Wikipedia:Reference desk/Archives/Science/2009 July 28

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July 28

gaps

Is there a list of gaps in knowledge such as the first seconds of the big bang or in the trail of evolution, etc. -- Taxa (talk) 00:37, 28 July 2009 (UTC)

Yes. List of unsolved problems. --Tango (talk) 00:58, 28 July 2009 (UTC)

What pH ranges denature melanin?

It's probably an equilibrium reaction so pHs that would cause dynamic equilibriums of a few power of 10 percentages like 99/90/10/1/0.1% denatured etc. or a formula to find some values myself would be sufficient. Sagittarian Milky Way (talk) 00:46, 28 July 2009 (UTC)

By definition, denature reactions are not reversable, so it would not be an equilibrium situation. Denaturing destroys the Tertiary structure of the protein in such a way that it would be impossible to get it back by simply returning to prior conditions. You don't get a liquid egg back just by cooling it down! Otherwise, I don't have the answer to your main question, but I wanted to make sure you get the terminology right. --Jayron32 04:06, 28 July 2009 (UTC)

Our denaturation (biochemistry) article disagrees, noting (with examples) that the process may be reversible. However, still, I don't know the answer to the original question, except that it also may depend on how severely and reversibly you want to do it. DMacks (talk) 04:33, 28 July 2009 (UTC)

As DMacks notes, there are quite a few proteins which will spontaneously refold under appropriate conditions. (They're almost entirely all small, single-domain proteins, and even among that class they're not a majority — but there are definitely a few.) Perhaps a bit more important to this question, however, is that melanins are not proteins. They're small molecules derived from tyrosine, so the refolding issues associated with protein re/denaturation don't really apply here.

Unfortunately, I don't have a good answer for the original question; it's out of my field. From a bit of Googling, it appears that the extended structure of melanin is still something of an open question — apparently individual melanin molecules combine into larger complexes in vivo, but it is undecided whether these are small oligomers (tetramers), large networks, or some combination thereof. Moreover, it also appears that 'melanin' is actually a mixture of a number of chemically-related compounds, so any measurements of physico-chemical properties ought to be taken with a grain of salt. TenOfAllTrades(talk) 13:01, 28 July 2009 (UTC)

Super fast raster scan

An experiment I am conducting requires a display which updates at least fifty times the frame rate of a normal monitor, could I modify a CRT television to do this, or could LED's or lasers achieve this speed? If made a CRT with multiple beams could this do the trick? Also is their any way to electronically create a scanning transparent "hole" area that lets light through from ALL angles, equivalent to the mechanical Nipcow disc-could an LCD do this or is it more complicated? Trevor Loughlin (talk) 02:47, 28 July 2009 (UTC)

What possible purpose could there be? "Displays" are there for someone or something to see. No human or other earthly animal could derive more info from a display that refreshed that rapidly than from a more normal one. No, you could not "modify a CRT television to do this." You could spend a huge amount of money to have such a pointless device engineered from scratch. Edison (talk) 05:20, 28 July 2009 (UTC)

Come, now, his experiment might have some angle you haven't thought of. Maybe he wants to film a scene of himself singing a song, with a high-speed camera capturing this at 2000 fps, while this experimental monitor is in the background playing back a scene from Apocalypse Now at 2000 fps, so when it's played back as a 60 fps video, you're watching him react in really slow motion to Captain Willard dancing in front of the mirror. Or he's making a monitor for the benefit of houseflies. Tempshill (talk) 05:56, 28 July 2009 (UTC)

One could modify just the vertical timebase (and its synchronising) of a CRT TV monitor to run faster and deflect less. The flyback speed cannot easily be increased so one might get about 8 to 10 usable lines updated at, say, 1500 Hz. That is a very shallow "widescreen" raster. Phosphor decay time would limit the speed of updating a picture element from white to black. I don't see any use for an LCD on a Nipkow disk. There are shine-through LCD frame display panels for use on overhead projectors but their rasters are for standard data formats. Cuddlyable3 (talk) 10:17, 28 July 2009 (UTC)

This is one of those areas that I've personally researched. In a project I was working on, we needed a 180Hz refresh rate display system...just three times the speed of a typical computer display.

You really can't do that to a CRT. What you are attempting is a research project in it's own right. The project that tried to drive a CRT at 180Hz failed for all sorts of complicated reasons - we never got much more than 120Hz. Getting sufficiently powerful coils with the right inductance to run at three times the usual rate was "non-trivial". Your idea of putting 50 beams into one CRT in order to get around that problem (aside from being an exceedingly tricky problem for making the device and aligning all of those beams to the shadow-mask) wouldn't work because the persistance of the phosphors. When you hit the phosphor with an electron beam to make it glow, it takes around 1/150th second for the light from the phosphor to drop back to somewhere near zero - which really limits you to around 150 frames per second - nowhere near the 3,000 frames per second you're looking for!

