@article {371, title = {Dynamic NMR microscopy of gas phase Poiseuille flow}, journal = {Journal of Magnetic Resonance}, volume = {149}, year = {2001}, note = {J Magn Reson421TCTimes Cited:17Cited References Count:16}, month = {Mar}, pages = {144-148}, abstract = {

Dynamic NMR microscopy has been used to study xenon gas undergoing Poiseuille flow in the regime where deterministic and stochastic motions are the same order of magnitude. For short observation time, the flow profile images are largely influenced by the longitudinal diffusion, manifested by large displacements in both positive and negative directions. For longer observation time, the effect of the mixing between the fast and slow flow components due to transverse diffusion becomes apparent. A spin-echo version of the dynamic NMR experiment yields images exhibiting strong distortions for longer observation time due to fast diffusion under the \"natural\" gradient from magnetic field inhomogeneity (compared to results obtained with a stimulated echo version). This effect is used as an edge-enhancement filter by employing a longer time duration of the imaging gradient in a stimulated echo experiment. (C) 2001 Academic Press.

}, keywords = {transport}, isbn = {1090-7807}, doi = {Doi 10.1006/Jmre.2000.2283}, url = {://WOS:000168078800021}, author = {Kaiser, L. G. and Logan, J. W. and Meersmann, T. and Pines, A.} } @article {376, title = {Exploring single-file diffusion in one-dimensional nanochannels by laser-polarized Xe-129 NMR spectroscopy (Cover Article)}, journal = {Journal of Physical Chemistry A}, volume = {104}, year = {2000}, note = {J Phys Chem A383EFTimes Cited:75Cited References Count:22}, month = {Dec 21}, pages = {11665-11670}, abstract = {

Single-file diffusion behavior is expected for atoms and molecules in one-dimensional gas phases of nanochannels with transverse dimensions that do not allow for the particles to bypass each other. Although single-file diffusion may play an important role in a wide range of industrial catalytic, geologic, and biological processes, experimental evidence is scarce despite the fact that the dynamics differ substantially from ordinary diffusion. We demonstrate the application of continuous-flow laser-polarized Xe-129 NMR spectroscopy for the study of gas transport into the effectively one-dimensional channels of a microporous material. The novel methodology makes it possible to monitor diffusion over a time scale of tens of seconds, often inaccessible by conventional NMR experiments. The technique can also be applied to systems with very small mobility factors or diffusion constants that are difficult to determine by currently available methods for diffusion measurement. Experiments using xenon in nanochannel systems can distinguish between unidirectional diffusion and single-file diffusion. The experimental observations indicate that single-file behavior for xenon in an organic nanochannel is persistent even at long diffusion times of over tens of seconds. Finally;using continuous flow laser-polarized Xe-129 NMR spectroscopy, we describe an intriguing correlation between the observed NMR line shape of xenon within the nanochannels and the gas transport into these channels.

}, keywords = {model}, isbn = {1089-5639}, doi = {Doi 10.1021/Jp002322v}, url = {://WOS:000165869600001}, author = {Meersmann, T. and Logan, J. W. and Simonutti, R. and Caldarelli, S. and Comotti, A. and Sozzani, P. and Kaiser, L. G. and Pines, A.} } @article {378, title = {Visualization of gas flow and diffusion in porous media}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {97}, year = {2000}, note = {P Natl Acad Sci USA294ZRTimes Cited:29Cited References Count:18}, month = {Mar 14}, pages = {2414-2418}, abstract = {

The transport of gases in porous materials is a crucial component of many important processes in science and technology. In the present work, we demonstrate how magnetic resonance microscopy with continuous flow laser-polarized noble gases makes it possible to \"light up\" and thereby visualize, with unprecedented sensitivity and resolution, the dynamics of gases in samples of silica aerogels and zeolite molecular sieve particles. The \"polarization-weighted\" images of gas transport in aerogel fragments are correlated to the diffusion coefficient of xenon obtained from NMR pulsed-field gradient experiments. The technique provides a unique means of studying the combined effects of flow and diffusion in systems with macroscopic dimensions and microscopic internal pore structure.

}, keywords = {xenon}, isbn = {0027-8424}, doi = {Doi 10.1073/Pnas.050012497}, url = {://WOS:000085941400005}, author = {Kaiser, L. G. and Meersmann, T. and Logan, J. W. and Pines, A.} } @article {388, title = {Relaxation-selective magnetic resonance imaging}, journal = {Chemical Physics Letters}, volume = {311}, year = {1999}, note = {Chem Phys Lett244VRTimes Cited:1Cited References Count:15}, month = {Oct 1}, pages = {379-384}, abstract = {

The Bloch equations with T-2 relaxation can be inverted in closed form with respect to T-2, using inverse scattering theory. Hence, radio frequency pulses can be calculated that cause a final magnetization response that is any desired function of T-2, provided that function is physically realizable (however, there are strong constraints on what is physically realizable). A useful subclass of such pulses are \&$\#$39;dressing\&$\#$39; pulses, which store the magnetization on the z-axis, with magnitude a given function of T-2. This enables spins to be selectively nulled according to their T-2- this is demonstrated by obtaining a relaxation-selective image of a phantom. (C) 1999 Elsevier Science B.V. All rights reserved.

}, keywords = {optimization}, isbn = {0009-2614}, doi = {Doi 10.1016/S0009-2614(99)00890-8}, url = {://WOS:000083071900007}, author = {Bush, S. D. and Rourke, D. E. and Kaiser, L. G. and Pines, A.} }