Steady-state characteristics of matrix converter

The matrix converter proposed by Venturini is very simple in structure and has powerful controllability. However, there are few applications especially in power electronics fields. This seems to be caused mainly by the fact that such power devices that were fast enough to suppress ringing oscillations in the supply lines and large enough to pay for more devices and more complicated control circuits than in conventional dc-link converter-inverter systems were not available. At present, static induction thyristors (SIThs) have been introduced and a new possibility for the matrix converter has been raised. This paper describes a new control strategy which is simple and practical and allows the output voltage of 0.866 times the supply voltage to be generated. Also, the new firing sequences which eliminate voltage and current spikes are proposed. Steady-state and distortion characteristics of the prototype PWM matrix converter with SITh are shown.     

A 1-Gb DRAM for file applications

A time-shared offset-canceling sensing scheme, a defective word-line Hi-Z standby scheme, and a flexible multimacro architecture have been developed for 1-Gb DRAM. These circuit technologies have been applied to a 1-Gb DRAM for file applications employing 0.25 μm CMOS process technology, a diagonal bit-line cell, and a two-stage pipeline circuit technique. In this DRAM, a 30% chip size reduction and a 400-MB/s data transfer rate have been achieved. A 100% improvement in yield has been estimated by Monte-Carlo simulation. The 1-Gb DRAM die size is 936 mm². The cell size is 0.54 μm². The operating current is 58 mA at 2 V and 100 MHz     

Scattering angle dependence of signal/background ratio of inner-shell electron excitation loss in eels

Scattering angle dependence of the signal/background ratio of Si K-shell and A1 K-shell electron excitation losses has been measured for single crystals and evaporated films. The ratio changed periodically with the scattering angle, and maxima were found to be located between Bragg reflections including the center beam. Thus the ratio is improved between the Bragg reflections and just outside the incident beam, which is very important as a practical technique for elemental analysis in the higher energy loss region in EELS.     

Optimal structure of sensor systems composed of nonidentical sensors

The sensor system has two types of contradictory failures; a fail-dangerous failure and a fail-safe failure. A method of obtaining the optimal structure is developed for the sensor system which is composed of general components. The optimal structure minimizes an expected damage, considering all possible boolean structures including noncoherent systems. A simple optimality criterion is obtained and several properties of the optimal structures are derived; a noncoherent structure can be optimal in some cases. A simple systematic search algorithm can be used effectively to determine the optimal system. Analytic solutions are obtained for systems composed of identical components. Illustrative examples are given.     

Oxygen Configuration in the Superconductor (Hg0.7Mo0.3)Sr2(Ca1?xRx)Cu2Oz (R = Nd and Pr)

Two series of Hg-based oxides (Hg_0.7Mo_0.3)Sr₂(Ca_1–x R _x )Cu₂O _z (R = Nd and Pr, 0.2 x 0.7) have been synthesized. Electrical-resistivity measurements show that these compounds are superconductors with maximum onset T _c of 107 and 102 K for Nd- and Pr-containing samples, respectively. The neutron powder diffraction experiments on both as-prepared and O₂-annealed samples of R = Nd revealed that the O(3) site at the HgO sheets are fully occupied and shifted towards the Hg/Mo site to form Mo–O bonds.     

Self-organized one-axis-oriented PZT films with nano-domain structure

{100} One-axis-oriented PZT films with a thickness of 2 μm were obtained on (111)Pt/TiO₂/SiO₂/(100)Si substrates by metal organic chemical vapor deposition (MOCVD). These were obtained irrespective of the film thickness up to 2 mm and with a Zr/(Zr + Ti) ratio from 0.20 to 0.75. This was found to be due to the higher growth rate of these orientation grains than {110} and {111)} orientation grains. These films had columnar grains 50–100 nm in width. Moreover, they were found to include 908 nano-domains 10–20 nm in width. Dielectric constant, ε_r and the field induced-strain were maximum around a Zr/(Zr + Ti) ratio of 0.5, which was in good agreement with previous reports on sintered bodies with 100 times larger domains. This means that the domain size had any effect on ε_r or field-induced strain.     

Fabrication of size-controlled polyimide nanoparticles

Polyimide particles were fabricated through the two-steps imidization of poly(amic acid) particles prepared by using reprecipitation method. PAA and PI nanoparticles were all spherical, and the changes of particle size, its distribution, and morphology were not observed before and after the imidization. The preparation of PI nanoparticles size-controlled between ca. 20-500 nm was also achieved by changing the experimental conditions, temperature of the poor solvent, the composition of two kind of poor solvent, and PAA-NMP solution concentration.     

Improvement of the Fischer–Tropsch Synthesis Activity of Co/SiO2 Catalyst by the Stepwise Impregnation Method with Chelating Agents

Co/SiO₂ catalysts were prepared by a stepwise impregnation of aqueous solutions containing Co nitrate or chelating agent, nitrilotriacetic acid (NTA) or trans-1,2-diaminocyclohexane-N,N,N′,N′-tetraacetic acid (CyDTA), with various concentrations of Co²⁺ and the chelating agent. Fischer–Tropsch synthesis activity of Co/SiO₂ catalysts having Co loadings of 5–20 mass% as metallic Co was improved by the stepwise impregnation method with these chelating agents. The catalyst prepared with CyDTA (Co loading = 20 mass%, Co²⁺/CyDTA = 4 mol mol⁻¹) yielded 1,500 and 815 g kg-cat⁻¹ h⁻¹ of C₅₊ and C_10–20 hydrocarbons at 503 K and 1.1 MPa, respectively, which was much greater than that with the catalyst prepared from the aqueous solution containing both Co nitrate and NTA.