arXiv subjects

B. Liu

Publications and source records attributed to B. Liu.

119 records · Page 7Linked to original sources

arXiv2009

Vacuum fluctuation effects on asymmetric nuclear matter

The vacuum fluctuation (VF) effects on asymmetric nuclear matter are investigated. Masses of nucleons and mesons are modified in the nuclear medium by calculating the loop-diagram corrections and the density dependence of hadron masses is obtained. The relativistic Lagrangian density with the isovector scalar $δ$ meson is used to calculate the nuclear equation of state (EOS) in the framework of the relativistic mean-field (RMF) approach, the effects of the in-medium hadron masses on the properties of neutron stars are finally studied. With the inclusion of the VF corrections, the nuclear EOS becomes softer and the neutron star masses are reduced.

hep-ph↗

arXiv2008

How to compute the atomic stress objectively?

Atomistic simulation has been a powerful study tool in mechanics research, but how to objectively compute the atomic stress equivalent to Cauchy stress is still controversial, especially on the velocity-related part in the virial stress definition. In this paper, by strictly following the classical definition of the Cauchy stress for continuum medium, the fundamental Lagrangian atomic stress is proposed and can be used to obtain the correct Cauchy stress under any circumstances. Furthermore, the Lagrangian virial stress is proposed, which is still in virial form but does not include velocities to avoid controversial velocity treatments. It is also found that the widely used classical virial stress is actually the Eulerian virial stress, which includes the velocities of atoms, and is valid only when the impulse-momentum theorem is applicable to estimate the internal forces. However this requirement for the Eulerian atomic stress can not always be met in practical cases, such as the material volume element in rotation and the examples presented in this paper, but the proposed Lagrangian atomic stress can avoid these velocity-related nonobjectivities.

physics.comp-ph↗

arXiv2007

Application of density dependent parametrization models to asymmetric nuclear matter

Density dependent parametrization models of the nucleon-meson effective couplings, including the isovector scalar δ-field, are applied to asymmetric nuclear matter. The nuclear equation of state and the neutron star properties are studied in an effective Lagrangian density approach, using the relativistic mean field hadron theory. It is known that the introduction of a δ-meson in the constant coupling scheme leads to an increase of the symmetry energy at high density and so to larger neutron star masses, in a pure nucleon-lepton scheme. We use here a more microscopic density dependent model of the nucleon-meson couplings to study the properties of neutron star matter and to re-examine the δ-field effects in asymmetric nuclear matter. Our calculations show that, due to the increase of the effective δcoupling at high density, with density dependent couplings the neutron star masses in fact can be even reduced.

nucl-th↗

arXiv2005

Neutron stars with isovector scalar correlations

Neutron stars with the isovector scalar $δ$-field are studied in the framework of the relativistic mean field ($RMF$) approach in a pure nucleon plus lepton scheme. The $δ$-field leads to a larger repulsion in dense neutron-rich matter and to a definite splitting of proton and neutron effective masses. Both features are influencing the stability conditions of the neutron stars. Two parametrizations for the effective nonlinear Lagrangian density are used to calculate the nuclear equation of state ($EOS$) and the neutron star properties, and compared to correlated Dirac-Brueckner results. We conclude that in order to reproduce reasonable nuclear structure and neutron star properties within a $RMF$ approach a density dependence of the coupling constants is required.

nucl-th↗

arXiv2003

Fine-Grained Authorization for Job Execution in the Grid: Design and Implementation

In this paper we describe our work on enabling fine-grained authorization for resource usage and management. We address the need of virtual organizations to enforce their own polices in addition to those of the resource owners, in regard to both resource consumption and job management. To implement this design, we propose changes and extensions to the Globus Toolkit's version 2 resource management mechanism. We describe the prototype and the policy language that we designed to express fine-grained policies, and we present an analysis of our solution.

cs.CR↗

arXiv2003

Two-Body Dirac Equations from Relativistic Constraint Dynamics with Applications to QED and QCD Bound-States and to N-N Scattering

