Dynamics of each component in miscible blends of polyisoprene and polyvinylethylene

The dynamics of the individual components in 1,4-polyisoprene/polyvinylethylene (PIP/PVE) miscible blends are studied using dynamic stress-optical measurements. While the homopolymers are thermorheologically simple and obey the stress-optic rule, the blends show failure of time-temperature superposition and complex stress-optic behavior. The way in which the stress-optic rule fails reveals the relaxation dynamics of each species. The dynamic modulus and complex birefringence coefficient are analyzed to infer the relaxation of each component. The entanglement molecular weight, M _e , and monomeric friction coefficient, ₀, of each species as a function of blend composition and temperature are determined from the contribution of each species to the dynamic modulus. The effect of blending on M _e of each component is small; however, its effect on ₀ of each species is dramatic. Blending strongly speeds the rate of relaxation of the high T _g component (PVE), while more modestly slowing the relaxation of the low T _g component (PIP). The dynamics of each species have different temperature dependencies in the blend, which leads to the failure of the superposition principle. Furthermore, both the difference between the friction coefficients of the two species and the difference in their temperature dependencies is greater in blends rich in the high T _g material (PVE).     

Distinctive Features of the Lateral Flow for a Convergent Air-Intake with a Convergent Nose Compression Surface

The results of numerical and experimental studies of a model configuration of a hypersonic vehicle realizing the principle of compression convergence of the entire jet captured by an air-intake from the oncoming stream are presented. The external flow past a convergent air-intake integrated with a transversely-concave nose compression surface is investigated over the freestream Mach number range from 2 to 6. The salient features of the flow pattern near air-intakes with sidewalls of different length are established and the influence of a limitation on the lateral flow near the external compression wedge on the flow rate characteristics of the air-intake is established. The numerical calculations are performed within the framework of the inviscid gas model using higher-order TVD schemes; the calculated and experimental results are compared.     

On a risk model with claim investigation

In this paper, a queue-based claims investigation mechanism is considered to model an insurer’s claim processing practices. The resulting risk model may be viewed as a first step in developing models with more realistic claim investigation mechanisms. Related to claim investigations, claim settlement delays and time dependent payments have been studied in a ruin context by, e.g. Taylor (1979), Cai and Dickson (2002), and Trufin et al. (2011). However, little has been done on queue-based investigation mechanisms. We first demonstrate the impact of a particular claim investigation system on some common ruin-related quantities when claims arrive according to a compound Poisson process, and investigation times are of a combination of exponential form. Probabilistic interpretations for the defective renewal equation components are also provided. Finally, via numerical examples, we explore various risk management questions related to this problem such as how claim investigation strategies can help an insurer control its activities within its risk appetite.     

高速列车空气动力学研究技术综述

随着我国高速铁路的快速发展,高速列车运行速度越来越快,包括气动阻力、横风效应、会车效应、隧道效应和气动噪声等一系列空气动力学问题日益突出. 利用模型试验、实车测量和数值计算等不同的研究手段,开展全面的高速列车空气动力学研究显得十分重要. 本文比较全面和系统地介绍了国内外高速列车空气动力学研究在模型试验、实车测量、数值计算等方面的技术现状和进展情况,对今后的发展方向和内容进行了展望.     

高温超导体时效与记忆效应实验研究

熔融织构的钇钡铜氧化物(YBCO)高温超导块材具有较高的临界电流密度和较好的力学性能,在制作高场磁体、悬浮列车等方面具有重要的应用。本文首先在恒定的液氮温度下,通过对不同等待时间, 场冷和零场冷条件下悬浮力特征的测试, 发现高温超导块材在液氮温度表现出较强的时效性;接着,对于不同温度循环引起的悬浮系统悬浮力时间弛豫特征研究显示出高温超导块材在低温下具有鲜明的记忆特性,随着温度的升高,其记忆效应逐渐消失,且正、负温度循环对其记忆效应影响表现出不一致性。所有这些特性表明,高温超导块材具有和自旋玻璃类似的性质,其根源为超导体内部复杂的微观结构。     

充液圆柱壳轴向冲击屈曲的实验研究与计算机数值模拟

借助落锤装置实现冲击加载,完成了一组充满水的金属薄壁圆柱壳试件轴向冲击屈曲过程的实验研究,同时利用LS-DYNA大型动力软件对冲击屈曲的全过程进行了计算机模拟.对于屈曲模态发展过程以及冲击力和液压的动态时程曲线,实验观察和数值结果均表现出较好的一致性.研究表明,在撞击过程中壳内形成很大的液体压力,在此内压和轴向压缩的联合作用下,壳壁发生轴对称塑性屈曲,屈曲模态为一系列依次发展的环带波纹.     

海洋工程地质的回顾与展望

本文通过对海洋工程地质发展的简单回顾阐述了其调查和评价的类别、方法与内容 ,对海底滑坡、砂土液化和原位土工测试等几个问题进行了重点展开 ,并对 2 1世纪的发展作了展望。     

基于卫星观测数据的预测模型及其应用

在战争中为了避开敌方军事卫星的侦查,需要对其过顶时间进行预警.对于参数公开的卫星,可以通过根数来进行准确的预报.而对于参数未知的卫星,提出了一种根据过往观测数据来对卫星过顶时间进行预测的思路:将卫星与地球之间复杂的三维耦合运动进行降维,并且以地面为参考系,发现卫星星下点运动轨迹具有高度的周期性·根据这种思路,可以通过获取的过往观测数据来对卫星未来的过顶时间进行准确预测.而对于战时地面运动单位躲避卫星的问题,可以根据所面对的不同侦查卫星通过设置一个固定的路线,让地面单位在该路线中有计划的行驶,能够躲避多种卫星的侦查.     

大学生孤独心理的调查与分析

文章对浙江大学华家池校区1050名学生进行了问卷调查,经统计分析后发现大学生产生孤独感的覆盖面很广.文章分析了孤独感与学生性别、类别、年级、生源、独生子女以及消费水平等6个层面的相关性关系,提出了克服大学生孤独心理障碍的几点教育建议.     

乙丙共聚物接枝马来酸酐反应机理的模拟研究

接枝反应;角鲨烷;乙丙共聚物接枝马来酸酐反应机理的模拟研究