Takeshi Fukao

A model of mass and energy flow in ecosystems

Abstract Ulanowicz and May propose a global closed ecosystem model from the viewpoint of mass and energy flow. They show a necessary and sufficient (or sufficient) condition for ecosystem stability, and explain a certain rule which is derived from field data. But their papers both contain a physical mistake: Mass does not circulate in the correct direction under the stability condition. In this paper two modifications of Ulanowicz and Mays models, in which the mistake is eliminated, are proposed to explain the rule, and a necessary and sufficient stability condition is shown.

Optimal linear fixed-interval smoothing for colored noise

A convenient canonical form of the optimal fixed-interval smoother and its error covariance matrix are derived for the continuous linear systems with the colored measurement noise. The technique of state augmentation is not used so that the proposed smoother has the same dimension as that of the original state vector to be estimated, which is especially convenient for the higher dimensional system from the computational aspect. It turns out that in the smoothing solution for colored noise it is required to retain the original measurements in addition to the filtering solution. An interesting special case where the signal and the noise processes have the identical statistical property is discussed. In this case no improved estimate is obtained by smoothing the measurements. This fact is interpreted physically in terms of observability. It is also pointed out that the proposed smoothing solution remains valid when the measurements contain no noise.

Coexistence of competing species over a linear habitat of finite length

Abstract The coexistence of two competing species over a linear habitat of finite length is investigated by considering the nonlinear effect. Approximate conditions for the coexistence of these species are derived by means of the fundamental mode of spatial variation. The approximation in theoretical computations is assessed by computer simulation.

A Macromodel of Mass and Energy Flow in Production Processes

A simple macromodel of mass and energy flow in production processes is proposed. The importance of mass recycling in production processes, i.e., mass reutilization for production, is pointed out. This type of model has a possibility of further extension to study the properties of production processes.