2,394 research outputs found
Density slope of the nuclear symmetry energy from the neutron skin thickness of heavy nuclei
Expressing explicitly the parameters of the standard Skyrme interaction in
terms of the macroscopic properties of asymmetric nuclear matter, we show in
the Skyrme-Hartree-Fock approach that unambiguous correlations exist between
observables of finite nuclei and nuclear matter properties. We find that
existing data on neutron skin thickness of Sn isotopes give an
important constraint on the symmetry energy and its
density slope at saturation density . Combining these
constraints with those from recent analyses of isospin diffusion and double
neutron/proton ratio in heavy-ion collisions at intermediate energies leads to
a more stringent limit on approximately independent of . The implication of these new constraints on the of
Pb as well as the core-crust transition density and pressure in neutron
stars is discussed.Comment: 18 pages, 9 figures, 1 table. Significantly expanded to include a
number of details and discussions. Title shortened. Accepted version to
appear in PR
Isospin- and momentum-dependent effective interactions for the baryon octet and the properties of hybrid stars
The isospin- and momentum-dependent MDI interaction, which has been
extensively used in intermediate-energy heavy-ion reactions to study the
properties of asymmetric nuclear matter, is extended to include the
nucleon-hyperon and hyperon-hyperon interactions by assuming same density,
momentum and isospin dependence as for the nucleon-nucleon interaction. The
parameters in these interactions are determined from the empirical hyperon
single-particle potentials in symmetric nuclear matter at saturation density.
The extended MDI interaction is then used to study in the mean-field
approximation the equation of state of hypernuclear matter and also the
properties of hybrid stars by including the phase transition from the
hypernuclear matter to the quark matter at high densities. In particular, the
effects of attractive and repulsive N interactions and different values
of symmetry energies on the hybrid star properties are investigated.Comment: 13 pages, 12 figures, version to appear in Phys. Rev.
Effects of momentum-dependent nuclear potential on two-nucleon correlation functions and light cluster production in intermediate energy heavy-ion collisions
Using an isospin- and momentum-dependent transport model, we study the
effects due to the momentum dependence of isoscalar nuclear potential as well
as that of symmetry potential on two-nucleon correlation functions and light
cluster production in intermediate energy heavy-ion collisions induced by
neutron-rich nuclei. It is found that both observables are affected
significantly by the momentum dependence of nuclear potential, leading to a
reduction of their sensitivity to the stiffness of nuclear symmetry energy.
However, the t/He ratio remains a sensitive probe of the density
dependence of nuclear symmetry energy.Comment: 20 pages, 11 figure
Probing the equation of state of neutron-rich matter with intermediate energy heavy-ion collisions
Nuclear reactions induced by stable and/or radioactive neutron-rich nuclei
provide the opportunity to pin down the equation of state of neutron-rich
matter, especially the density () dependence of its isospin-dependent
part, i.e., the nuclear symmetry energy . A conservative
constraint, , around the nuclear matter saturation density has
recently been obtained from the isospin diffusion data in intermediate energy
heavy-ion collisions. We review this exciting result and discuss its
consequences and implications on nuclear effective interactions, radii and
cooling mechanisms of neutron stars.Comment: 10 pages. Invited talks at (1) International Workshop on Nuclear
Multifragmentation, Nov. 28-Dec. 1, 2005, Catania, Italy and (2) XXIX
Symposium on Nuclear Physics, Jan. 3-6, 2006, Cocoyoc, Morelos, Mexic
High-energy behavior of the nuclear symmetry potential in asymmetric nuclear matter
Using the relativistic impulse approximation with empirical NN scattering
amplitude and the nuclear scalar and vector densities from the relativistic
mean-field theory, we evaluate the Dirac optical potential for neutrons and
protons in asymmetric nuclear matter. From the resulting Schr\"{o}%
dinger-equivalent potential, the high energy behavior of the nuclear symmetry
potential is studied. We find that the symmetry potential at fixed baryon
density is essentially constant once the nucleon kinetic energy is greater than
about 500 MeV. Moreover, for such high energy nucleon, the symmetry potential
is slightly negative below a baryon density of about fm
and then increases almost linearly to positive values at high densities. Our
results thus provide an important constraint on the energy and density
