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December 17

Mystery fruit (?) in hay bale

Here's a good, old-fashioned species ID question for everyone. I am a farm dweller (southeastern United States), and I have been coming across these things in bales of hay from time to time. They are what appear to be very tiny fruit, the largest being maybe 7 or 8 mm in diameter. They don't look ripe to me, but not knowing what they are, I guess that would be a hard call to make. They are yellow (obviously) and full of seeds (hence, fruit). I was brave enough to taste one, and decided I didn't like the taste; decidedly pepper-like, but quite bitter. The skin, though, has a slightly irregular, almost citrus-like texture. Any ideas? Evan ^{(talk|contribs)} 05:08, 17 December 2014 (UTC)[reply]

Horsenettle, Solanum carolinense --Digrpat (talk) 06:41, 17 December 2014 (UTC)[reply]

Yes indeed. I won't be giving it another taste then, in that case! Glad I spit. Thanks for the reply. Evan ^{(talk|contribs)} 06:52, 17 December 2014 (UTC)[reply]

Is that hay for horses ? If so, I'd be a bit concerned that they may get sick if they eat too many of those. StuRat (talk) 06:57, 17 December 2014 (UTC)[reply]

Yeah, I've been picking the fruit out before feeding the horses on the off-chance it was bad. I'll start being even more careful, and maybe have a chat with my new hay provider; never seen these in hay from anyone else. Evan ^{(talk|contribs)} 07:00, 17 December 2014 (UTC)[reply]

OK, but don't be too hard on him, it's apparently a bitch to get rid of that weed. I'll mark this Q resolved. StuRat (talk) 07:09, 17 December 2014 (UTC)[reply]

Resolved

Gap in teeth

Some people have a very prominent gap between their front teeth. Here is a photo of an example: Michael Strahan: Why I Never Closed the Gap in My Teeth. Is there a name for that (other than simply "gap")? Also, what causes this? Thanks. Joseph A. Spadaro (talk) 05:17, 17 December 2014 (UTC)[reply]

Diastema. Evan ^{(talk|contribs)} 05:19, 17 December 2014 (UTC)[reply]

Thanks! Never heard that term before. Thank you. Joseph A. Spadaro (talk) 18:12, 17 December 2014 (UTC)[reply]

Regarding what causes a it, there are physiologically important diestemata (plural) in animal dentition that serve to both prevent food impaction and to aid in occlusion. Animal dentitions are super strange from a human-focused perspective because there are gaps and missing teeth and all sorts of wacky things that exist quite normally that, if found in the human dentition, would appear quite odd.

But back to human diastemata -- a midline diastema, as exemplified by Michael Strahan, is sometimes caused by an overly large incisive papilla (I'd steer you toward Google images for this, rather than the Wiki article because the latter is very misleading: the photo is from a terrible angle, exhibits terrible shadowing and the palate manifests a torus palatinus which can easily be mistaken for the focus of the photo as used by the article). Also, if the incisive papilla happens to be positioned a little more anteriorly than normal, the central incisors (which are the two large front teeth) may not be able to erupt into proper position, thus forming a midline diastema.

Back to animals, for a second -- I did come across something very interesting recently while reading about the rhinarium, or mammal wet nose. Apparently the groove on the rhinarium, the philtrum, is embryologically similar to the groove primates (and humans) have under their nose, even if they do not possess a wet nose (i.e. haplorhines). There's much debate about how to classify the various prosimians based on some of the variations that exist with these structures (see here) and, apparently, the presence of the rhinarium and its philtrum creates a gap between the roots of the maxillary central incisors (see second paragraph here). As a dentist for humans, I can confirm that there is a gap between the roots of maxillary central incisors for humans, even when there is no gap between the crowns (and so, no diasthema) because the two maxillary bones fuse at the midline suture. I have not seen clinical or radiographic information related to what is meant when the aforementioned citation refers to a gap between the central incisor roots in strepsirrhini, so I can't know for sure the comparative anatomy. But in humans, the incisive papilla is the exit of the nasopalatine nerve from the nasopalatine canal and if the nerve would exit more anteriorly, I can see it being very much in the way of the two central incisors being close together. DRosenbach ^{(Talk | Contribs)} 01:55, 18 December 2014 (UTC)[reply]

Thanks, all. Joseph A. Spadaro (talk) 17:00, 19 December 2014 (UTC)[reply]

Missing teeth (technical terms)

Inspired by the previous question: Is there a technical name for adult teeth that are missing because they never developed? For example, suppose a person simply doesn't have cuspids and never did, is there a technical name for such missing teeth (or perhaps a name for a medical condition associated with having fewer teeth than normal)? Dragons flight (talk) 05:33, 17 December 2014 (UTC)[reply]

Hypodontia gives several terms to related this condition. Also "aplastic" can be used to describe any missing organ.--Digrpat (talk) 06:02, 17 December 2014 (UTC)[reply]

This is anecdote, but the lack of cuspids is rare. The lack of wisdom teeth is most common, and the human jaw is one of our rapidly evolving body parts. I mention this from my having had impacted molars extracted. μηδείς (talk) 06:54, 17 December 2014 (UTC)[reply]

Thanks. That's exactly what I was looking for. Dragons flight (talk) 02:54, 18 December 2014 (UTC)[reply]

Heat engine problem

Hi, I'm working on a homework question and basically I feel like I've gotten the whole thing but I'd really appreciate someone else to helping me check because I'm not sure if I did it right.

It's a heat engine problem, going from A to B to C Volumes and pressures are as follows A = 7x10^4 Pa, 2.5*10^-2 m^3 B = 3x10^5 Pa, 2.5*10^-2 m^3 C = 3x10^5 Pa, 7.5*10^-2 m^3

I got that the engine has a power output of 57.5 J by finding the area inside the points (just using 1/2 b*h) and an efficiency of 12% by finding the total heat added by Q=dU+Work from A=>B and B=>, but I'm just not sure if I'm doing it right. Can anyone please help me confirm with their steps?

166.137.252.91 (talk) 05:41, 17 December 2014 (UTC)[reply]

I think we're missing some information here. From A to B the pressure goes up and then from B to C the volume goes up. In both steps energy is being added to the gas. But we don't know what kind of gas it is, its mass or its specific heat.50.43.56.168 (talk) 08:28, 17 December 2014 (UTC)[reply]

I think I'm supposed to assume it's an ideal gas, and the temperature at A is 290K. 67.247.2.127 (talk) 02:45, 18 December 2014 (UTC)[reply]

Your first statement is incorrect. Joules is not a power output. J/s is power and is expressed in Watts (alternatively as horespower). --DHeyward (talk) 06:55, 18 December 2014 (UTC)[reply]

What's the centre of mass of the Local Group of galaxies?

What do the galaxies in the Local Group orbit around?Whereismylunch (talk) 07:51, 17 December 2014 (UTC)[reply]

According to our Local Group article: "Its gravitational center is located somewhere between the Milky Way and the Andromeda galaxies" (although the center of mass and gravity aren't technically the same, they may be close enough for you purposes). However, I don't think it's correct to say that everything in the Local Group orbits about that point, since the way that distance is critical in determining gravitational attraction ensures that each galaxy is far more affected by those galaxies near it than by those far away. So, in effect, each galaxy will orbit about a different center of gravity, as viewed from it's perspective.

To compare with magnetism, we might say that all compasses on Earth should point toward magnetic north, but local variations in the magnetic field, or nearby magnets, can easily change the direction the compass points. It's not that those things are more powerful than the Earth's magnetic north pole, they are just closer. StuRat (talk) 07:58, 17 December 2014 (UTC)[reply]

But what's at the gravitational centre? — Preceding unsigned comment added by 199.119.235.178 (talk) 08:58, 17 December 2014 (UTC)[reply]

Nothing. --Jayron 32 11:21, 17 December 2014 (UTC)[reply]

Or, more accurately, the gravitational center is never going to be made of anything, since it's a point, an abstract construct rather than a physical body. To be clear, something might be occupying the space that roughly corresponds to that point, but it needn't be a significant body contributing any particular amount of gravitational force. Snow talk 12:54, 17 December 2014 (UTC)[reply]

Wikipedia also has an article Centers of gravity in non-uniform fields which may be a bit technical, but does provide some explanation of the concept. --Jayron 32 13:51, 17 December 2014 (UTC)[reply]

I was about to link to the same article which explains that the concept is not really clearly defined for clusters of galaxies, but I think our "Local Group" article probably refers to roughly where the CofG would be if (suddenly and inexplicably) a uniform gravitational force suddenly appeared (from the edge of the universe? or the Great Attractor, or Dark flow?) and acted on the whole cluster. It is more usual to call this "point" the centre of mass. The theoretical point about which the galaxies seem to be revolving (on average, see StuRat's comment above) is not necessarily the same point, but might be somewhere near the centre of mass. Dbfirs 13:11, 18 December 2014 (UTC)[reply]

How accurate is reentry?

The recent test flight of the Orion spacecraft ended with a splashdown in the Pacific Ocean where is was picked up by the USS Anchorage. How far was the ship from the point where the spacecraft touched down? What was the predicted impact point and/or area? Once the retro rockets have been fired, does the spacecraft have any further control of where it lands? — Preceding unsigned comment added by 50.43.56.168 (talk) 08:13, 17 December 2014 (UTC)[reply]

Well, to give you some idea. The Mars Science Laboratory only went to our nearest planet and yet it missed point zero by 5½ miles. Better luck next time eh.--Aspro (talk) 09:00, 17 December 2014 (UTC)[reply]

The distances involved in a re-entry procedure are significantly shorter than those of an interplanetary trajectory, such that, under many conditions, a given error in trajectory at the outset results in a larger divergence (in terms of absolute distance between resulting arrival points) for the latter, relative to the former. Snow talk 12:34, 17 December 2014 (UTC)[reply]

It was 1.5 miles, not 5.5 miles. --Bowlhover (talk) 18:56, 17 December 2014 (UTC)[reply]

Which, considering a trip of 675 million kilometers and the necessity for incredibly accurate timing (in that each planet is in motion in its own orbit) is pretty impressive in it's own right. Sure, close is often not good enough in astronautics, which is why most missions now include a handful of opportunities for course corrections. Still, if I launched something 675 kilometers via mechanical means and managed to land it within 1.5 millimeters of my (swiftly moving) target, I dare say it would be regarded as the single most impressive thing I'd ever do. Snow talk 20:23, 17 December 2014 (UTC)[reply]

One of the points about splashing down in the ocean is one can ensure there aren't people anywhere near! So hopefully they were some distance away, especially as it was a test flight. Dmcq (talk) 11:33, 17 December 2014 (UTC)[reply]

To the question in the OP's heading, the answer would seem to be "not necessarily very accurate". The charts at Splashdown#Locations include "miss distances", which indicate rather variable results (though the entry for the Orion test does not include a miss distance). Deor (talk) 12:46, 17 December 2014 (UTC)[reply]

But they can be. @50.43.56.168: The closest to calculated landing point appears to be "Apollo 16 on April 27, 1972 at 0°43′S 156°13′W by USS Ticonderoga (CVS-14)" only missed by 0.55 km[1] (≈0.34 mile)! Though Aurora 7 on May 24, 1962 missed by 400 km (≈250 miles). As for control of landing point after the retros fire? Yes I believe they can control it,(see cached NASA source below) but the main concern would be to maintain the correct re-entry 'attitude', or the craft may either skip out of the atmosphere or burn up and 'land' as cinders. Where it lands would be a pretty low priority, so long as it's in one piece on water.

• Specifically the landing point from Splashdown#Locations was 23.6°N 116.4°W, 275 miles west of Baja California. However the Exploration Flight Test 1 page says "23.61°N 114.46°W" 640 miles (1,030 km) SSE of San Diego. 'Miss' distance unspecified as Deor noted.
• I can't find out "How far was the ship from the point where the spacecraft touched down?" however "The target landing accuracy of an Orion capsule using automatic bank angle control of downrange and crossrange, when subject to the full range of atmospheric, aerodynamic, navigation, control, and mass properties dispersions, is within 10 km (5.4 nmi)".[2] a google cache of http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20110013203.pdf, which appears to be unavailable at that URL

Those 'miss distances' may not be correct! Use with care. The actual HTML version, here, of the source for the Apollo 16 says "3.0 n mi from the target point" (5.56 km; 3.45 miles) not 0.55 km/0.34 miles! That may be a slip of the decimal point. The big 400 km Aurora 7 miss however is supported by the reference on page 225, [3] (PDF 8.162 MB), though the URL has changed.--220 of ^Borg 08:16, 20 December 2014 (UTC)[reply]

Lioness hunting tactics

I read yesterday in a Simon & Schuster mammal field guide from about 1985 that lionesses tend to kill their prey with a single blow to the back, breaking the spinal cord. I'm not naive enough to simply ask how could it be that striking with a paw leaves the prey with fatal damage but no damage to the lioness' paw, but I was just intrigued at everything that needs to go into such a technique. It seems obvious to me that lionesses do not consider their options like a person would, but of all the possibilities and all the alternatives, I find it fascinating that the lioness would consider this means of execution over, say, chomping on the trachea. I see Youtube videos on lionesses attacking buffalo and they seem to try to bit into the ventral neck, but the buffalo resists. What sort of force is required to tear out a trachea, and why would a lioness find that difficult? Is it really more efficient to snap a spinal cord? Thoughts and insights are welcome. Thanks! DRosenbach ^{(Talk | Contribs)} 17:18, 17 December 2014 (UTC)[reply]

The way the lioness kills her prey is directly related to how she approaches it. The typical approach would be to stalk and then attack from behind - this makes the back of the neck the clearest and easiest target for a killing blow. Going for the throat would require a frontal approach which could lose the element of surprise, as well as leaving the lioness open for a counter-attack from the prey's hooves, horns, etc.

