Wikipedia:Reference desk/Archives/Science/2017 November 3

= November 3 =

Tesla coils
Can Tesla coils be used as weapons on the battlefield, and if so, are there real-life examples of this (either in development or actually deployed)? 2601:646:8E01:7E0B:B9F4:7CD7:EC0A:69F7 (talk) 04:22, 3 November 2017 (UTC)
 * No, and no. Edison (talk) 05:48, 3 November 2017 (UTC)
 * Regarding the first question, why not? 2601:646:8E01:7E0B:B9F4:7CD7:EC0A:69F7 (talk) 06:26, 3 November 2017 (UTC)
 * Well, This dude actually built a portable, wearable Tesla coil gun, but it seems to lack any sort of real-world battlefield application, other than looking a bit scary. I'm quite certain that if it could be made into a usable weapon, somebody would have done it by now. Alansplodge (talk) 10:51, 3 November 2017 (UTC)
 * Slapping with a haddock could be used as a weapon, but the real question is whether it would be effective. A Tesla coil is fragile, power hungry and not terribly damaging. The best defence against them is some sort of tin hat or tin box to sit in, both of which are widely used by the opposing forces.
 * Also a Tesla coil is largely omnidirectional, meaning that it acts in all directions (your troops too), wastes energy in being effective in a direction where your enemy isn't, and makes it susceptible to the inverse square law, so seriously range limited.
 * Any sort of battlefield directed energy weapon needs to be just that: directed. It needs to put its energy in one direction, towards the enemy and them alone. This may also reduce the inverse square law effect (but look at far field and Fraunhofer beam for why lasers don't work how you probably think). Andy Dingley (talk) 10:56, 3 November 2017 (UTC)
 * Would that make this a war crime then? -- Jayron 32 13:39, 3 November 2017 (UTC)
 * No, but it might be tench warfare. Andy Dingley (talk) 18:41, 3 November 2017 (UTC)
 * Are we allowed to give military advice? What happens if someone loses a whole war because of reliance on it?  Will they sue the Foundation? --Trovatore (talk) 19:02, 3 November 2017 (UTC)
 * Don't worry about them. The Mule will eventually mess up their work.  All roads lead to Trantor and that's where all stars end.  -- Jayron 32 02:51, 4 November 2017 (UTC)
 * I should point out that railguns have military application. However, those use pulsed DC rather than alternating current, which excludes them technically and spiritually from all things Tesla. Wnt (talk) 19:09, 3 November 2017 (UTC)


 * [un-indent] Thanks, all! So, the reason why they're not used in war is because they're inefficient, indiscriminate, and (contrary to what the folks at Westwood would have you believe) are completely ineffective against armor? 2601:646:8E01:7E0B:0:0:0:EA04 (talk) 09:20, 9 November 2017 (UTC)

Technical Problem
Has any body noticed that it is just not possible to download the first pic in article Railgun in it's highest resolution? Why is it so ? RF regulars are kindly requested to pass it on to the appropriate Wikipedia people if it's a technical bug (as I don't know how to reach them, please) 124.253.7.215 (talk) 21:23, 3 November 2017 (UTC)
 * File:Railgun usnavy 2008.jpg worked for me just now, both via the "Original file" link on the image description page and via the "Download original file" item after clicking the download link in the media-viewer mode. Firefox-56.0.2. How exactly are you trying it? DMacks (talk) 21:34, 3 November 2017 (UTC)

Enabling works for new railway lines
Do enabling works for brand new railway lines such as demolition, utility and infrastructure diversions etc fall under railway civil engineering? Some people argue that it’s not railway civil engineering and is just general civil engineering. Clover345 (talk) 11:35, 3 November 2017 (UTC)
 * Civil engineering is a widely-recognized (perhaps the most widely-recognized) major engineering discipline. "Railway civil engineering" is not, though it seems like a useful subset or sub-discipline. As such, virtually everything that might plausibly fall under "railway civil engineering" will also fall under the banner of civil engineering (whether prefaced with "general" or not). &mdash; Lomn 13:28, 3 November 2017 (UTC)


