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November 8[edit]

How big does a camera pixel need to be for the small pixel width to visible light λ ratio to have negligible effect?[edit]

How do I calculate how many photons per pixel at native ISO and (impossible) 100% efficiency from stuff like luminance of what the pixel's photographing, focal length, pixel and sensor size, and f-stop? Sagittarian Milky Way (talk) 18:12, 8 November 2018 (UTC)

How do you use the photons per pixel and number of pixels to calculate the chance that a hypothetical photo where every pixel would be exactly between 127,127,127 and 128,128,128 in 8-bit per channel RGB if shot noise didn't exist would still not contain numbers besides 127 and 128 even though light is quantized and the time between photons is only an average? Sagittarian Milky Way (talk) 18:55, 8 November 2018 (UTC)

Sukhwan's paper was the first search-result! Characterization of Noise in Digital Photographs for Image Processing (HP Labs, 2008).
If you're wholly unfamiliar with photoelectric photoconversion, a good place to start reading is our articles on the photoelectric effect and quantum efficiency.
Your answer will require quantum mechanical statistics. All we can measure is whether an electron is actually ejected from a pixel's photoactive area; and we have to infer whether that electron was ejected by a "valid" incident photon, or if it was ejected by one of the many other sources of noise that can cause an electron ejection. We never actually know whether one individual photon was "valid" - we can only describe the aggregate statistical properties of the incident radiation.
In practice, we measure the approximate value in a well-calibrated laboratory, and we don't usually spend much time to describe it with an equation - because we already know that the equation to calculate that value would be really complicated, and it would depend on a lot of details we'd have to measure in a lab anyway.
Nimur (talk) 21:04, 8 November 2018 (UTC)
Cant be answered because Image sensor technology like sensor technology in general is in constant development and takes impressive huge leaps every year. Some companies just released 48 megapixel cameras in Smartphones. Just a few years ago you had to buy a chunky and very expensive digital camera with a huge sensor chip inside to get such resolutions. Today its all in a pin head on a circuit board so tiny, you need calipers to place it correctly in its little spot in these smartphones. In 10 years they can probably place nano cameras with battery and transmitter on dragonflies to follow them "live". I think i read somewhere some secret services actually already use such Insect-drones for high profile infiltration and surveillance. --Kharon (talk) 03:26, 10 November 2018 (UTC)
P.S.: Better watch our for them suspicious flies that keep following you :D --Kharon (talk) 03:35, 10 November 2018 (UTC)
Two related issues: first, you only know how many pixels your camera has. unless you take it apart you don't know whether the actual image sensor is huge with large pixels or small with tiny pixels. The second issue is the size of the lens. The small diameter, limited depth lens typical of smartphones simply cannot get as good a picture as a digital camera of the same quality with a bigger lens. The laws of physics make it so that super thin smartphone equals poorer-quality camera and tinny sound. --Guy Macon (talk) 04:04, 10 November 2018 (UTC)
Well I don't think you have to take it apart. For higher end smart phones from reputable brands, it's not that uncommon the sensor is known e.g. the global and Chinese version of the Xiaomi Redmi Note 5 [1] which for developed work income levels is probably mid range or low mid range comes [2] with the Samsung S5K2L7 [3] and S5K5E8 [4] sensors on the rear. While okay Xiaomi can be confusing with various models with different specs but the same name in different locations, generally the info out there. Crappy Chinese brands often publish completely fake info, but the better ones are generally better at that. And of course other non Chinese brands like LG, Samsung etc are likewise often reliable at least for their mid range and higher phones. In many developed countries, publishing such specs carries a legal risk if false, and the precise model of the image sensor is probably possible to check unlike say storage capacity of batteries so for reputable stores and reputable brands there tends to be a reasonable incentive not to lie. As for the image sensor specs, well that's more complicated, still for a reputable brand I think you can resonable trust the image sensor size specs amongst other things because again it's something easy to check. Nil Einne (talk) 12:32, 10 November 2018 (UTC)
These are easier to find for camera cameras. 36x24mm for cameras advertised as full frame, smaller like APS-C for cheaper cameras. The lens opening is well advertised (focal length divided by f/number), angle of view has the photo diagonal in degrees for each focal length. Some of the light hits outside the sensor corner though, you can't have vignetting and poor corner image quality in a decent camera. Sagittarian Milky Way (talk) 13:23, 10 November 2018 (UTC)

