非对称核物质的化学不稳定性与力学不稳定性

基于扩展的Skyrme有效相互作用,在Hartree-Fock近似下对非对称核物质的化学不稳定性与力学不稳定性进行了研究,并与简单的三参数势,即所谓的软势与硬势的计算结果进行了比较.结果发现两种模型给出的非对称核物质化学不稳定性与力学不稳定性之间的关系是完全不同的.通过研究化学不稳定性在临界温度附近的行为发现,对软势与硬势,化学不稳定性可能出现在温度高于临界温度的气化(全爆炸)机制中.而对于SKM势参数,化学不稳定性不会出现在温度高于临界温度的气化(全爆炸)机制中.这种差别也反映在压强密度平面上力学不稳定 关键词： 非对称核物质状态方程 化学不稳定性 力学不稳定性     

固体材料不稳定性的特征

基于分析势函数的二次变分,从理论上证明了固体材料不稳定性主要取决于材质不断退化的重要特征。另一特征是：材料往往会由基本变形路径漂移为一个轴向应变被限定的模态以至的失稳。文中以有限元方法计算模拟受周期性分布孔洞损伤的平面板材模型,结果显示,孔周边的应变局部化使变形路径转移到一个轴向应变被限定的失效模态。此类现象与金属板材拉胀实验中所观测到的结果相符合。     

Numerical Determination of the Instability Region for a Delay Model of Phage–Bacteria Interaction

In this paper we describe an algorithm to determine the instability region of the endemic equilibrium of a delay model for phage–bacteria interaction in open marine environment. The algorithm relies on a new geometric criterion for stability switches introduced by Beretta and Kuang for delay models for which the corresponding characteristic equations have delay-dependent coefficients [6]. The outputs of the algorithm presented in this paper, which can be equivalently applied to similar 2D delay models, show that for this kind of models large delays are usually stabilizing.     

Effects of Surface Waves and Marine Soil Parameters on Seabed Stability

ＩｎｔｒｏｄｕｃｔｉｏｎＴｈｅｍｏｓｔｉｍｐｏｒｔａｎｔｆｏｒｃｅｓｅｘｅｒｔｉｎｇｏｎｃｏａｓｔａｌｓｔｒｕｃｔｕｒｅｓ,ｓｕｃｈａｓｏｆｆｓｈｏｒｅｄｒｉｌｌｉｎｇｒｉｇｓ,ｏｆｆｓｈｏｒｅｏｉｌｓｔｏｒａｇｅｔａｎｋｓ,ｂｕｒｉｅｄｐｉｐｅｌｉｎｅｓ,ｂｒｅａｋｗａｔｅｒｓ,ｅｔｃ .ａｒｅｄｕｅｔｏｗａｔｅｒｓｕｒｆａｃｅｗａｖｅｓ.Ｔｈｅｗａｔｅｒｗａｖｅｓｐｒｏｐａｇａｔｉｎｇｏｖｅｒｔｈｅｏｃｅａｎｃａｎｃｒｅａｔｅｔｒｅｍｅｎｄｏｕｓｄｙｎａｍｉｃｐｒｅｓｓｕｒｅ .Ｔｈｅｐｒｅｓｓｕｒｅ…     

Hot-wire method for measurements of turbulent mixing induced by Richtmyer-Meshkov instability in shock tube

A constant temperature hot-wire anemometry method is applied to the study of mixing zones induced by the interaction of a shock wave with Mach number 1.25 in air with air/helium (heavy/light), air/argon or air/krypton (light/heavy) initially plane interfaces. The single wire gauge is positioned at various locations along the shock tube axis. At the present stage of our investigation, although the analysis of the hot-wire signal is not achieved yet, we report the interesting concept of using hot-wire anemometry as a diagnostic method for shock tube studies of the Richtmyer-Meshkov instability. Based on this preliminary work, we discuss prospective experimental signal conversion, in order to provide some new results for this field of investigation, in particular for resolving characteristics of the turbulent mixing zone which is of most interest. Received 3 August 2000 / Accepted 15 February 2001     

光纤陀螺零漂数据滤波方法的研究

在对光纤陀螺零偏稳定性数据建立时间序列模型（ARMA模型）的基础上,采用卡尔曼滤波算法对光纤陀螺的漂移数据进行了处理,并采用Allan方差法和最小二乘法对滤波后的数据进行了处理,拟合,最后求出滤波后数据中各噪声的误差系数。     

