21,900 research outputs found
Depolarization volume and correlation length in the homogenization of anisotropic dielectric composites
In conventional approaches to the homogenization of random particulate
composites, both the distribution and size of the component phase particles are
often inadequately taken into account. Commonly, the spatial distributions are
characterized by volume fraction alone, while the electromagnetic response of
each component particle is represented as a vanishingly small depolarization
volume. The strong-permittivity-fluctuation theory (SPFT) provides an
alternative approach to homogenization wherein a comprehensive description of
distributional statistics of the component phases is accommodated. The
bilocally-approximated SPFT is presented here for the anisotropic homogenized
composite which arises from component phases comprising ellipsoidal particles.
The distribution of the component phases is characterized by a two-point
correlation function and its associated correlation length. Each component
phase particle is represented as an ellipsoidal depolarization region of
nonzero volume. The effects of depolarization volume and correlation length are
investigated through considering representative numerical examples. It is
demonstrated that both the spatial extent of the component phase particles and
their spatial distributions are important factors in estimating coherent
scattering losses of the macroscopic field.Comment: Typographical error in eqn. 16 in WRM version is corrected in arxiv
versio
Nuclear three-body problem in the complex energy plane: Complex-Scaling-Slater method
The physics of open quantum systems is an interdisciplinary area of research.
The nuclear "openness" manifests itself through the presence of the many-body
continuum representing various decay, scattering, and reaction channels. As the
radioactive nuclear beam experimentation extends the known nuclear landscape
towards the particle drip lines, the coupling to the continuum space becomes
exceedingly more important. Of particular interest are weakly bound and unbound
nuclear states appearing around particle thresholds. Theories of such nuclei
must take into account their open quantum nature. To describe open quantum
systems, we introduce a Complex Scaling (CS) approach in the Slater basis. We
benchmark it with the complex-energy Gamow Shell Model (GSM) by studying
energies and wave functions of the bound and unbound states of the two-neutron
halo nucleus 6He viewed as an + n + n cluster system. In the CS
approach, we use the Slater basis, which exhibits the correct asymptotic
behavior at large distances. To extract particle densities from the
back-rotated CS solutions, we apply the Tikhonov regularization procedure,
which minimizes the ultraviolet numerical noise. While standard applications of
the inverse complex transformation to the complex-rotated solution provide
unstable results, the stabilization method fully reproduces the GSM benchmark.
We also propose a method to determine the smoothing parameter of the Tikhonov
regularization. The combined suite of CS-Slater and GSM techniques has many
attractive features when applied to nuclear problems involving weakly-bound and
unbound states. While both methods can describe energies, total widths, and
wave functions of nuclear states, the CS-Slater method, if it can be applied,
can provide an additional information about partial energy widths associated
with individual thresholds.Comment: 15 pages, 16 figure
Geometric invariance of mass-like asymptotic invariants
We study coordinate-invariance of some asymptotic invariants such as the ADM
mass or the Chru\'sciel-Herzlich momentum, given by an integral over a
"boundary at infinity". When changing the coordinates at infinity, some terms
in the change of integrand do not decay fast enough to have a vanishing
integral at infinity; but they may be gathered in a divergence, thus having
vanishing integral over any closed hypersurface. This fact could only be
checked after direct calculation (and was called a "curious cancellation"). We
give a conceptual explanation thereof.Comment: 13 page
Evidence of amplitude modulation due to Resonant Mode Coupling in the delta Scuti star KIC5892969
A study of the star KIC5892969 observed by the Kepler satellite is presented.
Its three highest amplitude modes present a strong amplitude modulation. The
aim of this work is to investigate amplitude variations in this star and their
possible cause. Using the 4 years-long observations available, we obtained the
frequency content of the full light curve. Then, we studied the amplitude and
phase variations with time using shorter time stamps. The results obtained are
compared with the predicted ones for resonant mode coupling of an unstable mode
with lower frequency stable modes. Our conclusion is that resonant mode
coupling is consistent as an amplitude limitation mechanism in several modes of
KIC5892969 and we discuss to which extent it might play an important role for
other delta Scuti stars
Quasi-periodic Oscillations in the X-ray Light Curves from Relativistic Tori
We use a relativistic ray-tracing code to analyze the X-ray emission from a
pressure-supported oscillating relativistic torus around a black hole. We show
that a strong correlation exists between the {\it intrinsic} frequencies of the
torus normal modes and the {\it extrinsic} frequencies seen in the observed
light curve power spectrum. This correlation demonstrates the feasibility of
the oscillating-torus model to explain the multiple peaks seen in black hole
high-frequency quasi-periodic oscillations. Using an optically thin,
monochromatic emission model, we also determine how a relativistically
broadened emission line and the amplitude of the X-ray modulations are
dependent on the observer's inclination angle and on the torus oscillation
amplitudes. Observations of these features can provide important information
about the torus as well as the black hole.Comment: 4 pages, 3 figures, submitted to ApJ
Depolarization regions of nonzero volume in bianisotropic homogenized composites
In conventional approaches to the homogenization of random particulate
composites, the component phase particles are often treated mathematically as
vanishingly small, point-like entities. The electromagnetic responses of these
component phase particles are provided by depolarization dyadics which derive
from the singularity of the corresponding dyadic Green functions. Through
neglecting the spatial extent of the depolarization region, important
information may be lost, particularly relating to coherent scattering losses.
We present an extension to the strong-property-fluctuation theory in which
depolarization regions of nonzero volume and ellipsoidal geometry are
accommodated. Therein, both the size and spatial distribution of the component
phase particles are taken into account. The analysis is developed within the
most general linear setting of bianisotropic homogenized composite mediums
(HCMs). Numerical studies of the constitutive parameters are presented for
representative examples of HCM; both Lorentz-reciprocal and
Lorentz-nonreciprocal HCMs are considered. These studies reveal that estimates
of the HCM constitutive parameters in relation to volume fraction, particle
eccentricity, particle orientation and correlation length are all significantly
influenced by the size of the component phase particles
HD 41641: A classical Sct-type pulsator with chemical signatures of an Ap star
Among the known groups of pulsating stars, Sct stars are one of the
least understood. Theoretical models do not predict the oscillation frequencies
that observations reveal. Complete asteroseismic studies are necessary to
improve these models and better understand the internal structure of these
targets. We study the Sct star HD 41641 with the ultimate goal of
understanding its oscillation pattern. The target was simultaneously observed
by the CoRoT space telescope and the HARPS high-resolution spectrograph. The
photometric data set was analyzed with the software package PERIOD04, while
FAMIAS was used to analyze the line profile variations. The method of spectrum
synthesis was used for spectroscopically determining the fundamental
atmospheric parameters and individual chemical abundances. A total of 90
different frequencies was identified and analyzed. An unambiguous
identification of the azimuthal order of the surface geometry could only be
provided for the dominant p-mode, which was found to be a nonradial prograde
mode with m = +1. Using and , we estimated the mass,
radius, and evolutionary stage of HD 41641. We find HD 41641 to be a moderately
rotating, slightly evolved Sct star with subsolar overall atmospheric
metal content and unexpected chemical peculiarities. HD 41641 is a pure
Sct pulsator with p-mode frequencies in the range from 10 d to
20 d. This pulsating star presents chemical signatures of an Ap star and
rotational modulation due to surface inhomogeneities, which we consider
indirect evidence of the presence of a magnetic field.Comment: 11 pages, 11 figures, accepted for publication in A&
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