Wikipedia:Reference desk/Archives/Science/2017 December 8

= December 8 =

Please identify a weapon
What is this weapon mounted on a Ugandan Army Casspir APC? I suspect is is a type of light mortar or grenade launcher. Roger (Dodger67) (talk) 09:00, 8 December 2017 (UTC)
 * My best guess would be the QLZ-87 grenade launcher. Mũeller (talk) 09:20, 8 December 2017 (UTC)
 * Perfect match, thanks, and I see Uganda is known to be a user. Roger (Dodger67) (talk) 12:05, 8 December 2017 (UTC)

Cheese Curd
From Cheese Curd:

Most varieties, as in Ontario, Quebec, Nova Scotia, Vermont, or New York State, are naturally uncolored. The American variety is usually yellow or orange, like most American Cheddar cheese, but it does not require the artificial coloring.

So what's making American cheese curd yellow or orange, if no artificial coloring is added? Is it because of some difference between Canadian milk and American milk? Or some other factor? Mũeller (talk) 09:17, 8 December 2017 (UTC)
 * Annatto.-- Jayron 32 09:21, 8 December 2017 (UTC)


 * Missing the point that Annatto is a plant pigment, not synthetic, so a rewrite is required. Roger (Dodger67) (talk) 12:07, 8 December 2017 (UTC)

Square signal as only clock signal?
We have so many signals like triangular, ramp, unit step, impulse, square, etc. Why do we use only square signal for the clock signal in digital electronics? Sunnynitb (talk) 13:59, 8 December 2017 (UTC)


 * For the same reason that the time "pips" on the radio are short and clear rather than fading in from no sound over a 30 second period. There is a definite sharp step that can be used to trigger events. -- Q Chris (talk) 14:28, 8 December 2017 (UTC)


 * Thank you for your reply, but I didn't get it. Please, if possible, explain it a little bit or provide me some link regarding this. Sunnynitb (talk) 15:27, 8 December 2017 (UTC)


 * The purpose of a clock signal is to ensure that several events occur at exactly the same time. A number of different electronic components receive the clock signal, and each of them performs an action at a certain point in time based on the clock signal. Suppose the clock signal were a triangular wave, and the components were supposed to perform their action at the peak of the clock wave.  It would be difficult for the component to tell exactly when the clock signal was at its peak, because the voltage a short time before the peak or a short time after the peak isn't much different than it is exactly at the peak.  So one component might perform its action a significant amount of time before or after another one.  A square wave has the desirable property that the signal changes very quickly at the point where the wave rises and at the point where it falls.  So if all the components are watching for when the clock signal changes, they will all detect that event at nearly the same point in time.  CodeTalker (talk) 17:44, 8 December 2017 (UTC)


 * And squares enable this at double data rate unlike other sharp-jumped waves like sawtooth waves. This is used for instance to make RAM since c. 2000 twice as fast as it would've been otherwise. Sagittarian Milky Way (talk) 18:05, 8 December 2017 (UTC)


 * adding to the answers above, many components are allergic to slowly-changing signals. they can latch up in some indeterminate state (metastability) or begin to oscillate. read any datasheet for a digital IC, it will specify maximum rise and fall times. 78.53.108.2 (talk) 23:35, 8 December 2017 (UTC)
 * Digital logic doesn't like inputs that are in an intermediate state - it tends to turn on two transistors, one pulling the next state high, and the other the same next stage low. This increases power usage, and can overheat the device. In addition, most loigc circuits use the rising (or falling) edge of the clock signal, rather than the actual high (or low) period to trigger the event. LongHairedFop (talk) 11:49, 9 December 2017 (UTC)
 * The square signal is a theoretical ideal. The physical truth differs. The square signal rises and falls as fast as possible to synchronize as best as possible. An impulse is a non-periodic square. An op amp usually has a slower rise. It is specified as rising in volts per time. Using it as a comparator at higher frequency, it outputs an trapezoid voltage. Increasing frequency, it outputs an triangle. Analog signals like a sawtooth wave was used to control the beam on cathode ray tubes. -- Hans Haase (有问题吗) 12:13, 10 December 2017 (UTC)


