Wikipedia:Reference desk/Archives/Science/2010 July 31

= July 31 =

Have cognitive scientists explained why it's tedious to not use pronouns?
Please see thread at

Reference_desk/Language

thanks

Andrew Gradman talk/WP:Hornbook 01:44, 31 July 2010 (UTC)


 * To quote your example from the Language desk: "After Jane Smith ate a sandwich, Jane Smith took a walk, where Jane Smith saw Jane Smith's favorite tree next to Jane Smith's favorite house ..." - I think it's pretty obvious. "Jane Smith" is much longer and slower to say, write or type than "she" and "her". SteveBaker (talk) 05:04, 31 July 2010 (UTC)


 * I think it's more than that. Try "Jo" for instance. Still more tedious. I think it's because we use pronouns to keep track of people "already" in working memory and we get puzzled at having to introduce 'new instances' of the same person. John Riemann Soong (talk) 06:00, 31 July 2010 (UTC)


 * Or even just "M" or "Q" or something other than "I", where the letter is meant to be a name. "After Q made James Bond a sandwich, Q took a talk, where Q saw Q's favorite gadget..." --Mr.98 (talk) 13:06, 31 July 2010 (UTC)


 * Yes - but having established that in most cases it is quicker to use the name once at the start - then use to 'her' and 'he' after that, we have that as a 'normal' way of speaking - so we use that same pattern even though it's no faster in the case of 'Jo' and 'Q'. SteveBaker (talk) 15:33, 31 July 2010 (UTC)
 * Languages such as Italian ("null subject languages") have an even faster way &mdash; once it's clear who's being referred to, you just omit the subject altogether, without replacing it with a pronoun, except for emphasis. Continually repeating the pronoun in Italian sounds as stilted as continually repeating the name would, in English.
 * Of course it's a bit easier to do that in Italian because it's a more inflected language than English; the verb ending (usually) tells you first-, second-, or third-person, and singular or plural. --Trovatore (talk) 21:41, 31 July 2010 (UTC)

1) After establishing who a personal pronoun represents, one has available a standard set of pronoun versions tabulated below. They are usually quicker to read than the corresponding name version. The name versions for ownership and reflexive seem particularly tedious compared to the pronoun versions. Only the pronoun versions distinguish between nominative and object immediately without the reader needing to look for context.                   NAME VERSION      PRONOUN VERSION Nominative        Steve             He Object            Steve             Him Ownership         Steve's           His Reflexive         Steve himself     Himself 

2) The first sentence below using names requires some effort at anaphore resolution which is obviated by the second version.

Bob shot Robert K. StJohn-Hollyoaks. Bob shot himself.
 * Cuddlyable3 (talk) 23:00, 31 July 2010 (UTC)

3) Personal pronouns can resolve gender ambiguity. It was Pat's mother that chose Pat's name. It was his/her mother that chose Pat's name.
 * Cuddlyable3 (talk) 14:35, 1 August 2010 (UTC)
 * That's not really an advantage though. Most languages have sexual dimorphism among names for a reason; sexually ambiguous names are exceptions to a trend. Besides, it's usually a problem when you don't know the gender of said person. Pronouns aren't used for these rather trivial "advantages". Some languages use kinship terminology rather than pronouns -- see Vietnamese pronouns. John Riemann Soong (talk) 19:17, 1 August 2010 (UTC)

