Fracture and microstructure of open cell aluminum foam

SEM and EDS measurements were used to scrutinize the microstructure of Duocel open cell 6101 aluminum foam in relation to its fracture properties. In-situ SEM tensile tests on the open cell aluminum foam were performed to investigate the different fracture modes of struts and Aramis/Digital Image Correlation software was used to map the strain in individual struts. Observations during tensile tests showed that the microstructure of the struts has a great influence on the fracture behaviour of the foam. In particular AlFeSi-precipitates, which are due to the casting of the 6101 aluminum alloy, and the morphology of the foam alters the fracture mode of the struts in the foam from transgranular to intergranular. Less energy is needed for intergranular fracture of struts and the strain to failure of the foam is decreased due to weak individual struts.     

The Underdoped Region of the Phase Diagram of YBa2Cu3O6+x

Here we present a reviewed phase diagram of the high-T _c superconducting YBa₂Cu₃O_{6+ x} compound, finely mapped in the strongly underdoped region (0 < x < 0.5), from the pure antiferromagnetic state to the superconducting regime. The Neèl and spin freezing temperatures have been measured by μSR experiments while the hole density per Cu atom in the CuO₂ planes has been determined from the resistive T _c and from Seebeck coefficients at 290 K. The phase diagram is discussed in comparison to those of La_{2− x} Sr _x CuO₄ and Y_{1− x} Ca _x Ba₂Cu₃O₆ cuprate systems.     

Innovation in Industrial Districts: Evidence from Italy

The aim of this paper is to show that Italian manufacturing firms belonging to Marshallian industrial districts carry out a higher innovative effort than is usually acknowledged. The empirical analysis makes use of a panel of 1,218 district and non-district firms belonging to traditional sectors. Data refers to the years 1992 and 1995. We have estimated an augmented Cobb-Douglas production function. The estimates make it possible to empirically identify three different determinants of firms' productivity: (i) the intentional innovative activity; (ii) the “district effect”; and (iii) the joint district and innovation effect. The results show that firms' membership in industrial districts and product innovations are key factors in explaining the productivity of firms working in traditional Italian sectors.     

Electrical and optical characterization of Na: CuInS2 thin films grown by spray pyrolysis

The structural, electrical and optical properties of Na-doped CuInS₂ thin films grown by spray pyrolysis were studied. These films crystallized in the sphalerite structure of CuInS₂, and showed to contain traces of indium sulfide and CuIn₅S₈ as impurity phases. All films were In-rich and showed p-type conductivity. The film conductivity was strongly affected by Na-doping, which decreased from 10⁻² to 10⁻⁵ S/cm by increasing the [Na]/[Cu] ratio from 0.005 to 0.03 in the spray solution. The band gap energy was observed to increase, from 1.4 to 1.45 eV, with increasing the [Na]/[Cu] ratio. Our results suggested that Na could be an effective acceptor impurity in sprayed CuInS₂.     

Anomalous Thermal Expansion in Superconducting Mg1− x Al x B2 System

The thermal lattice expansion in the superconducting Mg_{1? x} Al _x B₂ system (x = 0, 0.13, and 0.59) has been measured using high-resolution X-ray powder diffraction. An unusual large negative thermal expansion (NTE) appears for temperatures below T ^* = 60 K in the MgB₂. The NTE effect increases in Mg_0.87Al_0.13B₂ and disappears at high Al content in the Mg_0.59Al_0.41B₂ where the temperature dependence of volume follows a standard Einstein model in the whole temperature range. The anomalous behavior of the thermal expansion provides a direct evidence in the physics of diborides for the relevance of the proximity to the 2.5 Lifshitz electronic topological transition where the Fermi surface of the σband changes from a two-dimensional (2D) to a three-dimensional (3D) topology.     

Fracture criterion for kinking cracks in a tri-material adhesively bonded joint under mixed mode loading

The fracture behavior of a composite/adhesive/steel bonded joint was investigated by using double cantilever beam specimens. A starter crack is embedded at the steel/adhesive interface by inserting Teflon tape. The composite adherend is a random carbon fiber reinforced vinyl ester resin composite while the other adherend is cold rolled steel. The adhesive is a one-part epoxy that is heat cured. The Fernlund-Spelt mixed mode loading fixture was employed to generate five different mode mixities. Due to the dissimilar adherends, crack turning into the adhesive (or crack kinking) associated with joint failure, was observed. The bulk fracture toughness of the adhesive was measured separately by using standard compact tension specimens. The strain energy release rates for kinking cracks at the critical loads were calculated by a commercial finite element analysis software ABAQUS in conjunction with the virtual crack closure technique. Two fracture criteria related to strain energy release rates were examined. These are (1) maximum energy release rate criterion (G_max) and, (2) mode I facture criterion (G_II = 0). They are shown to be equivalent in this study. That is, crack kinking takes place at the angle close to maximum G or G_I (also minimum G_II, with a value that is approximately zero). The average value of G_IC obtained from bulk adhesive tests using compact tension specimens is shown to be an accurate indicator of the mode I fracture toughness of the kinking cracks within the adhesive layer. It is concluded that the crack in tri-material adhesively bonded joint tends to initiate into the adhesive along a path that promotes failure in pure mode I, locally.     

S7-200PLC在水电厂渗漏排水系统中的应用

根据中小型水电厂渗漏排水装置自动控制过程的特点和要求，结合“无人值班”(少人值守)水电厂远动通信的要求，论述了其常规设计制约整个水电厂的生产与调度的缺陷，提出了采用S7—200PLC构成的控制方案，并以某水电厂渗漏排水控制系统为例，重点探讨了其工作原理、硬件及软件结构。     

关于积分半群的两个结论

得到了生成元为闭算子的n次积分半群的表示定理，并根据积分半群的C半群的关系，进而得到了n次积分半群的谱映射定理。     

基于道路轮廓的自动生成道路路心线算法

在对面向车辆导航 GIS(VNGIS)和一般 GIS的共性和区别进行分析的基础上 ,提出了一种基于道路轮廓线的、自动生成道路路心线算法 ,同时介绍了路心线求取的一般算法 ,即先用基于层轮廓三维重建的最短对角线法来生成三角形网络 ;然后由三角形网络生成道路路心线 ;还介绍了在遍历道路网络时 ,几种确定初始轮廓和判断道路路口的方法 ;接着详细说明了单条道路模板跟踪算法 ,在算法中采用了双模板法和轮廓线生长准则 ,从而有效地完成了在道路跟踪过程中对道路轮廓线中白噪声的消除 ;最后叙述了道路网络的遍历算法 .实验研究证明 ,该算法可以快速、精确而又稳健地获取道路路心线 ,因此极大地加快了面向车辆导航电子地图的制作速度和精度 ,具有广泛的应用价值