The best answers address the question directly, and back up facts with wikilinks and links to sources. Do not edit others' comments and do not give any medical or legal advice.
The Yanomami Indians have an average intake of 50 mg of salt per day. They live in very hot and humid conditions, so they must sweat quite a lot. It's then impossible for them to lose the approximately 1 gram of salt per liter sweat like we do. This seems to suggest that the salt we lose in urine and sweat is just a way for the body to dump excess salt. Presumably, the salt concentration of sweat saturates at some level (say 1 gram per liter) if the intake is a lot more than 1 gram per day, and this is then the maximum amount of salt that the body can put in the sweat. So, is salty sweat really a sign that we're overdosing on salt? Count Iblis (talk) 01:28, 1 June 2016 (UTC)[reply]
The short answer is no. Climate adaptation plays a very large part, specifically: Most people have the ability to physiologically acclimatize to hot conditions over a period of days to weeks. The salt concentration of sweat progressively decreases while the volume of sweat increases. Urine volume also reduces. . Salt in the sweat comes from the blood, sweat depletes blood sodium concentration but it is not the mechanism which the body uses for regulating blood sodium concentration, that would be the kidneys. Vespine (talk) 02:41, 1 June 2016 (UTC)[reply]
As a type-2 diabetic who takes Jardiance I have been advised to consume as much water per day as possible, which is about 2 gallons. My lab results normally show a slightly too low sodium level, and I feel fine. μηδείς (talk) 03:48, 1 June 2016 (UTC)[reply]
Sweating isn't very effective in highly humid conditions. They might cool off in other ways, such as taking a dip in the river, or avoid activity in the hottest part of the day. Also, I believe they live in the rain forest, where there is plenty of shade. StuRat (talk) 14:42, 1 June 2016 (UTC)[reply]
Mammals need sodium and chlorine, which do not necessarily have to come through eating salt, but salt helps. E.g. eating fried flesh only ensures enough salt on its own. See e.g. http://www.jstor.org/stable/27848175 . See also Health effects of salt: the evidence for "salt is bad" consensus is quite flimsy. Recent research suggests that eating too few salt is as bad as eating too much salt. Tgeorgescu (talk) 23:45, 2 June 2016 (UTC)[reply]
I believe the consensus was that "too much salt is bad", not that any salt at all is bad. And that consensus still holds, although the exact amount which is "too much" is debatable. It's also been well known for a long time that too little salt is bad, but, for people on a Western diet, the chances of actually suffering from a lack of dietary salt is quite low. This would require not eating restaurant meals, processed foods, or adding salt or salt-containing spices and condiments to any food. StuRat (talk) 17:28, 3 June 2016 (UTC)[reply]
I'm not going to try to find it at home with my slow Internet, but People's Pharmacy has an article stating the AMA disagrees with some British research. I wanted to propose the dispute be mentioned on Wikipedia.— Vchimpanzee • talk • contributions • 21:54, 3 June 2016 (UTC)[reply]
I was recently reminded of the idea that a river will not run straight for more than ~10 times its width. I'm trying to reconcile that with the coastline paradox in my head. I keep coming back to "What is straight when you're referring to a river?" Am I not thinking about this the right way? Is that where the roughly part of the 10 times its width comes in? Dismas|(talk)02:05, 1 June 2016 (UTC)[reply]
It's almost certainly just a "rule of thumb". I'm no river expert but it doesn't some like some general rule of hydrology. It would depend on many things, what the river bed is made out of to start with; a river between two cliffs could easily be straight for a long way, or would you then call it a creek or a stream? Vespine (talk) 02:55, 1 June 2016 (UTC)[reply]
There are any number of ways to make such a measurement well-defined. For example, from the middle of the river one might measure the longest line-of-sight distance that one can travel before reaching a bank and compare that to the shortest distance one can travel. Whether any particular measure of straightness makes your aphorism approximately true, I don't know. Dragons flight (talk) 12:02, 1 June 2016 (UTC)[reply]
The Hudson River at Poughkeepsie meets that criterion (as well as a stricter "best fit linear approximation of a section of midline that's completely in the river divided by average river width of said section of midline"). The Hudson River at Manhattan is even straighter but maybe not for 10 river widths. Sagittarian Milky Way (talk) 14:31, 1 June 2016 (UTC)[reply]
The coastline paradox applies to fractal or similar sorts of curves. The banks of a river would have that property just as coastlines do, but the length or straightness would be measured along the centerline—the set of points that each are equally near to the nearest point on each side. I think the operation of finding the centerline would damp out any fractal deviations mcuh smaller than the width of the river, so I think the centerline should be a more ordinary sort of curve. (I have not attempted to prove this mathematically, though.) --69.159.60.83 (talk) 06:21, 1 June 2016 (UTC)[reply]
Is there a source for this aphorism? I ask not because a source is needed to ask this kind of question, but because reference to the source would help us know exactly what it is supposed to mean. John M Baker (talk) 14:09, 1 June 2016 (UTC)[reply]
Excellent! I know more about his father, but Luna was quite the scientist as well. Here [3] is an excellent monograph detailing properties of stream channels, with some discussion of width and meandering. Lots of cool graphs with detailed measurements of many characteristics, across many scales. I cannot easily search it, unfortunately. For even more on the topic, here [4] is a nice compendium of accessible copies of his works, many of which touch upon this issue. SemanticMantis (talk) 14:43, 1 June 2016 (UTC)[reply]
The Ping River has long straight segments.