1) the CCD charge wells hold 1000s of electrons for pixels of reasonable size, so the 8-bit number is the result of A-D conversion. 2) If it's RGB that means you'll lose some photons to the Bayer filter but you might want to ignore that too. 3) Maybe what you're really asking is how to compute the number of photons from the luminance. Answer: look at luminous efficiency to find some parameters to convert lumens to watts. Then find the photon energy by multiplying the photon frequency (which depends on the color) by Planck's constant. Make sure to get all the units consistent and it should just be arithmetic from there. (talk) 06:41, 11 November 2018 (UTC)

November 10[edit]

Celery powder less harmful than curing salt[edit]

Is there any evidence that processed meat cured with celery powder is less likely to cause cancer than meat cured conventionally? What do scientific research studies show? — Preceding unsigned comment added by Mister Johnston (talkcontribs) 00:58, 10 November 2018 (UTC)

I don't think there's really any evidence that cured meat causes cancer. One could argue that it's the smoking that introduces carcinogens. But for sure, fer suure, the nitrites in celery powder are exactly the same as the nitrites in curing salts, and will have exactly the same risk. Abductive (reasoning) 19:49, 10 November 2018 (UTC)
Not according to the IARC, which classifies cured meat as carcinogenic to humans. The sodium nitrite produces nitrosamines, which are carcinogenic. -- (talk) 09:17, 11 November 2018 (UTC)
No, there is not. Celery contains nitrites, which is why it's used. As to why celery is used, at least in the U.S. it's because of a big fat loophole in FDA labeling standards. If you use celery juice/salt instead of curing salt, you can label your product as "all natural" and "nitrate/nitrite free", even though the celery product you added to it contains nitrites. This is because the FDA considers "celery salt" to be just that, "celery salt", not "nitrate". Then you can stick this on your packaging/advertising and get people to buy it over competitors' products because they think it's "better for you", when chemically there's no difference. It's illegal in the U.S. mass market to sell uncured and unfermented sausages, etc., for a very good reason, because they might kill you from botulism. But the poorly-educated public has come to view preservatives as "bad", because they're supposedly "unnatural", without stopping to consider why preservatives are used in the first place. Botulism is perfectly "natural", so it must be good for you, right? -- (talk) 09:17, 11 November 2018 (UTC)
Actually, every such package I've seen in the U.S. always explicitly has fine print saying "nitrite/nitrate free except for that present naturally in celery..." or some such. That said, there is at least one noticeable distinction in that celery contains nitrate rather than nitrite. Supposedly the two are interconvertible pretty freely, but I am not sure if that applies before they are cooked or eaten. And I'm not sure how many of the carcinogens produced by nitrite are generated by chemical reaction within the meat during storage rather than after consumption. Note I'm saying "not sure" literally, doesn't mean there is a difference either! Wnt (talk) 23:27, 11 November 2018 (UTC)
To follow up a bit, here's a paper [5] that discusses some roles for nitrate supplementation in humans. They were expecting somehow to reduce blood sugar but it had no effect on that. I thought this demonstrated instantaneous conversion of nitrate to nitrite in the human liver, but [6] says that beetroot juice may or may not contain lots of nitrite, depending on whether bacteria are active, though industrially it is usually pasteurized lightly to prevent that, or keeping it cold slows it down. The original paper credits their beetroot juice to "Beet It", a company whose website claims that nitrate can "only" be converted to nitrite by bacteria on the tongue, according to the Google blurb (I didn't find the statement when I went to the site, but it's repeated here). Which to readers of the first papers is clearly bonkers, even if common sense failed them otherwise. Bottom line: I don't know how much nitrite is present in food products made with these juices, and I don't think I'd believe the stats without seeing an analysis of the specific product in question. Wnt (talk) 15:39, 12 November 2018 (UTC)
If you believe that nitrates/nitrites are actually bad for you (the jury is still out on that, and your body produces large amounts of nitrates/nitrites by itself regardless of what you eat), than most "uncured" meats that use celery juice/extract actually have more nitrates/nitrites than traditionally cured meats. That's because a certain minimum amount of nitrates are needed to ensure that pathogens don't grow on the meat, but since celery juice/extract is a natural product whose concentration may vary from batch to batch, extra is added to make sure that the food is safe no matter how weak that particular batch of celery was. The USDA has a limit on how much artificial nitrite can be added to food, but there is no such limit for celery powder. It's also a bit worse than that, as food with artificial nitrites is required to have vitamin C or E added to it to help prevent the nitrites from forming nitrosamines, but there is no such requirement for foods containing celery extract. To respond to Wnt's point, there's not really a meaningful distinction between artificial nitrites and the nitrates in celery, as the celery powder/extract is usually treated with bacteria to convert the nitrates into nitrites (see [7]), and your saliva is pretty good at converting any remaining nitrates into nitrites. In any case, most of your dietary nitrates/nitrates come from vegetables, not cured meats, so it's not worth worrying about. --Ahecht (TALK
) 16:22, 12 November 2018 (UTC)