Linear Stability Analysis of a Viscous Liquid Sheet in a High-Speed Viscous Gas

Air-assisted atomizers in which a thin liquid sheet is deformed under the action of a high-speed air flow are extensively used in industrial applications, e.g., in aircraft turbojet injectors. Primary atomization in these devices is a consequence of the onset and growth of instabilities on the air/liquid interfaces. To better understand this process, a temporal linear instability analysis is applied to a thin planar liquid sheet flowing between two semi-infinite streams of a high-speed viscous gas. This study includes the full viscous effects both in the liquid and gas basic states and perturbations. The relevant dimensionless groups entering the non-dimensional Orr–Sommerfeld equations and boundary conditions are the liquid and gas stream Reynolds numbers, the gas to liquid momentum flux ratio, the gas/liquid velocity ratio, the Weber number and the equivalent gas boundary layer to liquid sheet thickness ratio. Growth rates and temporal frequencies as a function of the wave number, varying the different dimensionless parameters are presented, together with neutral stability curves. From the results of this parametric study it is concluded that when the physical properties of gas and liquid are fixed, the momentum flux ratio is especially relevant to determine the instability conditions. It is also observed that the gas boundary layer thickness strongly influences the wave propagation, and acts by damping sheet oscillation frequency and growth. This is especially important because viscosity in the basic gas velocity profile has always been ignored in instability analysis applied to the geometry under study. This revised version was published online in July 2006 with corrections to the Cover Date.     

Flow-controlled growth in Langmuir monolayers

We propose a hydrodynamic mechanism, based on the Marangoni flow, to describe growth instabilities of liquid-condensed islands in the supercooled liquid-expanded phase of two-dimensional Langmuir monolayers. This Marangoni instability is intrinsic to Langmuir monolayers and is not controlled by the expulsion of chemical impurities from the liquid-condensed phase. The hydrodynamic transport of the insoluble surfactants is shown to overwhelm passive diffusion and to provide a mechanism for fingering instabilities. The model can explain the observations by Brewster-angle microscopy of ramified liquid-condensed islands in monolayers that do not contain the fluorescent dye impurities, which are normally believed to be responsible for Langmuir-film growth instabilities. Received 21 May 2000 and Received in final form 18 June 2001     

An Incompressible Three-Dimensional Multiphase Particle-in-Cell Model for Dense Particle Flows

A three-dimensional, incompressible, multiphase particle-in-cell method is presented for dense particle flows. The numerical technique solves the governing equations of the fluid phase using a continuum model and those of the particle phase using a Lagrangian model. Difficulties associated with calculating interparticle interactions for dense particle flows with volume fractions above 5% have been eliminated by mapping particle properties to an Eulerian grid and then mapping back computed stress tensors to particle positions. A subgrid particle, normal stress model for discrete particles which is robust and eliminates the need for an implicit calculation of the particle normal stress on the grid is presented. Interpolation operators and their properties are defined which provide compact support, are conservative, and provide fast solution for a large particle population. The solution scheme allows for distributions of types, sizes, and density of particles, with no numerical diffusion from the Lagrangian particle calculations. Particles are implicitly coupled to the fluid phase, and the fluid momentum and pressure equations are implicitly solved, which gives a robust solution.     

A Review of NMR Studies in RCo3 Systems Presenting d-Moment Instability

For the past few years, intermetallic systems with the formula RCo₃, where R is a rare earth, have attracted the attention of the magnetism community. In these systems, the magnetism associated to the Co ions presents a magnetic instability which gives rise to metamagnetic phase transitions observed as a change on the Co magnetic moment for some critical values of the molecular field acting on this sublattice. A number of publications about these systems is concerned with basic magnetic measurements and ⁵⁹Co NMR in compounds such as Y_1–x R _x Co₃, where R = Gd, Nd, Er. The Co ions are distributed among three crystal sites with different symmetries, one of these sites being further split into two magnetic sites, a fact in itself that considerably complicates the NMR spectra. Besides, as we have observed, the linewidths and even the number of lines appearing on the NMR spectra are strongly dependent on some NMR features, such as the radiofrequency power applied to the sample. Adding to this fact, these magnetic peculiarities depend on the compounds stoichiometry; therefore it is no surprise to find conflicting results in the literature. In the present paper a review of the NMR published data will be made, including some new results of our own.