I would expect there to be special geological cases where a river would remain straight for far longer. For example, say sedimentary layers change from hard to soft to hard, then uplift at one side turns all 3 layers on their side, so that now the soft layer erodes first, forming a straight river. A syncline is another case. StuRat (talk) 14:30, 1 June 2016 (UTC)[reply]
This map tells us nothing about the straightness of the stream bed with respect to the width of the stream. This map has straight segments of at least several miles long, but the Mississippi is nowhere straight for several miles. Detailed measurements or perhaps aerial photography might be better in some cases.Lol, not relevant at all. Maps at this scale never show detail of stream bed meandering. There are likely departures from that line on the scale of hundreds of meters, if not more. Nice try though. SemanticMantis (talk) 16:27, 1 June 2016 (UTC)[reply]
Look at this Google map of the Ping River, then switch to satellite view, and zoom in: [5]. It's hard to see the river through the tree cover, but the tree line, following the river, is relatively straight in many sections. StuRat (talk) 20:00, 1 June 2016 (UTC)[reply]
Leopold's aphorism is given in SemanticMantis's first link, at page 53 (PDF page 18). On page 60 (PDF page 25), the article says that a straight channel is one with a sinuosity less than 1.5. John M Baker (talk) 17:13, 1 June 2016 (UTC)[reply]
Thanks! I didn't have time to read at time of linking. As penance, here is the relevant quote from p. 53:
“
In the field it is relatively easy to find illustrations of either meandering or braided channels. The same cannot be said of straight channels. In our experience truly straight channels are so rare among natural rivers as to be almost nonexistent. Extremely short segments or reaches of the channel may be straight, but can be stated as a generalization that reaches which are straight for distances exceeding ten times the channel width are rare.
”
This is also a great example of the value of collaboration in finding references! I skipped this question until User:Tagishsimon found the Leopold link, then I found a paper that contained the aphorism, then you found the aphorism itself. Good job all! SemanticMantis (talk) 17:25, 1 June 2016 (UTC)[reply]
I had a moment, so out of curiosity, I did a search for rift valley river and came up with the Narmada River (what the hell is a rift valley doing in the middle of India? Must look up...) On Google Maps it looks like this: [6] Is that straight for more than 10x? I don't know. In any case, not just any rift makes a straight river. Wnt (talk) 17:21, 1 June 2016 (UTC)[reply]
That's a good contender at least. Zooming in, parts of the "straight" part would likely be classified as braided, you can see the multiple channels created by sandbars, a sort of reticulated effect. Actually I see suspicious discontinuities in the braiding, indicating that the photos were pasted together from different times or even different years. SemanticMantis (talk) 17:29, 1 June 2016 (UTC)[reply]
Good find! But, being passingly familiar wit Sacramento, I wonder to the what extent the stream bed is human engineered. Note the river there is neatly sandwiched between 160 and river road, and see e.g. maps here [8] for the extent of levees, channelization, weirs, etc deployed in the region. In short, I agree it's straight for more than 10x width, but I'm skeptical that the stream bed should be considered "natural" in that reach. SemanticMantis (talk) 14:29, 2 June 2016 (UTC)[reply]
Looking for more "rift valley rivers", I found the Jordan River and Luangwa River, both of which are quite convoluted despite the underlying geology. It seems apparent from inspection that once a river erodes and deposits enough of a floodplain, even with the straightest underlying geology, it is free to meander quite extensively. Wnt (talk) 00:26, 2 June 2016 (UTC)[reply]
Yes, it's almost as if one of the greatest living geologists/hydrologists of his era knew what he was talking about, perhaps more than the casual ref desk reader or responder! It's true he didn't have google maps to easily skim for counterexamples though :) SemanticMantis (talk) 14:29, 2 June 2016 (UTC)[reply]
Just because it's true doesn't mean it's a bad thing to test some examples and see how true it looks on the ground. It's harder to remember a principle than the physical sight of how it plays out on a satellite photo. Wnt (talk) 15:01, 2 June 2016 (UTC)[reply]
I think it's reasonable to test assertions by experts. And in this case, we're not really even challenging Leopold: Some of the paraphrases on the Internet assert that there are no natural straight stretches of more than ten times a river's width, but he only said that such stretches are rare. It seems the best candidates we have so far are the Sacramento and the Ping, but (as you point out) it's quite possible that the Sacramento is engineered, and it's hard to be sure about the Ping from the maps we have. The Hudson is really straight at Manhattan, but not for ten river widths, and I don't see a comparable straight stretch in Poughkeepsie. The Susquehanna is not all that straight. The Narmada is pretty straight and arguably qualifies, although Leopold would probably call it a braided rather than straight river. John M Baker (talk) 15:26, 2 June 2016 (UTC)[reply]
Oh yes, I was just teasing Wnt a bit, sorry if that wasn't clear. It certainly is interesting to look for exceptions, and it is good to note that this is not hard rule but a solid tendency. I had actually never even heard the assertion before, so I was very pleased to discover the scientific basis and original author of the conjecture/aphorism. SemanticMantis (talk) 15:56, 2 June 2016 (UTC)[reply]
It's in a location where it might be found (the general area of Strawberry Peak off the Angeles Crest Highway; the Station Fire (2009) still being recent enough). The flowers look similar to what I see online. The leaves — well, they're not as pointy. Some pictures seem to show the leaves bent in the middle, which these are not, but maybe they open up sometimes. They have a similar sort of scalloping, with soft ridges purpendicular to the spine of the leaf. Does anyone know? --Trovatore (talk) 05:23, 1 June 2016 (UTC)[reply]
A plant found in a region where poodle-dog bush is also found, that looks enough like it to make me wonder whether that's what it is.