The formulation of relativistic two-body bound state wave equations and the study of their relationship to quantum field theory began with work by Eddington and Gaunt in 1928. However, the large variety of approaches attempted in recent years shows that this problem still has no generally agreed-upon solution. We describe here a recent approach resulting from " Two-Body Dirac Equations" (emerging from Dirac's Relativistic Constraint Dynamics) that satisfies many of the requirements one would demand of a treatment of the relativistic two-body problem. We use its applications to QED bound states such as positronium, QCD quarkonia, and the nucleon-nucleon scattering problem to demonstrate the advantages of the approach.

hep-ph↗

arXiv2003

Fine-Grained Authorization for Job and Resource Management Using Akenti and the Globus Toolkit

As the Grid paradigm is adopted as a standard way of sharing remote resources across organizational domains, the need for fine-grained access control to these resources increases. This paper presents an authorization solution for job submission and control, developed as part of the National Fusion Collaboratory, that uses the Globus Toolkit 2 and the Akenti authorization service in order to perform fine-grained authorization of job and resource management requests in a Grid environment. At job startup, it allows the system to evaluate a user's Resource Specification Language request against authorization policies on resource usage (determining how many CPUs or memory a user can use on a given resource or which executables the user can run). Furthermore, based on authorization policies, it allows other virtual organization members to manage the user's job.

cs.DC↗

arXiv2003

Dynamic Nonlinear Effect on Lasing in a Random Medium

We have studied the dynamic effect of nonlinearity on lasing in disordered medium. The third-order nonlinearity not only changes the frequency and size of lasing modes, but also modifies the laser emission intensity and laser pulse width. When the nonlinear response time is comparable to or longer than the lifetime of the lasing mode, the nonlinearity changes the laser output through modifying the size of the lasing mode. When the nonlinear response is much faster than the buildup of the lasing mode, positive nonlinearity always extracts more laser emission from the random medium due to the enhancement of single particle scattering.

cond-mat.dis-nn↗

arXiv2002

Influence of the Preparation Process on Microstructure, Critical Current Density and Tc of MgB2 Powder-In-Tube Wires

MgB2 wires and tapes suffer from a limitation of the transport current densities, especially at low field, due to an unsufficient thermal stabilization caused by hot spots from a non-homogeneous microstructure, the presence of secondary phases and voids. For the preparation of MgB2 wires and tapes two different precursor routes, using MgB2 (ex-situ process) or Mg + B (in-situ process) are applied. The in-situ approach allows variation of many parameters in the wire preparation and the improvement of this approach is the central topic of this paper. We present an improved in-situ approach, the characterization of the filament microstructure, effects from stoichiometry and the corresponding superconducting properties. The transport current capability of such in-situ wires could be improved to the level of the reference ex-situ wires.

cond-mat.supr-con↗

arXiv2001

Asymmetric nuclear matter:the role of the isovector scalar channel

We try to single out some qualitative new effects of the coupling to the $δ$-isovector-scalar meson introduced in a minimal way in a phenomenological hadronic field theory. Results for the equation of state ($EOS$) and the phase diagram of asymmetric nuclear matter ($ANM$) are discussed. We stress the consistency of the $δ$-coupling introduction in a relativistic approach. New contributions to the slope and curvature of the symmetry energy and the neutron-proton effective mass splitting appear particularly interesting. A more repulsive $EOS$ for neutron matter at high baryon densities is expected. Effects on new critical properties of warm $ANM$, mixing of mechanical and chemical instabilities and isospin distillation, are also presented. The $δ$ influence is mostly on the {\it isovectorlike} collective response. The results are largely analytical and this makes the physical meaning quite transparent. Implications for nuclear structure properties of drip-line nuclei and for reaction dynamics with Radioactive Beams are finally pointed out.

nucl-th↗

arXiv1999

Mass formulas and thermodynamic treatment in the mass-density-dependent model of strange quark matter

The previous treatments for strange quark matter in the quark mass-density-dependent model have unreasonable vacuum limits. We provide a method to obtain the quark mass parametrizations and give a self-consistent thermodynamic treatment which includes the MIT bag model as an extreme. In this treatment, strange quark matter in bulk still has the possibility of absolute stability. However, the lower density behavior of the sound velocity is opposite to previous findings.

hep-ph↗