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March 6

Genetics and cousins

If a man marries a woman then his brother marries the woman's sister and both couples have children, how many genes do the children share with their cousins compared to regular cousins? --124.254.77.148 (talk) 02:21, 6 March 2010 (UTC)[reply]

They would be double cousins. That article says "Genetically, they are as related as half-siblings, sharing 25% of their DNA (a coefficient of relationship of 1/4)." --Tango (talk) 02:26, 6 March 2010 (UTC)[reply]

But, of course, that's just an average. They could actually share anywhere from 0% of their chromosomes (unless they are both male, in which case the cousins must share a Y chromosome) to 100%, which would also require that their two sets of parents were 100% genetically identical. Of course, the extremes are extremely unlikely, but exactly 25% is unlikely, too. (Or should I say impossible, since 46 chromosomes aren't divisible by 4.) StuRat (talk) 02:45, 6 March 2010 (UTC)[reply]

It is more complicated than that since chromosomes don't stay intact - genes can move around when the chromosomes are splitting. See Chromosomal crossover. --Tango (talk) 02:55, 6 March 2010 (UTC)[reply]

Also their parents wouldn't have to be genetically identical. Half of the parents' chromosomes aren't passed on to the children and that discarded half wouldn't have to match. Rckrone (talk) 19:24, 7 March 2010 (UTC)[reply]

Yes, you're correct, they would need to at least 50% genetically identical. StuRat (talk) 00:20, 8 March 2010 (UTC)[reply]

Please note that there is absolutely nothing tabboo about this arrangement (two siblings marrying, respectively, two other siblings), it is not incestuous or dangerous or anything like that. 82.113.121.104 (talk) 10:07, 6 March 2010 (UTC)[reply]

Except, apparently, in West Virginia and North Carolina. --80.177.170.180 (talk) 11:15, 6 March 2010 (UTC)[reply]

^{[citation needed]} --Tango (talk) 18:34, 6 March 2010 (UTC)[reply]

80 is just slightly confused I believe. Our article linked above mentions double first cousin marriages are forbidden in West Virginia and North Carolina which otherwise allows first cousin marriages. This isn't what's being discussed here however (the OP asked what is the relationship of children not whether the children of the relationships are allowed to marry and 82 didn't discuss that either). 82 is probably right that in most or all countries there's nothing illegal about marriages that result in double first cousins (i.e. siblings marrying siblings) even if the children/double first cousins can't marry in a few places. Even identical twins marrying identical twins likely isn't illegal in most or all places although given that their children would be genetically basically siblings, probably can't marry in many places. Of course, you also get the case where after divorce or death, a person may marry the former spouse of their sibling, in some cases it was expected upon death at least for a widow (i.e. Levirate marriage) Nil Einne (talk) 19:42, 6 March 2010 (UTC)[reply]

:Each of my grandfathers had some double cousins, and I've turned out ~~orl write~~ normal. --80.177.170.180 (talk) 11:14, 6 March 2010 (UTC)[reply]

red shift versus blue shift

In considering red shift and blue shift would not it make more accurate or reliable not to think in terms of eyes or ears as being stationary and the object moving as denoted by oneway pointers but rather as both observer and object being subject to motion using dual pointers such as <<<<<<>>>>>> and >>>>>>><<<<<<<? 71.100.11.118 (talk) 03:03, 6 March 2010 (UTC)[reply]

If you are talking about redshift of light in vacuum than it makes no difference. Dauto (talk) 03:12, 6 March 2010 (UTC)[reply]

I'm including a moving siren in air that passes me while riding down the highway. 71.100.11.118 (talk) 03:16, 6 March 2010 (UTC)[reply]

Than yes, you are right. It makes some difference whether the source, the observer, or both are moving.Dauto (talk) 04:05, 6 March 2010 (UTC)[reply]

For sound...yes...because the medium that it's passing through is "stationary" so the symmetry between moving observer and moving source is broken. But the redshift in light doesn't do that because in a vacuum, there is no stationary 'reference'. Light is weird. SteveBaker (talk) 06:53, 6 March 2010 (UTC)[reply]

