Wikipedia:Reference desk/Archives/Science/2015 March 21

= March 21 =

View posterior
What does "view posterior" mean, as in this image? (Attention: not for squeamish people.) Is it A: Given that it depicts a hollow structure, one might think it shows the posterior part; in other words, the view is towards the posterior side. Or, to the contrary, B: The view is from the posterior side. Thanks! &mdash; Sebastian 01:20, 21 March 2015 (UTC)
 * That view is toward the anterior. The tongue is anterior (and superior) to the epiglottis, and we are looking at the posterior surface of the epiglottis with the tongue beyond. -- Scray (talk) 03:40, 21 March 2015 (UTC)
 * Thanks, Scray! &mdash; Sebastian 03:45, 21 March 2015 (UTC)

Density of mixtures
How does the density of a real mixture change as a function of composition? For simplicity, assume a two component mixture. This means to take into account volume participation and other effects. Does it change exponentially, logarithmically, polynomially, etc.? Plasmic Physics (talk) 09:28, 21 March 2015 (UTC)
 * Volume of mixing is probably the article on the key aspect of this topic. DMacks (talk) 20:13, 21 March 2015 (UTC)


 * Thanks. It looks like the proportionality is too variable between mixtures to pin down to any one particular function. Plasmic Physics (talk) 23:44, 21 March 2015 (UTC)

Walvisbaai climate
The chart at Walvisbaai says that the city's highest average high temperatures come during the Northern summer, while its highest average low temperatures come during the Southern summer, i.e. mid-year days have a lot wider range between high and low than end-of-year days do. Why does its weather vary like this? It's profoundly arid, receiving less than 1cm of rain in an average year, so it's not the result of monsoons or other rain-related effect. Nyttend (talk) 12:44, 21 March 2015 (UTC)

Oops, never mind; I just noticed that I was looking at record temperatures, not average temperatures. Sorry. Nyttend (talk) 12:46, 21 March 2015 (UTC)


 * But it's still an interesting question. The place is almost as far south as the Tropic of Capricorn.  Why then are the extreme high temperatures for May, June, July, and August markedly higher than for any other months, when most of those months are colder by average high temperature than the rest of the year? --65.94.50.15 (talk) 23:39, 21 March 2015 (UTC)

the effects of irregular charge in an atom
Hi there,

The science acknowledge the existence of particles which have non-integer amount of electric charge.

I wonder, how would an atom behave if I replaced an electron with such a particle?

16:07, 21 March 2015 (UTC)~ — Preceding unsigned comment added by Exx8 (talk • contribs)
 * The particles of which I am aware that have fractional charge are quarks. I am not aware of quarks being observable for sufficiently "long" periods of time to be observable as components of atoms.  Robert McClenon (talk) 18:41, 21 March 2015 (UTC)
 * Add: Due to the phenomenon called color confinement, individual quarks (and hence their fractional charge) cannot be isolated. See also charge quantization. Abecedare (talk) 19:13, 21 March 2015 (UTC)

Quarks, fundamental particles?
Hi guys, I wanted to know, if quarks are fundamental particles, how come they emit an electron or a positron when they decay? that doesn't make sense to me, the decay mechanism makes it look like if quarks are made of electrons, positrons, neutrinos and antineutrinos, etc. Can someone of you explain this to me in a simple manner, since I don't know anything about physics? Thanks so much in advance.

--181.90.0.9 (talk) 16:45, 21 March 2015 (UTC)


 * (I'm not a physics expert, so I might be wrong, or explaining unclearly...) Are you sure they're emitting electrons/positrons? Isn't the usual decay mode for the quarks (other than the stable up and down) through absorbing/emitting W bosons?
 * Regardless, just because a particle is emitted at decay doesn't mean that the progenitor particle somehow "contains" the emitted one. A neutron doesn't somehow "contain" a proton, electron, and antineutrino. Instead what happens is that one of its constituent down quarks change flavour via the weak interaction, emitting a W and turning into an up quark: this is the only possible decay mode for the neutron that conserves baryon number. Double sharp (talk) 17:21, 21 March 2015 (UTC)


 * Mmm, no, I'm not sure at all about quarks emitting electrons and positrons, What you say makes a lot of sense, thanks a lot for pointing me in the right direction, I'm going to read about weak interaction and probably I will understand about the flavour changing process of quarks. Thanks again for for your great reply.

