644 research outputs found
Comparative study of excitonic structures and luminescence properties of Bi4Ge3O12 and Bi12GeO20
Published in physica status solidi (b), Vol. 245, No. 12, pp2733-2736, 2008.Bi12GeO20 crystals have been performed, in addition to relativistic molecular orbital calculations. Both materials consist of the same elements but form different crystal structures. Based on the obtained results, the excitonic reflection structures and luminescence properties of Bi4Ge3O12 and Bi12GeO20 are discussed in comparison with each other.Bookphysica status solidi (b). 245(12):2733-2736 (2008)journal articl
Exact Drude weight for the one-dimensional Hubbard model at finite temperatures
The Drude weight for the one-dimensional Hubbard model is investigated at
finite temperatures by using the Bethe ansatz solution. Evaluating finite-size
corrections to the thermodynamic Bethe ansatz equations, we obtain the formula
for the Drude weight as the response of the system to an external gauge
potential. We perform low-temperature expansions of the Drude weight in the
case of half-filling as well as away from half-filling, which clearly
distinguish the Mott-insulating state from the metallic state.Comment: 9 pages, RevTex, To appear in J. Phys.
Selective expression of RT6 superfamily in human bronchial epithelial cells.
RT6 proteins are glycosylphosphatidylinositol (GPI)-linked alloantigens that are localized to cytotoxic T lymphocytes and that have nicotinamide adenine dinucleotide glycohydrolase and adenosine diphosphate (ADP)-ribosyltransferase activities. In view of the importance of GPI-linked surface proteins in mediating interactions of cells with their milieu, and the varied functions of airway cells in inflammation, we undertook the present study to determine whether human homologues of the RT6 superfamily of ADP-ribosyltransferases (ART) are expressed in pulmonary epithelial cells. We hypothesized that these surface proteins or related family members may be present in cells that interact with inflammatory cells, and that they may thereby be involved in intercellular signaling. Using in situ analysis and Northern blot analysis, we identified ART1 messenger RNA (mRNA) in airway epithelial cells. As expected for GPI-anchored proteins, the localization of ART1 at the apical surface of ciliated epithelial cells was demonstrated by staining with polyclonal anti-ART1 antibody, and was confirmed by loss of this immunoreactivity after treatment with phosphatidylinositol-specific phospholipase C (PI-PLC), which selectively cleaves GPI anchors and releases proteins from the plasma membrane. Using in situ hybridization with specific ART3 and ART4 oligonucleotides, we also identified two additional members of the RT6 superfamily in epithelial cells. In accord with these findings, we identified ART3 and ART4 mRNAs through reverse transcription- polymerase chain reaction of polyadenine-positive RNA from human trachea. Interestingly, these proteins appeared to be preferentially localized to the airway epithelium. The localized expression of these members of the RT6 superfamily in human pulmonary epithelial cells may reflect a role for them in cell-cell signaling during immune responses within the airwa
Curve crossing in linear potential grids: the quasidegeneracy approximation
The quasidegeneracy approximation [V. A. Yurovsky, A. Ben-Reuven, P. S.
Julienne, and Y. B. Band, J. Phys. B {\bf 32}, 1845 (1999)] is used here to
evaluate transition amplitudes for the problem of curve crossing in linear
potential grids involving two sets of parallel potentials. The approximation
describes phenomena, such as counterintuitive transitions and saturation
(incomplete population transfer), not predictable by the assumption of
independent crossings. Also, a new kind of oscillations due to quantum
interference (different from the well-known St\"uckelberg oscillations) is
disclosed, and its nature discussed. The approximation can find applications in
many fields of physics, where multistate curve crossing problems occur.Comment: LaTeX, 8 pages, 8 PostScript figures, uses REVTeX and psfig,
submitted to Physical Review
Destruction of Superconductivity by Impurities in the Attractive Hubbard Model
We study the effect of U=0 impurities on the superconducting and
thermodynamic properties of the attractive Hubbard model on a square lattice.