Ultrasonic Sound[edit]

Could an ultrasonic sound explode human heads or cause weather problems, say one of 240dB-1000dB? déhanchements (talk) 16:26, 10 November 2018 (UTC)

I don't know, but I presume you've already read Sonic weapon. As documented there, "Studies have found that exposure to high intensity ultrasound at frequencies from 700 kHz to 3.6 MHz can cause lung and intestinal damage in mice . . . Tests performed on mice show the threshold for both lung and liver damage occurs at about 184 dB", so hugely larger energies (its a logarithmic scale, remember), are bound to cause grosser (in both senses) injuries to a human body. The range of 240dB-1000dB you quote, starts at the loudness of atomic bombs ("240-280 dB", according to a Quora answer and "A nuclear bomb. Decibel meters set 250 feet away from test sites peaked at 210 decibels. The sound alone is enough to kill a human being, so if the bomb doesn't kill you, the noise will" from the same set of answers), so I'm wondering what your envisioned source of your hypothetical sound is.
As for weather "problems" (as opposed to "detectable effects"), Effects of nuclear explosions (where "blast" might be roughly equated to sound) may be of some relevance (since it's dealing with the sort of energies implied by your "240dB-1000dB").
Overall, your question presumes energies which only governments (or natural forces) have the means to deploy, so some of those knowledgeable in the area might be constrained in what they can say. Others, however, might wish to present at least abstract calculations (and will be better qualified than I to do so). {The poster formerly known as} (talk) 17:20, 10 November 2018 (UTC)
Re the link to "sonic weapon" this may have been an accident. See [8]. (talk) 17:49, 10 November 2018 (UTC)
I'm wondering what your envisioned source of your hypothetical sound is. Hypothetically, the source of this sound is the Spirit of Katavi national park. déhanchements (talk) 19:59, 10 November 2018 (UTC)
The sonic capabilities of spirits of place are largely unexplored by conventional science, so your attribution of extensive capital disruption to one would be difficult to refute; I know its not something I'd be inclined to investigate at Chanctonbury Ring after dark! {The poster formerly known as} (talk) 22:23, 10 November 2018 (UTC)
Katavi national park in western Tanzania is named after the legendary hunter Katavi whose spirit is believed to possess a Tamarind tree and where the locals go begging for blessings[9]. Either a constant loud sound (85 dB(A) or above) or a one-time extremely loud sound (120 dB(A) or above) can cause permanent deafness but safari organizers[10] [11] are your source of reassurance if you are concerned this might occur. DroneB (talk) 00:19, 11 November 2018 (UTC)
Unless I have a wrong factoid buzzing around, it is not even possible for sound (in air) to reach 1000 dB. Strictly speaking, 1000 dB is a ratio, and doesn't mean anything without a reference value, but for the usual one used for sound intensity level, 1000 dBA or 1000 dB (SIL) is not a possible value, because air cannot carry that much power flux as sound. Above some much lower value (maybe around 190 dBA? can someone find it?) the mathematics of pressure waves in air breaks down, and you can have a shockwave, but not "sound". 1000 dB would be a ratio of a googol, so not even shockwaves are a sensible model — you'd have to start talking about black holes forming from that much energy all in one place. --Trovatore (talk) 23:20, 10 November 2018 (UTC)
Let's pretend I said 240dB-280dB, about that comment up there that mentions 1000dB, doesn't exist. And thank you DroneB, I can finally rest easy. déhanchements (talk) 02:10, 11 November 2018 (UTC)
Sound pressure level suggests 194 dB peak or 191 dB SPL for 1 ATM although the value in the table is disputed. There's some discussion in the talk post. (I don't mean the most recent post but back in 2008.) Nil Einne (talk) 09:26, 11 November 2018 (UTC)
Thanks, Nil. --Trovatore (talk) 01:21, 12 November 2018 (UTC)


