Asymptotic stability of a viscoelastic elliptic shaft

A finite viscoelastic shaft whose model is based on the spring and dash-pot (Kelvin element) is asymptotically stable as long as its angular speed is less than or equal to the square root of the least eigenvalue of the system. We construct numerically the least eigenvalue by using an iteration method where a definite integral is evaluated by the GAUSQZ method. With this construction, we show that a viscoelastic elliptic shaped shaft with both ends pinned is more stable than the tapered shaft with both ends pinned, or with one end built in and the other end free.     

Response of a viscoelastic half-space to time dependent moving surface loads

Through the use of nonpolar viscoelasticity theory, the problem of traveling loads with time dependent magnitude variability is considered. Employing a moving Lagrangian observer, a quadratic form is developed to ascertain potential time dependent magnitude variability induced shifts, bifurcations and wavelength interdependencies in the critical speeds associated with Rayleigh, plane and transverse wave phenomena. In terms of the moving Lagrangian formulation, a solution is developed which enables the characterization of response behavior in the various sub, trans and supercritical speed ranges associated with each of the different wave types. Based on the solution, the results of several numerical experiments are presented. These demonstrate various aspects of the foregoing phenomena.     

Refillable and magnetically actuated drug delivery system using pear-shaped viscoelastic membrane

We report a refillable and valveless drug delivery device actuated by an external magnetic field for on-demand drug release to treat localized diseases. The device features a pear-shaped viscoelastic magnetic membrane inducing asymmetrical deflection and consecutive touchdown motion to the bottom of the dome-shaped drug reservoir in response to a magnetic field, thus achieving controlled discharge of the drug. Maximum drug release with 18 ± 1.5 μg per actuation was achieved under a 500 mT magnetic flux density, and various controlled drug doses were investigated with the combination of the number of accumulated actuations and the strength of the magnetic field.     

LQG optimal control of discrete stochastic systems under parametric and noise uncertainties

In this paper, the linear-quadratic-Gaussian (LQG) optimal control problem is considered and a robust minimax controller composed of the Kalman filter and the optimal regulator is synthesized to guarantee the asymptotic stability of the discrete time-delay systems under both parametric uncertainties and uncertain noise covariances. Designed procedures are finally elaborated with an illustrative example.     

Expected power bound and stability of two-dimensional digital filters with multiplicative noise in the FMLSS model

This paper studies the two-dimensional (2-D) expected power bound (EPB) for 2-D digital filters with multiplicative noise in the Fornasini-Marchesini local state-space (FMLSS) model. By virtue of a class of linear matrix inequalities (LMIs), the novel existence criterion of 2-D EPB for 2-D digital filters in the considered model is obtained. The corresponding stabilization controller design method is presented based on the above criterion. Finally, two examples are presented to verify the effectiveness of our results.     

On the stability of stochastic chemical system

The stability of stochastic chemical system is considered. The definitions of almost sure stability and mean square stability and the corresponding stability theorems are presented and discussed. Examples concerning the stability of a two tank water heating system and a well-stirred reactor tank with random flows are studied in detail.     

Elasto-inertial particle focusing under the viscoelastic flow of DNA solution in a square channel

Particle focusing is an essential step in a wide range of applications such as cell counting and sorting. Recently, viscoelastic particle focusing, which exploits the spatially non-uniform viscoelastic properties of a polymer solution under Poiseuille flow, has attracted much attention because the particles are focused along the channel centerline without any external force. Lateral particle migration in polymer solutions in square channels has been studied due to its practical importance in lab-on-a-chip applications. However, there are still many questions about how the rheological properties of the medium alter the equilibrium particle positions and about the flow rate ranges for particle focusing. In this study, we investigated lateral particle migration in a viscoelastic flow of DNA solution in a square microchannel. The elastic property is relevant due to the long relaxation time of a DNA molecule, even when the DNA concentration is extremely low. Further, the shear viscosity of the solution is essentially constant irrespective of shear rate. Our current results demonstrate that the particles migrate toward the channel centerline and the four corners of a square channel in the dilute DNA solution when the inertia is negligible (elasticity-dominant flow). As the flow rate increases, the multiple equilibrium particle positions are reduced to a single file along the channel centerline, due to the elasto-inertial particle focusing mechanism. The current results support that elasto-inertial particle focusing mechanism is a universal phenomenon in a viscoelastic fluid with constant shear viscosity (Boger fluid). Also, the effective flow rate ranges for three-dimensional particle focusing in the DNA solution were significantly higher and wider than those for the previous synthetic polymer solution case, which facilitates high throughput analysis of particulate systems. In addition, we demonstrated that the DNA solution can be applied to focus a wide range of particle sizes in a single channel and also align red blood cells without any significant deformation.     

