Fault analysis of the interconnecting system between a commercial‐scale subsonic diagonal‐type MHD generator and an ac power system

Fault analyses are performed for the interconnecting system between a commercial‐scale subsonic diagonal‐type MHD generator and an ac power system through a line‐commutated inverter. The behavior of the interconnecting system is first examined for the case of single misfiring of one thyristor in the inverter. In this case, the load current increases because the inverter system is short‐circuited. Following the theory of inverter commutation, the load current decreases to the rated value and the MHD generator is restored to the rated condition. Next, the cases of a single‐line ground fault and of a three‐phase short circuit fault are investigated. The line voltage decreases and thus the load currents increase after the fault. This increase of load currents destroys the design‐point flow of the MHD generator. Phase‐control angle control of the inverters is required in order to restore the rated operation of the MHD generator. © 2001 Scripta Technica, Electr Eng Jpn, 136(1): 29–36, 2001     

Progress of fusion nuclear technologies in the broader approach framework

In the Broader Approach framework, the International Fusion Materials Irradiation Facility/Engineering Validation and Engineering Design Activities (IFMIF/EVEDA) project, the International Fusion Energy Research Center (IFERC) project, and the Satellite Tokamak project are implemented. In the IFMIF/EVEDA project, engineering design of IFMIF and engineering R&D include the construction and tests of an IFMIF prototype accelerator system up with a 9 MeV and CW deuteron beam, a liquid lithium test loop with free surface flow, and full scale irradiation test module including temperature control instrumentation. The commissioning of the EVEDA lithium test loop was completed in March 2011, and a lithium flow of ～5 m/s was obtained. As a part of the IFERC project, R&Ds on reduced activation ferritic/martensitic steels as blanket structural material, SiC_f/SiC composites as a flow channel insert material and/or alternative structural material, advanced tritium breeders and neutron multipliers, and tritium technology are carried out. At the beginning of 2011, the integrated DEMO design team was established among the IFERC project team and EU/JA home teams, where the design criteria, other design basis are discussed as an initial work. A high performance supercomputer with the peak performance of 1.3 Pflops is under installation at the Rokkasho BA site.     

Group delay ripple reduction and reflectivity increase in a chirpedfiber Bragg grating by multiple-overwriting of a phase mask with anelectron-beam

The phase errors in electron-beam-written step-chirped masks can be reduced by using a method based on the continuous movement approach and overwriting a pattern at the same place on the substrate several times. The group delay ripple of chirped fiber Bragg gratings fabricated by a four-times-overwritten phase mask is comparable with that of gratings obtained using a holographically written chirped phase mask     

Crystal structure and thermoelectric properties of chimney–ladder compounds in the Ru2Si3–Mn4Si7 pseudobinary system

Phase relationships of manganese-substituted ruthenium sesquisilicide alloys have been investigated by using X-ray powder diffraction and scanning and transmission electron microscopy. A series of chimney–ladder phases Ru_1?xMn_xSi_y (0.14 ? x ? 0.97, 1.584 ? y ? 1.741) are formed over a wide compositional range between Ru₂Si₃ and Mn₄Si₇. The compositions of these chimney–ladder compounds deviate slightly from the composition line connecting Ru₂Si₃ and Mn₄Si₇, which corresponds to the ideal composition line satisfying VEC (valence electron counting) = 14 rule. The occurrence of this compositional deviation is discussed in terms of the VEC rule and the atomic packing. The thermoelectric properties of the directionally solidified Ru_1?xMn_xSi_y alloys (0.55 ? x ? 0.90) have also been investigated as a function of the Mn content and temperature. The dimensionless figure of merit (ZT) for those alloys with a high Mn content (x ? 0.75) increased with the increase in Mn content. The ZT value for a crystal with x = 0.90 was as high as 0.76 at 874 K.     

Effect of gas introduction position on substrate etching by means of Ar-dominated graphite-cathodic-arc plasma beam in μT-FAD

Substrate etching by means of Ar-mixed graphite-cathodic-arc plasma beam was investigated in a newly-developed compact-type μT-FAD. The surface level and roughness change were measured as a function of the Ar gas flow rate, when Ar gas was introduced into the arc generation zone and in the vicinity of the substrate. When Ar gas was introduced to the arc generation zone, the etching rate was lower but the surface was relatively not roughened. When Ar gas was introduced in the vicinity of the substrate, the etching rate was higher but the surface was roughened. At the same gas flow rate (and pressure), the substrate was etched more than three times faster when Ar gas was introduced into the arc generation zone than to the vicinity of the substrate. After measuring the discharge and plasma conditions, the results were considered to be caused by the difference in the amount of plasma transported to the substrate.     

