Superconductivity and magnetism in niobium doped YBa2Cu3O7 Related high Tc ceramics

Magnetic characterization has been performed on the members of the cuprateniobate RBa₂Cu₂NbO₈ (R = Pr, Nd, and La) series and R_1.5Ce_0.5Sr₂Cu₂NbO₁₀ (R = Pr, Eu, Nd, and Sm) series. The PrBCNO samples show a signature in the magnetization of a magnetic ordering at 12K. The PrCSCNO sample is nonsuperconducting and shows two distinct orderings at 17K and 53K. No such magnetic phase transition is observed down to 2K in the Nd and La based RBCNO materials or the Nd, Sm, and Eu based RCSCNO materials. Measurements of the lower critical field curve, dc irreversibility line, and critical curent densities are reported for each of the superconducting NdCSCNO, SmCSCNO, and EuCSCNO compounds.     

Superconductivity and Structure

The degree of the isolation of the CuO₂ planes (e.g. distance or bond valence to the apical coordination) has been shown by quantitative algorithms to be the major factor in determining aspects of the doping curves. They include the magnitude of the optimal number of doped holes (h_op) and the corresponding T _cop. It is shown that the roots of these phenomenological laws lie in a related structural dependence of super-exchange. The latter is expressed in the pseudo-gap or Neel temperature of the undoped parent compound. A fruitful language can be developed which deals with a buildup of complex quantum chemical features by bringing two holes into vicinity of a super-exchange O, forming a “local” Cu₂O₇ pair. Structural considerations also dictate that stress is relieved by alternate orthogonal pair orientation. This leads to plaid patterns with primary and secondary channels of charge. The presence of these two types of charge channels is involved in the mechanism of superconducting charge transport. Similar structuring of doped charge into plaid patterns of “local” pairs has been proposed for “all” high T _c superconductivity. STM now gives pictorial representation of the remnants of such an electronic crystal structure. The response of these bond-ordering motifs to structural details is further discussed. These ideas supply organization to the manifold experimental situation and provide opportunities for a unifying theory for high T _c superconductivity in terms of real space structuring of “local” pairs, largely on crystal-chemical principles.     

Node-pair reliability of network systems with small distances between adjacent nodes

A new method for computing the node-pair reliability of network systems modeled by random graphs with nodes arranged in sequence is presented. It is based on a recursive algorithm using the “sliding window” technique, the window being composed of several consecutive nodes. In a single step, the connectivity probabilities for all nodes included in the window are found. Subsequently, the window is moved one node forward. This process is repeated until, in the last step, the window reaches the terminal node. The connectivity probabilities found at that point are used to compute the node-pair reliability of the network system considered. The algorithm is designed especially for graphs with small distances between adjacent nodes, where the distance between two nodes is defined as the absolute value of the difference between the nodes’ numbers. The maximal distance between any two adjacent nodes is denoted by Γ(G), where G symbolizes a random graph. If Γ(G)=2 then the method can be applied for directed as well as undirected graphs whose nodes and edges are subject to failure. This is important in view of the fact that many algorithms computing network reliability are designed for graphs with failure-prone edges and reliable nodes. If Γ(G)=3 then the method's applicability is limited to undirected graphs with reliable nodes. The main asset of the presented algorithms is their low numerical complexity—O(n), where n denotes the number of nodes.     

Ba（Mg1／3Ta2／3）O3微波陶瓷的损耗研究

本工作用ＸＲＤ，ＥＰＭＡ，ＳＥＭ等测试技术计算和示出了用不同活性粉料制备的Ｂａ（Ｍｇ１／３Ｔａ２／３）Ｏ３微波陶瓷晶格中Ｂ位离子有序度和元素的面分布情况，对它们在Ｘ面下的电行为作了探讨。实验结果表明，ＢＭＴ陶瓷的微波损耗主要与其密度有序度和微观结构的均一度有关。     