 * Digital electronics is (pretty much by its de facto definition) based on voltage levels of signal. So non-square signals are a bit of a problem for it.
 * "Digital" doesn't mean perfect though. When I started out as a wee sprog with BT, one of the first things I did was a very intensive month-long electronics course: two weeks analogue, two weeks digital. And the first thing we learned on the digital part was how analogue "digital" really was. We plotted transfer functions and calculated noise immunity for the various logic families (as far back as ECL). Then we looked at the time-based issues, such as rise times and signal ringing.
 * There are digital protocols that aren't based on voltage levels - current loops, Manchester coding and others, but these are generally specialised and used for either signal transmission or storage, rather than logic. Andy Dingley (talk) 23:10, 12 December 2017 (UTC)

The vast majority of electronic devices are CMOS. Digital CMOS chips have better performance with fast edge rates. This comes into play in a number of ways. The most obvious is measuring shoot through current in an inverter. A slow transition wastes current by going through the PMOS and NMOS device without going into the load. These circuits also have gain and with normal designs with proper fan-out, slow edge rates sharpen up. A non-square wave input will be a square wave output if there is gain. Another reason for desiring fast edge rates is to control jitter between state elements. Slow edge rates affect when a latch opens and closes. Modern digital electronics are built from libraries of cells that all have different sizes and functions. They are then used in different configurations with different fan-in and fan-out loads. If the component of clock uncertainty is defined as being between the 20%-80% full-scale, it becomes straight forward to understand why a square wave is the most desirable. Another metric is that the edge rate is a fundamental characteristic of overall speed. This is better understood by looking at Fourier transform of the clock. A 2 Ghz processor might be built on a process where the transistor unity gain Ft is 200GHz. --DHeyward (talk) 07:36, 14 December 2017 (UTC)

current mass ULAS J1342+0928
The mass of the black hole is given as 800 million solar masses. Since the light that this object is seen by is from 13 billion years ago, how large could we expect its mass to be now? I suppose in this time it has had a chance to merge/collide with galaxies.144.35.114.190 (talk) 14:57, 8 December 2017 (UTC)
 * Supermassive black holes (the technical term) can have masses of tens of billions of solar masses (at least several percent of the galaxy they're in). Sagittarian Milky Way (talk) 15:20, 8 December 2017 (UTC)
 * Though reading that article carefully, it does also say that the theoretical maximum is around 50 billion solar masses, as the rate of growth slows above 10 billion. Of course, there is also the possibility that it no longer even exists!
 * How could a black hole disappear? (besides Hawking radiation, which would take way more than the current age of the universe for an 800 million solar mass black hole) Sagittarian Milky Way (talk) 23:29, 8 December 2017 (UTC)
 * Seemingly odd it does not matter how big a black hole is - the gravitation is the same - equal to the speed of light. So in itself a tiny black hole has the same potential to grow as the biggest black hole we will ever find. It depends how much mass is in its reach and how much time you calculate for the grow. 13 billion years seems allot but if you put the Galactic year into perspective our home galaxy just made 58 turns in 13 billion years. Also galaxies are usually separated by millions of lightyears of empty space between them. Not that much traffic locally unless you are really close to something. If that giant black hole ate its own galaxy it might need another 500 billion years for another galaxy to cross its path.
 * Additionally odd is that according to its mass it seems to have already eaten a few hundred million suns aka every thing around it, if you consider only very, very, very few stars are as big or bigger than our 640 lightyears close neighbor sun Betelgeuse, which has 11.6 times or VY Canis Majoris estimated at 17±8 times the mass of our sun (see List of most massive stars). That is why there seems no possible explanation how a black hole could accumulate so much mass just a few hundred million years after the so called big bang. --Kharon (talk) 04:52, 9 December 2017 (UTC)
 * The speed of light escape velocity defines the black hole. If it was less light could escape and it wouldn't be a black hole and it'd just be matter, not some crazy thing that bends reality to the degree it can only have spin, change and mass. That's like saying strange how all the boats weigh as much as the water they displace. Well duh. Sagittarian Milky Way (talk) 05:29, 9 December 2017 (UTC)
 * There is so much wrong in this comparison that i feel the urge to look for the biggest book about physics i can find, to slap you with that until i fall asleep from exhaustion. --Kharon (talk) 08:28, 9 December 2017 (UTC)