There is a lioness-eye-view video of a hunt and kill available here:This is what hunting looks like from a lioness' point of view. (Don't watch it if you may be disturbed by seeing an animal get killed.) The narrator notes that a lioness "will generally sneak up to the prey, as close as possible, and then make a sprint for it." That sneak attack pretty much demands going for the back of the neck rather than the throat. - Eron^Talk 18:13, 17 December 2014 (UTC)[reply]

Yep, also going for the throat puts a lion in easy kicking/stomping range of a quadruped. But all of this is massive simplification. Does the field manual mention the technique is to jump on a zebra, overshoot, flip over, almost get trampled then run away? Because that happens a lot too :) Finally a serious spinal injury at the neck makes a mammal stop, nearly instantly - even if it's not dead it's not moving. But I wouldn't want to be around a wildebeest with its trachea recently ripped out. It will still be deadly for an important minute or so, and you lose all that tasty and nutritious blood. SemanticMantis (talk) 18:20, 17 December 2014 (UTC)[reply]

Here's a few refs - an old paper [4], and a newer ref [5]. The first (paywalled) link has a table with data on kill rates - males killed a bit more than females, immature and old prey made up the majority of kills, but "prime" healthy prey made up the plurality. Humorously, the latter is on a Lion King fan site, but it does have additional citations, and mentions the importance of cooperative hunting and scavenging. It reports (and you can also see in videos) that often several lions will jump on a prey at once, attacking various parts simultaneously. The point being that kills made by a solitary female are probably a rather small part of a lion's average weekly diet. SemanticMantis (talk) 18:33, 17 December 2014 (UTC)[reply]

Lions often hunt together, but as for pouncing on the prey together, that's only needed for large prey. StuRat (talk) 18:44, 17 December 2014 (UTC)[reply]

Buffalo made up over 60% of lion kills in this study [6]- though they do mention that smaller prey are probably underrepresented in their study, because the lions might finish eating before the observers could find the body. SemanticMantis (talk) 18:51, 17 December 2014 (UTC)[reply]

And for more throat-based killing, check out Cheetahs, they seem to be generally less effective at killing - this paper [7]] says

“

Cheetah spend several minutes killing prey. Five minutes is common, but 15-25 minutes was not rare, even with small impala fawns.

Some prey revive from strangulation killing attempts and have to be “strangled” two to three more times before death occured.

”

SemanticMantis (talk) 18:51, 17 December 2014 (UTC)[reply]

Many years ago I read a research paper on Lions' killing methods.(Sorry, can't find it now) They found that most prey were killed by a bite that forced the canines between the vertebrae, rather than crushing the vertebrae. Using high-speed photography and post mortem dissections, they found that lions have some rapid response muscle fibres in their jaw muscles, that can very quickly do a series of test bites until the canine teeth find the softer area between the vertebrae. An amazing bit of evolution!! 122.108.177.30 (talk) 03:44, 18 December 2014 (UTC)[reply]

Bugging the outdoors with spiderweb-like antennas

I ran across an interesting story at [8], in which three planes flew close overhead and fine spiderweb-like fibers were then seen sticking to the landscape. I am for now discounting the site's explanation of "geoengineering" entirely, but assuming the truth of their published lab analysis that indicates the presence of aluminum (1020 mg/kg), barium (34.1 mg/kg), and strontium (70.8 mg/kg). These are small but perhaps not negligible amounts, up to 0.1% aluminum in the sample as collected.

To be clear, I have found a fairly persuasive "debunk" of the story at [9]. If we assume that the witnesses were wrong about the association with the planes and the fall of the webs immediately afterward, or if it's just a remarkable coincidence, the webs are explained; if they were contaminated with soil the aluminum is explained; I'm not so sure about the rarer barium and strontium. The test was consistent with spider silk, which would be more impressive if they hadn't first identified it as wheat flour and bacitracin; suffice it to say that some non-metallic matrix containing peptide has to be the major constituent of whatever these fibers are.

But to be contrary, just because the fibers look natural doesn't rule out another explanation, since they might intentionally be camouflaged. My question is whether this data could be explained with some known form of antenna that could be sprayed through a nozzle as a plane flies overhead, land as an intact radio-reflective surface, and then have a signal bounced off it to measure changes to it, i.e. vibrations caused by the speech of nearby persons? (as a wild guess, probably wrong because it also contains titanium, see [10]). Alas, I'm not familiar with this literature. How thick would such a metal fiber actually have to be to be used this way? And is this metal composition actually practical to include in some sort of polymer "spider silk" that can be sprayed from a plane?

I'd also welcome any other possible explanations. Wnt (talk) 21:51, 17 December 2014 (UTC)[reply]

So much of this is such utter nonsense I'm not sure where to start. I don't even believe that a plane flying at 5000-8000 feet could distribute "spider web like fibers" to the ground in anything like a reliable fashion. This is also one of the major problems with chem trails, there is an absolutely immense volume of air to travel through from a mile up and there are all sorts of wind currents and turbulence to get through, to suggest that a spider silk would just gently fall all the way to the ground from where it was dropped by a plane a mile up is ridiculous. Also, known form of antenna and radio reflective surface are mutually exclusive concepts. I suppose you are talking about something like a Laser microphone but that already exists and would be a far simpler way to "bug" someone without the need to spread square miles of high tech spider silk antennas randomly around the country side. Vespine (talk) 23:58, 17 December 2014 (UTC)[reply]

Well, the non conspiratorial explanation is ballooning (spider) - which can reach the jet stream and return safely to the ground. Therefore, it should not be impossible to drop it from the height of a plane, though getting around the difference in velocity would indeed be an interesting technical problem. (for example, you can picture a flexible boom that wiggles back and forth, regularly reaching near zero airspeed) As for chem trails, so far as I know this is simply jet fuel that contains up to 0.3% sulfur;^[11] it is said to delay global warming by 6 months, kills 1000-4000 people every year, but hey, it makes the jet fuel 1.6 to 7 cents cheaper a gallon. Officially not a conspiracy, just business as usual, with a side spin of "good for the environment". (And where else did people think the chemtrails would be coming from, if not the fuel tank?) The presumed purpose of the scheme would not be to place a specific bug in a known location, but to place many bugs in multiple locations that are hard to identify as such, so that the conversations of a large number of people are simultaneously screened for bits of interest while being as easy to deny as possible. Wnt (talk) 00:36, 18 December 2014 (UTC)[reply]

I came across something that sounds vaguely similar. Google "Huntsville weather anomaly". Here's one site: http://valleywx.com/2013/06/04/mystery-blob-over-west-huntsville/ — Preceding unsigned comment added by 50.43.56.168 (talk) 01:35, 18 December 2014 (UTC)[reply]

Well for one, I wasn't saying that spider webs 'couldn't be dropped from a plane and land somewhere, my point was that it would not land anywhere near where it was dropped, to the point where it would be practically futile. Notice how low a crop duster flies to spray a field, that's not done from a mile up for precisely the same reason, the amount of spray that would actually reach the ground at the target location would be negligible. Similarly if you dropped cobwebs from a mile up, I propose it would be very difficult if not impossible to say with any level of confidence where those cobwebs would land. If it's purely a 'non targeted' attack and they don't care where it lands, and I'm assuming it's supposed to be covert since no one knows about it, then why wouldn't they just fly the mission at night when no one would notice? I suppose the conspirators were just too stupid to think of that? Or is it because they control all the media and so they don't care if a few people notice? I'm guessing this thread has already been tagged and will be deleted soon and me and you will disappear without a trace? Also, pollution from ships kills about 60,000 people a year, compared to 4000 a year from planes, so I guess the conspiracy should really be "chem wakes" not "chem trails"? And lastly, coal fired power plants kill hundreds of thousands globally with their pollution, what conspiracy is that? chem power plant? Vespine (talk) 02:40, 18 December 2014 (UTC)[reply]

This is an interesting argument. How well can the path of the dropped material be predicted, given extensive modelling of local weather? Wnt (talk) 13:39, 18 December 2014 (UTC)[reply]

What kind of answer do you expect? "Well enough"? The question is too vague. IF there was actually some practical requirement for the military to drop spider web like material from a plane flying a mile high, I doubt there is any challenge there that could not be overcome, given enough research and resources. I just don't think the practical need exists and there would be far easier and more efficient ways of achieving a similar result for less cost and effort. Vespine (talk) 23:02, 18 December 2014 (UTC)[reply]

The aerodynamic coefficient (I just made that up) will make a huge difference. Iron cannon balls will have a fairly predictable trajectory. Threads of spider silk, not so much.

Another point is that antennae must have some precisely controlled placement of the antenna elements, not the random distribution you'd get from a spider web tossed from a mile up. A fractal antenna could potentially be disguised as a natural object though, since fractals are common in nature. StuRat (talk) 18:20, 20 December 2014 (UTC)[reply]

December 18

Hydrochloric acid and methylbenzene

Why is hydrochloric acid acidic in everything except methylbenzene? I am really confused about this as my textbooks do not include anything of the sort and I have been told that this would appear in my exam. Please help. Thanks! pcfan500 (talk) 06:28, 18 December 2014 (UTC)[reply]

You'll probably want to review the concepts about what makes things "acidic" - see Brønsted–Lowry acid–base theory and Lewis acids and bases for an overview of the two big ones. In short, a compounds is an acid because it donates a proton (accepts an electron pair). Hydrochloric acid is a strong acid because the chloride doesn't hold on to the proton very well ... at least in water. Other solvents (like the aforementioned methylbenzene) don't do as good of job stabilizing the separated state, so the proton and the chloride want to stick together. I'm not sure why methylbenzene is being highlighted specifically - I'd expect other similar solvents (ethylbenzene, for example) to also behave similarly, sot it's not really the case that hydrochloric acid is acidic in "everything" but methylbenzene. -- 141.39.226.228 (talk) 08:45, 18 December 2014 (UTC)[reply]

why is time known as the fourth dimension?

why is time known as the fourth dimension? 94.98.4.75 (talk) 09:37, 18 December 2014 (UTC)[reply]

I've added a heading to this question. It's known as the fourth dimension because it is one in a physical sense, i.e. subject to the rules of physics in a very similar sense. Of course you can also see the sense in which it!s a dimension: just consider cases where we remove a dimension and use it for time instead, like a flipbook of animation . There are two dimensions shown at a time and the third dimension gets shown over time. 91.120.14.30 (talk) 11:23, 18 December 2014 (UTC)[reply]

To fully describe where an object can be found, you need 4 dimensions, with the 4th being time. Consider trying to describe the location of something which no longer exists, like the Lighthouse of Alexandria. You can go there now, but you won't find much. StuRat (talk) 11:37, 18 December 2014 (UTC)[reply]

You might (or might not) be interested in the technicalities given in articles such as Spacetime and Minkowski space. Dbfirs 12:37, 18 December 2014 (UTC)[reply]

(edit conflict) Geometry "works" with any numbers of dimensions. You know how there are all sorts of "math" you can do with shapes and lines and such? Calculating area, length, volumes, velocity, etc.? Well, the "rules" that allow you to make those calculations are not restricted to any number of dimensions. For example, you can establish a line in two dimensions by defining two sets of points, say point A = [0,0] and point B = [1,2]. You can then set up equations in either cartesian coordinates or vector coordinates to define the line that goes through those points. Well, you can do the same in 3 dimensions by defining the points in 3D space as A = [0,0,0] and B = [1,2,3] or some such, and then can write an equation to define that line. Now, the deal is, even though you can't picture a line in any more than three dimensions, the rules for writing the equation of a line still apply in any number of dimensions. You just do the algorithms and define the line. I can define a line in 4 dimensional space simply by saying A = [0,0,0,0] and B = [1,2,3,4], and the rules for writing the equation for THAT line (which has no reasonable PICTURE, but never mind that) are the same rules as writing lines in less dimensions. I can have any arbitrary number of dimensions, and the math for describing an object called a "line" in those number of dimensions is the same as it is in 2D, 3D, or whatever. So that brings us back to why even bother to treat time as a dimension like space dimensions: that is, we have the three spacial dimensions (up-down, left-right, forward-backward) and add time as a fourth number into that set. The reason why has to do with Einstein's theory of special relativity. What special relativity shows (among other things) is that you can vary how you move through time. Just as you can move through space at various rates, it turns out that time passes at different rates depending on certain conditions, such as the mass and velocity of an object relative to nearby objects (the effect of mass on time passage is actually covered by general relativity, not special, but whatever). Now, it turns out that because the rate of passage of time for an object is variable just as it's movement through space is variable, in order to completely describe the motion of an object, one needs to consider not only how it's position is changing, but also how it's timescale is changing with respect to other objects. In order to do that, you treat time like a dimension, and do your calculations in 4D rather than 3D; but the rules for doing so (as noted above) still apply. One last thing about time, however, is that the time "dimension" doesn't behave like the other "dimensions": it has it's own set of rules which is different than the others; however as long as you take those rules into account, you can still do math with it to predict the behavior of objects (and that's what physics is: the science of being able to predict the behavior of objects in motion). The specific set of dimensions (which includes the three spatial dimensions and the one time dimension) we use to do these calculations is called Minkowski space, named after the mathematician who worked out the math of such a system. The last question someone might ask is why do we have to do all that. The answer is because it is necessary to explain observable phenomena where normal 3D "Cartesian/Euclidian" space cannot, for example experimentally verifiable phenomena like time dilation, or the invariance of the speed of light. I know this was a little TL;DR but I hope it is clear enough to help one understand the entire point of treating time like a dimension. --Jayron 32 12:39, 18 December 2014 (UTC)[reply]

Your "TL" discussion makes sense. The way I like to "picture" the time dimension is to think of the state of the universe (or some portion of it) at a series of points in time - as with the flip-book discussed earlier. So the fourth point in that [x,y,x,t] coordinate system can be pictured as what that [x,y,z] system looks like as "t" changes. Beyond that, of course, it gets tricky trying to picture. But in math, as you say, you can have any number of dimensions and the equations still work, albeit getting more and more complicated with added dimensions. ←Baseball Bugs ^{What's up, Doc?} carrots→ 12:52, 18 December 2014 (UTC)[reply]

Actually imaginary time is the fourth dimension. The distance in relativity calculations seems to be determined by x² + y² + z² - t². Wnt (talk) 14:34, 18 December 2014 (UTC)[reply]

Not really. Normal, everyday time is the fourth dimension. Imaginary time is used only for very specialized calculations, such as to eliminate the singularity (division by infinity) at the Big Bang or in black holes. --Jayron 32 15:17, 18 December 2014 (UTC)[reply]

