This paper proposes a heuristic algorithm for constructing a new school timetable by revising partially the school timetable already constructed for the previous year. This algorithm is considered as an extension of the algorithm proposed in the author's previous paper which aims at constructing a new school timetable. It is noted that the assignments in the present algorithm begin with an almost filled school timetable, while the assignments in the previous algorithm begin with an almost empty school timetable. Numerical examples show that the computation time of the present algorithm is considerably shorter than that of the previous algorithm when a timetable for the previous year is available.

Analytic expressions for evaluating minimum propagation delay time tpd are derived, using a model which is effective for analysis of the device with a merged structure. Calculated results are in good agreement with experimental ones. Junction modifying coefficient k is newly introduced for the theory. k affects tpd through a variable function of current gains, and a deviation from the Klaassen's theory is pointed out. Role of the pnp transistor on the performance of the I2L gate is emphasized.

This paper proposes a new approach to the problem of efficient digital coding of the NTSC composite color TV signal. First, a new method, named Comb-Filter Integration method", of deriving a prediction function effective for the NTSC composite signal is introduced. This method is based on the technique of integrating a simple comb-filtering operation into an arbitrary linear prediction function tailored for monochrome TV signals, and thus coverting it to a prediction function effective for the NTSC signal. Practical examples of such composite prediction functions are shown. Then, 32 Mb/s and 44 Mb/s DPCM systems, using one of these prediction functions, are described along with their simulated performances. The results show that these systems are promising for the high-quality transmission of the NTSC signal.

A simple theoretical model for surface acoustic wave (SAW) ΔV/V waveguides on anisotropic crystals is presented. Applying the theory to the waveguides on Y-cut LiNbO3, the dispersion relations are calculated. Experimental results of the velocity dispersion were shown to be in a reasonable agreement with the theory. Although the observation of the SAW field revealed a small discrepancy from the theoretically predicted profile outside the waveguide, it can be concluded that the present model gives a very good approximate method to the study of ΔV/V waveguides on anisotropic substrates.

Results obtained from a study on junction properties of n-CdS/p-InP heterodiodes which were prepared as solar cells by the close-spaced technique are described. The junction properties were examined by means of injection electroluminescence. It has been shown that these diodes have very low interface state density at least in deep levels even for an as-grown sample from the fact that only an electroluminescence due to the band-to-band transitions was observed at room temperature. At liquid nitrogen temperature, however, luminescence spectra originated from both band-to-band and free-to-bound transitions were observed. The energy difference between the two spectral peaks was found to be 67 meV, which corresponds to the activation energy of typical acceptors in InP. The internal electroluminescent quantum efficiency was 12.8% at 77 K.

Atmospheric propagation affects the optimization problem of an optical terrestrial communication link. The optimum system parameters are computed for a CO2 heterodyne communication link for different atmospheric visibilities.

On a HeNe laser oscillating simultaneously at 0.63 and 3.39 µm, the effects of an axial and a transverse magnetic fields on the output as a function of a cavity detuning are investigated theoretically and experimentally. The experiment is carried out using the laser tube with Brewster windows and the resonant mirrors for 0.63 µm. The outputs are mainly characterized by 3.39 µm mode despite of low Q resonator at 3.39 µm. The output power versus cavity detuning at 0.63 µm presents the inverse pattern to the one at 3.39 µm. In the axial magnetic field, large Faraday rotation arises at 3.39 µm and it saturates in the vicinity of 60 Gauss. In the transverse magnetic field, σ modes of two wave-lengths occur when the windows have maximum transmission for σ polarization. For fields higher than about 60 Gauss, the σ mode of 3.39 µm is quenched and π mode appears because of the strong coupling of σ-π transition and its effect is enhanced by the competition between two wavelengths. The output powers versus cavity detuning agree well with our theoretical result which is analyzed by the semiclassical treatment of two transitions with a common upper level in a Zeeman laser. Furthermore the optical modulation on 3.39 µm line is also proposed by means of the competition effect.

The harmonic and phase distortions in the direct modulation of injection lasers are given theoretically with help of a large signal analysis by a Fourier-series-expansion method. It is shown that the distortions are relatively small when there is no-kink in the I-L curve and the magnitudes of the distortions are inversely proportional to the bias current above threshold and proportional to the photon lifetime in laser cavity. It is also shown that the maximum modulation frequency in the analog-modulation is limited by the phase distortion rather than the amplitude distortion.