Im by no means a science major so correct me if im wrong. But i believe some physics law state that energy cannot be created from nothing and energy cannot be destroyed only transformed.

With that in mind, I have difficulty understanding Dams. As far as I can tell there is 0 difference for a river whether or not it runs through a dam on its way down. and that generates massive amount of energy for us. Where does this energy come from? Here I dont mean dynamo nor gravity. I mean where would all this massive energy have gone if the dam hadnt been there since it seems like nothing else in the area would have changed if the water hadnt gone through the dam first. — Preceding unsigned comment added by (talk) 22:24, 10 November 2018 (UTC)

You are correct that energy can be transformed, it can exist as Potential energy or Kinetic energy. Examples of things that have potential energy are a book on a shelf, a stone on a mountain, an unused AA battery or water that has accumulated upstream of a Dam. Examples of kinetic energy are the mechanical movements of any machine that does physical work, sound vibration, fluid turbulence and heat. Potential energies readily transform to kinetic energy. Examples of that transformation are the sounds of the book or the stone falling, or the heating of a lamp filament by the battery in a Flashlight. Virtually all potential energy eventually converts to the kinetic energy of heat. That happens constantly to the potential energy of most rainfall. Humans manage to capture some of rainfall's energy in dams equipped to generate Hydroelectricity which is kinetic energy in a useful and saleable form that consumers can use to drive electric motors, heat their homes and power the Internet computer that brings you Wikipedia. DroneB (talk) 23:54, 10 November 2018 (UTC)
See Energy#Transformation, which uses dams as an example of transforming energy. Mikenorton (talk) 00:02, 11 November 2018 (UTC)
Are you saying energy can transfer between potential and kinetic energy? How do you differentiate between a book sitting on a shelf with potential energy, and 0 potential? (talk) 04:13, 11 November 2018 (UTC).
Yes that's correct, PE and KE can be exchanged. PE is measured relative to something else, one datum that could be used is the height of the bookshelf, or the surface of the Earth, or the centre of the earth, or far out beyond the solar system. They are all useful in certain circumstances. Greglocock (talk) 05:23, 11 November 2018 (UTC)

Both of you are completely missing the point of my question. Im not asking how a dam works. — Preceding unsigned comment added by (talk) 01:27, 11 November 2018 (UTC)