 * General civil engineering. For example, if a major water line needs to be moved it doesn't really need a railway civil engineer. A cantilever rail bridge (with a speed rating of x) spanning a gorge is a different story. 196.213.35.146 (talk) 13:30, 3 November 2017 (UTC)
 * I wouldn't hire a railway engineering firm to design and build a bridge (and I probably wouldn't go to an advertising "general" firm, either). I'd go to a firm that does bridges. Which, I think, illustrates nicely that the proposed division isn't universal or clean. An engineer with rail specialization would need to provide input on either the water line or the bridge (What's the maximum weight on the line? How deep does the line construction itself go? What's the maximum grade permissible on or near the bridge? What about turning radius?) but likely would not have the specialist knowledge to design either the water line or the bridge itself. Conversely, the engineer responsible for either of those projects would likely not have the specialist knowledge to derive the rail-applicable requirements that impact the designs (or for a great many other requirements). Engineering work of any substantial magnitude is not a single-subdiscipline affair. &mdash; Lomn 14:18, 3 November 2017 (UTC)


 * (ec) In part, the answer probably depends on why you're asking&mdash;there may be jurisdiction-specific situations that have explicit legal/regulatory definitions and requirements as to what constitutes "railway" civil engineering. One might also be taking a university course where the instructor has a particular and specific definition in mind.  The question could come up in dealing with a professional organization that has particular requirements for membership.
 * The first relevant Google hit I get is for the UK's Railway Civil Engineer's Association, which says "Railway engineering is an engineering discipline that deals with the design, construction and operation of railway systems." For membership, their criteria include:
 * "Those who are engaged in, or been engaged in, the development, design, construction or maintenance of engineering infrastructure for railway operations. Ordinary members will normally be professional engineers. ..."
 * There's some wiggle room there, but I would tend to interpret those in a manner akin to that suggested by 196.213 above. A railway engineer would determine the location and design of the new line, and would likely be involved in identifying required demolition projects and utility relocations.  Once those requirements were specified, however, it would not necessarily require railway-specific knowledge or training to carry them out; they're not railway engineering.  If a sewer pipe needs to be relocated to allow the construction of bridge footings, it doesn't matter if the bride is for road or rail use&mdash;the pipe just needs to be somewhere else.
 * Indeed, substantial demolition or utility relocation projects would likely require their own flavors of engineering experts, with specific training and qualifications that a railway engineer wouldn't be expected to have and wouldn't be permitted to sign off on. On a major project, I would expect multiple different types of engineers to collaborate.  And I am sure that there are some blurry edges associated with some tasks, as well.  Honestly, your best bet might well be to contact organizations like the RCEA directly, and just ask them how they handle this question. TenOfAllTrades(talk) 14:39, 3 November 2017 (UTC)


 * Interesting. But surely there are some significant differences between a railway bridge and a road bridge as they will be subject to different types of loading. Clover345 (talk) 14:47, 3 November 2017 (UTC)


 * See .  This  shows how the two disciplines interact.   At Upper Holloway, for example, the bridge carrying the main road from London to the north had to be reconstructed and various utilities relocated. 80.5.88.70 (talk) 15:47, 3 November 2017 (UTC)
 * Yes, there can be significant differences also in aesthetics, budget and whether there is a pre-existing foundation. The article Bridge gives an introduction to the many options available to the project engineer who needs to have expertise about the failures of bridges that first assumed national interest during the Victorian era when many new designs were being built, often using new materials. Blooteuth (talk) 16:53, 3 November 2017 (UTC)

Is it more common to classify civil engineers as infrastructure civil engineers or buildings civil engineers? Clover345 (talk) 17:47, 3 November 2017 (UTC)
 * Here are current examples of recruiters for both Civil Infrastructure Engineer and Buildings – Civil Engineer. Blooteuth (talk) 19:04, 3 November 2017 (UTC)

X-rays
1.As we know that most typical digital cameras (likes the ones in smartphones etc.), are able to detect infrared rays, unlike human eyes are (except in very rare cases). Are these typical digital cameras like the ones in our mobiles, or our DSLRs etc. also able to catch X-rays (let's, for sake of simplicity, limit the question to the X-rays that are produced by the machines used to look into the human-body in medical diagnosis works).

