具正负系数中立型时滞差分方程的振动性

以微积分为基本工具讨论一类具正负系数中立型时滞差分方程的振动性 ,得到了几个新的保证这个方程的所有解振动的充分条件 ,所得结果改进了已有文献中的相应结论 ,并给出了其应用。     

DQAINF: an algorithm for automatic integration of infinite oscillating tails

We describe an automatic quadrature routine which is specifically designed for real functions having a certain type of infinite oscillating tails. The algorithm is designed to integrate a vector function over an infinite interval. A FORTRAN implementation of the algorithm is included.The algorithm combines an adaptive subdivision strategy with extrapolation and requires that the decay of all the functions in the vector is the same. The algorithm is based on the assumption that the oscillating behavior is due to a periodic function with the property that it changes sign when evaluated at points of distance half a period. We assume that this period is known. The algorithm offers a choice of three different quasi-linear extrapolation procedures, namely the Euler transformation and two modifications of this transformation.This work was supported by The Norwegian Research Council for Science and the Humanities.     

具有高逼近阶及振荡核的W-K算子

本文具体彻底地解决了Kоровкин^[1]提出的“利用有限振荡核提高算子逼近阶”的问题，通过新构造一种含有2m次振荡核的W—K算子，应用复分析及Butzer^[3][6]方法，证得W—K算子对充分光滑周期函数的逼近阶可高达O（1/（n^2m 2)）。     

建构主义教学观对教师教学行为的影响

注重知识传输的传统教学弊端日益显现。建构主义教学主张学生在教师指导下 ,通过情境合作、交流、会话 ,积极主动地进行意义建构。这种教学观对教师提出了新的挑战 ,要求教师转变其教学行为。     

东鞍山贫铁矿石磁选预富集行为

针对东鞍山贫铁矿石(Fe质量分数34.60%)中含有赤铁矿、磁铁矿和少量的菱铁矿,提出了一种弱磁粗选-高梯度扫选的预富集工艺,并借助XRD、铁的化学物相分析及扫描电镜(SEM)考察了磁场强度和原料磨矿细度对东鞍山铁矿石预富集行为的影响.结果表明,在磨矿细度-0.074mm占70%(质量分数)、弱磁粗选磁场强度120mT、高梯度扫选Ⅰ磁场强度300mT及高梯度扫选Ⅱ磁场强度800mT的条件下,可获得Fe质量分数42.67%、回收率95.45%的预富集精矿;磁铁矿富集于弱磁粗选作业中,赤铁矿和菱铁矿在高梯度扫选作业中得到有效富集,尾矿中丢失的铁矿物主要为微细粒赤铁矿(＜10μm),由于受到的磁性捕获力弱而无法得到回收.     

Obtaining Fourier series graphically from large amplitude oscillatory shear loops

Large amplitude oscillatory shear (LAOS) flow has been used to characterize the nonlinear viscoelasticity of polymer melts and solutions. Results are frequently reported with shear stress versus strain loops, or with shear stress versus shear rate loops. A Fourier analysis of the stress response to LAOS is often desired for comparison with theory, or for quantitative comparison between resins. A method is presented which employs the discrete Fourier transform to obtain the Fourier series coefficients from LAOS loops.     

钨合金的冲击动力学性质及细微观结构的影响

简单介绍了钨合金(主要为W-Ni-Fe)的制备工艺和常用热处理方法,其后着重从动 态力学性能、剪切带的实验观察和研究、细微观结构对材料力学性能的影响等几方 面总结和评述了近年来针对钨合金取得的主要结果.并在文章的最后初步提出了有 前景的几个研究方向.     

Coriolis Effect on the Linear Stability of Convection in a Porous Layer Placed Far Away from the Axis of Rotation

The linear stability theory is used to investigate analytically the Coriolis effect on centrifugally driven convection in a rotating porous layer. The problem corresponding to a layer placed far away from the axis of rotation was identified as a distinct case and therefore justifying special attention. The stability of the basic centrifugally driven convection is analysed. The marginal stability criterion is established as a characteristic centrifugal Rayleigh number in terms of the wavenumber and the Taylor number.     

Applicability of normal and shear stress cells embedded in cohesionless materials

A normal stress cell and a shear stress cell have been designed and tested under very varied conditions including permanent strain. Results pooled from nine different tests with the cells embedded in cohesionless materials (sand and wheat) showed that the coefficient of variation of the normal stress-cell sensitivity was 0.04, while it was 0.10 for the shear cell. The agreement between predicted and measured sensitivity was considered to be good for the normal stress cell and reasonably good for the shear stress cell. The shear cell showed a systematic dependence, within acceptable limits, of the total stress state in the surrounding material. A qualitative explanation of this phenomenon is given. Paper was presented at the SEM VI International Congress on Experimental Mechanics held in Portland, OR in June 6–10, 1988.     

Flow Regimes of Interaction of a Turbulent Plane Jet into a Rectangular Cavity: Experimental Approach and Numerical Modelling

The present work is devoted to the experimental and numerical study ofthe interaction of a turbulent plane jet with a rectangular cavity.Several flow regimes have been found to occur: the non-oscillationregime, the stable oscillation regime and an unstable oscillationregime. The first two regimes have been particularly considered. Theexperimental study has been carried out using hot wire anemometry andsome visualisations. The numerical predictions based on statisticalmodelling have been made using on the one hand the standard k– model and on the other hand a two-scales split spectrum model. The structuralproperties of the flow have been described for the different situations.For the oscillatory regime, a parametrical study allowed to determinethe influence of the jet exit location and the Reynolds number on thefrequency of the jet flapping. The one point closures have been able topredict the oscillatory regime, and in particular the two-scales modelled to improved results because better account is taken of lag effectsin unsteady non-equilibrium situations.