The periodically driven Gunn diode is studied numerically as an example of a forced oscillator with spatial degrees of freedom.
The Gunn diode is an active element which exhibits self-sustained (current) oscillations in the microwave range when the applied DC voltage exceeds a characteristic threshold value. These oscillations can be understood in terms of a dissipative structure that has spatio-temporal order. When a periodic voltage is applied to the diode, highly nonlinear-dynamic phenomena can arise by interaction between the internally generated domain mode and the applied microwave signal. Several Arnol'd tongues in the plane of forcing frequency and amplitude were drawn in previous work.
Focusing on the 1/2 Arnol'd tongue, previous bifurcation analysis is extended in this paper. A transition from harmonic entrainment to 1/2 subharmonic entrainment and bifurcations of period-2 orbits are investigated by locating unstable as well as stable periodic orbits and calculating the corresponding characteristic multipliers. Chaotic oscillations are characterized through return maps and Lyapunov exponents.

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Recently acid rain has turned into a grave environmental problems. The authors made out artificial acid rain with any electric conductivity σ and value of pH, by a combination of adilute sulfuric acid and seven kinds of salts based on chemical analysis of ionic ingredient of rainwater. In this paper, apropagation of a streamer discharge on the surface of artificial acid rain is investigated in detail by using a high-speed Schlieren method and a current measuring system by LED.
The results obtained may be summarized as follows:
(1) A flashover voltage V_f of rainwater decreases gradually with increasing the σ and an effect of the V_f on the pH can not be seen obviously in this experimental conditions.
(2) On the propagation of the streamer discharge on the surface of artificial acid rain,
(i) in case of rain which has about the same pH and the different σ, the propagation length l_dof streamer-like density changes becomes larger as the σ is made larger.
(ii) in case of rain which has about the same σ and the different pH, a remarkable difference can not be seen in a propagation figure and a t-l_d characteristic of the streamer-like density changes, and in a current waveform.

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The paper describes the application of arc charges for numerically calculating electric field by the charge simulation method (CSM) in three-dimensional configurations. Analytical expressions with two kinds of elliptic functions were derived for potential and field strength of arc charges, the charge density of which changes as a function of angle. This permits of simulating rounded electrode surfaces without resort to numerical computation, thus resulting in good accuracy in electric field calculation. We formulated the CSM-program, which used arc, line and point charges as fictitious charges, for analyzing the electric field of plate electrodes employed in high voltage and laser technology. The calculation was performed for square and rectangular electrodes with rounded edges, that is, composed of a central flat part connected with circular edges on a sectional plan. The results show that the maximum field strength takes place on a diagonal line on the electrode corner. The heighest value in a three-dimensional arrangement is close to that in an axis-symmetric one with the electrode radius corresponding to the rotation radius at the three-dimensional corner, as far as the radius is not small.

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The breakdown time lags in PPS were measured in the ns and minute ranges and in a wide temperature range (-196 to 200°C). The temperature dependence of the electric breakdown strength became stronger at the longer time elapsed after the voltage application. With increasing the test temperature, the electric breakdown strength decreased from the maximum value at -196°C to the minimum value at 20°C, increased to a peak value at 100°C, and then decreased again. The time lags were normally distributed in both time ranges although the distribution of time lags in the ns range was exponential type for all of the seven kinds of polymeric insulating films, which were previously reported. The normal distribution of time lags suggests that the breakdown was not caused by a stochastic event such as an avalanche breakdown but by the process which started just the moment of the application of a voltage, regardless of the time range. The results in the minute range show that the breakdown was caused by the field distortion due to space charge, though the breakdown mechanism in the ns range was still obscure.

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It has been proposed that vapor-mist dielectrics in which mixing liquid droplets such as tetrachloroethlene in a gas have an ability of increasing flashover, impulse voltage, and of suppressing partial discharge. Vapor-mist methods have been performed on other materials and the effect of the mist can also be obtained on benzen, hexan, and even if water as general materials. Although these studies have been carried out, neither the discharge mechanism on vapor-mist nor the reason for the increase of the discharge voltage is fully understood. Because the mist have various size. On the other hand, agglomeration of water molecules can be studied with FT-IR method, and are classified into monomer, dimmer, trimmer (including polymer). Water give mist stats which are significant to discuss on effects.
This paper describes states of water mist and the effect of them under non-uniform field with positive and negative polarities. Water mist in vapor exist as dimmer and trimmer, and the amount of them decrease with the reduction of temperature. These mist have no effect on discharge suppression. When the mists, however, are formed by space charges, the inception voltage is increased by these mists in the negative polarity.

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We have constructed a prototype of PD measurement and expert system for degradation diagnosis using personal computer (PDM/ES-I). PDM/ES-I consists of three parts: PD measurement system (PDM), PD pulse data analyzing system (PDDANS) and degradation diagnosis system (DDS). PDM allows to obtain reproducible PD pulse data with the phase information in an alternating voltage cycle and the number of the alternating cycles. For CIGRE Method-II (CM-II) electrode system using 0.1mm thick polyethylene film (LDPE), temporal change of PD data is measured with PDM/ES-I up to breakdown of the sample (LDPE).
We found from the experimental results that five new statistical PD perameters monotonously have varied with aging time. The new PD parameters are θ_INC±: average of inception phase, Φ_nmax±: phase window of maximum PD pulses number, R_cc±: ratio of total charge of pulses occurring at faster window than a given threshold phase (positive default 0 deg, negative default 180 deg) to total charge, C^n±: concentration ratio of PD pulses number at Φ_nmax±, R_Q: ratio of sum total charge of absolute quantity of positive PD pulses (|Q₊|) and charge of absolute quantity of negative PD pulses (|Q_-|) to subtraction |Q₊| from |Q_-|. We also found that PD pulses occurrence distribution have correlation with aging time.
Finally we propose a model for a PD mechanism in which the statistical time lag of the discharge is dependent on over voltage of a void gap and the residual voltage depends upon the charge of partial discharges.

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A quantitative investigation on the relationship between arc duration and resistance in Ag contact in air were made by using a contact driving machine to open the contact at low speed (below 1 mm/s), and measured data were analized statistically. The two types of arc (metallic phase arc: short arc, and metallic phase plus gaseous phase arc: long arc) appeared at low opening speed and the type of an arcing has the correlation with the contact resistance. The contact resistance was high after generating long arc, while low after short arc. Characteristics of arc duration was that both of long arc and short arc appeared in period 1, and only short arc appeared concentratedly in period 2, and these states repeated reciprocally. A clear correlation existed between variations of arc duration and resistance

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Simultaneous, in-flight measurements of the three principal particle parameters, the velocity, size and the surface temperature were made of Nickel, Alumina and Tungsten powders which are injected into a 3MHz inductively-coupled r. f. plasma. The light pulse analysis technique newly developed enables us to detect the three particle parameters of single particle and thus the crosscorrelation between them can be analyzed for particles in thermal plasma processing. Measurements were carried out at plasma plume of 370mm down stream portion from main discharge region at a constant plasma power of 10kW and at a pressure of 170Torr. Results showed that the statistical properties of particle popuration, such as mean temperature or mean velocity changes significantly for each materials, reflecting the difference in the value of specific heat or melting point etc.. The cross-correlation analysis showed generally for the three materials that the smaller the diameter of the particle, the higher the surface temperature.

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