dependence of nuclear symmetry potential in asymmetric nuclear matter.Comment: 6 pages, 5 figures, revised version, to appear in PR
Probing isospin- and momentum-dependent nuclear effective interactions in neutron-rich matter
The single-particle potentials for nucleons and hyperons in neutron-rich
matter generally depends on the density and isospin asymmetry of the medium as
well as the momentum and isospin of the particle. It further depends on the
temperature of the matter if the latter is in thermal equilibrium. We review
here the extension of a Gogny-type isospin- and momentum-dependent interaction
in several aspects made in recent years and their applications in studying
intermediate-energy heavy ion collisions, thermal properties of asymmetric
nuclear matter and properties of neutron stars. The importance of the isospin-
and momentum-dependence of the single-particle potential, especially the
momentum dependence of the isovector potential, is clearly revealed throughout
these studies.Comment: 27 pages, 19 figures, 1 table, accepted version to appear in EPJA
special volume on Nuclear Symmetry Energ
Test on Existence of Histology Subtype-Specific Prognostic Signatures Among Early Stage Lung Adenocarcinoma and Squamous Cell Carcinoma Patients Using a Cox-Model Based Filter
BACKGROUND: Non-small cell lung cancer (NSCLC) is the predominant histological type of lung cancer, accounting for up to 85% of cases. Disease stage is commonly used to determine adjuvant treatment eligibility of NSCLC patients, however, it is an imprecise predictor of the prognosis of an individual patient. Currently, many researchers resort to microarray technology for identifying relevant genetic prognostic markers, with particular attention on trimming or extending a Cox regression model. Adenocarcinoma (AC) and squamous cell carcinoma (SCC) are two major histology subtypes of NSCLC. It has been demonstrated that fundamental differences exist in their underlying mechanisms, which motivated us to postulate the existence of specific genes related to the prognosis of each histology subtype.
RESULTS: In this article, we propose a simple filter feature selection algorithm with a Cox regression model as the base. Applying this method to real-world microarray data identifies a histology-specific prognostic gene signature. Furthermore, the resulting 32-gene (32/12 for AC/SCC) prognostic signature for early-stage AC and SCC samples has superior predictive ability relative to two relevant prognostic signatures, and has comparable performance with signatures obtained by applying two state-of-the art algorithms separately to AC and SCC samples.
CONCLUSIONS: Our proposal is conceptually simple, and straightforward to implement. Furthermore, it can be easily adapted and applied to a range of other research settings.
REVIEWERS: This article was reviewed by Leonid Hanin (nominated by Dr. Lev Klebanov), Limsoon Wong and Jun Yu
Shear viscosity of neutron-rich nucleonic matter near its liquid-gas phase transition
Within a relaxation time approach using free nucleon-nucleon cross sections
modified by the in-medium nucleon masses that are determined from an isospin-
and momentum-dependent effective nucleon-nucleon interaction, we investigate
the specific shear viscosity () of neutron-rich nucleonic matter near
its liquid-gas phase transition. It is found that as the nucleonic matter is
heated at fixed pressure or compressed at fixed temperature, its specific shear
viscosity shows a valley shape in the temperature or density dependence, with
the minimum located at the boundary of the phase transition. Moreover, the
value of drops suddenly at the first-order liquid-gas phase transition
temperature, reaching as low as times the KSS bound of .
However, it varies smoothly for the second-order liquid-gas phase transition.
Effects of the isospin degree of freedom and the nuclear symmetry energy on the
value of are also discussed.Comment: 6 pages, 5 figure
Energy dependence of pion in-medium effects on \pi^-/\pi^+ ratio in heavy-ion collisions
Within the framework of a thermal model with its parameters fitted to the
results from an isospin-dependent Boltzmann-Uehling-Uhlenbeck (IBUU) transport
model, we study the pion in-medium effect on the charged-pion ratio in
heavy-ion collisions at various energies. We find that due to the cancellation
between the effects from pion-nucleon s-wave and p-wave interactions in nuclear
medium, the \pi^-/\pi^+ ratio generally decreases after including the pion
in-medium effect. The effect is larger at lower collision energies as a result
of narrower pion spectral functions at lower temperatures.Comment: 4 pages, 4 figures, 1 table, minor modifications, version to appear
in Physical Review
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