Wikipedia:Reference desk/Archives/Science/2013 September 26

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September 26

Field interaction from photons or other electromagnetic radiation

If an sub-atomic particle like an electron moves through space it will interact with electrostatic and magnetic forces. Now if a photon or other electromagnetic entity moves through space, will it interact with any other force at all? (besides nuclear cores or gravity) Ie, would it be possible to detect or make a readout of vector direction of a photon source without significantly disturb the photon? Electron9 (talk) 01:01, 26 September 2013 (UTC)

Yes, a photon can interact with another photon, see Two-photon physics. The measurement of a photon properties is subject to the same fundamental constraints as any other measurement in quantum mechanics. --Dr Dima (talk) 01:11, 26 September 2013 (UTC)

Does it have to be the same wavelength photon? or amplitude? or even with the same vector/speed direction? Anyway my thinking was to find out the vector direction of photons before entering an object and then compare that with the photons that exit the same object. If possible.. Electron9 (talk) 01:22, 26 September 2013 (UTC)

No, it doesn't have to be the same wavelength. Regarding photons entering and exiting an object, you may want to read Borrmann effect and Mossbauer effect. --Dr Dima (talk) 06:14, 26 September 2013 (UTC) Regarding the momentum vector of the photon before and after, a local measurement of a photon momentum will change its momentum (or, equivalently, destroy the original photon and create a new one), so it is unclear what you would achieve in this case. If you were trying to use an act of Stimulated emission to amplify the photon population in your measurement (having created the population inversion in the medium beforehand), then indeed you may end up with "identical copies" of the original photon, and subsequently measure their distribution of momentum. --Dr Dima (talk) 06:40, 26 September 2013 (UTC)

The easiest way to detect photons is by using electrons. Dauto (talk) 04:20, 26 September 2013 (UTC)

How big is the blue stars in diameters

I was wondering how big is the blue main sequence stars. Because I am ignorant of radius, I dislike the radius usage and rather use diameter instead This shows how can blue main sequence stars O and B have luminosity of 30,000 and 1000 times. I was wondering is blue main sequence stars with planets around can have a substantial atmosphere if they were the diameter of Earth or twice the Earth diameter, or size of Mars. said Blue main sequence stars have luminosity of 2000 for B3 and 1400000 for O3 main sequence stars. When they use the radius of the size of that star, I am confused about the diameter. --69.233.252.198 (talk) 04:40, 26 September 2013 (UTC)

Have you looked at radius and diameter? The diameter is just two times the radius. --Bowlhover (talk) 05:46, 26 September 2013 (UTC)

Can life harbor of planets around white main sequence stars, or yellow-white main sequence stars

Because my college professor told me try to harbor life on planets around white (A) main sequence stars are quite difficult because their time of main sequence only last 1 billion year at the most, so when a planet around A main sequence stars can they have life harboring around the planets, or only simple bacteria can exist if at all? Can yellowish white (F) main sequence harbor intelligence life around their planets if the main sequence only last 3 billion years. I am not sure if F (yellow-white) main sequence star's planets can reach dinosaurs, something like reptiles if the main sequence lasts about 5 billion years. My astronomy professor told me life develop on celestial body needs to take a long time, in just few million years Main sequence is not going to receive any life forms around any planets. To get a intelligence life around celestial bodies to the parent star needs to take billions of years 4 Ga at least.--69.233.252.198 (talk) 04:49, 26 September 2013 (UTC)

Life, probably yes. Bacteria are a form of life, and as far as we know, bacteria came into being essentially as soon as the Earth had cooled enough to have liquid water. Complex life and intelligence are a lot harder - we work from a sample of one, and there seems to be a lot of randomness in the process. No-one knows if intelligence is inevitable or even likely. Maybe without the Chicxulub asteroid, we'd be dominated by stupid T-rexes. Or maybe Jurassic Park had it right and 64800000 BCE the first Velociraptor would have landed on the moon ("It's a small step for a man-eating monster, but a large jump for dinosaurierhood"). --Stephan Schulz (talk) 05:54, 26 September 2013 (UTC)

"What's a man?" "I don't know... man-eating just sounded cool!" MChesterMC (talk) 08:50, 26 September 2013 (UTC)

It's hard to know - but our Sun is 4.57 billion years old - Earth was formed 4.54 billion years ago and life appeared here about 3.5 billion years ago. So it took about a billion years between star/planet formation and first life. So even a star with just a billion years to live has enough time to form planets and jump-start life.

