An analytical technique to find approximate solutions of nonlinear damped oscillatory systems

Combining Krylov-Bogoliubov-Mitropolskii (KBM) and harmonic balance methods, an analytical technique is presented to determine approximate solutions of nonlinear oscillatory systems with damping. The first approximate perturbation solutions in which the unperturbed solutions contain two harmonic terms agree with numerical solutions nicely even if the damping force is significant. With suitable examples it has been shown that the combination of classical KBM and harmonic balance methods sometimes fails to measure satisfactory results; but the combination of extended KBM method (by Popov) and harmonic balance method always give the desired results. The method is illustrated by several examples and the solutions are compared to some existing solutions.     

KP差分-微分方程组及其精确解(英文)

通过定义平移算子和差分算子 ,并利用Lax配对的方法 ,找到了KP差分 -微分方程组的正确形式 .定义了差分指数函数 .借助穿衣算子法 ,得到了KP差分 -微分方程组的精确解析解 .还讨论了KP差分 -微分方程组及其解的展开形式 .     

Application of iterated Laplace transformation to tracer transients in heterogeneous porous media

The Laplace transformation technique has been widely applied to modeling of tracer transport in oil and geothermal reservoirs, and in groundwater aquifers. However, mathematical models of many flow and transport problems could only be obtained as Laplace space solutions, and hence, their computations had to involve a numerical inversion technique.In this work, we employ the iterated Laplace transformation technique to develop novel closed form solutions to the tracer transport models in heterogeneous media. Two types of configurations have been considered: tracer transport in single fracture located in low-permeability matrix and tracer transport in a double porosity medium consisting of flowing and dead-end pore systems. In addition, both linear and radial flow geometries have been considered for both configurations. Applications of iterated Laplace transform technique to these four types of models are presented as fundamental examples and their numerical results were used as benchmarking for the numerical inversion results from Stehfest and Dubner and Abate algorithms.As the technique is quite versatile, we expect that the method should gain widespread acceptance to develop solutions to a wide range of problems in flow and transport in porous media and improve the application of nonlinear regression technique to these solutions.This work has achieved four important objectives: first, two novel Laplace transform relations that are useful in tracer studies are presented. Second, the present work serves to verify/invalidate the results of numerical inversion algorithms. In addition, it provides better insight into tracer transport mechanisms. Finally, it serves as a powerful tool of design and interpretation of tracer tests. All four objectives are illustrated in this work.     

The conductance of aqueous solutions of electrolytes

Since the Debye-Hückel theory clearly indicates, from thermodynamic considerations, that strong electrolytes are substantially completely dissociated in aqueous solutions, it has been necessary to replace, in the explanation of the conductances of such electrolytes, the Arrhenius theory, which assumes partial dissociation and constant ion mobilities, with a theory which provides for changing mobilities with increasing ion concentrations. To this end Debye and Hückel, and Onsager, suggest two mechanisms: the “electrophoretic effect” and “the time of relaxation effect,” both dependent upon interionic electrostatic attractions and repulsions. Experimental tests of Onsager's relations show that his equations account accurately, at least for very dilute solutions, for the changes with concentration of the conductances of solutions of electrolytes containing ions of widely differing mobilities and valencies. For higher concentrations semi-empirical equations are available. In contrast to the Arrhenius theory, the newer ideas call for changes in the transference numbers with the concentration, which have been found experimentally. Precision transference measurements have also furnished an experimental test of Kohlrausch's law of independent mobilities of ions. The theory of interionic attractions and repulsions is, in addition, of utility in dealing with the ionic part of solutions of weak electrolytes. By computing degrees of dissociation in a manner which allows for changing ion mobilities a test is obtained of the Debye-Hückel limiting relation connecting activity coefficients with ion concentrations.     

Electroosmotic flow hysteresis for dissimilar ionic solutions

Electroosmotic flow (EOF) with two or more fluids is commonly encountered in various microfluidics applications. However, no investigation has hitherto been conducted to investigate the hysteretic or flow direction-dependent behavior during the displacement flow of solutions with dissimilar ionic species. In this investigation, electroosmotic displacement flow involving dissimilar ionic solutions was studied experimentally through a current monitoring method and numerically through finite element simulations. The flow hysteresis can be characterized by the turning and displacement times; turning time refers to the abrupt gradient change of current-time curve while displacement time is the time for one solution to completely displace the other solution. Both experimental and simulation results illustrate that the turning and displacement times for a particular solution pair can be directional-dependent, indicating that the flow conditions in the microchannel are not the same in the two different flow directions. The mechanics of EOF hysteresis was elucidated through the theoretical model which includes the ionic mobility of each species, a major governing parameter. Two distinct mechanics have been identified as the causes for the EOF hysteresis involving dissimilar ionic solutions: the widening/sharpening effect of interfacial region between the two solutions and the difference in ion concentration distributions (and thus average zeta potentials) in different flow directions. The outcome of this investigation contributes to the fundamental understanding of flow behavior in microfluidic systems involving solution pair with dissimilar ionic species.     

