MgB2（001）面超导结构的电子浓度第一原理分析

采用密度范函理论计算了金属化合物MgB2（001）薄膜结构的电子能带结构和状态密度,计算的交换相关能分别采用LDA和GGA。规范保守赝势的计算结果表明,晶格常数与实验值误差在很小的范围内,分析了引起MgB2（001）面结构超导转变时电子浓度和偏态密度的变化情况,发现构成该超导体结构的成健有3种,着重从结构的电子浓度变化分析了其超导特性,六角蜂窝状结构中硼原子间相互作用为sp^2杂化的共价健,镁原子和硼原子之间是离子健结合,镁原子层是金属健结合,镁原子的价电子部分转移到硼原子的pz轨道,部分电子为镁原子层共用。MgB2的超导机制为强烈的电子-声子耦合,为B原子间强烈的共价作用形成,是传统S波超导体。对Mg元素同一主族的其它硼化物进行布居分析,发现M出,中Mg原子电子转移明显强于BeB2和CaB2,说明电子浓度是引起超导转变的一个重要因素。     

金属间化合物YFe12-xMx（M=V,Cr）的结构和磁性研究

采用线性缀加平面波展式结合改进的局域轨道方法(APW+lo),基于密度泛函理论(DFT),优化、计算和分析了Y、Fe、V、Cr和YFe12-xMx(M=V、Cr;x=0～5)体系的结构和能量。系统的总磁矩和原子磁矩的计算表明,YFe12-xMx的磁矩主要来源于Fe,但是随着M浓度的增加而减小,这是因为M的加入不仅会降低体系中Fe的浓度,而且还将影响Fe之间相互作用导致Fe磁矩下降。利用计算获得的系统总的电子态密度和Fe的电子态密度对计算结果进行了分析。     

化合物SmCo5.85Si0.90的磁性及电子结构研究

用自旋极化的MS-Xα方法研究了原子簇Sm5Co28Si6的电子态密度、自旋能级劈裂及原子磁矩.结果显示,由于Sm-Co间的轨道杂化效应,使Sm原子的5d0空轨道上占据了少量5d电子.Co(3d)-Sm(5d)电子间的直接交换作用,构成Sm-Co间的主要耦合方式,这是化合物SmCo5.85Si0.90中形成铁磁性长程序的一个重要因素.Si的掺杂使2e晶位的负交换耦合作用明显减弱,Fermi面处电子间键合作用增强,化合物的系统自由能降低,从而有利于形成稳定的铁磁性结构.考虑到深层4f电子的局域性以及轨道杂化效应所产生的少量5d电子,可以得到Sm的原子磁矩为1.24μB,与顺磁盐中Sm3 的磁矩实验值(1.32～1.63μB)基本符合.     

第一性原理研究CuZr_2的电子结构及磁性质

运用密度泛函理论的第一性原理平面波赝势方法计算分析了CuZr_2相的电子结构及相关磁性质。计算的晶格参数与实验值相吻合。能带结构和态密度分析说明相成键峰主要来自Cus轨道,Cup轨道,Cud轨道,以及Zrd轨道。Mulliken布局分布显示了Zr向Cu电荷转移数为0.34。对电荷密度分析表明,Cu-Zr电子重叠较强,表现出明显的极性共价键。进一步对CuZr2的积分自旋态密度和磁矩的计算表明,CuZr_2磁性质表现为顺磁性,其磁性主要来源于Zr元素的d轨道贡献。CuZr_2的顺磁性将使ZW系镁合金产生较好的电磁屏蔽性能。     

立方氮化硼电子结构和光学性质的第一性原理计算

通过第一性原理计算可以预测材料的组分、结构与性能，设计具有特定性能的新材料，甚至可以模拟实验无法实现的工作。密度泛函理论巧妙地将电子之间的交换相关势表示为密度泛函，使得薛定谔方程在考虑了电子之间的复杂作用后，依然可以利用自洽的方法求解。利用CASTEP软件在不同机制下计算了立方氮化硼的能带结构、电荷密度分布、状态密度、...     

双钙钛矿Sr_2Fe_(1-x)Cr_xMoO_6电子结构与磁学性质的第一性原理研究

利用第一性原理系统计算了Sr2Fe1-x CrxMoO6体系中不同Cr含量(x=0,1/3,0.5和1)所对应Sr2Fe1-xCrxMoO6晶胞结构的电子结构和磁学性质。计算结果表明,体系的晶格常数、总磁矩及Fe离子磁矩由于Cr掺杂而降低,晶格发生畸变,并发现当Cr掺杂含量增加至0.5时自旋向上费米面附近态密度明显增加,超胞呈金属性,但Sr2Fe1-xCrxMoO6(x=0,1/3,0.5和1)仍保持半金属性。得出的计算结果与现有的实验和理论值吻合较好,该结果为其材料的进一步实际应用提供了理论依据。     

金属Ni的电子结构

用纯金属单原子(OA)理论、全势线性Muffin-Tin轨道(FP-LMTO)及第一原理离散变分方法(DVM)对Ni的电子结构与磁性进行了系统的研究,得到了金属Ni的轨道占据数、平衡晶格常数、结合能、原子磁矩、体弹性模量、态密度、能带结构等信息,并对结果进行了分析.     

