1,331 research outputs found
Temperature effects on the nuclear symmetry energy and symmetry free energy with an isospin and momentum dependent interaction
Within a self-consistent thermal model using an isospin and momentum
dependent interaction (MDI) constrained by the isospin diffusion data in
heavy-ion collisions, we investigate the temperature dependence of the symmetry
energy and symmetry free energy for hot,
isospin asymmetric nuclear matter. It is shown that the symmetry energy
generally decreases with increasing temperature while the
symmetry free energy exhibits opposite temperature
dependence. The decrement of the symmetry energy with temperature is
essentially due to the decrement of the potential energy part of the symmetry
energy with temperature. The difference between the symmetry energy and
symmetry free energy is found to be quite small around the saturation density
of nuclear matter. While at very low densities, they differ significantly from
each other. In comparison with the experimental data of temperature dependent
symmetry energy extracted from the isotopic scaling analysis of intermediate
mass fragments (IMF's) in heavy-ion collisions, the resulting density and
temperature dependent symmetry energy is then used to
estimate the average freeze-out density of the IMF's.used to estimate the
average freeze-out density of the IMF's.Comment: 9 pages, 7 figures, 1 figure added to show the temperature dependence
of the potential and kinetic parts of the symmetry energy. Revised version to
appear in PR
Quantitative spectroscopic analysis of heterogeneous mixtures: the correction of multiplicative effects caused by variations in physical properties of samples
Spectral measurements of complex heterogeneous types of mixture samples are often affected by significant multiplicative effects resulting from light scattering, due to physical variations (e.g. particle size and shape, sample packing and sample surface, etc.) inherent within the individual samples. Therefore, the separation of the spectral contributions due to variations in chemical compositions from those caused by physical variations is crucial to accurate quantitative spectroscopic analysis of heterogeneous samples. In this work, an improved strategy has been proposed to estimate the multiplicative parameters accounting for multiplicative effects in each measured spectrum, and hence mitigate the detrimental influence of multiplicative effects on the quantitative spectroscopic analysis of heterogeneous samples. The basic assumption of the proposed method is that light scattering due to physical variations has the same effects on the spectral contributions of each of the spectroscopically active chemical component in the same sample mixture. Based on this underlying assumption, the proposed method realizes the efficient estimation of the multiplicative parameters by solving a simple quadratic programming problem. The performance of the proposed method has been tested on two publicly available benchmark data sets (i.e. near-infrared total diffuse transmittance spectra of four-component suspension samples and near infrared spectral data of meat samples) and compared with some empirical approaches designed for the same purpose. It was found that the proposed method provided appreciable improvement in quantitative spectroscopic analysis of heterogeneous mixture samples. The study indicates that accurate quantitative spectroscopic analysis of heterogeneous mixture samples can be achieved through the combination of spectroscopic techniques with smart modeling methodology
Nuclear symmetry potential in the relativistic impulse approximation
Using the relativistic impulse approximation with the Love-Franey \textsl{NN}
scattering amplitude developed by Murdock and Horowitz, we investigate the
low-energy (100 MeV MeV) behavior of the nucleon
Dirac optical potential, the Schr\"{o}dinger-equivalent potential, and the
nuclear symmetry potential in isospin asymmetric nuclear matter. We find that
the nuclear symmetry potential at fixed baryon density decreases with
increasing nucleon energy. In particular, the nuclear symmetry potential at
saturation density changes from positive to negative values at nucleon kinetic
energy of about 200 MeV. Furthermore,the obtained energy and density dependence
of the nuclear symmetry potential is consistent with those of the isospin- and
momentum-dependent MDI interaction with , which has been found to describe
reasonably both the isospin diffusion data from heavy-ion collisions and the
empirical neutron-skin thickness of Pb.Comment: 8 pages, 5 figures, revised version to appear in PR
Differential isospin-fractionation in dilute asymmetric nuclear matter
The differential isospin-fractionation (IsoF) during the liquid-gas phase
transition in dilute asymmetric nuclear matter is studied as a function of
nucleon momentum. Within a self-consistent thermal model it is shown that the
neutron/proton ratio of the gas phase becomes {\it smaller} than that of the