Speed of lightning
What is the range of lightning speed observed? I'm a bit confused by some documentaries and websites that explain lightning discharge can travel at speeds near from the speed of light. --Email4mobile (talk) 04:04, 31 July 2010 (UTC)
 * Lightning propagating at near light speed is hard to believe. I can see the progress of a lightning stroke across the sky, and it looks orders of magnitude slower than light should be able to travel through the same portion of sky. There should be some quantitative answers from high speed photography done in the course of lightning research. Edison (talk) 04:09, 31 July 2010 (UTC)
 * Check out this incredible video.  It shows lightning propagating - filmed on a 9,000 frames per second camera - so the lightning is slowed down maybe 300 times.  The initial strokes take several seconds to grow in the video - which means 10's of milliseconds in reality.  It's hard to judge how high the clouds are in the video - but it's likely to be in the 500 meter-ish range.  So 500 meters in maybe 10 milliseconds is 50km/sec or 100 thousand miles per hour.  Light travels at 670 million miles per hour - so the lightning bolts seem to be propagating at a very small fraction of light speed.  This is a pretty rough calculation though - there is room for maybe a couple of orders of magnitude of error - so maybe at most 1% of light speed?  SteveBaker (talk) 05:01, 31 July 2010 (UTC)
 * Lightning leader propagates at 105 - 106 m/s, or sometimes even slower, see "Lightning: Physics and Effects" by Rakov and Uman. The subsequent "strokes" of lightning (the ones that propagate in the established channel), however, are much faster, sometimes in excess of 108 m/s. Speed of light is 3x108 m/s. --Dr Dima (talk) 05:28, 31 July 2010 (UTC)
 * You can see that latter effect in the video - once the channel is established, the subsequent strokes along that same path happen instantly - even at 9000 frames per second. I was talking about establishing the initial path. SteveBaker (talk) 15:28, 31 July 2010 (UTC)


 * As usual, the problem stems from a problem of definition. What do you define as the "speed" of lightning?  Lots of complicated things are happening in the course of a lightning bolt.  There are electromagnetic waves, that propagate at the speed of light, carrying information about bulk changes in ion distributions.  These waves help "prepare" the air mass for the next phase - dielectric breakdown.  The dielectric breakdown of air propagates at a difficult-to-determine speed.  At every point along an (as-yet undecided) path, the static electric field must be greater than the breakdown-strength of air - something like a megavolt per meter.  But that exact number depends on air density and humidity (among other parameters).  These values fluctuate on the microscopic scale - and are affected by the breakdown of neighboring regions - so it's a mess of electromagnetic wave propagation and fluid-dynamics.  The next phase is that after breakdown, current begins to flow.  Just like any electric current, we have both an electromagnetic wave (propagating at the speed of light in ionized air), and we have microscopic drift motion of electrons (and, unlike a copper wire, bulk drift velocity of ions).  Every constituent ion of air has a different ion drift velocity - because it depends on mass.  So, O- will drift at a different speed than O2- or N2- and so forth.  The current will flow at the speed of the electromagnetic wave that conveys information along this ionized path (which is still forming as the instantaneous static electric field overcomes the breakdown strength in new areas at the edges of the strike path).  Finally, the slowest part of all, is the incandescence - what we actually see.  The current releases so much energy that it heats the air.  The rate of heating depends on the current strength (which can very from a few hundred amps in a small lightning strike, up to nearly a mega-amp in a giant bolt).  The rate of heating depends on air parameters, (density, humidity, and so forth).  So when you finally see the "light" of the lightning, the bolt may have already existed for anywhere from a few nanoseconds to a few milliseconds before the air got hot enough to glow.  Lastly, the thermal and electromagnetic change that has been building up over these microsecond scales will seem instantaneous to the neutral air surrounding the lightning strike path.  This air is not ionized; it has not been affected significantly by the electromagnetic waves or the ionization that has communicated the change of state through the bolt path.  As far as this air is concerned, the change from "normal air" in its neighboring region to "ionized plasma with enormous electric current and heat" is "instantaneous".  So, there is a rapid shock front - a thunderclap - as the hot air acoustically transfers heat, pressure, and momentum away from the bolt at the sound speed in air (perturbed by pressure and humidity, not to mention rain-drops, which are non-negligible - they are a dense field of acoustic scatterers with dramatically different acoustic speeds, reflecting, dispersing, and attenuating any acoustic energy).  The amazing thing about lightning is that it occurs across many orders of magnitude - microscopic voltages between individual ions accumulate (each individual electron charge) and result in a bulk ion concentration of thousands of coulombs of static electricity.  Tiny perturbations in air pressure (chaotic variations of nano-meter size) between air particles dictate which air parcel will be most susceptible to instantaneous dielectric breakdown and ionization.   Electromagnetic waves travel at near the speed of light in vacuum; and then when the ion channel forms, they travel through that channel much slower (because of the plasma properties); but they still travel through the neutral air at near-vacuum speeds, so there is a complicated interplay there.  The rate of heating and incandescence are derived from this massively complex interaction, and the illuminated bolt you see tracing its way across the sky eventually expands at speeds on the order of kilometers-per-milliseconds.  Finally, just for the interested reader - transient luminous events associated with lightning, including jets, sprites, and elves, are not well explained.  Our physical understanding of the appropriate propagation speeds in sparse plasmas tell us that the jets appear above a lightning strike too soon at too-high an altitude - indicating an unknown form of information- or energy-transfer.  The most likely explanation is a nonlinear interaction between weak electromagnetic waves and sparse, ionized plasmas, somehow amplifying the energy and generating a "second" illumination about a hundred kilometers above the lightning strike.  These are rarely observed from the ground (though it has been done); but they are regularly observed by satellite.  Red Sprites and Blue Jets, from Univ. of Alaska's Geophysical Institute, and Lightning-induced Electron Precipitation from Stanford's Low Frequency radio group both have good descriptions, pictures, and links to active research on lightning physics, including efforts to experimentally verify the relevant timescales for each physical process in a lightning strike.  And, the Lightning Research Lab at Univ. of Florida experimentally triggers lightning strikes using rockets - again, attempting to characterize the physical parameters of the strikes, including the ion distributions and speed of bulk charge transfer.  Nimur (talk) 17:18, 31 July 2010 (UTC)


