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Contents 1 December 17 1.1 cough medecine 1.2 MRI flying object craziness... 1.3 Paraphrasing 1.4 I`ve got a question about a sombero 1.5 What does a ray's cheek do? 1.6 Why does dampening darken? 1.7 Turning Carbon Dioxide into useful fuel 1.8 Relevance of PCR to northern blotting 1.9 Rationale behind touchdown PCR 1.10 Intracortical networks of connections among subsets of cortical regions 1.11 Power Engineering Graduation Project 1.12 Gulls and dolphins 1.13 Moon pictures to show scale

[edit] December 17

[edit] cough medecine

Removed obvious vandalism. -- kainaw™ 02:54, 17 December 2007 (UTC)

[edit] MRI flying object craziness...

Anyone know if there's a list knocking around (in a similar vein to that famous 'list of rectal foreign bodies') of 'ferromagnetic objects eaten by MRI machines'? I was looking at this tonight and I found it darkly humorous. A friend of mine has actually seen several screwdrivers (at once) being pulled into an MRI at high velocity first hand... --Kurt Shaped Box (talk) 01:07, 17 December 2007 (UTC)

I don't know of any definitive list, but one not included in that list are firearms, and I recall reading a news story some years back about a police officer whose gun was sucked into an MRI magnet and discharged, I believe (apparently in 1999, according to this article which mentions the incident). Apparently it has happened more than once; here is another account of such a thing (with photos), though it must be a different time since it says no one got hurt. --24.147.86.187 (talk) 02:17, 17 December 2007 (UTC)

I remember seeing a video once which I believe is an MRI safety video shown to techs involved. I think most of these were demonstration cases but they did show some examples of real world damage. One of the most common hazards are I believe oxygen tanks and the like which are not removed. Of course, some people also forget about their magnetic cards and while not dangerous it would probably be annoying to have to replace all your magnetic cards when they get wiped Nil Einne (talk) 15:59, 17 December 2007 (UTC)

Did it feature a wrench being released into a magnetic field and allowed to impact with a pile of bricks and a bucket? If so, it's here - found it myself last night. Don't know about you - but my first reaction upon seeing that video was "Cool!" followed by "I want that job!". Maybe it doesn't quite achieve its purpose as a safety video, then... --Kurt Shaped Box (talk) 17:51, 17 December 2007 (UTC)

That's an amazing video. It's an absolute classic of the 'boring commercial training video' genre - interspersed with extremely violent and unlikely things happening with a monkey wrench and a multi-million dollar MRI machine! The section about 4 minutes into the video where they are "lowering" the wrench towards the magnet from about 15 feet away using a 200lb breaking strain nylon rope and a winch is incredible. It's like gravity decided to take a short vacation! SteveBaker (talk) 21:28, 17 December 2007 (UTC)

I wonder how many dudes watched that video and immediately decided to go back to the MRI room and fling paperclips into the magnet's gaping maw for kicks and giggles (and to see who could be first to get one to go all the way through and out the other side)? --Kurt Shaped Box (talk) 22:42, 17 December 2007 (UTC)

The thing about paper clips is that they'd be very hard to remove from the magnet. They aren't strong enough to stay bent - so as you try to pull them off, they just un-bend. With most small objects, the only way to remove them is to power down the magnet - but (if you could stand to watch the entire video), that's not an easy procedure. If you just cut the power, the superconducting coils stop superconducting - suddenly they have a resistance and whatever residual current there is (LOTS!) heats up the coils and boils the liquid helium - which then vents from the top of the machine (to avoid exploding) and suffocates everyone in the room. (You can just imagine them screaming for help in those tiny squeaky voices!) Powering one of these babies down correctly in order to pull off a stray paperclip is half a day's work! SteveBaker (talk) 16:57, 18 December 2007 (UTC)

Slightly related... We have been mandated to physically destroy all drives when getting rid of computers because it is possible that the drives have patient data on them. I have repeatedly suggested that we mount a box in the MRI room where we can place drives. The MRI will easily destroy the data (if not the hardware). Then, we won't have injuries caused by flying debris as some tech kid goes at a drive with a hammer to meet hospital policy standards. -- kainaw™ 17:03, 18 December 2007 (UTC)

It's only the ferric oxide that's magnetic - the disks are generally aluminium. The best thing for wiping hard drives is a 'degaussing coil'. In the old days of telephones with bells inside - you could put the drive down underneath your office phone - then go to another desk and telephone yourself. When the bell rang, the rapidly oscillating electromagnetic solenoid would do a fine job of erasing the drive! But putting anything with metal in it into the MRI room is just asking for trouble - and given the cost of MRI machines - I don't think you should be taking such a risk! SteveBaker (talk) 20:14, 19 December 2007 (UTC)

The phone thing wouldn't work with hard drivers tho would it? They tend to be fairly difficult to kill and you need a very strong degausser. I came across [1], about US$20k but maybe better then damaging your several million MRI machine and/or killing someone in the process Nil Einne (talk) 14:26, 21 December 2007 (UTC)

So, would a paperclip actually be harder to remove from the magnet than a wrench (or a swivel chair - did you see the video in the first link I posted)? That somehow sound bass-ackwards. My associate today confirmed that the magnet in his place of employment has also eaten a couple of floor buffers (wot? no article??) in his time there... --Kurt Shaped Box (talk) 22:40, 19 December 2007 (UTC)

