Surface treatment of titanium dioxide nanopowder using rotary electrode dielectric barrier discharge reactor

Titanium dioxide (TiO2) nanopowder (P-25;Degussa AG) was treated using dielectric barrier discharge (DBD) in a rotary electrode DBD (RE-DBD) reactor.Its electrical and optical characteristics were investigated during RE-DBD generation.The treated TiO2 nanopowder properties and structures were analyzed using x-ray diffraction (XRD) and Fourier-transform infrared spectroscopy (FTIR).After RE-DBD treatment,XRD measurements indicated that the anatase peak theta positions shifted from 25.3° to 25.1°,which can be attributed to the substitution of new functional groups in the TiO2 lattice.The FTIR results show that hydroxyl groups (OH) at 3400 cm-1 increased considerably.The mechanism used to modify the TiO2 nanopowder surface by air DBD treatment was confirmed from optical emission spectrum measurements.Reactive species,such as OH radical,ozone and atomic oxygen can play key roles in hydroxyl formation on the TiO2 nanopowder surface.     

Synthesis of β-Si3N4 by Chemical Vapor Deposition

Beta-type CVD-Si₃N₄ plates (up to 1.1 mm thick) have been prepared by adding TiCl₄ vapor to the system SiCl₄-NH₃-H₂ at deposition temperatures of 1350° to 1450°C, while α-type or amorphous CVD-Si₃N₄ was obtained without TiCl₄ vapor at the same deposition temperature. Three to four wt % 777V was included in the β-type CVD-Si₃N₄ matrix. The density, preferred orientation, and lattice parameters of β-type CVD-Si₃N₄ were examined.     

Oxidation of CVD Si3N4 at 1550° to 1650°C

A thermo gravimetric study of the oxidation behavior of chemically vapor-deposited amorphous and crystalline Si₃N₄ (CVD Si₃N₄) was made in dry oxygen (0.1 MPa) at 1550° to 1650°C. The specimens were prepared under various deposition conditions using a mixture of SiCl₄, NH₃, and H₂ gases. The crystalline CVD Si₃N₄ indicated a parabolic oxidation kinetics over the whole temperature range, whereas the amorphous CVD Si₃N₄ changed from a parabolic to a linear law with increased temperature. The oxidation mechanism is discussed in terms of the activation energy for the oxidation and the microstructure of the formed oxide films.     

An application of Markov potential theory to Markovian decision processes

The aim of this paper is to identify the denumerable stochastic systems which have an optimal strategy, namely, to give general sufficient conditions of the existence of an optimal strategy for denumerable Markovian decision processes. The aim is accomplished by using Markov potential theory and showing the range of the validity of a method to find an optimal strategy called Howard's technique. Since Markov potential theory helps to characterize the properties of evaluations of strategies on such processes, it plays an important role to find the sufficient conditions mentioned above

For Markov potential theory, new concepts are introduced such as absorbable chains, quasi-potentials, etc., and using them, sufficient conditions for the existence of a solution of the equation x = f+Px are generalized to the one's for cyclic chains and multi-chains

The results obtained in this paper are as follows : if a system represents a strong Markov chain for any strategy, then there exists an optimal strategy with respect to the total or the mean expected earnings, and for any stochastic system there exists an optimal strategy with respect to the discounted total expected earnings.     

Two-degrees-of-freedom dead-beat control system with robustness

This paper deals with the design of a two-degrees-of-freedom (TDF) dead-beat controller with both optimal robustness and minimum settling time. Based on the parametrization of all stabilizing TDF controllers, optimal robustness and minimum-time control are achieved simultaneously. The minimum-time dead-beat control is constructed for arbitrary real-rational reference input. At the same time, optimal robustness is achieved under the constraint that the error between reference input and output asymptotically vanishes for any plant perturbation that does not violate the internal stability. It is proved that under the same robustness criterion, irrespective of its length of settling time, the optimal robustness of the TDF system is always superior to that of the one-degree-of-freedom (ODF) system as long as its settling time is finite, and they become identical only when the settling time of the ODF system goes to infinity. A numerical example is given to illustrate the theoretical results.     

Stable identification scheme for linear discrete-time systems

This paper is concerned with the problem of identifying parameters in stochastic systems described by single-input single-output linear discrete-time equations. A stable estimation error system is developed by using the extended Kalman filter technique and the concept of strictly positive real transfer function. The identifier corresponding to the estimation error system is constructed, and the convergence of parameter estimates to the exact values is proved under some bounded conditions. It is shown that the recursive maximum likelihood identifier and the recursive extended least squares identifier are obtained by neglecting the correction terms in the proposed identifier. Numerical examples for a fourth-order system are presented to illustrate the effectiveness of the proposed method.     

SYSTEM TRANSFORMATIONS AND ADAPTIVE SYSTEMS

The purpose of this paper is to formulate the concept of system transformation and the concept of adaptive system in the framework of general systems theory, and to characterize both concepts as well as mutual relationships between them from a qualitative viewpoint.

We define a system transformation as a mapping on the class of all systems under consideration in a general and unified manner, and especially consider the variety of system behavior under parallel, cascade, and feedback transformation for linear functional time systems. We introduce the notion of open system in terms of system transformation. We then formulate class controllability and adaptability of an open system under system transformation, and characterize them in terms of basic system properties. In particular, we obtain a necessary and sufficient condition under which an open system is adaptive.     

A GENERAL APPROACH TO THE CHARACTERIZATION OF CHANGES IN SYSTEM BEHAVIOUR BY OUTPUT FEEDBACK

The purpose of this paper is to formulate in a general and unified manner the change of system behaviour produced by output feedback and then to clarify from a qualitative point of view its general structure and meaning.

In this paper feedback is defined as a system transformation on the class of general linear systems represented by input-output relations. As a measure indicating the degree of how the behaviour of a system S?X×Y changes under feedback transformation three classes of systems are introduced for S and their system theoretic meaning is considered in a general setting. Furthermore, a variety problem of several structured systems under feedback transformation is investigated by characterizing these classes in terms of basic system concepts.     

Fuzzy control of a manipulator using an actuator and multibrakes

This paper is concerned with the control of a manipulator with n-degrees of freedom by one actuator and n ? 1 brakes using fuzzy inference. All the links of the manipulator are excited by a motor placed on the base link, and the excitation torque is successively transmitted through each link from the base link until the final link. The brakes on the joints act at identical frequency with different phases, and the phases of timing on the brakes are controlled by fuzzy inference such that all the joint angles of links are followed to the desired trajectories. The effectiveness of the proposed method is illustrated by a simple example.     

Transformation of a continuous time-invariant linear system into a discrete one

A discrete-time time-invariant linear system (DILS) is considered which has resulted from the discretization of a continuous-time time-invariant linear system (CILS) by the zero order hold. In this system, the system and input matrices are given by exp(AT) and $ where A and B are the system and input matrices of the CILS, and T is a sampling interval. Since they involve the matrix exponential, their computations are not easy.

First, on the assumption that the Kalman canonical form of the CILS is sought, a formal Kalman canonical form of the DILS is determined. Second, with the use of this form and the decomposition of A into the projectors onto the generalized eigenspaces, an algorithm is presented which computes the system and input matrices of the DlLS.