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Polarization Transfer (polarization + transfer)
Selected AbstractsPolarization transfer in a pulsar magnetosphereMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2006S. A. Petrova ABSTRACT Propagation of radio waves in the ultrarelativistic magnetized electron,positron plasma of a pulsar magnetosphere is considered. The polarization state of the original natural waves is found to vary markedly on account of the wave mode coupling and cyclotron absorption. The change is most pronounced when the regions of mode coupling and cyclotron resonance approximately coincide. In cases when the wave mode coupling occurs above and below the resonance region, the resultant polarization appears essentially distinct. The main result of the paper is that in the former case the polarization modes become non-orthogonal. The analytical treatment of the equations of polarization transfer is accompanied by numerical calculations. The observational consequences of polarization evolution in pulsar plasma are discussed as well. [source] Polarization transfer for sensitivity-enhanced MRS using a single radio frequency transmit channelNMR IN BIOMEDICINE, Issue 5 2008D. W. J. Klomp Abstract Polarization transfer techniques are used to enhance sensitivity and improve localization in multinuclear MRS, by transferring polarization from highly polarized or even hyperpolarized nuclei to less sensitive spin systems. Clinical MR scanners are in general not equipped with a second radio frequency (RF) transmit channel, making the conventional implementation of polarization transfer techniques such as distortionless enhanced polarization transfer (DEPT) impossible. Here we present a DEPT sequence using pulses sequentially that can be used on a single RF transmit channel (SC-DEPT). Theoretical simulations, phantom measurements, and in vivo results from human brain at 3,T show that the SC-DEPT method performs as well as the conventional DEPT method. The results indicate that an independent second RF transmit channel for simultaneous pulsing at different nuclear frequencies is not needed for polarization transfer, facilitating the use of these methods with common clinical systems with minor modifications in the RF architecture. Copyright © 2007 John Wiley & Sons, Ltd. [source] HIGH-RESOLUTION MAGIC ANGLE SPINNING NMR ANALYSIS OF WHOLE CELLS OF CHAETOCEROS MUELLERI (BACILLARIOPHYCEAE) AND COMPARISON WITH 13C-NMR AND DISTORTIONLESS ENHANCEMENT BY POLARIZATION TRANSFER 13C-NMR ANALYSIS OF LIPOPHILIC EXTRACTS,JOURNAL OF PHYCOLOGY, Issue 3 2004Matilde S. Chauton Lipid composition in extracted samples of Chaetoceros muelleri Lemmermann was studied with 13C-NMR and distortionless enhancement by polarization transfer (DEPT) 13C-NMR, resulting in well-resolved 13C-NMR spectra with characteristic resonance signals from carboxylic, olefinic, glyceryl, methylene, and methyl groups. The application of a DEPT pulse sequence aided in the assignment of methylene and methine groups. Resonance signals were compared with literature references, and signal assignment included important unsaturated fatty acids such as eicosapentaenoic and docosahexaenoic and also phospholipids and glycerols. Results from the extracted samples were used to assign resonance signals in a high-resolution magic angle spinning (HR MAS) DEPT 13C spectrum from whole cells of C. muelleri. The NMR analysis on whole cells yielded equally good information on fatty acids and also revealed signals from carbohydrates and amino acids. Broad resonance signals and peak overlapping can be a problem in whole cell analysis, but we found that application of HR MAS gave a well-resolved spectrum. The chemical shift of metabolites in an NMR spectrum depends on the actual environment of nuclei during analysis, and some differences could therefore be expected between extracted and whole cell samples. The shift differences were small, and assignment from analysis of lipophilic extract could be used to identify peaks in the whole cell spectrum. HR MAS 13C-NMR therefore offers a possibility for broad-range metabolic profiling directly on whole cells, simultaneously detecting metabolites that are otherwise not detected in the same analytical set up and avoiding tedious extraction procedures. [source] Compositional and configurational sequence determination of methyl methacrylate/ethyl acrylate copolymers by one- and two-dimensional nuclear magnetic resonance spectroscopyJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 2 2003A. S. Brar Abstract Ethyl acrylate (E)/methyl methacrylate (M) copolymers of different compositions were prepared, and their compositions were determined with 1H NMR spectra. The complete spectral assignments, in terms of the compositional and configurational sequences of these copolymers, were made with the help of distortionless enhancement by polarization transfer and two-dimensional heteronuclear single quantum coherence spectroscopy. The ,-(CH3)M, CH (E), CH2, and ,CO carbons of both M and E units were found to be sensitive to various compositional and configurational sequences. