Retardation of diffusion in porous media with stagnation zones

The problem of diffusion in a porous medium with stagnation zones, which reduce the rate of transport of particles, is considered. A method based on the concept of entropy barriers associated with the small size of inlets into the stagnation zone is used to solve the diffusion problem. This method made it possible to reduce the diffusion problem in 3D structures to a set of one-dimensional equations that can be solved analytically. The calculations yielded an exact value of the effective diffusion coefficient, which is reduced due to random delays in the stagnation zones, and the transition time required to attain this reduction.     

Theory of relaxation spectra of polymer networks with interchain friction and long-range hydrodynamic interactions

The dynamic network model taken into account the friction relative to incompressible effective viscous medium (EVM), the hydrodynamic interactions of a network with the EVM, and the interchain friction is considered. Two collective network relaxation spectra (RS) arise. The first RS corresponds to the network motion relative to immobile EVM, the EVM does not take part in this motion. The second RS includes the combined viscous motion of the network and EVM because of long-range hydrodynamic interactions. This RS is finite and narrow for infinitely large network. The symmetry of this motion is in concordance with that of incompressible EVM. The existence of interchain friction leads to the narrowing of both types of relaxation spectra.     

基于联合变换相关器的像移测量仿真分析

对基于联合变换相关器的像移测量数学原理进行了说明,介绍了面阵CCD的安装位置以及输入图像的获取方法,分析了低信噪比输入图像、相对转动位移对测量精度的影响。应用MATLAB对输入图像进行傅里叶变换得到联合功率谱,对二值化处理的功率谱进行傅里叶变换得到相关输出,用质量中心算法计算出像移量。分析得出,输入图像信噪比大于5dB,测量均方误差小于0.05像素;输入图像相对转动位移在0.1°的范围内,转动位移对测量精度和峰噪比的影响可以忽略不计。综合分析表明像移测量均方误差小于0.05像素。     

Many-body effects in diffusion-limited kinetics

We review a novel approach to treating many-body effects in diffusion-limited kinetics. The derivation of the general expression for the survival probability of a Brownian particle in the presence of randomly distributed traps is given. The reduction of this expression to both the Smoluchowski solultion and the wellknown asymptotic behavior is demonstrated. It is shown that the Smoluchowski solution gives a lower bound for the particle survival probability. The correction to the Smoluchowski solution which takes into account the particle death slowdown in the initial process stage is described. The steady-state rate-constant concentration dependence and the reflection of many-body effects in it are discussed in detail.     

三阶泛函微分方程的周期解的存在性

本文利用重合度理论研究了一类三阶泛函微分方程方程的2π-周期解的问题,获得了该方程存在2π-周期解的若干新结论,改进推广了有关文献中的已有结果．     

Diffusion in quasi-one-dimensional structures with a periodic sharp narrowing of the cross section

The problem of diffusion of particles in a tube with periodically positioned partitions with circular orifices at the center of each was considered. Using an approach based on the methods and results of the theory of diffusion-controlled reactions and the idea of homogenization of the permeability of partitions, we derived a formula for the effective diffusion coefficient for the steady-state regime of the process. The accuracy and applicability domain of the formula were determined by comparing its predictions with computer simulation results.     

利用四氯乙烷胺化反应合成联氢化嘧啶衍生物的研究

利用均四氯乙及二氯甲烷的胺化反应,合成了联氢化嘧啶衍生物1～5,4a,8b-反-4,5,8a,9a-四氮杂全氢芴(6)和8b,8c-顺-3a,4a,7a,8a-四氮杂环戊并全氢芴(7)。化合物(6)和(7)的顺反异构体在酸催化下开环,异构生成较稳定的6b和7a。