河北省人力资源与经济发展关系的实证分析

本文通过对河北人力资源状况进行SWOT分析,并建构回归模型,验证了河北省人力资源与经济发展之间的关系。实证结论表明人力资源的数量、质量、结构、流动对河北经济的具体影响。并基于此提出一些对策性建议。     

Analysis of positive fractional-order neutral time-delay systems

In this paper, we consider an initial value problem for linear matrix coefficient systems of the fractional-order neutral differential equations with two incommensurate constant delays in Caputo’s sense. Firstly, we introduce the exact analytical representation of solutions to linear homogeneous and non-homogeneous neutral fractional-order differential-difference equations system by means of newly defined delayed Mittag–Leffler type matrix functions. Secondly, a criterion on the positivity of a class of fractional-order linear homogeneous time-delay systems has been proposed. Furthermore, we prove the global existence and uniqueness of solutions to non-linear fractional neutral delay differential equations system using the contraction mapping principle in a weighted space of continuous functions with regard to classical Mittag–Leffler functions. In addition, Ulam–Hyers stability results of solutions are attained based on fixed-point approach. Finally, we present an example to demonstrate the applicability of our theoretical results.     

知识管理实施中的问题与对策

本文就知识管理实施中的几个问题进行分析并从理论、技术和应用三方面给出相应的对策,认为知识管理的实施需要引入知识工程、系统工程的相关理论和方法,形成一整套系统的理论;而且需要借助语义网、本体、网格等技术从根本上解决在知识表示、共享、利用和更新等方面存在的问题;人作为知识管理实施的主体,培育实践社团是实施成功的关键。     

浅析上市公司曲线MBO的问题及对策

在我国的上市公司MBO被叫停的情况下,各种曲线MBO层出不穷。讨论了曲线MBO过程存在的问题,并提出了解决的方法,为我国上市公司企业改革提供借鉴。     

高等研究中心博士生培养模式创新与实践

研究生培养是清华大学高等研究中心最重要的工作之一,近年来我们从各个方面来提高研究生培养的质量。本文简介清华大学高等研究中心的研究生培养情况,并对具体实践过程中发现的问题进行了分析。     

产学研合作法律与政策瓶颈问题分析

分析现有国家和地方法律(法规)及政策在促进产学研合作方面遇到的瓶颈,并提出解决思路,以支持产学研合作的规范和可持续发展。     

物流金融业务创新分析

近年来我国兴起的物流金融业务创新活动为解决中小企业融资难题提供了有效的途径。为了准确认识和理解这种创新活动,本文从法律特性、核心思想、业务模式和未来发展几个方面对其做出分析和讨论。     

EPS板薄抹灰外墙技术在节能住宅的应用

外墙节能是建筑节能的重点项目。随着节能建筑的大量建成及节能要求的进一步提高,外墙外保温技术也不断发展。文章结合工程实例,通过透视EPS板薄抹灰外墙外保温系统技术的应用现状,就如何保证工程质量、围护结构的热工性能和使用功能,实现建筑物的节能目标,介绍一些体会供大家参考。     

浅谈当前我国村级会计人员的监督与管理

就我国农村税费改革的不断深入和农村经济的不断发展,针对农村会计人员监督与管理工作中暴露出的问题进行分折,提出了解决问题的对策。     

地面煤流201G皮带机改造方案

文章对地面煤流系统进行了改造,并提出了皮带机改造的方案及对策,对提高皮带机系统的可靠性,保证矿井安全、经济、稳定运行有重要的参考价值。     

高校贫困生资助工作体系中存在问题与对策研究

高校贫困生作为大学生中的一个特殊群体,受到了越来越广泛的关注。本文主要阐述了高校贫困生资助工作中存在的主要问题,强调贫困生的资助工作要将经济资助与精神资助相结合,并提出了相关的对策建议。     

浅析当今美术高考统考的现状与对策

自从2000年江苏省美术高考采取全省统考的模式至今,已有11年的历史,在此期间,美术高考由以前很少有人问津发展到现在炙手可热,美术统考模式的再三变化,使得美术高考统考成为目前江苏省乃至全国一个热门的话题.但其中所凸显的问题与弊端也需要我们进行深入的思考,以期寻求合理的解决方法.     

第二脱氢反应器设计及制造技术方案

苯乙烯装置的核心设备是苯乙烯第一、第二脱氢反应器,采用的是进口设备,已经使用15年,出现了苯乙烯流出量不够及填料支持强度不足问题。文章分析了第二脱氢反应器的结构特点、工作原理、操作工艺流程等,通过计算,提出了第二脱氢反应器替代进口设备的设计、制造技术方案。     

Transport Phenomena in Heterogeneous Media1

Classical work on transport in heterogeneous media is reviewed to show the broad interest in it as well as the specific need for a thorough treatment of a more comprehensive model. Such a model is presented and it consists of a random distribution of one or more dispersed phases in a continuous phase. Both the stab and spherical geometry are also considered. Both the transient and steady state transport solutions are developed for each of three different cases. The equivalent diffusivities are extracted from the steady state solutions. Applications are considered to illustrate the validity of the work. It is emphasized that the flux J_i for phase i can be complex as discussed elsewhere in the literature and all of this without any detraction from the exposition presented. It is also pointed out that this exposition is apparently the first to establish the connection between a realistic model, its transient solutions and its steady state solutions from which the equivalent diffusivities have been extracted. In the case of dead-end pores the results suggest application to experimental data to serve as a precision test for the presence and amount of dead-end pores. The advantages of testing under steady state conditions are discussed in detail. An appropriate diffusion cell design is referenced. The results can be useful in the research and design of barrier materials, catalysts, etc.