The leaves are generally not a great feature for plant ID. The margin and size can change with plant age and between individuals of the same species. Consider this [9] young PDB - its leaves look much like yours, and are far wider than many of the pictures I see with a general image search. The curling response is related to drought tolerance, so drier plants will have more curl to their leaves. Anyway, for you specific case: maybe? If you have a closeup of the flower that would help. If the flower has the right number of petals and stamens, we can also tell it is broadly of the right shape and color, and since it is growing at the right location and blooming at the right time and has the right stature, I would be fairly confident that your photo is at least one of the Eriodictyon. SemanticMantis (talk) 12:54, 1 June 2016 (UTC)[reply]
OK, thanks, SM. Unfortunately I didn't take any closer pictures — this one is a result of looking through my shots for the one that had the most of it, closest, to crop. I was really wanting to learn to identify it, so I don't have to be paranoid about all low-growing shrubs with purple flowers.
But come to think of it, while I think I know poison oak pretty well, it's entirely possible that I group some harmless sumacs in with it, and I'm mostly OK with that. --Trovatore (talk) 17:26, 1 June 2016 (UTC)[reply]
Haha prolific poison oak is one thing I don't miss about that region! I should amend my statement above though: leaf shape and size are not good ID characteristice. Leaf growth pattern (e.g. alternate, paired, etc) and Leaf#Venation are important parts of working through a taxonomic key. If you collect a sample, I'm pretty sure you could work through a key and be sure. SemanticMantis (talk) 17:38, 1 June 2016 (UTC)[reply]
Forgot substance
A few days ago I saw some Wikipedia article on a certain substance (forgot which) with an insane molecular formula. The numbers of oxygen, carbon and possibly nitrogen atoms were over 400, something like C350H600O700, perhaps there were other elements as well. The article also had an illustration of the ball-and-stick model with an antenna-shaped structure, structurally similar to chlorophyll. That's all I remember, would check any suggestions.--93.174.25.12 (talk) 09:52, 1 June 2016 (UTC)[reply]
Proteins have a unique and very large structure (though there are more errors (or variations - we can't really say for sure the biology doesn't want the variation) in individual proteins than people sometimes imagine). A generation of heroic chemists in the early 1900s struggled to produce an accurate empirical formula for albumin ... you have to respect those guys, even though they had no idea what they were headed into. Wnt (talk) 00:30, 2 June 2016 (UTC)[reply]
There is a particular type of small plant which grows on pond's surface. Their roots never reach the bottom of the pond. If people don't use the pond, then this plant leaves cover the entire surface like a green coat. From a distance it would look like there is no water. Most common types have small round leaves.
There is another type in Africa which don't cover the entire surface of ponds or lakes. But their leaves are very big in size and they have the shape of a large round plate. I saw that picture in National Geographic magazine. The picture was taken in 1903 in Africa. The children of a British officer were actually standing over those large flat leaves floating on the lake's surface. --Blade Ninja (talk) 11:53, 1 June 2016 (UTC)[reply]
The description in your first paragraph sounds like some sort of duckweed. As for the second paragraph, in most of the photos I've seen of children standing on aquatic plants' leaves, the plants have been the giant water lily, but that's native to South America, not Africa. Deor (talk) 12:48, 1 June 2016 (UTC)[reply]
Most data soucres for hardness either given minerals, metals, or construction materials (concrete, wood, etc.). Sucrose is none of those - can anyone find data on this? Tompw (talk) 17:10, 1 June 2016 (UTC)[reply]
Transfer factors have been used successfully. Whilst a hot bath may not be thought of today as a medical treatment, these were used too to increase the response; just as fever does.--Aspro (talk) 20:43, 1 June 2016 (UTC)[reply]
Hmm, I'm thinking imiquimod - that article references two other TLR7 modifiers; I haven't looked recently to know how many it is up to total. Wnt (talk) 22:21, 4 June 2016 (UTC)[reply]
A puzzle of Stefano Ludovico Straneo
This is not a usual RD question, but rather a request for small help in research for an article.
For no particular reason, yesterday I wrote an article about Stefano Ludovico Straneo (1902-1997), a prolific Italian entomologist, who described over 1200 beetle species and published over 200 papers during a 60+ years long academic career. I scrapped it from only a few online sources, but upon investigation I got a little stuck. One would expect to find some more information about so active author, but all that I found is fragmentary and mostly puzzling. I would appreciate some help, mostly from Italian-speaking friends and/or those with a better access to academic sources.
Puzzle #1: Certain professor Stefano Ludovico Straneo has published 40+ works and textbooks from the fields of mechanics, industrial design and electronics: [10], also between 1941 and 1996. Is that the same person?! It's a bit unusual to be an expert in engineering and entomology simultaneously, but too many details suggest that he was, but I don't have any solid proof apart from the same name and period.
