39,106 research outputs found
Mid- and high-J CO observations towards UCHIIs
A study of 12 ultracompact HII regions was conducted to probe the physical
conditions and kinematics in the inner envelopes of the molecular clumps
harboring them. The APEX telescope was used to observe the sources in the CO
(4-3) and 13CO (8-7) lines. Line intensities were modeled with the RATRAN
radiative transfer code using power laws for the density and temperature to
describe the physical structure of the clumps. All sources were detected in
both lines. The optically thick CO (4-3) line shows predominantly blue skewed
profiles reminiscent of infall. Line intensities can be reproduced well using
the physical structure of the clumps taken from the literature. The optically
thick line profiles show that CO is a sensitive tracer of ongoing infall in the
outer envelopes of clumps harboring ultracompact HII regions and hot molecular
cores.Comment: APEX A&A special issue, accepte
Growth Model of Au Films on Ru(001)
In an attempt to find generic features on the fractal growth of Au films
deposited on Ru(001), a simple simulation model based on irreversible
diffusion-limited aggregation (DLA) is discussed. Highly irregular
two-dimensional dentritic islands of Au particles that gradually grow on a
larger host lattice of Ru particles and have fractal dimension d_{f}~ 1.70
each, are generated via a multiple had-hoc version of the DLA algorithm for
single aggregates. Annealing effects on the islands morphology are reproduced
assuming different sticking probabilities at nearest-neighbour lattice sites of
Au films on Ru(001). Using simulation data, islands growth are described in
analogy to diffusion-limited, precipitate growth with soft impingement of
precipities. This leads to analyse thin film island growth kinetics in such
fractal systems and to predict a main peak in scattering intensity patterns due
to interisland interference. ----------------
Copies upon request to: [email protected]: CM-ICTP/92/12
Relativistic Energy Density Functional Description of Shape Transition in Superheavy Nuclei
Relativistic energy density functionals (REDF) provide a complete and
accurate, global description of nuclear structure phenomena. A modern
semi-empirical functional, adjusted to the nuclear matter equation of state and
to empirical masses of deformed nuclei, is applied to studies of shapes of
superheavy nuclei. The theoretical framework is tested in a comparison of
calculated masses, quadrupole deformations, and potential energy barriers to
available data on actinide isotopes. Self-consistent mean-field calculations
predict a variety of spherical, axial and triaxial shapes of long-lived
superheavy nuclei, and their alpha-decay energies and half-lives are compared
to data. A microscopic, REDF-based, quadrupole collective Hamiltonian model is
used to study the effect of explicit treatment of collective correlations in
the calculation of Q{\alpha} values and half-lives.Comment: 23 pages, 10 figure
A study of nozzle and ejector flow problems by the method of integral relations
The application of the method of integral relations to nozzle and ejector flow problems was examined. For nozzle flow problems, the general formulation is that the approaching flow may be rotational. Particular attention was given to the phenomenon of choking under nonuniform flow conditions. Numerical integration of the governing ordinary differential equations was also investigated. This scheme of analysis was also applied to study the interacting flow field within an ejector system
Mira science with interferometry: a review
Model-predicted and observed properties of the brightness distribution on
M-type Mira disks are discussed. Fundamental issues of limb-darkening and
diameter definition, of assigning observational data to diameter-type
quantities and of interpreting such quantities in terms of model diameters are
outlined. The influence of model properties upon interpretation of measured
data is clarified. The dependence of the centre-to-limb variation (CLV) of
intensity on wavelength, on stellar parameters and on variablity phase and
cycle may be used for analyzing the geometrical and physical structure of the
Mira atmosphere, for determining fundamental stellar parameters, and for
investigating the quality of models. Desirable future observations include
simultaneous observations in different spectral features at different phases
and cycles, observation of the position of the shock front and observation of
the time- and wavelength-dependence of deviations from spherical symmetry.Comment: 9 pages, no figure
Self-gravitating warped discs around supermassive black holes
We consider warped equilibrium configurations for stellar and gaseous disks
in the Keplerian force-field of a supermassive black hole, assuming that the
self-gravity of the disk provides the only acting torques. Modeling the disk as
a collection of concentric circular rings, and computing the torques in the
non-linear regime, we show that stable, strongly warped precessing equilibria
are possible. These solutions exist for a wide range of disk-to-black hole mass
ratios , can span large warp angles of up to ,
have inner and outer boundaries, and extend over a radial range of a factor of
typically two to four. These equilibrium configurations obey a scaling relation
such that in good approximation \phidot/\Omega\propto M_d/M_{bh} where
\phidot is the (retrograde) precession frequency and is a
characteristic orbital frequency in the disk. Stability was determined using
linear perturbation theory and, in a few cases, confirmed by numerical
integration of the equations of motion. Most of the precessing equilibria are
found to be stable, but some are unstable. The main result of this study is
that highly warped disks near black holes can persist for long times without
any persistent forcing other than by their self-gravity. The possible relevance
of this to galactic nuclei is briefly discussed.Comment: 13 pages, 21 figures, published in MNRA
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