A neural network model is proposed to explain the development of direction selectivity of cortical cells. The model is constructed under the following three hypotheses that are very plausible from recent neurophysiological findings. (1) Direction selectivity is developed by modifiable inhibitory synapses. (2) It results not from the direct convergence of many excitatory inputs from LGN cells but from cortical neural networks. (3) Direction-selective mechanism is independent of orientation-selective mechanism. The model was simulated on a computer for a few kinds of inhibitory connections and initial conditions. The results were consistent with neurophysiological facts not only for normal cats but for cats reared in an abnormal visual environment.

The capacity region of a binary symmetric two-user channel is studied in the strong interference case for the transmission of separate messages. It is shown that an outer bound and a jointly achievable capacity region coincide each other for a wide range of parameter values that specify the channel and that the exact capacity region is then obtained using single-letter mutual informations.

This paper reports the realization of 2 GHz surface-acoustic-wave delay line (SAW DL) oscillator, utilizing 3rd harmonic operation of double interdigital transducers (4F-IDTs). The simple design technique for the SAW DL harmonic oscillators is made clear, based on the state-of-the-art of microfabrication technique. 0.58 µm linewidth aluminum 4F-IDTs of a SAW DL filter have been successfully obtained on the rotated Y-cut quartz by conventional photolithographic contact printing without lift-off process. They consist of 618 lines and 0.4 mm overlap length. On the clarified design technique, a 2 GHz SAW DL oscillator was achieved without external filtering and matching networks. The frequency stability of the experimental 2 GHz SAW DL oscillator is also presented and discussed. The short-term stability of 2 part in 10⁸ at 1 sec. gate time was measured and a nearly parabolic frequency variation with temperature (the turn-over temperature was near 20) was obtained. It was found that SAW DL oscillators can be small, lightweight and stable GHz oscillators in many communication systems.

Single-mode fibers are prospective candidates for future high-capacity and long distance transmission media. In particular, low loss single-mode fibers, operating around 1.27 µm wavelength, where the material dispersion of silica glass falls to zero, are very attractive because of their huge bandwidth capability. Until now, however, the attainment of very low loss in the long wavelength region has been confined to only multimode fibers. Single-mode fibers with GeO₂ -SiO₂ glass system, which have the broadest low loss window ant the long wavelength region, were fabricated. The minimum loss of 0.5 dB/km at 1.3 µm wavelength, where dispersion of the fiber is negligibly small, was obtained by suitably designing waveguide parameters and reducing OH contamination. Also, practical structural features and the OH ion behavior are clarified in relation to reduction of OH absorption, which is the major problem in reducing loss at the wavelength of interest.

Stabilization of longitudinal mode was obtained by a technique of compensation for temperature at oscillating condition. Oscillation with fixed single mode was continued over twice level of the threshold in Channeled-Substrate-Planar lasers.

This paper presents a method for obtaining the average number of data packets waiting to be transmitted in Integrated Switched networks via a diffusion approximation. Evaluated in an example network, our method is found to give a good approximation for engineering purposes.