The problem is that we don't really know why life waited around so long before getting going. It's possible that it took that long for the bombardment by big space rocks to slow down enough - or for a stable atmosphere to form - or for the overall temperature to get low enough. There are many possibilities. That being the case, it's plausible that in some other solar system, the orbital dynamics of various gas giants could clear out all of the big rocks much sooner - or that the primordial composition of the future life-bearing planet could allow it to cool off much faster.

Because we still don't have solid knowledge of how life started on earth, it's also possible that the panspermia hypothesis is true and life arrived in the form of complete, working bacteria from some other source. That being the case, we'd have bacteria from the very moment the planet was suitable for them to take hold.

The limiting factor on higher life forms is the rate of evolution. Here on earth, it took at least a billion years for photosynthesis to evolve - which meant that there was no free oxygen in the atmosphere - and that prevented more complex life forms from appearing. Then another two billion years before we started having things that are recognisably plants and animals. On the plus side, it only took half a billion years to get from simple multicellular life to humans.

So what I think would be fair to say is that your college professor is correct if we assume that things around this hypothetical star proceeded like they did here. But: We can make alternative assumptions (such as that panspermia is correct) and that in this hypothetical world, then by chance, they'd have had multicellular, photosynthesizing life deposited onto the surface of an already reasonable planet after (say) a half billion years. That's not entirely unreasonable. If that were the case, then intelligent life and space-faring civilizations could easily evolve before the star died.

SteveBaker (talk) 14:11, 26 September 2013 (UTC)

The late heavy bombardment only ended about 3.8 billion years ago, and may have completely remelted the previously solid surface of the Earth. We have (some, but quite strong) evidence for complex communities of (unicellular) life 3.5 billion years ago. Indeed, some scientists argue that carbon isotope ratios in much older mineral samples (4.25 billion years old) already indicate life back then. It is in no way certain that life did not arise earlier than 3.5 billion years ago, and it may, indeed, have arisen multiple times, being extinguished or reduced to minimal levels again by the late heavy bombardment or similar events. --Stephan Schulz (talk) 14:36, 26 September 2013 (UTC)

Yes - which kinda emphasizes my final point. If you presume that the same sequence of events happens around some other star - then it's reasonable to come to the conclusion that 1 billion years isn't enough to come up with more than primitive single-celled life. The real question at the heart of this is whether life could start sooner and/or develop faster in solar systems where the initial conditions were different. If you read Late_heavy_bombardment#Possible_causes, you'll see that it's very possible for those dangerous rocks to stay put - or to be swept up by some super-Jupiter in a closer orbit to this alternate-Earth. In such a scenario, life could easily have started a half billion years sooner. The next issue is the question of why it took so long for photosynthesis to evolve - which seems to have been the major impediment to intelligent multicellular life. Why that took so long is an interesting question - especially following the discovery of an independently-evolved photosynthetic system in the Oriental hornet - which can't have taken more than a few million years to evolve. SteveBaker (talk) 18:41, 26 September 2013 (UTC)

It's a sample size of one - impossible to know for sure. At a wild guess I would be more skeptical about the redder stars; I'm not so sure life can get started without some hard UV to blast apart and reform polymers over and over again. But there are lots of ideas in the literature (clays, black smokers, all sorts of crazy things) which would disagree with my impression. Wnt (talk) 18:34, 26 September 2013 (UTC)

Yes - it is hard to know for sure. But those red stars could still get life started by panspermia...which is definitely getting increasing respectability in the scientific world as years go by. SteveBaker (talk) 18:41, 26 September 2013 (UTC)

Life may have evolved 3.5 billion years ago, or even earlier. But it was only simple single celled organisms. It took 3 billion years and the evolution of sexual reproduction to occur to allow the evolution of multicellularity in the Cambrian Explosion, which happened only .5 billion years ago. μηδείς (talk) 18:42, 26 September 2013 (UTC)

Of course, the development history of life on another planet may be totally different from the history of Earth. Without the separation of the Moon or late heavy bombardment, life on Earth might have started much earlier - pretty much as soon as the surface had cooled enough. Once life had a foothold on Earth, it had numerous setbacks - extinction event lists at least 15. I can certainly imagine advanced multicelluar organisms evolving in much less than a billion years under ideal conditions; and equally I can imagine multicelluar organisms never getting off to a good start even after many billions of years. Astronaut (talk) 18:53, 26 September 2013 (UTC)