 * The article says that lightning can travel at speeds near 60,000 m/s. While the flow of current can travel close to the speed of light in a lightning strike, the electrons would move much slower than that and the lightning itself slower still. ~ A H  1 (TCU) 23:47, 1 August 2010 (UTC)

Rechargeable batteries not recharging
Because I take lots of photos, I maintain eight NMH rechargeable AA batteries; at any given time, four are in the charger (although not always plugged in), two are in the camera, and the other two will be backups in the camera bag. Last time that I switched my batteries, I noticed that the ones in the camera and the ones in the camera bag seemed to hold only a small charge; apparently they're older. Today, I charged them, and when they were done, I put them into the camera, taking care to separate them and the other four. It turns out that two of the batteries, when placed in the camera, have only enough energy to produce a "Change batteries" message, even though they've charged all day. Should I assume that they're just too old and past their ability to hold a charge, and thus trash them? Or is there some practical way for me, the non-scientist, to do something useful with them? Finally — it's been so long since I got rid of rechargeable batteries that I don't remember what to do with them; is the trash safe, or is there a better option? I live in a rural area without any realistically-nearby HAZMAT centers. Nyttend (talk) 04:11, 31 July 2010 (UTC)


 * In my experience, there is a substantial chance that the charger goes bad and not the batteries. You can ask your friends to lend you their charger for a day, and see if the batteries charge better with a different charger. --Dr Dima (talk) 05:42, 31 July 2010 (UTC)


 * I own Energizer NiMH batteries that are old and although fully charged at the beginning, die within about 4 days because of current drainage. --Chemicalinterest (talk) 11:04, 31 July 2010 (UTC)
 * Dr Dima, this isn't an option because the other two batteries that I charged don't even cause the low battery indicator to appear, while the four batteries that I had in the camera also work for quite a long time. Nyttend (talk) 11:18, 31 July 2010 (UTC)
 * If some are older than others, then the older ones may behave as I have stated above. --Chemicalinterest (talk) 11:43, 31 July 2010 (UTC)
 * Rechargeable batteries should be recycled, but NiMH do not contain hazardous substances like other batteries do. --Chemicalinterest (talk) 11:44, 31 July 2010 (UTC)
 * I find that my camera seems to require fairly new NiMH batteries and that cells that have been recharged lots of times give a battery low indication almost immediately, but that when they no longer hold sufficient charge for the camera, they can still be used for less-demanding equipment for many more charge cycles. Slower charging (14 hours at 1/10 rating) and slower discharging in low-current applications seems to prolong their life, but eventually they have to go to recycling.    D b f i r s   12:40, 31 July 2010 (UTC)
 * Most probably the batteries are getting older so don't hold a full charge, so won't work in a high drain device like a camera, but would be fine in an alarm clock/remote control or other low drain device. Here in the UK most large supermarkets accept all types of AA and AAA batteries for recycling. Rjwilmsi  16:37, 31 July 2010 (UTC)
 * Hello most active Wikipedian! I don't normally see you at the desks. --Chemicalinterest (talk) 18:50, 31 July 2010 (UTC)
 * Hmm, I've never recycled batteries, because I didn't know that they could be. I'll see what can be done about using them in other devices; no reason to get rid of batteries that should work with those things.  Thanks, everyone, for the input!  Nyttend (talk) 12:59, 1 August 2010 (UTC)
 * Of course, the link to battery recycling would also be useful. ~ A H  1 (TCU) 23:41, 1 August 2010 (UTC)

