Evolution of an asymmetric turbulent shear layer in a thermocline

Large eddy simulations are used to examine the evolution of a shear layer in a thermocline with non-uniform density stratification. Unlike previous studies, the density in the present study is continuously stratified and has stratification in the upper half different from the lower half of the shear layer. The stratification in the upper half is fixed at J_u = 0.05, while the stratification in the lower half is increased to J_d = 0.05, 0.15, 0.25 and 0.35, leading to a progressively stronger asymmetry of the Ri_g profile in the four cases. Here, J is the bulk Richardson number and Ri_g is the gradient Richardson number. The type of shear instability and the properties of the ensuing turbulence are found to depend strongly on the degree of asymmetry in stratification. The shear instability changes from a Kelvin–Helmholtz (KH) mode at J_d = 0.05 to a Holmboe (H) mode at J_d = 0.35 and exhibits characteristics of both KH and H modes at intermediate values of J_d. Differences in the evolution among the cases are quantified using density visualisations and statistics such as mean shear, mean stratification and turbulent kinetic energy.     

Split-By-Nilpotent Extensions Algebras and Stratifying Systems

Let Γ and Λ be artin algebras such that Γ is a split-by-nilpotent extension of Λ by a two sided ideal I of Γ. Consider the change of rings functors G: =_ΓΓ_Λ ?_Λ ? and F: =_ΛΛ_Γ ?_Γ ?. In this article, by assuming that I _Λ is projective, we find the necessary and sufficient conditions under which a stratifying system (Θ, ≤) in modΛ can be lifted to a stratifying system (GΘ, ≤) in mod(Γ). Furthermore, by using the functors F and G, we study the relationship between their filtered categories of modules; and some connections with their corresponding standardly stratified algebras are stated (see Theorem 5.12, Theorem 5.15 and Theorem 5.18). Finally, a sufficient condition is given for stratifying systems in mod(Γ) in such a way that they can be restricted, through the functor F, to stratifying systems in mod(Λ).     

基于随机响应时间及准时交货激励的供应链博弈-协同模型与算法

在供应链战略合作伙伴关系的体系框架下,针对采购双方动态交互决策过程建立了以供应链中核心生产企业为主方,供应商为从方的Stackelberg博弈-协同模型.基于最优性分析讨论了准时采购过程中双方决策的交互影响关系,分析了Stackelberg均衡解的必要条件.最后提出了该模型的内嵌内点法的模拟退火算法.     

股权激励对公司价值的影响因素研究——基于A股市场2008—2010年的实证研究

股权激励作为一种制度安排,作用在于促进股东和公司管理层形成利益共同体,激励管理层最大限度地为股东和公司创造价值.通过实证研究影响公司价值的相关因素,求证股权激励确实对公司价值有正面影响,同时为上市公司的实施股权激励计划提出若干建议.     

Two‐dimensional modeling for stability analysis of two‐phase stratified flow

The effect of wavelength and relative velocity on the disturbed interface of two‐phase stratified regime is modeled and discussed. To analyze the stability, a small perturbation is imposed on the interface. Growth or decline of the disturbed wave, relative velocity, and surface tension with respect to time will be discussed numerically. Newly developed scheme applied to a two‐dimensional flow field and the governing Navier–Stokes equations in laminar regime are solved. Finite volume method together with non‐staggered curvilinear grid is a very effective approach to capture interface shape with time. Because of the interface shape, for any time advancement, a new grid is performed separately on each stratified field, liquid, and gas regime. The results are compared with the analytical characteristics method and one‐dimensional modeling. This comparison shows that solving the momentum equation including viscosity term leads to physically more realistic results. In addition, the newly developed method is capable of predicting two‐phase stratified flow behavior more precisely than one‐dimensional modeling. It was perceived that the surface tension has an inevitable role in dissipation of interface instability and convergence of the two‐phase flow model. Copyright © 2009 John Wiley & Sons, Ltd.     

Numerical modeling of slug flow initiation in a horizontal channels using a two-fluid model

This paper presents a methodology for modeling slug initiation and growth in horizontal ducts. Transient two-fluid equations are solved numerically using a class of high-resolution shock capturing methods. The advantage of this method is that slug formation and growth in a stratified regime can be calculated directly from the solutions to the flow field differential equations. In addition, by using high-resolution shock capturing methods that do not contain numerical diffusion, the discontinuity generated by slugging in the flow field can be modeled with good accuracy. The two-fluid model is shown to be well-posed mathematically only under certain conditions. Under these circumstances, the two-fluid model is capable of correctly predicting and modeling the flow physics. When ill-posed, an unbounded instability occurs in the flow field solution, and the instability amplitude increases exponentially with decreasing mesh sizes. This work shows that there are three zones associated with slug formation. In addition, long wavelength slugs are shown to initiate from short wavelength waves. These short waves are generated at the interface of the two phases by the Kelvin-Helmholtz hydrodynamic instability. The results obtained through numerical modeling show good agreement with experimental results.     

一种新型叠层光敏全息记录软片

通过化学反应，在三醋酸纤维素睛基的正反两面同时生成具有感光活性的光敏层的方法，获得了一种具有叠层光敏性的全息记录软片：重铬酸盐－三醋酸纤维素酯。由该软片记录的叠层体积全息光栅，具有迄今为止，最高的一级实验衍射效率（５４％）。     

Fundamental solutions for non-divergence form operators on stratified groups

We construct the fundamental solutions and for the non-divergence form operators and , where the 's are Hörmander vector fields generating a stratified group and is a positive-definite matrix with Hölder continuous entries. We also provide Gaussian estimates of and its derivatives and some results for the relevant Cauchy problem. Suitable long-time estimates of allow us to construct using both -saturation and approximation arguments.

     

The generation of three-dimensional internal waves and attendant boundary layers in a viscous continuously stratified fluid. Construction of an analytical solution

An analytical solution of a linearized problem of the emission of periodic internal waves by part of a plane which oscillates with a small amplitude in an arbitrary direction in a viscous exponentially stratified fluid is constructed. Solutions of the dispersion equation are given for all positions of the emitting surface (arbitrary, vertical, horizontal, and critical when one of the beam propagation directions is collinear with the emitting surface). The possibility of transition to the case of a uniform fluid, which is important for applications, is analyzed.     

分层流体中移动动量源生成准二维偶极子涡街特性实验

采用水平移动射流方法模拟移动动量源,实验研究了该移动动量源在密度分层流体中生成准二维偶极子涡街的机理,分析了偶极子涡街的演化特性. 在系列实验基础上,获得了移动动量源在密度分层流体中能够演化为偶极子涡街的(Re,Fr)组合条件. 对不同的Re取值,获得了偶极子涡街无因次形成时间及其无因次涡街平均波长倒数与Fr之间的相关关系,表明它们不依赖于Re数,而与Fr近似为幂指数关系. 关键词： 分层流体 移动动量源 偶极子涡街 涡街形成时间