Personally I don't know whether that chair removal was advisable. It looked to me like the kind of thing which is not counted in the 'safely removed by two people with their bare hands' the GE video talked about. The machine probably should have been ramped down. You may be able to remove paper clips with non ferromagnetic pliers perhaps although it would probably be a bit risky Nil Einne (talk) 14:26, 21 December 2007 (UTC)

I can't remember, I thought the video had some demonstrations of the stuff that can go wrong (as in real life photos or something) as opposed to simply constructed demonstrations but perhaps I'm wrong since it was in 2003. The video was definitely and old one, it may have been 2 videos. Presuming our friend who wanted to know about Physics in Medicine follows through with his/her plan and end up attending Auckland University perhaps he/she'll be able to tell us if they're still showing it in the Physics course. There is another GE video here with some of the same scenes. [2] (also available from http://www.biac.duke.edu/research/safety/safety.asx] or[mms://vidsrv1.mc.duke.edu/Radiology/MRISafety.wmv direct link]) but which doesn't talk about the cryogenic stuff much. There's also this Siemens video but it's probably a bit more boring although it does show some more stuff being 'sucked' towards the MRI machine (nearish to the middle). From what I've read, I think some kind of wrench scene is 'standard' practice in these videos. The [3] might also be of interest, particularly the chair video (also available here [4] I'm not particularly sure if that follows the GE recommendations of an object which can be removed by two people). The floor buffer news report is also of interest. You don't actually see anything but it seems to be a comedy of errors and it's fortunate that no one got seriously hurt. The janitor ignored the warnings signs and the floor buffer got pulled into the machine then the of three respondents, one lost an earing and the other's hearing aides were destroyed. The The Sahlgrenska Academy also show some demonstrations with watermelons. Some other stuff showing an oxygen bottle, with another tennis ball with steel, not really on safety but a cool MRI explosion video and various images of things that have stuck onto an MRI machine including the chair video linked to above, chair's and floor buffers/polishers actually seem to be the most common. Actually I just realised this is what the OP linked to but nevermind. Some more stuff if you're researching the topic in general and not just looking for 'cool' stuff [5], [6], needs free registration, [7] & [8]. On a more sobre note, these accidents can of course be deadly serious. According to [9] at least 8 people have been killed in the US from 1995 - 2005 from MRI related incidents including I presume the death of a 6 year old boy who was crushed by an oyxgen tank. (Many other deaths seem to to related to metal clips and stuff [10]) Nil Einne (talk) 14:10, 21 December 2007 (UTC)

[edit] Paraphrasing

It is my opinion that Wikipedia should allow paraphrasing in cases where sources are particularly scientific, heavily syntaxed, or in a foreign language. If this is already allowed, please tell me where the guideline for it can be found. Magnonimous (talk) 01:27, 17 December 2007 (UTC)

Uh...what? If we weren't allowed to paraphrase our sources, Wikipedia would consist of nothing but direct quotes. I'm really not sure what you're asking though, but this is really a question for the village pump, as this desk is reserved for questions about science, not about Wikipedia itself. Someguy1221 (talk) 02:54, 17 December 2007 (UTC)

[edit] I`ve got a question about a sombero

Hello,I got ANOTHER question and yes it is the SOB who asked about the empire state building.I`ve got another question from PHYSICS WEEKLY.A man with a sombero stands 34th Street,unaware that a physics expierment is in progress. If a penny hits His sombero,will the sombero be knocked off His head. —Preceding unsigned comment added by 71.249.154.50 (talk) 01:56, 17 December 2007 (UTC)

As I stated in answer to your previous question... The penny will not possibly make it to the street level. So, it is impossible for the penny to hit the sombrero unless this man is nearly as tall as the Empire State Building and his sombrero is overlapping one of the upper floors. If so, the answer would still be "no" because the sombrero would likely weigh a few hundred pounds and be unaffected in any way by a little penny. -- kainaw™ 02:57, 17 December 2007 (UTC)

If the penny hit the sombrero (which, as Kainaw points out - is dubious at best) then he'd certainly notice it. When the Mythbusters built a gun to shoot pennies at "from the top of the Empire State Building" speeds, they could shoot it at exposed skin without producing more than a brief stinging - no broken skin, no bruising. Sounds to me (without evidence) that this would probably not be enough to knock off the sombrero - but you'd definitely feel the impact. SteveBaker (talk) 03:50, 17 December 2007 (UTC)

(Pedantry alert!) It is highly unlikely that the penny would knock the sombrero from his head. This question is not necessarily related to the previous one. There are many cities with a "34th Street" and he may be in a city other than New York. The question does not state that the physics experiment in progress involves a penny being dropped from the top of the the Empire State building, nor that the physics experiment involves a penny at all or even that it is anywhere near the man. The mentioned experiment could be someone testing the aerodynamics of paper airplanes during a blizzard in Antartica. The question asked "if a penny hits his sombrero...", not if "a penny dropped from the top of the Empire State building hits his sombrero..." Statistically, if any penny hits his sombrero, that penny is much more likely to have come from a ground level or near ground level source and is unlikely to have the force necessary to knock the sombrero from his head. Hmm... the question doesn't even specify whether or not the man is wearing the sombrero, merely that he has one. He may be holding it in his hand, in which case it would be impossible for it to be knocked from his head. Statistical analysis of the variables would show that the likelihood of a penny hitting his sombrero and knocking it from his head approaches zero. Thus, the answer is "No." 152.16.16.75 (talk) 11:25, 17 December 2007 (UTC)