liquid phase for energetic nucleons, although the gas phase is overall more
neutron-rich. Clear indications of the differential IsoF consistent with the
thermal model predictions are demonstrated within a transport model for
heavy-ion reactions. Future comparisons with experimental data will allow us to
extract critical information about the momentum dependence of the isovector
strong interaction.Comment: Rapid Communication, Phys. Rev. C (2007) in pres
NUCLEAR CONSTRAINTS ON PROPERTIES OF NEUTRON STAR CRUSTS
The transition density and pressure at the inner edge
separating the liquid core from the solid crust of neutron stars are
systematically studied using a modified Gogny (MDI) and 47 popular Skyrme
interactions within well established dynamical and thermodynamical methods. It
is shown that the widely used parabolic approximation to the full Equation of
State (EOS) of isospin asymmetric nuclear matter may lead to huge errors in
estimating the \rho_{t} and P_{t}, especially for stiffer symmetry energy
functionals . The \rho_{t} and P_{t} decrease roughly linearly
with the increasing slope parameter of the using the full
EOS within both methods. It is also shown that the thickness, fractional mass
and moment of inertia of neutron star crust are all very sensitive to the
parameter through the . Moreover, it is shown that the
constrained in the same sub-saturation density range as the
neutron star crust by the isospin diffusion data in heavy-ion collisions at
intermediate energies limits the transition density and pressure to 0.040
fm^-3}< \rho_{t} < 0.065 fm^-3 and 0.01 MeV/fm^3 < P_{t} < 0.26\rho_tP_t\Delta I/I>0.014RM$ of neutron stars.Comment: 55 pages, 20 figures, 2 tables, new results and discussions added,
accepted version to appear in Ap
Prognosticators and Risk Grouping in Patients with Lung Metastasis from Nasopharyngeal Carcinoma: A more accurate and appropriate assessment of prognosis
<p>Abstract</p> <p>Background</p> <p>Lung metastases arising from nasopharyngeal carcinomas (NPC) have a relatively favourable prognosis. The purpose of this study was to identify the prognostic factors and to establish a risk grouping in patients with lung metastases from NPC.</p> <p>Methods</p> <p>A total of 198 patients who developed lung metastases from NPC after primary therapy were retrospectively recruited from January 1982 to December 2000. Univariate and multivariate analyses of clinical variables were performed using Cox proportional hazards regression models. Actuarial survival rates were plotted against time using the Kaplan-Meier method, and log-rank testing was used to compare the differences between the curves.</p> <p>Results</p> <p>The median overall survival (OS) period and the lung metastasis survival (LMS) period were 51.5 and 20.9 months, respectively. After univariate and multivariate analyses of the clinical variables, age, T classification, N classification, site of metastases, secondary metastases and disease-free interval (DFI) correlated with OS, whereas age, VCA-IgA titre, number of metastases and secondary metastases were related to LMS. The prognoses of the low- (score 0-1), intermediate- (score 2-3) and high-risk (score 4-8) subsets based on these factors were significantly different. The 3-, 5- and 10-year survival rates of the low-, intermediate- and high-risk subsets, respectively (P < 0.001) were as follows: 77.3%, 60% and 59%; 52.3%, 30% and 27.8%; and 20.5%, 7% and 0%.</p> <p>Conclusions</p> <p>In this study, clinical variables provided prognostic indicators of survival in NPC patients with lung metastases. Risk subsets would help in a more accurate assessment of a patient's prognosis in the clinical setting and could facilitate the establishment of patient-tailored medical strategies and supports.</p
Effects of isospin and momentum dependent interactions on liquid-gas phase transition in hot asymmetric nuclear matter
The liquid-gas phase transition in hot neutron-rich nuclear matter is
investigated within a self-consistent thermal model using an isospin and
momentum dependent interaction (MDI) constrained by the isospin diffusion data
in heavy-ion collisions, a momentum-independent interaction (MID), and an
isoscalar momentum-dependent interaction (eMDYI). The boundary of the
phase-coexistence region is shown to be sensitive to the density dependence of
the nuclear symmetry energy with a softer symmetry energy giving a higher
critical pressure and a larger area of phase-coexistence region. Compared with
the momentum-independent MID interaction, the isospin and momentum-dependent
MDI interaction is found to increase the critical pressure and enlarge the area
of phase-coexistence region. For the isoscalar momentum-dependent eMDYI
interaction, a limiting pressure above which the liquid-gas phase transition
cannot take place has been found and it is shown to be sensitive to the
stiffness of the symmetry energy.Comment: 6 pages, 4 figures, revised version, to appear in PL
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