6,400 research outputs found
Towards Understanding Astrophysical Effects of Nuclear Symmetry Energy
Determining the Equation of State (EOS) of dense neutron-rich nuclear matter
is a shared goal of both nuclear physics and astrophysics. Except possible
phase transitions, the density dependence of nuclear symmetry \esym is the most
uncertain part of the EOS of neutron-rich nucleonic matter especially at
supra-saturation densities. Much progresses have been made in recent years in
predicting the symmetry energy and understanding why it is still very uncertain
using various microscopic nuclear many-body theories and phenomenological
models. Simultaneously, significant progresses have also been made in probing
the symmetry energy in both terrestrial nuclear laboratories and astrophysical
observatories. In light of the GW170817 event as well as ongoing or planned
nuclear experiments and astrophysical observations probing the EOS of dense
neutron-rich matter, we review recent progresses and identify new challenges to
the best knowledge we have on several selected topics critical for
understanding astrophysical effects of the nuclear symmetry energy.Comment: 77 pages. Invited Review Article, EPJA (2019) in pres
On the Numerical Stationary Distribution of Overdamped Langevin Equation in Harmonic System
Efficient numerical algorithm for stochastic differential equation has been
an important object in the research of statistical physics and mathematics for
a long time. In this paper we study the highly accurate numerical algorithm of
the overdamped Langevin equation. In particular, our interest is the behaviour
of the numerical schemes for solving the overdamped Langevin equation in the
harmonic system. Three algorithms are obtained for overdamped Langevin
equation, from the large friction limit of the schemes for underdamped Langevin
dynamics. We derive the explicit expression of the stationary distribution of
each algorithm by analysing the discrete time trajectory, for both
one-dimensional and multi-dimensional cases. The accuracy of the stationary
distribution of each algorithm is illustrated by comparing to the exact
Boltzmann distribution. Our results demonstrate that, the "BAOA-limit"
algorithm generates the exact distribution for the harmonic system in the
canonical ensemble, within the stable regime of the time interval. The other
algorithms do not produce the exact distribution of the harmonic system.Comment: 19 page
Color Constant Descriptors Combining Image Derivative Structures
Color constant image description is a fundamental problem in many computer vision applications. In this paper, the diagonal-offset model is adopted as reflectance model to get color constant image descriptors. This model makes the descriptors much more robust, and also fits the real world images very well. By introducing 3D moment invariants, this paper contributes to give an illumination independent descriptor generation framework. In detail, 0-, 1- and even higher order color constant descriptors can be generated from such framework. These descriptors can characterize n-order derivative image information. Furthermore, the combination thereof can characterize not only original image but also n-order edge image color information. The experiments on real image databases show that all these descriptors are robust to illumination variation and affine transformation, and perform very well for object recognition under various situations
Constraints on the symmetry energy from observational probes of the neutron star crust
A number of observed phenomena associated with individual neutron star
systems or neutron star populations find explanations in models in which the
neutron star crust plays an important role. We review recent work examining the
sensitivity to the slope of the symmetry energy of such models, and
constraints extracted on from confronting them with observations. We focus
on six sets of observations and proposed explanations: (i) The cooling rate of
the neutron star in Cassiopeia A, confronting cooling models which include
enhanced cooling in the nuclear pasta regions of the inner crust, (ii) the
upper limit of the observed periods of young X-ray pulsars, confronting models
of magnetic field decay in the crust caused by the high resistivity of the
nuclear pasta layer, (iii) glitches from the Vela pulsar, confronting the
paradigm that they arise due to a sudden re-coupling of the crustal neutron
superfluid to the crustal lattice after a period during which they were
decoupled due to vortex pinning, (iv) The frequencies of quasi-periodic
oscillations in the X-ray tail of light curves from giant flares from soft
gamma-ray repeaters, confronting models of torsional crust oscillations, (v)
the upper limit on the frequency to which millisecond pulsars can be spun-up
due to accretion from a binary companion, confronting models of the r-mode
instability arising above a threshold frequency determined in part by the
viscous dissipation timescale at the crust-core boundary, and (vi) the
observations of precursor electromagnetic flares a few seconds before short
gamma-ray bursts, confronting a model of crust shattering caused by resonant
excitation of a crustal oscillation mode by the tidal gravitational field of a
companion neutron star just before merger.Comment: 19 pages, 10 figure and 1 tabl
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
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