Wikipedia:Reference desk/Archives/Science/2016 November 22

= November 22 =

How much medical personnel is needed to harvest and transplant organs?
How much medical personnel is needed to harvest and transplant organs? How difficult would it be for a mafia to kill people and steal their organs to sell them in a black market? Llaanngg (talk) 01:28, 22 November 2016 (UTC)


 * Basically, it's high-tech and has to be done fast, also compatibility has to be assessed (not any organ is fit to be transplanted into a specific person). There are countries wherein it is legal to sell your own kidney. Tgeorgescu (talk) 01:36, 22 November 2016 (UTC)
 * One country (Iran). Whoop whoop pull up Bitching Betty &#124; Averted crashes 15:48, 23 November 2016 (UTC)
 * And it doesn't even have to be your own kidney -- in Iran it's also legal to sell someone else's kidney if that "someone else" happens to be a pagan or a fire-worshipper. 2601:646:8E01:7E0B:F88D:DE34:7772:8E5B (talk) 03:20, 24 November 2016 (UTC)


 * This is a really hard one to answer because it depends on quality. Any serial killer can harvest and transplant an organ ... it might take, the patient might not bleed to death, you never know.  There is a certain researchable number required for a hospital with specific procedures and quality standards, but those include not killing people for their organs. Wnt (talk) 12:18, 22 November 2016 (UTC)


 * There's Robin Cook's novel Coma on the subject, although it's 40 year-old fiction. μηδείς (talk) 01:44, 23 November 2016 (UTC)
 * Organ theft is an article (although a poor one); it points to Organ theft in Kosovo. I heard stories  about kidney stealing in East Asia (kidneys being supposedly easier to harvest while keeping the "donor" alive, and much easier to preserve).  Tigraan Click here to contact me 16:54, 23 November 2016 (UTC)

I tried googling "organ transplant team", and I get lots of hospitals talking about the team, but they don't actually say how many people are present in the room during the surgery. It sounds like there is an anesthesiologist, at least one surgeon, and at least one nurse (all specifically trained in transplants). In the "harvesting" operation, there is a separate team for each organ, so this operation can get quite huge in terms of the numbers of people. I'm sure you do the same search I did, and email the transplant department at one of these hospitals and just ask how many personnel are in the operating room. Of course, as suggested, there could be a huge difference between "how many trained specialists it takes to perform a proper organ harvest" and "what's the least effort you could put into a harvesting operation and still make bank." Someguy1221 (talk) 03:29, 24 November 2016 (UTC)


 * Actually the answer to that question is surely zero. You just show the idiot a pig kidney or something, give him a shot of dope, make a little cut in his skin while he's out if you want to continue the realism, give him a few more "anti-rejection" pills with some ingredient that makes him feel good for however long it takes to get the cash out of him.  Or better yet, just take him to a back room and work him over till he coughs up the ATM code.  (Well, maybe that counts as an operating team, or at least a dental suite, depending on how you do it!) Wnt (talk) 21:32, 24 November 2016 (UTC)
 * Besides Organ theft, the article Organlegging may also be relevant. &#x2013; b_jonas 00:25, 25 November 2016 (UTC)

Servo horns
[[File:Micro servo.jpg|thumb|Small radio control rotary servo
 * alt=A small radio control servo. The plastic case is translucent, revealing the motor and electronics. On top a cross-shaped bellcrank lever provides the mechanical output]]

Servo horns are mechanical connectors for servo (radio control)s. They come in a great variety of sizes, shapes and materials. http://hitecrcd.com/uploads/hornssm.jpg As shown in this picture, a cross-shaped horn having a number of holes in the arms can be used as a lever to pull or push a segment of piano wire connected to another mechanical part. With a little modification, this horn can be connected to a larger mechanical part (e.g., a robotic arm) to rotate it directly.

Many servo horns have a raised circular rim in the center. The above-shown horn has exactly this feature. https://www.rcplanet.com/23957-tm_thickbox_default/Futaba_Servo_Horn_F_Spline_Small_X.jpg

Some other servo horns do not have this feature. http://gogo-rc.com/store/image/cache/data/Motor-Servo-ESC-Gyro/Servo/IMG_0385-01_go_x550-500x500.jpg

If you use the servo as an airplane actuator, the raised rim is useless. If you use it as a robot arm motor, the raised rim actually gets in the way between the servo and the movable part. Sometimes, I just use a knife to remove it.