LCD and plasma and LED and OLED displays all have the same problem. I don't think the tiny mirrors in a DLP projector could move that fast either...and that means that NONE of the 'conventional' display approaches used in consumer or even professional display products are going to come within a factor of 10 of what you claim to need.

I think you're going to need a laser display - but even then, it's an insanely difficult problem.

Scanning a laser display is typically done with mirrors that are moved around using piezo-electric crystals...but the momentum of the mirror and the force needed to accelerate it would be spectacular. That drives you to using a smaller, lighter mirror - but then the actuators that drive it have to be small - and you end up in a spiral of smaller mirror needing smaller actuators that have less power so you need an even smaller, lighter mirror...So I don't think you can move even a tiny mirror fast enough to do that.

Another approach is to aim the laser at a spinning cylinder with mirrors mounted onto it...let's say you make a 10 sided cylinder with mirrored facets...you'd have to machine it out of some very strong metal and polish it to make the mirrors. Point the laser at it and spin the cylinder and the laser will be reflected from one rotating facet after another. This will cause the laser to scan sideways 10 times for each revolution of the cylinder - just like the line-scan on a TV set. Use one cylinder for the horizontal line-scan and another spinning much more slowly for the vertical scan. The problem is that to get a 3000Hz refresh rate with 10 sided mirror cylinders, the vertical scan cylinder has to rotate at 300 revolutions per second and the horizonal one by 300 multiplied by the number of scanlines you need. If you have 500 scanlines - you need your line-scan cylinder to spin at 150,000 revolutions per second!! There isn't anything I could imagine that wouldn't disintegrate if you did that - and machining that cylinder to the precision needed to avoid vibrations would be a major engineering feat!

In the distant past, people scanned images using a tank of mercury and an acoustic stimulator that produced ripples in the liquid that travelled outwards. Aiming the laser at the liquid surface produced a scanning effect as the laser reflected off of each wave in turn. This works pretty well - although the scanning is very non-linear and you have to electronically pre-process your video stream to counteract that. In order to get 150,000 scanlines per second, you'd need to use a 150kHz audio source to make the ripples. I don't know what kind of quality of ripple you'd get if you did that (what's the speed of sound in mercury? That would determine the wavelength of the ripples.) That's maybe do-able. Then either some more complicated mirrors to get to a second mercury tank with 3kHz ripples - or (more conveniently) a 3000 revolutions per second spinning 10-sided mirror (which would still have to be insanely carefully machined and mounted to avoid it destroying itself...but not impossibly so. 3000 revs per second is 180,000 rpm - which is only 20 times faster than (say) a car engine spins...it's tough but just barely possible. You might even get a small piezo-electric actuator to vibrate a mirror at those kinds of speeds.

In order for the image to be bright enough - the laser would have to be a pretty powerful one - and of course if you want a color image, you need three of them.

The result is:

• Three dangerously bright lasers.
• A tank of poisonous mercury.
• A spinning death-trap.

Definitely a recipe for killing yourself if you don't know what you're doing!

From the relative naivity of your question - I doubt very much that you have the skills to come even within a factor of 10 of your goal. This is a multi-million dollar display research activity...and people who are about to launch into multi-million dollar display research activities don't usually start off by wondering if they can just adjust a TV!

I'm also puzzled by what you think you're going to drive this monster with? I can't think of any signal sources (like computer graphics cards, DVD players or anything else like that) which could provide a fast enough signal to drive this thing.

Perhaps you should tell us more about why you need it. I bet there is something else you could do that would work better.

SteveBaker (talk) 12:45, 28 July 2009 (UTC)

Just a small comment, but it is certainly possible to replace CRT phosphors with other materials that can reset much faster. I routinely work with fluorescent organic compounds with an excitation lifetime of a 100 ns or so. I suspect something similar is also achievable for LEDs. It would be an expensive custom job to create such a thing, but the engineering to create the screen strikes me as straightforward (provided money is no object). So, if you can get the rest of the control electronics to run at that speed I don't think designing an appropriate screen is really a limiting factor. Dragons flight (talk) 20:44, 28 July 2009 (UTC)

Quite a number of computer CRTs claim to support a refresh of 160Hz. You can get the comp to use this refresh as well. This is usually at rather low resolutions obviously (e.g. 640x480). Are these not really refreshing that fast? Nil Einne (talk) 01:48, 29 July 2009 (UTC)

Yeah - but they get pretty smeary at those rates. Looking at the screen with the naked eye - you really can't tell but for applications such as our OP evidently has in mind (see below), this smearing would result in a blurry image in the 3rd dimension. SteveBaker (talk) 02:50, 29 July 2009 (UTC)

