- Dettagli della rivista
- Formato
- Rivista
- eISSN
- 2083-8492
- Pubblicato per la prima volta
- 05 Apr 2007
- Periodo di pubblicazione
- 4 volte all'anno
- Lingue
- Inglese

#### Cerca

- Accesso libero

Variable–structure repetitive control for discrete–time linear systems with multiple–period exogenous signals

Pagine: 207 - 218

#### Astratto

A new method to construct a discrete-time variable-structure repetitive controller for a class of linear systems perturbed by multiple-period exogenous signals is presented. The proposed control scheme combines the features of the discrete-time multiple-period repetitive control (MP-RC) and variable-structure control (VSC) techniques. The MP-RC part is assigned to simultaneously track and reject periodic signals consisting of multiple uncorrelated fundamental frequencies. The VSC part is then integrated to provide a fast transient response and robustness against plant parameter variations. Stability and robustness analyses are also elaborated to ensure that the resulting closed-loop system satisfies the desired control objectives. Moreover, it is shown through an example that the repetitive control system constructed using the proposed control method can effectively track a sinusoidal reference signal despite the presence of a multiple-period disturbance.

#### Parole chiave

- repetitive control
- variable-structure control
- multiple-period signals
- fast transient response
- robustness

- Accesso libero

Application of the Drazin inverse to the analysis of pointwise completeness and pointwise degeneracy of descriptor fractional linear continuous–time systems

Pagine: 219 - 223

#### Astratto

The Drazin inverse of matrices is applied to the analysis of pointwise completeness and pointwise degeneracy of fractional descriptor linear continuous-time systems. It is shown that (i) descriptor linear continuous-time systems are pointwise complete if and only if the initial and final states belong to the same subspace, and (ii) fractional descriptor linear continuoustime systems are not pointwise degenerated in any nonzero direction for all nonzero initial conditions. The discussion is illustrated with examples of descriptor linear electrical circuits.

#### Parole chiave

- pointwise completeness
- pointwise degeneracy
- fractional systems
- descriptor systems

- Accesso libero

Decentralized static output tracking control of interconnected and disturbed Takagi–Sugeno systems

Pagine: 225 - 238

#### Astratto

This article describes a new procedure for the design of decentralized output-feedback tracking controllers for a class of interconnected Takagi–Sugeno (TS) fuzzy systems with external bounded disturbances and measurement noise. The main idea consists in transforming the decentralized tracking control problem, by using the descriptor redundancy formulation, to a robust decentralized stabilization one. The non-parallel distributed compensation (non-PDC) controllers proposed here are synthesized to satisfy robust _{∞} tracking performance with disturbance attenuation. The decentralized controllers design conditions are given in terms of LMIs via extended quadratic Lyapunov functions. Finally, simulations are presented: two numerical examples are dedicated to compare the conservatism of the proposed approach regarding the previous results available in the literature; then, the effectiveness of the decentralized controller design methodology is illustrated with a closed-loop simulation of two inverted pendulums connected by a spring.

#### Parole chiave

- interconnected Takagi–Sugeno systems
- decentralized static outputs tracking controllers
- criterion
- LMIs

- Accesso libero

Decentralized and distributed active fault diagnosis: Multiple model estimation algorithms

Pagine: 239 - 249

#### Astratto

The paper focuses on active fault diagnosis (AFD) of large scale systems. The multiple model framework is considered and two architectures are treated: the decentralized and the distributed one. An essential part of the AFD algorithm is state estimation, which must be supplemented with a mechanism to achieve feasible implementation in the multiple model framework. In the paper, the generalized pseudo Bayes and interacting multiple model estimation algorithms are considered. They are reformulated for a given model of a large scale system. Performance of both AFD architectures is analyzed for different combinations of multiple model estimation algorithms using a numerical example.

#### Parole chiave

- fault diagnosis
- large scale systems
- multiple models

- Accesso libero

On three methods for bounding the rate of convergence for some continuous–time Markov chains

Pagine: 251 - 266

#### Astratto

Consideration is given to three different analytical methods for the computation of upper bounds for the rate of convergence to the limiting regime of one specific class of (in)homogeneous continuous-time Markov chains. This class is particularly well suited to describe evolutions of the total number of customers in (in)homogeneous

#### Parole chiave

- inhomogeneous continuous-time Markov chains
- weak ergodicity
- Lyapunov functions
- differential inequalities
- forward Kolmogorov system

- Accesso libero

Stabilization analysis of impulsive state–dependent neural networks with nonlinear disturbance: A quantization approach

Pagine: 267 - 279

#### Astratto

In this paper, the problem of feedback stabilization for a class of impulsive state-dependent neural networks (ISDNNs) with nonlinear disturbance inputs via quantized input signals is discussed. By constructing quasi-invariant sets and attracting sets for ISDNNs, we design a quantized controller with adjustable parameters. In combination with a suitable ISS-Lyapunov functional and a hybrid quantized control strategy, we propose novel criteria on input-to-state stability and global asymptotical stability for ISDNNs. Our results complement the existing ones. Numerical simulations are reported to substantiate the theoretical results and effectiveness of the proposed strategy.

#### Parole chiave

- state-dependent neural networks
- quantized input
- stabilization

#### Astratto

In this paper, a new methodology for simulating bootstrap samples of fuzzy numbers is proposed. Unlike the classical bootstrap, it allows enriching a resampling scheme with values from outside the initial sample. Although a secondary sample may contain results beyond members of the primary set, they are generated smartly so that the crucial characteristics of the original observations remain invariant. Two methods for generating bootstrap samples preserving the representation (i.e., the value and the ambiguity or the expected value and the width) of fuzzy numbers belonging to the primary sample are suggested and numerically examined with respect to other approaches and various statistical properties.