So the purpose of that utterly useless answer was what? To show us all how clever you are? It didn't work - and it certainly didn't help the OP. You know full well what was being asking: We are told that this was in continuation of an earlier question about dropping pennies from the empire state building - and it was specified that: "If a penny hits His sombero..." - so that a penny hit the sombrero is a "given". Your response was a waste of electrons. Thanks. SteveBaker (talk) 13:56, 17 December 2007 (UTC)

I wish we had a WP:CIVIL template that contained about 30 pages of exceedingly sarcastic filler. I so much want to use a CIVIL template with the obvious intent that you beat me to the uncivil comment. -- kainaw™ 15:53, 17 December 2007 (UTC)

The question doesn't state what size the sombrero is. The physics experiment could be "The Physics of throwing Pennies horizontally at People wearing Small Sombreros." So the answer is possibly, but we don't have enough information. PLAYER ONE please insert FUNDING to continue. Lanfear's Bane | t 19:50, 17 December 2007 (UTC)

Since it's unspecified, I was assuming an ISO-standard sombrero - but if the penny turns out to be a pre-decimalisation British penny - then all bets are off. SteveBaker (talk) 21:24, 17 December 2007 (UTC)

To find an actual answer to this problem (instead of just being a smartass), we first need to find an estimate of the terminal velocity of the penny. This page says it's about 11 m/s, but Mythbusters says it's about 45 MPH[11], which is about 20 m/s. So we'll take the average of the two, and assume the speed of the penny as it strikes the sombrero is about 15 m/s. The mass of a penny is 2.5 g, so the kinetic energy of the penny as it strikes the sombrero is about 0.28 joules. The problem is complicated in that there are a lot of different ways that the penny could land on the sombrero, and there are a lot of different styles and masses of sombreros. But I'll assume that the penny lands such that it has maximum effectiveness in overcoming the gravitational potential energy barrier involved in getting the sombrero off of the head. I don't have data on the average mass of a sombrero, but the average mass of two straw hats I have is about 100 g. .28 joules is enough energy to lift a 100 g hat about 29 cm. So the answer is yes, if the penney hits the sombrero right, it could easily knock the sombrero off his head. MrRedact (talk) 21:31, 17 December 2007 (UTC)

Hmmm - I'd hoped this thread wouldn't come to this! But the penny is moving DOWNWARDS - and to remove a sombrero, you need some kind of upwards force. If the coin hits anywhere in the middle, it's mostly going to simply wedge the hat harder onto the victim's head. The best chance the coin has is to strike the edge of the sombrero - perhaps at the very edge at the back for maximum leverage. Then it has to rotate the hat backwards to a sufficient angle that gravity will do the rest and permit the hat to simply fall to the ground. Thus this is a question of the torque that can be applied to the edge of the sombrero - which has to be enough to overcome the frictional torque of the hat-band against our victims' hair. However, there is a limit to how much force it may apply because the copious brim of the headgear will bend - thereby reducing the amount of downwards force - and applying a force inwards towards the head - which again will tend to force the hat back onto the victims head. So in order to stand any reasonable chance to calculate the consequences, we need to know: The frictional coefficient of hair (or perhaps bald head) against hat brim. The statistical prevalence of baldness amongst sombrero-wearing residents of 34th street (weighted for seasonal factors and a gaussian distribution of hair spray concentrations). The tightness of the brim (and thus the force exerted by the brim normal to the surface of the head). The maximum force that may be applied to the brim of an ISO standard sombrero before it starts to deflect - and subsequently, the rate of resistance to that bend as a function of curvature. This will require a considerable amount of experimentation and measurement and an alarming number of expensive machines that go "beep" occasionally. A cost-conscious researcher who is not under pressure of time might consider it to be more cost-effective to find an undergraduate research assistant at the department of Sartorial Ballistics at NYU and have them stand on 34th street and await the inevitable. A second student should stand three blocks away to act as a control. SteveBaker (talk) 23:10, 17 December 2007 (UTC)

The question explicitly makes the assumption that the sombrero wearer is unaware that a physics experiment is in progress, so a research assistant probably wouldn't be a valid subject. That makes a difference because if the subject isn't a research assistant, he'd be more likely to be a tourist, who'd be more likely to be tilting his head up to admire the famous Empire State Building, or tilting his head down, wondering why there were so many pennies lying on the sidewalk in that area, either of which would make the sombrero easier to knock off. Another complicating factor is that sombreros commonly come with a string that can be tightened under the chin. If the man actually keeps his sombrero string tightened, it'd be really difficult to knock off the sombrero with 0.28 joules, no matter where or in what direction that energy was applied. So we also need to know what fraction of sombrero wearers on 34th street keep their drawstrings tightened. MrRedact (talk) 01:49, 18 December 2007 (UTC)

You are all assuming what the physics experiment is, it doesn't actually say... the OP simply mentions that he asked a previous question regarding the Empire State Building and then continues that a further experiment is taking place on 34th Street. For all we know the experiment could be some sort of explosion. (Also can't we squeeze a 'hats off' pun in here somewhere?). Lanfear's Bane | t 16:39, 18 December 2007 (UTC)

Well one good thing to come from this is that I learn what a sombrero was (or what a Mexican hat is called) Nil Einne (talk) 14:29, 21 December 2007 (UTC)

[edit] What does a ray's cheek do?

