火灾条件下钢结构材料的力掌性能研究

通过万能材料试验机 ,对建筑中常用的Q2 35钢在火灾条件下的力学性能进行了研究 ,获得了Q2 35钢的屈服强度、极限强度、弹性模量、极限应变等力学性能指标随火灾温度变化的规律 ,并对影响Q2 35钢力学性能指标的因素进行了分析     

On the behavior and shape of mixture failure rates from a family of IFR Weibull distributions

Populations of many types of component are heterogeneous and often consist of a small number of different subpopulations. This is called a mixture and it arises in a number of situations. For example, a majority of products in industrial populations are mixtures of defective items with shorter lifetimes and standard items with longer lifetimes. It is a well‐known result that distributions with decreasing failure rates are closed under mixture. However, mixtures of distributions with increasing failure rates are not easily classifiable. If the subpopulations involved in the mixture have increasing failure rates, there might be some upward movement in the mixture and later a general downward pull towards the strongest component. Little work has been done in describing the shape of mixture failure rates when all subpopulations do not have decreasing failure rate. In this paper, we present general results that describe the shape and behavior of a failure rate of a mixture obtained from two Weibull subpopulations with strictly increasing failure rates. © 2004 Wiley Periodicals, Inc. Naval Research Logistics, 2004     

Sr2FeNbO6的晶体结构

系统地研究了Sr2FeNbO6的晶体结构,并利用步进扫描的X光数据成功地确定了Sr2FeNbO6的晶体结构,利用Rietveld方法精修出Sr2FeNbO6是空间群为Pnma(62)的正交结构,其中,晶胞参数分别为a=5.616 1A,b=7.971 7A,c=5.613 0A.     

A critical look at the U.S. deceased‐donor organ procurement and utilization system

The U.S. system for procuring and utilizing deceased‐donor organs for transplantation has been studied and written about in many articles. The purpose of this paper is to examine the interactions between the elements that comprise this system, and point out improvement opportunities that may be affected through operations research/management techniques. The authors demonstrate the need for developing data‐driven and analytic tools. In fact, data is used to generate hypotheses and support claims throughout the paper. The paper also points out the need to fully leverage data that is available to researchers, and to seek data that is currently not deposited in a centralized archive.     

Shock wave mitigation using zig-zag structures and cylindrical obstructions

The present study focuses on the mitigation of shock wave using novel geometric passages in the flow field. The strategy is to produce multiple shock reflections and diffractions in the passage with minimum flow obstruction, which in turn is expected to reduce the shock wave strength at the target location. In the present study the interaction of a plane shock front (generated from a shock tube) with various geometric designs such as, 1) zig-zag geometric passage, 2) staggered cylindrical obstructions and 3) zig-zag passage with cylindrical obstructions have been investigated using computational technique. It is seen from the numerical simulation that, among the various designs, the maximum shock attenuation is produced by the zig-zag passage with cylindrical obstructions which is then followed by zig-zag passage and staggered cylindrical obstructions. A comprehensive investigation on the shock wave reflection and diffraction phenomena happening in the proposed complex passages have also been carried out. In the new zig-zag design, the initial shock wave undergoes shock wave reflection and diffraction process which swaps alternatively as the shock front moves from one turn to the other turn. This cyclic shock reflection and diffraction process helps in diffusing the shock wave energy with practically no obstruction to the flow field. It is found that by combining the shock attenuation ability of zig-zag passage (using shock reflection and diffraction) with the shock attenuation ability of cylindrical blocks (by flow obstruction), a drastic attenuation in shock strength can be achieved with moderate level of flow blocking.     

A melt-cast Duan-Zhang-Kim mesoscopic reaction rate model and experiment for shock initiation of melt-cast explosives

A melt-cast Duan-Zhang-Kim (DZK) mesoscopic reaction rate model is developed for the shock initiation of melt-cast explosives based on the pore collapse hot-spot ignition mechanism. A series of shock initiation experiments was performed for the Comp B melt-cast explosive to estimate effects of the loading pressure and the particle size of granular explosive component, and the mesoscopic model is validated against the experimental data. Further numerical simulations indicate that the initial density and formula proportion greatly affect the hot-spot ignition of melt-cast explosives.     

Dynamic necking of a near α titanium alloy at high strain rates:Experiments and modelling

The tensile behaviour of near α Ti3Al2.5 V alloy, conceived for applications in aerospace and automotive engineering, is characterized from quasi-static to high strain rates. The material is found to present noticeable strain rate sensitivity. The dynamic true strain rate in the necking cross-section reaches values up to ten times higher than the nominal strain rate. It is also observed that beyond necking the dynamic true stress-strain curves present limited rate dependence. The experimental results at different strain rates are used to determine a suitable constitutive model for finite element simulations of the dynamic tensile tests. The model predicts the experimentally macroscopic force-time response, true stress-strain response and effective strain rate evolution with good agreement.     

一维金属-介质光子晶体的特性

利用特征矩阵法对一维金属-介质光子晶体的特性进行了计算,发现此种光子晶体具有可见光透明,微波、紫外高反的光谱特性,而且存在比一维介质光子晶体更宽、反射更强的全向带隙.     

脉冲群间多普勒频率变化率的高精度测量算法

提出了一种脉冲群间多普勒频率变化率的高精度测量算法,该算法利用脉冲群内相邻脉冲对间的互相关函数估计脉冲群模糊频率,在连续脉冲群间选择任一相同模糊频率进行解模糊得到各脉冲群相对频率,由于这些相对频率包含相同的模糊,从而可以利用差分或滤波算法得到脉冲群间多普勒频率变化率。该算法具有相对频率估计精度高、解模糊过程简单、运算量小、多普勒频率变化率测量精度高等优点。计算机仿真和地面缩比试验均证明了该测量算法的有效性。     

灭火救援战术演习有关问题探讨

对灭火战术训练法之一———灭火救援战术演习的含义、特点、地位、作用以及演习的组织方式等方面进行了系统论述,为部队更有效地开展灭火战术演习,提高部队灭火救援作战能力,提供理论指导和借鉴。