#### Parole chiave

- bootstrap
- fuzzy data
- fuzzy numbers
- fuzzy sample
- imprecise data
- resampling

#### Astratto

Rough set theory is an important tool to extract knowledge from relational databases. The original definitions of approximation operators are based on an indiscernibility relation, which is an equivalence one. Lately, different papers have motivated the possibility of considering arbitrary relations. Nevertheless, when those are taken into account, the original definitions given by Pawlak may lose fundamental properties. This paper proposes a possible solution to the arising problems by presenting an alternative definition of approximation operators based on the closure and interior operators obtained from an isotone Galois connection. We prove that the proposed definition satisfies interesting properties and that it also improves object classification tasks.

#### Parole chiave

- rough sets
- Galois connections
- approximation operators

- Accesso libero

New models and algorithms for RNA pseudoknot order assignment

Pagine: 315 - 324

#### Astratto

The pseudoknot is a specific motif of the RNA structure that highly influences the overall shape and stability of a molecule. It occurs when nucleotides of two disjoint single-stranded fragments of the same chain, separated by a helical fragment, interact with each other and form base pairs. Pseudoknots are characterized by great topological diversity, and their systematic description is still a challenge. In our previous work, we have introduced the

#### Parole chiave

- RNA pseudoknot order
- conflict graph
- vertex coloring
- maximum independent set
- integer programming

- Accesso libero

Bounded–abstaining classification for breast tumors in imbalanced ultrasound images

Pagine: 325 - 336

#### Astratto

Computer-aided breast ultrasound (BUS) diagnosis remains a difficult task. One of the challenges is that imbalanced BUS datasets lead to poor performance, especially with regard to low accuracy in the minority (malignant tumor) class. Missed diagnosis of malignant tumors can cause serious consequences, such as delaying treatment and increasing the risk of death. Moreover, many diagnosis methods do not consider classification reliability; thus, some classifications may have a large uncertainty. To resolve such problems, a bounded-abstaining classification model is proposed. It maximizes the area under the ROC curve (AUC) under two abstention constraints. A total of 219 (92 malignant and 127 benign) BUS images are collected from the First Affiliated Hospital of Harbin Medical University, China. The experiment tests BUS datasets of three imbalance levels, and the performance contours are analyzed. The results demonstrate that AUC-rejection curves are less affected by class imbalance than accuracy-rejection curves. Compared with the state-of-the-art, the proposed method yields a significantly larger AUC and G-mean using imbalanced BUS datasets.

#### Parole chiave

- breast ultrasound (BUS) images
- reliable diagnosis
- abstaining classification
- imbalanced datasets

- Accesso libero

Deformed solitons of a typical set of (2+1)–dimensional complex modified Korteweg–de Vries equations

Pagine: 337 - 350

#### Astratto

Deformed soliton solutions are studied in a typical set of (2+1)-dimensional complex modified Korteweg–de Vries (cmKdV) equations. Through constructing the determinant form of the ^{[1]}| and trajectories are provided analytically, which are involved by an arbitrary smooth function ^{2}

#### Parole chiave

- (2+1)-dimensional complex modified Korteweg–de Vries equation
- Darboux transformation
- deformed soliton solution

- Accesso libero

Solution of an inverse kinematics problem using dual quaternions

Pagine: 351 - 361

#### Astratto

The paper proposes a solution to an inverse kinematics problem based on dual quaternions algebra. The method, relying on screw theory, requires less calculation effort compared with commonly used approaches. The obtained kinematic description is very concise, and the singularity problem is avoided. The dual quaternions formalism is applied to the problem decomposition and description. As an example, the kinematics problem of a multi-DOF serial manipulator is considered. Direct and inverse kinematics problems are solved using division into sub-problems. Each new sub-problem proposed is concerned with rotation about two subsequent axes by a given amount. The presented example verifies the correctness and feasibility of the proposed approach.

#### Parole chiave

- dual quaternions
- kinematics
- simulation
- robotics
- screw theory

- Accesso libero

A linear programming methodology for approximate dynamic programming

Pagine: 363 - 375

#### Astratto

The linear programming (LP) approach to solve the Bellman equation in dynamic programming is a well-known option for finite state and input spaces to obtain an exact solution. However, with function approximation or continuous state spaces, refinements are necessary. This paper presents a methodology to make approximate dynamic programming via LP work in practical control applications with continuous state and input spaces. There are some guidelines on data and regressor choices needed to obtain meaningful and well-conditioned value function estimates. The work discusses the introduction of terminal ingredients and computation of lower and upper bounds of the value function. An experimental inverted-pendulum application will be used to illustrate the proposal and carry out a suitable comparative analysis with alternative options in the literature.

#### Parole chiave

- linear programming
- approximate dynamic programming
- control applications
- neural networks

- Accesso libero

Image cipher applications using the elliptical curve and chaos

Pagine: 377 - 391

#### Astratto

A novel symmetric cryptosystem of the substitution permutation network type is presented for image encryption in 14 rounds. An algorithm is developed to generate 15 keys to encrypt images where each key is the image size. These keys are calculated using an elliptic curve with a constant zero value. The proposed curve is non-singular, non-supersingular, nor trace one. Chaos is employed to find a generating element in a cyclic subgroup and it is produced using the logistic map equation. In addition, a 16 × 16 substitution box is constructed using both chaos and an algorithm that defines a bijective function. The following tools are used in order to measure the degree of randomness of the encrypted figures: entropy, correlation, the discrete Fourier transform and a goodness-of-fit test with the chi-square distribution. Furthermore, an image size variable permutation is applied in the first round, and its inverse in the fourteenth.

#### Parole chiave

- elliptic curve
- chaos
- entropy
- discrete Fourier transform
- image ciphering