浅谈分子链极限伸长对硫化橡胶的影响——硬化,自均化,及应变分量偶合

硫化橡胶的大变形行为经常在超弹性范围内进行研究。以往的文献提出过各种超弹性模型理论,主要分成两类,一种采用连续介质力学原则,另一种以橡胶分子链网络结构作研究对象。唯象学的连续介质力学模型有两个明确的参数,已经证明Gent模型能完美地模拟橡胶大变形。Gent模型将左Cauchy-Green变形张量的第一个不变量限制为极限最大值,并把著名的neo-Hookean模型作为辅助形式。尽管Gent模型是唯象学的,但它解释了分子链网络的极限或有限延伸性。在过去十年里,研究者用Gent模型分析了各种均化和非均化变形模式。所有这些工作主要研究了分子链极限伸长后引起的硬化效应。本文分析了不可压缩各向同性均匀空心橡胶管的螺旋剪切变形,旨在识别Gent模型模拟的其他潜在定性的特征。这一基础性分析表明,分子链极限伸长使橡胶硬化、应力增加,同时导致了应变场均匀化及各种应变分量的偶合。

Effects of pooling,specialization,and discretionary task completion on queueing performance

Pooling,unpooling/specialization,and discretionary task completion are typical operational strategies in queueing systems that arise in healthcare,call centers,and online sales.These strategies may have advantages and disadvantages in different operational environments.This paper uses the M/M/1 and M/M/2 queues to study the impact of pooling,specialization,and discretionary task completion on the average queue length.Closed-form solutions for the average M/M/2 queue length are derived.Computational examples illustrate how the average queue length changes with the strength of pooling,specialization,and discretionary task completion.Finally,several conjectures are made in the paper.

Entropy optimization in cubic autocatalysis chemical reactive flow of Williamson fluid subjected to viscous dissipation and uniform magnetic field

This research elaborates magnetohydrodynamics (MHD) impact on non-Newtonian (Williamson) fluid flow by stretchable rotating disks.Both disks are rotating with different angular velocities and different stretching rates.Viscous dissipation aspect is considered for energy expression formulation.Entropy generation analysis is described via implementation of thermodynamic second law.Chemical processes (heterogeneous and homogeneous) subjected to entropy generation are introduced first time in literature.Boundary-layer approach is employed for modeling.Apposite variables are introduced for non-dimensionalization of governing systems.Homotopy procedure yields convergence of solutions subjected to computations of highly nonlinear expressions.The significant characteristics of sundry factors against thermal,velocity and solutal fields are described graphically.Besides,tabular results are addressed for engineering quantities (skin-friction coefficient,Nusselt number).The outcomes certify an increment in temperature distribution for Weissenberg (We) and Eckert (Ec) numbers.

Numerical Homogenization of the Elliptic Problem with Rapidly Varying Tensor or Boundary Condition

Homogenization is concerned with obtaining the average properties of a material. The problem on its own has no easy solution, except in cases like the periodic case, when it can be obtained in closed form. In this paper we consider a numerical solution of the elliptic homogenization problem for the case of rapidly varying tensor or boundary conditions. The method makes use of an adaptive finite element method to correctly capture the rapid change in the tensor or boundary condition. In the numerical experiments we vary the mesh size and do a posteriori error analysis on test problems.

Asymptotics of the quantization errors for in-homogeneous self-similar measures supported on self-similar sets

We study the quantization for in-homogeneous self-similar measures μ supported on self-similar sets.Assuming the open set condition for the corresponding iterated function system, we prove the existence of the quantization dimension for μ of order r ∈(0, ∞) and determine its exact value ξ_r. Furthermore, we show that,the ξ_r-dimensional lower quantization coefficient for μ is always positive and the upper one can be infinite. A sufficient condition is given to ensure the finiteness of the upper quantization coefficient.

