Evolution of Weighted Networks by Duplication-Divergence Mechanism

The duplication and divergence process is ubiquitous in nature and man-made networks. Motivated by the duplication-divergence mechanism which depicts the growth of protein networks, we propose a weighted network model in which topological evolution is coupled with weight dynamics. Large scale numerical results indicate that our model can naturally generate networks with power-law-like distributions of degree, strength and weight. The degree-strength correlation is illustrated as well. These properties are in agreement well with empirical data observed in real-world systems. Furthermore, by altering the retention probability δ, weighted, structured exponential networks are realized.     

浅析SNMP三个发展阶段的安全机制

一、SNMP的基本概念 网络管理中的简单网络管理协议(SNMP)模型由4部分组成:管理节点(management node)、管理站(management station)、管理信息库(MIB:Management Information Base)和管理协议(management protoco1).     

氦－镉激光器的失效机制

本文报道国产氦－镉激光器常出现的导致失效的一些现象，并阐明其机制。同时给出一些改进意见及修理方法。     

具有新光学性质的Zn-Zn2SiO4纳米同轴线阵列

采用气相沉积技术在Si衬底上生长了Zn-Zn₂SiO₄芯-壳结构纳米同轴线阵列。根部呈笋状的纳米同轴线,直径约100nm,长度可以超过10μm;同轴线芯直径约50nm、壳层厚约25nm。通过X射线衍射的表征以及能量色散谱的线扫描,确定纳米同轴线的芯为Zn,壳层为Zn₂SiO₄。我们提出了一种新的生长机制,同时也为生长均匀的纳米同轴线提供一种新的技术。观察阴极荧光谱发现,纳米同轴线有三个主要发光带:强度最大的中紫外300nm发光、较弱的可见光区560nm以及红外谱区865nm的发光。对纳米同轴线截面的300nm发光峰观测发现,中紫外发光来源于Zn₂SiO₄壳层。正是这种同轴线的结构,使得其具备特殊的光学性质。     

T-RBAC访问控制模型及其约束描述语言

一种结合了基于任务的访问控制模型TBAC和基于角色的访问控制模型RBAC特点的新型访问控制模型-T-RBAC.该模型采用了以任务为中心的"用户-角色-任务-权限"的四级访问控制结构,较好地解决了当前工作流系统中存在的安全性问题.此外,在新模型的基础上设计了一套描述约束机制的语言ETCL,该语言在RCL2000的基础上扩充了时间特性和任务的概念,使新模型具备了较完整的约束描述能力.     

Dynamic Mechanism of Sustainable Molecular Orientation Generated From Cyclic Rotational States

Recently, two papers presented by Ortigoso et al. [Phys. Rev. Lett. 93 （2004） 073001 and Phys. Rev. A 72 （2005） 053401] develop a novel strategy in which the best sustainable molecular alignment/orientation has been achieved. We intend to analyse the dynamic mechanisms, including those Ortigoso et al. have not clarified.     

能够检测过氧化物炸药的器件

三丙酮三过氧化物（TATP）是过去几年中恐怖分子用过多次的炸药之一，科学家通过测定它的分解机制，已经找到了一种可以检测TATP和相关的炸药的器件。一般的炸药是在爆炸时放出热能的，以色列科学家E·Keinan发现，TATP的机制则完全不同。TATP的每个固态分子快速地分解为4个气体分子。“熵爆炸”型机制和汽车安全气袋在事故发生时的反应机制相仿。Keinan和助手们开发了一种钢笔型检测器，当存在爆炸物质时，基于酶催化氧化反应，检测器释放的几种化学物质将会改变颜色。     

机械球磨与反应烧结合成Sr2CeO4发光体的研究

Sr₂CeO₄ phosphor was synthesized by mechanical milling and reactive sintering in this work. The solid state reaction of SrCO₃and CeO₂ (2∶1) started at about 850 ℃ and completed at 1 000 ℃ for about 4 h. Two types of formation mechanism of Sr₂CeO₄ were proposed. When the starting powder mixture was fired above 1 000 ℃, the unstable intermediate phase SrCeO₃was developed, which then reacted with SrCO₃to form the final product Sr₂CeO₄, however, SrCO₃and CeO₂ converted directly to Sr₂CeO₄ at a lower temperature. The XRD results showed the crystal structure of Sr₂CeO₄ was orthorhombic. The emission spectra displayed a broad band with maximum at about 465 nm. The mechanical milling of starting power mixture and the sintering temperature had no effect on this emission spectra.