2,948 research outputs found
Joint effect of lattice interaction and potential fluctuation in colossal magnetoresistive manganites
Taking into account both the Jahn-Teller lattice distortion and the on-site
electronic potential fluctuations in the orbital-degenerated double-exchange
model, in which both the core-spin and the lattice distortion are treated
classically, we investigate theoretically the metal-insulator transition (MIT)
in manganites by considering the electronic localization effect. An inverse
matrix method is developed for calculation in which we use the inverse of the
transfer matrix to obtain the localization length. We find that within
reasonable range of parameters, both the lattice effect and the potential
fluctuation are responsible to the occurrence of the MIT. The role of the
orbital configuration is also discussed.Comment: 4 figure
Effects of a Supermassive Black Hole Binary on a Nuclear Gas Disk
We study influence of a galactic central supermassive black hole (SMBH)
binary on gas dynamics and star formation activity in a nuclear gas disk by
making three-dimensional Tree+SPH simulations. Due to orbital motions of SMBHs,
there are various resonances between gas motion and the SMBH binary motion. We
have shown that these resonances create some characteristic structures of gas
in the nuclear gas disk, for examples, gas elongated or filament structures,
formation of gaseous spiral arms, and small gas disks around SMBHs. In these
gaseous dense regions, active star formations are induced. As the result, many
star burst regions are formed in the nuclear region.Comment: 19 pages, 11 figures, accepted for publication in Ap
Acceleration Method of Neighbor Search with GRAPE and Morton-ordering
We describe a new method to accelerate neighbor searches on GRAPE, i.e. a
special purpose hardware that efficiently calculates gravitational forces and
potentials in -body simulations. In addition to the gravitational
calculations, GRAPE simultaneously constructs the lists of neighbor particles
that are necessary for Smoothed Particle Hydrodynamics (SPH). However, data
transfer of the neighbor lists from GRAPE to the host computer is time
consuming, and can be a bottleneck. In fact, the data transfer can take about
the same time as the calculations of forces themselves. Making use of GRAPE's
special treatment of neighbor lists, we can reduce the amount of data transfer
if we search neighbors in the order that the neighbor lists, constructed in a
single GRAPE run, overlap each other. We find that the Morton-ordering requires
very low additional calculation and programming costs, and results in
successful speed-up on data transfer. We show some benchmark results in the
case of GRAPE-5. Typical reduction in transferred data becomes as much as 90%.
This method is suitable not only for GRAPE-5, but also GRAPE-3 and the other
versions of GRAPE.Comment: 9 pages, 6 figures, accepted for publication in PAS
Tidal disruption of dark matter halos around proto-globular clusters
Tidal disruption of dark matter halos around proto-globular clusters in a
halo of a small galaxy is studied in the context of the hierarchical clustering
scenario by using semi-cosmological N-body/SPH simulations assuming the
standard cold dark matter model (). Our analysis on formation and
evolution of the galaxy and its substructures archives until . In such
a high-redshift universe, the Einstein-de Sitter universe is still a good
approximation for a recently favored -dominated universe, and then our
results does not depend on the choice of cosmology. In order to resolve small
gravitationally-bound clumps around galaxies and consider radiative cooling
below , we adopt a fine mass resolution (m_{\rm SPH} = 1.12 \times
10^3 \Msun). Because of the cooling, each clump immediately forms a
`core-halo' structure which consists of a baryonic core and a dark matter halo.
The tidal force from the host galaxy mainly strips the dark matter halo from
clumps and, as a result, theses clumps get dominated by baryons. Once a clump
is captured by the host halo, its mass drastically decreases each pericenter
passage. At , more than half of the clumps become baryon dominated
systems (baryon mass/total mass ). Our results support the tidal
evolution scenario of the formation of globular clusters and baryon dominated
dwarf galaxies in the context of the cold dark matter universe.Comment: 9page, 13 figures. Accepted for publication in ApJ. A high-resolution
PDF of the paper can be obtained from http://th.nao.ac.jp/~takayuki/ApJ05
Complex Analysis of a Piece of Toda Lattice
We study a small piece of two dimensional Toda lattice as a complex dynamical
system. In particular the Julia set, which appears when the piece is deformed,
is shown analytically how it disappears as the system approaches to the
integrable limit.Comment: 17 pages, LaTe
Ultrafast Photoinduced Formation of Metallic State in a Perovskite-type Manganite with Short Range Charge and Orbital Order
Femtosecond reflection spectroscopy was performed on a perovskite-type
manganite, Gd0.55Sr0.45MnO3, with the short-range charge and orbital order
(CO/OO). Immediately after the photoirradiation, a large increase of the
reflectivity was detected in the mid-infrared region. The optical conductivity
spectrum under photoirradiation obtained from the Kramers-Kronig analyses of
the reflectivity changes demonstrates a formation of a metallic state. This
suggests that ferromagnetic spin arrangements occur within the time resolution
(ca. 200 fs) through the double exchange interaction, resulting in an ultrafast
CO/OO to FM switching.Comment: 4 figure
Slow relaxation to equipartition in spring-chain systems
In this study, one-dimensional systems of masses connected by springs, i.e.,
spring-chain systems, are investigated numerically. The average kinetic energy
of chain-end particles of these systems is larger than that of other particles,
which is similar to the behavior observed for systems made of masses connected
by rigid links. The energetic motion of the end particles is, however,
transient, and the system relaxes to thermal equilibrium after a while, where
the average kinetic energy of each particle is the same, that is, equipartition
of energy is achieved. This is in contrast to the case of systems made of
masses connected by rigid links, where the energetic motion of the end
particles is observed in equilibrium. The timescale of relaxation estimated by
simulation increases rapidly with increasing spring constant. The timescale is
also estimated using the Boltzmann-Jeans theory and is found to be in quite
good agreement with that obtained by the simulation
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