2. I have read somewhere that if the simple task of detaching the adhesive cellophane tape from it's roll, is done in strong vaccum, X-rays are produced ! Is that a fact or a myth ? Jon Ascton   (talk)  20:10, 3 November 2017 (UTC)
 * Theoretically hard X-rays hitting a CCD will cause flashes of light, which can be detected. However the camera optics does not work for X-rays. So, X-rays coming from any direction will be detected - the camera will not display any X-ray image. Ruslik_ Zero 20:26, 3 November 2017 (UTC)


 * The scotch-tape thing is real. here are researchers from UCLA actually imaging someone's finger bones this way! ApLundell (talk) 21:01, 3 November 2017 (UTC)


 * this article suggests that a ccd from an ordinary digital camera would be a poor way to detect gamma rays, but this article talks about an East Hartford company that proves it can be done, at least if the source is dangerously powerful. Neither are these are about the precise frequency of gamma waves that make up medical x-rays, but they may be close enough for your purpose. Ruslik0 is correct that in both cases, since x-rays will pass straight through the optics (and everything else), you won't get an image as much as you'll get random static. ApLundell (talk) 21:22, 3 November 2017 (UTC)
 * Related : If you've ever watched any of the videos coming from the space station, you'll know that all their DSLRs have bad pixels. Gamma Rays.
 * ApLundell (talk) 21:23, 3 November 2017 (UTC)
 * The semiconductor elements of the CCD array are affected by X-rays, so they will "detect" them as in the above responses. However, all of the rest of the semiconductor elements in the camera are also affected by X-rays at least to some extent, so enough X-rays to register on the CCD as a bloom may also be enough X-rays to produce a soft error while the camera tries to process the image, resulting in anything from a tiny glitch, to loss of the image, to a latch-up requiring the camera to be powered off and back on. A very large dose of X-rays can result in damage rendering the camera unusable.-Arch dude (talk) 23:15, 3 November 2017 (UTC)


 * There are a few phone apps that use the builtin CCD camera as a gamma/x-ray detector. DMacks (talk) 18:53, 4 November 2017 (UTC)

