Voltage resonant converters with multiple resonant switches operating at fixed switching frequency are presented. Resonant switches are connected in parallel so that the power conditioning is achieved by the phase-shift modulation method instead of the switching frequency modulation method. Switching losses are predicted to be very small due to it's zero-voltage switching. Steady state characteristics of the proposed converter are analyzed, and the analytical results are verified by experiments.

An AC-DC converter using a new switched-capacitor (SC) transformer and its design are presented. The features of this circuit are as follows. (1) The maximum voltage of capacitors is 1/n times that of a condenser-input-type rectificer circuit, where n is the number of chargetransfer capacitors. (2) The output voltage ripple is small, since the equivalent smoothing capacitor value is n times that of conventional SC transformers (series-parallel switching type). Using the presented design method, each element value is designed from the specifications of a test circuit. The experimental results of the test circuit show that (1) the efficiency of the SC transformer is very high (95%), and the total efficiency is 74% due to the losses of the clock generator and the control circuit, (2) the maximum output power is 40 W, (3) the value of the inrush current of the tested converter is only twice the value of the steady state current. The measured characteristics showed good agreement with the calculated ones.

A novel method of high frequency switching for dc-to-dc converter is presented. This method is based on the commutation with aid of inductor current, where a short interval (dead time) of both switches off is given for removing switching surges and switching losses. By the method of constant current-ripple using a saturable core, the condition of zero voltage switching is made independent of the duty ratio. The output voltage is regulated by pulse width modulation in the same way as that of the conventional converter of PWM control. The mechanism of commutation for giving a dead time is analyzed by assuming equivalent circuits, during which a zero voltage switching is realized. From calculations and experiments, it is found that a desired dead time is derived by connecting external capacitance to the gate-source terminal of the MOSFET.

This paper describes the dead angle and transfer characteristics of the feedback control circuit in a magnetic-amplifier-controlled DC-DC converter. The dead angle occurs depending on the inductance in the saturable core after saturation and the recovery time in the rectifier diode. It is necessary to select a suitable combination of core and diode because recovery time in the diode varies according to the inductance in the core after saturation. An amorphous core and a Schottky diode is the most suitable for obtaining a small dead angle. When the saturable reactor cores are varied, the converter DC gain shows different values. This is because the DC gain is in proportion to the flux changing rate in the saturable core and the current gain in the control transistor. Combining a control transistor with a large current gain and an amorphous core with a large flux changing rate effectively increases the DC gain. A core of large cross-sectional area and small magnetic path length effectively increases the control gain. The results will be very useful in designing converter control circuits.

The mechanism of noise suppression by a magnetic snubber is analyzed quantitatively. The magnetic snubber is a paralled circuit of a saturable reactor and a linear inductor connected in series with a small diode. The effects of magnetic characteristics of the saturable reactor and the linear inductor on the surge and noise are discussed through the comparison of analytical and experimental results. Then the design method of the magnetic snubber is described.

A new transformer with a Co-based amorphous core for use in the switching regulators of telecommunications systems is described. This transformer in fabricated by a two-step magnetic field annealing technique to decrease core loss. It is shown that this amorphous core reduces loss to 1/2 that of a conventional ferrite core. It is also shown that the weight and size of the new transformer are 3/5 and 1/2 those of a conventional transformer using the ferrite core. A 100 kHz series resonant converter with this transformer is 93% efficient with an output power level of 50% to 100%.

A wavelength tunable surface emitting laser using a multiple quantum well as a tuning element is proposed. Wave-length can be tuned continuously in 150 Å for a tuner with the refractive index change n_tu/n_tu of 4%, the filling factor ξ_tu of 0.3 and without absorption loss. The actual tuning width is limited to be 3.5 Å with n_tu/n_tu of 0.43-0.15%, considering an absorption loss.

A discrete-time digital transmission system in which the transmitter and receiver are both time-invariant finite-state machines and their states are always synchronized is investigated. In addition, the source is assumed to be first order Markov and the channel noiseless. An expression for a measure of performance we call the mean tracking time is derived. This expression is given in terms of state cycles" of the system. In a companion paper, a heuristic design algorithm based on this analysis is presented along with some interesting examples of good designs.

In a companion paper, we investigated a class of discrete-time digital transmission systems in which the transmitter and receiver are both time-invariant finite-state machines and their states are always synchronized. An expression for the mean tracking time of such a system was derived in terms of state cycles of the system. Using this analysis, we present here a heuristic design algorithm to find good transmitter-receiver pairs for given sources. This algorithm was programmed and some interesting design examples are shown to verity that it works.

In vector guantization, it is desirable to design a codebook on an image-to-image basis, because the codewords should be the representative vectors which describe the image most properly. However, the conventional codebook design algorithms are iterative methods in which we can not predict the execution time, and the overhead for the transmission of a designed codebook increases as the codebook size gets lager. In this paper, we propose an algorithm which updates a vector centroid sequentially and removes the overhead for the replenishment of a codebook by introducing the interframe coding technique for image sequence coding. With the proposed replenishment technique, we can obtain almost the same performance as that of the LBG algorithm for each frame. The experimental results demonstrate that a bit rate as low as 0.375-0.5 bit/pixel is sufficient for a good image quality because a new label is transmitted only in the changing areas.