What's the purpose for this useless(?) feature? -- Toytoy (talk) 02:44, 22 November 2016 (UTC)


 * I suspect that a long time ago Mr Futaba got his radio antenna wire wrapped up between the screw and the horn. It's tempting to think it might be a stiffener, but the webs are all wrong. It could be something to do with making sure the plastic flows nicely in the mould, but again, it doesn't look quite right for that. Greglocock (talk) 08:26, 22 November 2016 (UTC)


 * I can show you a round aluminum server horn made with this useless(?) feature. http://www.nihonbashimokei.net/data/rc-nihonbashi/product/ars-3216htg-hv.jpg and http://alturn-usa.com/products/CAD/Robot.jpg Mine comes with two plastic horns and two aluminum horns of the same designs and nearly identical dimensions (plastics shrink!). Anyway, I suspect it has anything to do with plastic moulding. I tried to attach this server horn to a wooden part. It's painful to create a 10 mm diameter and 2 mm deep recess into the wood because I don't have a tool for this job. -- Toytoy (talk) 09:00, 22 November 2016 (UTC)


 * I think it's a guard to help prevent the screw or shaft from coming in contact with anything that would loosen or damage it. --Modocc (talk) 10:36, 22 November 2016 (UTC)


 * I think it has nothing to do with screw protection. Many such horns have rims that are too low to make any difference. The disc-shaped aluminum horn even forces the screw to be more exposed. Please consult the 3D model I have created using Autodesk Fusion 360 at http://a360.co/2dgb3k7 -- Toytoy (talk) 14:42, 22 November 2016 (UTC)


 * That is a washer or built-up area for mechanical strength and stability. As you said, not all horns have them. Not all would, especially if they are used with specific applications in mind (part of a standard toy). My guess is that some are sold to hobbyists that place the servos into their makeshift models with insufficient clearance and then tend to blame the manufacturer for the result.  Thus the guard. It is inconvenient and useless when you don't want it though. -Modocc (talk) 15:05, 22 November 2016 (UTC)

Feynman Lectures. Lecture 38. Ch. 38–2. Fig. 38–3 Determination of momentum by using a diffraction grating.
Suggest please what is meant: does the wave train look like this or like this? If first, then how can the train be reflected simultaneously from all parts of the grating? Username160611000000 (talk) 06:40, 22 November 2016 (UTC) The wave train will be coming in horizontally. You are confused by the graph of the wave. The graph shows the amplitude of the field, with amplitude plotted on the y axis. But the wave actually extends fully vertically, as a plane wave. It does not vibrate backwards and forwards in the Y direction. Instead the magnetic field and electric field vary in amplitude over a cycle. The picture gives an animation of something that is not quite horizontal. Graeme Bartlett (talk) 09:54, 22 November 2016 (UTC)
 * Yes, in the animation I see the crests of the EM-wave going to the medium with higher refractive index. But when particles go, we don't know both x and y coordinates (and z). In Ch. 38-1 Feynman shows (Fig. 38–1) that uncertainty of position is a wave. Username160611000000 (talk) 11:44, 22 November 2016 (UTC)

Article from Cosmetics & Toiletries
I was looking for the article referred to at Lanolin Barnett G (1986). "Lanolin and Derivatives". Cosmetics & Toiletries. 101: 21–44. but I wasn't able to find it online. Does it have a DOI? 83.150.101.35 (talk) 15:44, 22 November 2016 (UTC)


 * It's probably in that in-between age - too modern to be out of copyright, but too old to be a priority for digitisation (or a DOI). You might get lucky and be able to visit an academic library that carries that magazine - but even if they carry that magazine, they might not have all the issues back to 1986.  If you're really desperate for something you can access online, you might also be able to do a search through your local library's online databases and come up with an article on the same subject.  --122.108.141.214 (talk) 11:34, 23 November 2016 (UTC)

Physical barriers to halt tumor progression
This applies mostly to solid tumors: are there any techniques in medicine that literally use a wall of bio-compatible material (ie metal or plastic, etc) to block off the growth or progression of an inoperable solid tumor?

Example: an inoperable spinal or brain tumor is growing and might hit really sensitive areas around it. Would it be feasible to use synthetic materials to block or direct away its growth from these areas?

Another idea is using physical methods to funnel away secretions from a tumor to prevent tumor cells from infiltrating into surrounding tissues.

74.71.135.72 (talk) 17:09, 22 November 2016 (UTC)


 * I doubt if the barrier method would work:


 * 1) Whatever makes the area inoperable for tumor removal would also make it inoperable for wall placement.


 * 2) It could grow around the barrier.