Obligatory reading: the article Doppler effect. Cuddlyable3 (talk) 00:29, 7 March 2010 (UTC)[reply]

red shift and blue shift for objects in the Universe

Is the average amount of red shift the same in opposite directions when observing from Earth or slightly less or more in any particular direction? 71.100.11.118 (talk) 03:14, 6 March 2010 (UTC)[reply]

I'm not really sure what you mean by the average amount of redshift - what are you averaging over? The Cosmic Microwave Background radiation is redshifted more in one direction than the other (see Cosmic Microwave Background#CMBR dipole anisotropy), if that helps. --Tango (talk) 04:42, 6 March 2010 (UTC)[reply]

For instance perhaps in a binary star system where the red shift will vary in degree and possible to the extent of going int the blue (assuming the system were close enough, the orbital speed high enough, etc.) 71.100.11.118 (talk) 05:24, 6 March 2010 (UTC)[reply]

It would depend what you take the average over. For example you could quantify the amount of redshift in terms of the relative velocity of the object, and then the average value for an orbiting object would be the same as the value for an inertial object with the same average velocity by definition. If you're averaging over the Doppler factor then in general that wouldn't work since the Doppler factor isn't linear in the relative velocity. Rckrone (talk) 19:11, 7 March 2010 (UTC)[reply]

Freeze data outside U.S.

Is it possible to find information on the dates for the first freeze in the fall and the last freeze in the spring for places outside the U.S.A.? All my effort so far has yielded no fruit - all the information I can find (online at least) seems to be limited to the U.S.A. which seems very strange - don't gardeners in, say, Romania or Korea need to know just as well?

69.140.13.88 (talk) 03:45, 6 March 2010 (UTC)Nightvid[reply]

Even the data available for the USA might not be reliable during the oncoming of global warming. For instance I've lived in Florida since 1951 and I've never experienced more than two weeks of temperatures below 40 Deg F. This year we still have temperature down to freezing in early March. 71.100.11.118 (talk) 04:03, 6 March 2010 (UTC)[reply]

Here's a very specific example for a small city in Germany [1]. Aaadddaaammm (talk) 11:09, 6 March 2010 (UTC)[reply]

Northern England (UK): earliest autumn freeze in the last fifty years was September 1st when a whole row of my still-flowering hydrangeas turned a surreal black! Night-frosts occur well into June (summer here), but I don't have exact dates. Parts of Scotland will fare worse. This site [2] might be of interest. Dbfirs 12:15, 6 March 2010 (UTC)[reply]

Static electricity damage

I recently discharged static electricity accidentally on a stereo. It's not a very high tech one but ever since i was unable to power it on. When plugged in, the 12:00 keeps flashing, that's about it. Any way an electronic device like this can be repaired? What component is likely damaged? Maybe there is something I can replace inside? Thx.

Our article has only one line about this topic. --Kvasir (talk) 05:02, 6 March 2010 (UTC)[reply]

You'd have to take it to an electronic repair shop. Once static electricity "sparks" or discharges, it becomes an electric current (and thus no longer static). Sending a pulse of unregulated electrical current through a device with hundreds of tiny electronic devices and hundreds of more little connections and wires means the current could have literally "fried" anything. There are hundreds of options as to what you fried, and there is no way, without carefully analyzing the device, to identify which little connection or tidbit or doofulator you fried. It would only take one. So, you'll need to find someone that speciallizes in repairing these devices, though theres a better than 50/50 chance that the stereo is unfixable even by an expert. --Jayron32 05:07, 6 March 2010 (UTC)[reply]

Beyond the 50/50 chance of being unrepairable, there is a much higher chance that a brand new one will be cheaper than the cost of repairing the old one. Electronics keep getting better and cheaper. Many electronic devices are now considered nearly disposable, like cell phones and mp3 players. -- kainaw ™ 05:12, 6 March 2010 (UTC)[reply]