Puzzle #2: There is a detailed biography of Straneo the entymologist at [11], but only a snippet view is available. Those fragments suggest that his father was Paolo Straneo (1874-1968), a physicist and a friend of Einstein, but I have only clues. Does anyone have an access to the full book (damn, those are proceedings of a 1996 entomologist symposium, I guess those are hard to obtain), or any other proof that Paolo is Stefano's father? All my searches came up short. Paolo seems to have an entire university named after himself (http://www.straneo.gov.it/), but it does not seem to contain any detailed biography.
All my google-fu for those names failed so far, and I remain puzzled on details, so this request is a bit of stab in the dark. Hope I got someone's attention... No such user (talk) 21:17, 1 June 2016 (UTC)[reply]
This appears to be a request for factual information not tied to any particular person, which is allowed. -- BenRG (talk) 23:58, 1 June 2016 (UTC)[reply]
Here [12] is a research article titled "Cleansing ability and Tolerance of Three Bowel Preparations for Colonoscopy" - it would seem to address your question. This article is also relevant, and addresses the importance of timing [13]. This response contains references. It presents no treatment, prognosis, nor any advice of any sort. Any responses that give medical advice may be removed, possibly by me :) SemanticMantis (talk) 14:18, 2 June 2016 (UTC)[reply]
You keep saying you won't be back, and you keep coming back. How about instead of asking new questions when you come back, you actually ask a complete question with enough context so people here know what you are talking about. It's hard to provide you with references when we don't even know what you are asking. --Jayron3202:45, 3 June 2016 (UTC)[reply]
The starting date will have a crucial effect on the time taken, as will the delta v of your spaceship, since a sufficiently fuelled ship can ignore orbital mechanics and just blast from planet to planet. You may be interested in Interplanetary Transport NetworkGreglocock (talk) 06:27, 2 June 2016 (UTC)[reply]
Unfortunately, making the trip longer in a manned ship means you need more food, water, oxygen, electricity, and shielding (to protect from radiation), all of which adds weight, meaning you need more fuel or sail to propel it all, and more fuel or sail to propel the additional fuel or sail, etc. It quickly spirals out of control. StuRat (talk) 13:07, 2 June 2016 (UTC)[reply]
OK, time is less critical then, but more time does still require more shielding for the electronics to survive radiation and micrometeorites, and a bigger power source, to last longer. StuRat (talk) 03:04, 4 June 2016 (UTC)[reply]
There isn't a movement for Earth - so presumably you cannot start from here. That is really going to complicate things, as you will have to build your ship on Mercury! 86.191.126.192 (talk) 08:35, 2 June 2016 (UTC)[reply]
Here is the voyage itinerary listing each planet to visit with the planet's greatest distance from the Sun expressed in AU or multiples of the distance from the Earth to the Sun.
this user enquires the specific process via which, viral hepatitis performs temporary relapses when the patient performs physical movement contrary to bed rest
I have a lot of small, green caterpillars on my gooseberry bush, and I'm trying to identify them. They are small (about 10-15mm long), green (the same shade as the leaves, with no obvious markings). At first I assumed theywould be some sort of sawfly larva (probably Small or Pale, judging by the description). However, all the sources I've found say that the sawflies pupate in the soil. These caterpillars roll up the leaves and pupate inside them. Can anyne ID them for me? Iapetus (talk) 18:29, 2 June 2016 (UTC)[reply]
Was it "inching" along in inchworm style? Do they look like this [14]? That could indicate Geometridae. But also maybe look at the cabbage loopers and kin in the Noctuidae. I think the former family pupates in leaves, and at least some of the latter do [15]. The problem with size of caterpillars is they can go through tons of instars, and even giants were once tiny. Are you saying the pupae are also 10-15 mm? Also where in the world is this? SemanticMantis (talk) 18:48, 2 June 2016 (UTC)[reply]
Location is SW England. They do look similar to the first image, although I think they have more pseudopods (although I haven't checked closely, and haven't seen any for a few days - I think I've got rid of them all). I'm not sure how they move, because I rarely see them do (they just sit right on the edge of the leaves and eat them). If disturbed, they'll sometimes grip the leaf with their pseudopods and rear up / curl up / wave their front around. 10-15mm seems to be the maximum size they reach. The pupae are smaller - about 7mm. They only affect my gooseberry bush - I have broccoli growing close by and they don't touch that.
I know humans occupy a lot of territory, so much that non-human animals are losing their natural habitats and being forced to live in wildlife parks and in human neighborhoods. But what if there is a population of humanoids existing on a fertile patch of soil, and neighboring humans want the land? Will the population of humanoids be forced to assimilate into the human society and interbreed, or will the population of humanoids be eliminated by killing, or will the population of humanoids be protected like other wildlife? 198.30.87.2 (talk) 18:30, 2 June 2016 (UTC)[reply]
Never mind. I just thought of the answer, even though there have been many instances in history where the three mentioned situations have all been done. 198.30.87.2 (talk) 19:08, 2 June 2016 (UTC)[reply]
I assume the OP is using the term humanoids to refer to groups of our species homo sapiens who are of a “different” culture. Examples may be Neanderthalians, Celtic tribes in Europe, Amerindians or the Ainu. Arguably, all three scenarios mentioned by IP 198… have been “deployed”. --Cookatoo.ergo.ZooM (talk) 19:44, 2 June 2016 (UTC)[reply]
Neanderthals (and Denisovans) were actually different sub-species. Replacement (either through extermination or by out-competing) happened, as did interbreeding (some of that may have been rape). But if there was any attempt to "preserve" those two, it obviously didn't work, as they are long gone (except some DNA mixed into our own). StuRat (talk) 20:12, 3 June 2016 (UTC)[reply]
What's the least radiation pressure detectable with no instruments or spaceflight?