If I recall correctly a half-silvered mirror will block (one polarisation of) light when charged (or carrying an electric current) - this could form the basis of a high speed light switch - since there are no moving parts. However it sounds like you'd need an array of these things - which as far as I know doesn't exist - eg you'd have to make it yourself - each array element would require an independent electrical supply - I'd guess you'd photlithography equipment at the least. 83.100.250.79 (talk) 14:00, 28 July 2009 (UTC)

If that was workable - we probably wouldn't be using DLP's to do that job...so probably those things don't switch as fast as you think they do. But DLP's are nowhere near fast enough...and really, neither is anything else that I can think of. Worse still - if you have a million pixels per frame and a 3,000 frames per second display - you need to feed it with with something like 75 Gigabits per second of data. That's extremely non-trivial...even if you manage to figure out a way to display it. SteveBaker (talk) 20:37, 28 July 2009 (UTC)

It's not the speed it's the heat that is a problem - a mirror reflects - these absorb the light. Why not check you understand first?83.100.250.79 (talk) 12:24, 29 July 2009 (UTC)

I am not giving much away, because it will result in a piece of consumer elecronics that no-one has a perfect version of even for use by large organisations. What if i had ONE spinning mirror for the horizontal scan and hundreds of individual lasers each with a light valve for the vertical "scan?" —Preceding unsigned comment added by Trevor Loughlin (talk • contribs) 15:00, 28 July 2009 (UTC)

As a point of interest, this user has invented a "retrocausal information transfer" device. He may actually be posting from the future. APL (talk) 15:26, 28 July 2009 (UTC)

As a second point of interest, are you trying to build a "swept volume" volumetric display? It sounds like it, but I don't see how those could ever become "consumer electronics". Hidden surface removal alone sinks it for most applications. APL (talk) 20:19, 28 July 2009 (UTC)

(ec) No - I bet I know exactly what he's planning to do. He wants to create a viewer-independent 3D display - probably by reflecting the 3000Hz image off of a moving screen or spinning the monitor or some such trick. However, there's no such thing as a free lunch - and the amount of information density required to do 3D in such a brute-force manner is HUGE. Getting this down to a price where a consumer could afford it is a major undertaking. If our OP had a hope in hell of doing that - he wouldn't be asking WP:RD/S whether it's possible to modify a TV set to do it! He'd be employing a bunch of professionals who already know the problems and have ideas for the answers. The trick for doing viewer-independent 3D is to take advantage of some of the natural constraints of the scenes you'll want to render. But we're not being told what it needs to do in enough detail to answer the question to speculate on that - and I'm not providing free consultancy in order that someone else can make a fortune! I charge $200 an hour for that (my email address is on my User: page)! Suffice to say that getting enough information into this thing will be a nightmare - and the cost of doing 3D in this way is pretty extreme. SteveBaker (talk) 20:30, 28 July 2009 (UTC)

Oh, I get it now. Not volumetric, but showing a different image to each degree of the circle around the volume. Even if you could work out the optics you'd need a monster of a computer to drive it. APL (talk) 04:30, 29 July 2009 (UTC)

The zoetrope shows a different scene to each viewer located around it. For sheer entertainment value, it provides hours and hours more fun than an average Hollywood movie. On the other hand, the back story and character development are generally rather shallow. Cuddlyable3 (talk) 20:57, 30 July 2009 (UTC)

Oh - this old thing again! [1] SteveBaker (talk) 20:43, 28 July 2009 (UTC)

Yes APL you have got it. You guys are not just nerds, you are smart. The high speed CRT or laser television image would create a circle with all the 3D pixels for each point of the image.For the hole,LCDs or alternatively a mechanical method capable of creating a scanning hole I have thought of(thousands of times better than the nipcow disk in terms of space to image size and definition) would provide the "hole" which would only have to scan at NORMAL television refresh rates. The speed requirements of the CRT/Laser screen behind it could be reduced by using multiple image circles with very little reduction in the viewing angle be for they interfered with each other.I admit the electronics for such a high data rate could be a slight problem. What about a programmable custom chip? Trevor Loughlin (talk) 14:26, 29 July 2009 (UTC)

That will be expensive and require an advanced engineering training. As much as I would like to encourage amateur hobbyists to engage in electronics design, let's be serious. A beginner will take one look at the HDL hierarchy or the ASIC netlist, and run away screaming in horror. But, don't let my dismal view on things dissuade you. Go ahead and download some free, free, opensource HDL and ASIC schematics from OpenCores Project Repository. You can buy starter kits for around two or three hundred dollars; but for the data rates I'm guessing you need, you may want to go for a high-end system. Funding should be no problem with all the casino earnings from the retrocausal information transfer device. Nimur (talk) 17:06, 29 July 2009 (UTC)

