Bistable Periodic Traveling Wave Solutions to Lattice Competitive Systems北大核心CSCD

该文研究了一类格竞争系统的双稳周期行波解的存在性.首先,将两种群竞争系统转化为合作系统;其次,构造合作系统的上下解,并建立比较原理,得到当初始函数满足一定条件时,解在无穷远处是收敛的;最后,利用黏性消去法证明系统连接两个稳定周期平衡点的行波解的存在性.     

Global weak solutions to the Novikov equation by viscous approximation

We study global weak solutions to the Novikov equation by vanishing viscosity method. We prove that global weak solutions can be obtained as weak limits of viscous approximations for a class of initial data. The proof relies on a space–time higher integrability estimate and the method of renormalization. In addition, we analyze the interaction of peakon and antipeakon and prove that wave breaking leads to energy concentration. By different continuations beyond the wave breaking, we obtain conservative solutions and dissipative solutions respectively.     

Hybrid viscosity approach for hierarchical fixed-point problems

Abstract

In this paper, we propose hybrid implicit and explicit viscosity iterative algorithms for solving general hierarchical fixed-point problems for a countable family of non-expansive mappings in uniformly smooth Banach spaces. These hybrid viscosity algorithms are based on the well-known viscosity approximation method and hybrid steepest-descent method. We obtain some strong convergence theorems under suitable conditions. Our results extend, improve, supplement and develop the recent results in the literature.     

Depolymerization using sonochemical reactors: A critical review

Ultrasonic irradiation has been proposed as a novel approach for degradation of polymer compounds, especially considering the fact that the reduction in the molecular weight (also the intrinsic viscosity) is simply by splitting the most susceptible chemical bond without causing any changes in the chemical nature. An overview of the application of ultrasound for the polymer degradation has been presented in this work, discussing the mechanism of degradation, kinetic modeling, effect of operating parameters and the type of reactors generally used for depolymerization. The effect of important operating parameters such as initial polymer concentration, presence of functional groups in the polymer chain, reaction volume, initial molecular weight, temperature, operating frequency, power dissipation and use of process intensifying additives have been discussed also giving guidelines about selection of the optimum parameters. It has been observed that the low concentrations and higher power dissipation (till an optimum) are favorable resulting in higher extents of degradation. Typically low frequency is recommended but for the case of water soluble polymers, higher frequencies would also give similar results due to the dominant action of chemical effects of cavitation. It has been demonstrated that the alkyl group substituent also affects the degradation rate of polymer. An overview of degradation using combined approach based on ultrasound and additives with comparison with individual approach has also been presented. It has been observed that the main contributing factor for the synergy of the combined approach is the selection of optimum loading of additives. Overall, it has been observed that efficient polymer degradation can be achieved using combined process based on the use of ultrasound.     

Effect of Nanoparticles on Thermal Properties Enhancement in Different Oils – A Review

The development of stable dispersion of nanoparticles in different oils is gaining momentum for close circuit applications as most of the mineral oils used are not very good thermal conductors. The enhancement of thermal conductivity with optimum enhancement of viscosity of oil with nanoparticles poses a serious challenge for use of such fluids in cooling. Transformer oil, mineral oil, silicon oil, hydrocarbon fuels, biodiesel, and some organic solutions have been used as the base fluids for studying the effect of nanoparticles for improving thermal efficiency. Innovative heat transfer fluids are produced by suspending metallic or nonmetallic nanometer-sized solid particles. Although a large number of sources are available on water-based nanofluids, the number of such reports on oil-based nanofluids is rather limited. The aim of this article is to summarize recent developments on the preparation methods of nanofluids based on oil, its stability, thermal conductivity enhancement, nanoparticle effect on viscosity, heat transfer characteristics, breakdown voltage, dielectric properties, and applications of such nanofluids.     