What's a good test for this?
Fire a laser at gold foil hung in a vacuum and see if moves? Fire pulses at the sky at various hertz and see if you hear (or feel?) anything? Is there a way to distinguish the sounds of air/ionized air expanding from the momentum of light pushing the air? How damaging is a beam that shows the momentum of light? Sagittarian Milky Way (talk) 23:27, 2 June 2016 (UTC)[reply]
I've always wondered how powerful traditional space opera laser guns could get before they reached genre-breaking wattages. The smallness, efficiency, and storage capacity may be near-magic but I want a real life physics laser beam after the muzzle. First of all I assume a laser beam that causes damage as fast as even the weakest guns we still fight with would burn friendly retinas if it bounced back, am I right? Even if you could afford them I don't know if perfect aim and not having to reload would make it worth it. Then again if the media is real 20th century rate of fire is already high enough that a lot of modern gunfighting is peeking around a wall and shooting a million times before you finally hit someone. And you could train fighters "close eyes, 1 second burst, open eyes" or something, have reduced power wargames till they have reflection geometry instincts, give them reflective eyepatchs, let them run from battle to a life pension if unpatched eye's destroyed. So maybe replacing a large portion of projectile guns with lasers might still be worth it.
What's the limiting factor? Is it the beam becoming so bright that it's hard to see what you're cutting or shooting pulses at? Is it heating the air so powerfully that the sound and/or heat reduces combat effectiveness more than the stronger beam helps it? (if beams this powerful would make space opera tactics suicidal let's say that either 1. Both sides wear armor that requires them 2. It's only used against lower tech planets without guns this strong)
Could you notice light's momentum with those beams and what would they sound and look and heat like? How good are they (cuts through x inches steel/concrete/humans per second, how long to boil x liters of y, many common things explode when hit or no (containers, rocks etc.), beam temperature, vaporizes so fast it's impossible to see blood or red or not quite that good at cauterizing, things like that (do non-gaseous substances who's bond breaking is exothermic explode on contact because the molecules decompose to gas like gunpowder exploding?)). How long will the best mirror shield survive and how much damage could the reflected beam cause? How many watts is it? What does the beam do to the air? Sagittarian Milky Way (talk) 23:51, 2 June 2016 (UTC)[reply]
Why not look at the website of the Air Force Research Laboratory's Directed Energy Directorate? They study military applications of laser light sources; as part of their mission, the Directorate "develops and transitions technologies in four core technical competencies: lasers systems, high power electromagnetics, weapons modeling and simulation, and directed energy and electro-optics for space superiority."
In reality, the biggest limiting factors are that lasers are less effective than conventional weaponry for most purposes; very powerful lasers are surprisingly inconvenient; and there are all sorts of legal, ethical, and treaty-obligation- reasons that forbid the use of laser energy during many types of combat.
The most convincing tests I've ever seen out of DED are the Boeing Airborne Laser and the Raytheon LaWSlaser product. Neither one was convincing enough to continue warranting a large amount of additional funding. Some obvious problems with both systems pertained to targeting accuracy; the incredible engineering challenges of sustainably delivering such quantities of optical energy and power; and the general assessment of their utility - especially in competition with more conventional weapon systems.
In the United States, our military and our government also have an obligation to uphold the 1980 Protocol on Blinding Laser Weapons - part of the Convention on Certain Conventional Weapons as well as many other international agreements. These agreements forbid our military from using unnecessary cruel and unusual weapons during warfare. For the most part, this means that our military will not field laser weaponry in combat.
Defense Secretary Robert Gates, who reined in a lot of ... ridiculous military expenditures that were encouraged by his predecessors..., had this to say about the Airborne Laser:
"There's nobody in uniform that I know who believes that this is a workable concept," as quoted in Nature, (2012), "Secret Weapons."
One may presume that some percentage of those 87 billion dollars - ostensibly approved as an emergency-measure to win the war in Iraq, including $65 billion to fund undisclosed classified military activities - probably helped pay for fuel on the laser airplane. Either way, those 87 billion dollars surely didn'tend the war in 2004. Nor have any of our major operational successes depended on infantrymen armed with laser rifles.
I have always suggested that our best and most cost-effective military technology strategy would have been to air-drop 87 million iPods. In the statistical aggregate, the average enemy combatant, faced with the choice between the horrors of war, and chilling out with two free iPods, would opt to remove himself from the fight... and we could use the left-over laser budget to airdrop some disco lights... win without fighting! But hey, what do I know about military strategy?
