9,581 research outputs found
Nuclear Bar, Star Formation and Gas Fueling in the Active Galaxy NGC 4303
A combination of Hubble Space Telescope (HST) WFPC2 and NICMOS images are
used to investigate the gas/dust and stellar structure inside the central 300
pc of the nearby active galaxy NGC 4303.
The NICMOS H-band (F160W) image reveals a bright core and a nuclear elongated
bar-like structure of 250 pc in diameter. The bar is centered on the bright
core, and its major axis is oriented in proyection along the spin axis of the
nuclear gaseous rotating disk recently detected (Colina & Arribas 1999).
The V-H (F606W - F160W) image reveals a complex gas/dust distribution with a
two-arm spiral structure of about 225 pc in radius. The southwestern arm is
traced by young star-forming knots while the northeastern arm is detected by
the presence of dust lanes. These spirals do not have a smooth structure but
rather they are made of smaller flocculent spirals or filament-like structures.
The magnitudes and colors of the star-forming knots are typical of clusters of
young stars with masses of 0.5 to 1 x yr^{-1} for about 80 Myr.Comment: ApJ, in press (February 1, 2000
Dynamical Susceptibility in KH2PO4-type Crystals above and below Tc
The time dependent cluster approximation called the path probability method
(PPM) is applied to a pseudo-spin Ising Hamiltonian of the Slater-Takagi model
for KH2PO4-type hydrogen-bonded ferroelectrics in order to calculate the
homogeneous dynamical susceptibility above and below the ferroelectric
transition temperature. Above the transition temperature all the calculations
are carried out analytically in the cactus approximation of the PPM. Below the
transition temperature the dynamical susceptibility is also calculated
accurately since the analytical solution of spontaneous polarization in the
ferroelectric phase can be utilized. When the temperature is approached from
both sides of the transition temperature, only one of relaxation times shows a
critical slowing down and makes a main contribution to the dynamical
susceptibility. The discrepancy from Slater model (ice-rule limit) is discussed
in comparison with some experimental data.Comment: 8 pages, 10 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
Modal test of the Viking orbiter
A modal test of the Orbiter Development Test Modal (ODTM) has been conducted to verify, or update, the mathematical model used for load analysis. The approach used to assure the quality and validity of the experimental data is defined, the modal test is described, and test results are presented and compared with analysis results. Good correlation between the analyses and the test data assures an acceptable model for incorporation into the mathematical model of the launch system
Cavity QED and Quantum Computation in the Weak Coupling Regime
In this paper we consider a model of quantum computation based on n atoms of
laser-cooled and trapped linearly in a cavity and realize it as the n atoms
Tavis-Cummings Hamiltonian interacting with n external (laser) fields.
We solve the Schr{\" o}dinger equation of the model in the case of n=2 and
construct the controlled NOT gate by making use of a resonance condition and
rotating wave approximation associated to it. Our method is not heuristic but
completely mathematical, and the significant feature is a consistent use of
Rabi oscillations.
We also present an idea of the construction of three controlled NOT gates in
the case of n=3 which gives the controlled-controlled NOT gate.Comment: Latex file, 22 pages, revised version. To appear in Journal of Optics
B : Quantum and Semiclassical Optic
Time-resolved infrared emission from radiation-driven central obscuring structures in Active Galactic Nuclei
The central engines of Seyfert galaxies are thought to be enshrouded by
geometrically thick gas and dust structures. In this article, we derive
observable properties for a self-consistent model of such toroidal gas and dust
distributions, where the geometrical thickness is achieved and maintained with
the help of X-ray heating and radiation pressure due to the central engine.
Spectral energy distributions (SEDs) and images are obtained with the help of
dust continuum radiative transfer calculations with RADMC-3D. For the first
time, we are able to present time-resolved SEDs and images for a physical model
of the central obscurer. Temporal changes are mostly visible at shorter
wavelengths, close to the combined peak of the dust opacity as well as the
central source spectrum and are caused by variations in the column densities of
the generated outflow. Due to the three-component morphology of the
hydrodynamical models -- a thin disc with high density filaments, a surrounding
fluffy component (the obscurer) and a low density outflow along the rotation
axis -- we find dramatic differences depending on wavelength: whereas the
mid-infrared images are dominated by the elongated appearance of the outflow
cone, the long wavelength emission is mainly given by the cold and dense disc
component. Overall, we find good agreement with observed characteristics,
especially for those models, which show clear outflow cones in combination with
a geometrically thick distribution of gas and dust, as well as a geometrically
thin, but high column density disc in the equatorial plane.Comment: 16 pages, 12 figures, accepted for publication in MNRA
On Phase Transition of -Type Crystals by Cluster Variation Method
The Cluster Variation Method (CVM) is applied to the Ishibashi model for
ammonium dihydrogen phosphate () of a typical hydrogen
bonded anti-ferroelectric crystal. The staggered and the uniform susceptibility
without hysteresis are calculated at equilibrium. On the other hand, by making
use of the natural iteration method (NIM) for the CVM, hysteresis phenomena of
uniform susceptibility versus temperature observed in experiments is well
explained on the basis of local minimum in Landau type variational free energy.
The polarization curves against the uniform field is also calculated.Comment: 14 pages, 10 figure
Intrinsic localized modes in the charge-transfer solid PtCl
We report a theoretical analysis of intrinsic localized modes in a
quasi-one-dimensional charge-transfer-solid (PtCl). We discuss strongly nonlinear features of resonant Raman
overtone scattering measurements on PtCl, arising from quantum intrinsic
localized (multiphonon) modes (ILMs) and ILM-plus-phonon states. We show, that
Raman scattering data displays clear signs of a non-thermalization of lattice
degrees-of-freedom, manifested in a nonequilibrium density of intrinsic
localized modes.Comment: 4 pages, 4 figures, REVTE
Two Phase Collective Modes in Josephson Vortex Lattice in Intrinsic Josephson Junction BiSrCaCuO
Josephson plasma excitations in the high superconductor
BiSrCaCuO have been investigated in a wide microwave
frequency region (9.8 -- 75 GHz), in particular, in magnetic field applied
parallel to the plane of the single crystal. In sharp contrast to the case
for magnetic fields parallel to the c axis or tilted from the plane, it
was found that there are two kinds of resonance modes, which are split in
energy and possess two distinctly different magnetic field dependences. One
always lies higher in energy than the other and has a shallow minimum at about
0.8 kOe, then increases linearly with magnetic field. On the other hand,
another mode begins to appear only in a magnetic field (from a few kOe and
higher) and has a weakly decreasing tendency with increasing magnetic field. By
comparing with a recent theoretical model the higher energy mode can naturally
be attributed to the Josephson plasma resonance mode propagating along the
primitive reciprocal lattice vector of the Josephson vortex lattice, whereas
the lower frequency mode is assigned to the novel phase collective mode of the
Josephson vortex lattice, which has never been observed before.Comment: 11 pages and 10 figure
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