Yesterday I went to the aquarium and saw a whole bunch of rays. Just behind their eyes they had large holes that led into some kind of internal cavity. The article on stingrays tells me these are called cheeks and are prized for making soups, but doesn't say what they are and what they are for. The gills, nose and mouth are all on the ventrical side so it isn't one of these organs which have migrated. Anyone know anything more? The bellman (talk) 02:39, 17 December 2007 (UTC)

These openings are called spiracles and they connect with the gill chambers as an auxiliary source of sea-water. I guess it makes sense when you think about the ray resting on the sea-bed, the spiracles would supply the gills with sea-water instead of the ray having to suck in sandy debris from under its body. Richard Avery (talk) 11:23, 17 December 2007 (UTC)

[edit] Why does dampening darken?

Why is a wet sidewalk darker than a dry one? Why does wetting dry concrete cause it to absorb more light and reflect less light? More generally, why does this happen for other materials (wet towels are darker than dry towels, etc.)? arkuat (talk) 05:42, 17 December 2007 (UTC)

That has to do with the reflective properties of the air-material, air-water and water-material interfaces. See Fresnel equations for details, but in essence the reflected fraction of light on an interface with 2 different refraction coefficients n0 and n1 is

Now the refractive index of air is about 1, of water about 4/3 and of asphalt it's a larger number which I don't know exactly. Considering dry asphalt, the reflected fraction is

Considering wet asphalt, it's more complicated: Light can be reflected at the air-water interface, or it can pass the air-water interface and be reflected by the water-asphalt interface. In the latter case it can either pass the air-water interface directly or be again reflected towards the water-aspalt interface etc. Calling the reflection coefficients r_air-w and r_w-asph, this mathematically results in the following infinitely nested expression for the total reflected light:

By defining

we can use the fact that X is "self-similar":

The total reflected fraction for the wet asphalt is therefore

Now we can substitute the known single-interface reflection coefficients (as computed with the formula from the Fresnel equations) (edit: the numbers are wrong, see below):

You can do a few more mathematical manipulations to show that high values of n_asphalt result in a lower total reflected fraction in the wet case or - if you are lazy - you can insert a high value (e. g. 20) for n_asphalt.

In reality things are more complicated due to rough surfaces etc.; this is a simple model (and from the fact that the differences in reflectance are rather small in this model, it seems to me that I've overlooked something - please tell me what). Icek (talk) 07:51, 17 December 2007 (UTC)

An answer the the questioner can understand? If that's not being too blunt. Richard Avery (talk) 09:15, 17 December 2007 (UTC)

I don't know whether the questioner or you (Richard Avery) understand the answer, but in short: Reflection from an air-asphalt interface is higher than the combined reflections occurring at the interfaces when water is between air and asphalt, because water has a refractive index lying between the refractive indexes of air and asphalt. Icek (talk) 10:54, 17 December 2007 (UTC)

That was an impressive amount of math - but there is a MUCH simpler way to answer this. Water is shiney - concrete isn't. When something is shiney, most of the incoming light is bounced off in a very narrow angle. If you stand in exactly the right place, you'll see the puddles are REALLY bright because they are reflecting the sun into your eyes. That doesn't happen with concrete - it's rough and reflects the sunlight off in all directions more or less equally. So from MOST angles, the puddles look darker because they aren't reflecting light in your direction - but from that one very special angle, the water acts like a mirror and the water is much, MUCH brighter than the concrete. So on the average, there may not be much of a difference between the two - but from most directions, the water is simply not reflecting any light in your direction but the concrete is sending some light towards you - so the water looks darker. SteveBaker (talk) 12:42, 17 December 2007 (UTC)

Thank you Steve. Not only did I miss what should have been obvious, but my model doesn't even really predict the correct sign of the effect: If the refractive index would be really so high that my model predicts a darkening with water, the dry material should be brighter than it is. At a relatively low refractive index (e. g. 5, the dry reflectance being 4/9 which is brighter than some asphalts I think), my model actually predicts that the reflectance is higher in the wet state. Icek (talk) 15:03, 17 December 2007 (UTC)

But Steve (and what kind of rapping name is Steve anyway), when you drop a drop of water onto concrete it absorbs it, and turns dark, and doesn't reflect most of the light to a specific angle like you've said. Care to explain that? --antilived^{T | C | G} 05:00, 18 December 2007 (UTC)

You're not looking at the right scale! Concrete is pretty much 100% waterproof - the water isn't being absorbed by the concrete - it's filling in the microscopic roughnesses in the surface of the concrete. Since the water has strong surface-tension, the surface of the water remains fairly smooth and it adheres well to the rough surface - making you think that it has been "absorbed". So the wet area reflects light specularly as I've described. SteveBaker (talk) 16:48, 18 December 2007 (UTC)