I'd say that normal everyday time is a fourth dimension. It's definitely the most common choice in any non-technical context. As you discuss above, there are lots of other choices for what dimension we might call the fourth (or fifth, sixth etc.) especially if one is delving into theoretical physics (e.g. string theory) or certain mathematical structures (e.g. octonians)SemanticMantis (talk)

Yes, "the" in this case refers to "the fourth dimension used in Minkowski space for relativity purposes". Imaginary time as a fourth dimension only has limited utility in understanding a few physical phenomena. --Jayron 32 15:58, 18 December 2014 (UTC)[reply]

My understanding of the "spacetime interval" (see Spacetime) is that we can treat time as a fourth dimension for calculating a distance if we treat c as the conversion factor between our measurements, and recognize that when measuring time we are measuring multiples of i. Wnt (talk) 19:14, 18 December 2014 (UTC)[reply]

I think the consensus nowadays is that treating time as an imaginary spatial coordinate is a cute mathematical trick, but probably too cute, because it seems more meaningful than it is. I believe there's a note on it in Gravity by Misner, Thorne, and Wheeler, a book we should probably have an article on if we don't already. --Trovatore (talk) 21:05, 18 December 2014 (UTC)[reply]

Per Trovatore, it's a matter of perspective. Because of the sign conventions of working in Special Relativity, the "time" dimension has the opposite sign of the spatial dimensions. Mathematically, this means that some of the terms have a value of i attached to them. The math is identical if you attach the i to each of the three spatial dimensions, and leave time in the real number set; or if you attach i to the time dimension and leave the three spatial dimensions in the real numbers. Conventionally, we tend to leave the i in the time dimension because it makes the math a bit easier (in the sense that we have one imaginary number and three real numbers), but time itself is a real number. The use of imaginary time only comes in, if I am not mistaken, in unusual situations where the standard sign convention [-,+,+,+] for [t,x,y,z] produces physically paradoxical results (such as singularities). At least, that's my understanding. --Jayron 32 21:18, 18 December 2014 (UTC)[reply]

And we do have an article on the book. It's called Gravitation. Not Gravity. --Jayron 32 21:21, 18 December 2014 (UTC)[reply]

Well, what I'm thinking is that if you use a two or three dimensional coordinate system, you can say that within that coordinate system, every two points has a defined distance between them. That distance doesn't change unless you look at it from a frame where the whole coordinate system is changed. But in a system of "four dimensions" with real time, the distance between any two points is not constant, but depends on the frame of reference of whoever is looking at it. So to say time is the fourth dimension in that case is sort of meaningless. I mean, you can make the color of the object the fourth dimension, if you're willing to have a coordinate system that you can't calculate distance in. But use time * i as the fourth dimension and you do have a real distance that is Lorentz invariant. Wnt (talk) 21:25, 18 December 2014 (UTC)[reply]

Here's a less coordinate-dependent way of phrasing things. It requires you to know a little differential geometry. The point is that the metric tensor has three positive eigenvalues and one negative one. This is just a fact; it's not based on which arbitrary coordinate system you choose.

The x₄=ict trick is sort of an attempt to obscure this fact, or if not actually an attempt, risks obscuring it. --Trovatore (talk) 21:29, 18 December 2014 (UTC)[reply]

Alright, I'll admit it... I'm in the fog here. I'm afraid I'm missing how spacetime coordinates have four eigenvalues in the first place. Wnt (talk) 00:22, 19 December 2014 (UTC)[reply]

Because there are four dimensions to move in: up-down, left-right, forward-backward, and past-future. --Jayron 32 01:32, 19 December 2014 (UTC)[reply]

Wnt and Jayron, I think you're both confusing imaginary time (as mentioned, for example, in A Brief History of Time) with the old (now disfavored) convention of using a pure imaginary value for the t coordinate instead of a flipped sign in the metric. They are different. "Imaginary time" is kind of the opposite of what you're thinking: it starts with a mixed-sign metric with all coordinates including t real-valued, and then considers (unphysical) imaginary values of t to make the metric effectively Euclidean. -- BenRG (talk) 19:30, 19 December 2014 (UTC)[reply]

Changes in Mammalian Milk composition - Biochemistry question

I understand that a cattle's food, environment, and artificial hormone shots can change the composition of it's Breast Milk. Any professional name for this phenomenon? I need it to efficiently search for some literature in this subject. Thx. Ben-Natan (talk) 13:10, 18 December 2014 (UTC)[reply]

One source suggests "biochemical alterations" in breast milk after heating. I'd think the preferred term in that case is denaturation. Though, it's certainly not what you're looking for. Let me see if I can find a better term. 71.79.234.132 (talk) 14:46, 18 December 2014 (UTC)[reply]

I just searched google scholar for /diet nutrition effect cow milk/ - These articles were near the top of the list [12] [13] [14]. From skimming the abstracts, it does not seem that there is a single term to cover all the food/environment/hormone effects on cow's milk. The term "ruminal biohydrogenation" and "Conjugated linoleic acid" are used quite a bit, and the keywords used by the articles should help further searchers, e.g. "mammary metabolism", "fatty acid desaturation" "milk fatty acids." The first linked ref above should be especially useful, as it is an Annual Reviews article, which are usually an expert summary of a broad field of research and give lots of references. SemanticMantis (talk) 15:33, 18 December 2014 (UTC)[reply]

circuit analysis

How do I solve the first order differential equation for an LR circuit WITHOUT using Laplace transforms ie from first principles? — Preceding unsigned comment added by 109.152.195.34 (talk) 13:46, 18 December 2014 (UTC)[reply]

The canonical solution for a linear first-order ordinary differential equation is a solution using the separation of variables method. In the case of an L-R circuit, you'd have a first-order equation in current with respect to time, parameterized by the inductance and resistance.

When I write out every step, this procedure takes longer than simply applying the Laplace transform by inspection, so in practice, mathematically-inclined people tend to memorize the solution of a simple circuit (instead of explicitly re-solving it). You must simply recognize the standard form, understand the relationship between the relevant variables, and recall the standard-form solution.

Nimur (talk) 15:27, 18 December 2014 (UTC)[reply]

How do the enzymes and nutrients in breast milk survive body temperature?

This source suggests that heating breast milk can denature some enzymes and nutrients. I haven't read the full article yet, so I can't tell what temperature they set the breast milk at. But human body temperature is 37 degrees Celsius. Can't the breast milk's enzymes survive when exposed to some heat but not too much heat? Would it be better for women to take stored breast milk from the refrigerator and heat it up with their own body temperature? Or would they have to acquire a wet nurse? 71.79.234.132 (talk) 14:57, 18 December 2014 (UTC)[reply]

Self-evidently those proteins do not degrade at body temperature; they are made at body temperature, stored at body temperature, and consumed at body temperature. --Jayron 32 15:14, 18 December 2014 (UTC)[reply]

Obviously this can't be a problem. We (and all other mammals) have evolved to do this without any refrigeration or whatever. Also, any degradation due to a brief period at body temperature would happen in the baby's mouth, throat and stomach anyway. Clearly the problems with heating milk (any milk, actually) happens at much higher temperatures. Efforts to (for example) sterilize milk might well suffer from this problem. SteveBaker (talk) 15:44, 18 December 2014 (UTC)[reply]

The temperature required to denature the proteins in breast milk would be roughly the same as required to cook an egg. The change in going from raw egg to cooked egg is mostly the process of protein denaturation.

Different proteins denature at different temperatures. In fact, a common experimental technique to measure the stability of the protein is to look at the circular dichroism of a protein as a function of temperature. (See also Protein_folding#Circular_dichroism). For most proteins you see a sigmoidal transition from "folded" spectra to "unfolded" spectra, with a characteristic transition point at a defined temperature. This temperature is called the "melting temperature" of the protein, and varies from one protein to another. Some are very unstable, and will unfold at or around room temperature (mostly proteins from psychrophiles). Some are stable at room temperature (25 C) or body temperature (37 C) but will unfold at 45 C or so. Different proteins unfold at different points, all the way up to 95+ C, where it becomes hard to measure. (There are proteins which don't unfold even under boiling conditions - mostly these are from thermophiles, but there are some mutants of proteins from mesophiles which have very high melting temperatures.) - So the answer to the original question is that there's a large swath of temperatures between 37 C and 100 C, and there are some proteins which are stable at 37 C but which will unfold at 45 C or 55 C or 65 C or 75 C, etc. And the temperature at which the unfolding/denaturation happens for one protein is not indicative of what will happen for other proteins.-- 141.39.226.228 (talk) 10:40, 19 December 2014 (UTC)[reply]

Resistance of electrically conductive paint.

I've been looking at these electrically conductive paints:

  http://www.solianiemc.com/assets/Specifiche/Conductive-Paint-Specification.pdf

...and trying to find out how much resistance I'd get if I painted strips of varying widths.

It quotes the resistance in units of ohms/sq - I have no idea what 'sq' means...square meter? square millimeter? Then the values are 0,3 (which I suspect is 0.3 in one of those places in the world where they use '.' and ',' in the opposite sense to the more common US/UK useage).

Anyway, if I use a layer of the stuff of the recommended thickness to paint a 'wire' that's N mm wide and some much longer length - what kind of resistance would I measure per mm of length for various values of N? (This seems like it might be a variant of: http://xkcd.com/356/ ...in which case, I apologize in advance!)

TIA SteveBaker (talk) 15:35, 18 December 2014 (UTC)[reply]

“

The reason for the name "ohms per square" is that a square sheet with sheet resistance 10 ohm/square has an actual resistance of 10 ohm, regardless of the size of the square.

”

- from Sheet_resistance#Units I don't know how to compare the resistance of an Nx1cm strip to a Nx1m strip, but this seems to say rather clearly (if counter-intuitively) that the resistance of a NxN square is equal to the resistance of a (2N)x(2N) square. It's unclear to me if the resistance would be different for a (2N)x(2N) square compared to a (N)x(4N) rectangle (but I'd guess they would be different). If you figure it out let us know :) SemanticMantis (talk) 15:47, 18 December 2014 (UTC)[reply]

Oh...that's strongly counterintuitive! So a square that's a mile by a mile has the same resistance as a 1" x 1" square?! I guess that as the distance increases, so do the number of parallel paths that the electrons can travel though...so the two numbers cancel out and the resistance stays the same. Weird!

So if the resistance of an NxN square is always the same - then I could mentally chop my 1cm wide strip of paint into 1cm squares that are in series and say that an N cm long by 1cm wire has N times the resistance of a 1cm x 1cm strip...which is just the ohms/sq number?

Which would mean that the ohms per meter of a strip of this stuff is inversely proportional to the width...which seems entirely reasonable.

Resistance = ohms/sq * length / width ?

If someone could confirm my intuition on this one, we can call it "answered". (And thanks to User:SemanticMantis for a great & fast reply).

SteveBaker (talk) 16:40, 18 December 2014 (UTC)[reply]

Upon further reflection, the geometry is probably more important than the area. So a circle of any area will also have the same resistance, but it will be different than the square resistance. And once the proportions of a rectangle are fixed, they should have the same resistance independent of area as well, I think... SemanticMantis (talk) 18:54, 18 December 2014 (UTC)[reply]

Sounds right. Read the second paragraph of the section linked by SemanticMantis. It says you just multiply the square resistance by the aspect ratio to get the resistance for a rectangle. Proving the exact result for painted traces with corners or other bends would be tricky, but I suspect that total length over width is still a good approximation. 12.195.117.49 (talk) 19:25, 18 December 2014 (UTC)[reply]

Specifically, SteveBaker, resistance is proportional to the length and inversely proportional to the cross section. With paint, the cross section is, for all intensive purposes, the same as the width, and by definition for a square, the length and width are the same. μηδείς (talk) 01:33, 19 December 2014 (UTC)[reply]

Ah...yeah - that makes sense. ...BTW: the phrase is: "all intents and purposes"...not "all intensive purposes".

Thanks everyone...I think I have everything I need. SteveBaker (talk) 04:17, 19 December 2014 (UTC)[reply]

Cloning by chance

This is a topic I've read about before, but I recently came across it in a graphic novel, so I'm interested in recalling the specifics: Given the size of the human genome, what are the chances of an individual being born with DNA identical to that of another individual? The story in question posits an interplanetary population of 100+ trillion humans, and one of the characters claims that "three people are born with my DNA every day," which seems impossibly high. Like I said, I know I've read about this idea in scientific literature before; just not sure what keywords to use or where to start looking. Evan ^{(talk|contribs)} 18:57, 18 December 2014 (UTC)[reply]

The human genome is about 3 Gigabases. So, there is around 4 to the power 3,000,000,000 possible combinations. Not, all of them are, of course, actually possible but this rough estimate still holds. So, the claim that "three people are born with my DNA every day" is false if the population is around 100 trillion. Ruslik_Zero 20:06, 18 December 2014 (UTC)[reply]

That's theoretically true - but some of those possibilities would imply that the mother gives birth to a tree or a duck or a elephant. Totally random DNA isn't likely to arise in a population. An oft-quoted number is that 99.9% of my DNA is identical to yours (or to any other human) - so taking that rough number says that only 3,000,000 base pairs are really likely to vary between people. Still, that's 4^3,000,000 - let's say 10^1,000,000 to pick a nice round number. Given that there are only around 10⁸⁰ atoms in the visible universe - it's still SPECTACULARLY unlikely that two people would ever have the same exact DNA by chance reshuffling of A's, G's, C's and T's.

However, we have to consider that the man and woman (who love each other *very* much and make some babies) each only have 23 pairs of chromosomes - their child doesn't get a random selection of A's, G's, C's and T's from each parent - it gets entire chromosomes. So for any given pair of humans, there are only 2²³ possible chromosomally unique children that they can have...about 8 million. If those children were to in-breed, so no new chromosomes appear then their children would still only have some combination of their grandma & grandpa's DNA. So if our 100 trillion humans were all descended from Adam and Eve, there would only be 8 million unique human chromosome combinations - and there would indeed be a bunch of people with the same DNA. However, copying errors, mutations and the fact that it's been a hell of a long time since our most recent common ancestors guarantees that there is considerably more variation than that.

