We review the physical basis of and recent developments in ferromagnetic Josephson junctions with a focus on the π state, which is useful for applications to superconducting devices. Among various novel phenomena that emerge from the interaction between the superconductor and ferromagnet, the π state (junction) works as a phase shifter in superconducting devices, and several proposals and demonstrations of applications to quantum computing elements (qubits), classical superconducting logic circuits, and cryogenic memory have been presented. As a new research trend in superconducting spintronics, we also introduce recent interesting works on the long-range Josephson effect caused by spin-triplet Cooper pairs.

Recently, several new ultra-low-power superconducting circuits, which can contribute to drastic improvement of power efficiency of information processing, have been proposed and implemented. These power-efficient superconducting circuits can be divided into dc-biased and ac-biased circuits. This paper overviews the current status of the development of power-efficient superconducting digital circuit technologies mentioning our researches mainly. Moreover, hybridization of dc-biased and ac-biased superconducting circuits is discussed for building low-power and high-performance digital information processing systems.

We report energy reduction in low-voltage rapid single-flux-quantum (LV-RSFQ) circuits using shunt-resistor-free Josephson junctions. The LV-RSFQ logic is one of energy-efficient derivatives of rapid single-flux-quantum (RSFQ) logic, which operates in a constant voltage mode. By lowering bias voltages, we can reduce power consumption at bias resistors which account for more than 90% of total power consumption, and also reduce the energy dynamically consumed during switching events because of slower transition of superconductor phase. Voltage drops across Josephson junctions cause a complicated trade-off between operation speed and power consumption. In this paper, we evaluated shunt-resistor-free LV-RSFQ shift-registers in terms of operation speed, power consumption, and energy-efficiency. Numerical simulation revealed their faster operation by up to 50% and accordingly higher energy-efficiency. Experimental results showed that a 0.5mV shift-register had superiority in operation speed and energy-efficiency.

We have been developing adiabatic quantum-flux-parametron (AQFP) circuits as an ultra-low-power superconductor logic for energy-efficient computing. In AQFP logic, logic circuits are designed by arraying the four types of building block cells, that include buffer, NOT, constant, and branch. The constant cell is a gate which always switches to a specific logic state when excited and is used in AND and OR gates. In this paper, we discuss the design method of the constant cell. Since the constant cell works thanks to the asymmetry in inductances or excitation fluxes, we analyzed the relationship between operation margins and asymmetry in inductances or excitation fluxes. The simulation results show that the asymmetry in excitation fluxes can easily increase the operation margins, compared to that in inductances. Taking into account the simulation results, we redesigned a constant cell, to which excitation fluxes are applied asymmetrically. We designed and fabricated AND and XOR gates using the constant cell. The measurement results show that the logic circuits designed using the constant cell work with wide operation margins.

Functional switching has been demonstrated based on quantum flux parametron (QFP) circuits with ferromagnetic patterns toward reconfigurable circuits. We form small ferromagnetic patterns of a PdNi alloy on a superconducting loop without degradation of superconductivity. Direction and strength of magnetization of ferromagnetic patterns are controlled by direction and magnitude of an applied magnetic field in a cooling process around the Currie points of the alloy. The ferromagnetic patterns induce a circulating current serving as one of the input currents in a three-inputs QFP majority gate. We obtained functional switching between the AND to the OR operation depending on the direction and strength of magnetization of the ferromagnetic patterns experimentally. The obtained operation margin agreed with a numerically obtained margin, though the magnitude of magnetization at the switching between two operation modes was different. This technique add new functionality and flexibility to the QFP-based integrated circuits.

Today's engineering students benefit from an educational program that integrates their knowledge so that they can better solve engineering problems and become natural innovators. The TekBots Platforms for Learning™ (TekBots^® PFL) developed at the School of Electrical Engineering and Computer Science (EECS) of Oregon State University (OSU) in the United States have integrated a curriculum into a coherent whole while providing an environment for innovation. The TekBots, which are an automobile robot and a platform for learning created for electrical and computer engineering students, have been designed to assist teaching many practical engineering skills; innovation, design, knowledge integration, and the “real” problem solutions of “real” systems. With the hands-on TekBots, the students can experience the real meaning to many of the seemingly ambiguous topics presented in lecture. The department of Electrical Engineering at Fukuoka Institute of Technology (FIT) has introduced this TekBots PFL to improve its engineering curriculum and has developed the TekBots course program used at FIT in a small scale. The program has been built by four subjects; Freshmen Laboratory for Electrical Engineering, C Programming, Mechatronics I and II. A TekBots project “TekBots Global Vision System” for a graduation thesis has also been carried out. Since two subjects, the Freshmen Laboratory for Electrical Engineering and the C Programming, have already been reported in our previous paper, this paper treats the results of implementation on the Mechatronics I and II. The Mechatronics I and II courses are hands-on laboratories for learning PWM programming and interrupt processing respectively. A microcontroller unit (MCU) is used to control the TekBots instead of the analog board used in previous courses. Intermediate student surveys for the Mechatronics I were carried out during term. It is shown that the surveys are not only useful for communication between students and faculty but also beneficial to an improvement of the TekBots course.

