冲击荷载作用下粘土孔隙水压的数值分析

为了分析冲击荷载作用下粘土的孔隙水压力的增长规律，为分析粘土介质的动态响应、动力固结加固提供理论依据，将冲击瞬态荷载简化为三角形荷载，通过编制瞬变动态弹塑性有限元程序，对冲击荷载作用下粘土孔隙水压的动态响应进行了模拟，得出了冲击荷载作用下粘土孔隙水压的增长规律，发现孔隙水压力峰值无论是随水平距离还是随深度的增加均呈指数形式衰减，和实际工程施工中孔隙水压的监测数据相吻合。     

DENSITY FUNCTIONAL FOR STRUCTURES OF COLLOIDS CONFINED IN A SLIT-LIKE PORE

A density functional theory is applied to calculating the local density profiles of colloids confined in a slit-like pore as well as the radial distribution functions of bulk colloids. The interaction between the colloidal particles is described using a hard-core Yukawa model. The excess Helmholtz energy functional is a combination of the modified fundamental measure theory of Yu and Wu （2002） for the hard-core contribution and a corrected mean-field theory for the attractive contribution. Comparison with the results from the Monte Carlo simulations shows that the corrected theory improves the density profiles of colloids in the vicinity of contact over the original mean-field theory. Both the present corrected theory and simulations suggest that there are depletion and desorption for the colloid with strong attraction between particles at low temperature.     

Capillary Imbibition and Pore Characterisation in Cement Pastes

The kinetics of capillary imbibition in ordinary Portland cement pastes has been studied experimentally and theoretically. Nuclear magnetic resonance stray field imaging (STRAFI) has been used to record water concentration profiles for various ingress times. The profiles follow a t law and thus a master curve can be formed using the Boltzmann transformation. The distribution of pore sizes within the sample as measured by NMR cryoporometry shows a prominent peak at 100Å. A computer model of the pore structure was developed consisting of a lattice of interconnecting pores with a size distribution consistent with the cryoporometry results. The Hagen–Poiseuille law was used to describe the kinetics of the water in this pore structure. The best agreement between the computer simulations and the experimental master curve was obtained by using a narrower range of pore sizes than indicated by the cryoporometry results.     

阶梯AlGaN外延新型Al0.25Ga0.75N/GaNHEMTs器件实验研究

本文报道了作者提出的阶梯AlGaN外延层新型AlGaN/GaN HEMTs结构的实验结果. 实验利用感应耦合等离子体刻蚀(ICP)刻蚀栅边缘的AlGaN外延层, 形成阶梯的AlGaN 外延层结构, 获得浓度分区的沟道2DEG, 使得阶梯AlGaN外延层边缘出现新的电场峰, 有效降低栅边缘的高峰电场, 从而优化了AlGaN/GaN HEMTs器件的表面电场分布. 实验获得了阈值电压-1.5 V的新型AlGaN/GaN HEMTs器件. 经过测试, 同样面积的器件击穿电压从传统结构的67 V提高到新结构的106 V, 提高了58%左右; 脉冲测试下电流崩塌量也比传统结构减少了30%左右, 电流崩塌效应得到了一定的缓解.     

增殖剂球床载气体流动特性

增殖剂球床是聚变堆或混合堆产氚包层可选结构之一,准确把握增殖剂球床中载带气体的流动特性有助于提高对球床载氚过程的认识并优化包层设计。采用离散元程序PFC3D模拟增殖剂小球的填充行为,在球床内不同位置随机截取不同尺寸的控制体,利用布尔运算中的"差集"得到孔隙范围,建立孔隙分布的三维几何模型,进一步划分网格并用计算流体力学(CFD)方法求解,得出控制体上单位长度的压降以及单元体内的速度分布特征,计算结果发现载带气体速度分布与γ分布很类似,且只要选取恰当的控制体,通过计算流体力学方法可以较好地分析整个球床孔隙内流体的流动,有利于进一步研究载氚及相关过程。     

Protein delivery based on uncoated and chitosan-coated mesoporous silicon microparticles