Enhancing MOEA/D with uniform population initialization,weight vector design and adjustment using uniform design

In order to exploit the enhancement of the multi- objective evolutionary algorithm based on decomposition （MOEA/D）, we propose an improved algorithm with uniform de- sign （UD）, i.e. MOEA/D-UD. Three mechanisms in MOEA/D-UD are modified by introducing an experimental design method called UD. To fully employ the information contained in the domain of the multi-objective problem, we apply UD to initialize a uniformly scattered population. Then, motivated by the analysis of the re- lationship between weight vectors and optimal solutions of scalar subproblems in the study of MOEND with adaptive weight ad- justment （MOEA/D-AWA）, a new weight vector design method based on UD is introduced. To distinguish real sparse regions from pseudo sparse regions, i.e. discontinuous regions, of the complex Pareto front, the weight vector adjustment strategy in MOEMD-UD adequately utilizes the information from neighbors of individuals. In the experimental study, we compare MOEA/D-UD with three outstanding algorithms, namely MOEA/D with the dif- ferential evolution operator （MOEA/D-DE）, MOEA/D-AWA and the nondominated sorting genetic algorithm II （NSGA-II） on nineteen test instances. The experimental results show that MOEA/D-UD is capable of obtaining a well-converged and well diversified set of solutions within an acceptable execution time.

Recent progress in quantifying substituent effects

This paper summarizes significant progress in quantifying organic substituent effects in the last 20 years. The main content is as follows： （1） The principle of electronegativity equalization has gained wide acceptance, and has been used to calculate the intramolecular charge distribution and inductive effect of groups. A valence electrons equalization method was proposed to compute the molecular electronegativity on the basis of geometric mean method, harmonic mean method, and weighted mean method. This new calculation method further extended the application of the principle of electronegativity equalization. （2） A scale method was established for experimentally determining the electrophilic and nucleophilic ability of reagents, in which benzhydryliumions and quinone methides were taken as the reference compounds, and the research field was extended to the gas phase conditions, organometallic reaction and radicals system. Moreover, the nucleophilicity parameters N and electro- philicity parameters E for a series of reagents were obtained. The definition and quantitative expression of electrophilicity in- dex co and nucleophilicity index co were proposed theoretically, and the correlation between the parameters from experimental determination and the indexes from theoretical calculation was also investigated. （3） The polarizability effect parameter was initially calculated by empirical method and further developed by quantum chemistry method. Recently, the polarizability ef- fect index of alkyl （PEI） and groups （PEIx） were proposed by statistical method, and got wide applications in explaining and estimating gas-phase acidity and basicity, ionization energy, enthalpy of formation, bond energy, reaction rate, water solubility and chromatographic retention for organic compounds. （4） The excited-state substituent constant Crcc obtained directly from the UV absorption energy data of substituted benzenes, is different from the polar constants in molecular ground state and the radical spin-delocalization effects constants in molecular radical state. The proposed constant Crcc correlated well with the UV absorption energy of many kinds of organic compounds, such as 1,4-disubstituted benzenes, substituted stilbenes, and di- substituted N-benzylidenebenzenamine. （5） The establishment of the steric shielding effect distinguished the three traditional steric effects. The stereoselectivity index Ci was proposed to quantify the stereoselectivity of the addition reaction of carbonyl with nucleophilic reagent. The shielding parameter Rs was defined to quantitatively express the specific surface of the reac- tion center screened by a group. Further, the Topological Steric Effect Index （TSEI） of a group was proposed on the basis of the relative specific volume of reaction center screened by the atoms of substituents. These parameters can be applied in esti- mating the intramolecular dihedral angles, stereoselectivity of reaction, enthalpies of formation of alkenes and alkylbenzene, acidity of substitutedimidazolium ionic liquid, and the reaction rate of alkane and hydroxyl radical. In addition, some sugges- tions and prospects for further studies on quantifying the organic substituent effects were presented in this paper.

An IIR adaptive electronic equalizer for polarization multiplexed fiber optic communication systems

An electronic digital equalizer for polarization multiplex coherent fiber optic communication systems is designed to compensate polarization mode dispersion (PMD) and residual chromatic dispersion (CD) of transmission channel. The proposed equalizer is realized with fraction spaced infinite impulse response (IIR) butterfly structure with 21 feedforward taps and 2 feedback taps. Compared with finite impulse response (FIR) structure, this structure can reduce implementation complexity of hardware under the same condition. To keep track of the random variation of channel characteristics, the filter weights are updated by least mean square (LMS) algorithm. The simulation results show that the proposed equalizer can compensate residual chromatic dispersion (CD) of 1600 ps/nm and differential group delay (DGD) of 90 ps simultaneously, and also can increase the PMD and residual CD tolerance of the whole communication system.