The extinction events only removed the top predators and macrofauna, and can as easily be credited for opening up opportunities for diversity as be blamed for removing the dinosaurs and trilobites. Without the moon's separation there would be no tides, vital for life that cannot live in stagnant water. The delay of that event and the late bombardment hardly effects the overall scheme of 3 Billion years from origin to multicellularity. Most planets with life probably harbor nothing more complex than bacteria. μηδείς (talk) 00:56, 27 September 2013 (UTC)

Without the Moon's separation there would be tides (note first sentence), though with only about 1/3 the maximum range they have now – people commonly forget that the Sun also has a significant tidal influence on the Earth. {The poster formerly known as 87.81.230.195} 212.95.237.92 (talk) 13:33, 27 September 2013 (UTC)

It depends what you define "life" as. Non-carbon based life might have a better chance in some circumstances.--Auric talk 20:29, 26 September 2013 (UTC)

Correct me if I'm wrong, but it's not only the main sequence life that counts, but also the variation during that "life." The sun is getting hotter, slowly but steadily, and the faster these changes happen (within 1 vs. 10 billion years) , the harder it would be on life. Even worse, the power laws seem to dictate an orbital radius that's roughly proportional to m² (luminosity is proportional to the 4th power of mass or slightly less, and radius to the square root of luminosity), and that would indicate that a planet orbiting a star of 1.5 solar masses should do so at a radius of 2.25 AU. On top of that, a type F star would be younger and more metallic than the Sun, and I've read that that's bad for the habitable zone in general; it would probably not even exist. - ¡Ouch! (^{hurt me} / _{more pain}) 14:09, 30 September 2013 (UTC)

Everett branch convergence

In the many-worlds interpretation of quantum physics, does anything prevent Everett branches from reconverging (by leading to the same future by different chains of events) at the same rate as they diverge? NeonMerlin 09:19, 26 September 2013 (UTC)

Surely separate branches can never produce exactly the same future because their futures have different pasts. If event A happens in branch 1 but not in branch 2, then all the descendants of branch 1 will have future states in which event A happened, whereas all the descendants of branch 2 will have future states in which event A did not happen. Gandalf61 (talk) 11:41, 26 September 2013 (UTC)

That does't really follow. In the long run the past is no more certain than the future, you only see the current evidence. Dmcq (talk) 11:55, 26 September 2013 (UTC)

Because some branches can gather in a circle or just assemble back in time , it is possible to reconnect .Thanks Water Nosfim — Preceding unsigned comment added by 81.218.91.170 (talk) 13:10, 26 September 2013 (UTC)

We know very little indeed about what the implications of many-worlds truly is. Heck, we don't know whether it's true - or complete bunkum - and there are reasons to believe that it's an unfalsifiable hypothesis anyway. So whether different parallel universes could ever recombine is anyone's guess. Any effort to give you an answer to your question should therefore be ignored!

That said, Gandalf61's answer is clearly incorrect because if two universes are precisely identical - then any past memories would also have to be precisely identical because if they differed then whatever systems stored that past history would have to identical too. There would be no conceivable test to determine whether two universes with wildly different pasts - but no differences whatever in the present that resulted from that, actually had different pasts.

God only knows where User:81.218.91.170 came up with that answer - but I guarantee there are no reliable sources to back it up.

Bottom line: We definitely don't know the answer to your question. We probably can't ever know the answer. It may well be logically impossible for there even to be an answer. SteveBaker (talk) 13:47, 26 September 2013 (UTC)

Steve - maybe I didn't explain myself very clearly above, but I think we are in agreement. Different Everett branches have different pasts so they cannot recombine in some mysterious way to produce a hybrid future state. In the Everett interpretation of Schrodinger's cat, there is a "cat dead" branch and a "cat alive" branch, and their descendants must remain separate. The two branches cannot recombine into a "cat both dead and alive" branch. Gandalf61 (talk) 14:16, 26 September 2013 (UTC)

But if you threw the box, cat and all, into a black hole, surely the resulting universe in both cases would be on a "that information is unknown" branch? MChesterMC (talk) 08:14, 27 September 2013 (UTC)

Different branches do recombine all the time, this is a trivial consequence of unitary time evolution. The entire multiverse in fact does not evolve in time at all, H|psi> = 0. Time doesn't exist at the multiverse level. Count Iblis (talk) 13:55, 26 September 2013 (UTC)

the word "branch" is really a bit misleading, as it suggests that quantum history has a tree structure. What really happens in the multi-world interpretation is that the probability wave function spreads out over a huge-dimensional state space. There are an infinite number of possible history-paths, including an infinite number that diverge and then come together again. Looie496 (talk) 15:41, 26 September 2013 (UTC)

