Wikipedia:Reference desk/Archives/Science/2008 November 23

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November 23

i need a help please in organic chemistry

important question I am a student at first year of medicine in italy and i searched for material in organic chemistry for the difference between the d/l structure and the r/s structure and i didn't fine info about this specific material and i need this in 2 days so first what D/L and R/S and what are the difference please answer fast and send me the answer to my e-mail because i don't have account my e-mail: [email address removed] and i am sireas about this thank u anyway .

—Preceding unsigned comment added by 151.60.86.123 (talk)  

Any answers will be given here, we don't respond by email. Therefore, I've removed your email address to protect you from spam. --Tango (talk) 01:47, 23 November 2008 (UTC)

You might want to look at Chirality (chemistry) or Wikibook's Organic Chemistry. -- JSBillings 01:52, 23 November 2008 (UTC)

There are three ways to consider the chirality of a molecule, and you will find all 3 systems in use:

• the d/l or +/- system: A polarized light source, when shined through a pure chiral compound, will rotate the light some number of degrees one direction or the other. If the light rotates right, this is called "dextrorotary" and if it rotates left its called "levorotary". In a pair of stereoisomers, one molecule will always rotate the light to the right, and this is indicated as either "+" or "d" (always lowercase d); while the other which rotates light to the left is called either "-" or "l".
• The R/S system (aka the Cahn–Ingold–Prelog priority rules): When looking at the stereocenter in a chiral molecule, assign the 4 groups attached to this atom a priority number based on molecular mass. Thus, the smallest attached atom is assigned "1" on up to "4" for the heaviest attached atom. Arrange the molecule so #1 is away from you and #4 is straight down. Look at 2 and 3. If the order increases to the right 2 --> 3 then the molecule is called the "R" stereoisomer. If the order increases to the left 3 <-- 2 then the molecule is the "S" stereoisomer. This system has no correlation to the d/l system above. Sometimes the R is the d isomer, and sometimes the R is the l isomer.
• The D/L system (which usually applies ONLY TO SUGARS). Note that this system uses capital D and L, not lowercase as above. The two systems have no connection to each other. In the D/L system, the molecule is compared to glyceraldehyde which has two enantiomers, labeled D and L. In this molecule, D=R=+ and L=S=- to compare to the other systems. If you look at the Fischer projection of glyceraldehyde, the middle carbon has one of two configurations. The D is the one with the H-C-OH fischer configuration, while the L has the HO-C-H fischer configuration. In all other sugars, such as glucose, look at the analogous carbon (the second one down on the Fischer projection). D-glucose has the same configuration at this carbon as D-glyceraldehyde, while L-glucose has the same configuration as L-glyceraldehyde. For sugars, which have MANY stereocenters (glucose has 4 for example, meaning it has 16 possible configurations) the R-S system makes little sense... --Jayron32.talk.contribs 02:50, 23 November 2008 (UTC)

D/L is also for amino acids. Also, D/L only tells you which of two enantiomers (it defines one stereocenter only, even if a molecule has more than one), so one needs some other method to figure out the rest (i.e., among different diastereomers). The name "glucose" defines all the relative stereochemistry (diastereomers), and one just needs "some way" to figure out which enantiomer. Either R/S or D/L would work equally well for that task. The advantage of D/L is that it also makes an implicit assumption about which stereocenter you're talking about, since every stereocenter has R/S possibilities. DMacks (talk) 17:12, 23 November 2008 (UTC)

Television Logo Removal

Is there any device or software that can not merely blur, but interpolate shapes in television pictures to restore the spoiled scene behind the opaque Digital On Screen graphic, as broadcast by ITV 2 and also can any device get rid of the non-opaque DOG on BBC HD, preferably in real time? Are there any programmable custom devices for doing this sort of video processing? Also what technology would be required to re-broadcast the logo so that it covered the entire screen on everyones television? Trevor Loughlin (talk) 02:29, 23 November 2008 (UTC)

Since the information 'behind' the logo has never been transmitted, it's impossible to restore the missing stuff. The old-style translucent logos could be somewhat removed - but an opaque one is a really hard problem. Silicon Graphics had a software solution that did a reasonable job of removing translucent logos - but I don't think they sold it commercially. Detecting the logo is mostly fairly easy (it's the one thing on the screen that doesn't move) - but with the animated logos we're starting to see on some channels - we're really screwed.

