彩色显示器上大色差的研究

在彩色显示器上新的主观色差评价实验表明:CIELUV颜色空间色差公式中彩度差的权重相对于明度差的权重而言显著偏高了.     

Calculations on the hyperfine constants of the ground states for lithium-like system

In this paper a relativistic many-body perturbation calculation is performed to calculate the hyperfine constants of the ground states for lithium-like isoelectronic sequence. Zeroth-order hyperfine constants are calculated with Dirac--Fock wavefunctions, and the finite basis sets of the Dirac--Fock equations are constructed by B splines. With the finite basis sets, the core polarization and the correlation effect are evaluated.     

Macroscale and microscale evolutions of mechanically alloyed FeZn systems

The present work aims to correlate, in time, macroscale and microscale phenomenological evolutions of the microstructure of Fe and FeZn alloys processed by mechanical milling (MM) and alloying (MA), respectively. Powders were characterized for particle size distribution (PSD), particle morphology (optical microscopy, OM, scanning electron microscopy, SEM), microhardness, crystallite size, differential scanning calometry (DSC) and transmission electron microscopy (TEM). Two macroscopic regimes of PSD behavior were distinguished: the first one dominated by the cold welding process; and, the other where both fracture and agglomeration play a significant role. Solid solubilization of Zn on bcc Fe was found to reduce the final microhardness as well as increase the lattice parameter and is very well predicted by Miedema's thermodynamical approach. Microhardness and solid solution formation kinetics were correlated in time and both could be precisely described by a logistic function. After 5 h of planetary milling, microhardness and the lattice parameter become stable as well as the PSD and particle morphology, indicating that the system has already reached steady state. Indeed, this condition can be monitored by both macroscopic and microscopic parameters. Prior to an homogeneous powder, DSC results suggest an endothermic solid-state amorphization reaction for samples processed for up to 1 h as a result of the formation of clean Fe/Zn interfaces during MA.     

Ab initio calculations of accurate dissociation energy and analytic potential energy function for the second excited state B1∏ of 7LiH

The reasonable dissociation limit of the second excited singlet state B¹∏ of ⁷LiH molecule is obtained. The accurate dissociation energy and equilibrium geometry of the B¹\Pi state are calculated using a symmetry-adapted-cluster configuration--interaction method in full active space. The whole potential energy curve for the B¹∏ state is obtained over the internuclear distance ranging from about 0.10nm to 0.54nm, and has a least-square fit to the analytic Murrell--Sorbie function form. The vertical excitation energy is calculated from the ground state to the B¹∏ state and compared with previous theoretical results. The equilibrium internuclear distance obtained by geometry optimization is found to be quite different from that obtained by single-point energy scanning under the same calculation condition. Based on the analytic potential energy function, the harmonic frequency value of the B¹∏ state is estimated. A comparison of the theoretical calculations of dissociation energies, equilibrium interatomic distances and the analytic potential energy function with those obtained by previous theoretical results clearly shows that the present work is more comprehensive and in better agreement with experiments than previous theories, thus it is an improvement on previous theories.     

铁磁金属量子阱态的共振隧穿

非铁磁金属层中的量子阱态在磁输运过程中的重要性已被广泛认识．铁磁金属层中自旋极化的量子阱态以前并没有详尽的理论研究；实验上也没有清晰地观测到自旋极化量子阱态的隧穿．文章介绍了最近由卢仲毅、张晓光和Pantelides预言的Fe／MgO／FeO／Fe／Cr和其他铁磁量子阱隧道结中的共振隧穿，并解释铁、钴、铬的△1能带的对称性在这种共振隧穿中的作用．     

X射线荧光光谱检测多层薄膜样品的增强效应研究

研究了X射线荧光光谱检测多层薄膜样品的增强效应。根据多层膜中的X荧光强度理论计算公式编写了计算机程序,并计算了Zn/Fe和Fe/Zn双层膜样品中不同薄膜厚度时Fe Kα的一次荧光强度、二次荧光强度、二次荧光与一次荧光强度比以及二次荧光在总荧光强度中比例。研究发现,在多层膜样品的X射线荧光分析中,激发条件不变的情况下,元素谱线的一次荧光相对强度、二次荧光相对强度和二次荧光在总荧光强度中所占比例都随薄膜厚度及位置的变化而变化。当Fe和Zn层厚度相同时,随厚度的变化,对于Fe/Zn样品,Fe Kα二次荧光强度占总荧光强度最高为9％,而对于Zn/Fe样品这一比例最高可达35％。     

