We report on an electronic structure study of a quasi-two-dimensional Co oxide Ca 3 Co 4 O 9 with Ca 2 CoO 3 rocksalt layers and CoO 2 triangular lattice layers by means of x-ray photoemission spectroscopy ͑XPS͒, ultraviolet photoemission spectroscopy ͑UPS͒, configuration-interaction calculation on a CoO 6 cluster model, and unrestricted Hartree-Fock calculation on a multiband d-p model. The Co 2p XPS spectrum shows that the Co valence of the rocksalt layer is similar to that of the triangular lattice layer. The cluster-model analysis of the Co 2p XPS spectrum indicates that the Co sites of the rocksalt and triangular lattice layers commonly have charge-transfer energy ⌬ of ϳ1.0 eV, d-d Coulomb interaction U of ϳ6.5 eV, and transfer integral ͑pd͒ of ϳ−2.3 eV. The Co 3d t 2g peak in the valence-band XPS spectrum remains sharp even above the spin-state transition temperature at ϳ380 K, indicating that the spin-state transition is different from the low-spin to intermediate-spin or high-spin transitions in perovskite LaCoO 3 . The line shape of the UPS spectrum near the Fermi level can be reproduced by the combination of unrestricted Hartree-Fock results for the charge-ordered insulating ͑COI͒ and paramagnetic metallic ͑PM͒ states. The analysis shows that the phase separation between the COI and PM states plays important roles in Ca 3 Co 4 O 9 .

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A channel layer substitution of a wider bandgap AlGaN for a conventional GaN in high electron mobility transistors (HEMTs) is an effective method of enhancing the breakdown voltage. Wider bandgap AlGaN, however, should also increase the ohmic contact resistance. Si ion implantation doping technique was utilized to achieve sufficiently low resistive source/drain contacts. The fabricated AlGaN channel HEMTs with the field plate structure demonstrated good pinch-off operation with sufficiently high drain current density of 0.5 A/mm without noticeable current collapse. The obtained maximum breakdown voltages was 1700 V in the AlGaN channel HEMT with the gate-drain distance of 10 μm. These remarkable results indicate that AlGaN channel HEMTs could become future strong candidates for not only high-frequency devices such as low noise amplifiers but also high-power devices such as switching applications.

This paper discusses the following three key issues on passive control using dampers for seismic protection of buildings:1 Major experimental research on passive control of buildings: Tests using the world’s largest shaking table “E-Defense” from March to April 2009 evaluated a full-scale 5-story steel building with and without dampers. 2 Codes and specifications: The Japanese building code requires that the nonlinear time history analysis be performed for buildings with dampers or that energy-based analysis be conducted when steel dampers are used. Unlike code rules leading to iterative design, the specifications of the Japan Society of Seismic Isolation (JSSI) give direct design method (DDM) for target performance set by designers. 3 Damage-free structure and its design: Backed by government support, a large team of researchers and designers has developed a structure damage-free against a catastrophic earthquake, using dampers and super-high-strength steel frames. The structure and its design rule using DDM are being studied for inclusion in projected code.

We have determined the crystal structure of Bi-substituted and Bi-free misfit layered cobalt oxides [Ca2CoO3]0.62CoO2, by a (3+1)-dimensional superspace group approach. Structural parameters have been refined with a superspace group of C2/m(1p0)s0 using powder neutron diffraction data. Bismuth atoms are found to substitute for both Ca and Co atoms in the rock salt-type [Ca2CoO3] subsystem. The resulting structural formula is expressed as [(Ca0.90Bi0.10)2(Co0.95Bi0.05)O3] p CoO2 with a refined b-axis ratio of p=0.6183. By Bi substitution, the modulation of the Co–O distances in the [Ca2CoO3] subsystem is markedly decreased relative to the Bi-free counterpart, whereas such a modulation in the [CoO2] subsystem is slightly increased. The observed increase in the Seebeck coefficient and electrical resistivity of the Bi-substituted phase can be explained in terms of the decrease in hole concentration in the CoO2 sheets.