Phase separation kinetics in mixtures of flexible polymers and low molecular weight liquid crystals

A dynamic Monte Carlo (MC) simulation is performed to investigate the phase behavior of mixtures of flexible polymers and low molecular weight thermotropic liquid crystals (LCs). The polymer is represented by three‐dimensional self‐avoiding lattice chains, while the LC is described by the Lebwohl‐Lasher nematogen model. The initially homogeneous rod‐coil mixture is, following a deep quench, separated into an isotropic phase rich in coils and a nematic phase rich in rods. The underlying spinodal decomposition (SD) process is then simulated and studied extensively. This is the first simulation of SD in a rod‐coil mixture where the nematic ordering is included. Concentration fluctuations with a conserved order parameter are thus coupled with orientation fluctuations with a nonconserved order parameter. It is found that the early stage SD in the rod‐coil mixture still exhibits the dominant spatial wavelength and that the scalar scattering functions in the late stage of SD obey the Furukawa scaling law. The kinetic difference between the so‐called isotropic and anisotropic SD regions is, however, much less pronounced than predicted recently by the mean‐field theory.     

Pulsed Plasma Polymerization of Cyclic Ethers: Production of Biologically Nonfouling Surfaces

Polymerization of low molecular weight cyclic ethers was investigated under pulsed plasma conditions. Film formation conditions were adjusted to optimize retention of ethylene oxide (EO) content of the monomers in the resultant plasma generated polymers. To a large extent this goal was achieved with the 12-crown-4 and 15-crown-5 monomers, but not with dioxane. Films obtained from the 12-crown-4 monomer under ultra low power inputs are shown to be highly resistant to protein adsorption, while exhibiting good chemical compositional stability and adhesion during prolonged immersion in aqueous solutions. The dramatic differences observed in contrasting polymer film compositions from 12-crown-4 and dioxane are believed to arise from distinctive differences in the low electron impact fragmentation patterns of these two compounds, as discussed in this report.     

基于渐进均匀化的平纹编织复合材料低速冲击多尺度方法

针对平纹编织复合材料低速冲击响应和损伤问题,提出了一种多尺度分析方法. 首先, 建立微观尺度单胞模型,引入周期性边界条件,采用最大主应力失效准则和直接刚度退化模型表征纤维丝和基体的损伤起始与演化,预测了纤维束的弹性性能和强度性能. 其次,将这些性能参数代入介观尺度单胞模型,基于Hashin和Hou的混合失效准则以及连续介质损伤模型对介观尺度单胞进行6种边界条件下的渐进损伤模拟.然后采用渐进均匀化方法,以介观尺度单胞为媒介预测了0$^\circ$和90$^\circ$子胞的性能参数,并建立平纹编织复合材料的子胞模型,进而扩展成为材料的宏观尺度低速冲击模型. 在此基础上,研究了平纹编织复合材料低速冲击下的力学响应与损伤特征.结果表明:宏观冲击仿真和试验吻合较好, 验证了多尺度方法的正确性;最大接触力、材料吸能和分层面积均随冲击能量的增大而增大,分层损伤轮廓逐渐从椭圆形向圆形转化;基体拉伸和压缩损伤的长轴方向分别与子胞材料主方向正交和一致,损伤面积前者远大于后者.      

Optimization research on the lubrication characteristics for friction pairs surface of journal bearings with micro texture

Meccanica - In the mechanical tribology research, reasonable and effective improvement of lubrication performance for friction pairs of sleeve bearings is one of the hot topics, surface micro...     

Uptake and elimination of lanthanum by excised roots of <Emphasis Type="Italic">Triticum aestivum</Emphasis> L.

In this paper, uptake and elimination of lanthanum by excised roots of Triticum aestivum L. in various conditions were studied. Lanthanum concentrations in the roots were determined by neutron activation analysis. Results showed that the uptake of La in the excised root was almost independent of vitality, and the bonding of La with the roots was tight, but could be removed by EDTA treatment. There was significant dose-dependent accumulation of La in the excised roots within the experimental concentration (0–40 μmol/l).     

Kinetic analysis of the cross reaction between dithioester and alkoxyamine by a Monte Carlo simulation

A model reaction of dithioester and alkoxyamine is proposed to probe the reversible addition–fragmentation chain transfer (RAFT) process. The kinetics of the model reaction is analyzed and compared with that of pure alkoxyamine homolysis with a Monte Carlo simulation. Although the pure alkoxyamine obeys the law of persistent radical effect, the model reaction results in higher concentration of the persistent radical during the main period of the reaction. However, for a very fast RAFT process or a very low addition rate constant, the time dependence of the persistent radical concentration is quite close to that of pure alkoxyamine. Furthermore, the cross termination between the intermediate and alkyl radicals causes a retardation effect for the model reaction when the intermediate is relatively long‐lived. The Monte Carlo simulation indicates that it is feasible to measure the individual rate constants of the RAFT process, such as the rate constant of addition, with a large excess of alkoxyamine. In addition, the special feature of the system with different leaving groups in the alkoxyamine and dithioester is also discussed. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 374–387, 2007     

Almost periodic random sequences in probability

In this paper almost periodic random sequence in probability is defined and investigated. It is also applied to random difference equations by means of exponential dichotomy. The existence of such kind of solutions of random difference equations is discussed.     

The Automatical Slotted-Line System Controlled with Micro-Computer IBM 80486

This paper reports an automatical slotted-lin system which has been developed by us. This system is controlled with IBM-PC 80486. Its software is designed with C Language. It can performs a variety of measurements such as high, medium and low SWR measurement, signal source SWR, attenuation, phase shift, scattering coefficient of two port network and dielectric constant measurement etc. rapily, exately and conveniently. In this paper, the hardware composition and software design are described. A series of typical measurement results of SWR at 30MM wave-band are given. This method is adaptable for MM-Wave band and other Micro-wave band.