超声波传感器在沙子料位检测中的应用

为提高混凝土的质量,配比很重要,其中沙子精确计量是关键因素之一。提出并设计了超声波系统测量沙子料位;为保证测量精度,采取自动增益控制电路和温度补偿。经实验证明:该方法简单、可行,为沙子质量的检测提供了一种新的参考方法。     

Orientation and relaxation in uniaxially-stretched poly(2,6-dimethyl 1,4-phenylene oxide) — atactic polystyrene blends

Infra-red measurements of the dichroic ratio of atactic polystyrene and poly(2,6-dimethyl 1,4-phenylene oxide) absorption bands provide a valuable method for the determination of orientation as well as relaxation of chains of both polymers during stretching of their compatible blends. Influence of strain rate, temperature of stretching, and molecular weight of the polymers on orientation of both polymer chains in blends containing up to 35% PPO has been studied. Orientation relaxation for both polymers has been analysed using Lodge's constitutive equation. Master curves have been obtained for PPO and PS in the blends at a reference temperature T₀ = T_g + 10°C. Results are interpreted in terms of an hindrance of relaxation of PS chains induced by interaction with a highly-oriented PPO network which slowly relaxes.     

纳米SiO_2粒子在环氧树脂中的分散工艺研究

研究了纳米SiO2在环氧树脂中的均匀分散工艺,探讨了超声波振荡和超声波分散时间对纳米SiO2/EP复合材料力学性能的影响,确定了最佳分散工艺。SEM表明,采用高剪切与超声波复合分散工艺比高剪切工艺的分散效果好;测试了复合材料的力学性能,进一步证明纳米SiO2具有增韧增强作用。     

A kinetic model for polystyrene (PS) pyrolysis reaction

A mathematical model for the pyrolysis reaction of polystyrene (PS) in a semi-batch reactor has been presented. The thermal degradation of PS was flexibly modeled by a combination of random and specific chain-end scissions. Numerical simulation was used to investigate the effect of operating conditions on the PS products spectrum, the results of which were validated by the experimental data. It was found that as the reaction temperature increased (decreased), the monomer fraction in the products became lower (higher) while the trimer higher (lower). No significant variation in the product composition was, however, observed while constant temperature was maintained. These results indicate the reaction temperature is an effective manipulated variable for the control of products composition of PS pyrolysis. The calculation of the optimum temperature trajectories through the optimization study can thus be of interest for achieving productivity enhancement in plastics pyrolysis processes. This paper is dedicated to Professor Dong Sup Doh on the occasion of his retirement from Korea University.     

Boundary feedback stabilization of the telegraph equation: Decay rates for vanishing damping term

We study a semilinear mildly damped wave equation that contains the telegraph equation as a special case. We consider Neumann velocity boundary feedback and prove the exponential stability of the closed loop system. We show that for vanishing damping term in the partial differential equation, the decay rate of the system approaches the rate for the system governed by the wave equation without damping term. In particular, this implies that arbitrarily large decay rates can occur if the velocity damping in the partial differential equation is sufficiently small.     

波浪对渤海近岸海冰冲击作用的数值模拟

海冰在波浪冲击作用下可能会发生断裂,通过数值模拟定量地描述波浪引起的海冰断裂对海工结构的运行安全以及分析海冰断裂处海水与大气之间的热交换有重要作用。该文利用建立的三维数值波浪水池,将海冰视为刚性平板,结合渤海冬季海冰、波浪的相关参数,研究海冰受波浪冲击的垂向冲击力、水平冲击力、弯矩和最大弯曲正应力随波高、冰长及冰厚的变化规律;并结合渤海海冰的弯曲强度,推断海冰发生断裂的极限参数,结果表明:在渤海海域某些特定条件下,海冰断裂极限波高、冰长和最小冰厚分别为0.504 m、4.273 m和0.098 m。     

Reactive compatibilization of PE/PS blends. Effect of copolymer chain length on interfacial adhesion and mechanical behavior

This paper deals with in situ compatibilization of PE/PS blends via Friedel-Crafts reaction, performed at the interphase. Two polyethylenes having different molecular weights, and the same PS, were used along a wide range of catalyst concentration. The influence of the graft copolymer architecture and content on the efficiency of blend compatibilization was studied. The emulsifying effect, morphological aspects and mechanical behavior were also assessed for these blends. The amount of copolymer formed increases with catalyst concentration and the short chain length fraction of the homopolymers. The high molecular weight (MW) copolymers behaved as better compatibilizers as they showed, at the cmc, greater graft copolymer concentration than the low MW ones. A substantial increase in interfacial adhesion and particle size reduction was observed, even at catalyst concentrations as low as 0.3 wt%. In correspondence, mechanical properties, like ductility and yield strength, were enhanced by the effect of this Friedel-Crafts reaction's compatibilization.     

基于可调功率因数的单相AC－DC变换电路设计

本文以2013年全国大学生电子设计竞赛A题为依据,设计的单相AC-DC变换电路32位的STM32f103作为主控制器,主电路由220V市电经过自耦变压器,隔离变压器降至20-30V交流电,后接全桥整流电路,使电路稳定输出36V直流电,主电路通过硬件电流电压PI闭环控制,双环控制来调节输入的电流和输出电压,输入的交流电压和交流电流通过互感器采到单片机内,程序通过改变产生的正弦波的相位来改变功率因数,从而达到功率因数可调的目的,使设计的电路能包含题目中要求的所有部分,并通过优化而达到题目的要求,在主电路中加入继电器,控制继电器断开从而实现过流保护的功能。     

基于次生波的输电线路智能驱鸟装置设计

为了减小鸟类对输电线路可靠性的影响,利用次声波驱鸟原理,设计了一种新型的智能型驱鸟装置,该装置具有一定的实用价值.     

地质雷达和瑞雷波检测公路工程质量技术研究

地球物理方法的应用,使公路工程质量检测技术变得更加简捷、高效和经济,能够有效缓解当前路况检测和公路工程维护所面临的压力.在介绍了地质雷达和瑞雷波探测法的基本工作原理的基础上,将这2种探测技术应用在公路工程质量检测中,详细介绍了它们对公路厚度、压实度、抗压强度、弯沉值、含水量、脱空区段等检测的具体实施方法和步骤,并指出了相关注意事项.分析认为,随着技术的更新和设备的完善,地质雷达和瑞雷波技术能够有效地应用到公路工程的质量检测过程中,有着很好的应用前景和推广价值.