In the transient boundary element method (BEM) analysis, we know that there is instability of solutions. In this paper, we analyze the 2-dimensional scalar wave equation for a multi-reflecting model with several boundary conditions, while varying ratios between boundary element size ΔR and time element size Δt.
For this analysis we consider two linearization methods to deal with singular integration. One is to use conventional space-time elements, and another is a new method which uses what we call space-time planar elements. The use of the space-time planar element is introduced to remove from the singular integration the contribution to a singular node from its adjacent nodes at each instant. In order to evaluate the solution's stability, we use the connection matrix, which represents the contribution from past source terms to the field being considered on the boundary.
In order to achieve a stable solution, we came to the following conclusions. First we find that the use of the space-time planar element is valid. The other has to do with the influence from the difference between boundary conditions. We find the instability under the Dirichlet condition problem at all nodes, while the Neumann condition problem at all nodes is stable. Usually, no problems are created with only the Neumann condition, and the certain Dirichlet conditions can be replaced by Neumann conditions because of symmetry. This type of problem leads to stability given the correct choice of ΔR and Δt which must satisfy the condition cΔt_??_ΔR.

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Plasma spraying is gradually becoming an important technique in the material processing field, with a feature of controlling the area or the thickness of deposited film. High temperature plasmas to heat ceramic particles with a high melting point have in the past been generated continuous D. C. power sources. We propose to apply a pulsed plasma using a high current of the order of tens of kA for plasma spraying of refractory materials. Numerical analysis of the short-time heating and acceleration of particles showed that alumina particles 20 microns in diameter reach the complete melting state after a residence time of 83 and 9.6 micro-second and a flying distance of 5.8 and 0.5 mm, when the temperature of the pulsed plasma is assumed to be 10, 000 and 20, 000 K, respectively, with a constant plasma velocity of 200m/s. Experiments were then performed using a specially developed plasma torch with a pulsed discharge current of 24kA peak and a duration of 400 micro-second. This current is provided from a capacitor with a maximum stored energy of 14kJ. The simultaneous, in-flight measurements of the particle's temperature, velocity and size were carried out for alumina particles injected into the pulsed plasma. Results showed that the surface temperature of the alumina particles reached values as high as 2, 700 to 3, 300K which was considerably higher than the melting point. The particle velocity was found to be around 200m/s which is comparable with that in the D. C. plasma mode. The experimental results confirmed the applicability of the pulsed plasma for the spraying of refractory materials.

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The reason for the occurrence of discharge instability at up to 4kHz operation of the XeCl excimer laser is found out related to the gas density fluctuation at the discharge area and to the pressure of Xe. We used Michelson interferometory system to measure the gas density and we measured the intensity of emission spectra from the discharge to estimate the discharge stability.
The discharge becomes unstable in case clearance ratio CR (=v•T/w, v: gas velocity, T: discharge period, w: discharge width) is 4 because of the gas density fluctuation induced by the spark discharge for pre-ionization. In case CR is 3 the gas density fluctuation rate becomes less than 0.3%, the discharge is stable at low Xe pressure but unstable at high Xe pressure operating at more than 3kHz. We proposed a new model to indicate that charged particles occurred by the discharge survived until the next dischenge initiation and cause discharge instability at high Xe pressure and high repetitive operation.

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Power capacitors are highly reliable equipment due to their completely enclosed configuration. They have usually worked without almost any trouble for a long time, Their dielectric strength can be however reduced due to some stresses such as over-voltage application or thermal degradation of the insulation material during their long period of operation and these events can result in the dielectric breakdown of the capacitors in extreme cases.
Since almost all power capacitors with oil-impregnated paper have been operated more than twenty years, some kind of failure should be expected for them, To prevent such accidents which might occur very soon, it is important to clarify the insulation deterioration mechanism and evaluate the degree of the deteroration before the capacitor breakdown occurs, To establish the diagnostic method of the deterioration of the capacitors with oil-impregnated paper, we have conducted thermally-and electrically-accelerated deterioration tests and investigated the changes of their characteristics, Based on the experimental results we obtained, it can be concluded that the behavior of the oil-dissolved gases can be used as a useful index to diagnose the insulation deterioration of these capacitors.

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This paper presents a new tomographic reconstruction algorithm for an annular cross section of toroidal plasma. The expansion consists of Fourier series in the azimuthal direction and Bessel and Neumann functions in the radial direction which satisfy boundary conditions both on the center coil section wall and on the vessel wall. The expansion coefficients are determined by the least-squares fitting method. The reliability of this algorithm is evaluated by use of numerical simulations. Since the normal equation is numerically close to singular, singular value decomposition is more suitable for finding the least-squares solutions as opposed to the direct solution of the normal equation. The error sensitivity estimation using Monte Carlo simulation reveals that the projection signal error appears mainly on the coefficients of the higher modes. This method becomes less sensitive to the projection signal error by weighting the axisymmetric mode.

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The effective lifetime of N₂ (A³∑⁺_u) in N₂/O₂ gas is determined by means of measurement of transient ionization current. They are analysed by our theory in which the reflection coefficient of N₂ (A³∑⁺_u) at the boundary is taken into accounT. Experimental values of the diffusion coefficient of N₂ (A³∑⁺_u), the collisional quenching rate coefficient of N₂ (A³∑⁺_u) by O₂, and the reflection coefficient are reported. However, the effective lifetime in high pressure region do not conform to the above theory of deexcitation by two body collision. Further, the electrode surface is studied by means of X-ray photoelectron spectroscopy (XPS), and the existence of the adsorbed O₂ molecules or O atoms on the electrode surface is confirmed.

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Stylus probe method is known as a means of measuring magnetic flux in the localized area of electrical sheet steels. Although the method is more convenient as compared with the search coil method, it is not authorized as a formal method of flux measurement mainly because of the unclearness in the evaluation of the measured value. In this paper the measurement of localized magnetic flux by the stylus method was evaluated theoretically in comparison with that by the search coil method, being based on local eddy currents analysis taking into consideration the magnetic domain structure. It was shown that the local variations of emf's with measuring position by the both methods increase as the ratio of domain width to sheet thickness becomes larger, and the differences between the measured values by the two methods do not exceed a few percent for ordinary measuring conditions in oriented silicon-iron sheets. It can be concluded from various analyses that the stylus probe method can be an effective technique of localized magnetic flux measurement in electrical sheet steels.

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