit the former species at its own expense, then is that still co-evolution? Chickens are bred to be bigger and bigger, so they are evolving. And humans are getting more food. Is this considered co-evolution? 50.4.236.254 (talk) 00:24, 4 July 2017 (UTC)[reply]

No, that would be selective breeding or genetic engineering. StuRat (talk) 00:27, 4 July 2017 (UTC)[reply]

Also see artificial selection. —Paleo Neonate - 06:56, 4 July 2017 (UTC)[reply]

"getting more food" is not evolution.

However, increased tolerance to alcohol, because of drinking fermented brew like beer and wine for many generations is evolution, so, you might say that Vitis vinifera and homo occidentalis (red link ?) coevolved , even-though it was all prompted by men, not by grapes.

Gem fr (talk) 13:39, 4 July 2017 (UTC)[reply]

Dating and job hunting parallels

For years, many have drawn parallels between dating and job hunting. Are they basically the same thing just with different end goals? I've seen one article mention that they are both markets with search friction. 82.132.184.18 (talk) 00:36, 4 July 2017 (UTC)[reply]

Including hooking up for a few years and then moving on to something else? ←Baseball Bugs ^{What's up, Doc?} carrots→ 01:31, 4 July 2017 (UTC)[reply]

This is probably more appropriate for the humanities reference desk. —Paleo Neonate - 06:54, 4 July 2017 (UTC)[reply]

I agree, but will nonetheless mention a few links.

market friction.

Market is such a large concept that it can be applied to pretty much everything, so why not dating and jobs? You just need to consider that girlfriend/boyfriend/husband/wife is some sort of job, while job is some sort of relationship, and voilà, they are pretty much the same, aren't they?

Our Matchmaking article does have a "other uses" section, related to business.

Our Job market article don't link to any dating related concept.

Gem fr (talk) 12:55, 4 July 2017 (UTC)[reply]

Eating Fish

The prettiest fish are the upscale elite in the MacQuarium. Blooteuth (talk) 18:02, 4 July 2017 (UTC)[reply]

Why people don't eat colourful fishes found in the sea? Why humans eat fish only with silver scales? And fishermen in the sea are not able to catch colorful fish. They always catch fish with silver scales in their net. — Preceding unsigned comment added by Forester7568769 (talk • contribs) 06:12, 4 July 2017 (UTC)[reply]

The premise of your question is wrong. Fishermen do catch more colourful fish and sell them. Here in Australia there are black, yellow or orange coloured fish for sale as well. Graeme Bartlett (talk) 06:22, 4 July 2017 (UTC)[reply]

How about Rainbow_trout#As_food and Salmon as food ? 06:38, 4 July 2017 (UTC)

People certainly do eat colo(u)rful fish, such as red grouper, red bream, parrotfish, gourami, and so on. Some fish lose their color when they die (e.g. mahi-mahi), so are not perceived as colofrul for that reason. Some of the food fish are pelagic (scombridae. carangidae) and have countershading color scheme, whereas the most colorful fish are usually smaller tropical reef fish which are not usually used as food in the West. Hope this helps. --Dr Dima (talk) 07:04, 4 July 2017 (UTC)[reply]

And to the second part of your question - regarding the scales - people who do not observe kashrut do eat fish "without scales", such as catfish or eel for example. Dr Dima (talk) 07:16, 4 July 2017 (UTC)[reply]

Colorful fish my be aposematic, warning their would-be predators they are poisonous or otherwise unpalatable. μηδείς (talk) 17:51, 4 July 2017 (UTC)[reply]

What is this crop?

What is this crop? It won't be anything unusual - I'm simply asking because I don't know anything about agriculture.

It's in the Vienne department of France.

Hayttom (talk) 12:42, 4 July 2017 (UTC)[reply]

sunflower Gem fr (talk) 13:08, 4 July 2017 (UTC)[reply]

Thank you, Gem fr! I suppose it must be this year's crop, and nearby fields with flowering sunflowers are older. (I hadn't compared the leaves.) Hayttom (talk) 15:14, 4 July 2017 (UTC) [reply]

Resolved

Tube trains and onrush of air

When waiting on an underground London Underground platform, as a hat-wearer, I'm acutely aware of the onrush of air that precedes the train's entry.

As a science ignoramus, I'm puzzled and curious that the most furious burst of air seems to end when the front of the train is still some metres away from me. I'd have thought it would increase in intensity until the train passed me. But it doesn't. I presume a well-known physical force or combination of forces is at play here. Enlighten me, but go easy, I'm a science ignoramus. --Dweller (talk) Become old fashioned! 13:35, 4 July 2017 (UTC)[reply]

Remember the train is slowing down as it enters the station. 79.73.134.123 (talk) 14:32, 4 July 2017 (UTC)[reply]

That's interesting. Logically feels right, but as a passenger, I always get the feeling they brake very late indeed. Can anyone find RS about how tube drivers brake their trains? Might vary a bit - the train stock is quite different on some lines. If relevant, I'm interested in the Northern line. --Dweller (talk) Become old fashioned! 15:30, 4 July 2017 (UTC)[reply]

Look at Drag (physics); the first diagram/4th image show you some line of airflow around a perpendicular plate

"it would increase in intensity until the train passed you" in the event that air stood completely still until directly in contact with train's head, then instantaneously pushed aside in a most violent rush. This would require air speed to go from zero (just before hit by train) to close to infinite (to instantaneously move aside and let the train take the place air at previously been), which is not possible. Hence, the process is smoother: things works quite like the train had some invisible air cushion moving with the train, that begins to push air aside quite ahead of the train, a few meters ahead. I guess this what you translate as "the most furious burst of air seems to end when the front of the train is still some meters away from me". When the train's head arrive at you level, the air has already been completely pushed aside.