Bytownite - industrial uses?
Does Bytownite have any industrial uses? Thank you, DuncanHill (talk) 15:11, 8 December 2017 (UTC)
 * According to this, No. -- Jayron 32 15:33, 8 December 2017 (UTC)


 * In general plagioclase feldspars are very common and have some routine industrial uses like ground up in ceramics or used for gravel.  But it isn't very common; also, the alkali feldspars are apparently used more than plagioclase.   Apparently feldspar is used in ceramics at 20-25%.   Amusingly, someone is tracking this conversation elsewhere  and thinks the rarity works against it.  The one thing I know it's being used for "industrially" is that some people are selling samples supposedly for healing chakras and such.  Not sure how much of an industry that is. ;) Wnt (talk) 17:33, 8 December 2017 (UTC)
 * The "Duncan Hill" who asked the question on MinDat is the "DuncanHill" who started this thread. Neither of me is the IP who originally asked on the article talk page. DuncanHill (talk) 18:03, 8 December 2017 (UTC)

Could x moles of acid or base stochiometrically react with more liters or molarity of reactant if it's added quicker?
(at least up to a point) If there's never much more acid/base concentration in the reactant container than needed to cause a reaction to happen (cause it's added as slow as it's used up) then might it stop after less reactant than if the acid/base is added all at once and the initial concentration's much higher? Or does it all even out by the end so it doesn't matter much as long as "all at once "is still reasonably civilized (no exploding, decomposing, boiling, igniting, large temperature rises etc.) and "slower" isn't so slow that something like evaporation or oxidation changes the nature of the reaction much? Sagittarian Milky Way (talk) 20:19, 8 December 2017 (UTC)


 * Given my PO's advice, I am not going to hat this, but are you seriously asking whether one should combine an acid and a base quickly? You'd probably not just be failed out of high school chemistry, but you expelled and your teacher fired.  This sort of BS question really doesn't belong here.  Do you contribute to WP, or are you simply WP:NOTHERE? μηδείς (talk) 22:03, 8 December 2017 (UTC)


 * It doesn't have to be a strong acid and a strong base, it could be supermarket vinegar and baby teeth or those drain cleaners that take hours to work and clogs. I think it doesn't matter with acid/base neutralization anyway since titration's very accurate (but you're the expert). Even so, I've poured baking soda straight into supermarket vinegar and didn't have <10 fingers when HS chem teacher got tarred and feathered. Sagittarian Milky Way (talk) 22:24, 8 December 2017 (UTC)


 * I can picture something different happening if some extra reaction could occur at an extreme pH value. For example, if you have a sodium carbonate (Na2CO3) solution and you slooooowly drip in less than one equivalent of hydrochloric acid while stirring rapidly, I would expect you to end up with a nice buffer of sodium bicarbonate (NaHCO3).  But if you pour in the HCl all at once without stirring, then that NaHCO3 will go fully to carbonic acid (H2CO3), which then can release carbon dioxide (CO2) by eliminating water (H2O).  If much of the carbon dioxide bubbles away into the air, then you would have to keep stirring for a very long time indeed to reverse that (by picking up traces of CO2 from the air, which happens, but would continue to happen past the original equilibrium point).  However, in this case, and I think in most others like it, exposure to concentrated acid effectively reduces the expected effect of the acid (in this case production of sodium bicarbonate), because (in this case) one proton is used up getting rid of the product that was created by another. Wnt (talk) 01:50, 9 December 2017 (UTC)

Using air bubbles to stabilize a ship
Cruiseships use stabilizers that act like wings to counteract the rolling movement of the ship. Would it be possible to get a similar result by using airbubbles? So, when a wave comes from starboard and the ship starts to tilt to portside, the ship would pump out air on starboard to decrease its buoyancy on that side? Joepnl (talk) 21:48, 8 December 2017 (UTC)


 * Any company that did this would open up its owners to liability for negligence if it sank, given that sinking due to loss of buoyancy is a well-documented factor. It's like telling your anger management patient to drink. μηδείς (talk) 21:58, 8 December 2017 (UTC)