Without a dam, the water would still fall somewhere and convert potential energy to kinetic energy. Most of the kinetic energy would quickly be converted to heat when obstacles or friction slow down the water. PrimeHunter (talk) 01:44, 11 November 2018 (UTC)
I would note that most modern hydroelectric dams tends to be massive constructions which can significantly affect the river they're built on hence why they can cause concern to environmentalists and also often those concerned about the people downstream. This discussion [12] and this source [13] aren't the best sources but I think they do illustrate the larger point namely it's probably not simple to compare the situation before the dam and after the dam. Nil Einne (talk) 05:09, 11 November 2018 (UTC)
where would all this massive energy have gone if the dam hadnt been there… It would have produced turbulence in the body of water, and friction with the earth. Any river canyon will show you the power of erosion generated by moving water. A dam stops that from happening by harvesting the energy. This can be an environmental problem, because a dam stops sediment from being carried downstream. For instance, the Aswan Dam has stopped the flooding of the Nile, which means farming along the Nile is now mostly dependent on chemical fertilizers and manmade irrigation, and the Nile delta is eroding away (as it's not being replenished by new sediment). -- (talk) 09:03, 11 November 2018 (UTC)
All this is really chickenfeed compared to the fact that the power of the tides is changing the dynamics of the earth-moon system so that both bodies will eventually turn the same face to each other and the day and the month will both be 47 days long. (talk) 11:34, 11 November 2018 (UTC)
And that pales into insignificance compared to the effects of our sun becoming a red giant well before that happens, according to our article. Mikenorton (talk) 13:46, 11 November 2018 (UTC)
  • ...which is why tidal power stations do exist and generate lots of power, even though they need much larger constructions than dams for the same power (quick-and-dirty summary: a mountain dam can harness water falling hundreds of meters, while tidal stations are limited to the amplitude of the tide, so the efficiency of the latter is lower). TigraanClick here to contact me 10:21, 12 November 2018 (UTC)

November 11[edit]

Java Programming[edit]

For java programming, what is the difference between read() and next()?

For example:

Let's say I import the java Scanner class. Then I proceed as follows:

Scanner userInput = new Scanner(; System.out.print("Enter the number of students: "); int numberOfStudents = userInput.nextInt(); System.out.println("The number of students you entered is: " + numberOfStudents);

My question is would this work if I replaced "int numberOfStudents = userInput.nextInt()" with "int numberOfStudents = userInput.readInt()"? What is the difference between next and read? When should one be used over the other?

ThunderBuggy (talk) 17:20, 11 November 2018 (UTC)

According to the documentation Scanner class does not have readInt method. Ruslik_Zero 20:27, 11 November 2018 (UTC)
So I would have had to create a readInt method before using it then, right? And the "next" methods are included with the Scanner class? ThunderBuggy (talk) 03:29, 12 November 2018 (UTC)
This isn't a general Java language question but, like nearly all Java questions, a question about different libraries used by Java. As Java has been around a while, there are many such libraries and they're often inconsistent. If we started again, we wouldn't have so many of these variations.
For the Scanner library class,[14] this implements and extends the Iterator<String> classinterface [15], which defines a next() method.
What Iterator does is that it allows next() to read, identify and move past a series of "tokens" in the input stream. That means you can write an input loop for a long series of tokens with just a simple loop. Then Scanner extends this, so that it recognises different types of token, such as nextInt() to read integers.
Don't mess with next() etc. by trying to rename or facade them as something else. Otherwise you lose the advantage of using Iterator in a consistent and clearly understood way. There is no readInt() in Scanner or Iterator.
readInt() comes instead from DataInputStream[16] rather than Scanner. This is part of rather than java.util.
Now we see the crucial difference! java.util is for chopping up bits of well-behaved data which are already loaded into memory. though is for dealing with the nasty real world of outside interfaces, data sources which stop halfway or timeout.
So for what you're doing here, then yes, base it on DataInputStream and readInt(), rather than Scanner and nextInt(). You're doing this because of the purposes of the different classes (DataInputStream understands real world IO), not simply the different methods. Andy Dingley (talk) 13:55, 12 November 2018 (UTC)
Iterator is an interface, not class. So, Scanner class implements it and extends Object class. Ruslik_Zero 20:43, 12 November 2018 (UTC)

Fat and the blood-brain barrier[edit]

According to Wikipedia the human brain is nearly 60 percent fat. Also according to Wikipeida fat cannot cross the blood–brain barrier, hence the need for the liver to convert fat into ketone bodies which can then cross the blood–brain barrier and nourish the brain during periods of starvation. "Unlike free fatty acids, ketone bodies can cross the blood-brain barrier". So explain to me how the brain came to be 60 percent fat if fat cannot reach the brain due to the blood–brain barrier. (talk) 19:51, 11 November 2018 (UTC)

See Lipogenesis. There's a reason you can get fat even if most of your energy comes from carbohydrates (such as sugars or starch) or protein and not fat. Nil Einne (talk) 20:35, 11 November 2018 (UTC)

