Temperature dependence of Mott transition in VO_2 and programmable critical temperature sensor

The temperature dependence of the Mott metal-insulator transition (MIT) is studied with a VO_2-based two-terminal device. When a constant voltage is applied to the device, an abrupt current jump is observed with temperature. With increasing applied voltages, the transition temperature of the MIT current jump decreases. We find a monoclinic and electronically correlated metal (MCM) phase between the abrupt current jump and the structural phase transition (SPT). After the transition from insulator to metal, a linear increase in current (or conductivity) is shown with temperature until the current becomes a constant maximum value above T_{SPT}=68^oC. The SPT is confirmed by micro-Raman spectroscopy measurements. Optical microscopy analysis reveals the absence of the local current path in micro scale in the VO_2 device. The current uniformly flows throughout the surface of the VO_2 film when the MIT occurs. This device can be used as a programmable critical temperature sensor.Comment: 4 pages, 3 figure

Synthesis of VO_2 Nanowire and Observation of the Metal-Insulator Transition

We have fabricated crystalline nanowires of VO_2 using a new synthetic method. A nanowire synthesized at 650^oC shows the semiconducting behavior and a nanowire at 670^oC exhibits the first-order metal-insulator transition which is not the one-dimensional property. The temperature coefficient of resistance in the semiconducting nanowire is 7.06 %/K at 300 K, which is higher than that of commercial bolometer.Comment: 3 pages, 4 figures, This was presented in NANOMAT 2006 "International workshop on nanostructed materials" on June 21-23th of 2006 in Antalya/TURKE

Dispersion of Vascular Plant in Kumo-do, Korea

AbstractThe vascular plants observed in the area were composed of a total of 228 taxa; 72 families, 172 genus, 201 species, 25 varieties, 1 sub-species and 1 cross species. The only endangered plants found in the area were Milletia japonica (Siebold & Zucc.) A.Gray. The endemic plants growing in the Geumodo except transplanted plants were Lespedeza x maritima Nakai and Carpinus coreana Nakai. which accounted for 0.8% of the vascular plants in Geumodo, 228 taxa. Specialized plants of Geumodo were a total of 41 species; 30 taxa in Grade I, 1 taxon in Grade II, 9 taxa in Grade III and 1 taxon in Grade V. Milletia japonica (Siebold & Zucc.) A.Gray was the only species found in important Grade IV to V. Currently, ferries ply to the island, attracting many tourists. This poses a threat to the rare plants living in the island and presses down the island to develop. Therefore, in the long-term perspective, the conservation plan such as comprehensive research and monitoring on the ecosystem shall be established to protect evergreen broad-leaved forests

Monoclinic and Correlated Metal Phase in VO_2 as Evidence of the Mott Transition: Coherent Phonon Analysis

In femtosecond pump-probe measurements, the appearance of coherent phonon oscillations at 4.5 THz and 6.0 THz indicating the rutile metal phase of VO_2 does not occur simultaneously with the first-order metal-insulator transition (MIT) near 68^oC. The monoclinic and correlated metal(MCM) phase between the MIT and the structural phase transition (SPT) is generated by a photo-assisted hole excitation which is evidence of the Mott transition. The SPT between the MCM phase and the rutile metal phase occurs due to subsequent Joule heating. The MCM phase can be regarded as an intermediate non-equilibrium state.Comment: 4 pages, 2 figure

Customized Energy Down-Shift using Iridium Complexes for Enhanced Performance of Polymer Solar Cells

School of Molecular Sciences(Chemistry)For the higher performance of polymer solar cells (PSCs), many researchers tried to develop new polymers that can absorb broader range of spectrum. However, there are some limits to absorb broader range with single donor. Therefore, multi donor systems and energy transfer systems have been researched. With two different donors it is easier to enhance absorption range. As a result, multi donor and energy transfer was successful to increase performance. However, the existing systems are applying polymer-polymer systems. When two different polymers are mixed, the compatibility between two polymers is critical to morphology of blend film. Also, in polymer-polymer energy transfer, the boundary between charge transfer and energy transfer is unclear. Therefore, for the first time, we developed customized iridium (Ir(III)) complexes, with Ir(III) complex incorporated into the active materials poly(thieno[3,4-b]-thiophene/benzodithiophene) (PTB7, amorphous) or poly(3-hexylthiophene) (P3HT, high crystalline) as energy donor additives. The Ir(III) complex with the 2-phenyl quinolone ligand energy donor increased the power conversion efficiency of the corresponding devices by approximately 20%. The enhancements are attributed to the improved molecular compatibility and energy level between the Ir(III) complex and the active materials, long F??rster resonance energy transfer radius, and high energy down-shift efficiency. Overall, we reveal Ir(III) complex additives for amorphous and highly crystalline polymer active materialsthese additives would enable efficient energy transfer in polymer solar cells, while retaining the desirable active layer morphology, thereby resulting in improved light absorption and conversion.ope

Phenotypic and Genomic Properties of Brachybacterium vulturis sp. nov. and Brachybacterium avium sp. nov.

Two strains, VM2412T and VR2415T, were isolated from the feces of an Andean condor (Vultur gryphus) living in Seoul Grand Park, Gyeonggi-do, South Korea. Cells of both strains were observed to be Gram-stain positive, non-motile, aerobic, catalase positive and oxidase negative. Growth was found to occur at 10-30°C, showing optimum growth at 30°C. The strains could tolerate up to 15% (w/v) NaCl concentration and grow at pH 6-9. The strains shared 99.3% 16S rRNA gene sequence similarity to each other but were identified as two distinct species based on 89.0-89.2% ANIb, 90.3% ANIm, 89.7% OrthoANI and 38.0% dDDH values calculated using whole genome sequences. Among species with validly published names, Brachybacterium ginsengisoli DCY80T shared high 16S rRNA gene sequence similarities with strains VM2412T (98.7%) and VR2415T (98.4%) and close genetic relatedness with strains VM2412T (83.3–83.5% ANIb, 87.0% ANIm, 84.3% OrthoANI and 27.8% dDDH) and VR2415T (82.8–83.2% ANIb, 86.7% ANIm, 83.9% OrthoANI and 27.2% dDDH). The major fatty acid of the two strains was identified as anteiso-C15:0 and the polar lipids consisted of phosphatidylglycerol, diphosphatidylglycerol, presumptively phosphatidylethanolamine and three unidentified glycolipids. Strain VR2415T also produced an unidentified phospholipid. The cell walls of the two strains contained meso-diaminopimelic acid as diagnostic diamino acid and the whole cell sugars were ribose, glucose, and galactose. The strains contained MK-7 as their predominant menaquinone. The genomes of strains VM2412T, VR2415T, and B. ginsengisoli DCY80T were sequenced in this study. The genomic G+C contents of strains VM2412T and VR2415T were determined to be 70.8 and 70.4 mol%, respectively. A genome-based phylogenetic tree constructed using an up-to-date bacterial core gene set (UBCG) showed that the strains formed a clade with members of the genus Brachybacterium, supporting their taxonomic classification into the genus Brachybacterium. Based on phenotypic and genotypic analyses in this study, strains VM2412T and VR2415T are considered to represent two novel species of the genus Brachybacterium and the names Brachybacterium vulturis sp. nov. and Brachybacterium avium sp. nov. are proposed for strains VM2412T (=KCTC 39996T = JCM 32142T) and VR2415T (=KCTC 39997T = JCM 32143T), respectively