Chlorine

Chlorine used in swimming pools is harmless but chlorine gas used in the world wars was lethal. Why? Is the chlorine in swimming pools used in very low concentrations so that it is not harmful? Many thanks for any help. Chevymontecarlo (talk) 06:23, 28 July 2009 (UTC)

see Chlorination 71.236.26.74 (talk) 07:04, 28 July 2009 (UTC)

It's also very important to note that ions can be very different from their neutral atom counterparts. Sodium is a metal that likes to pretty much blow up when you throw it in water, and as you said, chlorine is a lethal gas; yet sodium chloride (Na⁺ Cl^-) is something we all need to live. -- Aeluwas (talk) 07:27, 28 July 2009 (UTC)

True but irrelevant, since chloride is not used in swimming pools while chlorine is. Algebraist 13:47, 28 July 2009 (UTC)

Hmm, I thought the chloride in swimming pools was mostly in the form of hypochlorite ions... but I've never owned a pool. ;) -- Aeluwas (talk) 14:10, 28 July 2009 (UTC)

Yes chlorine is in small concentrations, also it's dissovled (mostly) in the water, rather than as a breathable gas.83.100.250.79 (talk) 11:05, 28 July 2009 (UTC)

To rephrase the question for the OP; water in small volumes is required for life, but if I immerse you in a large volume of water, you would die! See the deal? Very few things are harmful at all amounts or healthy at all amounts. Some harmless things become harmful depending on the amount/concentration. Chlorine is no different in this regard. In small amounts, it kills bacteria, but not you. In larger amounts, it'll kill you too. Most disinfectants/antiseptics have the same basic properties. --Jayron32 13:11, 28 July 2009 (UTC)

But harmless the stuff in swimming pools is not. Just opening the packet before I add it to the dispenser is enough to bring tears to my eyes and make me cough. I have lots of bleach holes in my gardening trousers from premixing it. --BozMo talk 14:23, 28 July 2009 (UTC)

It's still a concentration issue...think about how small an amount from the packet has an effect, but then how much it gets diluted before you swim in it. The relative amounts in "Large amount, immediate and serious effects vs small amount, mild and weaker effects" depend on the intrinsic nature of the chemical you're using. Some are extremely potent or reactive, so even only a few grams is a "large amount" of that chemical and a "small amount" is measured in parts per million dilution. DMacks (talk) 15:26, 28 July 2009 (UTC)

Large pools often use bottled chlorine gas. Google "chlorine gas pool accident" to see some examples of what can go wrong. Rmhermen (talk) 16:55, 28 July 2009 (UTC)

I have heard the new trend is towards salt-water pool sterilization. Vranak (talk) 17:46, 28 July 2009 (UTC)

Virtually everything has several levels...

1. A no effect level (NOEL) - any dose below this has no effect
2. (for drugs)A therapeutic level - the amount of drug necessary to give the desired result
3. A toxic level - the amount to start causing unwanted effects
4. A fatal level - speaks for itself.

So for tiny amount of chlorine in water, then no effect. *Carefully* sniff some gas, and it will make your nose smart - or as one student did when I was at school, sniff too much and you fall over and go to A&E (don't have chemistry lessons like that any more...)  Ronhjones  ^(Talk) 20:02, 28 July 2009 (UTC)

Unsolved problems in astronomy

What is the significance of the asterisks in the Unsolved problems in astronomy article?--Shantavira|^{feed me} 07:41, 28 July 2009 (UTC)

Probably the same as in the Unsolved problems in physics article http://en.wikipedia.org/wiki/Unsolved_problems_in_physics .

** Problems marked with two stars are considered by a significant number of physicists to be resolved, though there is still significant debate about them.

*** Problems marked with three stars are considered by some physicists to be outside the purview of physics, more properly philosophical in nature.

**** The existence of problems marked with four stars is disputed.

You're probably right since User:Allen 124 who created this page [2] later removed some of the same problems from the physics page [3] (although they were restored, as they should have been) Nil Einne (talk) 00:04, 29 July 2009 (UTC)

code for jpg please..

I am using some matlab image processing codes in my experiment.unfortunately .. i found the standard code for bmp files only..can any one help me with ..the jpg version of this code..

err... on trying with the jpg version .. i got some .. problems .. with matrix dimensions.. kindly if someone could fix .it.

CODE: %This code would attempt to analyse the flame area and do the following %1. Frequency analysis of flame area %2. Frequency Analysis of fractal dimension of each static image %3. Correlation Dimension or Embedding dimension of area %-------------------------------------------------------------------------- image_thresh = 70; n_img = 1000;%Number of images in present sequence sampling_freq = 315;%Hz %-------------------------------------------------------------------------- %The starting string of the file name

string_start = 'vc';

%The file extension extension = '.bmp';

%3-D array for image import %pile = ones(256,256,n_img); intensity = zeros(n_img,1); for image_num = 1:n_img %loop counter variable image_num

   img = zeros(256,256);
   %IMAGE LOADING
   image_num_name = image_num - 1;
   image_processed = zeros(256,256);

aniket .. 59.93.135.1 (talk) —Preceding undated comment added 08:38, 28 July 2009 (UTC).

