1,630 research outputs found
Balanced Truncation Model Reduction of a Nonlinear Cable-Mass PDE System with Interior Damping
We consider model order reduction of a nonlinear cable-mass system modeled by
a 1D wave equation with interior damping and dynamic boundary conditions. The
system is driven by a time dependent forcing input to a linear mass-spring
system at one boundary. The goal of the model reduction is to produce a low
order model that produces an accurate approximation to the displacement and
velocity of the mass in the nonlinear mass-spring system at the opposite
boundary. We first prove that the linearized and nonlinear unforced systems are
well-posed and exponentially stable under certain conditions on the damping
parameters, and then consider a balanced truncation method to generate the
reduced order model (ROM) of the nonlinear input-output system. Little is known
about model reduction of nonlinear input-output systems, and so we present
detailed numerical experiments concerning the performance of the nonlinear ROM.
We find that the ROM is accurate for many different combinations of model
parameters
SB9: The Ninth Catalogue of Spectroscopic Binary Orbits
The Ninth Catalogue of Spectroscopic Binary Orbits
(http://sb9.astro.ulb.ac.be) continues the series of compilations of
spectroscopic orbits carried out over the past 35 years by Batten and
collaborators. As of 2004 May 1st, the new Catalogue holds orbits for 2,386
systems. Some essential differences between this catalogue and its predecessors
are outlined and three straightforward applications are presented: (1)
Completeness assessment: period distribution of SB1s and SB2s; (2) Shortest
periods across the H-R diagram; (3) Period-eccentricity relation.Comment: Accepte for publication in A&A, 6 pages, 6 figure
Novel Ground-State Crystals with Controlled Vacancy Concentrations: From Kagom\'{e} to Honeycomb to Stripes
We introduce a one-parameter family, , of pair potential
functions with a single relative energy minimum that stabilize a range of
vacancy-riddled crystals as ground states. The "quintic potential" is a
short-ranged, nonnegative pair potential with a single local minimum of height
at unit distance and vanishes cubically at a distance of \rt. We have
developed this potential to produce ground states with the symmetry of the
triangular lattice while favoring the presence of vacancies. After an
exhaustive search using various optimization and simulation methods, we believe
that we have determined the ground states for all pressures, densities, and . For specific areas below 3\rt/2, the ground states of the
"quintic potential" include high-density and low-density triangular lattices,
kagom\'{e} and honeycomb crystals, and stripes. We find that these ground
states are mechanically stable but are difficult to self-assemble in computer
simulations without defects. For specific areas above 3\rt/2, these systems
have a ground-state phase diagram that corresponds to hard disks with radius
\rt. For the special case of H=0, a broad range of ground states is
available. Analysis of this case suggests that among many ground states, a
high-density triangular lattice, low-density triangular lattice, and striped
phases have the highest entropy for certain densities. The simplicity of this
potential makes it an attractive candidate for experimental realization with
application to the development of novel colloidal crystals or photonic
materials.Comment: 25 pages, 11 figure
The visual orbits of the spectroscopic binaries HD 6118 and HD 27483 from the Palomar Testbed Interferometer
We present optical interferometric observations of two double-lined
spectroscopic binaries, HD 6118 and HD 27483, taken with the Palomar Testbed
Interferometer (PTI) in the K band. HD 6118 is one of the most eccentric
spectroscopic binaries and HD 27483 a spectroscopic binary in the Hyades open
cluster. The data collected with PTI in 2001-2002 allow us to determine
astrometric orbits and when combined with the radial velocity measurements
derive all physical parameters of the systems. The masses of the components are
2.65 +/- 0.27 M_Sun and 2.36 +/- 0.24 M_Sun for HD 6118 and 1.38 +/- 0.13 M_Sun
and 1.39 +/- 0.13 M_Sun for HD 27483. The apparent semi-major axis of HD 27483
is only 1.2 mas making it the closest binary successfully observed with an
optical interferometer.Comment: submitted to Ap
Planetary systems around close binary stars: the case of the very dusty, Sun-like, spectroscopic binary BD+20 307
Field star BD+20 307 is the dustiest known main sequence star, based on the
fraction of its bolometric luminosity, 4%, that is emitted at infrared
wavelengths. The particles that carry this large IR luminosity are unusually
warm, comparable to the temperature of the zodiacal dust in the solar system,