For calibrating of thermocouple using the eutectic point, a dedicated eutectic point furnace with a general size cell is necessary to realize stable and reproducible plateaux. On the other hand, if the eutectic point can be realized by a method that is simple to use, it can find much wider application in metrology in the field. Therefore we made a eutectic point cell for thermocouple calibration with size small enough to fit in an electric furnace for palladium fixed point for a wire-bridge method. We report the result that we perform an uncertainty evaluation and compared the general size cell and small-type cell. As a result of having performed the uncertainty evaluation of the general size cell, the combined standard uncertainty is 14 mK, small-type cell, the combined standard uncertainty is 27 mK.

An equivalent circuit analysis has been studied to realize the design of quasi-distributed constant line filter. This analysis is based on a physical model derived from a structure of a quasi-distributed constant transmission line composed of winding of a common-mode choke coil combined with a grounding plate. A target frequency band of the analysis is set from 150 kHz to 100 MHz in consideration of the Comité international spécial des perturbations radioélectriques (CISPR) regulation and trends of power converter circuits with SiC or GaN semiconductors. In modeling of the equivalent circuit, the circuit parameters are classified into a series impedance element and a shunt admittance element. Parameters of the series impedance element can be obtained by using frequency dependences of the relative complex permeability of a Mn-Zn ferrite core. To identify parameters of the shunt admittance element, impedance between a short-circuited end of the series impedance element and the grounding plate are measured. Then parameters can be obtained by performing circuit calculation based on observed resonant frequencies of the measured frequency characteristic of the impedance, values of the impedance and reactance, and the like. The calculated attenuation characteristic using identified equivalent circuit parameters shows good agreement with the measurement result.

The paper presents a formative assessment method of the internal factors consisting of motivation and learning strategy of individual students. It enables educators to choose students to focus their supervision. The method considers the internal factors of students result in their learning behavior. The learning behavior is extracted from learning logs which are automatically taken from the e-learning sites to study programming. The internal factors of individual students are figured out through the decomposition of their learning behavior with the non-negative matrix factorization. For 48 students of C programming course of Ritsumeikan University, the method showed predicted active students who can solve difficulties by themselves. Consequently, the educators can focus their efforts on students needing cares in a timely fashion.

A electrostatic precipitator (ESP) is a means to collect PM. They are characterized by a high total particle collection efficiency with a low pressure drop. The particle behavior in ESP depends on the particle characteristic, electric field, space charge and flow pattern. It is important to understand the particle behavior in ESP. Particle image velocimetry (PIV) was used to grasp the particle behaviour in ESP. In this paper, results of Particle Image Velocimetry (PIV) of the particle flow velocity fields in a wire-to-plate type ESP model are presented. The ESP was an acrylic parallelepiped with a wire-electrode and plate collecting electrode. The positive and negative DC voltages were applied to the wire-electrode, placed at right angles to the main gas flow. The obtained results show that the particle flow velocity increased with increasing discharge current. This is attributed to increase in ionic wind. The particle velocity right under of the wire-electrode was the fastest.

The magnetic properties and the microstructure of Rh(001)/FeCo-Ti-N thin film, which showed uniaxial magnetic anisotropy were investigated. Uniaxial magnetic anisotropy constant (K_u) was calculated as 0.98 MJ･m^-3 in the film with the thickness of 23 nm, and the c/a was estimated to 1.08. The analysis of Fast Fourier Transform (FFT) patterns taken from HR-TEM image showed that the c/a of the FeCo-Ti-N film reached to 1.12 at the interface of Rh/FeCo-Ti-N layers, and it decreased with increasing distance from the interface. These results indicate that the lattice strain induced at the Rh/FeCo-Ti-N interface could increase K_u.

This paper proposes an integral equation to describe the stochastic fluctuation of partial discharge (PD) occurrence under sinusoidal voltage stress based on a simple PD model. In the model, the stochastic behavior of PD fluctuation is assumed to arise from the fluctuation of residual voltage after PD is build up across a discharge gap. For simplicity of calculation, the distribution of residual voltage is assumed to obey a normal distribution. Based on these assumptions, it is found that the proposed integral equation provides the basic characteristics such as the PD pulse distribution in applied voltage phase angle domain. The authors solved the equation with numerical method and showed several ϕ-n distribution patterns. The authors analyzed the relationship among ϕ-n distribution patterns and several discharge parameters such as partial discharge inception voltage, mean residual voltages and standard deviation of residual voltage, applied voltage.