Modified Single-Mode Leonov Rheological Equations for Polymer Melts and Solutions

The shear viscosity and the normal stress coefficients are important parameters in the flow of polymer melts and polymer solutions. Based on the Leonov model, modified single-mode rheological equations are presented by introducing relaxation time and temperature functions, and the shear viscosity and the normal stress coefficients are predicted. Without a complex statistical simulation, the experimental data of a low-density polyethylene melt, a poly(ethylene oxide) solution and a mixed decalin/polybutene oil solution were compared to verify the modified equations in very wide range of deformation rates. Furthermore, based on the equations, the relationship between the stress overshoot and the temperature is discussed. In addition, the predicted shear thinning behavior for the modified equations is also compared with other single-mode models.     

各向异性材料疲劳损伤模拟

根据连续损伤理论，考虑到了损伤能释放率等引起损伤的重要因素，提出了一个各向异性疲劳损伤模型。此模型结构简单，适用于各种各向异性材料。利用该模型对玻璃聚酯复合材料层板在单向受力情况下进行了寿命预测，预测值与实验值符合较好     

Molecular theories of nonlinear viscoelasticity of polymers

It is emphasized that considerable advances have been made recently in the development of the molecular theories of nonlinear viscoelasticity of concentrated solutions and melts of linear polymers. The new ideas in this exceptionally important field of the rheology of polymers are analysed. The methods by which the constraints (entanglements) imposed on the motion of macromolecules by the polymer environment are taken into account are also considered in the paper. The most detailed discussion is devoted to the model of topological constraints in the form of a tube and to the self-consistent theory of anisotropic micro-viscoelasticity which takes into account the relaxation nature of the interaction of macromolecules with their surrounding medium as well as the anisotropy of their mobility.Invited paper, presented at the XII-th All-Union Symposium on Rheology held in Riga (USSR), December 7–9, 1982.     

Rheograms for asphalt from single viscosity measurement

Asphalt materials are used in a variety of applications such as road paving, waterproofing, roofing membranes, adhesive binders, rust proofing and water resistant coatings. There are available in a number of grades distinguished in terms of their softening point and flow resistance. The selection of the proper grade of asphalt for a particular application is governed by the desired flow behaviour. A knowledge of the complete flow curve depicting the variation of melt viscosity with shear rate at the relevant temperatures is necessary not only for proper grade selection, but also for specifying processing conditions for aggregate mixing and spraying. The rheological data are also useful in assessing end use performance. The scientific techniques for generating the rheological data involve the use of expensive, sophisticated instruments. Generation of the necessary flow data using these instruments is beyond the financial and technical means of most processors of asphalt materials. The engineering techniques involving the use of inexpensive vacuum viscometers are relatively easy, but provide a single point viscosity measurement at low shear rate. In the present work, a method is proposed for unifying the viscosity versus shear rate a data at various temperatures for a number of asphalt grades. A master curve has been generated that is independent of the grade of asphalt and the temperature of viscosity measurement. The master curve can be used to generate rheograms at desired temperatures for the asphalt grade of interest, knowing its zero-shear viscosity at that temperature.NCL Communication Number 2914.     

An empirical equation of the relative viscosity of polymer melts filled with various inorganic fillers

Summary Based on Maron-Pierce's equation, an empirical equation was suggested, which relates the relative viscosity ( _r ) of the polymer melt filled with various inorganic filler, such as glass fiber, carbon fiber, talc, precipitated- and natural-calcium carbonate powder, and glassy small sphere, to the volume fraction () of the filler. The equation is _r = (1 –/A)^–2, whereA is a parameter relating to the packing geometry of the filler, which is similar to the parameter ₀ in Maron-Pierce's equation. In the equation _r is defined as the ratio of the viscosity of the filledsystem to that of the medium at the same shear stress not the shear rate. The applicability of the equation is above the shear stress about 10⁴ dyne/cm². The equation has a simple form and is considered to have a practical utility for filled-polymer melt systems.With 2 figures and 1 table