CZ－2CFP离轨方案分析

针对ＣＺ－２Ｃ／ＦＰ（分配器）的离轨要求，对被动和主动两种离轨方案进行计算、分析和比较，最后选择主动离轨方案对ＣＺ－２ＣＦＰ在卫星分离后进行离轨，即在卫星分离后，用箭上姿控喷管将ＦＰ调姿至所需姿态，然后用剩余推进剂离轨，改变ＦＰ的轨道，使近地点高度降低，加快轨道衰减，达到离轨目的。这种主动离轨方案直接利用箭上姿控系统进行离轨，无需重新设计新的离轨系统，从而保持了原系统的简单和可靠并可以节省大量的经费。而且，主动离轨方案可以将ＦＰ同其它在轨飞行物之间的碰撞概率减小两个数量级还多，这对保证卫星的安全有很大的好处。     

卫星编队飞行中的队形设计研究

目前关于卫星编队飞行的研究有显著的增加。多颗从属卫星(从星)在近距离内与主卫星(主星)组成特定的队形以完成相应的任务,是卫星编队飞行的特点及潜在优势。卫星在编队飞行时,其队形定义为以各颗卫星质心为顶点所构成的几何形状,而队形设计则是根据队形的几何形状求出各卫星的轨道根数(其中主星的轨道根数可以根据任务的要求事先确定)。基于相对轨道根数法,根据卫星相对运动方程,提出了“自然队形”的概念及队形设计的一般方法,并给出了具体的例子。     

Magnetotransport Properties and Mechanism of the A-Site Ordering in the Nd–Ba Optimal-Doped Manganites

The crystal structure and magnetotransport properties of the Nd_0.70Ba_0.30-MnO_3.00−δ manganites have been investigated. The stoichiometric A-site ionic disordered Nd_0.70Ba_0.30MnO_3.00 sample is orthorhombic (SG=Imma) ferromagnet below T _C ≈151 K. It has metal-insulator transition at T _MI ≈140 K and peak of magnetoresistance ∼50% in field of 9 kOe. The anion-deficient partly A-site ionic ordered Nd_0.70Ba_0.30MnO_2.60 sample is ferrimagnet with T _N ≈130 K and has nanometric ∼440 nm grains. The oxygen annealed stoichiometric partly A-site ordered Nd_0.70Ba_0.30MnO_3.00 sample consists of two perovskite phases: (i) A-site ionic completely ordered tetragonal (SG=P4/mmm) NdBaMn_2.00O_6.00 with a Curie point of ∼310 K and (ii) superstoichiometric orthorhombic (SG=Pnma) NdMnO_3.00+γ with a Curie point of ∼120 K. The magnetoresistance of this sample at the room temperature is about 7% in a field of 9 kOe. Considerable changes of the magnetic properties are interpreted as due to the ordering of Nd³⁺ and Ba²⁺ cations as well as the formation of nanometric grains.      

使用MATLAB绘制原子轨道和电子云图形

绘制原子轨道和电子云图形是量子化学、结构化学研究和教学的重要内容。以氢原子为例，以MATLAB为程序开发语言，设计了一种精确、快速、简便地绘制原子轨道和电子云图形的应用程序。介绍了该程序设计的过程，给出了源程序和运行结果示例，并讨论了MATLAB的三维球坐标图形、四维图形的绘制技术。研究结果表明MATLAB是解决结构化学数值计算和数据可视化问题的一种非常有效的工具。     

最大重迭对称性分子轨道和分子几何参数计算

建立了AMl级别的最大重迭对称性分子轨道计算方案(MOSMO)。采用通常的半经验分子轨道方法AMl级别中完全相同的参数，计算了各种分子的几何参数等。所得计算结果与实验值及HF／6-31G*从头算方法计算结果相符，说明提出的计算方案是可行的。同时，由于提出的计算方案过程简单，更易推广使用到从头算方法难以解决的大分子体系和超分子体系的结构和性质研究。     

按件供应模式应用研究

对进口件（即KD件）按件供应与成组供应模式进行了对比分析，结合按件供应在启动、运行期间的工作特点，对神龙公司按件供应管理模式进行了分析和探讨，分析了KD件按件供应中MRPⅡ与JIT的结合应用以及按件供应模式的信息组织方式，提出了缩短订货期、降低库存、提高市场需求响应度的具体建议，并在实际运用中取得了显著的经济效益和管理效应。