全级配混凝土单轴疲劳特性细观数值模拟

为研究全级配混凝土在等幅、变幅及阶梯重复荷载作用下的疲劳特性,揭示材料特性与疲劳应力水平对其疲劳寿命的影响规律,通过自编程序建立二维随机骨料模型,运用有限元软件和耐久性疲劳分析软件进行联合仿真,对全级配混凝土细观结构进行应力分析和疲劳分析,探讨了不同骨料分布、骨料形状及疲劳应力水平对混凝土疲劳性能的影响,并估算了疲劳寿命。结果表明:在阶梯重复荷载作用下,骨料形状和分布对混凝土疲劳寿命影响较小,而疲劳应力水平对疲劳寿命影响较大;圆形和椭圆形骨料混凝土疲劳寿命较高,多边形骨料寿命较低;在疲劳加载破坏过程中,骨料界面先起裂,然后裂纹逐渐扩展贯通,最后导致整个试件完全破坏,可见骨料界面是混凝土中的薄弱部位,其寿命直接影响整个混凝土试件的寿命。研究成果为后续混凝土疲劳性能研究提供了参考。     

The properties of equimolar copolycarbonates of bisphenol A with bisphenol S and 1,4-bis(hydroxymethyl)cyclohexane

Ranges of both alternating and random 1:1 copolycarbonates of Bisphenol-A (2,2-bis(4-hydroxyphenyl)propane) and Bisphenol-S (4,4′-dihydroxydiphenyl sulphone) and of Bisphenol-A and 1,4-dimethanoylcyclohexane have been synthesized in order to test the hypothesis that, other things being equal, a more random structured polymer should exhibit superior thermal ageing characteristics. Studies on these materials' mechanical and thermal properties establish that within each pair they are extremely similar and hence the original hypothesis is disproved.     

Synthesis of tertiary poly(amido-amine)s with amido- and amino-groups randomly arranged along the macromolecular chain

A new synthesis of poly(amido-amine)s from bis (secondary amine)s and acryloyl chloride has been studied, leading to polymers in which the amido- and amino-groups are randomly arranged along the macromolecular chain. A poly(amido-amine) based on piperazine, chosen as the mother compound, has been fully characterized by ¹³C n.m.r. as well as by identification and quantitative evaluation of its hydrolysis products.     

带可变随机函数和变异算子的粒子群优化算法

标准粒子群优化算法的收敛分析表明,改变随机函数、个体历史最优,群体全局最优,有助于提高该算法的性能。为此,本文提出了一种带可变随机函数和变异算子的粒子群优化算法,即通过改变速度更新方程中的随机函数分布来调节粒子在迭代过程中飞向个体历史最优和群体全局最优的比重,通过对个体历史最优和群体全局最优进行变异来增强种群的搜索能力。实验结果证实了该算法的有效性。     

FREQUENCY DOMAIN TESTS OF MULTIVARIATE GAUSSIANITY AND LINEARITY

A stationary multivariate time series { X _t } is defined as linear if it can be written in the form X _t = ∑^∞ _{j =−∞} A _j e _{t − j} where A _j are square matrices and e _t are independent and identically distributed random vectors. If the e _t } are normally distributed, then { X _t is a multivariate Gaussian linear process. This paper is concerned with the testing of departures of a vector stationary process from multivariate Gaussianity and linearity using the bispectral approach. First the definition and properties of cumulants of random matrices are used to obtain the expressions for the higher-order cumulant and spectral vectors of a linear vector process as defined above. Then it is shown that linearity of a vector process implies constancy of the modulus square of its normalized higher-order spectra whereas the component of such a vector process does not necessarily have a linear representation. Finally, statistics for the testing of multivariate Gaussianity and linearity are proposed.     

PP-R管材料熔融挤出过程MFR控制研究

分析了PP-R（无规共聚聚丙烯）管材料MFR（熔体流动速率）的变化对力学性能的影响，着重通过双螺杆挤出机研究了PP—R管材料熔融挤出过程中影响MFR变化的因素。结果表明，合适的加工工艺控制和优良的抗氧体系是保证PP-R管材料加工过程中MFR稳定的前提。     

Event-driven,pattern-based methodology for cost-effective development of standardized personal health devices

Experiences applying standards in personal health devices (PHDs) show an inherent trade-off between interoperability and costs (in terms of processing load and development time). Therefore, reducing hardware and software costs as well as time-to-market is crucial for standards adoption. The ISO/IEEE11073 PHD family of standards (also referred to as X73PHD) provides interoperable communication between PHDs and aggregators. Nevertheless, the responsibility of achieving inexpensive implementations of X73PHD in limited resource microcontrollers falls directly on the developer. Hence, the authors previously presented a methodology based on patterns to implement X73-compliant PHDs into devices with low-voltage low-power constraints. That version was based on multitasking, which required additional features and resources. This paper therefore presents an event-driven evolution of the patterns-based methodology for cost-effective development of standardized PHDs. The results of comparing between the two versions showed that the mean values of decrease in memory consumption and cycles of latency are 11.59% and 45.95%, respectively. In addition, several enhancements in terms of cost-effectiveness and development time can be derived from the new version of the methodology. Therefore, the new approach could help in producing cost-effective X73-compliant PHDs, which in turn could foster the adoption of standards.     

A RANDOM PARAMETER PROCESS FOR MODELING AND FORECASTING TIME SERIES

Abstract. A generalized autoregressive (GAR) process {Z ( t ) ; t = 0 , ±1, …} is defined to satisfy the recurrence relation Z(t) = A_θ (t)Z (t -l)+ u( t ), where {A_θ(t); t = 0,±1, …} is itself a stochastic process depending on a vector parameter θ and where {u( t ); t = 0, ±1, …} is white noise with Eu ² ( t ) = a ². This paper develops theory and methodology and implementing the class of GAR processes for time series modeling and forecasting. Conditions on the 'parameter process' { A _θ ( t ); t = 0, ±1, …} are obtained for the existence of a GAR process; necessary and sufficient conditions on { A_θ ( t ) ; t = 0, ±1, …} for existence of a stationary GAR process are also obtained. Procedures are developed for computing maximum likelihood estimates of the parameters 0 and u² and for computing the minimum mean squared error forecasts for GAR processes.     

一种新的无双线性对的无证书安全签密方案

针对现有的无证书签密方案存在安全性不高、计算效率较低等诸多不足, 在Sharmila签密方案的基础上, 设计了一种新的无双线性对的无证书安全签密方案, 并在随机预言模型下证明了方案具有机密性和不可伪造性。同时, 该方案不需要双线性对和指数运算, 并且在确保安全性的前提下, 仅比现有的最高效签密方案多出两次点乘运算。     

无双线性对的无证书安全签密方案

已有的无双线性对的无证书签密方案,大都存在着机密性漏洞和签名选择性伪造问题。针对此问题,基于有限乘法交换群上的离散对数难题,提出一种无双线性对的无证书签密方案,并进行了安全分析和证明。指出采用随机预言模型的证明方法可能忽略不解决DL难题时对签密方案的攻击,不能证明破解签密方案的难度与解决DL难题相等价。通过对参数的数学分析,证明了破解本签密方案的必要条件是解决DL难题,不存在不解决DL难题攻击本签密方案的多项式时间算法。与已知所有方案相比,所提方案安全性更高。