I don't buy the story's claim...but it's not so simple to dismiss it as that. SteveBaker (talk) 20:55, 18 December 2014 (UTC)[reply]

Note chromosomal crossover in meiosis is essentially a required event for proper gamete production (it can be omitted, but only with a significantly greater chance of abnormalities as I recall). This means that there are vastly. vastly more than 2²³ outcomes. Wnt (talk) 21:18, 18 December 2014 (UTC)[reply]

Depends on how you're defining "the same". A DNA database will try to claim an absurdly low probability, but will only look at as many markers as are needed to reach that -- and there is a risk that in a particular small ethnic group the different markers will not truly be independent, but will be more likely each to go a certain way. This risk seems to be very low, but it is not zero - consider the trivial case where a person turns out to be the identical twin of someone who was secretly swapped at birth, which however soap opera unlikely is not astronomically unlikely. However, the ways in which this can happen are fewer the more markers are examined. The identical twin will always come out the same, but fellow 100% Tasmanian aborigines will eventually be distinguished, assuming any known method of reproduction.

I still have in the back of my mind a nagging doubt whether it could ever happen that humans clone themselves naturally, if a diploid egg or sperm were to provide all the genetic material to the exclusion of the other gamete. Such embryos normally die, but that observation only holds up until a counterexample can be found. But with the number of large-scale genetic tests on the general population this is rapidly fading from absurdly unlikely to genuinely ruled out. Wnt (talk) 21:14, 18 December 2014 (UTC)[reply]

How much would it cost get tested for every genetic risk factor known to man?

How many are there (including the minor ones like propensity for male pattern baldness)? Hundreds? Thousands? Where would one go? Would that be an unusual request there? I guess they could give you the list of risky genes that can take effect before 30 (hundreds?). You'd take it home, cross out the ones that'd be unoverlookable by your age (bubble boy syndrome, complete immunity to chickenpox..) and only get tested for genes that could bother you before testing gets cheaper. How much would that cost? I don't think I'd actually do it though, I'd wait till it's cheaper and understanding of genetics isn't so piecemeal. Well, if it's tens of dollars (yeah right) I'd consider it but I'm curious how much I'd have to have to not mind spending the money. Also, how much is it to find out just the known genes for cancer? breast(40s) — colon, skinny male breast (!) is my parental history of cancer. I guess a single disease is cheaper to test for than many. (grandpa died from cigarette cancer at 56 before we could find out whether he would've died from regular cancer, other grandpa died a year after being well enough to make baby the original way, increasing the chances that it was cancer, but he might've smoked) Sagittarian Milky Way (talk) 22:23, 18 December 2014 (UTC)[reply]

That's not a question that is easy to answer, as there are many genetic risk factors about which we know, but which we don't know (i.e. we know they are inheritable, but we don't know which combinations of genes cause them). If you thrown in a research program to identify them all (or even just a few of them), the sky is the limit. On the other hand, if the genetic factors are well understood, testing all of them should not be impossibly expensive - a quality whole genome sequence cost Steve Jobs US$100000, and prices have come down significantly. I think the analysis of the genome should be highly automatable, at least in principle. --Stephan Schulz (talk) 22:55, 18 December 2014 (UTC)[reply]

Your question implies there is a test for every genetic risk factor known to man, but not every gene or set of genes that causes a disease that runs in a family has been identified. This is about the third time since halloween that we've had this question, you might want to serach the archives for lengthy previous answers. μηδείς (talk) 01:18, 19 December 2014 (UTC)[reply]
- Thanks Medeis, but what search terms should I use? I can't seem to find one, much less two after Halloween. Sagittarian Milky Way (talk) 15:00, 19 December 2014 (UTC)[reply]

You may want to look into 23andMe and in particular their pre November 22, 2013 test kits (probably available at elevated prices on eBay). Ariel. (talk) 08:13, 19 December 2014 (UTC)[reply]

It would probably cost you your life. When you add up the X-ray exposure, exposure to radioactive tracers, exposure to chemicals, tissue damage due to biopsies, blood drawn for hundreds of tests, etc., the net result is a pretty large insult to the body. Looie496 (talk) 15:37, 19 December 2014 (UTC)[reply]

He meant "genetic" and I have fixed the title to reflect that. μηδείς (talk) 19:24, 19 December 2014 (UTC)[reply]

- I think you're describing getting tested for every "disease with a non- nurture component known to man". Clearly no one is going to want a piece of their lung (much less every organ) pulled out of their body and many other invasive tests in their 20s with no evidence of malfunction. And I actually imagined "every blood test known to man, including thousands of toxins" as a child, pictured hundreds of vials of blood and thought the image amusing.

- If you could get a full genome without too much somatic expense then you should easily be able to get enough DNA for fewer genes. Sagittarian Milky Way (talk) 16:40, 19 December 2014 (UTC)[reply]

See $1,000 genome. Even so, be skeptical, because medicine is a racket. The 23andMe action corresponded with other efforts to have it declared "unethical" to get genetic testing done without getting certain common specific genetic tests done, starting with the infamous BRCA1. However, shortly after that decision the Supreme Court ruled against a broad class of gene patents, creating some hope again. Even so.... I think that one way or another, someone will step forward to demand a huge amount of protection money before the average person is allowed to find out about his genome, because that's how medicine works. Wnt (talk) 21:46, 19 December 2014 (UTC)[reply]

In your hair

After seeing a shampoo advert, I was wondering, what does caffeine do to your hair? Would the same results occur if you used tea, coffee or a high caffeine drink e.g. Monster or Red Bull? What would be the effects of each of those? Also why do some people pour beer or another alcoholic drink in their hair? 5.69.204.149 (talk) 23:34, 18 December 2014 (UTC)[reply]

Beer is supposed to give hair body. You can google beer shampoo for that answer. What caffeine does is wash out and run down the drain. μηδείς (talk) 01:23, 19 December 2014 (UTC)[reply]

Its just bogus marketing. There is no benifit in caffeine on your hair. They just play men to belive "activating" will prevent the loss of hair at advanced age but since this is a natural process caused by hormones "activation" will likely even speed up that natural process. --Kharon (talk) 11:58, 19 December 2014 (UTC)[reply]

Caffeine may not do much to your hair, but it can be absorbed through the skin [15]. There are products like caffeinated soap [16] that purport to deliver the drug through the skin. So if there's a lot of caffeine in shampoo, absorption through the scalp may deliver similar effects to taking caffeine orally. SemanticMantis (talk) 18:02, 19 December 2014 (UTC)[reply]

Anything that would deliver a clinically measurable dose of caffeine through the skin would have a lethal dose of caffeine per mouthful. Given how often people consume soap and shampoo, there'd be a flurry of deaths and an episode of Inside Edition with Bill O'Reilly exposing the danger. μηδείς (talk) 19:22, 19 December 2014 (UTC)[reply]

December 19

Did anyone ever make a weird mathematical treatment of physics with extra dimensions of time?

Where every possible spacetime really exists, more than that universes just like ours except one electron was on the other side of the electron cloud at 10^61 Planck times exist (if you even looked at it at the wrong time (slightly before 10^61), you couldn't distinguish the universes anyway, even in theory, it's almost not even a different universe). Of course people make weird unfalsifiable, Occam's Law-violating or even debunked physics theories all the time, a theory existing doesn't mean that it deserves serious thought. Sagittarian Milky Way (talk) 00:30, 19 December 2014 (UTC)[reply]

Imaginary time. μηδείς (talk) 01:21, 19 December 2014 (UTC)[reply]

OK...the title here is a question - the answer to which is "Yes...several versions of String theory suggest multiple time dimensions." The rest is not. But to comment on what you have to say:

Certainly if the Many worlds interpretation of quantum theory turns out to be true, then many universes are seemingly (or actually) completely identical. There is no problem with that - if a quantum-mechanical event causes a universe to split into two parallel paths, then one of them can go on to have another event that perfectly undoes the first one - and now you have a pair of parallel universes that are utterly identical. This causes no specific problems - if the hypothesis is true, then there would be vastly more universes than there are atoms in our universe - there would be no shortage of them and no 'cost' to creating new ones. We could even imagine that there are an infinite number of them.

Isn't the many worlds universe be more like an "exploding cone-time" where the Big Bang is a point, BB+1 Planck time is x wide, the third Planck time is x*x wide, the fourth Planck time is x*x*x wide and so on? That is not usually what two dimensions means. In 2-D time with perpendicular axes the Big Bang would be a line at the left edge and universes that won't split from ours for trillions of years would start already separated. Sagittarian Milky Way (talk) 18:11, 19 December 2014 (UTC)[reply]

The many worlds hypothesis may very well be unfalsifiable. We define "the universe" as "all of spacetime and everything that exists therein, including all planets, stars, galaxies, the contents of intergalactic space, the smallest subatomic particles, and all matter and energy." So anything we could detect or measure about these "parallel universes" would make them be a part of our universe. So by the very definition of the word "universe", anything that happens in a different one in undetectable. For this reason, the many worlds hypothesis must seemingly be unfalsifiable. That doesn't mean that it's "false" - it just means that we may never be able to prove or disprove it.
Occam's Razor isn't a "law" - it's not even a hypothesis - and it's not always true. It's just a handy guide that you can employ when there are many possible explanations for something and you want to pick the most likely one. So, if I can't find my TV remote, it might have fallen behind the sofa cushion, or it might be that a team of crack commandoes from North Korea may have broken into my home and removed the remote just to be really REALLY sure that I can never watch "The Interview". In terms of the science, I may not be able to decide which of those hypotheses are true right now...but Occam's razor suggests that I should probably do the experiment of looking behind the sofa cushion BEFORE I contact Homeland Security. It should be called "Occam's Very Rough Rule of Thumb" or something.

I hardly gave any thought whatsoever while writing those two words, if I knew that wasn't a common name for the idea then I wouldn't bothered to Google Occam. I knew it wasn't utterly unable to be wrong. Sagittarian Milky Way (talk) 18:11, 19 December 2014 (UTC)[reply]

A "theory" (the scientific term, meaning something that's proven and widely accepted) does deserve serious thought. Most useful hypotheses (thing that we think are good explanations, but are not yet proven) are sometimes worthy of serious thought - and sometimes not. Many Worlds is a pretty good hypothesis that could certainly explain bizarre stuff like Schrödinger's cat - and is taken seriously by many reputable physicists. So I think it does deserve serious thought, even though it's not proven, may never be proven, and may very well be unfalsifiable.

But physics "theories" (in quotation marks) go all the way to "the sun is made of iron" and Time Cube. Even if no one with a degree in a relevant field takes it seriously (note that I didn't say that's the case) it might be easy enough to add the terms needed to make Einstein's theory 3+2 dimensional (I haven't studied the equations, I can't tell) but have little enough physics sense to take it seriously. Sagittarian Milky Way (talk) 18:11, 19 December 2014 (UTC)[reply]

Is it possible that stored memory could be misinterpreted as another time dimension?165.212.189.187 (talk) 16:43, 19 December 2014 (UTC)[reply]

No. --Jayron 32 18:37, 19 December 2014 (UTC)[reply]

One recent proponent is Itzhak Bars who had an article in New Scientist some years ago. We have an article Multiple time dimensions. I remember reading a discussion of likelihood of multiple time dimensions in a popular science book (i.e. if there are Compact dimensions are they spacelike or timelike or both) a while ago, possibly The Road to Reality by Roger Penrose? JMiall ₰ 10:59, 20 December 2014 (UTC)[reply]

Is the heart's valves made of cartilage?

I read the articles here and eventually I don't understand if yes or not149.78.45.16 (talk) 02:53, 19 December 2014 (UTC)[reply]

No. See cartilage and heart.--Shantavira|^{feed me} 12:03, 19 December 2014 (UTC)[reply]

Is it true that any tendon has two sides - one connected to muscle and the other to the bone or cartilage?

Is it true that any tendon has two sides - one connected to muscle and the other to the bone or cartilage? another sentence that I think about is that always tendon needs to be connected to the muscle or the bone. not? 149.78.45.16 (talk) 02:58, 19 December 2014 (UTC)[reply]

Wikipedia has an article titled Tendon which may be able to help you learn more about tendons. --Jayron 32 03:56, 19 December 2014 (UTC)[reply]

There may be special cases (Patellar tendon), but the answer to your initial question is generally 'yes', as is stated in the first sentence in the lede of the article that Jayron32 linked to. --NorwegianBlue^talk 23:38, 19 December 2014 (UTC)[reply]

how many people with gonorhea eventually go on to develop prostatitis?

close trolling by blocked sock

The following discussion has been closed. Please do not modify it.

Or maybe a better question to ask is, how common is acute prostatitis, and of those with it, how many test positive for gonorrhea? — Preceding unsigned comment added by 199.119.235.174 (talk • contribs)

What's taking so long?Whereismylunch (talk) 4:20 pm, Today (UTC−5)

Assuming it is not developing prostatitis you are in a hurry for, you can google "gonorrhea percentage prostatitis". μηδείς (talk) 21:26, 19 December 2014 (UTC)[reply]

Hard to find an answer, compared to when I looked many weeks ago percentage of oropharyngeal cancer patients positive for hpv.Whereismylunch (talk) 22:27, 19 December 2014 (UTC)[reply]

According to UpToDate [17],

The pathogens associated with acute prostatitis reflect the spectrum of organisms causing cystitis, urethritis, and deeper genital tract infections (such as epididymitis). Gram-negative infections, especially with Enterobacteriaceae (typically E. coli or Proteus species), are the most common. In retrospective studies of men with acute bacterial prostatitis, such pathogens have been identified in positive urine cultures at the following frequencies:

E. coli – 58 to 88 percent
Proteus species – 3 to 6 percent
Other Enterobacteriaceae (Klebsiella, Enterobacter, and Serratia species) – 3 to 11 percent
Pseudomonas aeruginosa – 3 to 7 percent

Sexually active men may have sexually transmitted urogenital infections, which also acutely involve the prostate, in which case Neisseria gonorrhoeae and Chlamydia trachomatis are important pathogens. --NorwegianBlue^talk 23:29, 19 December 2014 (UTC)[reply]

At what frequency has gonorrhoeae been identified in positive urine cultures?Whereismylunch (talk) 01:19, 20 December 2014 (UTC)[reply]

I figured this was a troll when I saw he edited in a signature over the unsigned IP address, and he has been indeffed. μηδείς (talk) 03:35, 20 December 2014 (UTC)[reply]

HIV testing

I know about the window period for HIV testing, but (and I'm asking this question without much scientific knowledge so bear with my ignorance) is there a particular point at which testing will pick up HIV?