Rebroadcasting is also not reasonable - you'd have to rebroadcast on the same frequency - so your transmission would interfere with the original and result in a mess - the amount of transmitter power you'd need to put out to override the original channel would demand massive transmitter towers and so forth. Also, if you are jamming that channel - how can you receive that channel yourself in order to rebroadcast it?

The best way to get rid of logos is to pursuade everyone who is annoyed by them to turn off the TV. Only when ratings for logo-besmirched channels plummet - will the broadcasters realise what insanely annoying things these are. Better still - watch DVD's instead.

SteveBaker (talk) 03:33, 23 November 2008 (UTC)

Boycotting logo-covered channels is unlikely to work, because such channels will of course not realize WHY their ratings have dropped, and have no reason to suspect it is because of the silly logo. They are just as likely to replace the venerable old news anchor on the 6:00 news with some chick with big bazooms as they are to remove the logo... --Jayron32.talk.contribs 04:15, 23 November 2008 (UTC)

So either way, we win. ;) 67.184.14.87 (talk) 18:11, 23 November 2008 (UTC)

DScaler comes with a "Logo Killer Filter" intended to get rid of the translucent logos. I haven't used DScaler recently, but if I recall it was primitive and it didn't really work all that well. APL (talk) 05:17, 23 November 2008 (UTC)

I was thinking along the lines of a neural network that "knew" a lot about real world images and what the missing bits were most likely to be. For example, having grabbed a frame from "Supernatural" with a logo over a close-up of the main character, and reflecting the other side of the face, rotating it in my mind from previous frames I was able to manually use the "smudge" tool to convincingly restore an eye, eyebrow and hair. Another example would be trees. Analysis of the fractal structure could create a similar fractal to fill in the missing bits even without previous frame information. And as a last resort, if an image was not in the database,the image could be reduced to lines and curves, interpolated to join the curves and then filled in with texture graduating from one side to the other. Having said that, I am an accomplished painter, and programming software with that level of visual-spacial ability would be challenging and require a pretty good graphics card. As for animated logo's these could be predicted from previous frames and removed accordingly. Even if they were non-repeating a neural network could identify which parts were the logo.Trevor Loughlin (talk) 11:18, 23 November 2008 (UTC)

Another possibility, when dealing with a panning shot, is to take info from other frames to fill in what's under the logo in the current frame. A similar method could also be used when the object to be removed is moving (like mini football players running around at the bottom of the screen). Or, there is Marge Simpson's method of killing them with bug spray. StuRat (talk) 16:39, 23 November 2008 (UTC)

Visual software is nowhere near the ability to that sort of thing automatically. The human brain is still some many orders of magnitude more able to piece together things like this than any computer, assuming the conditions are not perfectly controlled for. --98.217.8.46 (talk) 18:34, 23 November 2008 (UTC)

I wouldn't say "nowhere near". That technology is probably less than 5 years off, IMHO. StuRat (talk) 22:45, 23 November 2008 (UTC)

There have been algorithms demonstrated at SigGraph (for example) over the past few years that can construct moderately convincing 'infill' for missing parts of an image - but it's not the "right" information - so the consequences for plot and storyline could potentially be rather serious. But the killer - the one thing we can't fix - is when the logo is animated. This is distressingly common these days (and INSANELY annoying) - and if a widespread static logo removal tool existed then they would certainly become more common. SteveBaker (talk) 01:48, 24 November 2008 (UTC)

Spacetime

Can spacetime be created and/or destroyed, unlike matter/energy? —Preceding unsigned comment added by 124.177.29.112 (talk) 07:50, 23 November 2008 (UTC)

This can be a theological question, and Christians believe that God created space and time, and can also wrap it up, so your answer is yes. Graeme Bartlett (talk) 10:00, 23 November 2008 (UTC)

Not Wikipedia:Reference desk/Religion 24.76.161.28 (talk) 10:06, 23 November 2008 (UTC)

Useless answer unbefitting of the Science desk. --98.217.8.46 (talk) 18:23, 23 November 2008 (UTC)

I'm not sure I see where this is going. How was it you instantly thought of religion when answering this question? It could equally just be curiosity. —Cyclonenim (talk · contribs · email) 10:54, 23 November 2008 (UTC)

The expansion of the universe can be thought of as spacetime being created (alternatively, you can think of it as spacetime just getting bigger). If the universe were to contract again towards a Big Crunch, that could be thought of as spacetime being destroyed. (The Big Bang and Big Crunch themselves can certainly be thought of as the creation and destruction of spacetime, respectively, although they aren't particularly well understood by our current science.) --Tango (talk) 12:42, 23 November 2008 (UTC)

