HL-2A装置反馈控制系统程序放电的实现

HL-2A装置反馈控制系统的主要任务是逐步实现对等离子体电流、位移、形状和密度的实时反馈控制，从而能够按照实验目的对托卡马克等离子体进行各种试验。主要介绍了HL-2A装置反馈控制系统的硬件组成以及软件的结构和特点。这个系统能够很好地满足HL-2A装置程序放电的要求。     

Aberration correction using a multi-segment mirror with feedback interferometry

A novel real-time aberration correction system using feedback interferometry and a multi-segment mirror for the wavefront corrector is described. The result is a simple and high-speed adaptive optics system demonstrating that feedback interferometry may potentially be an alternative method to conventional aberration correction techniques. Its high-speed processing and simplicity makes real-time correction practical. Our results show that the system can respond up to 37 Hz for sinusoidal phase variations with amplitude of one wavelength and improves Strehl ratio significantly.     

Existence and global attractivity of positive periodic solutions of functional differential equations with feedback control

Sufficient conditions are obtained for the existence and global attractivity of positive periodic solutions of the delay differential system with feedback control

The method involves the application of Krasnoselskii's fixed point theorem and estimates of uniform upper and lower bounds of solutions. When these results are applied to some special delay population models with multiple delays, some new results are obtained and some known results are generalized.     

Feedback boundary stabilization of the three-dimensional incompressible Navier–Stokes equations

We study the local stabilization of the three-dimensional Navier–Stokes equations around an unstable stationary solution w, by means of a feedback boundary control. We first determine a feedback law for the linearized system around w. Next, we show that this feedback provides a local stabilization of the Navier–Stokes equations. To deal with the nonlinear term, the solutions to the closed loop system must be in H^{3/2+ε,3/4+ε/2}(Q), with 0<ε. In [V. Barbu, I. Lasiecka, R. Triggiani, Boundary stabilization of Navier–Stokes equations, Mem. Amer. Math. Soc. 852 (2006); V. Barbu, I. Lasiecka, R. Triggiani, Abstract settings for tangential boundary stabilization of Navier–Stokes equations by high- and low-gain feedback controllers, Nonlinear Anal. 64 (2006) 2704–2746], such a regularity is achieved with a feedback obtained by minimizing a functional involving a norm of the state variable strong enough. In that case, the feedback controller cannot be determined by a well posed Riccati equation. Here, we choose a functional involving a very weak norm of the state variable. The compatibility condition between the initial state and the feedback controller at t=0, is achieved by choosing a time varying control operator in a neighbourhood of t=0.     

具有反馈控制和Beddington-DeAngelis功能性反应的非自治扩散模型的概周期解

讨论了一类具有反馈控制和B edd ington-D eA ngelis功能性反应的非自治捕食-食饵扩散模型,其中食饵可以在两个斑块有限制地扩散,但对捕食者来说,斑块间的扩散不受限制.本文结合运用Lyapunov函数,得到该模型存在唯一的全局渐进稳定的正概周期解的条件.     

Adaptivity and ‘Per learning’

One of the key points addressed by Per Bak in his models of brain function was that biological neural systems must be able not just to learn, but also to adapt—to quickly change their behaviour in response to a changing environment. I discuss this in the context of various simple learning rules and adaptive problems, centred around the Chialvo-Bak ‘minibrain’ model (Neurosci. 90 (1999) 1137).     

厦门海底隧道围岩稳定动态反演分析

位移反分析法作为联系理论与实际的桥梁,为工程决策、设计与施工提供了切实可行和有效的方法。为解决海底隧道勘察、设计与施工技术难题,减小设计与施工风险,通过对先行服务隧道建立动态反演预测模型,及时对主隧道前方地质情况进行超前预报,并对围岩稳定性进行准确判断,根据反馈信息,对主洞前方设计与施工方案进行科学合理地组织,必要情况下须对原设计的隧道支护参数与施工方法作调整和修正,做到动态信息化设计与施工,确保海底隧道顺利穿越。     

Stability and bifurcation in an electromechanical system with time delays

The effect of time delays occurring in a proportional-integral-derivative feedback controller on the linear stability of a simple electromechanical system is investigated by analyzing the characteristic transcendental equation. It is found that the trivial fixed point of the system can lose its stability through Hopf bifurcations when the time delay crosses certain critical values. Codimension two bifurcations, which result from non-resonant and resonant Hopf–Hopf bifurcation interactions, are also found to exist in the system.     

Chaotic attitude motion of a magnetic rigid spacecraft and its control

This paper deals with chaotic attitude motion of a magnetic rigid spacecraft with internal damping in a circular orbit near the equatorial plane of the earth. The dynamical model of the problem is established. The Melnikov analysis is carried out to prove the existence of a complicated non-wandering Cantor set. The dynamical behaviors are numerically investigated by means of time history. Poincare map, power spectrum and Lyapunov exponents. Numerical simulations indicate that the onset of chaos is characterized by the intermittency as the increase of the torque of the magnetic forces and decrease of the damping. The input-output feedback linearization method is applied to control chaotic attitude motions to the given fixed point and periodic motion.     

On a structural acoustic model which incorporates shear and thermal effects in the structural component

In this paper we consider a structural acoustic model which takes account of thermal effects over and above displacement, rotational inertia and shear effects in the flat flexible structural component of the model. Thus the structural medium is a Reissner-Mindlin plate into which an additional degree of freedom, viz. temperature variation in the plate, has been introduced and the constitutive equations for the structural acoustic model couple parabolic dynamics with hyperbolic dynamics. We show unique solvability of the mathematical model and investigate the effect of the presence of thermal effects on the mechanical dissipation devices needed to attain uniform stabilization of the two-dimensional model in which the structural component is a Timoshenko beam. It turns out that, as in linear structural acoustic models which use the Euler-Bernoulli equation or the Kirchoff equation to describe the deflections of the thermo-elastic structural medium, uniform stabilization of the energy associated with the model can be attained without introducing mechanical dissipation at the free edge of the beam. Open problems with regard to the stabilization of the three-dimensional model are outlined.