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We have investigated charging and flashover characteristics of a polymeric or glass insulator exposed to ac voltage in vacuum in order to develop compact and reliable high voltage VCBs (Vacuum Circuit Breakers). This paper focuses on charging characteristics of a cylindrical model insulator. The charging of an insulator is investigated using an electrostatic probe that measures the electric field near the triple junction on the grounded electrode. This method allows a time-resolved measurement of the charging process. The insulator was made of borosilicate, fused quartz or polymetyl methacrylate, and was in the shape of a right cylinder with 10 mm in thickness. It has been clarified that the charging is characterized by three sequential states; initiation, quasi-stable and stable states, and that the polarity of the charge is positive for these states irrespective of the voltage phase. The charging characteristics with ac voltage are compared to our previous results with dc voltage excitation. We find that the charge magnitude at the stable state coincides with that obtained by dc. The electric field on the grounded electrode, and therefore the charge magnitude, decreases with the surface roughness, and decreases as the insulation strength is increased. A computer simulation has been conducted to investigate the quasi-stable state, which clarifies that the transition in surface charge distribution being synchronous to the voltage phase is responsible for causing the quasi-stable state. Index Terms--Surface charging, charge distribution, flashover, surface roughness, solid insulator, glasses, PMMA, vacuum.

We propose a neuron-synapse integrated circuit (IC) chip-set for large-scale chaotic neural networks. We use switched-capacitor (SC) circuit techniques to implement a three-internal-state transiently-chaotic neural network model. The SC chaotic neuron chip faithfully reproduces complex chaotic dynamics in real numbers through continuous state variables of the analog circuitry. We can digitally control most of the model parameters by means of programmable capacitive arrays embedded in the SC chaotic neuron chip. Since the output of the neuron is transfered into a digital pulse according to the all-or-nothing property of an axon, we design a synapse chip with digital circuits. We propose a memory-based synapse circuit architecture to achieve a rapid calculation of a vast number of weighted summations. Both of the SC neuron and the digital synapse circuits have been fabricated as IC forms. We have tested these IC chips extensively, and confirmed the functions and performance of the chip-set. The proposed neuron-synapse IC chip-set makes it possible to construct a scalable and reconfigurable large-scale chaotic neural network with 10 000 neurons and 10 000(2) synaptic connections. Index Terms--Chaotic neural networks, mixed analog/digital system, chaos, large-scale neural networks.

This paper describes a simple and reliable method of improving the surface insulation strength of a spacer used in vacuum. The method is to roughen the spacer surface to an average roughness [R.sub.a] higher than 1 or 2 [micro]m. The material of the spacer examined is Si[O.sub.2], PMMA, PTFE or [Al.sub.2][O.sub.3] and their shape is a right cylinder with 10 mm in height and 54 mm in diameter. The spacer is subjected to a ramped dc voltage and its surface charging is observed by using an electrostatic probe embedded in the cathode. It has been found that [R.sub.a] decisively affects the charging, which decreases as [R.sub.a] increases. Increasing [R.sub.a] larger than about 2 [micro]m suppresses the charging until a higher applied voltage is reached, thus improving the insulation property. Index Terms--Charging, flashover voltage, insulating spacer, roughness, vacuum.

This paper studies the possibility of applying a gas mixture containing c-[C.sub.4][F.sub.8] in the gas insulation of power equipment. Environmental aspects such as global warming potential, ozone depletion potential, recycling loss and toxicity are discussed. Insulation characteristics of gas mixtures such as c-[C.sub.4][F.sub.8]/[N.sub.2], c-[C.sub.4][F.sub.8]/air, and c-[C.sub.4][F.sub.8]/C[O.sub.2] are examined experimentally under a quasi-homogeneous or an inhomogeneous electric field condition. Most of the characteristics are compared with those of S[F.sub.6]/[N.sub.2], which is now widely studied as the most plausible alternative to pure S[F.sub.6], for gas insulation. The experimental results, together with the discussion, suggest that gas mixtures containing c-[C.sub.4][F.sub.8] are possible substitutes for S[F.sub/6] and S[F.sub.6]/[N.sub.2].