Laser‐induced discharge in a rod–plane electrode in the presence of a negative dc electric field

Discharge induction experiments were performed between a plate and a rod on a plate electrode configuration with a gap length of 1 m using a high‐power CO₂ laser and a dc voltage generator. The electrodes are parallel planes. Each plate electrode consists of a central flat part having a diameter of 3 m with a circular edge on a cross section. The length of the rod is 10 cm. A chain of plasma beads of length 10 cm was created on the tip of the rod by the CO₂ laser and used for artificial triggering of negative high‐voltage sparkover. The behavior of streamer, leader, and return stroke was observed by an image converter camera. It was found that a positive upward traveling leader can be triggered from the tip of the rod on the lower plane to the upper plane by the chain of plasma beads created by the CO₂ laser. This apparatus is useful for study for realization of laser‐induced lightning. © 2000 Scripta Technica, Electr Eng Jpn, 132(4): 19–27, 2000     

Effects of a barrier on creeping discharge characteristics in SF6 and N2 gases under pulse voltages

This paper describes the effect of a barrier on creeping discharge characteristics in SF₆, N₂, and their mixtures. The barrier height effect on the discharge voltage was investigated under a positive pulse voltage. The discharge voltage increased with increasing barrier height in SF₆ gas. On the other hand, the discharge voltage hardly changed with the barrier height in N₂ gas. In order to clarify the mechanism of the initial creeping corona, it was observed by optical techniques, including an ultra-high-speed electronic imaging system (IMACON 468). The creeping corona path revealed differences in images at various barrier heights. The accumulated charge induced on the barrier by the initial corona in SF₆ gas was able to suppress the development of the later creeping corona, in contrast with N₂ gas. © 1998 Scripta Technica, Electr Eng Jpn, 125(4): 1–8, 1998     

Understanding the mechanism of heat stress tolerance caused by high trehalose accumulation in Saccharomyces cerevisiae using DNA microarray

DNA microarray analysis was performed to examine the stress tolerance mechanism of a Saccharomyces cerevisiae recombinant strain exhibiting high trehalose accumulation and heat stress tolerance. Results suggest that the upregulation of sugar transporter genes is one of the key events for heat stress tolerance of the recombinant strain.     

Theasaponin E1 destroys the salt tolerance of yeasts

Cells of Zygosaccharomyces rouxii in a medium containing a high concentration of NaCl were killed during incubation for 2–4 h with a low concentration of a mixture of saponins from tea seeds (TSS). The higher the concentration of NaCl in the medium, the higher the inhibitory effect of TSS on the growth of the yeast. The above inhibitory effect of TSS on the growth of the yeast was not observed when cells were incubated in hypertonic media composed of nonionic substances such as sugars. The ATPase activity of plasma membrane preparations from the yeast cells was slightly affected by the addition of TSS. It is shown that TSS facilitates leakage of glycerol from the yeast cells under NaCl-hypertonic conditions. The major inhibitor in the mixture of saponins was isolated and identified as theasaponin E₁. Its isomer, theasaponin E₂, did not have any effect on the salt tolerance of Z. rouxii or Saccharomyces cerevisiae.     

Competitive oxidation of formaldehyde and formate on amorphous copper-palladium-zirconium alloy electrodes in alkaline media

Raney-type Cu–Pd alloy electrodes were prepared from amorphous Cu–Pd–Zr ternary alloys by treatment with aq. HF, and competitive anodic oxidation reactions of HCHO and HCOO^– were studied on these electrodes in alkaline media. The initial HCHO oxidation product was HCOO^– even on Pd or Pd-rich alloy electrodes which should be more active to the HCOO^– oxidation than to HCHO. The product HCOO^– was oxidized only after a large decrease of the HCHO concentration in the electrolyte. The oxidation rate of HCOO^– was considerably lowered by the existence of even a small amount of HCHO, as well as by the introduction of CO. These results suggest that the HCHO electro-oxidation is accompanied by production of a surface contaminant such as adsorbed CO. The optimum nominal Pd atomic fraction in the Cu–Pd alloy electrodes suitable for the steady simultaneous oxidation of HCHO and HCOO^– in mixed solution was shown to be 0.25 and 0.4 in 1.0 M NaOH (M=moldm^–3) and 0.5 M K₂CO₃, respectively.     

A sinusoidal PAM-PWM inverter

A new strategy, using both PAM (pulse amplitude modulation) and PWM (pulsewidth modulation) in combination for a power inverter is described. The output waveforms in the proposed PAM-PWM inverter are investigated both theoretically and experimentally. The line-to-line voltage waveform includes the fundamental component and the sidebands of the carrier frequency. Lower-order harmonics are not included in the output waveform. The amplitude of the fundamental component increases 15 percent more than that of a conventional sine-wave inverter. Since each inverter arm does not operate during two-thirds of the period, the heat generated in the devices is reduced, i.e., the size of the inverter system can be minimized because of the reduction in the heat dissipating equipment.     

Critical current test results of 13 T-46 kA Nb3Al cable-in-conduit conductor

In the framework of ITER-EDA, a 13 T-46 kA Nb₃Al conductor with stainless steel jacket has been developed in order to demonstrate applicability of an Nb₃Al conductor with react-and-wind technique to ITER-TF coils. Using a 3.5 m sample consisting of a pair of conductors with 0% and 0.4% bending strain, the critical current performances of the Nb₃Al conductors were studied to verify that the conductor achieves the expected performance and the bending strain of 0.4% does not originate degradation. The critical currents were measured at background magnetic fields of 7, 9, 10 and 11 T at temperatures from 6 to 9 K. The expected critical currents were evaluated taking into account the variation of the strain in the cross-section due to the bending strain as well as self-field and non-uniform current distribution as results of an imbalance in the joint resistance and inductances. The calculation results indicate that the current distribution is almost uniform and the experimental results showed good agreement with the expected critical currents. Accordingly, we can conclude that the fabrication process of this conductor is appropriate and the react-and-wind technique using the Nb₃Al conductor is applicable to ITER-TF coils. In addition, the critical current of the Nb₃Al conductor is expected to be 108 kA at 13 T and 4.5 K, resulting in a sufficient margin against the nominal current of 46 kA. Furthermore, it was found that the decrease in the critical current by thermal strain can be made small by applying the bending strain to the conductor so as to reduce the compressive strain at higher fields, i.e. inner side of the coil, in the conductor cross-section.     

Implications of the ability to learn simple actions on the efficiency of the evolution of social behavior of agents

We investigate the effect of the ability to learn simple actions on the performance characteristics of the evolution of social behavior in agents situated in an inherently cooperative environment. Using a continuous predator–prey pursuit problem, we verified that relatively complex social behavior emerges from simple, implicit, locally defined, and thus robust and scalable interactions between the predator agents. Considering a distinct aspect of the phenomenon of emergence, we hypothesize that the ability of agents to learn how to perform simple, atomic acts of implicit interaction might facilitate the evolution of more complex behavior. The empirical results indicate that incorporation of the proposed approach to learning in genetic programming (employed as an algorithmic paradigm to evolve the social behavior of the agents) is associated with about a two-fold decrease in the computational effort of evolution.This work was presented, in part, at the 9th International Symposium on Artificial Life and Robotics, Oita, Japan, January 28–30, 2004