Effects of the Spin-Orbit Coupling and the Superconductivity in simple-cubic alpha-Polonium

We have investigated the mechanism of stabilizing the simple-cubic (SC) structure in polonium (alpha- Po), based on the phonon dispersion calculations using the first-principles all-electron band method. We have demonstrated that the stable SC structure results from the suppression of the Peierls instability due to the strong spin-orbit coupling (SOC) in alpha-Po. Further, we have explored the possible superconductivity in alpha-Po, and predicted that it becomes a superconductor with Tc ~ 4 K. The transverse soft phonon mode at q ~ 2/3 R, which is greatly influenced by the SOC, plays an important role both in the structural stability and the superconductivity in alpha-Po. We have discussed effects of the SOC and the volume variation on the phonon dispersions and superconducting properties of alpha-Po.Comment: 5pages, 5figure

Pressure-induced Phonon Softenings and the Structural and Magnetic Transitions in CrO2_{2}

To investigate the pressure-induced structural transitions of chromium dioxide (CrO$_{2}$), phonon dispersions and total energy band structures are calculated as a function of pressure. The first structural transition has been confirmed at P$\approx$ 10 GPa from the ground state tetragonal CrO$_{2}$ (t-CrO$_{2}$) of rutile type to orthorhombic CrO$_{2}$ (o-CrO$_{2}$) of CaCl$_{2}$ type. The half-metallic property is found to be preserved in o-CrO$_{2}$. The softening of Raman-active B$_{1g}$ phonon mode, which is responsible for this structural transition, is demonstrated. The second structural transition is found to occur for P$\geq$ 61.1 GPa from ferromagnetic (FM) o-CrO$_{2}$ to nonmagnetic (NM) monoclinic CrO$_{2}$ (m-CrO$_{2}$) of MoO$_{2}$ type, which is related to the softening mode at {\bf q} = R(1/2,0,1/2). The third structural transition has been newly identified at P= 88.8 GPa from m-CrO$_{2}$ to cubic CrO$_{2}$ of CaF$_{2}$ type that is a FM insulator

Can Sodium Abundances of A-Type Stars Be Reliably Determined from Na I 5890/5896 Lines?

An extensive non-LTE abundance analysis based on Na I 5890/5896 doublet lines was carried out for a large unbiased sample of ~120 A-type main-sequence stars (including 23 Hyades stars) covering a wide v_e sin i range of ~10--300 km/s, with an aim to examine whether the Na abundances in such A dwarfs can be reliably established from these strong Na I D lines. The resulting abundances ([Na/H]_{58}), which were obtained by applying the T_eff-dependent microturbulent velocities of \xi ~2--4 km/s with a peak at T_eff ~ 8000 K (typical for A stars), turned out generally negative with a large diversity (from ~-1 to ~0), while showing a sign of v_e sin i-dependence (decreasing toward higher rotation). However, the reality of this apparently subsolar trend is very questionable, since these [Na/H]_{58} are systematically lower by ~0.3--0.6 dex than more reliable [Na/H]_{61} (derived from weak Na I 6154/6161 lines for sharp-line stars). Considering the large \xi-sensitivity of the abundances derived from these saturated Na I D lines, we regard that [Na/H]_{58} must have been erroneously underestimated, suspecting that the conventional \xi values are improperly too large at least for such strong high-forming Na I 5890/5896 lines, presumably due to the depth-dependence of \xi decreasing with height. The nature of atmospheric turbulent velocity field in mid-to-late A stars would have to be more investigated before we can determine reliable sodium abundances from these strong resonance D lines.Comment: 14 pages, 8 figures, accepted for publication in Publ. Astron. Soc. Japan, Vol. 61, No. 5 (2009

Effect of Angelica gigas Nakai extract on hepatic damage in rats

Purpose: To determine the antioxidant and hepatoprotective effects of decursin and decursinol angelate (D/DA) isolated from Angelica gigas Nakai (AGN).Methods: The 2,2-diphenyl-1-picrylhydrazyl (DPPH) scavenging activity of D/DA was assessed in a rat model using blood tests, western blotting, and histopathological analyses to identify the pharmaceutical effects of D/DA on liver enzymes and liver morphology.Results: The DPPH scavenging activity of D/DA was 47.11 μg/mL. Administration of D/DA to carbon tetrachloride (CCl4)-treated rats led to a decrease (13.59 %) in the total liver mass of control rats. Decursin and decursinol angelate also lowered the levels of alanine aminotransferase (ALT) and aspartate aminotransferase (AST), but increased the concentrations of antioxidant enzymes in the liver, including catalase (CAT) and glutathione peroxidase (GPx). Histological examination revealed that D/DA also reduced hepatocellular damage in the rats.Conclusion: D/DA from AGN has significant anti-hepatotoxic and antioxidant activities, and thus, is a potential herbal drug for treating liver damage. Keywords: Decursin, Decursinol angelate, Antihepatotoxicity, Antioxidant, Angelica gigas Naka

Correlation Assisted Phonon Softenings and the Mott-Peierls Transition in VO2_{2}

To explore the driving mechanisms of the metal-insulator transition (MIT) and the structural transition in VO2, we have investigated phonon dispersions of rutile VO2 (R-VO2) in the DFT and the DFT+U (U : Coulomb correlation) band calculations. We have found that the phonon softening instabilities occur in both cases, but the softened phonon mode only in the DFT+U describes properly both the MIT and the structural transition from R-VO2 to monoclinic VO2 (M1-VO2). This feature demonstrates that the Coulomb correlation effect plays an essential role of assisting the Peierls transition in R-VO2. We have also found from the phonon dispersion of M1-VO2 that M1 structure becomes unstable under high pressure. We have predicted a new phase of VO2 at high pressure that has a monoclinic CaCl2-type structure with metallic nature