Selective catalytic reduction of NO under ambient conditions using ammonia as reducing agent and MFI zeolites as catalysts

Ambient temperature SCR of NO was studied over Ti, V and B silicalite-1, silicalite-1 and H-ZSM-5 catalysts. It was observed that even at 0°C silicalite-1 possesses some activity which falls off sharply with increasing temperature. An enhanced activity could be correlated to the titanium content in the Ti and Ti&z.sbnd;V silicalite samples. H-ZSM-5 and H-BS-1 show an unusually high transient activity probably due to weakly adsorbed ammonia species. These would not be adsorbed at higher temperature thus explaining the decreased activity as temperature is raised. Indeed with these catalysts no transient high activity was observed when the reaction was carried out at decreasing temperatures.     

71Ga NMR characterization of MFI-type Ga- silicate synthesized by the rapid crystallization method

MFI-type Ga-silicate was synthesized by the rapid crystallization method. A peak of ⁷¹Ga MAS NMR around 160 ppm proved that Ga was isomorphously substituted for Si with tetrahedral coordination. Less than 5% of the incorporated Ga was moved to extraframework with octahedral coordination by ion-exchange treatment to transform the Ga-silicate to the H-form, as could be seen by the appearance of the -7 ppm peak. High stability of Ga incorporated into the framework of MFI structure by the rapid crystallization method was confirmed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Impulse Breakdown Characteristics of Coated Electrodes in SF6 Gas

The authors investigated the impulse breakdown characteristics of coated high-voltage electrodes in SF6 gas with a varying nonuniform factor, electrode area, and coating material. From the viewpoint of the relation between breakdown stress and the stressed electrode area, it was clarified that with coated electrodes, breakdown voltage remains, with an increasing electrode area, nearly at the theoretically estimated level for SF6 gas breakdown without showing any decrease due to the area effect (in contrast to bare electrodes). Moreover, it was also recognized that repeated breakdown characteristics of coated electrodes differed depending on the coating materials.     

Two-dimensional DNAPL migration affected by groundwater flow in unconfined aquifer

The dense non-aqueous phase liquid (DNAPL) migration process was experimentally investigated in a laboratory-scale tank (150 cm width, 82.5 cm height, and 15 cm depth) to assess a site characterization on DNAPL contamination below a groundwater table. The heterogeneous ground of the tank model consisted of Toyoura sand (hydraulic conductivity, k = 1.5 x 10(-2) cm/s for void ratio, e = 0.62) and silica #7 sand (k = 2.3 x 10(-3) cm/s for e = 0.72). A series of experiments was carried out with or without lateral groundwater flow. Hydrofluoroether was used as a representative DNAPL. The main results obtained in this study are as follows: (1) the DNAPL plume does not invade into the less permeable soil layer with higher displacement pressure head; (2) the DNAPL plume migrates faster with lateral groundwater flow than without it; (3) lateral groundwater flow does not affect lateral DNAPL migration; rather, it promotes downward migration; and (4) pore DNAPL pressure without groundwater flow is higher than that with it. The above experimental results were compared with numerical analysis. The fundamental behaviors of DNAPL source migration observed experimentally are expected to be useful for assessing the characteristics of two-dimensional DNAPL migration in an aquifer.     

Spatiochromatic receptive field properties derived from information-theoretic analyses of cone mosaic responses to natural scenes

Neurons in the early stages of processing in the primate visual system efficiently encode natural scenes. In previous studies of the chromatic properties of natural images, the inputs were sampled on a regular array, with complete color information at every location. However, in the retina cone photoreceptors with different spectral sensitivities are arranged in a mosaic. We used an unsupervised neural network model to analyze the statistical structure of retinal cone mosaic responses to calibrated color natural images. The second-order statistical dependencies derived from the covariance matrix of the sensory signals were removed in the first stage of processing. These decorrelating filters were similar to type I receptive fields in parvo- or konio-cellular LGN in both spatial and chromatic characteristics. In the subsequent stage, the decorrelated signals were linearly transformed to make the output as statistically independent as possible, using independent component analysis. The independent component filters showed luminance selectivity with simple-cell-like receptive fields, or had strong color selectivity with large, often double-opponent, receptive fields, both of which were found in the primary visual cortex (V1). These results show that the "form" and "color" channels of the early visual system can be derived from the statistics of sensory signals.