Observation of a linear temperature dependence of the critical current density in a Ba_{0.63}K_{0.37}BiO_3 single crystal

For a Ba_{0.63}K_{0.37}BiO_3 single crystal with T_c=31 K, H_{c1}=750 Oe at 5 K, and dimensions 3x3x1 mm^3, the temperature and field dependences of magnetic hysteresis loops have been measured within 5-25 K in magnetic fields up to 6 Tesla. The critical current density is J_c(0)=1.5 x 10^5 A/cm^2 at zero field and 1 x 10^5 A/cm^2 at 1 kOe at 5 K. J_c decreases exponentially with increasing field up to 10 kOe. A linear temperature dependence of J_c is observed below 25 K, which differs from the exponential and the power-law temperature dependences in high-Tc superconductors including the BKBO. The linear temperature dependence can be regarded as an intrinsic effect in superconductors.Comment: RevTex, Physica C Vol. 341-348, 729 (2000

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 An-do, Korea

AbstractThe vascular plants observed in the area were composed of a total of 342 taxa; 104 families, 239 genus, 309 species, 30 varieties, 2 forms and 1 sub-species. The endangered species found in the area were Glehnia littoralis Fr. Schm. and Milletia japonica (Siebold & Zucc.) A.Gray. The five endemic plants were found growing in the area like Carpinus coreana Nakai., Celtis choseniana Nakai, Clematis trichotoma, Spiraea prunifolia for. simpliciflora and Weigela subsessilis L.H.Bailey. Specialized plants of Geumodo were a total of 45 species; 34 taxa in Grade I, 10 taxa in Grade III, and 1 taxon in Grade V. Glehnia littoralis Fr. Schm. and Milletia japonica (Siebold & Zucc.) A.Gray confirmed in this study formed a colony alongside the coast and mountain paths. Currently, the construction to build water supply and sewer systems destroyed part of the colony. Therefore, in the long-term perspective, the conservation plan such as comprehensive research and monitoring on the ecosystem shall be established to protect indeciduous plants in the warm temperate zone