Static damage is very insidious. It can cause chips to fail intermittently - or not fail at all for weeks after the event and then suddenly die. You could easily pay a stack of money to repair it - only to find that it fails again soon after. Also, diagnosing these faults is pretty tough so unless they do a "repair-by-replacement", swapping out all of the electronics in the unit - the cost of figuring out which chips died would be very hard. Electrostatic discharge may be of some interest. The most likely components to fail are the chips - knobs, buttons, wires, connectors, circuit board tracks, discrete transistors, resistors, capacitors, diodes and coils are unlikely to fail - and the fact that the display is flashing says it's not the display or the power supply. So probably there are a couple of chips in there - and one or more of them is 'fried'. Replacing the chips one at a time would be the most likely approach to succeed - but honestly, I agree with the others...much as it pains me to say so: forget it - buy a new one - contribute more nasty electronics waste to your local landfill. :-( SteveBaker (talk) 06:43, 6 March 2010 (UTC)[reply]

Most electrical devices have gold film to conduct the static to the sites of the device and way from the chips. This sometimes results in a slight shock when touching them, but protects the internal operations. —Preceding unsigned comment added by VCRVLC1010 (talk • contribs) 17:22, 6 March 2010 (UTC)[reply]

Old school trouble shooting: I might inject a signal in the audio output and if sound comes out the speaker, work back stage by stage until the bad one is found. No one should tinker with AC powered equipment unless he is trained in electrical safety. The spark might have fried the portion of the circuit which was touched (if the antenna, then the RF stage; if an RCA audio connector, then the audio stage. With soldered in ICs I wouldn't bother (because I am not good at unsoldering them). Once upon a time it was straightforward to replace a transistor. Edison (talk) 21:11, 6 March 2010 (UTC)[reply]

Thanks guys. I think it would be a fun project to diagnose the problem, knowing that it's *possible* to fix. I mean wouldn't hurt to play with it when you know you are prepare to replace it anyway, right? --Kvasir (talk) 08:57, 7 March 2010 (UTC)[reply]

Relativity

To my understanding, Einstein said that, in order for the laws of physics to remain consistent with the principle of relativity and the universality of the speed of light, a moving object must undergo length contraction, time dialation, and mass increase. If we were to view an object as consisting of a collection of charges, would it be possible to also derive the same results via electromagnetic theory? I saw the article on electromagnetic mass, which said that the velocity dependancy of the electron's mass was predicted before relativity using E&M, so I was wondering if the same was possible with time dialation and such, or whether they are considered to be beyond the perview of E&M theory. —Preceding unsigned comment added by 173.179.59.66 (talk) 07:15, 6 March 2010 (UTC)[reply]

None of the effects that you claim (length contraction, time dialation, and mass increase) actually occur in the reference frame of the moving object. An observer on the moving object would find everything normal, but would observe that the rest of the universe appeared distorted. (Sorry I don't know enough about E&M to answer your question, but Steve or some other expert will give a better answer.) Dbfirs 12:28, 6 March 2010 (UTC)[reply]

Let me try. You could solve the Maxwell equations for an electromagnetically bound system, say a low-mass negative charge orbiting a stationary high-mass positive charge (note: such orbits are not stable but that isn't important here). Then, you solve the Maxwell equations again for the same system, only now it's moving at a constant speed in a constant direction. Obviously, you don't get to use the Lorentz transformation to simplify your problem (that would be assuming your answer), no, you must solve it in the original frame of reference by using, among other things, a current rather than a stationary central charge. Since you solved it in the original frame of reference, you will find that your solution is length-contracted relative to your original non-moving solution. —Preceding unsigned comment added by 83.134.176.244 (talk) 12:52, 6 March 2010 (UTC)[reply]

Yes, and even Einstein himself derives "time dilation" from an argument based on a "light clock" (i.e. light bouncing back and forth between mirrors) which can be seen as a system comprised of an EM field obeying Maxwell's Equations with reflecting boundary conditions. If you want, those boundary conditions can be derived from microscopic physics based upon the Lorentz force of the light's EM fields on the charges in the conductor/mirror, which in turn reradiate. All of this could have been done with pre-1905 electromagnetic theory which is nonetheless fully relativistic! 69.140.13.88 (talk) 16:09, 6 March 2010 (UTC)Nightvid[reply]

Cool, thanks! —Preceding unsigned comment added by 173.179.59.66 (talk) 16:45, 6 March 2010 (UTC)[reply]

