非链式化学HF（DF）激光器工作气体中电子分离的非稳定性和气体放电等离子体的自组织现象

报道了放电引发的非链式HF（DF）激光器中的激活介质由电子碰撞负离子分离引起的电离非稳定性。这种非稳性出现在电极空间分离、脉冲CO2激光加热的基于sF6的混合气体的大体积放电中。实验研究了自引发体放电过程中由激光加热引起的放电等离子体的自组织现象以及由此在放电间隙的大部分区域形成的准周期等离子体结构。重点分析了等离子体结构随气体温度和注入能量的变化,讨论了等离子体自组织对电子碰撞分离不稳定性所产生的影响,解释了混合气体中由于电子碰撞使负离子消失导致的单等离子体通道移动的产生机理。     

Particle-laden viscous thin-film flows on an incline: Experiments compared with a theory based on shear-induced migration and particle settling

Particle settling in driven viscous films is a complex physical process involving different physical effects. A recent analysis by Cook (2008) [10] has identified a balance between hindered settling and shear-induced migration as the dominant large scale physics for particle/liquid separation. However, experimental data for this has been lacking. This paper presents new data including the role of particle size and liquid viscosity showing clear agreement with the theory. We discuss the role of timescales in the dynamics of the experiment and present results from a dynamic model.     

微小圆管中分裂火焰的实验与理论研究

对丙烷/空气在内径2 mm的圆管内的预混燃烧进行了实验研究,借助于高速数码摄像机发现了分裂火焰现象,其中一个为向上游传播的较亮的常规火焰,另一个为向下游传播的较暗的微弱火焰。这些火焰先后熄灭,经过一段时间后又重复发生自着火、分裂、反向传播、灭火过程。这种现象在富燃、化学恰当比以及贫燃火焰中都有存在。一维非稳态计算表明化...     

使用多孔蜗舌的贯流风机

将贯流风机的蜗舌替代为多孔板与容腔组合的结构,定性地研究其控制气动噪声的可行性。通过对气动特性和辐射声信号的实验测量,结合内部流场的非稳态雷诺平均数值模拟,分析了这种蜗舌改造对贯流风机的整体特性和内部流动特征的影响,结果表明多孔蜗舌对贯流风机的压力-流量曲线作用并不明显,但对风机的噪声有着重要的影响,改变蜗舌迎风面的穿孔率可以有效地控制贯流风机的噪声。     

Condition for convective instability of dark solitons

Simple derivation of the condition for the transition point from absolute instability of plane dark solitons to their convective instability is suggested. It is shown that unstable wave packet expands with velocity equal to the minimal group velocity of the disturbance waves propagating along a dark soliton. The growth rate of the length of dark solitons generated by the flow of Bose-Einstein condensate past an obstacle is estimated. Analytical theory is confirmed by the results of numerical simulations.     

Akhmediev breather evolution in optical fiber for realistic initial conditions

We study numerically Akhmediev breather dynamics in optical fibers under initial conditions that do not correspond to an ideal infinitesimal modulation on a plane wave. We examine two modifications that are commonly encountered in realistic experiments: (i) a finite-amplitude (not necessarily weak) initial modulation; (ii) the use of pulsed excitation. In the first case, we derive an expression for the propagation distance required to generate a train of compressed breather pulses. In the second case, we show that breather dynamics with pulsed excitation can be interpreted in terms of local breather states at different points on the pulse envelope.     

Spike patterns in a reaction–diffusion ODE model with Turing instability

We explore a mechanism of pattern formation arising in processes described by a system of a single reaction–diffusion equation coupled with ordinary differential equations. Such systems of equations arise from the modeling of interactions between cellular processes and diffusing growth factors. We focus on the model of early carcinogenesis proposed by Marciniak‐Czochra and Kimmel, which is an example of a wider class of pattern formation models with an autocatalytic non‐diffusing component. We present a numerical study showing emergence of periodic and irregular spike patterns because of diffusion‐driven instability. To control the accuracy of simulations, we develop a numerical code on the basis of the finite‐element method and adaptive mesh grid. Simulations, supplemented by numerical analysis, indicate a novel pattern formation phenomenon on the basis of the emergence of nonstationary structures tending asymptotically to a sum of Dirac deltas. Copyright © 2013 John Wiley & Sons, Ltd.     

On the Rayleigh-Taylor Instability for Two Uniform Viscous Incompressible Flows

The authors study the Rayleigh-Taylor instability for two incompressible immis- cible fluids with or without surface tension, evolving with a free interface in the presence of a uniform gravitational field in Eulerian coordinates. To deal with the free surface, instead of using the transformation to Lagrangian coordinates, the perturbed equations in Eule- rian coordinates are transformed to an integral form and the two-fluid flow is formulated as a single-fluid flow in a fixed domain, thus offering an alternative approach to deal with the jump conditions at the free interface. First, the linearized problem around the steady state which describes a denser immiscible fluid lying above a light one with a free interface separating the two fluids, both fluids being in （unstable） equilibrium is analyzed. By a general method of studying a family of modes, the smooth （when restricted to each fluid domain） solutions to the linearized problem that grow exponentially fast in time in Sobolev spaces are constructed, thus leading to a global instability result for the linearized problem. Then, by using these pathological solutions, the global instability for the corresponding nonlinear problem in an appropriate sense is demonstrated.     

Overview of diagnostic methods used in shock-tube investigations of mixing induced by Richtmyer–Meshkov instability

We present an overview of the diagnostic methods used in shock-tube investigations of mixing induced by Richtmyer–Meshkov instability. The different diagnostic techniques are first briefly presented, and then reviewed in a simple single table, which lists their advantages and disadvantages, their technological characteristics and domain of validity, the physical parameters measured, the laboratory in which they were developed and an assessment of their mean cost. Received 19 November 1997 / Accepted 3 March 1998     

交叉流聚丙烯中空纤维膜式氧合器的传质研究Ⅰ结构因子α、β的测定和氧合器传质效果评价

在膜式氧合器水气传递实验装置上分别对二种不同的交叉流微孔聚丙烯中空纤维膜式氧合器进行了水气传递实验，测得了氧合器的结构因子α、β，并用Ｍｏｃｋｒｏｓ和Ｌｅｏｎａｒｄ对Ｏ２传递建立的半经验数学模型拟合了血气传递实验中氧气在血中的传递速率。结果表明，理论计算与实验数据十分吻合，偏差小于１０％。讨论了α、β与膜式氧合器的传递效果的关系。