 * I can't think of a single invention that wouldn't raise eyebrows in the legal department before it got implemented. Joepnl (talk) 00:21, 9 December 2017 (UTC)


 * The rolling motion of a ship is not caused by wave action. It is an oscillatory motion that represents conservation of mechanical energy - similar to the motion of a pendulum. When the ship's mechanical energy is too great it manifests as a rolling motion of excessive amplitude. The solution to the problem is to reduce the mechanical energy by using a force (or torque) that does negative work on the ship; and this is the function of the hydrofoils (also called stabilizers). Dolphin  ( t ) 00:30, 9 December 2017 (UTC)


 * How would a ship roll if there are no waves? Look out of the window on a ship. Waves: the ship moves. No waves: the ship doesn't roll or pitch. I had the absurd idea that removing messages from trolls was OK but apparently it's not. Joepnl (talk) 00:58, 9 December 2017 (UTC)


 * A ship rolls at its natural frequency which is usually different to the frequency at which swells and waves arrive at the ship. Swells and waves will excite the rolling motion of a ship, but other things can do so too. For example, the wind blowing through the superstructure can excite the rolling motion even though the wind is steady in speed and direction rather than oscillatory like swells and waves. It is true that large swells and waves will excite strong rolling motion, but it isn't true to say that if there are no swells or waves there will be no rolling motion. Dolphin  ( t ) 01:13, 9 December 2017 (UTC)


 * We were discussing "The rolling motion of a ship is not caused by wave action". Yes there are other possible reasons, including winds, asteroids, and fat people running starboard but those are not the main reason a ship moves. Joepnl (talk) 01:44, 9 December 2017 (UTC)

Movement of cargo could cause a ship to roll.194.126.80.63 (talk) 01:04, 9 December 2017 (UTC)


 * Do you mean list or roll? And  who's the troll?  If they're blocked, revert'em. μηδείς (talk) 01:10, 9 December 2017 (UTC)


 * The actual cause of rolling is not relevant to the question, I think. The question was, can rolling be reduced by pumping air under the rising side of the ship? I suppose it is, but 1) you must pump so much air as to counterbalance the momentum of the ship and 2) the needed quantity of air must flow before the rolling-up ends (this can be very very much air very very quickly). And 3) the air must be eliminated from under the ship side before you begin to pump under the other side, lest the whole ship goes under (as Medeis remarks). These are possibly too many "must" for your idea to be really practicable. 194.174.76.21 (talk) 18:52, 11 December 2017 (UTC) Marco Pagliero Berlin


 * OK, it's probably a pie in the sky. I do think the cause of rolling is relevant when it would be implemented. That would be a device that predicts a wave coming in (these exist, but can't remember where I saw it). "We" don't want that wave, but pushing it away is what the hull already does, and would defeat the purpose anyway. But if you blow air into the wave, maybe 5 meters away from the ship, there is no upward force causes by pushing it down. The air should thin out the wave, making it less heavy/m3, and forcing it to even out in all directions. Then again, it probably needs too much air too fast. Joepnl (talk) 22:58, 11 December 2017 (UTC)


 * Am I missing something? Blowing air out the side of a ship under a wave at some distance would simply be a form of sideways propulsion, since there would be an equal and opposite reaction on the ship due to the expulsion of the air.  This sideways propulsion by the air would entirely defeat the intended effect of cancelling out the sideways motion caused by the wave, no? μηδείς (talk) 22:03, 12 December 2017 (UTC)


 * Deep water wave.gif think not, but then again there's a reason I'm asking questions :). A wave "pushes" a bit, by lifting objects that will want to slide of the wave like a surfboard. Waves look as if it's water moving, but in reality it's just water going around in circles which probably does push and pull a bit sideways, but on a big ship the problem is the up and down movement. The bubbles are intended to dampen the up and down force when a wave meets the side of the ship. Joepnl (talk) 00:22, 13 December 2017 (UTC)


 * Ships already do that with ballast tanks and baffles in the tanks. They replace air in the ballast tank with sea water to adjust how the ship rides.  Ballast can affect roll stability in heavy seas.  --DHeyward (talk) 04:11, 16 December 2017 (UTC)