高功耗抗恶劣环境计算机散热研究

以某高功耗军用加固计算机热设计为实例,介绍了热设计过程中,加固计算机主板芯片到风道这一传导路径热阻计算的具体方法,对比了军用加固计算机采用单、双风道各自的传导热阻.并用IcePak热分析软件对采用单、双风道的加固计算机主板温度分布进行了仿真计算,通过实践证明了双风道散热形式在高功耗加固计算机中的可实施性和优越性.     

一类中立时滞系统的一种改进的鲁棒自适应控制设计

The problem of adaptive robust control is addressed for a class of neutral delay systems. All uncertainties are assumed to be bounded by unknown constants. An improved adaptation law is proposed to estimate the square of these unknown bounds. Then, by making use of the updated values of the squared unknown bounds, an adaptive controller is designed to make the solution of the resultant closed-loop system uniformly ultimately bounded. Furthermore, this method avoids chattering and improves the performance. An example is given to illustrate the effectiveness of this method.     

ICP—AES techniques applied to analysis of precious metals in ores

A method for the simultaneous determination of precious metals and matrix elements in Fe and Cu ores is studied.The instrument used is ICAP-9000 polychromator and its accessory monochromator(N 1),Interferences of matrix are eliminated by matrix matching method,i.e.the influence of matrix was corrected by minus equivalent concentration method,The experiments show that the method is simple,sensitive and reliable;especially,suitable for determination of Au in Cu-Au ores.     

有约束的恒力铣削过程自适应模糊控制研究

讨论了自适应模糊控制的实现方法,并研究了其在有约束的恒力铣削加工过程中的应用.加工实验表明这种方法简单实用.     

Tuning the Learning Rate for Stochastic Variational Inference

Stochastic variational inference (SVI) can learn topic models with very big corpora. It optimizes the variational objective by using the stochastic natural gradient algorithm with a decreasing learning rate. This rate is crucial for SVI; however, it is often tuned by hand in real applications. To address this, we develop a novel algorithm, which tunes the learning rate of each iteration adaptively. The proposed algorithm uses the Kullback–Leibler (KL) divergence to measure the similarity between the variational distribution with noisy update and that with batch update, and then optimizes the learning rates by minimizing the KL divergence. We apply our algorithm to two representative topic models: latent Dirichlet allocation and hierarchical Dirichlet process. Experimental results indicate that our algorithm performs better and converges faster than commonly used learning rates.     

Stabilization of a Class of Switched Stochastic Systems with Time Delays Under Asynchronous Switching

This paper addresses stabilization problem for a class of switched stochastic systems with time delays by using piecewise Lyapunov–Krasovskii functional method. Asynchronous switching means the switching of the controller has a time delay to the switching of the system. We provide a set of Lyapunov–Krasovskii-type sufficient conditions for establishing the mean-square exponential stability. The mean-square exponential stability condition for the resulting closed-loop system is firstly derived by further allowing the Lyapunov–Krasovskii functional to increase during the running time of the active subsystem with the mismatched controller. Then, the corresponding solvability condition for stabilizing controllers is established. Finally, we present an example to show the effectiveness of the developed theory.     

管材焊缝超声波检测中缺陷的定位

基于管材焊缝超声一次波检测中缺陷的定位公式,分析了由探头K值和工件尺寸变化产生的定位误差,指出几种减小定位误差的修正方法;并对数字型仪器缺陷定位的原理及在实际检测中注意的问题进行了讨论。     

Efficient gene delivery to mesenchymal stem cells by an ethylenediamine-modified polysaccharide from mulberry leaves

This study investigates the use of a natural polysaccharide isolated from mulberry leaves as a nonviral gene vector. Ethylenediamine is chemically grafted to the backbone of a polysaccharide from mulberry leaves (MPS) to acquire nucleic acid binding affinity. A particle-size observation indicates that the cationic mulberry leaf polysaccharide (CMPS) can efficiently combine with plasmid transforming growth factor β1 (TGF-β1) to form nanoscaled particles. In addition, the electrophoresis assay indicates a retarded plasmid migration when the CMPS/pTGF-β1 weight ratio is increased to 30:1. The in vitro cell transfection experiment is performed based on bone marrow mesenchymal stem cells (MSCs) derived from rat femurs and tibias, and the findings reveal that the complex with a CMPS/pTGF-β1 weight ratio of 50:1 exhibits the highest cell transfection effect, which is significantly higher than that of branched poly(ethyleneimine) (PEI) (25 kDa; p = 0.001, Student's t-test) and slightly higher than Lipofectamine 2000. Moreover, the cytotoxicity assay also demonstrates that all of these tested complexes and the plasmid TGF-β1 are nontoxic to mesenchymal stem cells (MSCs). The results of the living cell imaging confirm that more of the CMPS/plasmid TGF-β1 nanoparticles can be taken up and at a faster rate by the MSCs than by the positive control Lipofectamine 2000; these data are consistent with the transfection efficiency data. Together, these results suggest that the CMPS/pTGF-β1 nanoparticle can potentially be developed into a promising alternative for the transfer of therapeutic genes into cells.     

Delay-dependent stability for discrete systems with large delay sequence based on switching techniques

This paper considers the exponential stability problem for a class of discrete time-varying delay systems with large delay sequences (LDSs). A new method based on a switching technique is presented to solve this problem. A switched delay system, in which one of the discrete subsystems may be unstable, is firstly employed to describe such a system, and then some new concepts about LDSs are introduced. Next, using a novel piecewise Lyapunov functional, explicit delay-dependent conditions are developed to show how long and how frequent the LDSs can be and still maintain the system exponentially stable. Without LDSs, the criterion obtained in this paper includes the established one as a special case. Two numerical examples are given to show the effectiveness of the proposed method.     

关于铱微柱的应变突变和应变速率敏感性问题研究

以聚焦离子束( FIB )制备的直径在1000 nm至7400 nm范围内的< 110 >取向铱单晶柱为材料,进行了单轴压缩试验。实验在纳米机械仪器Sementort中进行,结果表明,单晶柱的屈服强度与直径有显著关系,而与FIB制备无关。单晶柱的微压缩实验与整体铱在单轴压缩试验中的力学行为不同,微纳米尺度的流动应力随着柱直径的减小而增加,即尺寸效应。此外,塑性变形过程有明显的突变和大应变,重点研究了单轴压缩下铱单晶柱的应变突变的速度和应变敏感性问题。结果表明,压缩位移量随着持续时间和立柱直径的增加而增加,同时指出了应变敏感性( SRS )指数m,其值随着柱直径的减小而增加。