Mesoporous silicon is a biocompatible, biodegradable material that is receiving increased attention for pharmaceutical applications due to its extensive specific surface. This feature enables to load a variety of drugs in mesoporous silicon devices by simple adsorption-based procedures. In this work, we have addressed the fabrication and characterization of two new mesoporous silicon devices prepared by electrochemistry and intended for protein delivery, namely: (i) mesoporous silicon microparticles and (ii) chitosan-coated mesoporous silicon microparticles. Both carriers were investigated for their capacity to load a therapeutic protein (insulin) and a model antigen (bovine serum albumin) by adsorption. Our results show that mesoporous silicon microparticles prepared by electrochemical methods present moderate affinity for insulin and high affinity for albumin. However, mesoporous silicon presents an extensive capacity to load both proteins, leading to systems were protein could represent the major mass fraction of the formulation. The possibility to form a chitosan coating on the microparticles surface was confirmed both qualitatively by atomic force microscopy and quantitatively by a colorimetric method. Mesoporous silicon microparticles with mean pore size of 35 nm released the loaded insulin quickly, but not instantaneously. This profile could be slowed to a certain extent by the chitosan coating modification. With their high protein loading, their capacity to provide a controlled release of insulin over a period of 60-90 min, and the potential mucoadhesive effect of the chitosan coating, these composite devices comprise several features that render them interesting candidates as transmucosal protein delivery systems.     

多级孔WO3/ZrO2固体酸催化剂的制备与表征

采用复合模板表面活性剂辅助水热法一步合成了WO3/ZrO2多级孔固体酸催化剂,并应用X射线衍射、低温N2吸附-脱附、拉曼光谱及NH3程序升温脱附对催化剂进行了表征.结果表明,WO3的引入使得WO3/ZrO2催化剂的比表面积增大,表面的酸中心明显增加.在乙酸和正丁醇的酯化反应中,WO3/ZrO2多级孔固体酸催化剂表现出较...     

ZrO2-SiO2复合物表面酸性的调控及催化四氢呋喃聚合性能研究

采用醇-水溶液加热法制备了复合均匀的ZrO2-SiO2复合氧化物,通过调整复合物中ZrO2含量及焙烧温度对ZrO2-SiO2复合氧化物表面酸量及酸类型进行精细调控,并将其应用于催化四氢呋喃(THF)开环聚合反应.结果表明,当ZrO2含量小于30 mol%时,随着ZrO2含量的增加,复合物总酸量显著增加,且B酸与L酸酸量...     

平面张弦结构抗连续倒塌的动力分析

杆件由于爆炸、腐蚀等发生脆性破坏后引起剩余结构的振动和压杆由于失稳过程中的弹性突跳（Snap-through）引起的相邻结构振动是张弦结构倒塌过程中常伴生的两种动力现象。本文对第一种动力响应产生的原因、失效构件的模拟方法进行了分析,说明进行张弦结构抗连续倒塌的动力分析应采用初始条件法模拟构件的失效。根据张弦结构的特点,从构件失效和结构失效两方面提出了张弦结构倒塌失效的评估准则,并采用变换荷载路径法通过静力连续倒塌分析找出张弦结构各部分的关键构件;然后采用初始条件法按考虑几何非线性、阻尼比、材料非线性等分别模拟这些关键构件失效引起的动力响应,得到了平面张弦结构各部分构件失效的动力特性、动力放大系数和失效构件的位置,并对不同失效时间进行动力响应分析得到张弦结构动力效应与构件失效时间的关系曲线。最后给出张弦结构进行抗连续倒塌分析的一些结论和建议,如进行连续倒塌动力时程分析时初始失效杆件选取和失效时间取值以及弹性动力放大系数与塑性动力放大系数的区别等,为张弦结构的抗连续倒塌设计提供技术支持和参考。     

砌体结构破坏倒塌过程的离散单元模拟

基于传统颗粒离散单元模型（DEM）,开发了一种绑定式离散单元模型（BTDEM）用于砌体结构崩塌机制的研究,并对一个典型砌体结构的破坏倒塌过程进行数值模拟。结果证实BTDEM方法能够详细地模拟出砌体建筑结构的崩塌过程,同时还可以模拟出砌块的破碎,是一种普适性较强的模拟砌体结构建筑的高效数值方法。BTDEM方法具有计算速度...