R.M. Gregory, A.D. Bain, "The effects of finite rectangular pulses in NMR: Phase and intensity distortions for a spin-1/2," Concepts in Magnetic Resonance Part A 34A (2009) 305-314. http://dx.doi.org/10.1002/cmr.a.20147
Pulses in NMR spectrometers have a finite length, but the usual hard-pulse assumption ignores it, and treats the pulse as a rotation of the frame of reference about the direction of the radiofrequency (RF) magnetic field. However, at frequency offsets comparable to the size of the RF field, there are substantial distortions, mainly in the phase of the signal. This effect is well known and can be easily calculated to show that, despite the complex geometry, the phase distortion is almost linear with the offset. This means that it can be corrected by a first-order phase correction or by small corrections to pulse-sequence timing. In this article, we give an analysis of these effects. The deviations from a linear phase correction are analyzed for a general rectangular pulse and illustrated with experimental spectra. The split-operator approximation for the evolution of this system provides a mathematical foundation and a useful method for this analysis. Furthermore, the relationship between the exact behavior of a signal is compared to the Fourier transform of a rectangular pulse. For typical offsets, the match between these approaches is not good, but it improves as the offset increases. Overall, the detailed analysis of the finite pulse effects gives exact results of the response of a spin system, but also some mathematical and physical insights.
See original: Feature article: Concepts in Magnetic Resonance
EvoMRI: Added mention of polymath project. re: http://ff.im/beKZB
EvoMRI: Cameron, do you have a reference for the second grant? I am only aware of... re: http://ff.im/beKZB
Liked "Academic impact as Greek tragedy: comment now on UK plan to tie govt funding of univs to econ "impact" of..." http://ff.im/cpZdeFri, 04/12/2009 - 3:29pm | by daniel
EvoMRI: Liked "Academic impact as Greek tragedy: comment now on UK plan to tie govt funding of univs to econ "impact" of..." http://ff.im/cpZde
Perentie tries to swallow echidna. Echidna too spiky, Perentie gets horribly injured. Dies. [Tetrapod Zoology]Fri, 04/12/2009 - 3:21pm | by daniel
In case it isn't obvious, I've decided to do a little series on 'over-eager swallowing'. And here's the latest instalment. Here's an unfortunate Perentie Varanus giganteus that died after trying to swallow a Short-beaked echidna Tachyglossus aculeatus...
Also check out the featured ScienceBlog of the week: Applied Statistics
See original: Sixth Annual ARL Leadership Symposium
funny! RT @vaughanbell: Tongue-in-cheek evolutionary psychology agony aunt. http://is.gd/5ccgi via @edyong209Fri, 04/12/2009 - 3:03pm | by sandygautam
Have you ever played the 6 Degrees of Kevin Bacon with OLPC team members? I think you could make the case that OLPC is the center of the technology world - Nicholas Negroponte would get you pretty far, himself.
Or more to the point, OLPC spin-offs? On this the Digital Lifestyle conjectures a hot idea OLPC's screen technology in the Apple Tablet:
Mary Lou Jepsen, former OLPC chief technology officer who has since left to form Pixel Qi, a company founded to commercialize the same revolutionary [OLPC] display technology. Pixel Qi's VP of Engineering is none other than Dr. Carlin Vieri who came to Pixel Qi from Apple, where according to his bio on the company site, "he engineered new generation display electronics for the iPhone and other devices."See how we're connecting the dots? We wouldn't be the least bit surprised to see Pixel Qi acquired by Apple just around the same time as the tablet is announced. No need to clue the competition to your display choice early. It would be similar to Apple's acquisition of Fingerworks just before multitouch at Apple took off.
Personally, I would be surprised. Dancing around my home office screaming "Hell's Yes! That's clock stopping hot, baby!" surprised. But that's just me. The rest of y'all would freat when Steve Jobs made the tablet use Aquatic Sugar.
See original: Apple Tablet To Use OLPC Screen Technology?!
RT @vaughanbell: @edyong209 Full respect for Gladwell's hair. He and Pinker should go head to head in a mane off.Fri, 04/12/2009 - 2:57pm | by sandygautam
RT @vaughanbell: Just finished Malcolm Gladwell's book Outliers. Really very good, probably his best work.Fri, 04/12/2009 - 2:57pm | by sandygautam
sandygautam: RT @vaughanbell: Just finished Malcolm Gladwell's book Outliers. Really very good, probably his best work.
I would have thought that there were methods to avoid the slices folding up over the edge of the cryomicrotome.... re: http://ff.im/cquWvFri, 04/12/2009 - 2:56pm | by daniel
EvoMRI: I would have thought that there were methods to avoid the slices folding up over the edge of the cryomicrotome.... re: http://ff.im/cquWv
EvoMRI: The Brain Observatory - In Memory of H.M. http://ff.im/cquWv
Liked "RT @WhatsNewsSite: Watch the sectioning of H.M.'s brain live! Thank you Henry Gustav Molaison...." http://ff.im/cqpUYFri, 04/12/2009 - 2:48pm | by daniel
Johann Hari is a London based journalist writing for the Independent. He provides this simple metaphor on Copenhagen choices:
Imagine you are about to get on a plane with your family. A huge group of qualified airline mechanics approach you on the tarmac and explain they’ve studied the engine for many years and they’re sure it [...]
See original: A flying metaphor for Copenhagen