An efficient finite-element program utilizing approximate analytical solutions is described for the analysis of topographic waveguides for acoustic surface waves. In this method, the only ridge region is divided into triangular elements, and therefore it is possible to use computer memory more economically. Calculations have been made for the rectangular ridge waveguide, the dovetail ridge waveguide, the truncated knife edge waveguide and the wedge waveguide. The results obtained agree well with the earlier theoretical and experimental results.

A numerical approach for the solution of the scattering by an inhomogeneous H-plane discontinuity of arbitrary shape in a rectangular waveguide is described. The approach is a combination of the finite-element method and the analytical method. The validity of the method is confirmed by comparing numerical results for a waveguide-type dielectric filter, a right-angle corner bend, an inductive strip-planar circuit mounted in a waveguide, a T-junction and an inhomogeneous waveguide junction with the earlier theoretical and experimental results.

An extended state transition model and verification algorithm are proposed for specification and verification of protocols. The state transition model is an extention of Zafiropulo's two process protocol model to specify protocols designed for communication between more than two processes. A concept of Reduced Implementation Sequence (RIS)" is introduced to establish a protocol verification algorithm. By using RIS, potential movements of modeled systems are compactly described and the computation time necessary for verification becomes much shorter than that required for the method based on the traditional reachability analysis.

The distance transformation of a digital picture (DT) is one of the most important techniques in image processing. In this paper, we propose a new variant called the max-type distance transformation for binary pictures (max-type DT). This transformation can be compared to the propagation of a wave, which propagates with a constant velocity to the pixels whose connectivity numbers are less than two. The connectivity number is calculated on the binary pattern obtained by regarding the pixels which the wave has not reached yet as 1-pixels and all the others as 0-pixels. The transformed value of a pixel is defined as the time when the wave reaches the pixel. After the transformation, the pixels on the core line of an input picture are given larger distance values increasing along the core line. Therefore, the max-type DT is effectively used in thinning and structure analysis of binary pictures. In the structure analysis using the max-type DT, both distance information and topological properties of binary pictures are used together. As an example, experimental results using hand-printed characters are shown. The max-type DT can also be applied to extract shape features by measuring the length of the core line such as the major axis of an ellipse.

Some graph theoretic problems are considered and these problems are proved to be complete for nondeterministic log-space. These graph problems concern matching, connectivity, feedback node set, diameter, radius and so on. A consideration is also mode in connection with the Jones' open problem.

A newly devised beam-steerable antenna which is capable of steering its radiation beam without moving a main reflector is presented. This is the offset type spherical reflector antenna with two specific subreflectors. With the application of mathematical programming, a new technique to determine the shapes of the subreflectors is proposed in order to compoensate for the spherical aberration and the asymmetrical distortion of the aperture distribution, which deteriorates the electric characteristics. An experimental antenna has demonstrated its excellent performance and supported the adequacy and availability of the designing procedure. The results suggest the feasibility of the beam-steerable antenna for satellite communication use.

Expressions are derived for estimating the scattered and diffracted field in the presence of the polygonal cylinder using high frequency technique which is closely related with equivalent current or equivalent moment method proposed formerly. As the first step, we verified the method by applying it to various kinds of polygonal cylinders. The numerical results for radiation patterns are compared with those obtained by other methods when they are available. The agreement between them is fairly good and difference between them is not recognised in the figures except in a small part of region where observation point lies near a shadow boundary of the polygonal cylinder. The discrepancy is few decibels. Next we study a possibility of estimating the diffracted field of smooth convex cylinder by approximating it with corresponding polygonal cylinder. As an illustration we consider radiation of electric and magnetic line source in the presence of conducting circular cylinder since the exact solution of the problem is readily obtained. The approximation of smooth object with corresponding edged object is found to be useful from the standpoint of diffraction. The method is also applied to estimate the diffracted field by curved wedge and curved half plane.