As for the issue of protecting eye from reflections, there's a simple solution to that. Lasers only produce light at one particular wavelength/frequency, so you can wear eye protection that blocks that frequency only, and still see fine using all the other frequencies. Of course, if the laser were pointed directly at your eyes, it would burn a hole through the eye protection, and then through your head. StuRat (talk) 19:20, 3 June 2016 (UTC)[reply]
Also, just to point this out, real lasers don't look like the "blasters" common in science fiction/fantasy. You can't see a laser beam unless it's either aimed right at you, or there's stuff like dust in the way of the beam that scatters some of the laser light into your eyes. One of the things that makes a laser a laser is that the light it produces is collimated; all the photons are traveling in the same direction. For you to see something, light from that thing has to enter your eye. You may have noticed that you can't see the beam of a laser pointer (again, unless there's stuff in the way that scatters some of the light). See the picture for another example. The glowing thing is the fluorescent light source for the laser, not the laser itself. Note that the laser beam isn't visible, only the spot where it hits the target. On the broader topic, you might find this TV Tropes page interesting. --71.110.8.102 (talk) 19:54, 3 June 2016 (UTC)[reply]
I've heard there's a power level above which the air in the beam is ionized, thus showing the beam's location (which makes sense, that has to happen eventually). Sagittarian Milky Way (talk) 23:43, 3 June 2016 (UTC)[reply]
Let's look at practical technology.
The 100 watt CO2 infrared laser in my laser cutter would cause really nasty burns at distances of tens of meters - at 5' long by six inch diameter, it's on the upper limits of what you could fit it into a large rifle-like gun. The laser's 30,000 volt power supply is pretty inefficient though - you'd need to supply about 600 watts to power it. A standard laptop battery (15 watt/hours), would power it for about 90 seconds - maybe enough to pull off a couple of dozen decent shots.
I don't think you could kill someone with this - the range is pretty terrible. I don't think it would be better than a regular rifle, or even a handgun.
To drill holes through people with an efficiency comparable to a bullet, you'd need a more powerful laser - but not too much more. A 3000 watt laser can cut steel - so maybe a 1000 watt laser would be lethal - and a backpack with a couple of dozen laptop batteries would give you a reasonable number of shots.
The IR laser would be completely invisible and wouldn't harm the shooter at all.
In the end, the question is more about the power source than the type of weapon. Explosive charges are a pretty dense energy source (3 to 5 MJ/kg) but a lithium/air battery is more like 8 to 9 MJ/kg - so propelling bullets using an electrical system seems like a better bet for futuristic weapons - hence "rail guns" and similar tricks. SteveBaker (talk) 02:50, 4 June 2016 (UTC)[reply]
Fascinating figure! I looked up TNT and it is 4.1 MJ/kg; gunpowder is only 3! Dynamite it adds is 7.5, but gasoline - not counting air - is 47.2. So a potato cannon is, by rights, one of the most futuristic weapons available; we just need to respect it more and hone it into deadly form. Still amazed at those lithium batteries - and just think that someday, when the right computer virus is deployed, most of them will be going off all at once. Wnt (talk) 13:07, 4 June 2016 (UTC)[reply]
In space, at long distances, speed may be critical, though. By the time your projectiles hit the target it may have already fried you with a laser, so you'd best use a laser, too, or something else that travels at the speed of light, if you hope to disable the enemy ship and survive the encounter. Also, firing projectiles in space would cause the ship to move, unless countered by an opposing force. StuRat (talk) 03:00, 4 June 2016 (UTC)[reply]
June 3
Hole size vs cost
When drilling a hole in metal, the smaller the hole the faster/less costly it is, but this only applies up to a point. When the hole size gets too small the drill bit becomes too small and thus is prone to breakage. Approximately what is the hole size at this inflection point?
Check this out. Lots of good tips about holes in general but point 14 is relevant i.e. "Deep, narrow holes with length to diameter ratios of larger than three should be avoided." 196.213.35.146 (talk) 10:16, 3 June 2016 (UTC)[reply]
Thanks! "length to diameter ratios of larger than three should be avoided" means anything that's smaller than ~1.6mm should avoided for a 5mm depth. But what about sizes above that? Are holes bigger than 1.6mm, let's say 2mm, cheaper or more expensive than 1.6mm holes? Johnson&Johnson&Son (talk) 10:25, 3 June 2016 (UTC)[reply]
Without more information about the commercial environment in which this/these hole/holes is/are to be drilled, there can be no single/satisfying answer to the question. For example, if a hobbyist is occasionally to drill one of these holes in a piece of stainless he will find one answer to the question. If a small workshop is to drill these holes a couple of dozen times they will find a different answer. If a factory uses automatic machine tools to do it as mass production they will find a third answer; and if an ultra-high production factory dedicated to drilling and fabricating components in stainless steel does it they will find yet another answer. Dolphin(t)11:48, 3 June 2016 (UTC)[reply]
Quite true. Knowing the purpose to the hole is also important. If you are going to tap a thread you need to consider the pitch and diameter of the stud/bolt going into the hole to get the maximum strength over a 5mm depth. So it's not about the cheapest hole but the strongest join. 196.213.35.146 (talk) 11:57, 3 June 2016 (UTC)[reply]
So there must be another bound to the ratio, right? Bits that are too thin for their length have problems, but on the other end, bits that are very wide can never drill a clean shallow hole well in a single pass, due pitch of drill blade and the the taper of the tip. So for 5 mm depth, it must also more difficult/expensive to drill e.g. a 200 mm diameter hole than a 2 mm diameter hole (using conventional metal drill bits). I don't know what the cost/ease graph looks like between these points. I suspect that a lot of the answers are "it depends", and you might not find any good general rules, just empirical data for specific situations. For further searching - perhaps unsurprisingly the depth/diameter ratio is known as the aspect ratio of the hole. There has been much research on how to drill thin deep holes (e.g. [16][17]). It seems to overcome the limits you have suggested, lasers and ultrasound and other things are used rather than conventional drill bits. Those papers are not directly relevant to this question, but many of the references contained will be. Here [18][19] are a couple of other articles that might help you with the literature and search terms. SemanticMantis (talk) 13:09, 3 June 2016 (UTC)[reply]
I've stumbled upon a story whose author purpotedly describes how in late 1970s Pavel K. Oshchepkov obtained electric energy out of thin air. According to this (translated from Moskovsky Komsomolets): "Pavel Kondratyevich showed me a bulb from the flashlight with two wires wielded to it, their other ends were hanging freely in the air. And the bulb was glowing. [The inventor] said that the wire is made from a sly allow of copper and aluminum, the left end is purely copper, the right end is pure aluminium. Throughout the entire length, from left to right the copper content gradually decreases, while the aluminium content gradually increases. The electron is forced to run with an acceleration from aluminium to copper. The average speed of the electron in copper is higher than in aluminium. Thus the electrons run. Hence, there's an electric current, with no violation of the thermodynamics laws". Is this ever workable? Brandmeistertalk14:27, 3 June 2016 (UTC)[reply]
The description sounds exaggerated, if not entirely fictionalized.