Namibia "hammocks"
The article on Namibia says "Near the coast there are areas where the dunes are vegetated with hammocks", linking hammock (ecology). The source linked to currently consists of the words "index.php". The article on hammocks lists a number of different things in Florida -- there are xeric hammocks, but these are wet, surrounded by well-drained sandy soil. By contrast, the article on Namibia describes the entire country as arid or semi-arid. Stupid searches get nothing but photos of tourists, obviously; "xeric hammocks" and Namibia turns up nothing much. Your mission: figure out if there are really (ecological) hammocks in Namibia, what kind they are, whether they are in some special foggy microclimate that is not arid so that it is actually too wet around them for trees like in Florida. Wnt (talk) 23:12, 3 November 2017 (UTC)
 * The coast of Namibia is known for its significantly different climate to inland. The Atlantic coast of Southern Africa has much colder currents than the Indian Ocean coast and this leads to the famous cold fogs of coastal Namibia. Although these lead to some rainfall, notable itself in this largely arid climate, they also produce significant precipitation as dew on plots of coastal vegetation. So the vegetated plots (whatever they're called, I'm unfamiliar with hammocks) become self-sustaining. Andy Dingley (talk) 23:41, 3 November 2017 (UTC)
 * Thanks to the Wayback Machine, Here's that source article as it appeared in March 2016. The word "hammock" does not appear, but "hummock" does (and the article hammock (ecology) suggests that the one derives from the other).  The relevant sentence is "Vegetated dune-hummock areas are common near the coast", but I don't know if it's correct to interpret that as meaning hammocks.  --69.159.60.147 (talk) 04:44, 4 November 2017 (UTC)
 * The distinction between a hummock and a hammock is subtle. One is an slightly elevated coastal area with woody vegetation.  The other is a high mound near the sea with trees.  Most importantly for our discussion, one has a "u" in it, while of absolute importance to settling the dispute, the other has an "a".  As to which applies to the coast of Namibia, I'm not entirely sure.  Perhaps choosing a third term which is more universal may be useful.  -- Jayron 32 04:59, 4 November 2017 (UTC)
 * ... and etymologists seem unclear and not in agreement about whether or not one word was derived from the other in the sixteenth century. I agree that choosing a more world-wide term would be more appropriate for this area and this article.    D b f i r s   08:43, 4 November 2017 (UTC)
 * The "dune-hummock" tip is highly informative -- dune hummocks = nabkhas are well known in coastal areas around the world; their anchoring by bushes in Finland is described, for example.  There are a number of single hummocks visible as images, though this photo suggests the hummocks can be densely packed in larger areas.  This link suggests a more specific location and suggests the mist is salty.  There is a lot of information about Namibian dunes overall  but I'm still a bit unclear whether the dune-hummocks are classified in any higher-level unit than the single little hump. Wnt (talk) 11:40, 4 November 2017 (UTC)
 * Hey User:Wnt, I'm confused about what you're unclear on. Out side of the slightly more specific sense described in our article, hammocks are generally just raised bits of vegetation; often there is some interesting process that forms them. I don't think there's anything intrinsic/necessary about moisture, but often they have something distinct going on ecologically, behaving as relatively isolated communities, often centered around a few sort of ecosystem engineer species that provide refugia or food etc. I am not terribly familiar with hammocks in Namibia, but e.g. here they are clearly referred to as hammocks, though I can't figure out what they mean by "nama plants", except that I'm pretty sure it's not nama_(plant), as that is a new world genus. I think it might be a garbling of the plant called "!Nara" in the Nama language, Acanthosicyos_horridus, which is endemic to Namibia and provides a mechanism for dune/hammock building as described here . Sometimes, when speaking of hammocks, the word can mean either one specific hammock, but it can also be used to stand for the set of all of them in the region. E.g. "a hammock species", or "the hammock [ecology/community/system]." Does that help at all? SemanticMantis (talk) 19:05, 4 November 2017 (UTC)
 * Our article describes the hammocks as stands of trees, while the dune hummocks I was looking at in our other article are individual bushes anchoring a mound a few meters in size. The source you cited is useful - I ran down its source at a doctoral thesis online  which says "The characteristic plant at the study site is Acanthosicyos horridus, the nara, a member of the Cucurbitaceae, and an endemic of the Namib sand dunes. The species grows  in  the  dune  valleys  were  there  is access  to  underground water."  The thesis uses the word "nara" a bazillion times, so indeed the other source was in error.  Crucially, it explains (p. 16) that "Nara  plants  form  dense,  tangled  bushes  and  as  sand  is  trapped  underneath  the  branches,  a  hummock  reaching  considerable  size  is  built  up.  These  hummocks  can reach  sizes  up  to  4m in  height  and  cover  an  area  of  up  to  1000  m2,  forming  micro-ecosystems  within  the  dunes  of  the  Namib  Desert."  So bushes not trees, centered on underground water rather than avoiding it, but also a large formation; I'm not sure now which is larger.  In short, although you weren't sure how I was unsure, you led me to the exact thing to explain what I was unsure about. ;)  Now I just have to figure how to bring this back to the article. Wnt (talk) 23:20, 4 November 2017 (UTC)
 * Cool, good job sorting it out. My two cents is that it hardly matters to maintain any distinction between hammocks and hummocks, they are both just raised bits of vegetation that have something interesting about them. I once saw a fascinating talk about how topography influences plant competition. Guy put up a map that looked like a range of rolling hills, showed how elevation had strong effects on species filtering, then revealed the punch line of the scale: the peaks were just a few cm high. Anyway, he called them hammocks, as I recall :) microtopography is a redlink, but you can find plenty of research on the topic using that keyword, and some of it highly relevant to the concept of hammock/hummock. SemanticMantis (talk) 17:27, 5 November 2017 (UTC)
 * In "What is a hammock?" I find "In the Everglades a hammock refers to 'isolated patches of small broadleaf trees, many of them West Indian species, in the sawgrass or maidencane marsh or limestone pinelands'." Bus stop (talk) 17:39, 5 November 2017 (UTC)
 * That's a nice clear definition, but it only applies to the Everglades, and does not cover general usage in plant community ecology. So it's not going to apply to the hammocks that are raised isolated patches of endemic cucurbits in Namibia. SemanticMantis (talk) 15:32, 6 November 2017 (UTC)
 * We also have the article Hummock. Admittedly it is hardly perfectly on target, vis-a-vis the question asked, but I just thought I would bring it to everyone's attention. Bus stop (talk) 21:24, 6 November 2017 (UTC)