On the stability of control systems with randomly time-varying characteristics†

The purpose of this paper is to study the stability conditions of randomly time-varying control systems.

First we define the stability, in the stoehastic sense, of the control system with randomly time-varying characteristics and secondly we obtain the conditions for global stability in the mean for a control system which is governed in each time interval by two different differential equations with probability p and 1-q respectively.

Finally we examine the stability condition for the concrete control systems by experiments of the Monte Carlo method.     

A method of predicting failure or life for stochastic systems by using autoregressive models

This paper discusses on-line detection and prediction problems of the failure or life of stochastic systems by using autoregression (AR) models. We regard the change of the equipment from an ordinary state to failure as a variation of the characteristics of a time aeries signal. An AR model is fitted to the time aeries signal and the change is detected by variations of the model. Using four types of performance index of the variations, we detect the failure of a cutting tool of a lathe and predict the width of flank wear.     

Project Execution Capability, Organizational Know-how and Conglomerate Corporate Growth in Late Industrialization

In many successful late-industrializing countries in the 20thcentury, business groups with operating units in technologicallyunrelated industries have acted as the microeco-nomic agentof growth. This paper explores why this business form has characterizedcountries which industrialized ‘late’, and why thisform succeeded in the early phases of catching up whereas theadvanced-country conglomerate has had an undistinguished performance.The paper uses internal resource-base theories of the firm toexplore the significance of organizational knowledge and resultingincreasing returns in the group form which, even in mature marketsand especially in late industrialization, constitute a sustainablesource of competitiveness. In the case of late industrializationforeign technology acquisition capability became a necessarycondition for corporate success. In the best diversified businessgroups this capability was transformed into organizational knowhow that provided a key resource in the effectiveness of corporategrowth through diversification. The first two parts of the paperbriefly survey diversified industrial groups in historical contextsand then across a broad array of late-industrializing countries.Then the paper considers why diversification was not prevalentamong firms attempting to catch up in earlier historical periods,why the strategy of leading late industrializing firms was oneof diversification rather than specialization and why theirchosen diversification path was one involving technologist collyunrelated industries. This is followed by the core argumentof the paper about the transformation of technology acquisitioninto a competitive asset and illustrated with evidence fromSouth Korea. Finally, the paper analyzes why the behavior ofthe late industrializing group differs from that of the Americanconglomerate.     

High-Temperature Reaction Between Cemented Tungsten Carbide and Copper

Interdiffusion in the system cemented tungsten carbide-molten copper has been studied in the range ≤1120°C with special emphasis on the effects of WC grain size and Co content. Techniques used for analyzing the diffusion layers obtained are EPMA, optical microscopy, and microhardness measurement. A Cu-bonded WC layer develops with simultaneous diffusion of Co from the cemented carbide into the bulk copper. The Cu-bonded WC layer grows until a Co-rich layer forms at the Cu/WC-Co interface; further heating pushes the Cu-bonded WC layer deep into the bulk cemented carbide without any significant change in layer thickness. When the WC grain size is reduced and the cobalt content increased, the penetration of copper into cemented carbides increases. A tentative mechanism of interdiffusion has been proposed based on the experimental results.     

On the estimation of noise covariances in linear discrete-time systems

This paper is concerned with an approach for estimating or tracking the time-varying input and measurement noise covariances in time-varying discrete-time linear systems. The approach is firstly to introduce the estimators for the case where the noise co-variances are unknown constants. (The estimators are defined as the mean squares of the estimators of noises based on all the available measurement data.) They arc then transformed in sequential form, and are subsequently modified by incorporating a fading memory to yield estimates for time-varying noise covariances. The time-varying noise covariance estimates are evaluated as the fading mean squares of the estimates of noises based on all the measurement data up to present time. A numerical example for a simple system indicates acceptable performance of the proposed method.     

A STRATEGY FOR THE DEVELOPMENT OF NEW ENERGY TECHNOLOGY IN THE GLOBAL ENVIRONMENT ERA (The Revised Sunshine Project)

The Japanese R & D Programme on solar energy under the Sunshine Project of MITI will be described. The programme is aiming at practical use of solar energy in the 21st century.     

Preparation of Cerium-Activated Silica Glasses: Phosphorus and Aluminum Codoping Effects on Absorption and Fluorescence Properties

Cerium-activated silica (SiO₂) glasses were prepared by plasma torch chemical vapor deposition (CVD). In Ce-doped SiO₂ glasses, most Ce exists as Ce⁴⁺ ions; the remaining small amount of Ce³⁺ ions exhibits a broad fluorescence spectrum with a large Stokes shift, ∼9600 cm^-1, from the excitation spectrum peak of 324 nm. Aluminum and phosphorus codoping considerably increases the Ce³⁺ ratio and shifts the peaks of both spectra to shorter wavelengths. P codoping is the more effective way to achieve this result and in some cases produces an absorption spectrum similar to that of a Ce-doped phosphate glass. These findings are consistent with the solvatiorn shell model for codoping, as previously proposed. To codope P, a soot remelting method was devised to deal with the highly volatile P₂O₅.     

Crystallization and Transformation of Distorted Tetragonal YNbO4

Distorted tetragonal YNbO₄ crystallizes from an amorphous material prepared by the simultaneous hydrolysis of yttrium and niobium alkoxides. It can be preserved at room temperature by quenching and has a unit cell with α=0.5164 nm and c= I,0864 nm. The structure contains tetrahedral NbO⁴ groups.