A transversal equalizer composed of a surface-acoustic-wave tapped delay line and PIN diode control circuits is described. In the amplitude frequency response, the change, which can be expressed in terms of a cosinusoid, can be obtained by controlling the amplitude of the echo signals.

Various minimization problems associated with the diagnosis of systems represented by directed graphs are shown to be NP-complete. These problems include () finding the minimum number of test points, test connections and blocking gates on a SEC graph (single entry single exit connected acyclic graph), respectively, to make it distinguishable, and () finding a test set with the minimum number of tests to locate a faulty vertex on a SEC graph with test points, test connections and blocking gates attached, respectively. The NP-completeness results indicate that these problems are all intractable in the sense that it is most unlikely that some algorithm can solve them in polynomial time of the problem size.

The stationary characteristics of gain-guiding semiconductor lasers with a symmetrical structure are theoretically examined, solving the wave equation by the Galerkins method and taking the effect of transverse carrier diffusion into consideration. For wide stripe lasers, the carrier density distribution becomes flat with the increase of the current density. And with the more increase of the current density, a hole-burning, a mode deformation and a kink" in the current density-light output characteristics appear. For the narrower stripe lasers, the current density where the hole-burning occurs increases and surpasses the normal driving current level. Hence the transverse mode profile can be approximated by the gaussian one with a small numerical error, which verifies the assumption in our previous papers(8),(9). The influence of the current profile on the characteristics is larger for wide stripe lasers than for narrow ones. However it less affects them compared with the transverse carrier diffusion even for wide stripe lasers. That is, the effect of current density profiles on the characteristics is weakened by the transverse carrier diffusion.

A new acousto-optic tunable filter utilizing collinear acousto-optic interaction along the direction near to the optic axis is proposed and demonstrated by using LiNbO3 crystal. This near axis interaction lowers the driving frequency and also expands the angular aperture in the ordinary plane. The acousto-optic figure of merit M2 (p2/ρv3) of this filter is 7.510-18 sec3/g and tuning from 700 nm to 420 nm can be obtained by changing the acoustic frequency from 56 MHz to 119 MHz. At 514.5 nm the filter bandwidth of 1.1 nm and the angular aperture of about 6 in the ordinary plane have been obtained.

The performance of the tapered velocity coupler for single mode fibers is investigated theoretically and experimentally. An improved analytical solution convenient for analyzing and designing the tapered velocity couplers is derived. The mode cross-talk in the tapered region and the mode conversion loss due to the discontinuity at the ends of the fibers are measured and are compared with the theoretical results. Simultaneous shaping of the multiple single mode fibers into tapered structure is successfully realized and a low loss splicing (less than 0.2 dB) is achieved either by using adhesives or by the thermal fusion technique.

A general formula giving cutoff frequencies of modes in an optical fiber having an arbitrary refractive-index profile is derived from the stationary expression of the propagation constant. It is found that the cutoff frequency is inversely proportional to the square root of the overlap integral of the refactive-index and mode-power profiles. From this general formula, an approximate formula for actual calculation is derived, which is relatively accurate when applied to lower order modes. The single-mode condition (cutoff frequency of LP11 mode) can be calculated with a good accuracy using this approximate formula. The single-mode limits computed for some practical nonuniform-core profiles show good agreement with rigorous values.

Effects of the taper-joining of two single-mode fibers, where the fibers are first spliced by fusion, and are then heated and stretched to form the taper-joint, are analyzed and discussed. Due to reductions both in the lateral and angular offsets in the process of forming the taper, the loss can be reduced by one tenth, which is much smaller than that in the case where fibers are spliced after the formation of the taper. It is also pointed out that the joint must be kept straight to avoid the radiation loss due to curving of the joint. Finally, it is ascertained experimentally that the taper joint can be obtained by the arc-discharge method in both the splicing and the stretching processes.

By the derivative expansion method we solved a certain perturbation problem which well represents the phase lock loop. We derived the equation which describes the dynamics of a slowly varying parameter E, where E can be regarded as the averaged energy of the system approximately.

By refining the deconvolution technique proposed previously by the same authors for determining the impulse response of optical fibers, the time resolution has been improved. In some cases an impulse response consisting of several independent pulses is obtained; probably these pulses correspond to separate LP-mode groups.

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.

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.