6,396 research outputs found
A perspective of Middle-Atmosphere Dynamics (MAD) studies at the New International Equatorial Observatory (NIEO)
The equatorial region has attracted many MAD studies mainly based on data of limited locations and resolutions. Established at NIEO are: (1) Climatology of the equatorial middle atmosphere (all of the mean zonal flow, the meridional and/or east-west circulations and the planetary/gravity waves are described based on massive, reliable data statistics); (2) Troposphere-stratosphere coupling at the equator (the candidate location of NIEO is just at the stratospheric fountain area where the tracers and waves are pumped up into the middle atmosphere); and (3) Mesosphere-thermosphere coupling at the equator; thermospheric superrotation, which may be caused either by ion drag or by tidal breaking, is examined in detail by observations covering a wide altitude range from the mesosphere through the thermosphere
Double-Exchange Model on Triangle Chain
We study ground state properties of the double-exchange model on triangle
chain in the classical limit on spins. The ground state is determined
by a competition among the kinetic energy of the electron, the
antiferromagnetic exchange energy between the spins, and frustration
due to a geometric structure of the lattice. The phase diagrams are obtained
numerically for two kinds of the models which differ only in the transfer
integral being real or complex. The properties of the states are understood
from the viewpoint of the spin-induced Peierls instability. The results suggest
the existence of a chiral glass phase which is characterized by a local spin
chirality and a continuous degeneracy.Comment: 6 pages, 4 figure
Structural Transition of Li2RuO3 Induced by Molecular-Orbit Formation
A pseudo honeycomb system Li2RuO3 exhibits a second-order-like transition at
temperature T=Tc=540 K to a low-T nonmagnetic phase with a significant lattice
distortion forming Ru-Ru pairs. For this system, we have calculated the band
structure, using the generalized gradient approximation (GGA) in both the high-
and low- T phases, and found that the results of the calculation can naturally
explain the insulating behavior observed in the low-T phase. The detailed
characters of the Ru 4d t2g bands obtained by the tight-binding fit to the
calculated dispersion curves show clear evidence that the structural transition
is driven by the formation of the Ru-Ru molecular-orbits, as proposed in our
previous experimental studies.Comment: 5 pages, 5 figures, 4 tables, submitted to J. Phys. Soc. Jp
Gauge-boson propagator in out of equilibrium quantum-field system and the Boltzmann equation
We construct from first principles a perturbative framework for studying
nonequilibrium quantum-field systems that include gauge bosons. The system of
our concern is quasiuniform system near equilibrium or nonequilibrium
quasistationary system. We employ the closed-time-path formalism and use the
so-called gradient approximation. No further approximation is introduced. We
construct a gauge-boson propagator, with which a well-defined perturbative
framework is formulated. In the course of construction of the framework, we
obtain the generalized Boltzmann equation (GBE) that describes the evolution of
the number-density functions of gauge-bosonic quasiparticles. The framework
allows us to compute the reaction rate for any process taking place in the
system. Various processes, in turn, cause an evolution of the systems, which is
described by the GBE.Comment: 28 page
A self-consistent first-principles calculation scheme for correlated electron systems
A self-consistent calculation scheme for correlated electron systems is
created based on the density-functional theory (DFT). Our scheme is a
multi-reference DFT (MR-DFT) calculation in which the electron charge density
is reproduced by an auxiliary interacting Fermion system. A short-range
Hubbard-type interaction is introduced by a rigorous manner with a residual
term for the exchange-correlation energy. The Hubbard term is determined
uniquely by referencing the density fluctuation at a selected localized
orbital. This strategy to obtain an extension of the Kohn-Sham scheme provides
a self-consistent electronic structure calculation for the materials design.