and their existence is likely to be a consequence of a fairly recent collision
of large objects such as planets or planetary embryos. Thus, the age of BD+20
307 is potentially of interest in constraining the era of terrestrial planet
formation. The present project was initiated with an attempt to derive this age
using the Chandra X-ray Observatory to measure the X-ray flux of BD+20 307 in
conjunction with extensive photometric and spectroscopic monitoring
observations from Fairborn Observatory. However, the recent realization that
BD+20 307 is a short period, double-line, spectroscopic binary whose components
have very different lithium abundances, vitiates standard methods of age
determination. We find the system to be metal-poor; this, combined with its
measured lithium abundances, indicates that BD+20 307 may be several to many
Gyr old. BD+20 307 affords astronomy a rare peek into a mature planetary system
in orbit around a close binary star (because such systems are not amenable to
study by the precision radial velocity technique).Comment: accepted for ApJ, December 10, 200
Multi-Line Geometry of Qubit-Qutrit and Higher-Order Pauli Operators
The commutation relations of the generalized Pauli operators of a
qubit-qutrit system are discussed in the newly established graph-theoretic and
finite-geometrical settings. The dual of the Pauli graph of this system is
found to be isomorphic to the projective line over the product ring Z2xZ3. A
"peculiar" feature in comparison with two-qubits is that two distinct
points/operators can be joined by more than one line. The multi-line property
is shown to be also present in the graphs/geometries characterizing two-qutrit
and three-qubit Pauli operators' space and surmised to be exhibited by any
other higher-level quantum system.Comment: 8 pages, 6 figures. International Journal of Theoretical Physics
(2007) accept\'
SB9: The ninth catalogue of spectroscopic binary orbits
The Ninth Catalogue of Spectroscopic Binary Orbits (http://sb9.astro.ulb.ac.be) continues the series of compilations of spectroscopic orbits carried out over the past 35 years by Batten and collaborators. As of 2004 May 1st, the new Catalogue holds orbits for 2386 systems. Some essential differences between this catalogue and its predecessors are out-lined and three straightforward applications are presented: (1) completeness assessment: period distribution of SB1s and SB2s; (2) shortest periods across the H-R diagram; (3) period-eccentricity relation.Facultad de Ciencias AstronĂłmicas y GeofĂsica
Testing Rotational Mixing Predictions with New Boron Abundances in Main Sequence B-type Stars
(Abridged) New boron abundances for seven main-sequence B-type stars are
determined from HST STIS spectroscopy around the BIII 2066A line. Boron
abundances provide a unique and critical test of stellar evolution models that
include rotational mixing since boron is destroyed in the surface layers of
stars through shallow mixing long before other elements are mixed from the
stellar interior through deep mixing. Boron abundances range from 12+log(B/H) =
1.0 to 2.2. The boron abundances are compared to the published values of their
stellar nitrogen abundances (all have 12+log(N/H) < 7.8, i.e., they do not show
significant CNO-mixing) and to their host cluster ages (4 to 16 Myr) to
investigate the predictions from models of massive star evolution with
rotational mixing effects (Heger & Langer 2000). Only three stars (out of 34)
deviate from the model predictions, including HD36591, HD205021, and HD30836.
These three stars suggest that rotational mixing could be more efficient than
currently modelled at the highest rotation rates.Comment: 10 figures, 7 tables; accepted for publication in the Astrophysical
Journa
An Optical Study of BG Geminorum: An Ellipsoidal Binary with an Unseen Primar Star
We describe optical photometric and spectroscopic observations of the bright
variable BG Geminorum. Optical photometry shows a pronounced ellipsoidal
variation of the K0 I secondary, with amplitudes of ~0.5 mag at VRI and a
period of 91.645 days. A deep primary eclipse is visible for wavelengths <
4400A; a shallower secondary eclipse is present at longer wavelengths. Eclipse
timings and the radial velocity curve of the K0 secondary star indicate an
interacting binary where a lobe-filling secondary, M_2 ~ 0.5 Msun, transfers
material into a extended disk around a massive primary, M_1 ~ 4.5 Msun. The
primary star is either an early B-type star or a black hole. If it did contain
a black hole, BG Gem would be the longest period black hole binary known by a
factor of 10, as well as the only eclipsing black hole binary system.Comment: 27 pages, includes 8 figures and 5 tables, accepted to A
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