Am I right in thinking that HIV tests will test positive after seroconversion occurs? Is seroconversion the same as acute HIV infection (early HIV symptoms)? After the acute HIV infection, is the patient seroconverted and the HIV detectable?

What about during the acute HIV infection?36.224.250.37 (talk) 18:20, 19 December 2014 (UTC)[reply]

Seroconversion. μηδείς (talk) 21:17, 19 December 2014 (UTC)[reply]

"Seroconversion" occurs when the infected person produces antibodies against HIV antigens in sufficient amounts to be detected. Tests that detect the HIV virus itself will usually be positive a few days before seroconversion. There are tests that detect HIV proteins and tests that detect HIV nucleic acids. See Diagnosis of HIV/AIDS for details. According to that article, nucleic acid testing (NAT) appears to be preferred in the EU for blood donor screening (somewhat unclear in the article). I doubt that that is generally true, although it may be true in some EU countries (I know that it's true in Denmark). The EU blood directive [18] does not mandate the use of NAT testing for HIV. In Norway (which is not technically part of the EU, but which through the EEA agreement is more faithful to EU regulations than most EU countries), combined tests (that detect both HIV proteins and antibodies against HIV) are used in blood donor screening. --NorwegianBlue^talk 23:03, 19 December 2014 (UTC)[reply]

What is the nature of the relationship between seroconversion and the acute HIV infection? Does seroconversion occur while a patient is having primary HIV symptoms (if any)?36.226.148.49 (talk) 04:33, 20 December 2014 (UTC)[reply]

The HIV/AIDS article gives the symptoms of the initial acute phase of the infection. Have you understood the seroconversion article? μηδείς (talk) 05:58, 20 December 2014 (UTC)[reply]

Relative concentration of Chitinase in various fruits

Chitinase#Presence in food says:

Bananas, chestnuts, kiwis, avocados, papaya, and tomatoes, for example, all contain significant levels of chitinase.

Where can I find the relative concentration of Chitinase in these and other fruits? -- ToE 20:08, 19 December 2014 (UTC)[reply]

I don't know, but this pdf would be a decent ref for that sentence if you care to add it [19]. SemanticMantis (talk) 20:35, 19 December 2014 (UTC)[reply]

If you are interested in chitinases as food allergens, this web search may be of interest. --NorwegianBlue^talk 23:14, 19 December 2014 (UTC)[reply]

Thanks so far. The food-allergens.de page says: "almost 50% of these allergic [latex alergy] patients also show hypersensitivity to some plant foods, especially chestnut, banana, and avocado, but also to kiwi, papaya, tomato and others." I don't know if that is because the former three have a greater concentration than the latter, or because they have different forms of Chitinase, which I understand describes a group of enzymes.

The allergen.org site gives specific allergens, such as Mus a 2 from banana, a "Class 1 chitinase", and Ziz m 1 from Chinese-date, a "Class III chitinase", but it doesn't seem to give the typical concentrations in the food source and doesn't explain the difference between the chitinase classes. -- ToE 12:33, 20 December 2014 (UTC)[reply]

December 20

Tiny islands

Google Maps (I have no real data to back this up) makes it look as if there are many mountains in the sea of which just the top is above sea level. So if the sea level would go up a little, say 300 ft, many of them would disappear, where if it would go down a little, again 300 ft, a lot less new islands would appear. Is that true, and if so how come? Erosion perhaps? Joepnl (talk) 00:04, 20 December 2014 (UTC)[reply]

Yes, there are lots of different types of islands. Some are newly created by undersea volcanic activity, others are the remains of eroded rock, and yet others are mountaintops from before the last post-glacial rise in sea level. See New islands and Sea level#Changes through geologic time for a few details. I'm sure some experts here can add further to this reply. Dbfirs 00:14, 20 December 2014 (UTC)[reply]

Other relevant articles include seamount and guyot.--Jayron 32 00:56, 20 December 2014 (UTC)[reply]

(edit conflict) When a new volcanic island forms, a thin ring of coral forms around the edges. The volcano becomes extinct (often cause the crust leaves the hotspot of the mantle that caused the volcano behind), the mountain erodes and/or subsides, leaving behind a coral reef on top of a submerged mountain. The corals cannot live where it's too dark (tens of feet or meters, it's one of those, I don't remember) and will die if they're not wet. But no problem, if they die from depth new ones build their exoskeletons on top of the dead ones until they reach the tide level and can't grow up anymore, so they are always right below the sea level if they've been there enough millennia. 100,000 years ago the sea level was 20 feet higher than now in one of the hottest periods in millions of years (though I think this would happen (if not double) if we burn the carbon till 2100 or something and then wait for the ice to stop melting (centuries), so not especially hot by 2014 standards), the highest sea level in at least 400,000 years and maybe millions (I don't remember), 100 Kyr is short enough that the coral reefs killed by the low sea level of the last ice age have not have time to be eroded away yet and are still there as islands. Sagittarian Milky Way (talk) 01:27, 20 December 2014 (UTC)[reply]

Also, it is often in the nature of land to be barely above sea level (wave and freak 5000 year hurricane created islands like Coney Island and the more well known Atlantic City island, river deltas, river islands, coastal wetlands.. Those don't look like mountains on Google Earth, though. Sagittarian Milky Way (talk) 01:38, 20 December 2014 (UTC)[reply]

If the surface of the Earth were randomly bumpy, the greatest number of islands would exist when the sea covered half its surface (for a proof of this, ask at the math desk). If the sea level sank, so that more than half of the surface was land, more of the random islands would become part of the mainland. If the sea level rose so that more than half the random surface was covered with water, more islands would sink below the surface.

The Earth has two great differences: the ocean covers 71 percent of it, and its surface is far from random. So the question is an empirical one which I cant answer. But see Zealandia and Kerguelen Plateau for interesting reading. μηδείς (talk) 04:18, 20 December 2014 (UTC)[reply]

If Venus were terraformed and given an ocean would probably have to be made of comets) Earth would likely have almost 50% more land by percentage and many more islands (Venus has only two continents). If Mars was terraformed it would likely be only 33% water in one ocean and have few islands. Go figure. Sagittarian Milky Way (talk) 16:29, 20 December 2014 (UTC)[reply]

You seem to be assuming arbitrary water levels? Wnt (talk) 17:38, 20 December 2014 (UTC)[reply]

@Wnt, if anyone still cares, I was assuming that staying indoors when the weeks long days cause jet lag would be annoying enough, they wouldn't want depressing near-constant heat-shielding cloud on top of that (even if all the comets or moons hit on the side that increases spin the day will be long) So you would want to avoid deserts caused by too large landmasses. Deserts next to water cause the highest heat indexes on Earth. Thin air would be good for reducing the avg temperature of high latitudes, as is the low axis tilt, but a lot of water would be needed to reduce the day-night temperature differences. Do might as well just keep Ishtar Terra and Aphrodite Terra above water. I'm not sure if the tropical one would be habitable, maybe to genetically engineered rainforests? I would want low albedo = high land on Mars, and the thick greenhouse effect of extra GHGs should trap heat and keep the continentality from getting extreme. It also avoids wasting land and fills in the ocean to its original beachline. See: File:Mars_topography_(MOLA_dataset)_with_poles_HiRes.jpg and Oceanus Borealis. Sagittarian Milky Way (talk) 01:47, 23 December 2014 (UTC)[reply]

Were blacksmiths losing their hearing?

I'm not sure whether I'm in the right section of RD, my question is rather between history, trade and medicine. Traditional blacksmiths of the past were being exposed to constant metallic noise during their life, but did that make any impact on their hearing? Were they losing their hearing during their life? Do blacksmiths use any protection for their ears today?--Lüboslóv Yęzýkin (talk) 08:47, 20 December 2014 (UTC)[reply]

In the introduction to An Inevitable Consequence: The story of industrial deafness (if you google that title you will find an online PDF copy) Dick Bowlder writes "There are references going back over several hundred years to the fact that some noisy occupations - in particular those involving the hammering of metal - will cause permanent deafness or tinnitus. Tinsmiths in the middle ages had “ringing in the ears”. But the first authoritative reference was in 1831 when Dr Fosbroke, writing in The Lancet, states that "Blacksmith's deafness is a consequence of employment.” And yes, blacksmiths today use hearing protection [20][21] Richerman (talk) 11:13, 20 December 2014 (UTC)[reply]

See Google Books for Fosbroke's original article, and here for Bowdler's paper. Fosbroke cites Daniel Sennert (in Latin) for his own historical reference on the subject. Tevildo (talk) 11:17, 20 December 2014 (UTC)[reply]

Thank you both! My grand-dad (unfortunately he died long before my birth) was both a skilful blacksmith and a talented musician who played the button accordion. I wonder how these two activities could combine. Probably he played music deliberately as a compensation to his noisy work. Interesting how many blacksmith-musicians there were (and are).--Lüboslóv Yęzýkin (talk) 00:10, 21 December 2014 (UTC)[reply]

So, after a while a blacksmith's hammers and anvils would wear out ? :-) StuRat (talk) 00:31, 21 December 2014 (UTC) [reply]

Is not keeping bread in a fridge really a good piece of advice?

It is commonly stated (including in the WP article: Staling) that keeping bread in a fridge makes it go stale (or more precisely: speeds up the staling process).

This contradicts my own experience: I keep my bread in a fridge at between 0 and 5 Celsius. I keep it in the fridge to stop it going mouldy (or more precisely: to slow down the going mouldy process) and I have not experienced my bread going stale, (even if I keep it long enough to start going mouldy even in the fridge).

Some possibilities:

it depends on the type of bread (though the advice I constantly come across does not refer to particular types of bread),
the staling referred to is not something that bothers me.

I have come across one person checking for themselves [22] , but they used white baguette loaves from a local bakery, which is probably not the most commonly consumed type of bread (in the UK, and many other countries, at least).

The type of bread I am referring to as not seeming to go stale in the fridge is cheap supermarket own-brand, medium sliced, wholemeal, in a plastic bag with no holes, bought in the UK. Ingredients: Wholemeal Wheat Flour, Water, Yeast, Salt, Spirit Vinegar, Emulsifier (Mono- and Di- Acetyltartaric Esters of Mono- and Di-Glycerides of Fatty Acids, Sodium Stearoyl-2-Lactylate), Soya Flour, Rapeseed Oil, Preservative (Calcium Propionate), Palm Fat, Flour Treatment Agent (Ascorbic Acid).

I notice that some of these ingredients are mentioned as anti-staling agents in the Staling article.

Why does this issue matter? People might be wasting bread because they believe the advice about not keeping bread in a fridge, and thereby having it go mouldy. (Advice is often given that bread can be frozen instead, and not go stale or mouldy, but this is less convenient and so less likely to be done.)

Note that this is not a question about why refrigerating bread makes it go stale (I have found copious information about that), but whether it is really true and a significant effect for all types of bread, and therefore whether saying not to put bread in the fridge, without further qualification, is a good piece of general advice. FrankSier (talk) 12:58, 20 December 2014 (UTC)[reply]

I'm from the UK and my family doesn't keep bread in the fridge - not because of anything we've been told, but simply because we have a bread bin, and the fridge has other things in it which need to be kept in there. We do, however, keep bread in the freezer, then bring it out when we need it (thawing it out first, of course), and that has never affected the bread in any way. I think this idea of bread going stale when put in the fridge comes from people putting sandwiches in the fridge (sometimes half eaten), so, being exposed to the air, they will go stale (whether they are in the fridge or not). Putting cling-film over them helps to preserve the bread, in my experience. KägeTorä - (^影_虎) (Chin Wag) 17:52, 20 December 2014 (UTC)[reply]

@FrankSier: The Staling page is not well referenced, having only one footnote to a ten year old book, though the first rather technical external link is downloadable for free. It does say bread "... stales most rapidly at temperatures just above freezing" Perhaps the chemical composition of bread has changed in the last ten years, and this is no longer accurate? Then again, a quick Google turned up heaps of sites saying that bread does indeed go stale faster if stored in a fridge! By up to six times! [23]

It certainly appears that the prevailing advice is to store bread at 'room' temperature. (or freeze it)
Comment on mold. Totally personal OR, avoid touching the bread with your hands and you will get far less mold. You might want to try it, get a piece and put your thumb on it, then leave it to 'moulder'. There is a very high likelihood that you will get a thumb shaped patch of green.
More OR, there are many types of bread and I have found that some types, IIRC unsliced wholegrain are more resistant to going stale (and to mould) Though often the mould gets the bread before the 'stale' (especially in humid summer weather as here in Australia. Ǝ 220 of ^Borg 18:03, 20 December 2014 (UTC)[reply]

Wikipedia has an article on this! Retrogradation (starch) explains the temp effect. The solution is to buy that white plastic foam stuff from the mall that comes in plastic bags, often miss-labeled as bread. It has additives to ensure that it remains as tasteless and bland as the day you purchased it. Enjoy. --Aspro (talk) 20:10, 20 December 2014 (UTC)[reply]

Note that the type of refrigerator also makes a difference. Cheap frost-free freezer/fridge combo units periodically heat the freezer to drive off the frost, and that might affect the fridge compartment temperature, too. You want a stable temperature to retain moisture. Constantly changing the temp will tend to cause water migration, causing bread to either get stale or soggy (and probably moldy, too). StuRat (talk) 20:28, 20 December 2014 (UTC)[reply]

Linguistic tangent here — to the best of my recollection, this is the first time I have ever encountered the word "staling". Is it technical jargon among food scientists? Or maybe a UK thing? --Trovatore (talk) 20:15, 20 December 2014 (UTC) [reply]