I'm out of my field here, but my impression is that CPT invariance means that there should be multiple pasts for a given moment of time just as there are multiple futures, provided that there are multiple futures for particles of any charge or parity. However, we live in a gradient of entropy with less in the past than in the future, so does that mean there are fewer pasts than futures? Or are there as many pasts, just more 'orderly' on average? Hmmm. In any case, the trivial case of this is the double-slit experiment - there are two worlds, one with the particle going through the one slit, one the other, but we find ourselves in a world where we're looking at a dot and there is no way to tell which was our past. Wnt (talk) 18:29, 26 September 2013 (UTC)

The entropy increases, but this does not mean that the number of future states increases. Unitary time evolution implies that this number stays exactly the same. So, how can entropy increase? Thing is that if you were to define the entropy as logarithm of the number of states an isolated system really can be fund in then that entropy would stay constant. The entropy one uses in thermodynamics is defined in a different way, it is proportional to the logarithm of the number of microstates that have the same macroscopic properties as the given system has.

Consider the following example. If you do a free expansion experiment with an ideal gas that initially fills half of a totally isolated container, then the entropy will increase by N k Log(2), because the number of states each of the N molecules can be in will have doubled. But if you look more carefully, then you see that the number of states the molecules can really be in must be the same as you started out with, because each initial states evolves determinstically according to the Schrodinger equation to a final state, the transform from initial to final state is unitary, which then implies that the number of states actually stays the same.

But what matters for thermodynamic entropy is that the gas when it has expanded has certain macroscopic properties (e.g. in this case it has a larger volume) and given those macroscopic properties there are then a larger number of microstates that are compatible with it, than in case of the initial state (with a smaller volume). But most of those microstates are not states the gas can be found in, clearly almost none of them will evolve back to the initial state under time reversal, while any of the states the gas really can be in would evolve back to the initial volume under time reversal (note that this is thought experiment where we assume perfect isolation). Count Iblis (talk) 20:54, 26 September 2013 (UTC)

Colour variations on displays

Do all screens whether a tv, pc monitor, laptop or tablet have varying colours even on the same model? For example, would all screens of a particular make and model have the same sorts of colour hues or would they differ slightly? Clover345 (talk) 11:13, 26 September 2013 (UTC)

How accurately can you measure (or perceive) color and brightness? All that matters to the manufacturer is that the color accuracy and consistency are as good as its customers need. You can buy scientific-grade equipment, if you're willing to pay a premium; otherwise your products will fall along the spectrum, ranging from "professional consumer" to "bargain basement." Start by reading colorimetry. Nimur (talk) 12:04, 26 September 2013 (UTC)

Colours do vary, even in sets of same make and model. Variation comes primarily from user adjustment and the display technology (CRT, LCD, etc). All due respect to Nimur, but whether a set is a cheapie or an expensive professional item has little or nothing to do with it, providing the set is not defective or maladjusted. There are six basic aspects of colour reproduction in television:-

• Choice of primary colour filters in TV cameras (not applicable perhaps to this question)
• The colour accuracy of photographic film when movies or film-based programmes are televised (not applicable perhaps to this question, however if comparing one receiver with another some time later, may trick you)
• Accuracy of gamma in the televion station cameras
• The choice of primary colour phosphors or pigments in the reciver
• Adjustment of signal strength of each primary colour circuit in the reciever
• Accuracy of gamma in the reciever.

The television industry industry very early in the days of colour television standardised the primary colour filters used in cameras. You can asume variation here is neglible. Standardisation of primary colours is assisted by the fact that although there are a vast number of TV and monitor manufacturers, thaere are only a few manufacturers of the actuall displays in the World, which they sell to the various set makers, along with other critical parts.

The television industry very early in the days of colour television standardised the colour phosphor primary colurs for use in receivers. You could neglect variation here too, however Japan standardised on a slightly different red than Europe and USA. So reception with a Japanese receiver in USA or Europe will be slightly inaccurate. It is unlikely that you would notice it, however I recall comparing a Philips receiver with a Sanyyo TV some years ago and side by side you can see a difference when a full red test signal is used.

The pigments used in LCD and plasma displays are not as accurate as CRT displays, but they are getting very good.