Blu-Ray video files?
I have Sony PMB software, and average graphics card which my Cyberlink video software tells me needs upgrading on a dual core computer running Windows XP. The Cyberlink software is needed to write to my new Blu-Ray drive, because unless there is some sort of upgrade for XP(?) it only "knows" about DVD/CD... —Preceding unsigned comment added by 80.1.80.10 (talk) 06:21, 31 July 2010 (UTC)
 * Question moved to to the computing/IT reference desk by CS Miller (talk) 09:55, 31 July 2010 (UTC)

difference between taxis and tropism
What is the popular explanation of difference between taxis and tropism in biology? —Preceding unsigned comment added by 113.199.157.152 (talk) 11:34, 31 July 2010 (UTC)
 * Try the articles on taxis and tropism where this distinction is amply covered. If you have any specific questions, feel free to ask and we'll try to help. --- Medical geneticist (talk) 14:06, 31 July 2010 (UTC)

Working prototypes
How are working prototypes of machinery or consumer goods usually built, without going to the expense of a robotic production line? Supposing I had a cool idea, and I was sufficiently trained/experienced in the relevant science to know that it could work, but I wasn't a master craftsman in all the dozens of disciplines required to produce a working model by hand. If I was working on it by myself, how could I get one built within a realistic budget? I have read the rapid prototyping article, and I think 3D photocopying is ace :-)) but isn't the plastic used by an additive modelling machine too weak for moving parts? 213.122.216.120 (talk) 12:05, 31 July 2010 (UTC)
 * There are companies that specialise in making prototypes. Or you could try Meccano or woodwork or making it at a different scale that would be easier to make. 92.15.12.218 (talk) 13:27, 31 July 2010 (UTC)
 * It's normally chiselled from universal matter, obviously you can only make substances for which you know the molecular composition this way, but you don't have to start with machined or mass-produced parts 84.153.192.227 (talk) 13:55, 31 July 2010 (UTC)
 * See also Reprap, Fab lab 92.15.12.218 (talk) 14:25, 31 July 2010 (UTC)


 * Very often, companies will use the 3D printer (aka rapid-prototyper) to make plastic parts to check that everything fits together right and that parts can move as desired without interfering with each other. They may also be painted and assembled to show to marketing departments, etc.  Then they may use the plastic version to make molds from which metal parts may be made.  There are also 3D printers that can use Direct metal laser sintering to produce metal parts directly.  Alternatively, CNC milling machines can automatically make some types of part by 'subtractive' approaches (they carve the part out of a solid block) rather than using additive techniques.  Failing that, they may just use an old-school engineering shop to hand machine the parts in small quantities for prototypes using drills and lathes and other traditional tools.


 * For doing something yourself, commercial 3D printers and CNC machine tools are still hideously expensive. If you are moderately good with your hands, you could build your own RepRap or a three-axis router (I built one of those!).  But if you aren't skilled with your hands - then you may have to find a small engineering company who'll make one-off parts in appropriate materials.  It's not going to be cheap though.  Depending on what you're trying to make, you might be able to get creative with stuff like Lego Technics, Erector-set/Meccano, whatever - or build it from available parts from places like McMaster-Carr who have everything from nuts and bolts to gearwheels, motors, you name it.  A lot depends on what you're trying to make.  If you've invented a new kind of super-tanker or airplane - then you've got a big problem - but if you've invented a new kind of mousetrap - then it shouldn't be too hard to figure out how to prototype it.


 * Electronics and computer parts are a whole different set of problems - and again, there are companies that will do that for you - and (if you have the right skills) there are lots of ways to build this kind of thing yourself.  If you need a computer-controller, then consider the Arduino range of systems.  You can get a computer board for under $30 and program if from your PC...but again, what skills do you have along those lines?