But the problem is that if the water surface is rough at larger scales, the direction of the specular highlights should be more or less randomly distributed, adding to the apparent brightness. Icek (talk) 05:26, 19 December 2007 (UTC)

Yes - it the water was rough, that would be true. But why do you think the water surface is ever rough? Gravity tends to make all of the tiny puddles have the same orientation. SteveBaker (talk) 20:09, 19 December 2007 (UTC)

The water somehow follows the original surface on larger scales and doesn't leave any spot dry - so it has to be rough. If we look at this image, we can see the tiny specular highlights in the wet part, and if you scale the image so that you cannot distinguish them anymore, the dry part still looks brighter. But I think there is one further effect which should make the wet part actually brighter: The color of the dry dust is due to light which enters dust particles and gets partially absorbed and partially reflected. In the wet case, less light reaches the particles and water should have a lower absorbance than the dust particles. Icek (talk) 03:49, 20 December 2007 (UTC)

I think all this discussion of the "roughness" of the water surface is ignoring the effects of surface tension too much. But thanks for the basic explanation: interaction of reflection and refraction indices of three different phases (air, water, and solid) rather than two (air and solid). --arkuat (talk) 22:48, 20 December 2007 (UTC)

I think my original explanation was valid - but I messed up the numbers (apparently nobody checked my math). My r_air-w was wrong, it shouldn't be 16/49 but only 1/49!

gives realistic numbers. Icek (talk) 07:46, 20 December 2007 (UTC)

[edit] Turning Carbon Dioxide into useful fuel

Allright Smartguys,

[Here]'s an article from MIT Tech Review describing a solar parabolic mirror that focuses solar rays onto a ferric-oxide ceramic, heating it up 1500 Centigrade, which liberates oxygen from the iron. The ceramic is then brought into vicinity of CO2. The hot iron steals an oxygen atom from the CO2, leaving a CO molecule. This is described as reversed combustion. So, my question is, how is CO then turned into a Hydrocarbon fuel? My guess is that water H2O is somehow used to convert CO into HCHCHC molecules, right? Can anyone state the simple steps in terms of + / - bond energy required for each step? Thanks!

--InverseSubstance (talk) 05:53, 17 December 2007 (UTC)

Well, you can burn carbon monoxide directly in air to get back to carbon dioxide - so there might not be a need to do any more steps to recover the energy at the output. But let's be really clear about this for the benefit of readers who may not fully understand what's going on here: This process isn't using Carbon dioxide as a 'fuel' - no energy is extracted from the CO2. What we have here is a solar power plant whose output energy is in the form of carbon monoxide. It's not going to help global warming any more than a regular solar power plant does because the CO2 it pulls out of the air gets turned back into CO2 when you burn whatever fuel it produces. So whether this is really of much interest depends on the overall efficiency of the plant - and how convenient the fuel it generates is for existing energy consumers. I'll defer to our chemists to answer your question properly. SteveBaker (talk) 12:36, 17 December 2007 (UTC)

As to the use of CO as fuel, you might want to see our articles on Coal gas, Producer gas, Syngas, Water gas, and the links onwards from those articles.

Atlant (talk) 13:23, 17 December 2007 (UTC)

It is plausible that this could be someone's idea of a closed loop system. Use solar power to turn CO2 into CO. Burn the CO to boil water and turn a turbine to create electricity. Capture the CO2 and use solar power to turn the CO2 into CO. However, if the mirror can reach temperatures of 1500C, why not use the mirror to boil the water and take the CO2 and CO out of the equation? I know - it will only work when the sun is out - but it is apparent that CO will burn to CO2 much faster than this can turn CO2 into CO anyway. So there will always be lag time waiting for fuel. -- kainaw™ 13:28, 17 December 2007 (UTC)

Having read the article, I think you must be right. This thing can't just pull CO2 out of the air - it needs pure CO2 to be fed to the hot iron ceramic because any oxygen in the mix would presumably bind to the iron in preference to the oxygen atoms from the CO2 - which would result in major inefficiencies in the system. So they first have to purify their CO2, which would be a costly and energy-intensive process. However, if it's a "closed loop" arrangement then that wouldn't be an issue - the CO2 would simply convert to CO and then back to pure CO2 to go back to the hot iron. But as you say - why they don't just use solar power to produce steam is anyone's guess. SteveBaker (talk) 14:06, 17 December 2007 (UTC)

What's the energy density of CO versus, say, H₂ or Methane? Does it at least make CO a competitive energy storage medium?

Atlant (talk) 16:30, 17 December 2007 (UTC)

The standard enthalpy change of combustion is -283 kJ/mol. If you want to liquify it, you need to cool it to 81 K (compared to about 20 K for hydrogen), the density is (according to the NIST Chemistry Webbook) about 30 mol/l, so you get about 8490 kJ/l. Liquid hydrogen has 0.07 kg/l = 35 mol/l, corresponding to 8464 kJ/l. So the energy density per volume is about the same, with less prohibitive temperature requirements for carbon monoxide. Methane has a higher boiling point of 111 K, a liquid density of 422.62 g/l = 26.3 mol/l, and a standard enthalpy of combustion of -891 kJ/mol, thus it has an energy density of 23,472 kJ/mol 23,472 kJ/l, and is clearly the best choice of the 3 gases if volume is the limiting factor and refrigeration is possible. Icek (talk) 18:37, 17 December 2007 (UTC)

(Presumably, that last number was meant to be "23,472 kJ/l".) Thanks for that great analysis!