It's also relevant to note that Einstein's 1905 paper, in which he set out the principles of special relativity, was entitled "On the Electrodynamics of Moving Bodies" (emphasis added). See History of special relativity for more detail on the origins of the theory. Tevildo (talk) 21:23, 6 March 2010 (UTC)[reply]

Circular DNA

In published sequences of circular DNA molecules (I'm thinking chloroplast DNA specifically), how do they determine the numbering system? Ie. who/what decides which nucleotide is the first? Aaadddaaammm (talk) 11:07, 6 March 2010 (UTC)[reply]

it would make sense for the first one to be the first one that was created while the strand of DNA was being copied. 82.113.121.104 (talk) 13:18, 6 March 2010 (UTC)[reply]

That would make sense, but I seriously doubt that's the case - often which nucleotide is copied first is not known exactly. I imagine the choice is somewhat arbitrary, and made by the team who initially sequenced the DNA. They may choose a prominent feature (like the start of a gene), or they may not. For example, the start position of the E. coli genome is about a million base pairs away from the origin of replication. In the footnote to the E. coli sequencing paper (Blattner et al. Science, 277(5331) page 1453) they note that the zero position was originally defined as the first residue of the thrA gene, which had been previously used in mapping the chromosome, but that they decided to move the start position for the complete genome 189 nucleotides upstream, to include the thrA promoter with the gene. I do know that once a choice has been made for one piece of DNA (say the pBR322 plasmid), derivatives/related DNA (like the pET vector series) tend to use the same numbering system. I'll also note that even for linear DNA like nuclear chromosomes, the numbering system is arbitrary, as telomeres, centromeres, and other unsequenced/unsequencable repeat systems make a global numbering system unwieldy/impractical. -- 174.21.226.184 (talk) 16:51, 6 March 2010 (UTC)[reply]

This is more of a question than an answer: Doesn't the loop have to detach into a more conventional linear sequence in order to reproduce? With 'normal' DNA, the two sides of the helix are unzipped and replicated - that doesn't seem reasonable for circular DNA (unless it doesn't do the "double helix" thing) because you'd end up with an inextricable tangle. If my guess is right then the circle has to break somewhere when being copied - and maybe there is a special place where that has to happen? If THAT is true - then that would be the logical place to start the numbering. But I have no clue whether any of that is true - I'd like to hear the answer. SteveBaker (talk) 17:35, 6 March 2010 (UTC)[reply]

(edit conflict) Answering SteveBaker's question: Various topoisomerase enzymes either cut one strand of the double helix and rejoins it after it has rotated around the other strand or cut both strands, let another double helix pass through, and rejoin the strands. But this happens many times during the copying of the DNA. Icek (talk) 17:54, 6 March 2010 (UTC)[reply]

For general unknotting of DNA, there are a whole group of specialized proteins: the topoisomerases. (See also this link.) TenOfAllTrades(talk) 17:49, 6 March 2010 (UTC)[reply]

DNA replication forks can be generated without cutting the DNA exactly at the site of the fork, as described indirectly by Theta structure and more comprehensively in these lecture notes. That page also discusses negative DNA supercoils, which can compensate for some of the twisting related to unwinding of DNA, and which are released by the topoisomerases cited above. Rolling circle replication is another relevant concept, especially for circular bacteriophage DNA and viroids. -- Scray (talk) 19:43, 6 March 2010 (UTC)[reply]

Here's a great, freely available, textbook chapter relevant to the current discussion - specifically, it deals with various modes of DNA replication. This doesn't answer the OP, but does address Steve's question (the short answer is "no"; circular DNA does not get linearized per se, but topoisomerases are needed to relax negative supercoils and the daughter segments have to be joined to form the circular "progeny" DNA). -- Scray (talk) 20:02, 6 March 2010 (UTC)[reply]

Surviving in a Vacuum

Last nights episode of QI said that a person can survive for a short time in a vacuum, basically until they can't hold their breath anymore and die from suffocation. Is this actually true? I would have thought they'd be exploded by the lack of pressure and boil alive because the boiling point in a vacuum is much lower. Also, Stephen Fry said someone in a vacuum would simultaneously defecate, urinate and vomit because of the pressure. Is that also true?