It is possible to use dissimilar metals to build a thermoelectric generator. Those can be built into a real device, and they can extract energy if you put heat energy into the system. The description above may have been corrupted (by hearsay) from a real demonstration of some similar device, or the device's capabilities might have been intentionally exaggerated for the purposes of promoting some scammy pseudoscience.
There are a lot of neat thermodynamic properties at any junction between dissimilar metals; more typically, at least one material is a semiconductor; but none of these neat properties permit perpetual extraction of energy. Aluminum/copper isn't a fantastic pairing either, at least not if you're aiming for a big effect - though those metals can be used to build a simple thermostat! To a casual observer, the thermoelectric effect may seem like creation of energy, but if you study it carefully, you see that it's just energy conversion. It is unlikely that you could use a bimetallic junction or a thermocouple to produce enough energy to power a light bulb - certainly not with the wire leads exposed to ordinary room temperature.
Ok so room temp is out. But maybe the heat of your hand would work? Or a hot cup of tea? Or are we talking more like a bonfire? I don't know how to get a back-of-the-envelope estimate for converting heat in BTU to electrical watts in this manner. Also in the late 70s the story is surely about incandescent bulbs but there are some rather bright and low-watt LEDs out there now. It sounds to me like these principles could be used to make a hot beverage run a small LED for a classroom demo, and that sounds fun :) SemanticMantis (talk) 16:39, 3 June 2016 (UTC)[reply]
No comment on the conservation of energy issues with which the original question seems rampant, but as far as your unit-conversion question, we don't need backs of envelopes any more when we've got the magnificent units program available!
$ units
586 units, 56 prefixes
You have: btu/hour
You want: watt
* 0.29307222
/ 3.4121282
So if you have an energy source that's capable of generating one BTU per hour, multiply by 0.29 to get its power-delivery rate in watts. (Assuming 100% efficiency, of course.) —Steve Summit (talk) 17:15, 3 June 2016 (UTC)[reply]
Haha thanks for the math plus the tip on the Units program :) I guess I was thinking about a total conversion for a specific yet hypothetical device, including efficiency estimates, but this is at least a start. SemanticMantis (talk) 19:07, 3 June 2016 (UTC)[reply]
Does house current induce amnesia?
I just took a moment to read the news just now and came across the case of some poor sap who got carjacked and forced into the stolen car. His captor soon realized the man had "seen his face", and came up with the most drastic way to fix that, for which now I think he is facing the death penalty. My first thought, needless to say, was gee, that was stupid, why didn't he just rip the cord out of a table lamp and give him a couple of minutes of electroconvulsive therapy? Then I had to look it up... is house current suitable for ECT side effects? While modern forms claim to be slightly more refined, ECT opponents describe it as basically house current perhaps hopped up to 150V or so. [20] On the other hand, the level and permanency of the amnesia is prone to dispute. [21] It's not clear to me whether that is a triumph of psychiatric restraint or just that electric current doesn't do as much as people think. So... is there any empirical data? Do people exposed to electrical accidents -- or incidents -- involving heads and house current (whether 110 or 220V, I won't be picky) report lasting amnesia from the event? Also, it is my impression that current across the head shouldn't stop the heart, but would it kill another way? Wnt (talk) 18:00, 3 June 2016 (UTC)[reply]
This would seem to fall into the same category as inducing amnesia by hitting somebody in the head with a frying pan. Sure, it's possible either might work, but the chances of doing so, without causing permanent damage, is quite remote. StuRat (talk) 19:13, 3 June 2016 (UTC)[reply]
According to the ECT article, "Retrograde amnesia occurs to some extent in almost all ECT recipients...", which is different from a frying pan. And there is a limit to how many times you can hit someone with a frying pan without killing him but I don't actually know if there is a limit to how much you can abuse him with ECT, if his future mental condition is not an issue for you. (Avoiding permanent damage would not be a priority for the culprits here; avoiding a murder charge would be) Wnt (talk) 20:06, 3 June 2016 (UTC)[reply]
I'd prefer to keep it out of play;. Last time I asked a hypothetical question about a living person here I got a lot of threats and policy-brandishing, and I'd rather keep things on the level of pure mad science. :) Besides, these "he saw our faces, what do we do" stories all end the same way, and not the way I would have thought of. Wnt (talk) 20:06, 3 June 2016 (UTC)[reply]
In the movie We need to talk about Kevin, a physician holds the hand of a patient in the air for a sec during a diagnostic. Then he lets it loose. It was implied that if the patient maintains his hand in the air, that would be a sign of autism. If the patient left his hand fall, then that implies normality.