 * If you don't have the skills to make things yourself and you fancy yourself as an inventor - then you should definitely consider learning those skills. There are plenty of courses at community colleges and such like that will teach you many of these skills and give you access to their workshops and machinery to practice on.  I took a welding class like that and was able to use their equipment to do all the welding on a classic car I was restoring.  The $200 I spent on the course (plus welding gloves & mask) were well worth it because in the end, I didn't have to go out and spend $2000 on a welding machine - or pay someone else $800 to weld up my car - and now I have a skill that I didn't have before.  A lot of basic metal and wood-working skills are easy to teach yourself - just buy tools and potter around in the garage making stuff - and you'll get better at it.  Useful shop tools like used drill presses can be bought very cheaply on Craig's list as engineering companies fail in our declining economy.


 * We could give you a much more concise answer if we had more specific information about what you're trying to build and what skills you have.


 * SteveBaker (talk) 15:13, 31 July 2010 (UTC)
 * I kept the question vague because I don't have an invention of my own (yet!). I'm just honestly curious about how prototyping works. Never understood how ideas made the leap from the Eureka moment in the bath, to having a working example that might convince investors it's worth hiring specialist craftspeople or setting up a production line. Guess I shouldn't be too surprised that it's mostly self-improvement plus trial-and-error, if you haven't got money to burn. Thanks a lot for the replies. 213.122.216.120 (talk) 17:43, 31 July 2010 (UTC)


 * Where I work we've gone through this a few times, and let me tell you when we started we had the same questions as you because we're all software developers and none of us had ever developed hardware.
 * The first steps are obviously brainstorming and coming up with ideas and sketches. First broad ideas are sketched out on the white board, then the best ones are sketched out in more detail. Our artist likes to use a 3d modeling program to sketch out how things fit together, but he could have used pen and paper without too much more difficulty.  If the device has electronics (and if we're designing them ourselves) a draft circuit diagram is drawn at this point. Probably using specialized software, but again, pen and paper wouldn't be too much of a hassle either.
 * Next, usually a very rough prototype is made to make sure we're not crazy. This was done with scrap wood and everyday tools of the sort that most people already have hanging around somewhere. None of us are what you would call 'carpenters' or 'craftsmen', so this is always good for a laugh! But it also provides the important function of making sure that the basic idea of what we're building is right.   (If the device has electronics, a rough draft of the electronics would also be made on a breadboard or something. Or maybe just a rat's nest of wires!)
 * Finally, if we still thought we were on the right track, we find a local plastics shop and give them our sketches and 3d models. Ideally, at this point you would want the design finalized by someone who knows what the heck they're doing, but we've found this isn't strictly necessary if you're willing to put up with a lot of trial and error.  The plastics shops makes us some prototype pieces of the plastics parts. (Using 3d printing if we only want one or two, some sort of molding process otherwise.)   We also get circuit boards made. (This is very cheap if you don't mind soldering the bits and pieces on yourself.)   Then we spend another fun day putting the pieces together ourselves.
 * The result is a professional-looking prototype that does what it's supposed to do and if you don't look too closely you can't tell it's held together with superglue!
 * I'm sure companies that do this stuff on a regular basis have a much more streamlined and efficient process, but I think our experience more closely approximates the 'garage inventor' scenario that you're imagining. APL (talk) 19:55, 31 July 2010 (UTC)
 * That "streamlined and efficient process" is to find a professor with a vaguely similar research idea and make his graduate students build a prototype for you.  Graduate students "know how to build things!"  But seriously, there's an important distinction between a prototype that does something useful, and a prototype that is packaged professionally.  If you need a quick turnaround with a slick interface, you need to find a good machinist, a good electronics assembly technician, and so forth.  They will make a device that looks clean, works smoothly, to whatever spec you ask for.  If you care less about presentation and packaging, and are concerned with innovating, then you spend less effort on things like appearance, usability, and reliability - "proof of concept" - to demonstrate that it's worth throwing more resources at a project in the future. Then you find somebody with resources.  Nimur (talk) 20:16, 31 July 2010 (UTC)

