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od 2020-09-20 |
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1. |
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Optimization of transverse gradient coils with coaxial return paths by simulated annealing Coils with coaxial return paths are used to generate transverse magnetic field gradients. This paper describes optimization of such coils by the method of simulated annealing, a method known to be able to find the global minimum of a function. The adaptive simulated annealing (ASA) program has been analyzed and applied to optimization of a family of coils with 8-16 building blocks, each carrying equal current. Positions of the blocks along the longitudinal axis of the coils were optimized. A new subclass of coils is proposed; the diameter of return paths of this subclass of coils is not fixed but may be varied, The new coils provide greater gradient uniformity than those for which only positions of the blocks are optimized, All optimized coils should find applications in high-precision and high-resolution imaging and spectroscopic experiments.
(C) 1996 Academic Press, Inc. |
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Journal of Magnetic Resonance Series B, 112(3), 207-213, (1996) |
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Molecular dynamics of solid cortisol studied by NMR Polycrystalline cortisol (hydrocortisone; 11 beta,17 alpha,21-trihydroxy-4-pregnene-3,20-dione; C21H30O5) has been investigated by continuous and pulse proton NMR methods between 78 and 400 K at Larmor frequencies of 7, 25 and 60 MHz. A reduced value of second moment was found above 90 K and is ascribed to reorientation of two methyl groups. A single asymmetric minimum was found in the temperature dependence of the spin-lattice relaxation times and this also is attributed to reorientation of two methyl groups. The asymmetry suggests an asymmetric distribution of correlation times of the motion. Using the Cole-Davidson distribution, the best computer fit yields the following parameters characterizing the motion: E(s) = 11.8 ±0.1 kJ mol(-1), tau(0) = 4.6 ±0.4) x 10(-13) s, distribution parameter delta = 0.62.
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Molecular Physics, 88(3), 605-610, (1996) |
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Magnetic field gradient system for nuclear magnetic resonance microimaging In this study we present an orthogonal magnetic field gradient system for nuclear magnetic resonance (NMR) microimaging applications. The construction details are given for a prototype assembly for proton microscopy inside a 50-mm vertical bore magnet, which is designed to fit into a commercial 300-MHz NMR probe. This system has been used to acquire images of the human spinal cord in vitro. Its performance has been evaluated and compared to that predicted by computer simulation.
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Magnetic Resonance Materials in Physics Biology and Medicine - MAGMA, 4(24), 85-91, (1996) |
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4. |
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Dynamics of t-butyl groups in a series of related molecular solids The dynamics of the lowest temperature phase of a series of closely related t-butyl compounds (CH3)CXH, whre X=O, S, Se, has been studied using 1H NMR. The obtained data allowed the separation of the dynamics arising from methyl group and from t-butyl group. The activation parameters of the motions are given. It is shown that the t-butyl group is more mobile than constituent methyl groups and that coupling between these two motions is associated with the observed order-disorder phase transition.
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Molecular Physics Reports, 14, 83-87, (1996) |
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5. |
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Molecular dynamics in glassy di-isobutyl phalate as studied by 1H NMR This volume contains the proceedings of the International Workshop on "Non-Equilibrium Phenomena in Supercooled Fluids, Glasses and Amorphous Materials", held in Pisa in the early fall of 1995 as a joint initiative of the Unviersity of Pisa and of the Scuola Normale Superiore
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World Scientific Series in Contemporary Chemical Physics - Non Equilibrium Phenomena in Supercooled Fluids, Glasses and Amorphous Materials, 12, Eds. Giordana M. et al., World Scientific, Singapore, (1996) |
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