We measure the high-temperature thermoelectric properties of the Na x CoO 2−δ single crystal for the first time. The Na x CoO 2−δ single crystals are prepared by a flux technique, and the resulting flaky single crystals are very thin on the c-axis. The inplane electrical resistivity (ρ), the thermoelectric power (S) and the in-plane thermal conductivity (κ) are measured in the range of 300 K to 800 K. The estimated power factor (PF = S 2 ·ρ −1 ) and the figure-of-merit (Z = S 2 ·ρ −1 κ −1 ) are about 2.4 mW m −1 K −2 and 0.12 mK −1 at 300 K, respectively. These factors increase with temperature, and reach the value of PF = 7.7 mW m −1 K −2 and Z = 1.5 mK −1 at 800 K, and the dimensionless value of Z T exceeds the criterion of 1. The PF and Z exceed the values of typical "high-temperature thermoelectric materials", such as p-type FeSi 2 and Si 0.7 Ge 0.3 . These results suggest that Na x CoO 2−δ could be a very promising material for use in high-temperature thermoelectric power generation devices.

Comparative genomic hybridization (CGH) was performed with nine strains of Bradyrhizobium japonicum (a symbiotic nitrogen-fixing bacterium associated with soybean) and eight other members of the Bradyrhizobiaceae by DNA macroarray of B. japonicum USDA110. CGH clearly discriminated genomic variations in B. japonicum strains, but similar CGH patterns were observed in other members of the Bradyrhizobiaceae. The most variable regions were 14 genomic islands (4-97 kb) and low G þ C regions on the USDA110 genome, some of which were missing in several strains of B. japonicum and other members of the Bradyrhizobiaceae. The CGH profiles of B. japonicum were classified into three genome types: 110, 122 and 6. Analysis of DNA sequences around the boundary regions showed that at least seven genomic islands were missing in genome type 122 as compared with type 110. Phylogenetic analysis for internal transcribed sequences revealed that strains belonging to genome types 110 and 122 formed separate clades. Thus genomic islands were horizontally inserted into the ancestor genome of type 110 after divergence of the type 110 and 122 strains. To search for functional relationships of variable genomic islands, we conducted linear models of the correlation between the existence of genomic regions and the parameters associated with symbiotic nitrogen fixation in soybean. Variable genomic regions including genomic islands were associated with the enhancement of symbiotic nitrogen fixation in B. japonicum USDA110.

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The thermoelectric properties of Na,CoO,, single crystal have been evaluated at high temperatures (300 < T < 800 K) for the first time. The Na,CoO,, single crystals are prepared by a flux technique, and the flaky single crystals are very thin on the c-axis. The in-plane electrical resistivity (p), the thermoelectric power (S) and the in-plane thermal conductivity ( K ) are measured in the range of 300 K to 800 K. The estimated power factor (PF = S'*p-') and the figure-ofmerit (Z = S'.g'K") are about 2.4 mWrn-'Ke2 and 0.12 mK-' at 300 K, respectively. These factors increase with temperature, and reach the value of PF = 7.7 mWm-'K2 and Z = 1.5 m K ' at 800 K, and the dimensionless value of ZT exceeds the criterion of 1. The PF and Z exceed the values of typical "high temperature thermoelectric materials". These results suggest that Na,CoO,, could be a very promising material for use in the high-temperature thermoelectric power generation devices.

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