Removal of the interaction on a critical fraction of of the sites results in the destruction of off-diagonal long range order
in the ground state. This critical fraction is roughly independent of filling
in the range , although our data suggest that might be somewhat larger below half-filling than at . We also
find that the two peak structure in the specific heat is present at both
below and above the value which destroys long range pairing order. It is
expected that the high peak associated with local pair formation should be
robust, but apparently local pairing fluctuations are sufficient to generate a
low temperature peak
Insulator-Metal Transition in the One and Two-Dimensional Hubbard Models
We use Quantum Monte Carlo methods to determine Green functions,
, on lattices up to for the 2D Hubbard model
at . For chemical potentials, , within the Hubbard gap, , and at {\it long} distances, , with critical behavior: , . This result stands in agreement with the
assumption of hyperscaling with correlation exponent and dynamical
exponent . In contrast, the generic band insulator as well as the
metal-insulator transition in the 1D Hubbard model are characterized by and .Comment: 9 pages (latex) and 5 postscript figures. Submitted for publication
in Phys. Rev. Let
Few-electron molecular states and their transitions in a single InAs quantum dot molecule
We study electronic configurations in a single pair of vertically coupled
self-assembled InAs quantum dots, holding just a few electrons. By comparing
the experimental data of non-linear single-electron transport spectra in a
magnetic field with many-body calculations, we identify the spin and orbital
configurations to confirm the formation of molecular states by filling both the
quantum mechanically coupled symmetric and anti-symmetric states. Filling of
the anti-symmetric states is less favored with increasing magnetic field, and
this leads to various magnetic field induced transitions in the molecular
states.Comment: 14 pages, 3 figures, Accepted for publication in Phys. Rev. Let
Thermodynamics of doped Kondo insulator in one dimension: Finite Temperature DMRG Study
The finite-temperature density-matrix renormalization-group method is applied
to the one-dimensional Kondo lattice model near half filling to study its
thermodynamics. The spin and charge susceptibilities and entropy are calculated
down to T=0.03t. We find two crossover temperatures near half filling. The
higher crossover temperature continuously connects to the spin gap at half
filling, and the susceptibilities are suppressed around this temperature. At
low temperatures, the susceptibilities increase again with decreasing
temperature when doping is finite. We confirm that they finally approach to the
values obtained in the Tomonaga-Luttinger (TL) liquid ground state for several
parameters. The crossover temperature to the TL liquid is a new energy scale
determined by gapless excitations of the TL liquid. The transition from the
metallic phase to the insulating phase is accompanied by the vanishing of the
lower crossover temperature.Comment: 4 pages, 7 Postscript figures, REVTe
Quest for a potent antimalarial drug lead: synthesis and evaluation of 6,7-dimethoxyquinazoline-2,4-diamines
Quinazolines have long been known to exert varied pharmacologic activities that make them suitable for use in treating hypertension, viral infections, tumors, and malaria. Since 2014, we have synthesized approximately 150 different 6,7-dimethoxyquinazoline-2,4-diamines and evaluated their antimalarial activity via structure-activity relationship studies. Here, we summarize the results and report the discovery of 6,7-dimethoxy-N(4)-(1-phenylethyl)-2-(pyrrolidin-1-yl)quinazolin-4-amine (20, SSJ-717), which exhibits high antimalarial activity as a promising antimalarial drug lead
Electrical Conductivity of Fermi Liquids. I. Many-body Effect on the Drude Weight
On the basis of the Fermi liquid theory, we investigate the many-body effect
on the Drude weight. In a lattice system, the Drude weight is modified by
electron-electron interaction due to Umklapp processes, while it is not
renormalized in a Galilean invariant system. This is explained by showing that
the effective mass for is defined through the current, not
velocity, of quasiparticle. It is shown that the inequality is required
for the stability against the uniform shift of the Fermi surface. The result of
perturbation theory applied for the Hubbard model indicates that as a
function of the density is qualitatively modified around half filling
by Umklapp processes.Comment: 20 pages, 2 figures; J. Phys. Soc. Jpn. Vol.67, No.
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