Nitrogen-doped carbon materials exhibit a catalytic activity, such as an oxygen reduction reaction (ORR). In this study, we performed nitrogen doping on a carbon nanoballoon (CNB) which is a nanometer-sized carbon particle in the form of a hollow sphere made of graphite by radio-frequency (RF) magnetron plasma in a gas mixture of nitrogen and helium. Nitrogen-doped CNBs (N-doped CNBs) were prepared by different plasma irradiation conditions: the sample installation positions, input powers, and irradiation times. The samples were examined for chemical state by X-ray photoelectron spectroscopy (XPS). Hydrodynamic voltammetry was used for the evaluation of the catalytic activity of a N-doped CNB with a pyridinic N concentration of 0.4-1.0at.%. As a result, the onset potential was measured to be 0.13 V vs. RHE (reversible hydrogen electrode), which was close to the previously reported data of highly oriented pyrolytic graphite (HOPG) with a pyridinic N concentration of 0.57at.%, which was prepared by annealing under NH₃.

One of the weak points of all solid insulation system is the breakdown strength along the interface between two solid dielectrics. The low breakdown voltage is considered to be due to the small cavities formed in the interface due to surface morphology. In this paper, we investigated the effects of dielectric material and compressive force on interfacial breakdown voltages. The results that we obtained are as follows: (1) most of the interfacial breakdowns between two solid dielectrics were developed by avoiding the contact area for high-pressure region, (2) in cases of polymethyl methacrylate (PMMA) and high-density polyethylene (HDPE), the breakdown voltages increased with increasing the compressive force, (3) mechanically soft insulating material was found to be better than hard material, because cavities existed between two solid dielectrics by compressive force become small, and (4) although the same compressive force was applied to the interface, the breakdown voltages increased with increasing uniformity of the surface.

Our previous study showed that transient earth voltage sensor detects high frequency components mainly caused by electromagnetic waves propagating through space, as well as low frequency components caused by partial discharge (PD) current flowing through the ground. This paper presents more detailed investigation on the influence of the length of the PD measuring circuit on the TEV low frequency component based on lumped circuit constant and antenna theories.

This paper deals with partial discharge inception voltage (PDIV) of enameled wire undergoing mechanical stress with micro cellular coating wire under ac voltage application. A model coil sample with smaller winding diameter than usual one was prepared. It was found that measured PDIV of the inside part of the winding model is smaller than that of the outside of the model. A good agreement is obtained between measured PDIV with that estimated by electric field calculation and Paschen's law of air.

The authors have developed a micro cellular film with lower permittivity than the conventional film and investigated the decrease effect of partial discharge inception voltage (PDIV) of the cellular film wire under AC voltage and impulse voltage. This paper deals with quantitative evaluation of the PDIV using PDIV analysis by Volume-Time theory.

This paper describes an integral equation to calculate the stochastic fluctuation of partial discharge (PD) occurrence under sinusoidal voltage stress based on a simple PD model. For the simplicity of calculation we used a symmetric PD model for positive and negative PD characteristics with measurements of a symmetric electrode system. In this paper we made a progress in calculation using asymmetric PD characteristics using different PD parameters for positive and negative PDs. The stochastic behavior of PD fluctuation is assumed to arise from the fluctuation of PD delay time after the inception voltage and the fluctuation of PD inception voltage (PDIV) as before but different parameters for positive and negative ones. The authors solved the equation with numerical method and showed several φ-n, φ-q distribution patterns as before but more realistic characteristics.

This paper presents a topology optimization method using a greedy algorithm for submodular maximization. This method is based on a shape representation using the normalized Gaussian network. The weight coefficients of Gaussians are discretized to +1/-1, and then their values are greedily inverted. Hence, the computational cost of the present method is relatively smaller than that of evolutionary algorithms. The present method is applied to a magnetic shield optimization problem. It is shown that Pareto solutions can be obtained by the present method. In addition, it can be found from the numerical results that the stochastic greedy algorithm can effectively reduce the computational time compared with the conventional greedy algorithm. As a result, it is shown that a 3-D optimization problem with over 3000 design variables can be solved within acceptable computational time.

A cancer treatment by ultra-short pulse high electric field is one of new biological applications. This work focuses on the design of a compact high power nanosecond pulsed electromagnetic wave generator for the cancer treatment. We have been developing Nonlinear Transmission Line using magnetic switches that can output a pulse train with multiple pulses as a burst pulse for the treatment. However, there was the problem of uniformity of pulses, which was the first pulse of the output train was bigger than the following pulses. In this study, we improved the generator so that it could output the burst pulse train with uniform amplitude.