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Shift Parameters (shift + parameter)
Selected AbstractsQRS Amplitude and Shape Variability in MagnetocardiogramsPACING AND CLINICAL ELECTROPHYSIOLOGY, Issue 2 2000MARKUS HUCK In magnetocardiography, averaging of QRS complexes is often used to improve the signal-to-noise ratio. However, averaging of QRS complexes ignores the variation in amplitude and shape of the signals caused, for example, by respiration. This may lead to suppression of signal portions within the QRS complexes. Furthermore, for inverse source, reconstructions of dipoles and of current density distributions errors in the special arrangement may occur. To overcome these problems we developed a method for separating and selective averaging QRS complexes with different shapes and amplitudes. The method is based on a spline interpolation of the QRS complex averaged by a standard procedure. This spline function then is fitted to each QRS complex in the raw data by means of nonlinear regression (Levenberg-Marquardt method). Five regression parameters are applied: a linear amplitude scaling, two parameters describing the baseline drift, a time scaling parameter, and a time shift parameter. We found that both amplitude and shape of the QRS complex are influenced by respiration. The baseline shows a weaker influence of the respiration. The regression parameters of two neighboring measurement channels correlate linearly. Thus, selective averaging of a larger number of sensors can be performed simultaneously. [source] Mn and Si influence on the hyperfine properties of the fcc and hcp phases in the Fe,Mn and Fe,Mn,Si systemsPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 6 2009Javier Martínez Abstract A study of the hyperfine properties of the fcc and hcp phases of the Fe,Mn and Fe,Mn,Si systems, performed on a systematic and accurate set of samples belonging to the 15 at% to 30 at% Mn and 0 at% to 12 at% Si composition ranges, is presented. The samples were characterized using Conversion Electron Mössbauer Spectroscopy. The evolution with the Mn and Si contents of the hyperfine parameters of both phases has been determined. A constancy of the isomer shift parameter of the hcp phase with both constituents of the alloy was observed. While constancy and a linear decrease of the isomer shift values of the fcc phase with Mn and Si, respectively, were determined. The magnetic hyperfine field of the fcc phase presents two different values depending on the Mn content in the binary system and a decrease with the addition of Si when the ternary alloy is considered. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Correlating sideband patterns with powder patterns for accurate determination of chemical shift parameters in solid-state NMRMAGNETIC RESONANCE IN CHEMISTRY, Issue 10 2008M. S. Ironside Abstract Powder patterns and sideband patterns have different strengths when it comes to using them to determine chemical shift parameters. Here, we show that chemical shift parameters can be determined with high accuracy by analysing the correlation pattern from a 2D experiment which correlates a powder pattern in the indirect dimension with a sideband pattern in the direct dimension. The chemical shift parameters so determined have greater accuracy than those obtained by analysing a sideband or powder pattern alone, for the same signal-to-noise ratio. This method can be applied for both resolved correlation patterns and to cases where two components share similar isotropic chemical shifts. The methodology is demonstrated in this paper, both theoretically and experimentally, on the 31P signals of the bis-phosphonate drug, pamidronate. Copyright © 2008 John Wiley & Sons, Ltd. [source] Analysis of a Pentacoordinate Iron Dicarbonyl as Synthetic Analogue of the Hmd or Mono-Iron Hydrogenase Active Site,CHEMISTRY - A EUROPEAN JOURNAL, Issue 10 2010Tianbiao Liu Abstract Pentacoordinate iron dicarbonyls, (NS)Fe(CO)2P (NS=2-amidothiophenylate, P=PCy3 (4), PPh3, (5), and P(OEt)3 (6)) were prepared as potential biomimetics of the active site of the mono-iron hydrogenase, [Fe]-H2ase. Full characterization including X-ray diffraction, density functional theory (DFT) computations, and Mössbauer studies for complexes 5 and 6 find that, despite similar infrared v(CO) pattern and absorption frequencies as the active site of the [Fe]-H2ase, the geometrical distortions towards trigonal bipyramidal, the negative isomer shift parameters, and the differences in CO-uptake reactivity are due to the "non-innocence" of the NS ligand. Ligand-based protonation with a strong acid, HBF4,Et2O, interrupted the extensive ,-delocalization over Fe and NS ligand of complex 4 and switched on CO uptake (1,bar) to form a CO adduct, mer -[(H-NS)Fe(CO)3(PCy3)]+ or 4(CO)-H+. The extrinsic CO is reversibly removed on deprotonation with Et3N to regenerate complex 4. In a 13CO atmosphere, concomitant CO uptake by 4 -H+ and exchange with intrinsic CO groups provide a facile route to 13C-labeled 4(CO)-H+ and, upon deprotonation, 13C-labeled complex 4. DFT calculations show substantial Fe character in the LUMO of 4 -H+ typical of the d6 FeII in a regular square-pyramidal geometry. Thus, the Lewis acidity of 4 -H+ makes it amenable for CO binding, whereas the dianionic NS ligand renders the iron center of 4 insufficiently electrophilic and largely of FeI character. [source] | ||||||||||