Atlant (talk) 23:20, 17 December 2007 (UTC)

It's not really what the article advocates, but if I had to guess, I'd think the real goal is to create a "free" process that converts CO2 into more or less anything else. Right now, all of the processes that chemically reduce CO2 require both significant inputs of energy and the consumption of reactants like CaO. This reactor apparently requires only CO2 and an input of heat (currently provided by sunlight) in order to reduce CO2, with no expensive reactants. Since heat and CO2 are two things that power plants have in abundance, this could be a virtually free way to reduce the carbon emissions per unit of energy produced by the plant. Dragons flight (talk) 16:39, 17 December 2007 (UTC)

Methanol would be the next locical step. There is a catalytic pathway to form it catalytical at high tem from CO and Hydrogen.--Stone (talk) 15:49, 17 December 2007 (UTC)

Allright! That article on Methanol helped me understand the process better. Thanks! --InverseSubstance (talk) 17:44, 17 December 2007 (UTC)

[edit] Relevance of PCR to northern blotting

For PCR: PCR allows isolation of DNA fragments from genomic DNA by selective amplification of a specific region of DNA. This use of PCR augments many methods, such as Southern and northern blotting and DNA cloning, that require large amounts of DNA, representing a specific DNA region. - but PCR is all about DNA and northern blotting is all about RNA, right? Are they talking about making probes? While I'm on the topic, I wonder why we don't have RNA PCR using an RNA polymerase derived from Taq or wherever? --137.120.3.221 (talk) 09:48, 17 December 2007 (UTC)

If you make cDNA from mRNA you can PCR the RNA sequence too. This is quite common especially if you want to amplify the ORF as seen in the mature RNA. David D. (Talk) 10:00, 17 December 2007 (UTC)

Then perhaps the current northern blotting article is somewhat misleading. What about the RNA polymerase idea? Or is it just not worth it? Seans Potato Business 10:18, 17 December 2007 (UTC)

Why is it misleading, the article does not mention PCR?

The RNA polymerase idea would not work since the template is DNA but the product would be RNA. Thus, the amplification would not be exponential as the original DNA template would be the only one used each time. In PCR, with DNA polymerase, the products are also new templates. David D. (Talk) 12:44, 17 December 2007 (UTC)

Oh yeah, sure. Are there no RNA polymerases out there that use RNA as a template? Some viruses with RNA genomes that don't use reverse transcriptase? Anyway, the northern blotting article is misleading because it says that it uses RNA and in actuality it can use cDNA that has been produced from mRNA. --Seans Potato Business 13:44, 17 December 2007 (UTC)

Northern blots are never done with cDNA, so the article is correct. PCR from an RNA starting material would use cDNA. The RT-PCR link that JWSchmidt mentions below explains the process. David D. (Talk) 16:02, 17 December 2007 (UTC)

• There is a PCR method that is relevant to the goal of northern blotting; see RT-PCR. The quoted statement at the start of this thread might better say something like, "PCR augments other methods, such as Southern and northern blotting that attempt to detect a specific DNA sequence. In general, methods such as Southern and northern blotting require a larger amount of starting nucleic acid than do the related PCR-based methods of target sequence detection." --JWSchmidt (talk) 14:34, 17 December 2007 (UTC)

So you're saying that the article should say that RT-PCR is an alternative to northern blotting? It doesn't really augment northern blotting? I'm pretty sure that the original says that you amplify the DNA for use in northern blotting. Even if you change DNA to nucleic acid, it still isn't right if you can't use PCR to amplify RNA for direct use in a northern blot. --Seans Potato Business 19:57, 17 December 2007 (UTC)

" amplify the DNA for use in northern blotting": this is wrong although I didn't notice that in the northern blotting article. David D. (Talk) 20:26, 17 December 2007 (UTC)

• "PCR augments other methods...." in the sense that it can "supplement" for-, make up for a deficiency in-, or be an alternative to the older methods. Its probably best to not use the word "augment" at all because it gets people thinking that it is used to improve the other methods, which is not generally the case....its usually a matter of providing a more sensitive alternative detection method. --JWSchmidt (talk) 03:23, 18 December 2007 (UTC)

[edit] Rationale behind touchdown PCR

According to the touchdown pcr article, the idea is that more specific primer-template annealing occurs at higher temperatures, so that the early phase amplifies the sequence of interest and due to the exponential nature of PCR, the later phases using lower anealling temperatures will amplify mostly the sequence of interest. However, it will also clearly amplify sequences to which the primers bind non-specificially, so where is the incentive? There must be something better about the lower annealing temperature phase to make it worth changing from the more specific one (i.e. if touchdown PCR gives acceptable results, traditional PCR will give even better results - so why bother?) --Seans Potato Business 10:32, 17 December 2007 (UTC)