--181.90.0.9 (talk) 18:12, 21 March 2015 (UTC)


 * Richard Feynman explains precisely this problem in this video. Quarks don't contain electrons any more than your body contains the words that you speak; they're just produced on the spot.  --Bowlhover (talk) 00:08, 22 March 2015 (UTC)

Force affect
Hello,

I would like to know the scientific effect of the following:

A metre, from ‘A’ to ‘B’ is the size of a luggage holder, situated on the left hand side of a Bus, in between the two left tires, holding people along, inside. When it continues its journey, it accelerates, when it is braking, it is trying to stop, of course when it accelerates hard or brakes hard, any vehicle will have a greater effect on people as well on Luggage.

Q:

1)Where should you put your luggage, in point A or B?

I think point 'B'. I also had a massive argument with someone as they thought point 'A' is where the bag wouldn't get squashed... Who's right?

(SuperGirlsVibrator (talk) 20:42, 21 March 2015 (UTC))
 * You don't specify where your points A and B are. Nor have you defined the "best" that you seek in placing the bag. Safety in the event of a crash? The contents not being crushed in normal motoring?
 * But let us assume A is the front and B the back of the luggage compartment with respect to the direction of travel. In short, there are likely to be larger forces exterted when braking (or crashing) than accelerating, and so I would tend to place stuff at point A such that it can be resisted by the structure directly in front of it, rather than at point B where it might, just, fly forwards and impact point A. --Tagishsimon (talk) 21:03, 21 March 2015 (UTC)
 * Hello, a Bus would have less accelerating and more/less braking power than a Car. Point A is suitable for Cars, but for Buses shouldn't it be point B? There would be/are other luggage's if kept starting from/at point A up to where my luggage would be... When the braking affect (hard or crashing) takes place of the Bus, isn't it less likely get squashed at point B. And when it accelerates, it would definitely take off slowly which won't squeeze the bag at point B...
 * Am I right?
 * (SuperGirlsVibrator (talk) 18:51, 23 March 2015 (UTC))

Bitcoin
I still don't understand how it works. Let say I have some bitcoins. I then use it to buy an item A from someone. If I give him the bitcoin first, what's going to stop him from not giving me item A? Vice versa, he can send me the item first and what going to stop me not giving him the bitcoin?

Second question, I know all bitcoin data are public and can be accessed by anyone, but it's pretty massive. Where do they store all of that data?146.151.91.70 (talk) 23:19, 21 March 2015 (UTC)


 * First question: nothing, and nothing. Bitcoin is more prone to fraud than regular money, not less.
 * Second question: It is not stored in a central repository. Every user of Bitcoin downloads all of the public data before they can verify transactions.  --Bowlhover (talk) 00:03, 22 March 2015 (UTC)


 * The obvious approach is to use a trusted escrow (trusted because they've followed through (if the transacting parties have) thousands of times before). --Tardis (talk) 03:04, 22 March 2015 (UTC)


 * Well, sort of. Let's say you give a shopkeeper $20 in person.  Nothing is stopping him from denying that you've paid him.  If you pay for something with a credit card, there's nothing to say that a merchant can't just lie and say they already gave you the product in question when they never did.  There's no honor among thieves, and bitcoin is no more or less susceptible to humans lying than any other medium of exchange.  If someone is going to lie, it is inconsequential which means of payment they lie about.  -- Jayron 32 23:30, 22 March 2015 (UTC)
 * Not sure I entirely agree. Yes people can lie, but Bitcoin has some differences which can be an advantages and disadvantages depending on your POV. For example, my impression is credit card companies tend to be fairly generous with their anti fraud policies. If it comes to a shopkeeper vs a customer and the shopkeeper says they gave the product and you say you never received in, the absence of good evidence (e.g. security tapes or at least other witnessess) they'll probably side with the customer and reverse the transaction. At the very least, it's possible to get your money back, without the shopkeeper really being able to do anything about it. Even with something like a bank transaction, if it's within a country there is some added security in that these aren't generally designed to be anonymous. If I buy something of Trademe in NZ and don't receive anything, if I paid with Bitcoin and it turns out the person's details are all fake, my ability to track them down is likely to be limited. They might not even live in NZ, perhaps they're actually from Alaska. If I pay by bank transaction as most people do, the person's identity could probably be determined. Perhaps they used fake ID to open accounts, although they will probably at least be on CCTV. While it's possible to open an account remotely, so there is also a chance they never stepped foot in NZ, for various reasons this is far less likely. Of course the usefulness of this is likely be limited, unless it was a very large sum of money but still.... Probably cash or cash equivalents have the most similarities with Bitcoin. Nil Einne (talk) 12:09, 23 March 2015 (UTC)
 * Alaskan? As in the Alaskan Mafia?  Alaskans don't even have internet service, given the vicious mass penguin-attacks that wi-fi signals cause. μηδείς (talk) 16:54, 23 March 2015 (UTC)
 * Not really wifi-related. A penguin invasion from Antarctica is what you get for keeping your penguin in a metal box. - ¡Ouch! (hurt me / more pain) 08:06, 24 March 2015 (UTC)