一种改进的超宽带平面巴伦

设计了一种改进的基于共面波导和带状线传输的超宽带平面巴伦.采用低介电常数材料作为介质基板,引入一段切比雪夫多节阻抗变换器,并改进了使共面波导两地等势的方式.这些措施有效地增加了工作带宽,降低了介质损耗.设计并制作了一种50Ω非平衡到100Ω平衡馈电转换的超宽带平面巴伦,在0.1~3GHz的频率范围内,测试得到的插入损耗小于1.5dB,输出端接匹配负载时电压驻波比小于2,实验结果和仿真结果吻合良好.     

Exponential stability of switched linear impulsive time-varying system and its application

This paper aims at the problem of exponential stability for switched linear impulsive time-varying system. By constructing two different switched discretized Lyapunov functions, some new sufficient conditions ensuring the global exponential stability of switched linear impulsive time-varying system are provided, which can be employed to the case when all subsystems are unstable. Furthermore, we apply theoretical results to the consensus of multi-agent system with switching topologies. Finally, numerical examples demonstrate the effectiveness of given results.     

Viscoelasticity of blood and viscoelastic blood analogues for use in polydymethylsiloxane in vitro models of the circulatory system

The non-Newtonian properties of blood are of great importance since they are closely related with incident cardiovascular diseases. A good understanding of the hemodynamics through the main vessels of the human circulatory system is thus fundamental in the detection and especially in the treatment of these diseases. Very often such studies take place in vitro for convenience and better flow control and these generally require blood analogue solutions that not only adequately mimic the viscoelastic properties of blood but also minimize undesirable optical distortions arising from vessel curvature that could interfere in flow visualizations or particle image velocimetry measurements. In this work, we present the viscoelastic moduli of whole human blood obtained by means of passive microrheology experiments. These results and existing shear and extensional rheological data for whole human blood in the literature enabled us to develop solutions with rheological behavior analogous to real whole blood and with a refractive index suited for PDMS (polydymethylsiloxane) micro- and milli-channels. In addition, these blood analogues can be modified in order to obtain a larger range of refractive indices from 1.38 to 1.43 to match the refractive index of several materials other than PDMS.     

Uniform exponential stability of periodic discrete switched linear system

Let {Π_τ(m, n): m?≥?n?≥?0} be the family of periodic discrete transition matrices generated by bounded valued square matrices Λ_τ(n), where $\tau :[0,1,2,?)\to \Omega$ is an arbitrary switching signal. We prove that the family {Π_τ(m, n): m?≥?n?≥?0} of bounded linear operator is uniformly exponentially stable if and only if the sequence $n?{\sum }_{k=0}^n{e}^{i\alpha k}{\Pi }_{\tau }(n,k)w\left(k\right):{\mathbb{Z}}_{+}\to \mathbb{R}$ is bounded.     

New conditions on finite-time stability of linear discrete-time system

This paper is concerned with the problems of set-based finite-time stability (SFTS) and set-based finite-time boundedness (SFTB) for both certain and uncertain linear time-varying systems. The concepts of SFTS and SFTB are defined. Different from existing results, sufficient conditions for SFTS and SFTB are directly derived from the basic definitions of finite-time stability (FTS) and finite-time boundedness (FTB) by using the convex hull technique rather than utilizing the weighted quadratic functions. Thus, more practical constraints on the system states can be dealt with. Furthermore, intervals, zonotopes and polytopes are employed to describe the typical compact convex sets. For linear uncertain systems, the uncertain time-varying state sets are assumed to be represented by interval matrices and matrix zonotopes, respectively. Finally, numerical examples are provided to illustrate the effectiveness of the main results.     