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 313,326, 2003 [source] Microstructure of glycidylmethacrylate/vinyl acetate copolymers by two-dimensional nuclear magnetic resonance spectroscopyJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 23 2001A. S. Brar Abstract Glycidylmethacrylate/vinyl acetate copolymers were prepared by solution polymerization with benzene as a solvent and benzoyl peroxide as an initiator. Copolymer compositions were determined from 1H NMR spectra, and comonomer reactivity ratios were determined by the Kelen,Tudos (KT) method and the nonlinear least-squares error-in-variable method (EVM). The reactivity ratios obtained from KT and EVM were rG = 37.4 ± 12.0 and rV = 0.036 ± 0.019 and rG = 35.2 and rV = 0.03, respectively. Complete spectral assignments of 13C and 1H NMR spectra were done with the help of distortionless enhancement by polarization transfer and two-dimensional 13C,1H heteronuclear single quantum coherence and total correlation spectroscopy. The methyl, methine, and methylene carbon resonance showed both stereochemical and compositional sensitivity. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 4051,4060, 2001 [source] Direct detection of non-proton-bearing 15N nuclei by long-range couplings using polarization transferMAGNETIC RESONANCE IN CHEMISTRY, Issue 10 2010Karel D. Klika Abstract The application of the QDEPT and QHSQC principles to long-range interactions for the direct detection of non-proton-bearing 15N is proffered as a general solution together with multiselective polarization transfer and triple INEPT for overcoming convoluted responses. Copyright © 2010 John Wiley & Sons, Ltd. [source] Simultaneous separation of intracellular and extracellular lactate NMR signals of human erythrocytesMAGNETIC RESONANCE IN MEDICINE, Issue 2 2007Götz Kohler Abstract Intracellular/extracellular lactate (Lac) distribution has been determined before in human and animal erythrocytes (red blood cells [RBCs]) with various methods. However, all previous methods determine intra- and extracellular Lac separately or indirectly. Now, 13C-NMR spectroscopy has been used to monitor intra- and extracellular Lac simultaneously in intact RBCs. Isolated human RBCs were incubated with [3- 13C]-Lac, [3- 13C]-pyruvate (Pyr), and [1- 13C]-glucose (Gluc). A distortionless enhancement by polarization transfer (DEPT) sequence was used (TR = 3.3 s, N = 128) to monitor the 13C-NMR resonances in both compartments. The intra- and extracellular methyl group resonances of Lac and Pyr were clearly separated by 9.6 Hz and 7.0 Hz, respectively, under normoxic conditions due to the RBC chemical-shift effect. The results show that the chemical-shift effect of RBCs is convenient to monitor intra- and extracellular Lac simultaneously in intact RBCs under normoxic conditions. Magn Reson Med 58:213,217, 2007. © 2007 Wiley-Liss, Inc. [source] Polarization transfer in a pulsar magnetosphereMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2006S. A. Petrova ABSTRACT Propagation of radio waves in the ultrarelativistic magnetized electron,positron plasma of a pulsar magnetosphere is considered. The polarization state of the original natural waves is found to vary markedly on account of the wave mode coupling and cyclotron absorption. The change is most pronounced when the regions of mode coupling and cyclotron resonance approximately coincide. In cases when the wave mode coupling occurs above and below the resonance region, the resultant polarization appears essentially distinct. The main result of the paper is that in the former case the polarization modes become non-orthogonal. The analytical treatment of the equations of polarization transfer is accompanied by numerical calculations. The observational consequences of polarization evolution in pulsar plasma are discussed as well. [source] Polarization transfer for sensitivity-enhanced MRS using a single radio frequency transmit channelNMR IN BIOMEDICINE, Issue 5 2008D. W. J. Klomp Abstract Polarization transfer techniques are used to enhance sensitivity and improve localization in multinuclear MRS, by transferring polarization from highly polarized or even hyperpolarized nuclei to less sensitive spin systems. Clinical MR scanners are in general not equipped with a second radio frequency (RF) transmit channel, making the conventional implementation of polarization transfer techniques such as distortionless enhanced polarization transfer (DEPT) impossible. Here we present a DEPT sequence using pulses sequentially that can be used on a single RF transmit channel (SC-DEPT). Theoretical simulations, phantom measurements, and in vivo results from human brain at 3,T show that the SC-DEPT method performs as well as the conventional DEPT method. The results indicate that an independent second RF transmit channel for simultaneous pulsing at different nuclear frequencies is not needed for polarization transfer, facilitating the use of these methods with common clinical systems with minor modifications in the RF architecture. Copyright © 2007 John Wiley & Sons, Ltd. [source] Sensitivity Enhancement in Two-Dimensional Solid-State NMR Spectroscopy by Transverse MixingCHEMPHYSCHEM, Issue 6 2004Robert Tycko Dr. Abstract The sensitivity of two-dimensional (2D) 13C,13C solid-state NMR spectroscopy under magic-angle spinning (MAS) is shown to be enhanced by the use of transverse polarization transfer in place of the conventional longitudinal polarization transfer. Experimental results are reported for 2D spectroscopy of a 20-residue, filament-forming peptide derived from the E. coli RecA protein, containing five uniformly 13C-labeled residues, performed at 14.1 T with high-speed MAS and with finite-pulse radio-frequency-driven recoupling of dipolar interactions in the mixing period. Significant sensitivity enhancements observed at short mixing periods result from a more rapid build-up of cross-peaks under transverse mixing than under longitudinal mixing and from the gain inherent in 2D measurements in which both orthogonal transverse polarization components in the t1 period contribute to each free-induction decay signal detected in the t2 period. [source] | |||||||||||||