Well, that code is extremely incomplete, and doesn't really do anything that matters. But in any case this is the wrong place for your question, you'll have better luck at Wikipedia:Reference desk/Computing. Looie496 (talk) 15:56, 28 July 2009 (UTC)

When maths go horribly wrong

Okay, so I'm trying to calculate the relative abundance of the two nitrogen isotopes, knowing the mass of both isotopes and of nitrogen as a whole. Nevertheless, somewhere down the road the equation goes horribly wrong:

Step 1: X * 14,0035 + (1-X) * 15,0001 = 14,0067

Step 2: X + (1-X) * 15,0001 = 14,0067
                              -------
                              14,0035

Step 3: X + (1-X) * 15,001 = 1,000229

Step 4: X + (1-X) = 1,000229
                    --------
                     15,001

Step 5: X + 1 - X = 0,066681

Step 6: 1 = 0,066681

Can anyone please point out in which step I made the mistake? Thanks a lot! --Leptictidium (mt) 11:08, 28 July 2009 (UTC)

• Step two and step four both appear to be erroneous. Correct solution should be:

$140035X+(1-X)150001=140067\implies -9966X+150001=140067\implies X={\frac {4967}{4983}}$ Noodle snacks (talk) 11:17, 28 July 2009 (UTC)

Through which mathematical operation does $140035X+(1-X)150001=140067$ become $-9966X+150001=140067$? --Leptictidium (mt) 11:38, 28 July 2009 (UTC)

Take $140035X+(1-X)150001$

multiply out $(1-X)150001$ to become $150001-150001X$

which makes $140035X+150001-150001X$

which is $-9966X+150001$ -- Finlay McWalter Talk 11:46, 28 July 2009 (UTC)

You messed up between step 1 and step 2. Let's replace those constants with nice simple names so I don't have to type those L-O-N-G numbers all the time!

Step 1 is essentially:

  A = 14,0035
  B = 15,0001
  C = 14,0067
  X * A + (1-X)* B = C

In getting to step 2 you tried to divide though by A but screwed up. When you divide both sides of the equation by something - you have to divide EVERYTHING in the equation by that something:

  X*A   + (1-X)*B   = C
  X*A/A + (1-X)*B/A = C/A     -- Divide through by A
  X     + (1-X)*B/A = C/A     -- Cancel A/A

You missed out the A to the right of (1-X)*B! But that approach is ugly.

A better way to simplify would be to collect up the 'X' terms:

  X*A + (1-X)*B = C
  X*A + B - X*B = C    -- Multiplied out (1-X)*B
  X(A-B) + B    = C    -- Collected & factored out the X terms
  X(A-B)        = C-B  -- Subtract B from both sides
  X = (C-B)/(A-B)      -- Divide through by (A-B)
  X = (14,0067 - 15,0001) / (14,0035 - 15,0001)  -- Substitute A,B,C back into the equation
  X = 0,9967890828     -- Do the arithmetic.
  X = 0,99679          -- Round off to 5 decimal places.

QED SteveBaker (talk) 12:07, 28 July 2009 (UTC)

Vibrating parts of the body

Sometimes a few parts of the body vibrate involuntarily for a while and then get back to normal.Like say the right eyelid vibrating,left forearm parts vibrating etc.The nature of vibraion is only short lived. So what is the cause of such vibrations?? What do they indicate??117.193.146.232 (talk) 14:29, 28 July 2009 (UTC)

Some sort of spasm or tremor? DMacks (talk) 15:20, 28 July 2009 (UTC)

Ya kinda tremor ...short lived tremors. —Preceding unsigned comment added by 117.193.131.226 (talk) 17:36, 28 July 2009 (UTC)

These are commonly known as tics or "nervous twitches". The cause isn't really very well understood (many people show them when anxious) -- however there is a neurological disorder called Tourette's syndrome in which tics occur very frequently. Looie496 (talk) 15:49, 28 July 2009 (UTC)

Do not confuse tics which have neurological origin with twiches which are small muscles spasms. 71.203.58.148 (talk) 19:41, 28 July 2009 (UTC)

Looie i dont think tics as you mentioned above answers the question.As a further add on..I myself have experienced some vibrations or tremors you may say ,on my eyelids.It is something which you can feel. —Preceding unsigned comment added by 117.193.131.226 (talk) 17:49, 28 July 2009 (UTC)

I do want to note that Wikipedia can't give any medical advice which includes guessing why your eyelid might be vibrating. You can ask if there is anything else besides tics that might cause that sensation. Sifaka ^talk 17:53, 28 July 2009 (UTC)

