661 research outputs found
High-temperature Superconductivity in Layered Nitrides \beta-LiMNCl (M = Ti, Zr, Hf): Insights from Density-functional Theory for Superconductors
We present an ab initio analysis with density functional theory for
superconductors (SCDFT) to understand the superconducting mechanism of doped
layered nitrides \beta-LiMNCl (M=Ti, Zr, and Hf). The current version of
SCDFT is based on the Migdal-Eliashberg theory and has been shown to reproduce
accurately experimental superconducting-transition temperatures Tc of a wide
range of phonon-mediated superconductors. In the present case, however, our
calculated Tc4.3 K (M=Zr) and 10.5 K (M=Hf) are found to be less
than a half of the experimental Tc. In addition, Tc obtained in the present
calculation increases with the doping concentration x, opposite to that
observed in the experiment. Our results indicate that we need to consider some
elements missing in the present SCDFT based on the Migdal-Eliashberg theory.Comment: 18 pages, 13 figures, submitted to Physical Review
Subaru Spectroscopy and Spectral Modeling of Cygnus A
We present high angular resolution (0.5) MIR spectra
of the powerful radio galaxy, Cygnus A, obtained with the Subaru telescope. The
overall shape of the spectra agree with previous high angular resolution MIR
observations, as well as previous Spitzer spectra. Our spectra, both on and off
nucleus, show a deep silicate absorption feature. The absorption feature can be
modeled with a blackbody obscured by cold dust or a clumpy torus. The deep
silicate feature is best fit by a simple model of a screened blackbody,
suggesting foreground absorption plays a significant, if not dominant role, in
shaping the spectrum of Cygnus A. This foreground absorption prevents a clear
view of the central engine and surrounding torus, making it difficult to
quantify the extent the torus attributes to the obscuration of the central
engine, but does not eliminate the need for a torus in Cygnus A
Quantum criticality around metal-insulator transitions of strongly correlated electrons
Quantum criticality of metal-insulator transitions in correlated electron
systems is shownto belong to an unconventional universality class with
violation of Ginzburg-Landau-Wilson(GLW) scheme formulated for symmetry
breaking transitions. This unconventionality arises from an emergent character
of the quantum critical point, which appears at the marginal point between the
Ising-type symmetry breaking at nonzero temperatures and the topological
transition of the Fermi surface at zero temperature. We show that Hartree-Fock
approximations of an extended Hubbard model on square latticesare capable of
such metal-insulator transitions with unusual criticality under a preexisting
symmetry breaking. The obtained universality is consistent with the scaling
theory formulated for Mott transition and with a number of numerical results
beyond the mean-field level, implying that the preexisting symmetry breaking is
not necessarily required for the emergence of this unconventional universality.
Examinations of fluctuation effects indicate that the obtained critical
exponents remain essentially exact beyond the mean-field level. Detailed
analyses on the criticality, containing diverging carrier density fluctuations
around the marginal quantum critical point, are presented from microscopic
calculations and reveal the nature as quantum critical "opalescence". Analyses
on crossovers between GLW type at nonzero temperature and topological type at
zero temperature show that the critical exponents observed in (V,Cr)2O3 and
kappa-ET-type organic conductor provide us with evidences for the existence of
the present marginal quantum criticality.Comment: 24 pages, 19 figure
Effects of acute exercise on expressions of functional receptors on CD56dim and CD56bright natural killer cells
PURPOSE: Mobilization and cytotoxicity of natural killer (NK) cells are regulated by cell surface receptors such as adhesion molecules and activating/inhibitory receptors. In this study, we examined the effects of acute exercise on the expression of these cell surface molecules and receptors.
METHODS: Six healthy male college students (22.8 ± 0.8 years olds) exercised on the cycle ergometer for 30 min at intensities corresponding to the individual onset of blood lactate accumulation level (70-85%VO2max). Venous blood samples were collected at rest (PRE); just before the end of exercise (END) and 30 (POST 30), 60 (POST 60), 120 (POST 120) and 180 (POST 180) min post exercise. The densities of cell surface molecules and receptors on CD56dim and CD56bright NK cells were determined by flow cytometry. One-way ANOVA and MANOVA were used for statistical analyses.
RESULTS: At PRE, expressions of CD16, CD56, CD44, CD62L, CD314, CD335, CD159a and CX3CR1 differed between CD56dim and CD56bright NK cells. Expressions of adhesion molecules CD62L and CX3CR1 changed significantly in both subsets during and after exercise. The expressions of CD62L tended to decrease at END, and then they increased significantly at POST 30. These changes were mainly due to the proportional changes in CD62Lnegative cells. The opposite patterns of changes were seen in the expressions of CX3CR1. Additionally, the expressions of CX3CR1 decreased at POST 120 and 180 only in CD56dim NK cells. The changes in the expressions of CD44 were similar to those seen in the expressions of CD62L. Although changes in the expression of adhesion molecules were statistically significant, they were relatively unclear in histogram analyses. With regard to the expressions of NK cell activating/inhibitory receptors, most changes were observed in CD56dim NK cells. The expressions of CD16 decreased at END and returned at POST 30. The expressions of CD212 dropped from END to POST 30. In contrast, the expressions of CD335 increased from END to POST 30. Exceptionally, changes in the expressions of CD226 were found in both subsets. The expressions decreased at POST180.
