Norihiko Adachi

Simple pivoting algorithm for root-locus method of linear systems with delay

A simple and efficient method for the computation of root loci is proposed. The method solves characteristic equations by pivoting procedures. The algorithm is simple, and applicable to linear systems with time delay. Some theoretical results are given to validate the algorithm. The efficiency of the method is shown by several numerical examples.

An immune algorithm for multiagent: application to adaptive noise neutralization

A new information processing architecture is extracted from the immune system. By focusing on informational features of the immune system (i.e. specificity, diversity, tolerance, and memory), an immune algorithm is proposed. The algorithm proceeds in three steps: diversity generation, establishment of self-tolerance, and memorizing non-self. The algorithm may be used typically to model the system by distributed agents where the system (the self) as well as the environment (the non-self) are unknown or cannot be modeled. Agent-based architecture based on the local memory hypothesis and network-based architecture based on the network hypothesis are discussed. Agent-based architecture is elaborated with the application to an adaptive system where the knowledge about environment is not available. Adaptive noise neutralization is formalized and simulated for a simple plant.

Diagnosability and Distinguishability Analysis and Its Applications

As systems become more complex, it becomes necessary to understand, simplify, and apply fault diagnosis and fault-tolerant design. Although some graph-theoretical diagnostic models such as self-diagnosis model have been studied, the model can not be applied to most systems due to the assumption that each unit has its own testing capability. This paper presents a graph-theoretical diagnosis model expressed by a set of fallible units, a set of measurements, and an incident matrix indicating binary relation between these two sets. Since this model explicitly separates tested units (fallible units) and testing units (measurements), we can discuss diagnostic aspects from both sides. Diagnosability and distinguishability of the model with multiple faults are discussed from combinatorial point of view. Measures of t-fault diagnosability and t-out-of-s diagnosability which was introduced on the self-diagnosis model are discussed. Conditions for these diagnosabilities are expressed by a topological concept of fault distance. The concept of distinguishability is generalized to multiple fault situations called t-fault distinguishability. A lower bound for the distinguishability is obtained by using fault distance. The new concept of s-distinguishability class (s-dc) is presented. This analysis is recommended in the design of systems to attain a required level of diagnosability and distinguishability as well as in the analysis of present systems to investigate their diagnostic aspects. Two application examples are presented: Diagnosability and distinguishability analysis of error-correcting codes, and design of instrumentation systems of large plants with a required level of diagnosability.

Compliant motion control of redundant manipulators

Two control schemes, called extended hybrid control and extended impedance control respectively, are developed for assuring the compliant motion of redundant manipulators. In the two control schemes, the basic compliant motion task is accomplished while the redundancy is utilized to realize some additional constraints which optimize any user-defined objective functions. Further, real-time implementations are given and some experimental results on a 3-DOF planar redundant manipulator are also presented to illustrate the two proposed schemes and demonstrate their capabilities for optimizing various objective functions.<<ETX>>

Influence of predation on species coexistence in Volterra models

Abstract The possibility of predator-mediated coexistence of all species in model ecosystems of the Volterra type is discussed, that is, asymptotic behaviors of systems of two competing species are analyzed when one or two predators are added. All species in the communities can coexist in two distinct ways mathematically, that is, the species may coexist at equilibrium or may coexist in persistent oscillations. The stability of all species at equilibrium increases when one or two predators are added. The conditions for oscillatory coexistence in limit cycles or in chaotic behaviors of two-predator systems are more complicated than in those of one-predator systems. It is concluded that predator-mediated coexistence can be promoted by an intimate relationship between the competitive ability of the prey and the diet preference of the predators.

Oscillations in Prey-Predator Volterra Models

This paper gives some results on oscillatory behaviors of Lotka-Volterra models. We are concerned with dynamics of biological communities with two trophic levels, particularly with those of two-prey, one-predator systems and two-prey, two-predators systems. The possible behaviors of trajectories of the systems are discussed by perturbation methods and Hopf bifurcation theory. It is shown that the addition of one or two predators to two-species competing system can increase species diversity. Three patterns of the coexistence are possible mathematically; n n(i) n ncoexistence at the globally (or locally) stable equilibrium n n n n n(ii) n ncoexistence in the stable periodic motion of Hopf type (a limit cycle) n n n n n(iii) n nthe coexistence in chaotic motions.

Dynamics and stability of ecological models

Abstract The purpose of this paper is to exemplify some recent results concerning the dynamic behaviors of Lotka-Volterra models. First we review the role of Lotka-Volterra models in ecological modelling and then work with dynamics and stability behaviors of the models related to the structure of the hierarchy. It is shown that the hierarchy makes stable coexistence of species possible in a periodic or chaotic motion which is impossible for the subsystem. Since Lotka-Volterra models are rather simple, the existence of nonlinear phenomena requires us to study in detail the dynamic behaviors of simple mathematical models.

An algorithm for computing multivariable root loci by pivoting

An efficient and robust algorithm for computing multivariable root loci is proposed. This algorithm solves a set of characteristic equations by pivoting. The algorithm is based on Kuhns algorithm for finding roots of a polynomial by pivoting. Some theoretical results which validate the algorithm are obtained and several examples are computed to show the efficiency of the algorithm.

Hopf bifurcation in an adaptive d.c. servo system

Occurrence of Hopf bifurcation is demonstrated in a practical adaptive servo system by computer simulations and experimental results. The bifurcation is caused by a decaying term added to the adaptive law for improving the robustness of the system. The bifurcation analysis is successfully applied to the design of stable adaptive controller.

A Computing Method to Locate the Roots of Interval Polynomials

となる係数 をもつ2n+1個 の多項式 を端点多項式 と呼ぶ. この とき,(1)式 に含 まれるf∈ δ(s)は端点多項式 の凸 結合で表 される.ま た,Ω とその支持超平面 との共通部 分 は,一 次元の場合 に露 出稜,二 次元の場合 に露出面 と 呼 ばれ る. 【定理1】 エッジ定理1) 複数個 の多項式の凸結合の根 の集合の境界は,パ ラメー タ空 間で のすべ てのエ ッジ(稜)に 対応 する根 の集合 に 含 まれ る. 区間多項式の根 とは,f∈ δ(s)に属す る多項式の根 の 集合 をいい,根 の集合の複素平面上での存在領域 をDで 表す.エ ッジ定理 によれば,複 数個 の多項式で作 られ る凸 結合の根 の存在領域 は,パ ラメータ空間(a0, ..., an)Tで の露出エ ヅジに相当する多項式 の根 を調べ ることに よって 確 定する2). ここで,あ る一つの端 点多項 式 と,こ の端点多項式 に 対 し,一 つの係数 だけが異 なる端点多項式 との凸結合 か らなる集合 を考 える.