Effects of Transverse Field on Internal Energy and Specific Heat of a Molecular-Based Materials

The molecular-based magnetic materials AFe11 Fe111（C2O4）3 have a honeycomb structure in which FeII （S = 2） and FeIH （S= 5/2） occupy sites alternately. They can be described as mixed spin-2 and spin-5/2 Ising model with ferrimagnetic interlayer coupling. The influences of the transverse field on the internal energy and the specific heat of the molecalar-based magnetic system have been studied numerically by using the effective-field theory with self-spin correlations and the differential operator technique.     

A mathematical-physics approach for studying far-infrared absorption in structurally disordered solids

A rigorous analysis is performed in order to characterize the mathematical structure of the integrated coefficient of optical absorption corresponding to structural disorder in amorphous solids. In this approach, the integral of the aforementioned coefficient is considered for the low region of the far-infrared range. Two basic ingredients in our formulation are the dipole-moment matrix element and phonon density of states.     

Pt interactions with annealed and chemically-etched Nb-doped SrTiO3(0 0 1) surfaces: Metal/oxide surface chemical effects on band bending behavior

XPS and LEED have been used to characterize the interaction of sputter-deposited Pt (maximum coverage <5 ML) with Nb-doped SrTiO₃(0 0 1) surfaces prepared either by annealing in O₂ and then UHV, or by chemical-etching in aqua regia. The annealed surface exhibits an ordered (1 × 1) LEED pattern, with additional diffraction spots and streaks indicating the presence of oxygen vacancies. Increasing Pt coverage results in the decrease of the observed Pt(4f_7/2) binding energy and the uniform shift of the Sr(3d), Ti(2p) and O(1s) levels to smaller binding energies, as expected for Pt cluster growth and surface-to-Pt charge donation on an n-type semiconductor. The etched surface is disordered, and exhibits a hydroxylated surface with a contaminant C film of ∼23 ? average thickness. Pt deposition on the etched surface results in an immediate decrease in the intensity of the OH feature in the O(1s) spectrum, and a uniform shift of the Sr(3d), Ti(2p) and O(1s) levels to larger binding energies with increasing Pt coverage. The observed Pt(4f_7/2) binding energy on the etched surface (∼72 eV) is independent of Pt coverage, and indicates substantial electronic charge donation from the Pt to surface hydroxyl species. The observation of band bending towards higher binding energies upon Pt deposition (behavior normally associated with p-type semiconductors) demonstrates that sub-monolayer quantities of adsorbates can alter metal/oxide interfacial charge transfer and reverse the direction of band bending, with important consequences for Schottky barrier heights and device applications.     

Deformation constrained relativistic mean-field approach with fixed configuration and time-odd component

Deformation constrained relativistic mean-field (RMF) approach with fixed configuration and time-odd component has been developed and applied to investigate magnetic moments of light nuclei near doubly-closed shells. Taking ¹⁷O as an example, the results and discussion are given in detail.     

Microscopic calculation of the magnetic field of neutron stars

Based on the Dirac equation describing an electron moving in a uniform and cylindrically symmetric magnetic field which may be the result of the self-consistent mean field of the electrons themselves in a neutron star, we have obtained the eigen solutions and the orbital magnetic moments of electrons in which each eigen orbital can be calculated. From the eigen energy spectrum we find that the lowest energy level is the highly degenerate orbitals with the quantum numbers pz = 0, n = 0, and m ≥0. At the ground state, the electrons fill the lowest eigen states to form many Landau magnetic cells and each cell is a circular disk with the radius λfree and the thickness λe, where λfree is the electron mean free path determined by Coulomb cross section and electron density and λe is the electron Compton wavelength. The magnetic moment of each cell and the number of cells in the neutron star are calculated, from which the total magnetic moment and magnetic field of the neutron star can be calculated. The results are compared with the observational data and the agreement is reasonable.     

First-principle electronic structure calculations for magnetic moment in iron-based superconductors: An LSDA + negative U study

In order to resolve a discrepancy of the magnetic moment on Fe between the experimental and calculation results, we perform first-principle electronic structure calculations for iron-based superconductors LaFeAsO_1-xF_x in which x=0.0 and x=0.125 by using the LSDA + U framework. Consequently, we confirm in both the mother and doped compounds that negative U correction is crucial in matching the calculated magnetic moment with the observed one. A reason of the negative correction is that the Coulomb interaction on Fe orbitals is unexpectedly screened than LSDA’s expectation. We discuss which type of situation emerges when the negative U is a good correction in these compounds.     

Analysis of the valence electronic structures and calculation of the physical properties of Fe,Co, and Ni

The valence electronic structures of Fe, Co and Ni have been investigated with Empirical Electron Theory of Solids and Molecules. The magnetic moments, Curie temperature, cohesive energy and melting point have been calculated according to the valence electronic structure. These calculations fit the experimental data very well. Based on the calculations, the magnetic moments are proportional to the number of 3d magnetic electrons. Curie temperatures are related to the magnetic electrons and the bond lengths between magnetic atoms. Cohesive energies increase with the increase of the number of covalent electrons, and the decrease of the number of magnetic and dumb pair electrons. The melting point is mainly related to the number of covalent electron pairs distributed in the strongest bond. The contribution from the lattice electrons is very small, the dumb pair electrons weaken the melting point; however, the contribution to melting point of the magnetic electrons can be neglected. It reveals that the magnetic and thermal properties are closely related to the valence electronic structures, and the changes or transitions between the electrons obviously affect the physical properties. Supported by the National High Technology Development Program of China (Grant No. 2007AA03Z458)     

The stabilization effect of the substituted atoms and themagnetism for intermetallic compounds YFe12-xCrx

<正>Based on density functional theory,using the scheme of the linearized augmented plane wave and the improved local orbital（APW+lo）,this paper analyses and calculates the lattice parameters,formation energy and magnetism of the rare-earth permanent magnetic materials YFe_12-xCr_x（x=0⁵）.The stabilization effect and the possible positions of the substituted atom Cr are analysed.Magnetic moments for the system and the atoms are obtained.     

基于QFT的光电稳定控制系统设计与分析

为了克服模型摄动和各种扰动对机载光电稳瞄系统的影响,提出一种基于定量反馈控制理论（QFT）的光电稳定控制系统设计方法。该方法以方位回路作为讨论对象,基准模型参数值均为方位回路参数值,通过综合考虑被控对象的模型不确定范围（不确定范围取为基准值的±15%）和系统的性能指标,可实现一定范围模型摄动系统的强鲁棒性。在加入模拟幅值为0.06的力矩扰动作用下,设计系统的输出位置误差小于2×10-7rad,加入速度扰动,以国外某典型直升机角振动测试频谱作为速度扰动信号,设计系统位置误差限制在8×10-7rad内。仿真结果表明：设计的控制系统总体性能优于经典PID设计的系统。     

负电子亲和势光电阴极量子效率公式的修正

量子效率是表征负电子亲和势（NEA）光电阴极发射性能的最重要的特性参数,准确建立量子效率公式为揭示各个阴极参量对整体性能的影响以及NEA光电阴极的优化设计提供了重要的理论指导.在对NEA光电阴极体内及表面光电发射过程的分析基础上,考虑入射光子能量、表面能带弯曲区以及表面势垒对电子发射的影响,对表面逸出概率和电子衰减长度进行了修正,并利用积分法推导了NEA光电阴极的量子效率公式,其理论预测曲线与实验曲线基本一致,从而验证了修正公式的实用性.为NEA光电阴极的研究提供了有效的理论参考依据. 关键词： 负电子亲和势光电阴极 量子效率 能带弯曲区 衰减长度