ZnO材料电子结构的模拟计算与特性分析

方向是通过密度泛函理论研究新材料的电子结构性质,对ZnO材料进行第一性原理研究,研究涉及的材料物性包括几何构型、电子结构特性等方面。所使用的是线性化缀加平面波方法的基本理论(LAPW),其中主要内容包括LAPW方法的简要理论和所使用的WIEN2K软件的介绍。具体的描述对ZnO材料的电子结构的计算与分析,并与半导体的典型结构特性相比较,得出结论。     

超导薄膜FeSe和FeS_(0.5)Se_(0.5)的磁性与电子特性的研究

作为磁性超导体系的重要组成部分,新型铁基超导薄膜FeSe已经成为凝聚态物理研究的热点。本工作基于密度泛函理论的第一性原理,研究了FeSe以及S原子替位掺杂FeS_(0.5)Se_(0.5)超导薄膜的磁性结构、磁矩、能带和电子特性。研究发现,FeSe和FeS_(0.5)Se_(0.5)的基态结构均为条形反铁磁性,且在布里渊区中心Γ点和边界M点的费米面上都分别出现了3个空穴型能带和2个电子型能带,两者的费米能级都主要由Fe-3d电子以及As-4p(S-3p)电子构成,并且费米面处的Fe-3d电子态密度几乎与总能态密度相等,说明体系的超导电性主要来源于平面层内的Fe离子。然而,与纯的FeSe相比,FeS_(0.5)Se_(0.5)薄膜费米面上电子-空穴口袋的嵌套减弱,Fe离子磁矩减小,体系的反铁磁性减弱,表明S离子的掺杂有利于增强体系的超导电性。     

Fe掺杂CdTe电磁性质的第一性原理研究

使用基于密度泛函理论的第一性原理方法,计算研究了Fe掺杂CdTe的晶格结构与电磁性质变化。研究发现,掺杂体系的晶格常数与电子结构等随掺杂Fe原子的位置不同而异。通过能带结构与电子态密度的分析表明,不同占据位的Fe原子表现出迥异的电子能级分布、轨道杂化等,从而引起体系电子性质与原子磁矩的显著变化。其中,替代位与间隙位Fe杂质的原子磁矩分别为3.76和3.14玻尔磁子。这一研究对深入理解掺杂CdTe类稀磁半导体的物理性质有重要意义。     

Estimation of Parameters of Universal Distribution of Moments of Failure of Products

A method is proposed for estimating the parameters of a mixture of exponential and Weibull distributions for which the accuracy of preliminary estimates obtained by graphical analysis is refined in accordance with the criterion of maximum likelihood. The efficiency of the proposed method is supported by the results of statistical modeling.     

Evaluation of optical properties of highly scattering media by moments of distributions of times of flight of photons

A novel method for the determination of the optical properties of tissue from time-domain measurements is presented. The data analysis is based on the evaluation of the first moment and the second centralized moment, i.e., the mean time of flight and the variance of the measured distribution of times of flight (DTOF) of photons injected by short (picosecond) laser pulses. Analytical expressions are derived for calculation of absorption and of reduced scattering coefficients from these moments by application of diffusion theory for infinite and semi-infinite homogeneous media. The proposed method was tested on experimental data obtained with phantoms, and results for absorption and reduced scattering coefficients obtained by the proposed method are compared with those obtained by fitting of the same data with analytical solutions of the diffusion equation. Furthermore, the accuracy of the moment analysis was investigated for a range of integration limits of the DTOF. The moment analysis may serve as a comparatively fast method for evaluating optical properties with sufficient accuracy and can be used, e.g., for on-line monitoring of optical properties of biological tissue.     

Analysis of the rate of propagation of the wave of change of boiling modes

An approximate analytical expression is derived for the velocity of the front of the wave of change of boiling modes on a rod and on a plate. The impact of the Thomson effect and of the heater orientation in the gravity field is included. Adequate agreement is demonstrated between the derived relations and experimental data.     

Estimation of potentialities of methods of summation of direct measurement errors

Conventional methods for summation of direct measurement errors are considered. Conditions under which these methods provide consistent results are stated. It is proposed to utilize for characteristic of the total error, its interval estimator or the half-sum of the value obtained by adding up its arithmetic and geometric random errors.Translated from Izmeritel'naya Tekhnika, No. 4, pp. 10–12, April, 1995.     

空压机轴承箱蜗壳温度探头油封改造

由于空压机进气侧轴承箱蜗壳温度探头密封效果不好,使空压机及其后续管道受到油污染。后将温度探头的O形圈密封改为骨架油封,杜绝了轴承箱漏油问题。文章简介空压机的结构和技术参数,详细介绍了骨架油封的制作和优点。     

Characteristics of mechanical properties of materials in studies of conditions of attainment of marginal states

It is shown that conditions of attainment of marginal states in the material of structural components are formulated on the basis of analysis of force and deformation criteria of formation and development of destruction. The parameters of these criteria are data on types of structural materials, standard and special characteristics of their mechanical properties, structural forms of considered elements of the equipment, and their operating stress loading. In this case, the construction of a system of state equations for describing interrelation of current damage, external actions, and responses to them is based on the concept of calculating variations in properties of materials at all stages of the design life cycle.     

Determination of parameters of microstructural inhomogeneity of deformation of metals by the method of modeling

The article suggests a method of evaluating the microstructural inhomogeneity of deformation of metals by modeling. The method includes the measurement of deformations of metal according to meshes of a dividing grid with small base and the calculation of the distribution parameters of microdeformations in model representation. It is shown that the modeling method makes it possible objectively to evaluate the microinhomogeneity of deformation of metals independently of the chosen mesh size of the dividing grid. New structural characteristics are introduced: the base and wave of variation expressing the degree of crumbling or amalgamation of metal grains by inhomogeneity of deformation.Translated from Problemy Prochnosti, No. 7, pp. 40–44, July, 1991.