This has been discussed many times before (well not sure about the defecate, urinate and vomit bit), you may want to search to read the previous answers. But basically Space exposure covers it well. In particular note that it's estimate people could survive about 90 seconds but holding your breath is a bad idea Nil Einne (talk) 11:14, 6 March 2010 (UTC)[reply]

And the pee, poo and puke is from Decompression sickness, linked to in the Space exposure article. Nanonic (talk) 12:44, 6 March 2010 (UTC)[reply]

The BBC should invite three representatives from the Ref Desk along to be panellists on QI. Highest-scoring copmetitors ever, I think. Vimescarrot (talk) 21:54, 6 March 2010 (UTC)[reply]

How could Steven fry still come over as the all encompassing smart arse?--Aspro (talk) 23:12, 6 March 2010 (UTC)[reply]

For this covered in fiction, watch the movie Sunshine. Aaadddaaammm (talk) 09:40, 7 March 2010 (UTC)[reply]

Or even better the movie 2001: a space odessey. 195.35.160.133 (talk) 11:43, 9 March 2010 (UTC) Martin.[reply]

Cos he has all the answers on the card?

Space question

I'm trying to understand the concept of space but I just doesn't make sense to me. Space has nothing in it right? Except for planets and moons and bits of rock floating about. So why aren't those things sucked towards each other to fill the emptiness? How can there be an area with absolutely nothing in it? On earth we have air to fill the gap, but in outter space there's nothing? Please help me to understand. How can something exist when it's nothing? —Preceding unsigned comment added by W359 (talk • contribs) 16:50, 6 March 2010 (UTC)[reply]

Space (even the space between galaxies) does have very small amounts of 'stuff' in it - odd stray molecules of gas. The "air" that we breathe is also "mostly vacuum" - there are big gaps between the molecules. It's only when you get a liquid or a solid that the molecules come close to touching - and even then, the individual atoms have nuclei that are an unimaginably tiny fraction of the size of the atom - so even something as solid as a rock or a table is almost all empty space. The difference between what we call "air" and what we call "vacuum" is just a matter of degree. The reason the air stays in our atmosphere is the same as the reason we stay stuck on the ground - gravity. The reason that gravity doesn't suck all of the planets into the sun is because the are orbiting and as they whirl round in their orbits, the centrifugal force of that motion exactly counters the gravity of the sun. The sun and other stars don't get sucked into the giant black hole in the middle of our galaxy is because they too are orbiting. Galaxies sometimes do collide with each other and get pulled apart by each other's gravity. That's believed to be happening to our galaxy right now. But what (in general) stops galaxies from just being smooshed together by their own gravity is because space itself is stretching as the universe expands after the Big Bang. That expansion is enough to overcome the mutual gravitation between distant galaxies simply because gravity gets so weak over such enormous distances. SteveBaker (talk) 17:26, 6 March 2010 (UTC)[reply]

When you ask why things aren't sucked together to fill the emptiness, perhaps you're referring to the fact that on Earth a vacuum tends to collapse—for example, if I suck the air out of a glass bottle, the resulting (partial) vacuum will noisily collapse the instant I remove the bottle from my lips. The reason for this is the surrounding air pressure. There's really no such thing as a "suck"—everything is a "push". So it isn't that the vacuum is sucking air into the bottle; rather, the relatively high-pressure air outside the bottle pushes its way into the bottle. In space there is no surrounding air, so there is no similar push. In fact, if I were to put a cap on an "empty" bottle here on Earth, travel into space, and then remove the cap, the high-pressure air inside the bottle would immediately push its way out of the bottle and drift off into space, rapidly spreading out until it's almost a vacuum itself (the same almost-a-vacuum that existed there already), and leaving an almost-vacuum inside the bottle. A vacuum has no inherent "sucking" power, so the vacuum of space doesn't suck stars and planets and things together; everything that we call a "suck" on Earth is really a "push" from the surrounding air pressure. The important force at work in the vacuum of space is gravity, which Steve talked about above. —Bkell (talk) 18:06, 6 March 2010 (UTC)[reply]

Orders of magnitude (voltage) help.

