Relationship between microstructure and mechanical properties of polyether block amide foams

The mechanical behaviors of five polyether block amide foams, obtained by mold-opening foam injection process, were investigated with regard to their microstructures. The materials vary in mass ratios of hard versus soft segments, and/or in process packing time. The resulting microstructures have been characterized in terms of cavity size and shape ratios, by analyzing scanning electron microscope images after careful sample preparation. The foam mechanical responses have been characterized in compression at small and large strain. At small strain, the initial linear part of the stress–strain curve is enhanced firstly by the hard segment mass ratio and secondly by the fineness of the microstructure. Similar results have been obtained at large strain. The foam viscoelasticity at large strain has been characterized by stress relaxation and strain recovery tests, relevant for foam applications. Reduced packing time and pressure have been shown to lead to the presence of undesired large cavities. The morphological defects appear to have a negligible impact on the macroscopic mechanical behavior of the foams at infinitesimal strain, but lead to critical inconsistency at large strain. Furthermore, the mechanical behavior of the tested polyether block amide foams is controlled first by hard versus soft segments ratio, and second by the microstructure fineness.     

关于IPv6

IP源自70年代的早期科研网络,最初只是一个简易的客户/服务器连接.在过去10年间,它成为大范围的客户/服务器通信以及P2P通信的主要媒介,而在未来的几十年内,它的作用更将进一步发展扩大.对于IP的爆炸性部署使得20年来以IPv4为基础的旧的设计在各方面都显示出不足:IPv4地址的迅速枯竭;对于更简便的配置的需求;对于IP层面上安全性的需求;对于更好地支持QoS的需求;新式移动设备,如PDA、手机等,要求不间断的移动连接性;三重服务应用的兴起,使得对于多播支持的要求越来越高等等.这些都使得面向IPv6的转化不可避免、IPv6的部署迫在眉睫.     

IPv6 on DSL: the best way to develop always-on services

The deployment of IPv6 has become an issue of strategic importance for many economies, and telecom operators and ISPs play a key role in ensuring the availability of this new protocol on broadband access networks. It cannot be denied that the complexities exist in deploying IPv6 in an IPv4 world. Knowing this, telecom operators and ISPs have to ensure a viable transition strategy that takes into account transparent interoperability and mature integrated functionalities for deploying advanced applications on both IPv4 and IPv6. This potent combination will enable operators and ISPs to exploit the richer services offered by IPv6 while interoperating IPv4 during this long transition period, creating a new business model that will generate return on investment without waiting for the whole world to be fully IPv6 deployed. Only the use of IPv6 at the end-user site can drive differentiated services, achieving returns in not only investments, but also in services innovation and flexible communication solutions. So both IPv4 and IPv6 protocols have now to be implemented on digital subscriber line access networks. Solutions are mature and are beginning to be deployed.     

Numerical study of natural convection in asymmetrically heated channel considering thermal stratification and surface radiation

This article consists in a numerical study of the influence of thermal stratification and surface radiation on laminar airflow induced by natural convection in vertical, asymmetrically heated channels. Several cases are investigated to spotlight their influence on fluid dynamics and thermal quantities. Thermal stratification is obtained by a weak gradient of temperature outside of the channel, and then the temperature at the bottom end of the channel is considered as a function of time. Significant effects on vertical velocities, mass flow, and flow structure are shown. Surface radiation is also considered but appears less predominant than thermal stratification for the selected conditions of this article. The impact on heat transfer is also evaluated for each studied configuration. It is observed that local and mean Nusselt numbers weakly increase for the investigated cases.     

A multi-objective optimization problem in mixed and natural convection for a vertical channel asymmetrically heated

Structural and Multidisciplinary Optimization - This paper deals with a multi-objective topology optimization problem in an asymmetrically heated channel, based on both pressure drop minimization...