Comments on “Discrete-Time Adaptive Backstepping Nonlinear Control via High-Order Neural Networks”

The purpose of this comment is to point out some mistakes in the above paper. It is shown that the main results of the paper cannot stand in general. Also, it is pointed out that after some corrections, the proposed control algorithm is still applicable to a more simple system. For simplicity, all the symbols in this comment are the same as those in the above paper.     

Comments on “Generalized Lyapunov Equation Approach to State-Dependent Stochastic Stabilization/ Detectability Criterion”

This note gives a correct proof for the first part of Theorem 3.2 in the above paper, which is an important theorem of the above paper.      

Comments on “A class of proportional-integral sliding mode control with application to active suspension system”

In this note, we first show that Theorem 2 in the above paper is incorrect. Then, we also show that Theorem 1 is not enough to support the claim in the above paper that the proportional-integral sliding mode control method is more robust than the linear quadratic regulator method when applying on the active suspension system with mismatched uncertainties.     

Comments on “direct bilinear routh stability criteria for discrete systems”

The above paper¹ discusses useful Routh-like stability criteria for discrete systems. Unfortunately, however, previous work on the subject escaped the attention of the author. This note co-ordinates previous work with results obtained in the above paper. It also points out some of the more recent developments on the subject.     

CORRECTION TO “SINGULARITY COMPUTATION FOR ITERATIVE CONTROL OF NONLINEAR AFFINE SYSTEMS”

The ball‐on‐plate example in the above paper by the authors [3] contains a mistake in the vector field. This note presents the singularity result of the corrected vector field.     

A “mixed” small gain and passivity theorem in the frequency domain

We show that the negative feedback interconnection of two causal, stable, linear time-invariant systems, with a “mixed” small gain and passivity property, is guaranteed to be finite-gain stable. This “mixed” small gain and passivity property refers to the characteristic that, at a particular frequency, systems in the feedback interconnection are either both “input and output strictly passive”; or both have “gain less than one”; or are both “input and output strictly passive” and simultaneously both have “gain less than one”. The “mixed” small gain and passivity property is described mathematically using the notion of dissipativity of systems, and finite-gain stability of the interconnection is proven via a stability result for dissipative interconnected systems.     

On “uniformity” in definitions of global asymptotic stability for time-varying nonlinear systems

We discuss the lack of “uniformity” in definitions of uniform global asymptotic stability (UGAS) that have been used in various textbooks, monographs, and papers over the years. Sometimes UGAS is taken to be the combination of uniform local stability (ULS) and uniform global attractivity (UGA). Other times it also encompasses uniform global boundedness (UGB). This paper contains an explicit, smooth scalar example that shows that these definitions do not agree in general, even when the right-hand side is locally Lipschitz in the state uniformly in time (and thus bounded in time). We also discuss various notions of global asymptotic stability with relaxed uniformity (with respect to the initial time) requirements for the behavior of the solutions. In particular, we consider class- estimates and Lyapunov characterizations.     

Erratum to “On the Synthesis of Haptic Textures” [Jun 08 527-536]

In the above titled paper (ibid., vol. 24, no. 3, pp. 527-536, Jun 08), it is stated in Sec. IV-D3 that the characteristic number of the first variant of the "god object" method applied to texture synthesis is 1. This statement is not always true, and clarification of this issue is presented here.     

Comments on “Delay independent robust stability of uncertain linear systems”

The purpose of this note is to give a counterexample to a possible implication of the main result of the above paper [1].     

Corrections to “Basins of Attraction in Fully Asynchronous Discrete-Time Discrete-State Dynamic Networks” [Mar 06 397-408]

This paper brings a correction to the formulation of the basins of fixed-point states of fully asynchronous discrete-time discrete-state dynamic networks presented in the above titled paper (ibid., vol. 17, no. 2, pp. 397-408, Mar 06). In our subsequent works on totally asynchronous systems, we have discovered that the formulation given in that previous paper lacks an additional condition. We present in this paper why the previous formulation is incomplete and give the correct formulation.     