Last night, I started the Orders of magnitude (voltage) article (I love the 'orders of magnitude' series of articles - they are really handy for answering Ref.Desk questions!). I've found good examples for every order of magnitude from 10⁰V (a AA battery) up to 10⁸V (typical lightning bolts) which is probably about the largest voltage out there. So we're good for the positive orders of magnitude. But what I'm missing is good examples (preferably common/not-obscure) of voltages of 0.1V downwards (preferably with something I can reference). Help! SteveBaker (talk) 17:49, 6 March 2010 (UTC)[reply]

Nano volts? Each is a minute capsule filled with a gel-like substance excreted by the shark, sensitive to electrical discharges as small as .005 microvolts... [3] and Ampullae of Lorenzini --Aspro (talk) 18:29, 6 March 2010 (UTC)[reply]

How much voltage is generated by a radio antenna (or the antenna in a cell phone, GPS receiver, or wireless networking card)? I can't find the answer immediately, but it can't be very much. Certainly less than a volt, I would think. —Bkell (talk) 18:37, 6 March 2010 (UTC)[reply]

Yeah - I wondered about that - it seemed like it ought to be a great example at the very low end of the scale. SteveBaker (talk) 19:35, 6 March 2010 (UTC)[reply]

As our EEG article says, typical EEG voltages measured from the scalp are in the 10µV to 100 µV range. Looie496 (talk) 18:41, 6 March 2010 (UTC)[reply]

The voltage imposed on a portable radio's antenna or a TV's rabbit ears is extremely low. The output of a typical microphone is extremely low. The voltage from Pioneer spacecraft received at the antenna is very low. The voltage imposed in a short wire by moving it in the Earth's magnetic field is quite low. I say "quite low" because I do not have time right now to go from deciBels and impedance to voltage or to do the basic physics calculations. Edison (talk) 21:04, 6 March 2010 (UTC)[reply]

The dBm article contains a suitable list of typical radio-frequency powers - conversion from dBm to volts is left as an exercise for the reader. :) Tevildo (talk) 21:26, 6 March 2010 (UTC)[reply]

Thermocouple voltages are typically in the micro Volts. This might be intersting to your average reader. Best of luck! 65.209.6.2 (talk) 22:39, 6 March 2010 (UTC)[reply]

See the article Johnson–Nyquist noise. A 50 ohm resistor at room temperature delivers upwards of 1 nV = 10^-9 V r.m.s. Cuddlyable3 (talk) 00:19, 7 March 2010 (UTC)[reply]

Electronvolt? 82.132.136.207 (talk) 01:21, 7 March 2010 (UTC)[reply]

An electronvolt is a unit of energy/mass, not a unit of electrical potential (voltage). Its dimensions are "charge" * "potential difference"; so its an energy unit, just like Joule = Coulomb * Volt. --Jayron32 01:23, 7 March 2010 (UTC)[reply]

A bit like trying to use light-years to measure time. Tonywalton ^Talk 01:30, 7 March 2010 (UTC)[reply]

You also get a voltage due to random electrical thermal noise, this will be of the same sort of order as the weakest radio signal you can detect in an antenna. Also voltages from thermocouples are under 1 volt. Graeme Bartlett (talk) 06:17, 7 March 2010 (UTC)[reply]

Thermal noise voltage is Johnson-Nyquist noise already mentioned.Cuddlyable3 (talk) 18:01, 7 March 2010 (UTC)[reply]

Steve, we already have a list of voltages at Volt#Common_voltages. Maybe you should merge the two lists. --Heron (talk) 10:49, 7 March 2010 (UTC)[reply]

There is certainly an argument for replacing the list in Volt with a link to the new article - but there is a family of "Orders of Magnitude..." articles that have value simply from being in the same format and with common names...so merging my new article into Volt would not be acceptable. Having orders of magnitude articles for all of the common units (mass, length, time, etc) has huge value. SteveBaker (talk) 23:11, 7 March 2010 (UTC)[reply]

I agree. Actually I was thinking of getting rid of the list, not the OOM article. --Heron (talk) 18:12, 8 March 2010 (UTC)[reply]

Uncommon features of a protein

How do you know if a feature of a protein is uncommon or common among other proteins? By features, I mean things like a binding interface made up mostly of hydrophilic residues, a disulfide bond connecting two monomers in a dimer, etc. —Preceding unsigned comment added by 70.68.120.162 (talk) 18:01, 6 March 2010 (UTC)[reply]

