Using delays and time-varying gains to improve the static output feedback stabilizability of linear systems: a comparison

We address the output feedback stabilization problem of linearfinite-dimensional SISO systems. Limitations of static time-invariantoutput feedback on stabilizability are well known. We investigateand compare the possibilities of two recently proposed simplemodifications/generalizations of static time-invariant outputfeedback to remove such limitations. The first approach consistsof introducing a time-delay in the control law, which can betreated as an additional control parameter. The second approachconsists of making the gain time-varying. We show that bothapproaches are complementary. Existing theoretical results arebrought together in a unifying framework. Numerical proceduresfor the construction of the controllers are provided. Robustnessw.r.t. both parametric and delay uncertainty are dealt with.As an illustration the stabilizability of all second-order systemsis completely determined.     

FIRE OCCURRENCE PATTERNS AT LANDSCAPE LEVEL: BEYOND POSITIONAL ACCURACY OF IGNITION POINTS WITH KERNEL DENSITY ESTIMATION METHODS

ABSTRACT. Based on kernel density estimation methods, this paper introduces an alternative approach of fire occurrence modeling that addresses the inherent positional inaccuracies of recorded wildland fire ignition points. These observations, recorded in longitude and latitude using only degrees and first minutes, contain positional inaccuracies of about ± 700 to ± 925 meters in x and y axes. Kernel density estimation was applied to these historical fire observations recorded between 1985 and 1995 in Halkidiki peninsula, Greece, as well as, to simulated inaccurate points into which positional inaccuracies of the same magnitude were randomly introduced. Substantial differences were observed when a regular grid of quadrants was superimposed over the two point distributions. Although, at higher grid resolution these mismatches were minimized, the problem of generalization appeared. Contrar‐ily, the concept of “moving window” assisted to retain high grid resolution and minimize the effect of inaccurate point observations. In addition, the kernel approach, which considers also the relative position of points within the “moving window,” produced more realistic estimates.     

The exact boundaries of the stability domains of linear differential equations with distributed delay

For a differential equation with a distributed varying delay, sufficient criteria for the asymptotic and uniform stability of solutions are obtained. The constructed examples demonstrate exactness of the boundary of the obtained stability domain.     

Asymptotic Stability for a Class of Neutral Systems with Discrete and Distributed Time Delays

In this note, the asymptotic stability for a class of neutral systems with discrete time and distributed time delays is considered. Delay-dependent criteria are proposed to guarantee the stability for such systems. Some numerical examples are given to illustrate that our results are less conservative than previous results.     

An approximation to the minimum traveling wave for the delayed diffusive Nicholson's blowflies equation

In this work, we study the approximation of traveling wave solutions propagated at minumum speeds c ₀(h ) of the delayed Nicholson's blowflies equation: In order to do that, we construct a subsolution and a super solution to (?). Also, through that construction, an alternative proof of the existence of traveling waves moving at minimum speed is given. Our basic hypothesis is that p /δ ∈(1,e ] and then, the monostability of the reaction term. Copyright © 2017 John Wiley & Sons, Ltd.     

Dynamics of milling processes with variable time delays

A milling-process model with a variable time delay associated with each cutting tooth is presented in this article. The source of this variable time delay is the feed rate. The effect of the feed motion on the entry cutting angle, the exit cutting angle, and the amplitude of feed mark is also discussed. Loss-of-contact effects are also considered. The system dynamics is described by a set of delay differential equations with periodic coefficients and variable time delays. A semi-discretization scheme is presented for analyzing the stability of periodic orbits of this system. The analysis provides evidence of period-doubling bifurcations and secondary Hopf bifurcations. Good agreement is found between the numerical results obtained from this work and the results of related experimental studies.     

Global stability for infinite-delay,dispersive Lotka-Volterra systems: Weakly interacting populations in nearly identical patches

A Lotka-Volterra-like model ofm interacting species which can disperse amongn discrete habitats and where species interaction terms involve general unbounded delays is shown to possess a globally stable equilibrium when the undelayed intraspecific competition term dominates interspecific interactions as well as the delayed intraspecific competition effect and when then habitats are nearly identical.     

±100 kV三电极场畸变气体火花开关

设计了一种用于直线变压器驱动源的三电极场畸变气体火花开关。开关采用SF6气体绝缘,开关尺寸和电感较小,实测开关电感约为67 nH。在工作电压80 kV、工作系数为70%时,开关触发时延为40.0 ns,抖动约2.8 ns。对比研究了钨铜合金和黄铜两种电极材料对开关静态和触发击穿特性的影响,研究结果表明：铜钨合金电极开关的自击穿电压分散性、触发时延及抖动、自放电概率和电极表面烧蚀均小于黄铜电极,更适宜作为三电极场畸变开关的电极材料。     

多棒极型触发真空开关极性效应

基于有限元分析软件ANSOFT对触发真空开关触发极附近的静电场分布进行了仿真,并对其工作在不同的极性配置方式下开展了一系列实验。主要研究触发真空开关极性配置方式与导通时延的大小及其分散性的关系,同时分析了静电场对初始等离子体扩散的影响,从而为触发真空开关的结构优化设计提供理论依据。仿真结果表明：当触发极工作在正极性配置下,可以增强触发极附近阴极表面的电场强度,从而有利于阴极斑点的形成,减小导通时延及其分散性,提高其可靠性。实验验证了触发真空开关在正极性配置下的工作可靠性高、时延小,与仿真分析结果一致。     

开关触发延迟时间和抖动测量的不确定度分析

为明确脉冲功率装置开关触发延迟时间和抖动测量的可信度,进行了不确定度评定。使用拟合的线性关系式结合示波器水平分辨力导致的不确定度建立开关延迟时间不确定度的数学模型;根据抖动的定义建立抖动的测量不确定度数学模型。两者均按B类不确定度评定。以相关实验数据为基础计算了各个不确定度分量、合成标准不确定度以及扩展不确定度。按工程测量要求置信概率为95％,取包含因子为2,可得初级实验平台（PTS）单路样机激光触发开关触发延迟时间测量的扩展不确定度为0.38 ns;抖动测量的扩展不确定度为0.13 ns。延迟时间和抖动测量结果的不确定度满足实验分析的要求。