Formation mechanism of cavitating spalls

The dynamics of formation of cavitation zones in a liquid upon reflection of a shock pulse from the free surface is studied numerically in a one-dimensional formulation using the Iordanskii-Kogarko-van Wijngaarden two-phase model. It is shown that the formation of a system of cavitation zones (clusters) with a dynamically increasing volume concentration of the gas phase near the free surface is due to oscillations of the structure of the rarefaction wave profile. The fast relaxation of tensile stresses in the cavitation zone ends in the formation of a quasistationary mass-velocity field, which provides for almost unbounded growth of cavitation bubbles in subsurface clusters and explains the occurrence of the spall layers observed in experiments. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 49, No. 2, pp. 65–73, March–April, 2008.     

Blumlein快放电电路传输线电容和储能电容的研制

为减小Blum lein电路中的寄生电阻与电感,自行设计了传输线电容与储能电容,以平行平板电容器结构代替了原来的无感电容与传输线电容的结构,使得电路中寄生电感下降1倍以上,电路性能得到很大改进,满足了S2激光器产生辉光放电的要求.     

一种基于小波的多光谱图像压缩方法

文章提出一种基于Karhunen2Loeve变换(KLT)和小波量化编码的多光谱图像压缩方法。该法首先使用KL变换步骤来去除谱间冗余,而后对各变换波段图像进行小波变换,并利用均匀阈值网格编码量化方法来量化小波子带图像,最后使用算术编码对量化结果进行熵编码。为使编码器能为所有谱段各子带获取率- 失真意义上最优的量化阈值,本文提出基于子带图像统计特性和网格编码量化器率- 失真特性的比特分配算法。实验表明,本方法能高效地压缩多光谱图像,表现出优异的压缩性能。     

新型快速显微多道分光光度技术对血红蛋白的光谱分析

用新型快速显微多道分光光度(MMSP)技术,在生理环境(pH、温度、氧分压和渗透压)改变下,对单个活态人血红细胞内血红蛋白分子的吸收光谱进行监测。发现生理环境的改变,引起血红蛋白吸收光谱曲线540,575 nm特征吸收峰的峰高、峰位和峰形发生了不同程度的变化。MMSP技术提示血红蛋白分子的结构、浓度和功能与上述生理环境密切相关。     

纳米二氧化锡电极的制备及其用于水体中大肠杆菌的快速计数研究

制备了新型纳米二氧化锡电极, 将此电极用于水体中大肠杆菌的快速计数研究. 实验结果表明, 用该电极为工作电极, 采用计时电流法能简便、快速、灵敏地对水体中的大肠杆菌进行计数. 通过大肠杆菌脂质过氧化后丙二醛含量的检测, 对大肠杆菌在纳米二氧化锡电极上的电化学响应机理进行了初步的探讨.     

离子色谱整体固定相的最新进展

整体固定相是近年来新兴的一种多孔性固定相介质,它在离子态及极性化合物的分离中得到了越来越广泛的重视。本文就离子色谱领域整体固定相的发展以及最新的研究动向进行了综述,讨论了离子色谱整体固定相的优点、分类以及在分离分析离子态物质方面的应用等。     

与医用CT配套的便携式材料试验机的研制及其在混凝土损伤研究中的应用

混凝土内部细观裂纹的演化规律研究可以解释其动态特性和损伤破坏机理.X射线CT技术是无损探测混凝土内部细观裂纹萌生、扩展、贯通的有效手段.与医用CT配套的便携式材料试验机是进行混凝土CT试验的关键加载设备.本文概要介绍研制便携式材料试验机的研制过程.论述实现动态加载的几个关键技术问题,包括加载设备的便携式要求、加载波形显示、加载控制、试件安装和粘结技术等.经过试验,表明所研制的加载设备达到了使用要求.混凝土动力压缩条件下突发性裂纹的出现是其动态强度提高的原因之一.     

单轴拉伸条件下细观非均匀性岩石损伤局部化和应力应变关系分析

岩石在拉应力状态下的力学特性不同于压应力状态下的力学特性．利用细观力学理论研究了细观非均匀性岩石拉伸应力应变关系包括:线弹性阶段、非线性强化阶段、应力降阶段、应变软化阶段.模型考虑了微裂纹方位角为Weibull分布和微裂纹长度的分布密度函数为Rayleigh函数时对损伤局部化和应力应变关系的影响,分析了产生应力降和应变软化的主要原因是损伤和变形局部化.通过和实验成果对比分析验证了模型的正确性和有效性．     

Poly(N‐isopropylacrylamide) Nanoparticle‐Incorporated PNIPAAm Hydrogels with Fast Shrinking Kinetics

Summary: Novel temperature‐responsive poly(N‐isopropylacrylamide) (PNIPAAm) nanoparticle‐containing PNIPAAm hydrogels were prepared by radical polymerization. In comparison with conventional PNIPAAm hydrogels, the PNIPAAm gels thus prepared exhibit much faster response rates as the temperature is raised above the lower critical solution temperature. The improved properties are a result of the incorporation of PNIPAAm particles, which first shrink and then generate pores for water molecules to be quickly squeezed out of the bulky PNIPAAm gels.

Schematic illustration of the shrinking process: (I) First PNIPAAm particles shrink and generate pores; (II) the bulky gels then shrink further at a rapid rate.     

IP router architectures: an overview

In the emerging environment of high performance IP networks, it is expected that local and campus area backbones, enterprise networks, and internet service providers (ISPs) will use multigigabit and terabit networking technologies where IP routers will be used not only to interconnect backbone segments but also to act as points of attachments to high performance wide area links. Special attention must be given to new powerful architectures for routers in order to play that demanding role. In this paper, we identify important trends in router design and outline some design issues facing the next generation of routers. It is also observed that the achievement of high throughput IP routers is possible if the critical tasks are identified and special purpose modules are properly tailored to perform them. Copyright © 2001 John Wiley & Sons, Ltd.