Hydrophilic or hydrophobic areas can be determined from the DNA sequence, which is the most easily accessible information. Long-distance interactions are much more difficult to detect. Looie496 (talk) 18:44, 6 March 2010 (UTC)[reply]

While the presence or absence of hydrophobic and hydrophilic residues (or, more likely, their relative abundances) can be readily established from the gene sequence, that information almost certainly won't tell you whether those hydrophobic residues are surface-exposed or packed snugly in a globular protein's hydrophobic core. One doesn't know if hydrophobic residues, separated in the primary sequence, are grouped together to form a binding region on the folded protein. Similarly, one can't easily determine from the primary sequence whether or not a cysteine residue is free or if it forms a disulfide bridge, nor if it is on the surface as part of a dimerization motif. (And you're totally out of luck if you're hoping to predict something really weird like this: a heptasulfane bridge connecting two monomers in SOD1.) That said, there are tools for secondary structure prediction (and limited tertiary-structure guessing); see the ExPASy link below. TenOfAllTrades(talk) 19:10, 6 March 2010 (UTC)[reply]

For a curated database of protein structures, you might try SCOP ([4]) or CATH ([5]) — though it sounds like you're most interested in inter-protein binding...? Perhaps someone else here has suggestions for databases of protein-protein interaction motifs and post-translational assembly of protein complexes...? I might recommend looking through the list of tools linked from ExPASy here to see if there's anything that does what you're looking for. TenOfAllTrades(talk) 19:10, 6 March 2010 (UTC)[reply]

To answer the basic premise of the question, "how can you find out if a feature found in one instance is common in all instances", testing testing and yet more testing while recording the results of all the tests and building up a database of information which can be queried for correlations. —Preceding unsigned comment added by Bartender, bloodwine! (talk • contribs) 22:21, 6 March 2010 (UTC)[reply]

The answer will depend on how you classify your features, if you use a fine grained classification there will be only a few things in it, whereas broad schemes will include many members. If you stick with features named in literature or Wikipedia you can expect that there will be many members. Graeme Bartlett (talk) 04:17, 7 March 2010 (UTC)[reply]

perfect circle

Is there is no such thing as a perfect circle in nature? —Preceding unsigned comment added by RiseWave (talk • contribs) 19:18, 6 March 2010 (UTC)[reply]

The word 'perfect' is a Value judgment.--Aspro (talk) 19:37, 6 March 2010 (UTC)[reply]

No, a perfect circle is defined as a figure which has all points on its edge the same distance from its center. It's not based on a value judgment. --70.250.214.164 (talk) 20:23, 6 March 2010 (UTC)[reply]

Measured from the centre with what ? A knotted string, ears of barely corn, ... ect.--Aspro (talk) 20:59, 6 March 2010 (UTC)[reply]

Maybe the question should be better phrased '“have human engineers matched or exceeded the Accuracy and precision of circles that occur in nature? “ '(As for my example of 'perfection': I think octopus rings are 'perfect' circles of deliciousness unmatched (as yet) by any processed food manufacturer -but that is just my own value judgement based on my own pallet).--Aspro (talk) 21:45, 6 March 2010 (UTC)[reply]

The geometric circle is an abstraction in the geometry introduced in the books of Euclid's Elements. It does not exist as a physical object. Buckminster Fuller observes in Synergetics that it is unrealizable.

...We find local spherical systems of Universe are definite rather than infinite as presupposed by the calculus's erroneous assumption of 360-degreeness of surface plane azimuth around every point on a sphere. All spheres consist of a high-frequency constellation of event points, all of which are approximately equidistant from one central event point. All the points in the surface of a sphere may be interconnected. Most economically interconnected, they will subdivide the surface of the sphere into an omnitriangulated spherical web matrix...--Synergetics 224.07 Cuddlyable3 (talk) 00:11, 7 March 2010 (UTC)[reply]