Spacetime is not a substance. It's a model for talking about the relationship between time and space (but they are not interchangeable like mass/energy). If time cannot be destroyed or created, then I would suspect space cannot either. The Big Bang would have been the exception to this. --98.217.8.46 (talk) 18:23, 23 November 2008 (UTC)

I don't even see a necessity for an exception for the Big Bang. As far as we know, space was simply scrunched up to an INFINITE degree - this is a little more satisfying than the idea that space was 'created'. SteveBaker (talk) 01:42, 24 November 2008 (UTC)

General relativity can explain stretching or shrinking of space time, and can allow it to be started or ended in singularities. But there is no human technology capable of creating new spacetime continua. The space time that we inhabit in this universe could well be unique. There are theories that a spacetime bubbles could be formed by a collapsing blackholes, or that alternate universes could exist. But experimental or observational evidence is lacking! This indicates that our universe's space time is special (at least for us). It is not easy to create or destroy. Graeme Bartlett (talk) 04:13, 24 November 2008 (UTC)

It's really not clear to me what creation or destruction of spacetime even means. So, we have a spacetime metric, we can use this to measure the "distance" in spacetime between two events, and we could even extend this to measure a "volume" of spacetime - say the volume of spacetime occupied by my desk between midnight 23rd Nov 2008 and midnight 24th Nov 2008. And maybe this "volume" can be said to measure a quantity of spacetime. But this volume measure is immutable and timeless because it is bounded by specific spacetime events. In other words, the volume occupied by my desk between midnight 23rd Nov 2008 and midnight 24th Nov 2008 is always the same, regardless of whether I calculate it today, tomorrow or in a million years time. I don't see how we could have a meaningful measure of spaectime that is ever subject to any change whatsoever. Gandalf61 (talk) 16:29, 24 November 2008 (UTC)

Actually, now that I think back at it, I accidentally destroyed some spacetime the other day. I started reading an article on Wikipedia, and before I knew it, three hours had been totally obliterated! --98.217.8.46 (talk) 03:08, 25 November 2008 (UTC)

Adrafinil vs Piracetam?

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This question has been removed. Per the reference desk guidelines, the reference desk is not an appropriate place to request medical, legal or other professional advice, including any kind of medical diagnosis or prognosis, or treatment recommendations. For such advice, please see a qualified professional. If you don't believe this is such a request, please explain what you meant to ask, either here or on the Reference Desk's talk page. --~~~~

-hydnjo talk 13:02, 23 November 2008 (UTC)

Protein folding

Do we know if proteins fold faster in vivo than they do in vitro or vice versa? Donek (talk) 14:42, 23 November 2008 (UTC)

No data, but my knee-jerk expectation is that it depends on pH and temperature and the conformation of the protein and the greater context is moot. In general, you could probably create in vitro conditions that would meet or exceed the "optimal speed" in vivo, but it depends on the protein. SDY (talk) 15:59, 23 November 2008 (UTC)

In vivo, in addition to temperature and pH, protein folding is strongly influenced by other proteins present. Therefore, proteins may fold differently in vivo than they would in vitro. See Chaperone (protein). --NorwegianBlue ^talk 17:59, 23 November 2008 (UTC)

Thanks, I was also considering the pressure effect other proteins might have on an amino acid chain as it is being translated. A protein starts folding before the chain is complete maybe due to the crowded environment in which it is translated. Donek (talk) 13:24, 24 November 2008 (UTC)

I was under the impression proteins generally didn't fold properly in vitro. --151.200.180.11 (talk) 15:16, 25 November 2008 (UTC)

Balloon

Why does a balloon go flying when you let the gas inside escape? —Preceding unsigned comment added by 65.92.229.32 (talk) 21:41, 23 November 2008 (UTC)

The air inside is under pressure because of the elasticity of the rubber balloon. When you release the end the air escapes because of that pressure - the balloon causes a force on the air pushing it out. Since every action has an equal and opposite reaction, there is a force on the balloon in the opposite direction which it why it goes flying. --Tango (talk) 22:24, 23 November 2008 (UTC)

That every action has an equal and opposite reaction is Newton's third law. The fact that if one object goes in one direction, the other has to go in the opposite direction is given by the law of conservation of momentum. --Bowlhover (talk) 02:15, 24 November 2008 (UTC)