14,272 research outputs found
Imprints of the nuclear symmetry energy on gravitational waves from the axial w-modes of neutron stars
The eigen-frequencies of the axial w-modes of oscillating neutron stars are
studied using the continued fraction method with an Equation of State (EOS)
partially constrained by the recent terrestrial nuclear laboratory data. It is
shown that the density dependence of the nuclear symmetry energy
affects significantly both the frequencies and the damping
times of these modes. Besides confirming the previously found universal
behavior of the mass-scaled eigen-frequencies as functions of the compactness
of neutron stars, we explored several alternative universal scaling functions.
Moreover, the -mode is found to exist only for neutron stars having a
compactness of independent of the EOS used.Comment: Version appeared in Phys. Rev. C80, 025801 (2009
Tidal coupling of a Schwarzschild black hole and circularly orbiting moon
We describe the possibility of using LISA's gravitational-wave observations
to study, with high precision, the response of a massive central body to the
tidal gravitational pull of an orbiting, compact, small-mass object. Motivated
by this application, we use first-order perturbation theory to study tidal
coupling for an idealized case: a massive Schwarzschild black hole, tidally
perturbed by a much less massive moon in a distant, circular orbit. We
investigate the details of how the tidal deformation of the hole gives rise to
an induced quadrupole moment in the hole's external gravitational field at
large radii. In the limit that the moon is static, we find, in Schwarzschild
coordinates and Regge-Wheeler gauge, the surprising result that there is no
induced quadrupole moment. We show that this conclusion is gauge dependent and
that the static, induced quadrupole moment for a black hole is inherently
ambiguous. For the orbiting moon and the central Schwarzschild hole, we find
(in agreement with a recent result of Poisson) a time-varying induced
quadrupole moment that is proportional to the time derivative of the moon's
tidal field. As a partial analog of a result derived long ago by Hartle for a
spinning hole and a stationary distant companion, we show that the orbiting
moon's tidal field induces a tidal bulge on the hole's horizon, and that the
rate of change of the horizon shape leads the perturbing tidal field at the
horizon by a small angle.Comment: 14 pages, 0 figures, submitted to Phys. Rev.
Compositional redistribution during casting of Hg sub 0.8 Cd sub 0.2 Te alloys
A series of Hg(0.8)Cd(0.2)Te ingots was cast both vertically and horizontally under well-defined thermal conditions by using a two-zone furnace with isothermal heat-pipe liners. The main objective of the experiments was to establish correlations between casting parameters and compositional redistribution and to develop ground-based data for a proposed flight experiment of casting of Hg(1-x)Cd(x)Te alloys under reduced gravity conditions. The compositional variations along the axial and radial directions were determined by precision density measurements, infrared transmission spectra, and X-ray energy dispersion spectrometry. Comparison between the experimental results and a numerical simulation of the solidification process of Hg(0.8)Cd(0.2)Te is described
A potential superhard material m-BCN
We here propose a new superhard material m-BCN with comparable Vickers hardness to cBN by the use of first-principles calculations. The calculations show that the mentioned m-BCN is a thermodynamically and kinetically stable semiconductor. Hydrostatic calculation shows that it is anisotropic and its incompressibility is very close to c-BN. Structural analysis shows that its excellent mechanical property and thermodynamically stability are inherited from diamond and cBN. These results provide a new clue to find new superhard phase.Запропоновано новий надтвердий матеріал m-BCN, твердість за Віккерсом якого за розрахунками за першими принципами порівняна з твердістю cBN. Розрахунки показали, що згаданий m-BCN за термодинамічними і кінетичними показниками є стабільним напівпровідником. Гідростатичний розрахунок показав, що він є анізотропним і його нестисливість дуже близька до нестисливості cBN. Структурний аналіз показав, що його відмінні механічні властивості і термодинамічна стабільність успадковані від алмаза і cBN. Дані результати забезпечують нову схему пошуку нових надтвердих фаз.Предложен новый сверхтвердый материал m-BCN, твердость по Виккерсу которого по расчетам по первым принципам сравнима с твердостью cBN. Расчеты показывают, что упомянутый m-BCN по термодинамическим и кинетическим показателям является стабильным полупроводником. Гидростатический расчет показал, что он анизотропный и его несжимаемость очень близка к несжимаемости cBN. Структурный анализ показал, что его отличные механические свойства и термодинамическая стабильность унаследованы от алмаза и cBN. Данные результаты обеспечивают новую схему поиска новых сверхтвердых фаз
