浅议数据库的安全技术

数据库管理系统安全技术越来越被人们所重视。本文就数据库安全相关标准、数据库系统面临的安全威胁、数据安全传输常用协议以及数据库安全技术研究趋势谈了自己的一些看法。     

环境磁学参数简介

环境磁学是20世纪80年代一门新兴的学科,是介于地球科学、环境科学及磁学的边缘科学。它通过研究磁性矿物在环境系统中的迁移、转化和组合的规律,根据物质在磁性特征上的联系及其反映在环境上的内涵,探索不同空间尺度的环境作用、环境问题和人类活动影响,揭示环境变化过程和机制。由于环境磁学具有快速、高效、经济以及对样品无破坏性等优点,近些年来得到越来越广泛的应用。但其采用的方法及涉及到的参数繁多,很容易混淆,本文简要介绍了环境磁学涉及的参数及其基本物理含义,为应用环境磁学解决气候、环境污染等问题提供参考。     

基于节点稳定概率和链路贡献度的应用层组播树生成算法

组播技术从IP组播向应用层组播的发展,解决了IP组播部署难的问题.应用层组播依靠终端主机进行组播数据的转发,需要解决应用层组播的稳定性.最小延迟组播树的生成等问题.首先分析了影响应用层组播稳定和延时的3个因素:节点稳定概率、节点出度约束和节点间的通信延时.根据这些影响因素抽象出基于稳定概率的度约束边带权应用层组播树生成T-SDE模型,给出稳定度在T-SDE下的表达形式,并证明T-SDE问题属于NP-hard;其次通过分析节点对组播树稳定和延时的贡献,给出3种基于节点稳定概率和链路贡献度的T-SDE问题的近似解决算法;实验表明,该类算法生成的组播树在平均延时、最大延时和稳定度等方面有较大优势.     

氧化亚铜微米晶的水热合成与生长机理

氧化亚铜是一种重要的P型半导体材料，目前因其独特的可见光催化性能在科研领域引起了广泛的重视。以CuSO4·5H2O为铜源，以α—D-葡萄糖为还原剂，并利用水热还原反应合成出了不同形貌的Cu2O微米晶。利用X射线粉末衍射分析（XRD）、透射电子显微镜（TEM）对合成的样品进行了形貌与结构的表征与分析。结果表明所合成的晶粒尺寸均匀且分散性好。讨论了不同条件下的晶粒生长机理，运用扩散机制与聚集机制解释了不同形貌的成因。     

Effects of Ti addition on low carbon hot strips produced by CSP process

Large quantity of fine Ti（C,N） particles, 15-30 nm in size, were observed in low carbon hot strips added to a small amount of Ti and produced by CSP process. The results showed that the precipitation of Ti（C,N） mostly took place during soaking and hot rolling, which is significantly different from that in the conventional production. These fine Ti carbonitride particles could be very effective on the austenite grain refinement by hindering grain growth of recrystallized austenite. Their precipitation behavior was discussed and compared with that of the steels produced in the conventional production.     

A spectral Integral method (SIM) for layered media

A spectral integral method is presented for electromagnetic scattering from dielectric and perfectly electric conducting (PEC) objects with a closed boundary embedded in a layered medium. Two-dimensional layered medium Green's functions are computed adaptively by using Gaussian quadratures. The singular terms in the Green's functions and the non-smooth terms in their derivatives are handled appropriately to achieve exponential convergence. Numerical results, compared with the ones obtained by using other methods, demonstrate the spectral accuracy and high efficiency of the proposed method. They also confirm that the spectral integral method (SIM) is applicable to concave objects.     

EMD方法在多光谱遥感图像融合中的应用

多光谱图像具有较高的光谱分辨率,而其空间分辨率比较低,致使融合后的多光谱图像空间细节的表现能力不足。为了克服这种融合图像空间细节表达能力差的问题,本文提出了用EMD(EmpiricalModeDecomposition)方法对多光谱图像进行分解,提取空间细节和纹理信息,并将其叠合到融合图像上的方法。实验表明:改善了视觉效果,提高融合图像的空间表达能力。     

基于CPS-20B1智能控制器的恒压变频供水系统

采用CPS-20B1智能型变频调速供水控制器和变频器的恒压供水的控制策略,并自动地调整泵组的运行台数和电机的转速。利用内置的PID控制器调节变频器的输出,实现闭环自动调节、恒压供水。运行结果表明,该控制系统在管网流量变化时具有稳定供水压力,工作可靠和节约电能显著等特点。     

双相机空间定位硬件系统的构成研究

本文针对交汇测量的工作原理，设计并具体实现了同步精度高，数据存储量大的测量系统，并详细介绍了该系统的硬件组成及各部分的工作原理和实现的功能，改进了现有系统工作方式的缺陷，解决了多台测量摄像机的同步工作和图像海量数据的存储难题，拓宽了此类系统的应用范围。     

Aspects of microstructure in low carbon steels produced by the CSP process

The solidification structure, microstructure evolution during rolling and precipitates with nanometers in dimension of the low carbon steels produced by CSP process with thin slabs have been studied in recent years. Important differences in microstructure and mechanical properties between the CSP products and the conventional one were observed. These differences may arise from the much rapider solidification rate and cooling rate after casting of the thin slabs. Some aspects of the microstructure for the low carbon steels of the CSP thin slabs are summarized and compared with the conventional one.