Transformation ratio of “ring-dot” planar piezoelectric transformer

A piezoelectric transformer (PT) is a device, which can be used for transforming an ac voltage via ultrasonic vibrations. The best characteristics are achieved in the vicinity of mechanical vibration resonance. “Ring-dot” type design of homogeneously poled disk PT was originally proposed by Berlincourt. Only experimental data were published in preceding studies. An analytical continuum model is presented in this work. The effects of dimensions, material properties and electrical load on the voltage gain as well as on the efficiency are calculated. Hard lead zirconate titanate ceramics (PZT, APC841 type) was used for sample fabrication. Studied PTs typically attain transformation ratio equal 20 without load. For load impedance around 5 kΩ, the observed efficiency was above 90%, whereas the transformation ratio dropped down to the values around 2. The model correspondence with experiment is limited by employed approximations. Model limitations are discussed with respect to experimental data.     

“Kronecker Basis” Based Average Consensus Analyses for High‐Order Linear Multi‐Agent Systems with Multiple Time Delays

This paper investigates the average consensus for multi‐agent systems governed by high‐order linear dynamics with multiple time delays. Necessary and sufficient conditions for high‐order average consensus under balanced communication topology are provided by using a newly defined mathematical concept – the Kronecker basis. Furthermore, previous studies for average consensus governed by first‐order, or high‐order integrator can be regarded as special cases of our results. Simulation results are employed to demonstrate the effectiveness of our results for high‐order average consensus.     

STABILIZATION AND H∞ CONTROL FOR UNCERTAIN STOCHASTIC TIME‐DELAY SYSTEMS VIA NON‐FRAGILE CONTROLLERS

This paper considers the problems of robust non‐fragile stochastic stabilization and H_∞ control for uncertain time‐delay stochastic systems with time‐varying norm‐bounded parameter uncertainties in both the state and input matrices. Attention is focused on the design of memoryless state feedback controllers which are subject to norm‐bounded uncertainties. For both the cases of additive and multiplicative controller uncertainties, delay‐independent sufficient conditions for the solvability of the above problems are obtained. The desired state feedback controller can be constructed by solving a certain linear matrix inequality.     

Comments on “Equivalence of characterizations of fixed models”

In this note we present a proof to the conjecture given in the above paper, and therefore establish the equivalence of characterizations of fixed modes for the general case.     

H∞ identification of “soft” uncertainty models

The paper investigates the problem of identifying uncertainty models of causal, SISO, LTI, discrete-time, BIBO stable, unknown systems, using frequency domain measurements corrupted by Gaussian noise of known covariance. Additive uncertainty models are looked for, consisting of a nominal model and an additive dynamic perturbation accounting for the modeling error. The nominal model is chosen within a class of affinely parametrized models with transfer function of given (possibly low) order. An estimate of the parameters minimizing the H_∞ modeling error is obtained by minimizing an upper bound of the worst-case (with respect to the modeling error) second moment of the estimation error. Then, a bound in the frequency domain guaranteeing to include, with probability α, the frequency response error between the estimated nominal model and the unknown system is derived.     

How Healthcare Professionals “Make Sense” of an Electronic Patient Record Adoption

This article examines how healthcare professionals experience an Electronic Patient Record (EPR) adoption process. Based on a case study from two surgical wards in Danish hospitals, we analyze the healthcare professionals' conceptions of the technology, how it relates to their professional roles, and aspects of the implementation process from a “sensemaking” perspective.     

Comments on: “Fault detection for continuous‐time switched systems under asynchronous switching”

In this note, a defect occurred in Theorem 1 in the study Du et al. (Int. J. Robust Nonlinear Control 2013; doi: 10.1002/rnc.2961) is addressed. Additionally, the correction of the theorem is presented. Copyright © 2014 John Wiley & Sons, Ltd.     

Comments on: ‘Diagonal dominance for multivariable Nyquist array methods using function minimization’

The above paper (Leininger, 1979) claims to give a ‘new’ method for achieving diagonal dominance in multivariable systems. This is, however, not the first time that a function minimization approach has been used to obtain dominance. An optimisation oriented method was first proposed in 1975 (Ahson, 1975). This method is based on a new formulation of diagonal dominance criterion which takes into account model parameter uncertainties.     

Remarks on “Measuring Ambiguity in the Evidence Theory”

In a recent paper, a functional AM (ambiguity measure) is introduced and an attempt is made to show that this functional qualifies as a measure of total aggregated uncertainty in the Dempster-Shafer theory. We show that this attempt fails due to a particular error in the proof of one of the principal theorems in the paper. Some additional remarks are made regarding recent research pertaining to the subject of the discussed paper.