For full solid-state key telephone systems, high breakover voltage IC switches, which can connect to the central office lines directly and form a large scale matrix within a small volume, has been desired. Firstly, this paper compares several kinds of IC switches, which are suitable for formation of speech path matrix and shows that the photo-coupled PNPN crosspoint switch, connected in bridge format, is superier to the others because of low transmission loss, small matrix volume, reliability against lightning, self-latching speech path during power suspension and NTT technical requirements satisfaction. Secondly, the paper clarifies required electrical conditions for the PNPN element and the crosspoint circuit. They are breakover voltage above 300 V, dv/dt firing torelance above 160 V/0.1 µs, on-resistance within 9 Ω, less than 0.97 V forward voltage drop and restricting the reverse leak current which flows in the optically triggered PNPN element. Next, the IC switch structure is described, along with available technologies to satisfy the electrical requirements, such as canal isolation, highly efficient photo coupling structure and light shielding of anode junction. Actual IC switch characteristics satisfy all required values.

This paper examines, from the viewpoint of network topology, the reliability of fiber optic networks for local area networks (LAN). The emphasis is on the comparison between the previously proposed simple transmission type (ST type) and the optical access type networks. The failure of an active device in a certain node station interrupts communication between other surviving node stations in the ST type fiber optic network, where fiber optic data highway is directly connected to optical active devices. In an optical access type network, optical signals in a data highway are dropped or inserted by optical passive devices and the failure of active devices does not disturb communication between other node stations. The availability expressions for the ST type and optical access type bus, loop, and star configurations are introduced to compare network reliability. Numerical calculation shows that an optical access type double loop configuration is more reliable, in comparison with other configuration discussed in this paper.

A nonperturbative method is presented for describing approximately the behavior of a self-oscillation of electric voltage in the Van der Pol equation over a wide range of the value of external parameter µ. To express an appreciably distorted wave form for the steady self-oscillation at µ1, a phase F of the voltage x, defined by x2A cos F (ωt), is approximated by a combination of several straight lines as a function of ωt from 0 to 2π with several numerical coefficients determined mainly from asymptotic behaviors of x for µ1 and µ1. It is shown that the resultant expression for x can describe well the numerical result over the wide range of µ. A bursting phenomenon induced by an oscillation of µ with a long period is also discussed on the basis of the present method, and the analytical results are in good agreement with the numerical ones.

Stimulated Raman scattering was investigated in optical fibers, pumped by a mode-locked and Q-switched Nd:YAG laser or a CW Nd:YAG laser. The critical powers for the first five Stokes, at which each Stokes begins to build up, decreased with an increase in the length of fiber and became constant values above 200 meter long in the case of a mode-locked and Q-switched pump. The first and the second Stokes were observed with 0.6 W and 2.1 W of CW pump power input, respectively, in a 35 km single-span fiber. Experiments showed that the pulse wave separation effect played an important role in stimulated Raman scattering characteristics of optical fibers.

A characterization of circuits and cut-sets of a 2-connected series-parallel graph is given using the representation tree. Cut-sets correspond to subtrees of the representation tree called P-subtree and circuits are characterized in the dual form.

A simple formula for the power spectral density of a pulse train generated by a finite Markov chain is given. It contains neither an infinite series of matrices nor an inverse matrix and a tedious calculation can be dispensed with. A similar formula for the case of a periodic Markov chain is also given.

The accuracy of an approximate scalar finite-element formulation for the analysis of dielectric optical waveguides is examined numerically. It is confirmed that this approach can give more accurate results for the waveguide with smaller index variation in the lateral direction of the region in which most of the energy is concentrated or the waveguide with wider guide-width.

A practical dual scanning diversity system is described and its diversity effect in a digital FM with limiter discriminator detection is experimentally verified using a Rayleigh fading simulator.

A transient analysis of the electromagnetic field by our new numerical method has been shown to be useful for obtaining the physical meaning of the characteristics of the component of the microwave circuit. In this communication, the transient variation of the field distribution in the waveguide having the tuning window is brought about.