In this paper we discuss a fall-safe of an asynchronous sequential machine. Though several methods have already been reported on the realization of the fail-safe circuit, we can find advantages of the method explained in this paper in the following points: First the state transition function in the form of an ON-SET function, second the consideration for a masked-fault. In order to realize the state transition function only by ON-SET functions, the delay circuit is inserted into input circuit and the input for one state transition is re-formed into two parts. It is reported that a guarantee against a masked-fault is easily attained because of ON-SET realization. In the method described in this paper the state assignment of the input and of the excitation circuit adopt the constant weight equidistant codes and the circuit is guaranteed to be rece-free. By this method the circuit can be operated with the guaranty of a fail-safe even if masked-faults exist.

The light emitted from the exit end of an optical fiber can be used as the reference wave in recording a hologram and/or the illuminating wave in reconstructing it. The fundamental problems associated with such an application have been investigated. First, the radiation characteristics of a step-index fiber was analyzed and a simple scalar description, suitable for the holography application, of the far radiation field was derived. It was found that the wavefront of the radiation field is identical with that of a spherical wave radiating from the center of the fiber end. The rough estimation for the size of the far field pattern was given and the orthogonality property of the radiation field was proved. Then the wavefront reconstructing characteristics of the hologram were discussed. The resolution capability of the system was determined by using the point spread function. A reduction coefficient concept has been introduced to describe the effects of the reference and illuminating wavefronts on the diffraction efficiency. It was deduced that recording with a spherical reference wave and illuminating with light derived from a fiber result in negligible reduction of the efficiency. The feasibility of the method was proved experimentally and some theoretical predictions were also confirmed.

Two-dimensional Gunn devices are suitable for integrating many logic devices on an epitaxial GaAs layer grown on a semi-insulating substrate. In this paper, a planar Gunn device with two separated cathodes is proposed and the fundamental logic operations, such as the exclusive OR, the inclusive OR and the inhibitor functions, are discussed theoretically and experimentally. The domain dynamics in this planar device has been examined by the computer simulation. The regions of the reliable operations are also shown by a diagram. Our experimental results confirmed the above logic operations.

The three types of definitions for the multivariable reactance function are presented, and the equivalence among these definitions are also shown. Viewed from the other standpoint, the new two definitions can be considered as new theorems on the function which indicate the important properties of multi-variable positive real function.

An algorithm is presented to solve the congruence equation of the type AX B (mod M) using Fermat's theorem, where M is any prime. It uses only integer multiplication mod M. If p is an integer such that 2^p11M2^p1, and M3 or p3, the number N of necessary multiplications mod M satisfies p1N2p2.