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121.
Electron magnetic resonance (EMR) studies of paramagnetic centers exhibiting monoclinic and triclinic local site symmetry have gained renewed importance, since such centers occur often in various technologically important materials and biological systems. The intricate low symmetry aspects, which arise for such centers, bear on meaningful interpretation of EMR data and their correlation with structural data. This review provides a primer for experimentalists who wish to utilize efficiently the modeling techniques for analysis and interpretation of EMR data for transition ions, especially ions located at low symmetry sites in crystals. This requires proper understanding of the low symmetry effects observable in EMR spectra as well as related theoretical questions concerning, e.g., (i) existence of physically equivalent zero-field splitting (ZFS) parameter sets, (ii) clear definitions of the axis systems, (iii) proper forms of spin Hamiltonians, and (iv) distinction between apparent and actual low symmetry cases. The question (i) involves consideration of the orthorhombic standardization, which provides basis for standardization of monoclinic and triclinic ZFS parameters. Thus, the aspects pertaining to orthorhombic site symmetry are also outlined. To solve other questions several modeling techniques have been utilized and related computer packages have recently been developed in our group: (1) the superposition model calculations of the zero-field splitting parameters (ZFSPs) in arbitrary symmetry, (2) the procedure for diagonalization of the 2nd-rank ZFSPs and transformation of respective 4th- and 6th-rank ZFSPs, (3) the pseudosymmetry axes method for approximation of the 4th- and 6th-rank ZFSPs to higher symmetry, and (4) the closeness factors and norm ratios for quantitative comparisons of various ZFSP sets. These modeling techniques enable deeper analysis and interpretation of the low symmetry aspects involved in the fitted and theoretical ZFSPs. The computer packages facilitate extracting useful structural information inherent in monoclinic and triclinic ZFSP sets. Illustrative examples taken from recent studies of low symmetry ion-host systems are discussed. 相似文献
122.
对粘接结构进行超声导波无损检测与评估是一个有挑战性的前沿性课题.针对此问题,研究了SH0导波在界面为理想连接的三层板状粘接结构中传播时的相位变化情况.首先基于波传播的控制方程,建立了粘接结构中反射和透射SH0导波相对于入射SH0导波的相位差解析模型.然后利用数值模拟计算了铝/环氧树脂/铝粘接结构中反射和透射SH0导波的相位差曲线.最后分析了入射角度和频厚积的变化对反射和透射SH0导波相位差的影响.结果表明,对于具体的粘接结构,反射和透射SH0导波在其中传播时的相位差变化主要依赖于入射角度、频率等参数.在特定的频厚积下,当声波水平入射时,反射和入射SH0导波同相位.无论入射角度为多大,随着频厚积的增大,反射SH0导波的相位差曲线均会产生周期性谐振.对于透射SH0导波,当声波垂直入射时,其相位差曲线的改变无规律可循;但是随着入射角度逐渐增大,透射SH0导波的相位差曲线逐渐变规则.所得结果可为实验时研究板状粘接结构中SH0导波的传播特性以及提取SH0导波回波中的有用信息和定位提供一定的理论指导. 相似文献
123.
R. M. Lees Li-Hong Xu S. Twagirayezu D. S. Perry M. B. Dawadi B. E. Billinghurst 《Molecular physics》2018,116(23-24):3554-3563
ABSTRACTThe infrared Fourier transform spectrum of the S–H stretching fundamental band of 12CH3 32SH has been recorded using synchrotron radiation at the far-infrared beamline of the Canadian Light Source in Saskatoon. The S–H stretch is a hybrid band predominantly of perpendicular b-type with a small parallel a-component. With both ΔK = +1 and ΔK = ?1 sub-bands present, the assignments are well determined from ground-state combination difference relations. The identified sub-bands access S–H stretching ground torsional substates from K′ = 0–14 for A and E torsional species. The substate origins have been obtained by expanding the term values in J(J + 1) power series, and have been fitted to a simple 6-parameter Fourier Hamiltonian to deduce the torsional energies. The oscillation amplitude of the S–H stretching torsional curves is 0.547 cm? 1 compared to 0.653 cm? 1 for the ground state, implying an increase on the order of 6.9% in the torsional barrier height. The vibrational wavenumber for the S–H stretch mode is found to be 2603.5 cm? 1. 相似文献
124.
Jinxi Liu Weiyi Wei Daining Fang 《Acta Mechanica Solida Sinica》2010,23(1):77-84
This paper investigates shear horizontal (SH) waves propagating in a periodically layered structure that consists of piezoelectric (PE) layers perfectly bonded with piezomagnetic (PM) layers alternately. The explicit dispersion relations are derived for the two cases when the propagation directions of SH waves are normal to the interface and parallel to the interface, respectively. The asymptotic expressions for dispersion relations are also given when the wave number is extremely small. Numerical results for stop band effect and phase velocity are presented for a periodic system of alternating BaTiO3 and Terfenol-D layers. The influence of volume fraction on stop band effect and dispersion behaviors is discussed and revealed. 相似文献
125.
Shear horizontal (SH) waves in free and clamped monoclinic plates with an arbitrary inhomogeneity across the plate are considered. Firstly, some general properties of dispersion spectra of, specifically, the SH waves are pointed out. Secondly, analytical and numerical modeling of the SH dispersion branches is presented. Closed-form estimations are compared with exact curves computed for a free plate with continuously varying properties. 相似文献
126.
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128.
We examined CH/π hydrogen bonds in protein/ligand complexes involving at least one proline residue using the ab initio fragment molecular orbital (FMO) method and the program CHPI. FMO calculations were carried out at the Hartree–Fock (HF)/6‐31G*, HF/6‐31G**, second‐order Møller–Plesset perturbation (MP2)/6‐31G*, and MP2/6‐31G** levels for three Src homology 3 (SH3) domains and five proline‐recognition domains (PRDs) complexed with their corresponding ligand peptides. PRDs use a conserved set of aromatic residues to recognize proline‐rich sequences of specific ligands. Many CH/π hydrogen bonds were identified in these complexes. CH/π hydrogen bonds occurred, in particular, in the central part of the proline‐rich motifs. Our results suggest that CH/π hydrogen bonds are important in the recognition of SH3 and PRDs by their ligand peptides and play a vital role in the signal transduction system. Combined use of the FMO method and CHPI analysis is a valuable tool for the study of protein/protein and protein/ligand interactions and may be useful in rational drug design. © 2011 Wiley Periodicals, Inc. J Comput Chem 2011 相似文献
129.
130.
Complete diagonalization of the energy matrix and high order perturbation formulae of spin-Hamiltonian (SH) parameters possessing D4h symmetry for the 4d9 ion based on the crystal- and ligand-field theory in tetragonal symmetry are expressed and applied to the study of local distortion structure of the KCl:Ag2+ crystal. The calculated results agree well with experimental findings. Both complete diagonalization of energy matrix and high order perturbation approach are appropriate for the investigations of SH parameters of 4d9 ions in tetragonal crystals. Tetragonal distortion due to the Jahn-Teller effect for the tetragonal Ag2+ center at the K+ site of KCl crystal is also acquired from the calculations. 相似文献