The colour accuracy depends on the adjustment of the TV set ("colour" control and/or "tint control" user controls, and internal controls accessible to technicians. This variation can be significant. Some people never adjust their sets properly. Some shops intentionally missadjust TV sets as a sales technique, as some customers like to say "I'll buy that one, I like it's nice colours."

"Gamma" is the term for the correspondence between the electrical signal and the colour intensity over the range from black to maximum light output. The relationship is not linear. Gamma accuracy can vary depending on the display technology - CRT, LCD, plasma, and on how well teh user adjusts the brightness and contrast controls. — Preceding unsigned comment added by 1.122.206.159 (talk) 13:25, 26 September 2013 (UTC)

The way I was interpreting the question was with regard to the variation you see by feeding identical inputs to multiple units within a single product-model - amongst products that are built from ostensibly identical parts. For example, an LCD panel's backlight brightness is specified in nits; but if you build a hundred units, the actual brightness follows something like a bell-curve. There is absolutely a correspondence between price you pay (as an end consumer) and the product vendor's ability to tightly control the statistical distribution of part quality. Now that we live in a mostly-digital-video-signal, mostly-solid-state technology ecosystem, it is arguable that even cheap products are "good enough..." for users who don't notice minute details. The color and illumination variance is lower in this type of technology, compared to, say, phosphor screens (as Steve mentions below); and analog imperfections are avoided for most of the signal path, right up to the point where you're emitting or collecting photons. Ultimately, though, the degree you can tolerate imperfection depends on how accurately you can actually detect variation. Graphics professionals (like Steve) and image processing scientists (like myself and my colleagues) pay lots of attention to minutia that most people won't even notice; but our efforts manifest, perhaps somewhat ambiguously, as "better overall products." As I recall, somebody famously called our color accuracy "26% better" a few years ago, a stunningly quantitative figure. Nimur (talk) 13:52, 26 September 2013 (UTC)

The TV we have in our living room has a menu option marked "STORE MODE" - which makes the picture much brighter and more vibrant (too much more, I would argue) as well as disabling the controls on the side of the TV. There is a pop-up there that says that using this mode may shorten the life of your TV and consume more electricity! So judging color quality by what you see in the store is at best of dubious value! SteveBaker (talk) 18:06, 26 September 2013 (UTC)

Back in the era of CRT monitors, it was extremely common for the colors to drift over time due to screen burn, miscalibration of the analog parts and just general age. My personal experience has been that modern LCD panels do not seem to exhibit these problems - but our article Screen burn-in has a section on plasma, LCD and OLED displays that suggests that they are also prone to this phenomenon. Using a screen saver should alleviate the issues of certain common patterns being "burned" into the display - but a general overall degradation of brightness and color performance must still occur. So if our article is to be believed (and it does have some pertinent references) - then the answer to your question is "they differ" - but only after the displays have been in use for some large amount of time and with differing degrees of usage. However, I work in computer graphics where it is important to have color consistency between the displays used by (for example) different artists working on 3D models for the same game. Back in the era of CRT's, we'd have little devices that you stuck on the bottom right corner of the display's screen that adjusted the analog signals from the computer to achieve a stable color balance as the CRT aged - and between different CRT's being used by different people. Since we switched over to LCD displays, we haven't had to do that. But perhaps with OLED's becoming popular, we'll have to revisit that decision! SteveBaker (talk) 13:33, 26 September 2013 (UTC)

Steve, we still use those on LCD displays. Unless you are using specific, expensive monitors, color replication is still a problem. Even on a single brand of monitor, you get variation that is enough to warrant it.217.158.236.14 (talk) 14:08, 26 September 2013 (UTC)

• I'd just like to add that all of this is sort of a moot point, because the color that a viewer perceives on a monitor is strongly dependent on the lighting of the room where the viewer sits. Our brains are designed to minimize our awareness of that fact, but it is true nevertheless. So attempting to precisely control monitor properties is a waste of effort unless you can also precisely control the viewer's environment. If that is not possible, then the only way to get consistent perceptions is to calibrate each monitor individually and use it in a place with consistent illumination. Looie496 (talk) 15:36, 26 September 2013 (UTC)

And you need specially calibrated light-bulbs; and you need matte-gray walls painted with calibrated paint; and you need a government certification for every combination of room wall and lightbulb.... Nimur (talk) 17:30, 26 September 2013 (UTC)