There are two related issues, efficiency of primer binding and specificity of primer binding. Lower temperature can increase efficiency of binding and increase yield of amplified DNA, but at the risk of having unwanted amplification products dominate the PCR. Higher temperature can increase the specificity but can also decrease the yield. "There must be something better about the lower annealing temperature phase" <-- just to get enough product to work with. --JWSchmidt (talk) 14:20, 17 December 2007 (UTC)

[edit] Intracortical networks of connections among subsets of cortical regions

I'm seriously stuck. I've read this phrase over and over again but it doesn't make sense. Does anybody understand what could be meant by: "Intracortical networks of connections among subsets of cortical regions"???
It is supposed to be a solution to the binding problem and a mechanism called reentry (we don't yet have a neuro article about it) is supposed to be part of this solution. Lova Falk (talk) 18:55, 17 December 2007 (UTC)

Articles such as Cerebral cortex, Visual cortex, Broca's area discuss the fact that the cerebral cortex is functionally divided into areas that carry out specialized functions. Watch a falling apple. Although different cortex areas specialize for processing color and motion, we are usually consciously aware of seeing a unified "object" that has both color and motion.....we do not experience the motion and color as independent "reports" of what is in the visual field. What "binds" the activity of multiple cortical areas into a single coherent conscious experience? Many people imagine that there is a homuncular "center of consciousness" that might collect and unify all of the computational results from many distributed cortical areas. However, that does not seem to be the case and many people suspect that our conscious awareness is also distributed and largely co-extensive with the many specialized and distributed cortical areas that include the various specialized areas of visual cortex, such as those for color and motion detection. Conscious unification of what is going on in multiple cortical areas would seem to depend on the continual function of "intracortical networks" that connect "subsets of cortical regions". Some theories propose that cortical brain activity only enters into conscious awareness when there is a special type of feedback in such intracortical networks, allowing a kind of "resonance" in the neurons of linked cortical regions. Of course, connections to other brain regions such as the thalamus are also important, so I doubt if intracortical networks can by themselves account for "binding". --JWSchmidt (talk) 21:00, 17 December 2007 (UTC)

[edit] Power Engineering Graduation Project

I am Power Engineering undergraduate student, and I am seeking for a research subject for my graduation project.
Can you suggest a subject please :) Smart_Viral ^(talk) 18:58, 17 December 2007 (UTC)

You can try to find ways to reduce the transmission loss. That is basic and challenging both as an undergraduate. I am very concerned about the huge amount of power that we lose in transmission. Power is one of the most important factors in moving and shaking today's world, and if you think calmly, you can get plenty of decent ideas. By the way, I guess that the duration of your project is one year, right? - DSachan (talk) 19:44, 17 December 2007 (UTC)

Yes two semesters. Thank you. Smart_Viral ^(talk) 21:04, 17 December 2007 (UTC)

Another idea might be to think about, and plan for, how one might address the intermittency problems created by large scale use of solar / wind power. Dragons flight (talk) 21:23, 17 December 2007 (UTC)

"Advanced Strategies to Contain and Minimize System Collapse After a Local Fault" -- Of late, the power grid in North America seems to have lost a lot of its former resilience, and relatively minor, local faults have cascaded into major, region-wide power outages.

Atlant (talk) 23:27, 17 December 2007 (UTC)

One possibility would be to do a further study on whether there is a higher incidence of health risks due to prolonged close exposure to high voltage electric current in power lines or transformers. A number of studies have been laying down what seems to be a pretty convincing case of this, but further research is definitely needed. One paper done in 2000 discusses this here.[12] Another possible angle on this would be to find some way to affordably reduce this potential health risk. That could be a very good seque into becoming very wealthy if it produced something that can be manufactured and marketed. Saukkomies 01:21, 18 December 2007 (UTC)

Perhaps I'm mistaken, but wouldn't your first project suggestion be more suited to someone involved in epidemiology rather then power engineering? Nil Einne (talk) 12:24, 18 December 2007 (UTC)

I'm pretty sure that doing that particular research project would ensure that one's career in power engineering never even gets started.

Atlant (talk) 14:02, 18 December 2007 (UTC)

An article in this month's Scientific American suggests that high-voltage direct current transmission technology will become increasingly important as more and more energy is generated from renewable resources in remote locations and has to be distributed over longer distances to reach major population centres; that might make an interesting research topic. However, the most pertinent advice you can get on suitable topics will come from your supervisors, or from looking at the work done by previous students on your course. Gandalf61 (talk) 15:34, 18 December 2007 (UTC)

Just FYI: The increased use of HVDC transmission also has positive impacts on the problem I raised: system stability. Because there's no phase or frequency relationship between the various generators in an HVDC system, it's easier to manage power flows.