Electron, not elementary anymore? Quasiparticles.
Hi, I just wanted to know if the electron is really an elementary particle. The article about the quasiparticle called "holon" states:

"The electron can always be theoretically considered as a bound state of the three, with the spinon carrying the spin of the electron, the orbiton carrying the orbital location and the holon carrying the charge, but in certain conditions they can become deconfined and behave as independent particles."

So, if the electron can be theoretically considered a bound state of these three particles (or quasiparticles) doesn't that mean that the electron is not elementary? — Preceding unsigned comment added by 181.90.0.9 (talk) 23:23, 21 March 2015 (UTC)


 * These quasiparticle states only exist within solids. They aren't really properties of the electron, but rather an emergent phenomenon that occurs when electrons and atoms are bound together in a lattice.  Certain propagating excitations of the system behave as if they were particles of pure charge, or pure spin, etc.; however, those excitations only exist within the solid.  In free space, such particles don't exist.  The current understanding of physics is that an electron is an elementary particle with no component parts.  Dragons flight (talk) 03:07, 22 March 2015 (UTC)


 * Hi Dragons flight, thanks for your reply. I've just read that some researchers managed to split an electron into 2 separate particles, the holon and the spinon, also, doesn't quarks also only exist within solids and get anihilated when in free space? But that doesn't stop quarks from being called a fundamental particle. --181.90.0.9 (talk) 06:52, 22 March 2015 (UTC)


 * To give an analogy consider the difference between fish in the ocean and waves in the ocean. I can pick up a fish and remove it from the ocean and it still exists, but how would one pick up an ocean wave and remove it from the ocean?  It doesn't make sense, ocean waves are fundamentally a property of the medium in which they occur and can't be separated from it.  In the same way, quasiparticles are fundamentally a property of the medium in which they occur and could never be separated from it.  If someone says that electrons can be split into holons and spinon, they are at best oversimplifiying, since those effects only exist in the context of a sea of electrons within a solid to begin with.  We can use particle accelerators to identify the individual quarks within isolated protons, and many particle interactions depend on the fact those constituents exist.  There is no such substructure observed within isolated electrons.  The whole notion of "quasiparticles" as opposed to real "particles" is that quasiparticles are a kind of fake particle-like behavior that happens in certain conditions when very large numbers particles are brought together but which can't be present when individual particles are isolated.  Dragons flight (talk) 18:00, 22 March 2015 (UTC)


 * The classic example of a quasiparticle is the phonon, which is perhaps the best known. It's important to remember that concepts like wave-particle duality are not confined to any one frame of reference, size scale, or physical system.  For any system with wave-like behavior, there will always be a particle-like behavior that goes along with it and visa-versa.  Whether or not these behaviors are physically meaningful (that is, whether the calculations of them describe some observable behavior) differs from system to system, but fundementally, all these "quasiparticles" are are useful models for explaining behavior in some system.  -- Jayron 32 23:27, 22 March 2015 (UTC)

Mystery fluid inside a rear projection television
At 8:28 of this video, there's some mysterious fluid that is contained inside one of the projectors of a rear projection tv. What is that fluid and what is its purpose? ScienceApe (talk) 23:47, 21 March 2015 (UTC)
 * Our article Rear projection television links to another, Liquid Fidelity that might be relevant. {The poster formerly known as 87.81.230.195} 2.218.13.204 (talk) 03:43, 22 March 2015 (UTC)


 * It appears to be a coolant, I remember a friend of mine (who had a rear projection tv) telling me about the same thing. It may serve two purposes, cooling and the use of the purity of the liquid for its optical refractive index and optical coupling ability. Old style laser systems used purified water for the optical coupling medium between the laser rod and the mirror system, water was used as the cheapest heat transfer medium. Read-write-services (talk) 22:31, 22 March 2015 (UTC)