Don't forget the monitor hood lined with black velvet. (some of them costing more than what I would spend on a monitor). Ssscienccce (talk) 03:05, 27 September 2013 (UTC)

Yet another factor (at least with LED screens) is the vertical angle between you and the screen, e.g. colour and contrast will both vary depending on whether you sit or stand.--Shantavira|^{feed me} 16:13, 26 September 2013 (UTC)

Tools like the "LaCie blue-eye" has the ability to monitor ambient room light - and that's plenty good enough for what we do. The objective for us is not to have perfect color - because we know that our end-users are using who-knows-what displays and calibrations. The idea is that all of our artists see the same thing - so that they aren't continually correcting and re-correcting the color of each other's work to make it look good with whatever they are building themselves. Doubtless LCD's do have color differences - both between manufacturers and between screens made by the same manufacturer - but the differences are tiny compared to old-school CRT's. SteveBaker (talk) 18:06, 26 September 2013 (UTC)

A Sony leaflet for their Full HD widescreen medical monitors writes: "every LCD panel used in the LMD-2450MD is precisely color calibrated at the factory, providing consistent characteristics. The colorimetry of an LCD display, by nature, can exhibit inaccurate color characteristics and gamma curves, which can make precise color matching between multiple monitors a challenge." So yes, even within the same lot, batch or model, there can be color variations. Ssscienccce (talk) 03:05, 27 September 2013 (UTC)

When dental veneers go wrong...

When someone has veneers done - but they end up with a set of teeth that looks like Barney the dinosaur's choppers or that they're wearing a mouthguard. What exactly is it that's gone wrong to cause that? I presume that they didn't go into it expecting their teeth to look like that afterwards... --Kurt Shaped Box (talk) 18:48, 26 September 2013 (UTC)

Our resident dentist can answer this question :) .Count Iblis (talk) 20:37, 26 September 2013 (UTC)

It seems that I've been summoned. :)

Veneers are done by first trimming away the superficial 0.5 or so of enamel on the facial of the teeth being restored, taking impressions of those prepared teeth and then cementing very thin laminates made of porcelain. Depending on the original anatomical relationship of the teeth being restored, the dentist/dental lab may be forced to put porcelain in places that do not necessarily make the veneers appear as though they reflect the normal anatomy associated with teeth. A primary cause of what you refer to as "Barney the Dinosaur teeth" and what dental school educators generally refer to as "teeth that look like Chicklets" is the complete lack or even partial deficiency of the gigival papilla -- the pink triangles of gum tissue that normally exist between teeth. If they are missing or deficient (either due to periodontal disease, etc.) rather than having "black triangles" the dentist/dental lab will often close these spaces with porcelain for esthetic or functional reasons. In terms of esthetics, even though Chicklets look quite unnatural, black triangles between anatomically-shaped teeth might look worse, and in terms of function, black triangles may cause a whistling sound when the patient talks and food particles may be more likely to become trapped, which may lead to cavities along the already more susceptible restorative margin between porcelain and tooth. DRosenbach ^{(Talk | Contribs)} 15:58, 29 September 2013 (UTC)

searching of arm anatomy illustration

I'm looking for an arm anatomy illustration a long time... But it's very important for me that it will be the same same to the real thing as much is possible... (I even agree to pay money for that, particular if it's on 3D format). Until now I've saw only some things that are not real, it says that they does not reflect the real things. My target is to know well the names of the veins of the arm, from the start to the end. thank you. 95.35.246.240 (talk) 21:17, 26 September 2013 (UTC)

http://teleflexhandbook.com/chapter-13-right-heart-cath-from-the-arm has a couple of pictures that might give you most of what you want. Looie496 (talk) 00:26, 27 September 2013 (UTC)

Keep in mind that there is considerable variability in the venous anatomy of the upper extremities (more than in the legs). The number of venous branches and their respective lengths show great inter-individual differences in the arm, so it's unlikely that an illustration will match someone's arm exactly. A Nigerian study noted 10 types of venous patterns (link), the abstract of another study mentioned four patterns. One example is the Median cubital vein between the cephalic and basilic veins in the H-shaped pattern, present in 70% of population, while 30% has the M-pattern, with five segments, the cephalic and basilic veins and the intermediate cephalic, intermediate basilic and intermediate antebrachial veins. 3-D views that you can turn and zoom in can be found at several sites (for example anatomyexpert or healthline). Ssscienccce (talk) 01:26, 27 September 2013 (UTC)