Better yet, just go see your physician. Any number of things can cause twitches, including nervous disorders at the extreme end. On the other hand, it may be nothing, so get it checked out. Regards, --—Cyclonenim | Chat  18:31, 28 July 2009 (UTC)

The article you are looking for is Fasciculation. Small, rythmic contractions of an eyelid is a very common phenomenon - so common, in fact, that it has a name in Norwegian (leamus). This term is usually used about fasciculations of an eyelid, but can also be used about fasciculations of other muscles. This was one of the first hits on google.no (the site is well-reputed), and I'll translate the relevant part:

By definition, fasciculations are involuntary muscle contractions, that are sufficiently strong to be visible (or palpable) on your skin, but not strong enough to cause movement of the joint that the muscle controls. Fasciculation is a completely normal phenomenon, and only in exceptional cases a sign of disease. Most people experience fasciculations to a lesser or greater extent in periods of their life. When fasciculations are a sign of disease, they are always accompanied by other, more serious symptoms.

--NorwegianBlue ^talk 18:54, 28 July 2009 (UTC)

In my opinion, the last sentence is the one you need to pay most attention to. See your physician. Regards, --—Cyclonenim | Chat  18:55, 28 July 2009 (UTC)

killed while having sex

has anyone ever been killed while having sex? have they been killed bya third party? or by an accident? and is it more likely to happen in gay or straight sex? Questionabout"theman" adolf (talk) 14:40, 28 July 2009 (UTC)

I doubt there are statistics re: gay or straight in terms of death-while-sex, but certainly people have been killed while having sex both by third parties and by accidents. Why would you presume that it hadn't happened? That people were somehow immune from death by accident or murder while having sex? --98.217.14.211 (talk) 15:14, 28 July 2009 (UTC)

Do automobile, motorcycle and airplane crashes count? How about shootings by jealous spouses? Edison (talk) 15:21, 28 July 2009 (UTC)

There have probably been heart attacks. Or does auto-erotic asphyxiation count (see also Michael Hutchence)? AlmostReadytoFly (talk) 16:00, 28 July 2009 (UTC)

A few years ago, various magazines, including I think the UK's Bizzare, ran photos of a man killed by a falling rock while having sex with a chicken. (He was indulging his avian lust in a cranny in a cliff, and a piece of the cliff face immediately above him became loose.) 87.81.230.195 (talk) 16:04, 28 July 2009 (UTC)

Sounds like Gaia took care of business in that case. 91.32.124.87 (talk) 16:45, 2 August 2009 (UTC)

Mostly all spermatozoids are killed when males have sex.--Quest09 (talk) 17:53, 28 July 2009 (UTC)

Millions of males a day die while having sex, see this. -- penubag  (talk) 20:09, 28 July 2009 (UTC)

Clearly the OP is asking about humans. Same goes for Quest09's response. --Sean 21:38, 28 July 2009 (UTC)

See Nelson_Rockefeller#Death if that counts. 70.90.174.101 (talk) 03:11, 29 July 2009 (UTC)

Heart attacks are fairly common during sex, but does dying of a heart attack count as "being killed?" Edison (talk) 18:43, 29 July 2009 (UTC)

How much does a ton of carbon cost at the Chicago Exchange?

I was planning on buying some carbon offsets, and was looking at the website liveneutral.org. Liveneutral buys carbon credits from the Chicago Climate Exchange, and doesn't do anything else, like reforestation. Liveneutral's price is a set $12/ton. How can I find out what those credits actually cost at the Chicago Climate Exchange? Their website is a little confusing...

Thanks! — Sam 63.138.152.238 (talk) 17:41, 28 July 2009 (UTC)

If I'm reading the chart right, it looks like it's trading at about $0.50 per metric ton. It looks like it peaked about a year ago at over $7 per metric ton. APL (talk) 18:23, 28 July 2009 (UTC)

That's what I figured as well. I'll have to write to them to see how they can explain charging $12/ton when all they appear to do is buy carbon credits. — Sam 63.138.152.155 (talk) 20:11, 28 July 2009 (UTC)

Gears

How does the gear system in clocks work??? —Preceding unsigned comment added by 117.193.131.226 (talk) 17:51, 28 July 2009 (UTC)

Well.. from minutes to hours there is a 60:1 step down gear, hopefully that doesn't need more explanation. If you are wondering about old wind up watches then the second counter mechanism is controlled by an Escapement.

There's more info at Wheel train (horology) which should give you all the answers you need.83.100.250.79 (talk) 18:05, 28 July 2009 (UTC)

I think the article you are looking for is Movement (clockwork) (which is oddly not linked from the clock article). — Sam 63.138.152.238 (talk) 18:06, 28 July 2009 (UTC)

It is now. Livewireo (talk) 20:11, 28 July 2009 (UTC)

What is it called when a swallowing attempts to pull down your own throat?