Same here (Detroit). I would say "going stale". StuRat (talk) 20:24, 20 December 2014 (UTC) [reply]

Don't know if any of you folks have heard of a little amateur project called Wikipedia but they have an article on Staling :-¬ ) P.S. Stu, you forgot a “/” before 'small' in your last post. --Aspro (talk) 20:37, 20 December 2014 (UTC)[reply]

Thanks, but our article doesn't discuss the linguistic aspects of the term. I would guess "staling" is UK-English, while "going stale" is US-English. StuRat (talk) 21:05, 20 December 2014 (UTC) [reply]

How about verbification then? Or the American habit of turning a noun into a verb in order to avoiding having to learn correct English grammar.--Aspro (talk) 21:24, 20 December 2014 (UTC)[reply]

[24]? DMacks (talk) 21:28, 20 December 2014 (UTC)[reply]

No, StuRat, the verb "to stale" does not exist in British English with that meaning. I thought it must be American when I saw the article. Staling in British English means putting rungs on a ladder (or possibly urinating if you are talking about horses). Dbfirs 22:20, 20 December 2014 (UTC)[reply]

Then what is it, Australian English ? Wiktionary lists it, but not where on Earth it's used: staling. StuRat (talk) 22:27, 20 December 2014 (UTC) [reply]

@StuRat: I haven't head the term in Oztralia either, so not common Oz-English either. Definitions of terminology are important though, see [25]

Oh, here's what a google for "staling" turned up, [26] appears it is a baking industry technical term. 220 of ^Borg 05:22, 21 December 2014 (UTC)[reply]

I was wrong to say that it doesn't exist, but it's certainly not used in modern British English. The OED has a sense "To grow stale; get out of fashion, become uninteresting" with a couple of cites from the nineteenth century. I'm puzzled to understand why Wikipedia has an article that doesn't use modern English. Merriam-Webster has "to become stale" but, from the reactions above, I deduce that the verb is as rare in America as it is in the UK. Google Books seems to indicate that the verb is used of bread by food scientists, though many of the authors have non-English surnames. A couple of authors with English surnames have published books in America with this usage. Google ngrams seems to indicate that the word is used in both American and British English, but is similarly rare in both. Perhaps it's just restricted to food science? Dbfirs 22:50, 20 December 2014 (UTC)[reply]

I suspect that the reason for the article name is that the alternative "Going stale" is an unusual form for an article name. StuRat (talk) 23:21, 20 December 2014 (UTC) [reply]

Staleness would be a much better article name, IMO, and the redirect already exists. I was only aware of the equine usage until now - thanks to Dbfirs for informing us of the ladder usage. Should this go to WP:RM? Tevildo (talk) 23:44, 20 December 2014 (UTC)[reply]

Ironically, the ladder usage is not the latter usage. StuRat (talk) 23:49, 20 December 2014 (UTC)[reply]

"Staleness"? don't be silly. Hale is to health as stale is to stealth. μηδείς (talk) 00:34, 21 December 2014 (UTC)[reply]

...and wale is to wealth ? :-) StuRat (talk) 00:40, 21 December 2014 (UTC)[reply]

Don't be silly, that is as weal is to wealth. μηδείς (talk) 05:40, 21 December 2014 (UTC)[reply]

@Aspro: Our OP actually mentions the Staling page in their post, about 'para' 6. Concur about the mislabelled 'foam'. A major supermarket here (Oz) got taken to court for advertising their 'foam' as "fresh bread" when it had actually been partly baked up to 6 months before! [27] [28]. 220 of ^Borg 05:22, 21 December 2014 (UTC)[reply]

FrankSier On the "Bread and the technology of bread production" webpage, 'Section 3.3. Staling of bread' says

"Storage temperature is an important factor to be considered in any discussion of bread staling. Staling becomes more rapid as the temperature of storage is reduced from room temperature to 35°F. Below 35°F., staling becomes slower as temperature is lowered, until at 0°F. [frozen] it is very slow, and bread products will keep for months without apparent staling." [29] www.classofoods.com

Nb. 35 °Fahrenheit =1.67 °Celsius. So I hope that helps, though it apparently contradicts a lot of websites and the earlier quote "... stales most rapidly at temperatures just above freezing". Keeping your refrigerator at a constant say 1.0 °C is likely to be a problem, which might be why conventionally people are saying to not put bread in the fridge to keep it 'fresh'. Likely it will either be slightly too warm or freeze. The page also gives technical descriptions of the staling process that may be easier to follow than some of the scientific papers I linked to earlier. 220 of ^Borg 05:22, 21 December 2014 (UTC)[reply]

A to D s

What sort of A/D s are used in GHz sampling rate digital scopes ?--86.169.152.43 (talk) 13:31, 20 December 2014 (UTC)[reply]

Fast ones? The usual suspects (Analog Devices, Maxim, TI) all sell ADCs in that sort of range. The exact model used in a particular scope will generally be commercially sensitive. Tevildo (talk) 19:34, 20 December 2014 (UTC)[reply]

David L. Jones does a teardown of two Agilent scopes in these YouTube videos - the 3000 series and the incredibly expensive 90000 series. You can search his site for teardowns of different scopes and other pieces of test and analysis equipment. -- Finlay McWalterᚠTalk 19:46, 20 December 2014 (UTC)[reply]

Could fat tissue be a beneficial cancer?

Naybe the ancestral version of the fat cell was a more harmful cell, and it evolved to be more beneficial? Thanks.2601:7:6580:5E3:7CBD:D2E0:7058:C21D (talk) 18:00, 20 December 2014 (UTC)[reply]

Neigh be my answer to that possibility. Why would you think that ? StuRat (talk) 20:30, 20 December 2014 (UTC)[reply]

Fat cells aren't an infection, they are cells which develop normally in various differentiations from the body's stem cells, originating with a single fertilized egg. See also cell type, lipoma, and liposarcoma. Under the article cell type expand the mesoderm] section, you will see that fat cells (Lipoblast → Adipocyte) and muscle cells differentiate from the same progenitore as bone and cartilage cells. μηδείς (talk) 20:51, 20 December 2014 (UTC)[reply]

As explained in the article, adipocytes famously don't replicate under most circumstances, including weight gain. This actually puts them at the far end of the spectrum from cancer cells that undergo uncontrolled replication. (of course, liposarcomas do manage to replicate, or they wouldn't be cancer) Wnt (talk) 23:53, 20 December 2014 (UTC)[reply]

adipose tissue excretes estrogen and the latter appears to be a risk factor for a number of cancers. I believe overweight people are more susceptible to the latter. --AboutFace 22 (talk) 23:30, 21 December 2014 (UTC)[reply]

Could slow-growing cases of prostate cancer be beneficial in some cases?

Note:i'm not asking about if a gene that causes or predisposes to prostate cancer also has beneficial effects. I mean does the cancer it self help in some way, for example, like kicking in increased ability of sperm to impregnate.I suspect a counterargument will be that it occurs at advanced age that we haven't until the last few thousand years survived to, so we haven't had time to evolve to make it serve a purpose. But it could have been triggered at a younger age back when we lived less long. thanks.Rich (talk) 18:23, 20 December 2014 (UTC)[reply]

I doubt that, but I've noticed that organs which change their function during our lives are quite prone to cancer and/or benign tumors. This would include our reproductive organs and female breasts, which change during puberty and again during pregnancy. They all have a built-in design to "wait until you get the signal, then grow rapidly", so it's not that surprisingly that the "wait until you get the signal" part gets ignored at times. StuRat (talk) 20:36, 20 December 2014 (UTC)[reply]

The genes in prostate tissue that are blamed for cancer are the result of natural selection, thus likely (though not absolutely certainly) beneficial. (An example of why they wouldn't be is if environment has changed or if there has been rapid selection for change at some other site in the genome that makes their present form maladaptive) Now as prostate cancer runs through the gamut of the Gleason Grading System, it gradually goes from being pretty much harmless (except by implication of what will happen) to outright dangerous; this requires mutations that benefit the individual cells but are definitely not part of the starting genome. You can argue that the genetic code that makes such mutations possible is also selected for; but whether that makes these mutations 'part of the plan' is sort of a philosophical question. Like a lot of theoretical questions in biology, it seems to become something of a mirage the more closely you look at it. Wnt (talk) 00:00, 21 December 2014 (UTC)[reply]

Re: "The genes in prostate tissue that are blamed for cancer are the result of natural selection, thus likely (though not absolutely certainly) beneficial." By that logic most genetic diseases would be beneficial. The sickle-cell gene is one of the few where this seems to be the case.

Mutations naturally occur, some of which cause genetic diseases. If they prevent reproduction, then they won't be passed on, but the same mutation can always recur. Since prostate cancer often occurs late in life and is fatal, if ever, even later still, there wouldn't be much evolutionary pressure to prevent it. StuRat (talk) 00:06, 21 December 2014 (UTC)[reply]

What's the top of the Gleason scale labeled ? "To the Moon, Alice". :-) StuRat (talk) 00:08, 21 December 2014 (UTC) [reply]

Well, for example, metformin appears to reduce the risk by turning down the production of c-MYC protein. [30] The prostate could have evolved to have lower levels of c-MYC on its own, without prompting. Now, does that mean that there is a compensating advantage, maybe the man produces more nutritious semen that puts more of a spring in the step of his spermatozoa? Or does some aspect of the modern diet of processed food or endocrine disruptors have toxicity that metformin reverses by the same means as it tends to oppose high blood sugar? Or is it some unintentional negative aspect of the continual rapid evolution of sperm in competition with other males? Well, if I looked it up harder on PubMed I could likely find out, but for purposes of discussion here, well, the point is, it could be a number of things. The point is, the organ doesn't come ready made to be cancer proof as its only priority, or else prostate cancer would be a lot less common - and by extension, it is possible to look for treatments that will reduce the risk, though there may be unintended side effects. Wnt (talk) 00:33, 21 December 2014 (UTC)[reply]

Electrical wiring – wrapping electrical tape around swtiches and receptales

Is wrapping electrical tape around switches and receptacles (inside electrical boxes) required, recommended, or prohibited? I've seen wiring done either way, i.e. with and without taping. I've done some searching; it seems that even among electricians there's no clear-cut answer. Many seem to be of the opinion that it's unnecessary, but some say it may be beneficial sometimes. Does the National Electrical Code say anything about the practice? What is the common/recommended/prescribed practice in other parts of the world? Thanks. --173.49.11.192 (talk) 19:44, 20 December 2014 (UTC):[reply]

Visitors to the US often suffer a culture shock. On the one-hand everything’s all hi-tech, then on the other-hand, the electrical practices and mains power quality are third world. This is a UK site on DIY: Electrical connection--Aspro (talk) 20:26, 20 December 2014 (UTC)[reply]

It seems like it could be counter-productive, to me. Specifically, it could act as a thermal insulator, allowing the wires to overheat, especially if there's an intermittent connection inside the box. Also, I don't expect electrical tape would last for decades, and once it gets old, then what do you do, open up all your walls and replace it ? StuRat (talk) 20:41, 20 December 2014 (UTC)[reply]

??? There is no thermal insulation issue at all. If you have an intermittent connection you have bigger problems, the tape certainly won't hurt. And yes, the tape will last for decades, but it doesn't matter - the tape is really only for the 5 minutes when you put the outlet back in the wall, and you are working live, otherwise you don't need it. Ariel. (talk) 20:19, 21 December 2014 (UTC)[reply]

I disagree with you there. Especially in old homes, they specifically tell you not to add blown in insulation, as this can cause the wires to overheat. Wrapping electrical tape around everything is sure to add some thermal insulation, even if just by blocking air flow. And yes, if you are aware of an intermittent connection, you should have it repaired, but not everybody is aware in time to prevent a fire, or can afford to have it fixed. (I have an intermittent connection in the bathroom overhead lights of my 1920's house, and, not wanting to pay an electrician hundreds of dollars to rip open my stucco ceiling to make repairs, I just disabled them at the wall switch and put a floor lamp in that room.) StuRat (talk) 15:38, 22 December 2014 (UTC)[reply]

The US home improvement show This Old House has a video about this. The wrapping with electrical tape is shown beginning at minute 2. I think the thermal insulation issue would be minimal for the method shown in the video; it isn't "wrapping electrical tape around everything". Personally, I think I'd rather have my circuit breaker trip if some stray piece of metal touched one of the hot screws, rather than having a single layer of old electrical tape provide partial protection. Jc3s5h (talk) 16:30, 22 December 2014 (UTC)[reply]

I'll second Aspro's answer. The question amazes me. Required? No. Reccommended? Not in this neck of the wood. Prohibited? Possibly, though there are things that are so ridiculous, that no-one will contemplate makings laws explicitly stating that they are prohibited. Dangerous? Hmm, it depends. I'd guess that it usually isn't, except when it is. Clearly difficult to regulate. Third world? Definitely. --NorwegianBlue^talk 21:07, 20 December 2014 (UTC)[reply]

Thanks for the replies so far. About the comment that US electrical practices look third-world to visitors, I'm not sure about that. People here are not dying in droves in electrical fires or of electrocution. I take that as empirical evidence that the electrical practices here are at least reasonable. On the comment that there are things so ridiculous that no-one would contemplate making laws explicitly against them, my belief is that if something is ridiculously dangerous, it will be prohibited under some general rules, if not detailed, specific ones. --173.49.11.192 (talk) 22:10, 20 December 2014 (UTC)[reply]

Yes, beyond a certain point more safety regulations may actually make things less safe. For example, if you require smoke detectors that are so sensitive they go off every time you cook, then people will disable them and be less safe. StuRat (talk) 22:22, 20 December 2014 (UTC)[reply]

"people are not dying in droves in electrical fires"...oh, some *on*. It took me about 60 seconds to fact-check your comment (something which you should have done before making it). the ESFi report for 2014 says: "In the United States, 50,900 fires each year are attributed to electrical failure or malfunction, resulting in 490 deaths and 1,440 injuries. Arcing faults are a major cause of these fires."...is 490 per year a 'drove'? I think so. In the UK, there were 25 deaths due to electrical fault fires in 2012. The US population is five times larger than the UK, but still, that suggests that deaths in house fires due to electrical faults are three times more common in the USA than the UK...and that's despite the fact that the US supply is only 110 volts rather than 240 volts. So, the US standards clearly aren't "reasonable" - I think the word "terrible" would be a better choice! Sorry, User:173.49.11.192 you could not be more incorrect. SteveBaker (talk) 00:10, 21 December 2014 (UTC)[reply]