 * 3) It could push the barrier into the sensitive area. Indeed, by adding material you may make this happen sooner, as now there is more total material near the sensitive area, not less. StuRat (talk) 17:43, 22 November 2016 (UTC)
 * "Secretions" that spread the cancer to other parts of the body, a.k.a. metastasis, travel from the tumor through the blood and/or lymphatic system(s). If you can cut off the tumor's blood supply and lymphatic drainage, that will kill it. Usually in such a situation you'd just remove the tumor, though there is research into killing tumors by blocking angiogenesis. --47.138.163.230 (talk) 18:28, 22 November 2016 (UTC)


 * One specific problem with tumors is that they do not stop growing when they push up against other tissues. Putting one in an artificial container might cause it eventually to necrotize and induce sepsis. μηδείς (talk) 18:37, 22 November 2016 (UTC)


 * It simply would increase pain. This picture, aware to click face+cancer1.jpg If You really wanna see, replace the space by a / in the link. Tumors requred to be stopped growing and cut out. Today cancer cells can be analized to choose a more helpful therapy. Every thing else takes time, money and chances to survive. -- Hans Haase (有问题吗) 15:04, 24 November 2016 (UTC)

Momentum of photons in a high refractive index material
This is a little about the question two above this one, more about the Emdrive, which celebrates its first peer publication today; mostly about me not knowing much about Snell's law or refraction and Wikipedia's articles definitely not helping...

Suppose we have a photon drive? (I mean laser propulsion) mounted in a submarine. The photons from the drive pass through a window into a hypothetical fluid of low viscosity in which there is very slow light propagation, let's say, a millimeter per second. How much thrust does the submarine receive?

Now the way I understand it from some random Arxiv articles which may or may not be written by cranks, the momentum of a photon is classically held to increase as it enters into a high refractive index material, as it is pulled in by a force normal to the surface. The photon, going at essentially the speed of light before that, presumably does not accelerate, but the refractive index is dependent on a phase velocity that can (I think) exceed c. The one clear thing is that the change in the sin of the angle (relative to the perpendicular) is inversely proportional to the change in overall photon momentum.

To me, that means that the hypothetical submarine produces photons with an unsatisfyingly low photon-drive momentum, but they acquire extra momentum as they enter the hypothetical fluid, and so the submarine (perhaps) is driven forward with an equal but opposite reaction.

The application to Emdrive I'm thinking of is, what if the device could release some kind of 'free soliton' that escapes the apparatus and passes through the vacuum as if it were a photon in a material with very high refractive index? Does that make any sense? Wnt (talk) 21:14, 22 November 2016 (UTC)


 * I have not yet looked at or read any of that, but I will get to it when I have time (and I'm not drinking). For now I'll note from our article on slow light that "Slow light is a dramatic reduction in the group velocity of light, not the phase velocity". Based primarily on that and the fact that energy and information propagates (at a far more fundamental level than the signal energy which is what the group velocity represents) with the phase velocity which varies with refractive index but is not as dramatic as slow light, I would think that most low energy photon's wavelengths and momentum energy are conserved; otherwise prisms would not split white light into its constituent colors unaffected AFAIK. That said, as a result of the light's altered refracted path, I would presume that there is an even tinier deflection of the submarine's momentum such that their total or combined momentum in any direction is always conserved. I'll also add that charges do not like to be separated, which is why we have large masses of atoms which are electrically neutral for the most part, but neither are any of these charges isolated, so even with conductive shielding I would think its still possible for very low frequency radiation to cause charges to migrate and create transient internal and external dipoles affecting the body.   In other words, the EMdrive engine might work here on the ground, but not in space. -Modocc (talk) 23:58, 22 November 2016 (UTC)


 * Crap... I'm always mixing up group and phase velocity, but I should have remembered slow light is really a matter of seeing the delay when you turn it on and off. It is very confusing to me to think of what happens to one lone photon in a slow light material, to make it go so... slow.  I suppose that for the thought experiment I can replace that with "material of a ridiculously high refractive index", though I don't actually know if that is even conceivable.  (I don't know it's not...) Wnt (talk) 01:06, 23 November 2016 (UTC)
 * A standing wave or stationary wave has a group velocity of zero, but the phase velocity is c if the cavity holds a vacuum. At the other end, for highly conductive mediums such as plasma, differences in phase velocity depend on the ions' effective masses and (density if I recall correctly but don't quote me on this since its been nearly two decades since I studied that subject) which means that the light wave is interacting with the ions as it passes thru the medium. It is the wave nature of particles and their fields that explains some of these effects which is why its important to study and understand the unification of forces and how energy actually propagates, which is always at speed c or less. -Modocc (talk) 01:51, 23 November 2016 (UTC).

