2,477 research outputs found
Constraints on the Symmetry Energy Using the Mass-Radius Relation of Neutron Stars
The nuclear symmetry energy is intimately connected with nuclear
astrophysics. This contribution focuses on the estimation of the symmetry
energy from experiment and how it is related to the structure of neutron stars.
The most important connection is between the radii of neutron stars and the
pressure of neutron star matter in the vicinity of the nuclear saturation
density . This pressure is essentially controlled by the nuclear symmetry
energy parameters and , the first two coefficients of a Taylor
expansion of the symmetry energy around . We discuss constraints on these
parameters that can be found from nuclear experiments. We demonstrate that
these constraints are largely model-independent by deriving them qualitatively
from a simple nuclear model. We also summarize how recent theoretical studies
of pure neutron matter can reinforce these constraints. To date, several
different astrophysical measurements of neutron star radii have been attempted.
Attention is focused on photospheric radius expansion bursts and on thermal
emissions from quiescent low-mass X-ray binaries. While none of these
observations can, at the present time, determine individual neutron star radii
to better than 20% accuracy, the body of observations can be used with Bayesian
techniques to effectively constrain them to higher precision. These techniques
invert the structure equations and obtain estimates of the pressure-density
relation of neutron star matter, not only near , but up to the highest
densities found in neutron star interiors. The estimates we derive for neutron
star radii are in concordance with predictions from nuclear experiment and
theory.Comment: 24 pages, 13 figure
Stellar Superfluids
Neutron stars provide a fertile environment for exploring superfluidity under
extreme conditions. It is not surprising that Cooper pairing occurs in dense
matter since nucleon pairing is observed in nuclei as energy differences
between even-even and odd-even nuclei. Since superfluids and superconductors in
neutron stars profoundly affect neutrino emissivities and specific heats, their
presence can be observed in the thermal evolution of neutron stars. An
ever-growing number of cooling neutron stars, now amounting to 13 thermal
sources, and several additional objects from which upper limits to temperatures
can be ascertained, can now be used to discriminate among theoretical scenarios
and even to dramatically restrict properties of nucleon pairing at high
densities. In addition, observations of pulsars, including their spin-downs and
glitch histories, additionally support the conjecture that superfluidity and
superconductivity are ubiquitous within, and important to our understanding of,
neutron stars.Comment: 88 pages, 35 figures. Some new references added. To be published in
the book "Novel Superfluids", Eds. K. H. Bennemann and J. B. Ketterson
(Oxford University Press
A Study of the Employment Program in the Federal Bureau of Investigation
This study will examine the selection, processing and hiring of applicants for the position of Special Agent in the Federal Bureau of Investigation (FBI). Specific inquiry will be made regarding the selection, processing and hiring in an average sized mid-western field office of the FBI, between 1966 and 1976. This study is important as it examines the complete employment picture of the FBI. This analysis can reveal information which will furnish guidance in the hiring and retention of personnel
Isospin Asymmetry in Nuclei, Neutron Stars, and Heavy-Ion Collisions
The roles of isospin asymmetry in nuclei and neutron stars are investigated
using a range of potential and field-theoretical models of nucleonic matter.
The parameters of these models are fixed by fitting the properties of
homogeneous bulk matter and closed-shell nuclei. We discuss and unravel the
causes of correlations among the neutron skin thickness in heavy nuclei, the
pressure of beta-equilibrated matter at a density of 0.1 fm, and the
radii of moderate mass neutron stars. The influence of symmetry energy on
observables in heavy-ion collisions is summarized.Comment: 8 pages, 5 figures; Proceedings for the 21st Winter Workshop on
Nuclear Dynamics, Breckenridge, Colorado, February 5-12, 2005; To appear in
Heavy Ion Physic
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