Plant health question (Podocarpus macrophyllus)
I have a Podocarpus macrophyllus that I bought several weeks ago. It's shaped like a lollipop, with a roughly spherical clump of branches on top of a straight stem. At a glance, it looks green. But upon closer examination the "core" of that spherical clump is largely composed of brown or wilting needles. The outer "layer" all around is dark green or lighter green (new growth). I've never owned anything similar before, and would like to know if this inner browning is a natural part of the growth of the plant, or whether I should be concerned. Any tips regarding pruning would also be welcome. Thank you! 61.189.63.171 (talk) 13:24, 31 July 2010 (UTC)
 * Is the soil very dry or very wet? 92.15.12.218 (talk) 13:37, 31 July 2010 (UTC)


 * If the outer layer is, as you say, green with new growth, then the plant is growing. I can't imagine a podocarpus being this shape naturally so it sounds as though it has been continuously trimmed to make it a lollipop shape. I'm thinking maybe the trimming has caused a dense outer covering of shoots that is preventing light and air getting to the centre which has started to die back. There would be cut stems over the surface of the plant, under the new growth, to indicate previous trimming if my idea is correct. If you have new growth then you should not be too concerned, but it is odd. Richard Avery (talk) 07:44, 1 August 2010 (UTC)

Farm Pond Spray Fountain
Would like step by step information on how to construct a spray fountain in a large pond to assist with aeration. What specific parts are needed and how to assemble. ≈≈≈≈ —Preceding unsigned comment added by 198.203.175.175 (talk) 18:48, 31 July 2010 (UTC)
 * The article Water aeration has some links, or search for "pond fountain spray how to" or similar. Basicially you put a fountain in the pond with a spray nozzle. Note that over aeration can be harmful to plants.
 * There are literally hundreds of pond fountain options - they will have instructions for installation.Sf5xeplus (talk) 12:41, 1 August 2010 (UTC)

Who coined the term 'fine-tuned Universe'?
Or when? I was horsing around in the web, but couldn't figure out. Twilight chill t   20:52, 31 July 2010 (UTC)
 * The earliest source I found is 1990 Richard Swinburne Argument from the fine-tuning of the universe in Physical cosmology and philosophy, J. Leslie, Editor. Collier Macmillan: New York. pp. 154-73. Wikipedia has an article on Fine-tuned Universe. Cuddlyable3 (talk) 22:17, 31 July 2010 (UTC)
 * I think it may have been George Coyne, a Jesuit astronomer who was using the term in talks and publications as early as 1982. Coined by Coyne, heh. Looie496 (talk) 00:58, 1 August 2010 (UTC)

The modern idea of Fine-tuned Universe can be traced back to Leibniz's optimism that "we live in the best of all possible worlds", famously lampooned by Voltaire in his novel Candide in 1759..Cuddlyable3 (talk) 13:08, 1 August 2010 (UTC)

Corner reflector
What is a three surface corner reflector? --The High Fin Sperm Whale 21:20, 31 July 2010 (UTC)


 * Imagine a hollow cube with three faces removed. What you have is three squares joined along three edges:

/|\       / | \       /  |  \      |   |   |      |  / \  |      | /   \ |      |/     \|       \     /        \   /         \ /


 * The deal is that whichever surface an incoming beam hits, it will bounce off again, hit a second surface, then a third - then head back in exactly the exact reverse direction it arrived in. SteveBaker (talk) 21:34, 31 July 2010 (UTC)
 * Also see Corner reflector. --Cookatoo.ergo.ZooM (talk) 21:38, 31 July 2010 (UTC)
 * Wait a minute, if a beam of light comes at an angle close to 0 degrees relative to the normal of one of those surfaces, could the beam miss any other surfaces completely and reflect in a non-reverse direction? ~ A H  1 (TCU) 23:36, 1 August 2010 (UTC)
 * Well, in an idealized corner reflector, the three surfaces are infinitely large and eventually, either the ray hits another of the surfaces - or it's literally at zero and bounces right back into the source. Of course, real corner reflectors aren't infinitely large - so they don't reflect back 100% of the light.  But for most practical purposes, they are highly effective. SteveBaker (talk) 01:51, 2 August 2010 (UTC)