Caused by trying to swallow with too little "lube". Sagittarian Milky Way (talk) 18:23, 28 July 2009 (UTC)

"Getting something stuck in your throat". Couldn't find any specific medical term on wikipedia. 71.236.26.74 (talk) 06:00, 29 July 2009 (UTC)

Oropharyngeal dysphagia. Axl ¤ [Talk] 06:52, 1 August 2009 (UTC)

Hot air

What's the effect called where hot air, or heated air, distorts light so it all seems blurry/wriggly? You can see it on hot days over long distances, or above a toaster (where I saw it this morning) for example. Regards, --—Cyclonenim | Chat  18:27, 28 July 2009 (UTC)

Heat shimmering/heat shimmer. [4]. - Nunh-huh 18:34, 28 July 2009 (UTC)

Caused by refraction of light in different densities of air at different temperatures. Sjschen (talk) 18:36, 28 July 2009 (UTC)

See also Schlieren photography. DMacks (talk) 18:41, 28 July 2009 (UTC)

The effect is refraction. See also mirage. Red Act (talk) 18:55, 28 July 2009 (UTC)

"Heat wave distortion" gets a few ghits too. Aaadddaaammm (talk) 19:22, 28 July 2009 (UTC)

The answer to your question is refraction of light.To get into more detail consider this.You have lit a bonfire.The air vertically above the bonfire is much hotter than the air surrounding the fire.Hotter the air, the lesser is its density.The air surrounding it is comparitively denser.Obviously the air nearer to you is very dense.Now the light has to travel through this range of varying densities of air and hence suffers a series of refractions which make the air to give it a quivering appearance.The densities of air also keep varying constantly which further add to the quivering effect.gdsrinivas 19:29, 28 July 2009 (UTC) —Preceding unsigned comment added by Gd iitm (talk • contribs)

The reason for the ripples is just turbulance in the air - much as smoke tends to curl and bend, so does the clear air that causes this shimmering. The difference between the refractive index of warm and cold air explains why the light coming through is distorted differently - and as the hot and cold air mix, you get this effect. SteveBaker (talk) 20:14, 28 July 2009 (UTC)

Turbulance? Hmm, I would say above your toaster it is very unlikely to be "turbulence" which I think is generally characterized by multiple length-scales of eddies? The formation of simple laminar and eddy flow as the buoyant laminar flow breaks up seems much more likely. But I couldn't be bothered to calculate a Reynolds number to check so I'll have to give SB the benefit of the doubt. And as Steve has said using the right technical term isn't the most important thing.... --BozMo talk 22:25, 28 July 2009 (UTC)

A quick look through my Fluid Dynamics library seems to indicate that twenty years ago (when all the books were written) the correct term for the flow above your toaster was laminal flow transitioning to an irregular "vortex street". Emphatically not turbulence. There you go then, that should change your whole perception of things. Unless I am out of date which is possible. --BozMo talk 22:40, 28 July 2009 (UTC)

Yeah - that's all true - but I don't see that same kind of shimmering over my toaster (at least, I just tried it with my toaster and it doesn't seem to generate anything like that). We're talking about much larger differences in temperature and much larger sources...I doubt that the airflow stays laminar under those kinds of situtaion. SteveBaker (talk) 02:33, 29 July 2009 (UTC)

My guess is actually that the "shimmer" is a coherent higher frequency eddy structure and that the distortion from the pure turbulence would be whiter in frequency terms. However both could exist in the same flow and I didn't do any serious stuff on flow since the early nineties. --BozMo talk 06:03, 29 July 2009 (UTC)

By the way are you a chemical engineer? In pipeflows people tend to talk about laminar or turbulent as though these were the only flow types but when talking of ddc buoyancy wakes jets etc they use a fuller range of flow regimes. --BozMo talk 06:14, 29 July 2009 (UTC)

Chains and Pulleys

Recently I paid a visit to a big construction site. There heavy objects were lifted, adjusted,shifted etc using a multiple grooved hand operated pulley. This pulley had many grooves and had lengthy chains running through it. It wasn't a usual one. Also the chain was pulled effortlessly and had to be pulled long for a small movement. How does this work??? —Preceding unsigned comment added by 117.193.129.196 (talk) 19:47, 28 July 2009 (UTC)

To start - it sounds like a Block and tackle - this explains the easy of use and long pull.

They can also be used with chains -see http://www.h-lift.com/chainblock.htm

Potentially it may have been more complicated than block and tackle - some have ratchets to stop the thing falling.83.100.250.79 (talk) 19:55, 28 July 2009 (UTC)

Also there are chain lifting gears with continuous (looped) pulling chain with gears to give mechanical advantage plus ratchets.

