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.     

On mathematical models of adaptive systems

The aim of this paper is to present a mathematical model for a system to control an object favourably which is unknown for the system—an adaptive system. We make the concept of adaptiveness precise first and consider systems as stochastic sequential machines (SSM's) to answer the question : what kind of logical structure is necessary and sufficient for a SSM to be adaptive. Some necessary conditions for a SSM to be adaptive are shown, and for a specified class of SSM's, the necessary and sufficient conditions to be adaptive are given. Furthermore, some examples of adaptive SSM's are shown.     

Bearing Resistance of Wind Turbine Generator System

The vertical axis wind turbine generator is mainly used for small size wind turbine applications, and is independent of wind direction. Its rotating part (shaft unit) should be rotated by an extremely small torque so as to increase the generation efficiency. However, commercially available bearings are not necessarily suitable for the shaft unit because their static and dynamic load ratings are frequently larger than those required for the vertical axis wind turbine. As a result, the frictional force and the rotating torque of commercially available bearings are too large for the shaft unit to rotate lightly. In this study, through an experiment with an actual vertical axis wind turbine, the bearings used for the shaft unit are reviewed in accordance with IEC61400‐2. Design of a shaft unit with the bearings having the most suitable load rating and frictional force for the vertical axis wind turbine is attempted. The newly designed shaft unit will be applied to the vertical axis wind turbine and will be tested.     

MICROBIOLOGICAL QUALITY OF SELECTED STREET FOODS IN PORT HARCOURT, NIGERIA

The microbiological quality of selected ready‐to‐eat foods sold on the streets of Port Harcourt, Nigeria, was evaluated. Twenty to twenty‐eight samples each of 10 different types of foods were analyzed. About 50% of the foods were deep fat fried, 20% were baked, 10% each were either boiled, pasteurized and frozen, or fermented and chilled products. Methods of food preparation and handling practices influenced the shelf lives of the foods, and their implications on microbiological quality and safety are discussed. The heterotrophic counts were highest for yogurt and ice cream and lowest for chin‐chin and buns. Bacterial counts for pancake, moi moi, cake, meat pie and egg roll on McConkey agar gave comparable results with counts obtained on Deoxycholate agar. Eleven bacteria genera were isolated. Bacillus spp. and Klebsiella spp. occurred in most of the foods, followed by Staphylococcus spp. and Micrococcus spp., while other species exhibited a random distribution. Generally, the foods were microbiologically safe despite defective handling practices.