Electron-temperature control by varying dc voltage to a mesh grid covered by thin film in plasmas

We discuss theoretically how the resistance of a film deposited on the metal grid affects the efficiency of electron-temperature control by employing a grid-bias method, in which, by using a naked metal grid, the electron temperature decreases from 3.4 to 0.12 eV with a decrease in the grid potential from 40 to − 60 V, being accompanied by an electron-density increase from 0.6 × 10⁹ cm^− 3 to 6.0 × 10⁹ cm^− 3 at an argon gas pressure of 5.0 mTorr. The electron temperature can be varied even when the grid is covered with a film with finite resistance, although the range of electron temperature variation is restricted. This method is applicable to reactive plasmas in which grids are often covered by films with finite resistance.     

Two-dimensionally quantized friction observed with two-dimensional frictional force microscope

Using a two-dimensional frictional force microscope, we studied the two-dimensional nature of the atomic scale friction between a Si₃N₄ sharp tip and a cleaved graphite surface, which is composed of only C atoms and is a good conductor. As a result, we observed the two-dimensionally quantized friction with the lattice periodicity of the graphite surface, similarly to mica, MoS₂ and NaF surfaces. Thus quantized friction occurs at material surfaces which are composed of not only some elements but also of a single element, and the quantized friction does not depend on the conductivity of the surface.     

Application study of a high‐temperature superconducting fault current limiter for electric power system

Using high‐temperature superconductors, a superconducting fault current limiter (SFCL) was fabricated and tested. The superconductor and a vacuum interrupter serving as a commutation switch were connected in parallel with a bypass coil. When a fault occurs and excessive current flows, the superconductor is first quenched and the current is transferred to the bypass coil because of the voltage drop of the superconductor. At the same time, since a magnetic field is generated by the current flowing in the bypass coil, the commutation switch is immediately driven by an electromagnetic repulsion plate connected to the driving rod of the vacuum interrupter (VI), and the superconductor is separated from this circuit. Using the test model, we were able to separate the superconductor from the circuit by the movement of the VI within a half current cycle and to transfer all current to the bypass coil. Since the operation of the commutation switch is included in the current limiting operation of this test model, it will be a useful circuit in the development of SFCL in the future. Moreover, since it can make the energy consumption of the superconductor small during the fault state due to the realization of a high‐speed switch with simple composition, the burden on the superconductor is reduced compared with the conventional resistive type of SFCL and it is considered that the flexibility of SFCL design is increased. Cooperation with a circuit breaker was also considered; trial calculations of the parameters and energy of operation were conducted and a discussion of the installation of the SFCL in an electric power system is presented. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 155(4): 20–29, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20265     

Preparation and properties of disyndiotactic poly(alkyl crotonate)s

Ethyl, n-propyl, iso-propyl and n-butyl crotonates were polymerized by group transfer polymerization (GTP) using ketene trialkylsilyl acetals as initiators in the presence of mercury (II) iodide as catalyst and iodotriethylsilane as co-catalyst. Predominantly disyndiotactic polymers with number-average molecular weights ranging from 56,000 to 90,000 were obtained almost quantitatively. Thermal and mechanical properties of poly(alkyl crotonate)s, such as glass transition temperature (T_g), refractive index, transmissivity, Izod impact strength, Young's modulus, hardness, tensile strength, tensile elongation at break, gas permeability coefficient and density were measured. All the polycrotonates have 65–90 °C higher T_g than the corresponding polymethacrylates.     

Phase Diagram Mapping of the Fe<Subscript>3</Subscript>Al-Cr-Mo-C Pseudo-Quaternary System at 800 °C Using a New Diffusion-Multiple Technique

A new diffusion-multiple technique was used for mapping the phase diagram in the pseudo-quaternary Fe₃Al-Cr-Mo-C system at 800 °C. The following five carbide phases were formed in an Fe₃Al matrix phase (B2) with composition gradients of Cr, Mo, and C in the diffusion-multiple samples: κ-Fe₃AlC, M₅C, M₆C, Cr₇C₃, and M₂C (M: Mo, Cr, Al, and Fe). It was assumed that B2 phase is in equilibrium with κ, M₅C, M₆C, and Cr₇C₃ but not with M₂C phase at 800 °C. Complex phase equilibria among those phases were efficiently mapped by the diffusion-multiple technique. The results from the technique were consistent with those obtained from the conventional bulk alloy method.     

Studies on chains of bubbles rising through quiescent liquid

The liquid velocity profile induced by a chain of bubbles is studied theoretically and a comparison with measurements is made. The wake velocity and the bubble shape involved in the theoretical development are considered based on the wake theory and the previous empirical relation for single bubbles, respectively. The shape and wake volume of chain bubbles can be treated in the same manner as those of single bubbles by using relative velocity. As a result, using the previous results of the drag coefficient and shape of single bubbles enables the prediction of the rising velocity of chain bubbles.     

Manufacturing process and properties of nuclear RPV shell ring forged from hollow ingot

A shell ring for an RPV of a 1300 MWe type PWR was forged from a 200-ton hollow ingot, and its very high quality regarding the internal qualities, tensile properties, fracture toughness, fatigue properties and underclad cracking properties were confirmed. The steel was refined by a basic oxygen furnace and degassed by a vacuum treatment furnace.The manufacturing process of a large hollow ingot has been established by an improved core structure which enabled segregation of chemical components to be decreased and a clean inner surface to be obtained.     

Alternating finite automata on ω-words

Alternating finite automata on ω-words are introduced as an extension of nondeterministic finite automata which process infinite sequences of symbols. The classes of ω-languages defined by alternating finite automata are investigated and characterized under four types of acceptance conditions. It is shown that for one type of acceptance condition alternation increases the power in comparison with nondeterminism and for other three acceptance conditions nondeterministic finite automata on ω-words have the same power as alternating ones.