—Preceding unsigned comment added by 83.100.250.79 (talk) 19:56, 28 July 2009 (UTC)

It's a simple matter of mechanical advantage. If you wrap a rope or chain around a pair of pulleys so that the rope goes up and down between them several times...let's say 6 times...then for every foot you pull on the rope, you've only moved the bottom pulley one sixth of that...two inches...that's because you had to shorten all six lengths of rope equally - and one foot of rope shared out six ways is two inches off of all of them. However, when you pull on that rope with a certain amount of tension - you are effectively pulling on all six lengths of rope at once - so the pulley at the bottom moves up with the force of six times the amount of tension. You are exchanging a big, gentle movement for a small powerful one...that's called "Mechanical advantage" - and it's the same principle as using a long lever - where you move one end of the lever gently through a large distance - and the other end moves through a much smaller distance - but is able to apply proportionately more power. Similar ideas explain how the hydraulics in your car brakes allow you to apply all of that force to slow the car down using a large (but fairly gentle) push on the brake pedal.

The grooves you see in the pulleys are there to stop the rope or chain from getting tangled up as it goes around and around them - pulleys that are designed for chains also have dimples in the pulley to allow the chain links to settle into them and reduce the tendancy to slip. SteveBaker (talk) 20:11, 28 July 2009 (UTC)

Our chain hoist article could use improvement (I think it would benefit from a photo of a hand chain block with and without its cover), but here is a video revealing the internals and showing how they work: https://www.youtube.com/watch?v=3j55IAg3GgE Note that the one in the video has a two part load chain, doubling its capacity, but with either a one or two part load chain there will be one loop of lighter chain which is operated by hand and one length of heavier chain for the load. The bitter end of the load chain is usually attached to the hoist to keep it from running through; the working end is attached to the load hook for a single part load chain but passes through a pulley at the load hook and is attached back up at the hoist. Less common these days is the somewhat similar looking differential chain hoist, as described in this video: https://www.youtube.com/watch?v=OXzGSB4i1UU -- ToE 16:06, 13 July 2016 (UTC)

Birds vs. Insects

Why have insects (specifically ones possessing flight) failed to inhabit the ecological niche of birds (and vice versa)? What limits an insect's size that doesn't constrain a bird's?

Alfonse Stompanato (talk) 21:03, 28 July 2009 (UTC)

Having an exoskeleton and inefficient lungs limits the size of insects. - Nunh-huh 21:10, 28 July 2009 (UTC)

Our Meganeura (giant prehistoric "dragonflies") article says (with references):

Controversy has prevailed as to how insects of the Carboniferous period were able to grow so large. The way oxygen is diffused through the insect's body via its tracheal breathing system puts an upper limit on body size, which prehistoric insects seem to have well exceeded. It was originally proposed (Harlé & Harlé, 1911) that Meganeura was only able to fly because the atmosphere at that time contained more oxygen than the present 20%. This theory was dismissed by fellow scientists, but has found approval more recently through further study into the relationship between gigantism and oxygen availability. If this theory is correct, these insect giants would have been perilously susceptible to falling oxygen levels and certainly could not survive in our modern atmosphere.

However, more recent research indicates that insects really do breathe, with "rapid cycles of tracheal compression and expansion". If correct, then there is no need to postulate an atmosphere with higher oxygen partial pressure.

So I think the answer is "nobody knows". Insects don't have lungs, so that certainly places some limit, but not necessarily the limit that they're at now. --Sean 21:34, 28 July 2009 (UTC)

Well in a way they have - or rather one specific species has. The Humming-bird Hawk-moth seems to occupy the same niche in England and Europe that Humming birds do in the tropics. (I can't believe we don't have an article on Humming bird hawk moths - have I given the wrong name?) --TammyMoet (talk) 08:24, 29 July 2009 (UTC)

Macroglossum stellatarum. --Cookatoo.ergo.ZooM (talk) 10:09, 29 July 2009 (UTC)

Also fixed the link to the redirect above. --Stephan Schulz (talk) 11:24, 29 July 2009 (UTC)

Thank you! --TammyMoet (talk) 12:02, 29 July 2009 (UTC)

apparent size of celestial body?

How do astronomers measure the apparent size of a celestial body from Earth? Would it be in degrees of how much of the sky it covers? Or how many millimetres the object covers if a ruler is held out at a certain distance from the observer, or etc? Is there a term for this? Is it called "apparent size" or ? --69.165.137.164 (talk) 21:43, 28 July 2009 (UTC)

Our apparent size article would be a good place to start:) DMacks (talk) 21:48, 28 July 2009 (UTC)

"Angular subtense" or "angular diameter" is a term used to describe that which you ask about. Degrees, minutes, and seconds (or decimal fractions of a degree) could describe the apparent size. Edison (talk) 18:41, 29 July 2009 (UTC)