There could be other reasons for the difference, such as a larger portion of people living in poverty in the US, who can't afford to keep the gas on, so end up using iffy electrical space heaters, instead. I would guess deaths from kerosene heaters are also higher in the US, for the same reason. StuRat (talk) 00:36, 21 December 2014 (UTC)[reply]

There's also a much higher occurrence of wooden or wood-shingle construction in the US (at least from my familiarity with CA and MA homes) than the UK (where essentially no-one lives in a wooden building). Postulating the same incidence of electrical fires between the two, you would expect a higher death rate among the people in the wood buildings than the people in the brick buildings. So a higher death rate from electrically-started fires does not necessarily indicate more dangerous electrics, but may indicate more inflammable houses. -- Finlay McWalterᚠTalk 01:11, 21 December 2014 (UTC)[reply]

I didn't look up the statistics when I made my comment. If your figures are correct, the UK is doing significantly better than the US in terms of preventing electrical fire deaths. However, and not to make light of the personal tragedies behind the statistic, I won't call 560 deaths per year among a population of 300+ millions "dying in droves". By comparison, the number of deaths from road accidents dwarfs that figure, and the risk of road accidents is something that people routinely tolerate. --173.49.11.192 (talk) 00:58, 21 December 2014 (UTC)[reply]

Well, it's a matter of cost-effectiveness. Making cars significantly safer is usually difficult & costly compared to the cost of a car. When we do find a measurable improvement (such as rear-view cameras, and tire pressure sensors), the law does change to force those improvements to become universal. Mandating improved house wiring standards would make an utterly negligible percentage difference to the cost of a house. That said, have you heard the kerfuffle about faulty car airbags - which have only caused maybe 6 deaths and 130 injuries? Government is holding inquiries and all manner of remedies have been proposed. But everyone is silent about the 4x larger death rate from electrical faults. It really doesn't make a whole lot of sense. SteveBaker (talk) 01:56, 21 December 2014 (UTC)[reply]

I think the airbag deaths are considerably higher, they just are going slow on "processing" the claims so it doesn't seem as bad as it is. And a safety device blasting shrapnel into your face seems a lot worse than one which simply fails to stop a fire from spreading. The first is causing death or injury, while the second is only failing to prevent it. StuRat (talk) 07:24, 21 December 2014 (UTC)[reply]

I thought this discussion was about poor electrical practices leading to faults which may cause fires? When did it become about stuff which fail to stop a fire from spreading? Nil Einne (talk) 12:23, 21 December 2014 (UTC)[reply]

I was referring to the wood construction of houses in the US, with no corresponding safety feature required, like sprinklers, which allows electrical fires to spread and become more dangerous. This was part of my explanation for why exploding airbags are more of a concern to the public than house fires. StuRat (talk) 15:27, 22 December 2014 (UTC)[reply]

It was suggested above that 110 V is safer than 240 V. This may be true for the electrocution risk, but the reverse is true for the fire risk. Fewer volts means more amps to deliver the required watts. More amps means more heating of the wiring. That's why in the UK ELV (12 V) halogen downlighters are more strictly regulated than 240 V ones. --catslash (talk) 16:32, 21 December 2014 (UTC)[reply]

Steve, You are mixing old installation with new. The new boxes and outlets are very safe, but the US has a lot of old houses, and it's mostly those that have issues. If everyone had the money to upgrade there would be much fewer problems. So it's not that people ignore it - it's that it takes a long long time for upgrades and improvements. Ariel. (talk) 20:34, 21 December 2014 (UTC)[reply]

Going back to the original question, does anyone know if the NEC has anything to say about the practice of wrapping electrical tape around switches and receptacles? --173.49.11.192 (talk) 17:08, 21 December 2014 (UTC)[reply]

It's completely unnecessary, but many people do it anyway. The worry is if the outlet moves in the wall it might contact the box and short, (or if you want to work on it live, it's easier if it's covered). If you have to work with old boxes, the threads for the screws are worn sometimes, but the outlet might move and touch, but it's definitely not necessary with new boxes. If you plan to work on it live, then you need the tape when you put it back in the wall. In short: If you are working live, do it. If not, then with new stuff don't do it. If you have 100 year old electrical boxes then consider it. Ariel. (talk) 20:19, 21 December 2014 (UTC)[reply]

My understanding regarding fires in American homes due to electricity is that it is in no small part caused by the abortive switch from copper to aluminum wiring (and back to copper) in the second half of the last century and homes with hybrid wiring, which causes corrosion and heating and fires due to the resulting resistance. This article mentions the issue.

Why does running water cause the need to urinate?

Why does the sound of running water cause a person to need to urinate? Or is that just an urban legend? Thanks. Joseph A. Spadaro (talk) 23:50, 20 December 2014 (UTC)[reply]

I think it's real. See mirror neuron. (A zoo moved it's water fountain by the bathrooms and added a plaque saying it was relocated there "due to it's inspiration effect on small children".) As for why this might have evolved in humans, a group of people traveling on foot would stay together and make better time if they all stopped to urinate at the same time. They would also be harder to track by predators, such as wolves, than if they left small puddles of urine every mile. StuRat (talk) 23:52, 20 December 2014 (UTC)[reply]

You might find your answers in our article Classical conditioning. I have the same problem when some post a question about diets and it reminds me that its time to make sure that the food in the fridge is not getting out of date (well that's my excuse) and if someone asks about sex, the wife suddenly remembers she promised to pop over and see her mother.--Aspro (talk) 00:01, 21 December 2014 (UTC)[reply]

OR alert! - In later life I have found that when I run the tap to do the washing up I usually need to go for a pee - maybe it's to put off doing that boring job! I used to think it was just the power of suggestion until a veterinary friend of mine told me that the best way to get a cow to urinate, so you can get a urine sample, is to run a tap. Richerman (talk) 01:10, 21 December 2014 (UTC)[reply]

There's also scent marking in other mammals, such as dogs, which try to urinate to stake their claim whenever they detect urine from another animal. Perhaps we inherited a remnant of that behavior. StuRat (talk) 02:47, 21 December 2014 (UTC)[reply]

December 21

First date similarity to job interview

Is there scientific basis when people say that a first date is exactly the same or similar to a job interview

In what ways are they supposed to be the same? (It can't be every possible way--I don't think many people submit a resume before going on a first date.) --173.49.11.192 (talk) 01:04, 21 December 2014 (UTC)[reply]

(e/c)It doesn't sound like the sort of thing scientists would spend much time on. Not much grant money in it. Typing first date interview in Google, brought up a bunch of hits with some explanations, such as this one. Matt Deres (talk) 01:05, 21 December 2014 (UTC)[reply]

Strength of 3D Printer Plastic

They printed a wrench on the International Space Station. For the printer and source material they use for that printer that they have there, what's the spec on the shear stress a wrench made with it is likely to be able to take before it bends and breaks? 75.75.42.89 (talk) 02:30, 21 December 2014 (UTC)[reply]

I can't give you numbers, but I can say that the printer, designed by Made in Space inc., "uses an extrusion based method that layers hot liquefied ABS plastic to build a defined object". So they're in the envelope of what acrylonitrile butadiene styrene can do. -- Finlay McWalterᚠTalk 02:59, 21 December 2014 (UTC)[reply]

Yeah - but this is more of a test than an effort to make a useful tool. They actually plan to ship the wrench back to earth as soon as possible to test it's strength compared to one made on an identical machine here on earth.

But there are 3D printing technologies that produce really strong nylon parts - and laser-assisted metal sintering can produce metal parts in several useful metals. These are early days for zero-g 3D printing and because most (all?) normal 3D printers rely on gravity, it'll probably take many iterations of this technology before they can use it "for real".

In many respects, 3D printing in space is actually easier than here on earth. The need for "support materials" in earthly 3D printing is reduced or even eliminated in zero-g - and without the effects of convection on heat flow, it may be easier to control some kinds of materials.

SteveBaker (talk) 07:28, 21 December 2014 (UTC)[reply]

The article describes it as a "ratcheting socket wrench". Do we know if it functions as such, or does it just have the exterior resemblance of of a socket wrench? If it truly ratchets, do we know how many parts it is comprised of, what assembly was required, and whether any surfaces need post-printing finishing? A typical ratcheting socket wrench is composed of many parts, including bearing and springs, although I could imagine an ersatz, non-reversible (or perhaps double-sided, reverse by flipping), plastic wrench with only two pieces which snap together. -- ToE 12:59, 21 December 2014 (UTC)[reply]

See for example this article, which says the wrench consists of "...a sequence of 21 prints..." that resulted in "...a working socket wrench complete with ratchet action...". As an aside, there are a few simple ratchet wrenches over at Thingiverse that shows ways to make one with fewer parts. WegianWarrior (talk) 13:08, 21 December 2014 (UTC)[reply]

Thanks WegianWarrior. It's nice to hear that the thing actually ratchets. FWIW, it's not clear that that tool itself took 21 prints. Instead, it appears to have been amongst the items manufactured during a sequence of 21 prints. "It also marks the end of our first experiment – a sequence of 21 prints that together make up the first tools and objects ever manufactured off the surface of the Earth." -- ToE 17:50, 21 December 2014 (UTC)[reply]

Made in Space's blog entry gives some more details: "The ratchet was designed as one print with moveable parts without any support material. The parts and mechanisms of the ratchet had to be enclosed to prevent pieces from floating in the microgravity environment." and "The ratchet took 4 hours to print ...". It also has a detailed image of the a copy printed on earth, showing that the handle is labeled "3 in-lb"-- ToE 12:34, 22 December 2014 (UTC)[reply]

I wonder how enclosed interlocking/ratcheting parts were made separately without support material without getting stuck together during creation. 75.75.42.89 (talk) 13:03, 22 December 2014 (UTC)[reply]

Physics in the movie Gravity

I just finished watching the movie Gravity. I was surprised that it actually portrayed the physics relatively realistically compared to other Hollywood films, but there was one particular scene that I found a bit odd. When Sandra Bullock's and George Clooney's characters arrive at the International Space Station using Clooney's MMU, their velocity relative to the station is too great and they have only a limited amount of fuel left to both correct their course and slow down enough to grab onto the external handles. Because of the bumpy landing neither character get a permanent hold, but Bullock's foot is tangled in some ropes while she grasps a tether that keeps Clooney suspended away from her. If I didn't describe that very well it looks something like this:

0[ISS]0-----------------8[Bullock]8--------------C[Clooney]C

Now at this point with both the ropes and the tether pulled tight and all of the objects at rest with respect to each other, as I see it there is no force on Clooney or Bullock and she should be able to reel his tether in and climb up the cables to the ISS. But instead of that Clooney makes some bizarre statement about him pulling her with him and ends up letting go and flying off into space. Is there any possible force that would have been causing him to drag her and then push him off into space once he let go? 139.195.41.154 (talk) 11:57, 21 December 2014 (UTC)[reply]

If the tether is pulled taut, there will be some pent-up potential energy in the tension of the tether, like a rubber band pulled taut. Being at "rest" may mean that all forces are balanced, but it doesn't mean that all energy is nil. Just like a stretched rubber band can be motionless and under balanced forces, when one end is let go, the other end flies off in the other direction. Clooney's character was screwed either way: If the line holding Bullock to the ISS broke, the both of them would be pushed out into space. If the line between Clooney and Bullock broke, Clooney drifts out into space, and Bullock drifts towards the ISS. He's a goner either way, but by letting his end of the rope go, he saves her. --Jayron 32 14:14, 21 December 2014 (UTC)[reply]

I also thought that scene was a terrible exception to a very good movie. It looked like Clooney had reached the end of his tether, was motionless in space, but some malignant ongoing force was hell-bent on pulling him away as a plot device. It should be apparent that once Clooney was truly motionless relative to Bullock his inertia could not add additional tension to the tether between them, and once Bullock was truly motionless relative to the shuttle the tension on her tether couldn't increase. Now there are a hundred ways you can try to salvage the physics by saying that X wasn't really motionless, the cables were about to slip, the tether was unravelling like the rope in a Western cliffhanger, there was a leak in the jetpack, there were extra dimensions of spin and revolution that weren't immediately obvious, whatever... but the scene just didn't carry over that message to me as a viewer. It didn't feel right. Wnt (talk) 16:28, 21 December 2014 (UTC)[reply]

Forgetting for the moment the truly appalling acting, that film was marred by continual glaring physics errors. To move from a Hubble orbit to an ISS orbit to a Tiangong orbit will take enormous amounts of delta-V, certainly not possible the way it was depicted. MMU from Hubble to ISS? Please. For a film claiming to realistically depict spaceflight, it was deeply disappointing. Fgf10 (talk) 19:40, 21 December 2014 (UTC)[reply]

That is not a physics error, it's a "geography" error. They are simply pretending that those satellites are all in similar orbits. --65.94.50.4 (talk) 02:01, 22 December 2014 (UTC)[reply]

I don't know that they ever claimed 100%. They had to take more than a little dramatic licence to make it happen. Mingmingla (talk) 23:56, 21 December 2014 (UTC)[reply]

I could excuse this because we can't rule out (well, at least not with certainty) that one or more satellites might have been moved prior to the events depicted. Of course, that would be unlikely to actually be done... Wnt (talk) 01:13, 22 December 2014 (UTC)[reply]

This "strange" force is called tidal force and can be quite strong is the rope is long enough. Ruslik_Zero 20:50, 21 December 2014 (UTC)[reply]

It's not at all difficult to calculate. Assume a tether 650 m long. Picked out of the air as one ten thousanth the distance to Earth center. Inverse square law, the g differential is 0.0002 which means 100 kg George is being pulled by 20 grams force. Yeah, I know grams are not force. So, if he's strong enough to pick up a pencil on Earth, he's strong enough to pull himself up and join Sandra. And if the cable is a lot less than half a mile, then it's a lot less force. Grade for the movie as lesson in orbital mechanics, B. That is, 'way above average, given the miserably low standards of Hollywood in this regard. Jim.henderson (talk) 21:12, 21 December 2014 (UTC)[reply]