Introducing an approximation for the residual exchange-correlation energy
functional, we have the LDA+U energy functional. Practical self-consistent
calculations are exemplified by simulations of Hydrogen systems, i.e. a
molecule and a periodic one-dimensional array, which is a proof of existence of
the interaction strength U as a continuous function of the local fluctuation
and structural parameters of the system.Comment: 23 pages, 8 figures, to appear in J. Phys. Condens. Matte
X-ray Linear Dichroism in cubic compounds: the case of Cr3+ in MgAl2O4
The angular dependence (x-ray linear dichroism) of the Cr K pre-edge in
MgAl2O4:Cr3+ spinel is measured by means of x-ray absorption near edge
structure spectroscopy (XANES) and compared to calculations based on density
functional theory (DFT) and ligand field multiplet theory (LFM). We also
present an efficient method, based on symmetry considerations, to compute the
dichroism of the cubic crystal starting from the dichroism of a single
substitutional site. DFT shows that the electric dipole transitions do not
contribute to the features visible in the pre-edge and provides a clear vision
of the assignment of the 1s-->3d transitions. However, DFT is unable to
reproduce quantitatively the angular dependence of the pre-edge, which is, on
the other side, well reproduced by LFM calculations. The most relevant factors
determining the dichroism of Cr K pre-edge are identified as the site
distortion and 3d-3d electronic repulsion. From this combined DFT, LFM approach
is concluded that when the pre-edge features are more intense than 4 % of the
edge jump, pure quadrupole transitions cannot explain alone the origin of the
pre-edge. Finally, the shape of the dichroic signal is more sensitive than the
isotropic spectrum to the trigonal distortion of the substitutional site. This
suggests the possibility to obtain quantitative information on site distortion
from the x-ray linear dichroism by performing angular dependent measurements on
single crystals
Trajectory analysis of Polar Patrol Balloon (PPB) flights in the stratosphere over Antarctica in summer and spring: A preliminary result
Actual trajectories of two PPB's which flew in the Antarctic stratosphere in austral summer and spring are compared with those calculated based on objective analysis data of Japan Meteorological Agency (JMA). The differences between the actual and calculated trajectories are discussed to check reliability of the JMA objective analysis data for the stratosphere, and to detect subsynoptic scale variability due to gravity waves and others
Precipitating clouds observed by 1.3-GHz boundary layer radars in equatorial Indonesia
International audienceTemporal variations of precipitating clouds in equatorial Indonesia have been studied based on observations with 1357.5 MHz boundary layer radars at Serpong (6.4° S, 106.7° E) near Jakarta and Bukittinggi (0.2° S, 100.3° E) in West Sumatera. We have classified precipitating clouds into four types: stratiform, mixed stratiform-convective, deep convective, and shallow convective clouds, using the Williams et al. (1995) method. Diurnal variations of the occurrence of precipitating clouds at Serpong and Bukittinggi have showed the same characteristics, namely, that the precipitating clouds primarily occur in the afternoon and the peak of the stratiform cloud comes after the peak of the deep convective cloud. The time delay between the peaks of stratiform and deep convective clouds corresponds to the life cycle of the mesoscale convective system. The precipitating clouds which occur in the early morning at Serpong are dominated by stratiform cloud. Concerning seasonal variations of the precipitating clouds, we have found that the occurrence of the stratiform cloud is most frequent in the rainy season, while the occurrence of the deep convective cloud is predominant in the dry season
Ground State Properties of One Dimensional S=1/2 Heisenberg Model with Dimerization and Quadrumerization
The one dimensional S=1/2 Heisenberg model with dimerization and
quadrumerization is studied by means of the numerical exact diagonalization of
finite size systems. Using the phenomenological renormalization group and
finite size scaling law, the ground state phase diagram is obtained in the
isotropic case. It exhibits a variety of the ground states which contains the
S=1 Haldane state, S=1 dimer state and S=1/2 dimer state as limiting cases. The
gap exponent is also calculated which coincides with the value for the
dimerization transition of the isotropic Heisenberg chain. In the XY limit, the
phase diagram is obtained analytically and the comparison is made with the
isotropic case.Comment: 4 pages, 7 figure
Combined wind profiler-weather radar observations of orographic rainband around Kyushu, Japan in the Baiu season
International audienceA special observation campaign (X-BAIU), using various instruments (wind profilers, C-band weather radars, X-band Doppler radars, rawinsondes, etc.), was carried out in Kyushu (western Japan) during the Baiu season, from 1998 to 2002. In the X-BAIU-99 and -02 observations, a line-shaped orographic rainband extending northeastward from the Koshikijima Islands appeared in the low-level strong wind with warm-moist airs. The weather radar observation indicated that the rainband was maintained for 11h. The maximum length and width of the rainband observed in 1999 was ~200km and ~20km, respectively. The rainband observed in 2002 was not so developed compared with the case in 1999. The Froude number averaged from sea level to the top of the Koshikijima Islands (~600m) was large (>1), and the lifting condensation level was below the tops of the Koshikijima Islands. Thus, it is suggested that the clouds organizing the rainband are formed by the triggering of the mountains on the airflow passing over them. The vertical profile of horizontal wind in/around the rainband was investigated in the wind profiler observations. In the downdraft region 60km from the Koshikijima Islands, strong wind and its clockwise rotation with increasing height was observed below 3km altitude. In addition, a strong wind component perpendicular to the rainband was observed when the rainband was well developed. These wind behaviors were related to the evolution of the rainband
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