CONCLUSION: These results suggest that acute exercise influences the expressions of cell surface molecules and receptors. Changes were mainly observed at END and POST 30 in CD56dim NK cell. However, the delayed changes were also seen in some receptors. The changes in several receptors were related to cell mobilization. In contrast, the changes in other receptors were not directly related to mobilization and cytotoxicity
Millimeter Interferometric Investigations of the Energy Sources of Three Ultraluminous Infrared Galaxies, UGC 5101, Mrk 273, and IRAS 17208-0014, based on HCN to HCO+ Ratios
We present interferometric observations of three ultraluminous infrared
galaxies (ULIRGs; UGC 5101, Mrk 273, and IRAS 17208-0014) in the 3-mm
wavelength range, using the Nobeyama Millimeter Array. Both the HCN (J=1-0) and
HCO+ (J=1-0) molecular lines were observed simultaneously. HCN emission was
clearly detected at the nuclear positions of these ULIRGs, and HCO+ emission
was detected at the nuclear positions of UGC 5101 and IRAS 17208-0014. The HCN
to HCO+ brightness-temperature ratios toward the nuclei of the three ULIRGs
were derived and compared with those of lower luminosity galaxies known to be
dominated by active galactic nuclei (AGNs) or starbursts. In UGC 5101 and Mrk
273, where there is evidence for obscured AGNs from previous observations at
other wavelengths, we found high HCN/HCO+ ratios (>1.8) that are in the range
found for AGN-dominated galaxies. In IRAS 17208-0014, where the presence of a
powerful obscured AGN has been unclear, the ratio (1.7) is in between the
observed values for starburst- and AGN-dominated galaxies. The high HCN/HCO+
brightness-temperature ratios in UGC 5101 and Mrk 273 could be the consequence
of an HCN abundance enhancement, which is expected from chemical effects of the
central X-ray emitting AGN on the surrounding dense molecular gas. Our proposed
millimeter interferometric method based on HCN/HCO+ ratios may be an effective
tool for unveiling elusive buried AGNs at the cores of ULIRGs, especially
because of the negligible dust extinction at these wavelengths.Comment: 15 pages (emulateapj.sty), 8 figures (figures 1-5 resolution
reduced), Accepted for publication in Astronomical Journal, A PDF file with
high resolution is availble at
http://optik2.mtk.nao.ac.jp/~imanishi/Paper/HCN/HCN.pd
Universality Classes of Metal-Insulator Transitions in Strongly Correlated Electron Systems and Mechanism of High-Temperature Superconductivity
We study three regimes of the Mott transitions characterized by classical,
marginally quantum and quantum. In the classical regime, the quantum degeneracy
temperature is lower than the critical temperature of the Mott transition, Tc,
below which the first-order transition occurs. The quantum regime describes the
Tc=0 boundary of the continuous transition. The marginal quantum region appears
sandwiched by these two regimes. The classical transition is described by the
Ising universality class. However, the Ginzburg-Landau-Wilson scheme breaks
down when the quantum effects dominate. The marginal quantum critical region is
categorized to a new universality class, where the order parameter exponent
beta, the susceptibility exponent gamma and the field exponent delta are given
by beta=d/2, gamma=2-d/2 and delta=4/d, respectively, with d being the spatial
dimensionality.The obtained universality classes agree with the recent
experimental results for organic conductors, kappa-(ET)2Cu[N(CN)2]Cl and
transition metal compounds such as V2O3. The mode coupling theory shows that
the marginal quantum criticality further generates non-Fermi-liquid properties
in the metallic side. A mechanism of high temperature superconductivity emerges
from the density fluctuations at small wavenumber. The mode coupling theory
combined with the Eliashberg equation predicts the superconductivity of the d
wave symmetry with the transition temperature of the correct order of magnitude
for the realistic parameters for the cuprate superconductors.Comment: 47 pages including 8 figure
Heisenberg realization for U_q(sln) on the flag manifold
We give the Heisenberg realization for the quantum algebra , which
is written by the -difference operator on the flag manifold. We construct it
from the action of on the -symmetric algebra by the
Borel-Weil like approach. Our realization is applicable to the construction of
the free field realization for the [AOS].Comment: 10 pages, YITP/K-1016, plain TEX (some mistakes corrected and a
reference added
Comments on D-branes in Kazama-Suzuki models and Landau-Ginzburg theories
We study D-branes in Kazama-Suzuki models by means of the boundary state
description. We can identify the boundary states of Kazama-Suzuki models with
the solitons in N=2 Landau-Ginzburg theories. We also propose a geometrical
interpretation of the boundary states in Kazama-Suzuki models.Comment: 28 pages, 2 figure
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