It's been a while since I saw the movie, but the way I remember that scene was that there wasn't enough strength in the ropes to bring both of the two characters to a stop (relative to the station); they were starting to part or untangle or whatever, and the two people were still moving. If so, there is no problem; Clooney lets go and the ropes are strong enough to stop one person. Does the scene really show them coming to a stop, or are people being fooled by perspective or something? --65.94.50.4 (talk) 02:07, 22 December 2014 (UTC)[reply]

Here's the scene. I think this counts as fair use from our perspective, if not the Youtube uploader's. There's a moment early on at which the rope holding Bullock and Clooney jerks and they seem to come to rest relative to the station. Seemingly they should then have bounced back and started drifting toward each other. But later shots (especially the long shots) seem to show them both drifting away from the station again, at a constant distance from each other, with the rope between them still taut for some reason. When Clooney lets go he immediately "falls", the rope goes slack, and Bullock starts moving rather rapidly toward the station. It's not a tidal force—there's only about 6m of rope between them, and ~20m from Bullock to the station, and anyway the rope is oriented tangentially to Earth, not radially, so the tidal force would bring them together, not apart. There's not enough rotation for it to be a centrifugal force. And of course no gravitational/fictitious force could pull one person toward the station and the other away. Maybe it was magnets. -- BenRG (talk) 04:17, 22 December 2014 (UTC)[reply]

Or was there any rotation involved (both of them revolving around ISS)? Was it supposed to be the centrifugal force that was pulling JC away ? (In that case, the rope should have wound round the ISS). I don't recollect the mention of rotation in the scene, though - WikiCheng | Talk 12:09, 22 December 2014 (UTC)[reply]

With particular reference to the OP's question: [31]. And some other sources representing how the film became a bit of a whipping-boy for physicists, engineers, astronauts and other relevant experts in the wake of its original theatrical release: [32], [33], [34], [35], [36]. But for my money, it was comedian Louis C.K. who struck on one of the more glaring oddities that make it hard to suspend disbelief and follow the narrative: starting at 0:47. Snow talk 23:25, 22 December 2014 (UTC)[reply]

Not quite a robot, so what do you call it?

I recently bought a kiddie Build-Your-Own-Robot kit on a whim, thinking it would amuse my cats. This so-called "robot" is made up of a hollow sphere that pops into a little square frame with a dome on top. Within the sphere is a simple motor with a weight attached. The motor causes the sphere to spin, and the weight keeps it off-balance so that it can turn and move around obstacles. Basically it just skitters around the floor bumping into things. It certainly isn't a robot, but is there a word in science/robotics for something like this?146.235.130.59 (talk) 22:52, 21 December 2014 (UTC)[reply]

Why isn't it a robot? It's certainly not a complicated one, but it behaves just as our wikipedia article on robots indicates that it should. Mingmingla (talk) 23:54, 21 December 2014 (UTC)[reply]

I wouldn't call it a robot simply because there is no way to give it data or receive data from it. It's just a motor in a plastic shell. It can't see, hear, make decisions, or be programmed to perform a task. It's like the engine in a car or a clock, just a series of moving parts. Clocks and car engines aren't robots, surely?146.235.130.59 (talk) 13:35, 22 December 2014 (UTC)[reply]

It sounds like a Marvelous Toy. ←Baseball Bugs ^{What's up, Doc?} carrots→ 03:41, 22 December 2014 (UTC)[reply]

Robots are usually presumed to do some sort of work, the word comes from the Slavic robotiti to work as in slave labor. μηδείς (talk) 04:39, 22 December 2014 (UTC)[reply]

Like entertain cats? Nil Einne (talk) 14:00, 22 December 2014 (UTC)[reply]

I think the def of a robot they are using here is that it must change position on it's own, without control by a person. Compare it to Roomba, an only slightly more sophisticated robot. (talk) 15:16, 22 December 2014 (UTC)[reply]

Good point, StuRat. So at what point does something stop being a wind-up toy and start being a robot? The specific "robot" I am talking about is just a motor in a plastic case. The motor alone wouldn't be called a robot, neither would the case. If I take out the motor and turn it on it just sits there spinng, and the case is just an empty piece of plastic. Put the two of them together and neither one of them is changed at all. The motor just spins, the case is just a case, but together they give the illusion of intelligent movement. Is that enough to call it a robot?146.235.130.59 (talk) 19:41, 22 December 2014 (UTC)[reply]

Still similar to a Roomba. It has a chip in it that tells it to change direction when it runs into something. If you took that out it would just run into a wall and stay there. So, probably not enough to call it a robot at that point (a powered-wheel lawn mower would do that much, if you disabled the dead man switch). StuRat (talk) 01:58, 23 December 2014 (UTC)[reply]

How do we feel about using "automaton" in this context? {The poster formerly known as 87.81.230.195} 212.95.237.92 (talk) 20:14, 22 December 2014 (UTC)[reply]

We're making a mistake by looking for a Platonic ideal of the meaning of the concept "robot". Concepts are used and defined in context. Obviously a cat toy is not a "robot" displacing unskilled laborers from factories. A toy salesman, however, might find the cachet of a robotic cat toy pleasing. The etymology has been given. We can't provide the metaphysical Answer. For closely related words, google "robot synonym". μηδείς (talk) 02:55, 23 December 2014 (UTC)[reply]

December 22

What is the difference between tap water to the physiology solution?

I know the tap water is hypotonic, but what are the values of the tap water compared to physiology solution? 5.28.180.110 (talk) 04:04, 22 December 2014 (UTC)[reply]

I assume you are talking about blood? See isotonicity which gives you (grams of NaCl/L water) and human serum albumin. μηδείς (talk) 04:35, 22 December 2014 (UTC)[reply]

When I take a shower does I lose my body water?

asked and answered

The following discussion has been closed. Please do not modify it.

I don't understand if it depends on the temperature? (I mean if it's always true that you lose your body water when you take a shower, even when the temperatures are high or the same of the body temperature). 5.28.180.110 (talk) 04:12, 22 December 2014 (UTC) Same question by Tel Aviv IP, see prior answer: https://en.wikipedia.org/wiki/Wikipedia:Reference_desk/Archives/Science/2014_December_15#When_taking_a_shower.2C_does_the_body_loses_liquids_.28.2Fwater.29.3F μηδείς (talk) 04:21, 22 December 2014 (UTC)[reply]

Why weren't compound bows invented much sooner?

Leonardo's crossbow was a very simple design scaled up massively, but it still looks like a crossbow. Yet in the 1960s there was a sudden profusion of many different designs for compound bows with pulleys/eccentric pulleys/cams, extra limbs, and many other creative features. Reading [37] it sounds like "modern glues and fibreglass" was a key advance, but..... was it really necessary for the invention? Aluminum alloys are used, but wouldn't steel or even bronze have worked in ancient times? Ultra-high-molecular-weight polyethylene is used for the cables, but is there no classical sort of ultra-strong "thong from the hide of the yellow ox" that might have done the job? And Leonardo didn't merely fail to make a compound bow... he failed to try. I just don't get how people missed such innovations for so long only to end the drought so abruptly; can it be explained scientifically?

I'll admit that I haven't used a compound bow and there are many aspects of the eccentric/cam design that aren't obvious to me, so more general explanations (or preferably better clarification in the article itself!) would be very welcome also. Wnt (talk) 04:49, 22 December 2014 (UTC)[reply]

This is an old design infact. See Laminated bow or Yumi#Shape. Such products seem much more result of an artisan tradition than result of one ingeniouse inventor. --Kharon (talk) 13:21, 22 December 2014 (UTC)[reply]

The main purposes of the compound bow are to reduce the accelerated mass of the limbs, and to get a better force/draw curve. I don't think the theory the first idea was obvious before Isaac Newton. You can get a lot of the second advantage with less hassle and less complex engineering with a composite bow. --Stephan Schulz (talk) 14:46, 22 December 2014 (UTC)[reply]

I think there's a couple of things at play here. At the article notes, compound bows are complicated to make and consist of some rather specialized kinds of materials including rubbers, plastics, aluminum, carbon fibers, and other goodies. By the time these were in regular use, the problems of making easier to use bows had already been solved with guns. It wasn't until relatively recently that guns became deadlier than bows for an expert to use, but they've long had advantages in being simpler to use. The original point and click program! The end result being that the iron mongers that might have spent their time and expertise making bows easier to use (i.e. making them into compound bows) instead put their skills into developing rifling and tweaking the cross-section of bullets. Matt Deres (talk) 14:51, 22 December 2014 (UTC)[reply]

Hmmm, I'm getting the feeling from this that the compound bow is an emergent property of modern technology. With the accompanying skepticism of whether emergent properties are really real and meaningful... but nonetheless, an interesting representative. Wnt (talk) 00:27, 23 December 2014 (UTC)[reply]

I see the compound bow as a very sophisticated hobbyist development. Guns long ago rendered bows obsolete for military and subsistence hunting purposes. Use of bows continued for aesthetic reasons, for target shooting and in a subset of hunting for pleasure as a hobby or a sport. As leisure time and the money available for hobby and sport activities increased in the 20th century, the equipment used in hobbies and sports became ever more sophisticated, incorporating cutting edge technologies. A modern America's Cup yacht is perhaps the ultimate example, with the compound bow representing a more economical but still very sophisticated example. Cullen³²⁸ Let's discuss it 01:47, 23 December 2014 (UTC)[reply]

many versions forms of the arm veins

In the past, someone gave me here (in our page) a link for site or book that shows how many versions there are in the forms of the arms veins. I looked for it and I couldn't find it. I would like to get help. 5.28.180.110 (talk) 07:43, 22 December 2014 (UTC)[reply]

Well, we have the illustration File:Sobo 1909 597.png, which may be of some help. This page discusses some of the observed variations. Are these of any use to you? Deor (talk) 19:07, 22 December 2014 (UTC)[reply]

Yes. these are. Thank you! But I looked for the information that was given here before :) I remember that there are more than three versions (I think even 50 or something like that) 5.28.180.110 (talk) 23:22, 22 December 2014 (UTC)[reply]

Was this your previous question? Deor (talk) 23:53, 22 December 2014 (UTC)[reply]

Yes, it is! Thank you deeply :) (How could you do that?!...)5.28.180.110 (talk) 04:24, 23 December 2014 (UTC)[reply]

I don't like to destroy my reputation as a man of mystery. ... However, in this case I just entered arm veins in the reference-desk search box at the top of this page, and that thread came up third in the list of results. Deor (talk) 04:57, 23 December 2014 (UTC)[reply]

If so, I don't have a good answer for that :/ I looked for this and I saw a lot of results. 5.28.180.110 (talk) 12:18, 23 December 2014 (UTC)[reply]

Given a perfectly sealed airship, could it remain in the air for years?

Would an airship, or a kind of balloon, made with a tough material, with the same density as air at 10,000 m, ever fall back to Earth? --Noopolo (talk) 18:46, 22 December 2014 (UTC)[reply]

There's be some diffusion across the material of the gas-bag in the long term. So even "perfectly sealed" it would slowly lose lifting gas.

But the reality is that most airships that don't crash or get shot down, are eventually lost to storms. List_of_airship_accidents APL (talk) 19:41, 22 December 2014 (UTC)[reply]

Are you presuming the balloon contains lighter-than-air gas such as hydrogen or helium? ←Baseball Bugs ^{What's up, Doc?} carrots→ 20:05, 22 December 2014 (UTC)[reply]

Yes, and the balloon is made of something really tough, like a thin sheet of titanium. Noopolo (talk) 20:09, 22 December 2014 (UTC)[reply]

First, let's just suppose it were possible to create a perfectly sealed container that's lightweight and durable. Did you want the balloon to maintain a certain usable altitude? Or just to rise until it reaches some kind of equilibrium and "hangs" there? ←Baseball Bugs ^{What's up, Doc?} carrots→ 20:51, 22 December 2014 (UTC)[reply]

In theory yes, in reality, no. Lightning, UV light, hurricanes, tornadoes, etc., would get it eventually. StuRat (talk) 02:01, 23 December 2014 (UTC)[reply]

Obviously a calamity could occur. The question seems to be what happens if there is no calamity. Would it rise clear out into space and drift away? Or would it reach some sort of equilibrium and hang there? Of course, any sort of wind would move it around. But would it stay at a more-or-less fixed altitude? ←Baseball Bugs ^{What's up, Doc?} carrots→ 02:51, 23 December 2014 (UTC)[reply]

Even hydrogen has mass, so obviously it would reach equilibrium even with the lightest of containers. The greatest equilibrium height that has been achieved in practice seems to be around 25 miles. Dbfirs 08:57, 23 December 2014 (UTC)[reply]

Baumgartner's video

Why in this particular Red Bull's video the altimeter shows something like 4,469 ft (1,363 m) when Felix had already landed (although the airspeed looks correct)? Aren't they live-streamed parameters? Brandmeister^talk 21:10, 22 December 2014 (UTC)[reply]

Because that's the altitude of the place, 40 miles east of Roswell, where he landed. Google Earth gives an altitude of 4462 ft at the landing location given in the Red Bull Stratos article. -- Finlay McWalterᚠTalk 21:41, 22 December 2014 (UTC)[reply]

QNH is the technical term. Tevildo (talk) 22:23, 22 December 2014 (UTC)[reply]

The longest half life medication is known?

asked and answered

The following discussion has been closed. Please do not modify it.

5.28.180.110 (talk) 23:23, 22 December 2014 (UTC)[reply]

See answers to a similar question at Wikipedia:Reference desk/Archives/Science/2014 December 16#Is it known which drug is with the longest half life. Plasmic Physics (talk) 02:15, 23 December 2014 (UTC)[reply]

This Tel Aviv IP is repeatedly asking the same questions multiple times, over and over again, redundantly. μηδείς (talk) 02:48, 23 December 2014 (UTC)[reply]