I'm not aware of one, though similar tests are used to determine whether a patient is truly unconscious (you attempt to drop their hand in their face; if it moves away, it is assumed they're conscious on some level) and some Googling suggests that there are types of seizures or movement disorders that might be diagnosed that way (in fact, tying in to the unconsciousness test mentioned earlier, see here for example). Epilepsy is more common in autistic folks than the general populace and they may exhibit stiffening seizures, but that's the closest link I've found (so far anyway). Oh! There's also this (possibly better cite here), but that doesn't seem to be the same kind of thing you're describing. Matt Deres (talk) 02:42, 4 June 2016 (UTC)[reply]
I'm almost used to seeing "loose" when the writer means "lose"; the reverse error is a new one on me. I assume it's just a typo, though. --Trovatore (talk) 02:44, 4 June 2016 (UTC)[reply]
Well to be honest I had overlooked or forgotten that little oddity as well "Braniff became the registered operator of the planes while on U.S. domestic service, and the planes were physically re-numbered with temporary adhesive vinyl. Registration was then returned to Air France or British Airways on the trans-Atlantic leg. Over American soil, the Concorde was limited to Mach 0.95, though crews often flew just above Mach 1; the planes flew at Mach 2 over open water."Greglocock (talk) 04:03, 5 June 2016 (UTC)[reply]
The uploader supplied information for this states they weren't show if this tree was what they were told
it was called. In context it's not clear if the name was a species common name or a locality one.
According to Hydrogen, it "is very rare in the Earth's atmosphere (1 ppm by volume) because of its light weight, which enables it to escape from Earth's gravity more easily than heavier gases". So if hydrogen were a bit heavier, like oxygen or nitrogen, and thus stayed on Earth, and considering its hazards, the life on Earth would have been in danger (assuming that if the hydrogen weight is theoretically increased to permit its stay on Earth, it would still be hydrogen)? 93.174.25.12 (talk) 18:01, 4 June 2016 (UTC)[reply]
The problem with hypotheticals is they're hypothetical. To make hydrogen heavier you'd have to do one of two things: add particles to the hydrogen atom, or change the mass of the proton and/or electron. Considering the first case, if you add neutrons you get heavier isotopes of hydrogen, but all except deuterium are unstable. Adding electrons gives you hydrogen ions, but that doesn't change the atom's weight to any meaningful degree because electrons have a tiny mass, and you can only add so many before the nucleus can't hold on to any more. If you add other particles you wind up with something that's not hydrogen anymore. In the second case, you'd change all of physics and chemistry, so it's hard to make predictions about what the universe would look like. But, it's worth noting that we already have a fairly dangerous gas present in large quantities on Earth. It's called oxygen. You're only able to survive around large amounts of oxygen because you're descended from life that adapted to it. When photosynthetic organisms started producing oxygen in large quantities, it killed all the life that couldn't adapt to it or hide from it. And even still, too much oxygen can injure or kill you. Oxygen is so reactive we have to station people throughout our communities to jump into action when it starts reacting too vigorously with things. --71.110.8.102 (talk) 20:01, 4 June 2016 (UTC)[reply]
Does anyone know if these are the same species? We have an article for Appias albina, and the name seem to be used interchangeably with Appias albina semperi in the resources that I've been able to find. --Pine✉02:59, 5 June 2016 (UTC)[reply]
Screw held under spring pressure
In general there's three ways to secure a screw/bolt[22]:
Which of the three above general categories does a screw held under spring pressure (case 4) fall under?
When there's very little spring pressure it's no different than no spring at all, so let's consider the case where the spring is held under high tension. Johnson&Johnson&Son (talk) 03:18, 5 June 2016 (UTC)[reply]
I suggest a rapid investigation of the boltscience website. To some extent all bolted joints resemble your 4th case, but intentionally adding a compliance is rarely done in production these days on hard joints. Spring washers (etc) are anathema in properly designed hard joints. Electrical engineers still use them when they want to mash copper wire against steel, it seems to work, but then they often seem to use huge threads for the job in hand.Greglocock (talk) 03:55, 5 June 2016 (UTC)[reply]
How it came that the atomic numbers of, say, lithium, beryllium, boron and carbon are smaller that in nitrogen or oxygen, and yet they are solids while nitrogen or oxygen with larger atomic numbers are gases? I'd expect that the heavier the element, the more likely it would be in a solid state. --93.174.25.12 (talk) 07:09, 5 June 2016 (UTC)[reply]
The Ping River has long straight segments.
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![[14]](https://i.ytimg.com/vi/w9rBK5akmJI/maxresdefault.jpg){kind=link}
![[22]](http://i.imgur.com/ghfwPHe.png){kind=link}