In recent communications systems, various kinds of traffic are transmitted all together. The mixed delay and non-delay system, which integrates loss-sensitive delay (data) traffic and delay-sensitive realtime (voice) traffic, is a typical example of these systems. In the mixed delay and non-delay systems, the non-delay traffic generally suffers loss with a relatively large probability due to the existence of the delay traffic. In order to improve the GOS (Grade of Service) of the non-delay traffic and to increase the efficiency of the overall systems, the alternative routing scheme is introduced. In design of the alternative routing systems, analysis of overflow traffic essential. This paper focuses on the moments of the number of the overflow calls from the mixed delay and non-delay systems with Poisson inputs and exponential service times. In the case of same mean service time, explicit formulas are presented for the moments, whereas a recursion formula and its calculating algorithm are derived in the case of different mean service times. Through the numerical results, a limiting property of the moments is discussed. An example is given to show the application of the obtained formulas.

High-count cable using optical fiber ribbon, is useful for reducing the construction time of optical fiber cable networks. In addition, if the cable is maintenance-free, the network maintenance cost can be reduced. Therefore, we developed a high-count, maintenance-free cable. First, we studied high-density cable packaging using optical fiber ribbon. Next, we solved the problem of loss increase caused by hydrogen generation, and frozen water. Then we developed 1000-fiber water blocking cable composed of water-blocking tapes, an aluminum tape with plastic coating and a surface treated tensile member. Finally, we tested the developed cable and confirmed that it satisfies the requirements for conventional cables.

Site attenuation (CSA) is investigated theoretically and experimentally for soil ground test sites as well as for metal ground test sites. In this study, half-wave tuned dipole antennas are used in the arrangements specified in ANSI standard. The CSA is evaluated numerically by introducing effective reflection coefficients, which yield an excellent agreement between theoretical and experimental results. It is found that, for horizontal polarization, differences in the CSA values between soil ground test sites and metal ground test sites decrease with increase in antenna separation distance. The deviation may reach about 4 dB for a separation of 3 m. On the contrary, in the case of vertical polarization, the CSA values of soil ground test sites deviate more than 6 dB from those of metal ground test sites at longer separation distances, such as 10 m or 30 m. In addition, theoretical investigations were made on effects of dimensions and terminations of the dipole antennas used in site attenuation measurements.

Use of a gold catalyst with cooling of the laser-tube wall results in enhancement of the output power in an open-cycle fast-axial flow CO₂ laser. When Al₂O₃ spheres (diameter 3 mm) covered with numerous gold-catalyst hemispheres (40Å) on their surface were inserted within the gas-circulation loop, the total output increased by 16% from the open-cycle CW 500 W value to 580 W, with simultaneous cooling of the plasma-tube wall down to 30. The total oscillator power-increment was about 16%, in which 9% was enhanced with cooling the plasma wall and 7% was due to Au catalyst. From this slight modification without changing any physical configuration of setup and the gas composition, the oscillator output-power exceeding 700 W/m could be readily achieved in an open-cycle fast-axial flow laser. Taking into account both the catalytic contributions and the cooling effect of the plasma-tube wall on the population of the upper lasing level n₂, thereby, the gain parameter G, and other laser parameters such as the saturation irradiance I_s and the measure of homogeneity m, involving the dependences on both the gas-flow velocity v and the discharge current I_dis, the oscillator output-power is theoretically calculated and compared with the experimental results, and good agreement is obtained.

The QPI (quasiparticle injection) devices have the most transistor-like characteristics in many superconducting three-terminal devices. In particular, Quiteron which operates with the principle of energy gap's suppression only to modulate the conductance of the output junction has a promising feature, such as a large gain, non-latching operation, and binary inversion. In this paper, we have investigated the behavior of the energy gaps to analyze the characteristics of the QPI devices. First we have introduced the nonequilibrium GL equation. Then we have derived a set of equations for QPI devices by using this equation. It is found that the energy gap of middle layer has the singularity under quasiparticle injection.

The notion of alternating context-free grammar (ACFG for short) was introduced by Moriya in 1989. In this paper, we study the relationships between some complexity classes and the classes of languages generated by restricted types of ACFG's. Two restricted types of ACFG's considered are linear ACFG's and ε-free ACFG's. For an ACFG G, let L_left (G) denote the language of terminal strings generated by leftmost derivations in G. Let {L_left (G)G is an ε-free ACFG} and ACFL_linear{L_left (G)G is a linear ACFG's}. The main results of the present paper are as follows:
(1) the class of languages that are log-space many-one reducible to languages in ACFL_linear is equivalent to P, and
(2) the class of languages that are log-space many-one reducible to languages in is equivalent to PSPACE.