The problem here is the word "perfect" - absolute perfection is impossible in the real world because the world is ultimately made of lumpy molecules with fuzzy edges and all sorts of wiggling with temperature and they have this annoying habit of moving when you try to measure their positions accurately. So there is no such thing as a perfect anything - in nature or otherwise. We talk about the perfect symmetry of snowflakes (they aren't even close to perfectly symmetrical) or that light moves in straight lines (well, not if there is anything with mass causing gravitation anywhere within an infinite distance). However, if you're prepared to live with some very tiny imperfections, nature can come pretty close. Drop a small rock in a still pond and the ripples will move outwards in almost perfect circles. SteveBaker (talk) 00:17, 7 March 2010 (UTC)[reply]

Right, in sufficiently deep-water pond the ripple from a small rock form a near-perfect circle. Also, halos around sun or moon are usually near-perfect circles. A rainbow also has a shape of a circular arc (not a complete circle, though). In still air the soap bubbles are near-perfect spheres. "Near-perfect" really means that the size of the deviations -- stochastic or systematic -- from the perfect circular shape are much smaller than the circle radius. Some of it is indeed due to the "fuzziness" of edges, to thermal motion, to medium anisotropy, to spontaneous symmetry breaking in a general sense, and so on. --Dr Dima (talk) 04:34, 7 March 2010 (UTC)[reply]

Is the sun a perfect circle within the "noise smaller than radius" train of thought? Aaadddaaammm (talk) 09:42, 7 March 2010 (UTC)[reply]

The apparent Sun disk may or may not be close to circular. It depends on the atmospheric conditions, and on how close to the horizon the Sun is. If you are talking about the Sun proper, and not about its apparent disk, then the question arguably becomes moot, as the Sun does not have a well-defined surface at all. The Sun has very low oblateness (of order of 10^-6), so in the sphere-vs-ellipsoid sense the Sun is a near-perfect sphere. However, on a more local scale there are convection cells, filaments, etc., so the "surface" (if you pick a criterion to define one somehow) will have pits and bumps on it. Those pits and bumps will emerge and dissipate on a fairly short time-scale(s). See supergranulation, Coronal loops, Solar flares, Coronal Mass Ejection. --Dr Dima (talk) 19:16, 10 March 2010 (UTC)[reply]

The best freehand drawer of circles (video). Cuddlyable3 (talk) 17:53, 7 March 2010 (UTC)[reply]

Convergent evolution

Do species via convergent evolution have similar DNA because they evolved to be the same, even though they have different ancestors? —Preceding unsigned comment added by Firesidedragon (talk • contribs) 21:25, 6 March 2010 (UTC)[reply]

No. There's lots of ways that DNA could work to produce the same results. A superficial similarity in physical appearance does not mean any genetic connection. --Jayron32 22:09, 6 March 2010 (UTC)[reply]

A similar phenotype can be expressed by different genotypes. The farther apart two species are, the more likely convergent evolution does not result in the same physical features. For example, a bat's wing is very different from a bird's. Imagine Reason (talk) 22:43, 6 March 2010 (UTC)[reply]

And hummingbirds wings are way different from bees, even though both can hover in a flower. StuRat (talk) 05:14, 7 March 2010 (UTC)[reply]

Yea, convergent evolution usually refers to phenotypes, but in principle there's no problem with convergent DNA sequences. Aaadddaaammm (talk) 09:44, 7 March 2010 (UTC)[reply]

Appropriate Technology Film

Hi

I saw an excellent film about 1987 produced I think by the BBC and a United Nations agency looking at the use of appropriate technology in a number of different areas: housing, birth control (Spain), using simple medical workers in a Far Eastern country etc.

I have been unable to trace its name and production details. I would like to get hold of it and find out if there has been a follow up.

If you can help with the these details it would be much appreciated. If not you may be able to refer me to someone at the BBC who may be able to assist.

Thanks —Preceding unsigned comment added by Michael in Dublin (talk • contribs) 23:32, 6 March 2010 (UTC)[reply]

I found a list of videos about appropriate technologies here. You may find a clip from the film you saw. Cuddlyable3 (talk) 23:47, 6 March 2010 (UTC)[reply]

You might find it by using the advanced search of the BFI website [6] --80.176.225.249 (talk) 23:51, 6 March 2010 (UTC)[reply]