Because underground is a tunnel, you might also be interested in piston effect and Venturi effect (the effect that push you toward the fast moving train, which will kill you if you stand too close at first).

Gem fr (talk) 14:42, 4 July 2017 (UTC)[reply]

Thanks. I'll check out those links. And you explained that really well. --Dweller (talk) Become old fashioned! 15:30, 4 July 2017 (UTC)[reply]

Number of breasts/litter size

How does the number of breasts relate to the size of offspring? The 'one-half rule' (number of mammaries equal half of litter size) seems to apply well across mammals. There are some exception though. Some animals like some moles have less breasts than 'needed'. The reason is that the youngster do not tend to fight. However, what explains too many breasts per younger? Cows have 4 breast per calf. Why? --Hofhof (talk) 13:18, 4 July 2017 (UTC)[reply]

Moved from the Humanities desk. Roger (Dodger67) (talk) 13:53, 4 July 2017 (UTC)[reply]

Mammary_gland#General, Mammary_gland#Evolution

most of the time "why?" isn't a pertinent question regarding evolution.

As long as all offsprings get fed, it's not important whether they share a single breast, or have 2, 4 or more to choose from. :Now, obviously, more breast than "needed" is a safer arrangement that the reverse, so evolution certainly favors that.

On the other hand, "too much" is pretty neutral, evolution-wise. A 2-breasted cow just wouldn't get any edge over the normal cow.

Note that males have breast, usually not functional (there ARE exception of male lactation), but there, still. Why? well, why not...? Evolution didn't care to wipe them off completely, since they cost close to nothing as they are.

Gem fr (talk) 15:09, 4 July 2017 (UTC)[reply]

Some thoughts:

1) Too few could definitely be a problem. Even when all working, that means the litter-mates may have to fight to get a spot (wasting energy and potentially causing injuries) and the mother may need to take longer to nurse them all, providing less time to eat and do all the other things needed to keep them all alive.

2) There's also a risk that some may become non-functional for whatever reason (infection, cancer, etc.).

3) Even when functional, they may become sore and the mother may refuse to nurse with those nipples. This seems like it would be particularly an issue with animals that are teething while nursing. StuRat (talk) 15:50, 4 July 2017 (UTC)[reply]

Pinging Hofhof. -- Roger (Dodger67) (talk) 16:12, 4 July 2017 (UTC)[reply]

The Virginia opossum normally produces more offspring than it has teats. This is a means of natural selection, as is the fact that many viviparous sharks practice sibling cannibalism in the womb. μηδείς (talk) 18:05, 4 July 2017 (UTC)[reply]

Gorilla warfare

Chimpanzee warfare exists. What about gorilla warfare? Do gorillas ever have conflicts bigger than one-on-one, or is "gorilla warfare" always just a spelling mistake? 208.95.51.38 (talk) 16:35, 4 July 2017 (UTC)[reply]

Kekeke. It's guerilla warfare. μηδείς (talk) 17:44, 4 July 2017 (UTC)[reply]

Btw, guerilla has no relation to gorilla; it is from Spanish guerrilla (guerra +‎ -illa), diminutive of guerra ("war"), coined during the Peninsular war. — 2606:A000:4C0C:E200:65B0:9134:56E3:14CB (talk) 18:48, 4 July 2017 (UTC)[reply]

That is why I asked if "gorilla warfare" was always a spelling mistake. 208.95.51.38 (talk) 19:09, 4 July 2017 (UTC)[reply]

I thought you meant it the other way around (that geurilla was meant to be gorilla). 2606:A000:4C0C:E200:65B0:9134:56E3:14CB (talk) 19:23, 4 July 2017 (UTC)[reply]

It's not traditional war, but this ape went ape on the zoo-going Dallas public in broad daylight, wounding four (including a child) and alarming countless birds before confronting police and going down in a hail of bullets. In 2004, the immediate theory was that this was an isolated act of revenge, committed by someone who could no longer tolerate being enslaved, oppressed and mocked by local greater primates. In 2017, they'd take one look at the name "Jabari" and it'd be settled: probably not working directly for the WWF, but clearly poisoned by their radical online propaganda. InedibleHulk (talk) 17:53, July 4, 2017 (UTC)

There is an article about actual "gorilla warfare" in The Atlantic -- but I can't read it without unblocking ads:

Yong, Ed. "Why Are Gorillas Committing Mob Violence?". The Atlantic. — 2606:A000:4C0C:E200:65B0:9134:56E3:14CB (talk) 19:29, 4 July 2017 (UTC)[reply]

The first humans

Is it true that all humans have the same forefather? Discovery channel said that there was a race of only 2000 humans in Africa, and they migrated to different continents.

After thousands of years they became African, European, Indian, Arab, Asian. — Preceding unsigned comment added by Luckynumberninetynine (talk • contribs) 16:36, 4 July 2017 (UTC)[reply]

See [14]. Tgeorgescu (talk) 16:41, 4 July 2017 (UTC)[reply]

See Y-chromosomal Adam. Loraof (talk) 17:35, 4 July 2017 (UTC)[reply]

Emergency room presentations of anxiety

Are Presentations of anxiety common in ER departments? Or do they tend to present complaining of "life threatening" symptoms which they suspect is something else? 82.132.229.246 (talk) 18:01, 4 July 2017 (UTC)[reply]