November 12[edit]

Physics : Time[edit]

I wanted to know how could time possibly slow down with speed if it does will it affect biological growth of a human.Navjot1200 (talk) 11:39, 12 November 2018 (UTC) -

Time dilation depends on the relative speed of the observer. Your own time does not slow down from your own perspective, and everything happens exactly the same regardless of your speed (if gravity/acceleration is the same). It doesn't even make sense to ask how fast you are moving unless it is measured relative to something else. According to relativity there does not exist "fixed points" in the universe or an "absolute speed" compared to such points. You age normally but if you move very fast relative to observers then it looks to them like you are aging slower. However, if you are moving fast enough for time dilation to be significant for an observer on Earth then you are probably on a spacecraft where the gravity/acceleration may not be the same as on Earth, and that does affect biological processes. This may be avoided by a rotating spacecraft where your acceleration due to the rotation corresponds to the gravity of Earth. Gravity and acceleration are indistinguishable in the theory of relativity. PrimeHunter (talk) 12:45, 12 November 2018 (UTC)
Just to nitpick, while gravity and linear acceleration are indistinguishable, using a rotating spacecraft to create pseudogravity is distinguishable from Earth's gravity or from a spacecraft accelerating in a straight line. On a rotating spacecraft there would be an acceleration gradient between your head and your feet; since your feet are rotating faster, they would experience more pseudogravity. If you ran in such a spacecraft, running with the rotation direction would make you feel heavier, while running against the rotation would make you feel lighter. You would also experience Coriolis forces, so if you jumped in the air or suddenly stood up, you would feel a force pushing you backwards compared to the direction of rotation. --Ahecht (TALK
) 16:21, 13 November 2018 (UTC)
How is that scenario distinguishable from a spacecraft in orbit rather than in straight-line free-fall?--Jayron32 16:53, 13 November 2018 (UTC)

November 13[edit]

November 14[edit]

Electric/electronic device getting charged with static electricity[edit]

Why some non-earthed devices get charged with static electricity (and others not)?--Doroletho (talk) 00:21, 14 November 2018 (UTC)

It depends where they and whatever touches them are on the Triboelectric series. --Guy Macon (talk) 02:13, 14 November 2018 (UTC)

Aerothermal heating[edit]

I was expecting to find something else in the link above. It actually forwards to Aerodynamic heating (heating of a solid body produced by its high-speed passage through air). I was interested in a purported home heating/cooling system, that paired with a heat-pump, could harvest energy out of thin air (literally). That is, it can recover energy from air around the house. Supposedly, it could save up to 2/3 of power spent heating or cooling. Is this a viable heating and aircon system? Or is it an 'air-con' scheme? Is it possible to obtain energy from air (which has some energy in it, if not at absolute zero)? Or is it like the water powered car (that converts water into hydrogen with a battery, just to burn it in a fuel cell). I don't want to link to the companies offering it, but 'Air Source Heat Pumps' or 'Aerothermal heat pumps'. There's a Air source heat pumps article, but it is in chronically need of references and a more scientific background. --Doroletho (talk) 00:48, 14 November 2018 (UTC)

Your statement "air (which has some energy in it, if not at absolute zero)" is factually incorrect. You need a temperature difference to extract any energy from the air. See Heat engine.
A heat pump is simply a clever way of using less electricity to heat your home. A normal electric heater gives you one watt of heating for one watt of electricity. A heat pump is basically an air conditioner that is trying to cool the great outdoors and which has the cooling fins inside your house instead of outside. Every watt you put into it gives you one watt of heat, just as in the electric heater, but it also cools down the cold side (which is outside) by pumping heat to the warm side (which is inside), so you get more heat for the same amount of electricity.
I agree that the articles on this are a mess, and a quick look showed me some things that simply are not true, like "By definition, all heat sources for a heat pump must be colder in temperature than the space to be heated." Whoever wrote that has no understanding of how heat pumps work. I am a bit busy at the moment, but in a week or so I will clean up the articles. --Guy Macon (talk) 02:39, 14 November 2018 (UTC)