Aoyama Gakuin University

About: Aoyama Gakuin University is a education organization based out in Tokyo, Japan. It is known for research contribution in the topics: Superconductivity & Thin film. The organization has 3494 authors who have published 6419 publications receiving 115648 citations. The organization is also known as: Aoyama gakuin daigaku.

Coupling Transition of the Vortex Liquid in Bi 2 Sr 2 CaCu 2 O 8 + δ with Columnar Defects

Abstract: The interlayer Josephson coupling in the vortex fluid phase of heavy-ion irradiated Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}} is probed by Josephson plasma resonance. The introduction of columnar defects changes the nature of the vortex liquid dramatically. We show that two types of vortex liquid, the well-coupled and the decoupled pancake vortex liquids, appear in the irradiated crystals. The pancake vortices tend to couple with increasing magnetic field, which is opposite to the pristine crystal. The double resonance peaks appear as a function of field in a narrow temperature range well above the irreversibility line. This implies an occurrence of the coupling transition in the liquid phase. {copyright} {ital 1997} {ital The American Physical Society}

Flat-Bands on Partial Line Graphs-Systematic Method for Generating Flat-Band Lattice Structures-

Abstract: We introduce a systematic method for constructing a class of lattice structures that we call “partial line graphs”. In tight-binding models on partial line graphs, energy bands with flat energy dispersions emerge. This method can be applied to two- and three-dimensional systems. We show examples of partial line graphs of square and cubic lattices. The method is useful in providing a guideline for synthesizing materials with flat energy bands, since the tight-binding models on the partial line graphs provide us a large room for modification, maintaining the flat energy dispersions.

The effects of gas nitriding on fatigue behavior in titanium and titanium alloys

Abstract: Fatigue behavior has been studied on gas-nitrided smooth specimens of commercial pure titanium, an alpha/beta Ti-6Al-4V alloy, and a beta Ti-15Mo-5Zr-3Al alloy under rotating bending, and the obtained results were compared with the fatigue behavior of annealed or untreated specimens. It was found that the role of the nitrided layer on fatigue behavior depended on the strength of the materials. Fatigue strength was increased by nitriding in pure titanium, while it was decreased in the Ti-6Al-4V and Ti-15Mo-5Zr-3Al alloys. Based on detailed observations of fatigue crack initiation, growth, and fracture surfaces, the improvement and the reduction in fatigue strength by nitriding in pure titanium and both alloys were primarily attributed to enhanced crack initiation resistance and to premature crack initiation of the nitrided layer, respectively.

Intensity-Dependent Photoresponse of Biphotochromic Molecule Composed of a Negative and a Positive Photochromic Unit

Abstract: Light-selective multiple photochromic systems are important for advanced photoswitching of chemical reactions and biological activities. While UV light has been frequently utilized to induce photochromic reactions, visible light is energetically acceptable to avoid undesired reactions. However, many of the reported multiphotochromic systems still rely on UV light to induce at least a part of photochromic reactions. In this work, we designed a biphotochromic molecule showing intensity-dependent multiple coloration with a visible-light source by incorporating two T-type photochromic units; a colorless positive photochromophore and a colored negative photochromophore in a molecule. The negative photochromophore acts as a visible-light sensitizer for the positive photochromic reaction. The compound shows an intensity-dependent color change under visible-light irradiation. The weak visible-light excitation leads to gradual decoloration from orange to yellow, whereas intense laser excitation clearly changes the...

Fault-tolerant operation of single-phase SR generators

Abstract: This paper studies fault-tolerant operation of multipole single-phase switched reluctance generators (SRGs), in particular, an 8/8-pole switched reluctance machine. The multipole single-phase SRG system is advantageous for reduced cost and higher efficiency compared to polyphase equivalents. However, using the classical phase-leg topology, a phase fault may prevent generating operation completely, since redundancy in the number of phases does not exist like polyphase systems. A new power converter topology which connects two coil banks in parallel is proposed for higher fault tolerance with minimum additional cost. Faulty coils can be disconnected with the proposed converter and the SRG can continue generating operation after coil faults with reduced output power. Output power per coil current under faults is studied. Open- and short-circuit coils are studied through linear analysis, finite-element analysis and static torque measurement. Generated currents under faults with the proposed converter are measured. The capability of the system to disconnect faulty coils dynamically is also shown.