Let me throw out an idea which is not really in the above sources to see if it makes any sense. The idea of a "normal force" when the light enters gives me the sense that light in a high refractive index material exists in something akin to a bound state. Perhaps its interaction with the various charged particles moves them back and forth and moves it back and forth also - this is contrary to classical modelling of light in vacuum, but there is an entire field of quantum electrodynamics I don't know. Since it's light, of course, it can't find an orbit that guarantees it can't escape, so it's not really bound, but a photon subject to total internal reflection as it passes around a fiber optic would seem to be in something like a bound state. Anyway, the key thing I want to confirm there is that light should be attracted in some sense to a high-RI medium, and presumably, the medium to it as well - thus, the rear end of the submarine should, I think, be hit with a constant stream of atoms of the high-RI liquid that are being pulled toward the light as it enters. As such, it should, I think, get more thrust than it would from light pressure in vacuum. This momentum then gets repaid when the light exits the high-RI medium at a later time, pulling those molecules against the wall of some container, and so the submarine effectively pushes off the wall of the container. And there is, therefore, extra momentum being carried in the fluid while the light is propagating, so the light is able to carry more momentum per energy than it could in vacuum.

Since the cosmos is full of vacuum, of course the extra momentum in that case has to push off something pretty local. But if there were some frequency or analog of light for which the refractive index of vacuum were higher, then it ought to be possible to operate a photon drive in that frequency that delivers more thrust than a (regular) photon drive, and that doesn't have to push off anything - the momentum in this light can go right off to infinity like any other light. Wnt (talk) 13:21, 23 November 2016 (UTC)


 * Stepping back, I think it's easier to simply ignore the refraction involved and the difficulty you will have with total internal reflection of such a material and think about this in terms of radiation pressure by absorption irrespective of how it is "absorbed" per our article on this pressure here which just gives the pressure to be the energy flux divided by c which is the photons' momentum. --Modocc (talk) 18:59, 23 November 2016 (UTC)
 * I don't see the relevance. If a photon is absorbed by a material, its momentum stops; if it enters a material of high refractive index, its momentum increases - and I'm not aware of any defined physical limit on how much it can increase, though it is not actually extraordinary as I postulated at the outset since refractive indices don't really go that high AFAIK. Wnt (talk) 19:11, 23 November 2016 (UTC)
 * Momentum always sums. So if you run off a pier onto a boat it doesn't matter whether you stop running or continue running about the deck your mass-energy contributes to its momentum the moment you do. --Modocc (talk) 19:19, 23 November 2016 (UTC)
 * I started checking your two sources above and I'm highly skeptical of Buenker's theory: "The present theory concludes that the reason photons are slowed down upon entering water from air is that their relativistic mass p/v increases faster with n than does their momentum, which in turn requires that Einstein's famous E=mc2 formula does not hold for light dispersion because the energy of the photons is expected to be the same in both media." His theory is certainly on the fringe for we know that photons can interact with matter both elastically and inelastically, with the inelastic interactions (such as with x-rays) shifting the photon's energy and momentum as opposed to the elastic interactions that do not. --Modocc (talk) 22:48, 23 November 2016 (UTC)
 * To be clear -- is it known what the momentum of a photon is while it passes through a material with some arbitrary refractive index, or what change in momentum is transmitted to the material when a photon enters or leaves it from vacuum? If so, can you point me at the mainstream opinion about those values? Wnt (talk) 01:18, 24 November 2016 (UTC)
 * The article on Hamiltonian Optics has a section that shows a proportional change in momentum with refraction. Sometime in the last few years I read about competing formula, with conflicting evidence, although it might have been resolved by identifing different momentum. I don't recall drawing any firm conclusions from what I had read at the time and I conveniently seem to have forgotten most of it too.   See Momentum (Abraham–Minkowski controversy)  --Modocc (talk) 02:54, 24 November 2016 (UTC)
 * That seems basically in line with what I was thinking above, though oddly it calculates $$\mathbf{v}=\mathbf{p}_A-\mathbf{p}_B$$ which I think is the negative of the amount by which the photon's momentum changes when it goes from refractive index A to B, or in other words, the positive momentum I'd expect something - presumably something on the surface of the refractive material - to acquire. (That's a little odd when I think of it, because wouldn't that mean that light could pry the very top atom off a piece of glass?  But I suppose there's some finite distance it penetrates before it interacts and its angle doesn't literally change in a tenth of an angstrom... does it?)  Anyway, after frustrating myself with errors in math notation, trigonometry, and R, I will just say for now that it seems to vary, so that for example light passing from n=1 to n=2 material should gain additional momentum by a factor varying from 1 (for light passing perpendicular to the surface) to sqrt(3) (for light just grazing the surface).  It seems easiest just to lay out the momentum vectors given that their magnitude = the refractive index and their x component remains constant.  Despite the dependence on angle though, the added momentum is always perpendicular to the surface.
 * Anyway, the bottom line I get for a simple straight line propagation of the light is that the total momentum of the light ought to be directly proportional to the refractive index of the medium. So a photon drive beaming out through a fluid with a refractive index of 100, if one was to be had, would produce 100 times the thrust of one in vacuum. Wnt (talk) 21:36, 24 November 2016 (UTC)