The Chemical Potential

The definition of the fundamental quantity, the chemical potential, is badly confused in the literature: there are at least three distinct definitions in various books and papers. While they all give the same result in the thermodynamic limit, major differences between them can occur for finite systems, in anomalous cases even for finite systems as large as a cm³. We resolve the situation by arguing that the chemical potential defined as the symbol μ conventionally appearing in the grand canonical density operator is the uniquely correct definition valid for all finite systems, the grand canonical ensemble being the only one of the various ensembles usually discussed (microcanonical, canonical, Gibbs, grand canonical) that is appropriate for statistical thermodynamics, whenever the chemical potential is physically relevant. The zero–temperature limit of this μ was derived by Perdew et al. for finite systems involving electrons, generally allowing for electron–electron interactions; we extend this derivation and, for semiconductors, we also consider the zero–T limit taken after the thermodynamic limit. The enormous finite size corrections (in macroscopic samples, e.g. 1 cm³) for one rather common definition of the c.p., found recently by Shegelski within the standard effective mass model of an ideal intrinsic semiconductor, are discussed. Also, two very–small–system examples are given, including a quantum dot.     

高温超导带材交流损耗的数值计算与分析

高温超导带材在许多领域得到越来越广泛的应用。交流损耗计算对于高温超导带材具有重要意义。该文介绍了两种交流损耗的数值计算模型,并以其中一种模型为例,对带材的交流损耗进行计算,与Norris公式计算结果作了比较,证明结果有效。最后提出了交流损耗数值计算中存在的问题。     

Extraction of local coordination structure in a low‐concentration uranyl system by XANES

Obtaining structural information of uranyl species at an atomic/molecular scale is a critical step to control and predict their physical and chemical properties. To obtain such information, experimental and theoretical L₃‐edge X‐ray absorption near‐edge structure (XANES) spectra of uranium were studied systematically for uranyl complexes. It was demonstrated that the bond lengths (R) in the uranyl species and relative energy positions (ΔE) of the XANES were determined as follows: ΔE₁ = 168.3/R(U—O_ax)² ? 38.5 (for the axial plane) and ΔE₂ = 428.4/R(U—O_eq)² ? 37.1 (for the equatorial plane). These formulae could be used to directly extract the distances between the uranium absorber and oxygen ligand atoms in the axial and equatorial planes of uranyl ions based on the U L₃‐edge XANES experimental data. In addition, the relative weights were estimated for each configuration derived from the water molecule and nitrate ligand based on the obtained average equatorial coordination bond lengths in a series of uranyl nitrate complexes with progressively varied nitrate concentrations. Results obtained from XANES analysis were identical to that from extended X‐ray absorption fine‐structure (EXAFS) analysis. XANES analysis is applicable to ubiquitous uranyl–ligand complexes, such as the uranyl–carbonate complex. Most importantly, the XANES research method could be extended to low‐concentration uranyl systems, as indicated by the results of the uranyl–amidoximate complex (～40 p.p.m. uranium). Quantitative XANES analysis, a reliable and straightforward method, provides a simplified approach applied to the structural chemistry of actinides.     

双势垒磁性隧道结中量子阱共振隧穿效应的第一性原理理论

磁性隧道结材料中自旋相关的量子阱态所导致的共振隧穿现象具有很重要的研究和应用价值，文章介绍了最近在Fe（001）／MgO／Fe／MgO／Fe双势垒磁性隧道结中存在的量子阱共振隧穿效应的理论研究工作，通过量子阱态的第一性原理的计算以及结合对中间Fe薄膜孤岛结构所导致Coulomb阻塞效应的分析，证实了最近Nozaki等人（Nozaki T et al．Phys．Rev．Lett．，2006，96：027208）实验中得到的振荡效应确实来源于中间Fe层多数自旋电子在Г点处形成的△1对称性的量子阱态．Coulomb阻塞效应的存在正是导致实验中低温下量子阱共振隧穿效应不够明显的主要原因．