Atlant (talk) 17:46, 18 December 2007 (UTC)

thanks Smart_Viral ^(talk) 17:09, 21 December 2007 (UTC)

[edit] Gulls and dolphins

Maybe it's just me - but does anyone else see the similarity in body shape between gulls and dolphins when viewed side-on (if we ignore the wings and flippers)? I don't think that this could technically be described as Convergent evolution, as they are from completely different ecosystems - but is there a term that describes this phenomenon? --Kurt Shaped Box (talk) 19:25, 17 December 2007 (UTC)

Aerodynamic? David D. (Talk) 19:40, 17 December 2007 (UTC)

That makes sense - they both have to 'glide' smoothly through a fluid - convergent evolution is quite likely. A dolphin looks quiet a lot like an upside-down racing yacht too (complete with 'keel')...I'm betting that's no accident either. —Preceding unsigned comment added by SteveBaker (talk • contribs) 21:20, 17 December 2007 (UTC)

That would have to be a case of convergence. Dorsal fins exist to stabilize and help the creature turn, and such keels serve the exact same purposes on a ship. 81.93.102.185 (talk) 22:18, 17 December 2007 (UTC)

The design you're talking about - that streamlined curvy shape of the dolphin and seagull - is also found in a number of other animals as well. It's a fairly useful design, and as was noted, an example of convergent evolution. It is interesting to note that in the time of Elizabeth I a Master Shipwright by the name of Mathew Baker set about to design a new type of fighting ship that could outperform the traditional sailing ships of the day. He wanted to design the hull of his new ship so that it would be able to be faster, more stable, and more responsive than the bulky floating castles that were being built by the Spanish and other nations. To accomplish this, he went to nature for inspiration, and ended up taking the actual dimensions of a codfish's anatomy, and replicated it in designing the hull of his ship. There is a famous drawing of his somewhere (but after a futile search I can't seem to find it online) in which Baker superimposes an oversized codfish on top of his ship's design to show the common features of both. The result of Baker's design was a new breed of ship, the first of which was the famous HMS Revenge. Elizabeth was so captivated by Baker's design that she ordered more of these ships to be built, even though many of her advisors were opposed to the idea. When the Spanish Armada arrived off of England's southern shores in 1588, many of the English ships that were used to defeat the Spanish had been constructed using Baker's new hull design. They were able to sail circles around the Spanish ships, outmaneuvering them, outsailing them, and due to improvements in English cannons, they could stand out of range of the Spanish ships' artillery and outgun them. This new development in shipbuilding won the day for the English, and changed the way that ships were built from that point on.

So, this all is meant to show that convergent evolution might also apply to artifacts that are constructed - not just developed through natural selection of species. The fact that a human being designed something based on another design in nature might be seen as yet another kind of "evolution"... At any rate, the shape of the gull and dolphin is the same basic shape of a codfish, which is also the same basic shape of the Galleons that Mathew Baker designed in Elizabethan time. -- Saukkomies 09:55, 19 December, 2007 (UTC)

This doesn't seem to be mentioned anywhere in the WP article, but I remember seeing a documentary where it was stated that the design of the Supermarine Spitfire was inspired by the body and wings of gulls. So, yet another occasion that this particular shape has helped to protect the green fields of England from the forces of darkness? ;) --Kurt Shaped Box (talk) 22:33, 19 December 2007 (UTC)

[edit] Moon pictures to show scale

Have anyone yet put maps of countries onto a spherical model of the moon, in order to give a good impression of the scale of the moon compared to earth? 81.93.102.185 (talk) 19:55, 17 December 2007 (UTC)

You mean putting the countries on the moon at their actual size, showing that not as many fit (since the moon is smaller than the earth)? When I was young, I had a book that showed that the visible surface of the moon was about the right size to hold Australia. But I don't remember the book. -- Coneslayer (talk) 20:23, 17 December 2007 (UTC)

Yes, that would be the exact way. And thanks, that does give a rough sense of scale. :) 81.93.102.185 (talk) 20:24, 17 December 2007 (UTC)

That is an interesting idea. I don't think I've seen maps like that. A quick search turns up the usual comparison graphics showing the whole Earth and the whole Moon globes at scale, like this one at the Wikipedia Commons. I did find a picture showing the United States on Mars. It was apparently made with the free and cool program Celestia, via an add-on created by the person who made that Mars image, available here. So it probably wouldn't be too hard to make a similar image for the Moon. Pfly (talk) 21:10, 17 December 2007 (UTC)

According to moon and Australia, the surface area of the moon is about five times greater. Algebraist 23:57, 17 December 2007 (UTC)

I guess the idea is that the equatorial plane (i. e. cut the central slice of the moon) has an area comparable to Australia in size. Pallida  Mors 06:20, 18 December 2007 (UTC)

The thing that makes this messy is that you can't take a continent that's curved to match the radius of the earth, flatten it out and then re-curve it onto a sphere of different radius without some severe distortions to it's shape. So when you try to make maps like this (less so for Mars - more so for the Moon), the distortions become so great that the effect you were trying to achieve of showing relative scale gets overwhelmed by the distortions you have to introduce in order to make a valid comparison. I presume this is the reason why the map that Coneslayer recalls seeing was incorrect - according to Pallida_Mors_76, it should have been less than half that size - but whoever made the map didn't think to re-project it correctly for the curvature of the moon. SteveBaker (talk) 16:34, 18 December 2007 (UTC)

That's true -- mapping the United States onto the Moon, like that Mars version above, would be a reprojection mess. I suppose one could achieve the desired effect by using a political unit appropriate for the scale... maybe the British Isles on the Moon would not distort too badly yet give a sense of the size of the Moon. Just a random thought. Pfly (talk) 23:04, 19 December 2007 (UTC)