Nucleon axial form factors from two-flavour Lattice QCD
We present preliminary results on the axial form factor and the
induced pseudoscalar form factor of the nucleon. A systematic
analysis of the excited-state contributions to form factors is performed on the
CLS ensemble `N6' with and lattice spacing . The relevant three-point functions were computed with
source-sink separations ranging from to $t_s \sim \
1.4 \ \text{fm}$. We observe that the form factors suffer from non-trivial
excited-state contributions at the source-sink separations available to us. It
is noted that naive plateau fits underestimate the excited-state contributions
and that the method of summed operator insertions correctly accounts for these
effects.Comment: 7 pages, 12 figures; talk presented at Lattice 2014 -- 32nd
International Symposium on Lattice Field Theory, 23-28 June, 2014, Columbia
University New York, N
Quantum groups and double quiver algebras
For a finite dimensional semisimple Lie algebra and a root
of unity in a field we associate to these data a double quiver
It is shown that a restricted version of the quantized
enveloping algebras is a quotient of the double quiver algebra
Comment: 15 page
FUSE Observations of Nebular O VI Emission from NGC 6543
NGC 6543 is one of the few planetary nebulae (PNe) whose X-ray emission has
been shown to be extended and originate from hot interior gas. Using FUSE
observations we have now detected nebular O VI emission from NGC 6543. Its
central star, with an effective temperature of ~50,000 K, is too cool to
photoionize O V, so the O VI ions must have been produced by thermal collisions
at the interface between the hot interior gas and the cool nebular shell. We
modeled the O VI emission incorporating thermal conduction, but find that
simplistic assumptions for the AGB and fast wind mass loss rates overproduce
X-ray emission and O VI emission. We have therefore adopted the pressure of the
interior hot gas for the interface layer and find that expected O VI emission
to be comparable to the observations.Comment: 4 pages, 4 figures, 1 table, using emulateapj.cls style. Accepted for
publication in ApJ Letter
A New Approach toward Transition State Spectroscopy
Chirped-Pulse millimetre-Wave (CPmmW) rotational spectroscopy provides a new
class of information about photolysis transition state(s). Measured intensities
in rotational spectra determine species-isomer-vibrational populations,
provided that rotational populations can be thermalized. The formation and
detection of S0 vinylidene is discussed in the limits of low and high initial
rotational excitation. CPmmW spectra of 193 nm photolysis of Vinyl Cyanide
(Acrylonitrile) contain J=0-1 transitions in more than 20 vibrational levels of
HCN, HNC, but no transitions in vinylidene or highly excited local-bender
vibrational levels of acetylene. Reasons for the non-observation of the
vinylidene co-product of HCN are discussed.Comment: Accepted by Faraday Discussion
Radiation-induced growth and isothermal decay of infrared-stimulated luminescence from feldspar
Optically stimulated luminescence (OSL) ages can determine a wide range of geological events or processes, such as the timing of sediment deposition, the exposure duration of a rock surface, or the cooling rate of bedrock. The accuracy of OSL dating critically depends on our capability to describe the growth and decay of laboratory-regenerated luminescence signals. Here we review a selection of common models describing the response of infrared stimulated luminescence (IRSL) of feldspar to constant radiation and temperature as administered in the laboratory. We use this opportunity to introduce a general-order kinetic model that successfully captures the behaviour of different materials and experimental conditions with a minimum of model parameters, and thus appears suitable for future application and validation in natural environments. Finally, we evaluate all the presented models by their ability to accurately describe a recently published feldspar multi-elevated temperature post-IR IRSL (MET-pIRIR) dataset, and highlight each model's strengths and shortfalls
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