Stabilization and destabilization of nonlinear systems via intermittent stochastic noise with application to memristor-based system

This paper considers the stabilization and destabilization of a given nonlinear system by an intermittent Brownian noise perturbation. We give some distinct conditions and conclusions on almost sure exponential stability and instability, which are related to the control period T and the noise width δ. These results are then exploited to examine stabilization and destabilization via intermittent stochastic perturbation and applied to the stabilization of a memristor-based chaotic system. Two numerical examples are presented to illustrate the theoretical results.     

New results on the trade-off performance of LTI system with colored noise and encoder-decoder strategy

This paper studies the trade-off performance between tracking performance and control input energy of the multi-input multi-output(MIMO), linear and time-invariant(LTI) system over an additive coloured Gaussian noise(ACGN) channel and the encoder-decoder strategies. The restriction that filter in the encoder-decoder strategy must be diagonal matrix is not necessary. And some new results are derived according to the inner-outer factorization. The results show that the trade-off performance is correlated to the unstable pole, non-minimum phase zero of the system. Also new poles and zeros generated by the non-diagonal encoder-decoder strategies may affect the trade-off performance. At last, two examples with different filters and different encoder-decoder strategies are discussed to validate the conclusions. The various encoder-decoder strategies revealed by the simulations may enhance or deteriorate the trade-off performance proposed in this paper.     

基于产业链管理的煤电产业共生系统目标模式及其稳定性分析

煤电产业共生系统是一种基于资源、环境与社会三方面高度协作的先进产业组织模式,稳定性作为煤电产业共生系统的重要维生机制,对共生体的存在与发展至关重要。从煤电产业共生系统的目标模式及其共生策略两方面对系统稳定性进行深入探讨。利用Logistic模型,通过对煤电产业共生系统不稳定的原因及其影响因素的分析,深入探讨煤电产业共生目标模式及其对稳定性的影响机理,从两个角度对系统稳定性进行研究。结果表明:保证煤电产业共生系统的稳定性不仅需要产业共生系统内各主体从自身出发促进合作、自动形成凝聚力,从而实现长期稳定的发展并获取利益,而且还需要强化产业共生系统外政府的管控机制,利用政策鼓励企业间的诚信合作并建立信用机制,增加成员间的相互信任,减少矛盾与冲突,从而维护产业共生系统企业间的长期稳定关系。     

A neutral system approach to stability of singular time-delay systems

This paper is concerned with the problem of delay-dependent stability for a class of singular time-delay systems. By representing the singular system as a neutral form, using an augmented Lyapunov–Krasovskii functional and the Wirtinger-based integral inequality method, we obtain a new stability criterion in terms of a linear matrix inequality (LMI). The criterion is applicable for the stability test of both singular time-delay systems and neutral systems with constant time delays. Illustrative examples show the effectiveness and merits of the method.     

基于STM32数控钻床钻孔噪声识别系统的设计

随着数控钻床的广泛使用,钻孔过程中钻头的工作状态成为操作者关心的焦点。因钻头在快速钻孔时总要由于磨损而变钝,若不及时处理很容易出现钻头折断的现象。这使得操作者在作业时精神始终处在高度的紧张状态中,人很容易产生疲劳,对安全生产极为不利。为了解决这一问题,文章介绍了一种以STM32单片机为核心的数控钻床钻孔噪声识别系统,系统在钻头变钝时,实时发送控制器信号,实现数控钻床自动停机。此设计大大增加了数控钻床的安全性,有效降低了工人的劳动强度。     

移动荷载作用下桥梁动力响应的精细时程积分计算

桥梁与车辆的耦合振动方程为时变系数微分方程,用解析的方法求解这类问题有很大的局限性,解决这类问题的最为有效的工具之一是数值方法中的有限单元法.对移动衙载这种简化模型在时程积分时采用了精细积分法,为了保持精细时程积分法的高精度,对动力方程中的非齐次项进行离散计算时选用了积分精度较高的科茨积分格式,对于Euler-Bernouili梁单元采用二节点的Hermite插值函数,模拟了移动常量荷载、移动简谐荷载作用下的等截面和变截面简支梁桥模型的振动情况,并与解析的结果及一些其它的数值解法进行了对比,显示了采用精细时程积分时对动力响应过程的数值模拟的高精度.