3,903 research outputs found
Collapse of the random phase approximation: examples and counter-examples from the shell model
The Hartree-Fock approximation to the many-fermion problem can break exact
symmetries, and in some cases by changing a parameter in the interaction one
can drive the Hartree-Fock minimum from a symmetry-breaking state to a
symmetry-conserving state (also referred to as a ``phase transition'' in the
literature). The order of the transition is important when one applies the
random phase approximation (RPA) to the of the Hartree-Fock wavefunction: if
first order, RPA is stable through the transition, but if second-order, then
the RPA amplitudes become large and lead to unphysical results. The latter is
known as ``collapse'' of the RPA. While the difference between first- and
second-order transitions in the RPA was first pointed out by Thouless, we
present for the first time non-trivial examples of both first- and second-order
transitions in a uniform model, the interacting shell-model, where we can
compare to exact numerical results.Comment: 8 pages, 7 figure
Reduction of the spin-orbit potential in light drip-line nuclei
The isospin dependence of the spin-orbit interaction in light neutron rich
nuclei is investigated in the framework of relativistic mean field theory. The
magnitude of the spin-orbit potential is considerably reduced in drip line
nuclei, resulting in smaller energy splittings between spin-orbit partners. The
effect does not depend on the parametrization of the effective Lagrangian. The
results are compared with corresponding calculations in the non-relativistic
Skyrme model.Comment: 8 Pages, LateX, 4 P.S. Figures, submit. Phys. Lett.
Surface-peaked effective mass in the nuclear energy density functional and its influence on single-particle spectra
Calculations for infinite nuclear matter with realistic nucleon-nucleon
interactions suggest that the isoscalar effective mass of a nucleon at the
saturation density, m*/m, equals 0.8 +/- 0.1. This result is at variance with
empirical data on the level density in finite nuclei, which are consistent with
m*/m ~ 1. Ma and Wambach suggested that these two contradicting results may be
reconciled within a single theoretical framework by assuming a radial-dependent
effective mass, peaked at the nuclear surface. The aim of this exploratory work
is to investigate this idea within the density functional theory by using a
Skyrme-type local functional enriched with new terms, and , where and
denote the kinetic and particle densities, respectively. We show that each of
these terms can give rise to a surface peak in the effective mass, but of a
limited height. We investigate the influence of the radial profile of the
effective mass on the spin-orbit splittings and centroids. In particular, we
demonstrate that the term quenches the 1f5/2-1f7/2
splitting in 40Ca, which is strongly overestimated within conventional Skyrme
parametrizations.Comment: 8 pages, 8 figures, submitted to Phys. Rev.
Monopole giant resonances and nuclear compressibility in relativistic mean field theory
Isoscalar and isovector monopole oscillations that correspond to giant
resonances in spherical nuclei are described in the framework of time-dependent
relativistic mean-field (RMF) theory. Excitation energies and the structure of
eigenmodes are determined from a Fourier analysis of dynamical monopole moments
and densities. The generator coordinate method, with generating functions that
are solutions of constrained RMF calculations, is also used to calculate
excitation energies and transition densities of giant monopole states.
Calculations are performed with effective interactions which differ in their
prediction of the nuclear matter compression modulus K_nm. Both time-dependent
and constrained RMF results indicate that empirical GMR energies are best
reproduced by an effective force with K_nm \approx 270 MeV.Comment: 30 pages of LaTeX, 18 PS-figure
Manual of Criminal Law and Procedure
Intended to aid to Alaska law enforcement officers in the performance of their duties in the field, this manual was designed to provide brief, quick access to major points of substantive and procedural criminal law. The manual contained discussion and procedural guidelines for investigatory stops, identification procedures including line-ups, arrest, search and seizure, interrogation, as well as discussion of justification for the use of nondeadly and deadly force whether by peace officers or civilians, culpability, entrapment, trial preparation, and media relations. The section on substantive criminal law deals with a selection of crimes most likely to be encountered by "street" officers as defined with the recently enacted Revised Alaska Criminal Code (effective January 1, 1980), desribing elements of each crime, investigative hints, and differences with previous provisions of the criminal code, where relevant.Alaska Department of Law
Grant No. 78-A-014Introduction / Criminal Procedures / Substantive Criminal Law / Justification / Culpability / Entrapment / Trial Preparation / Media Relations / Appendice
Relativistic Hartree-Bogoliubov theory in coordinate space: finite element solution for a nuclear system with spherical symmetry
A C++ code for the solution of the relativistic Hartree-Bogoliubov theory in
coordinate space is presented. The theory describes a nucleus as a relativistic
system of baryons and mesons. The RHB model is applied in the self-consistent
mean-field approximation to the description of ground state properties of
spherical nuclei. Finite range interactions are included to describe pairing
correlations and the coupling to particle continuum states. Finite element
methods are used in the coordinate space discretization of the coupled system
of Dirac-Hartree-Bogoliubov integro-differential eigenvalue equations, and
Klein-Gordon equations for the meson fields. The bisection method is used in
the solution of the resulting generalized algebraic eigenvalue problem, and the
biconjugate gradient method for the systems of linear and nonlinear algebraic
equations, respectively.Comment: PostScript, 32 pages, to be published in Computer Physics
Communictions (1997
On the Thermodynamic Limit of the Lipkin Model
The thermodynamic limit of the Lipkin model is investigated. While the limit
turns out to be rather elusive, the analysis gives strong indications that the
limit yields two analytically dissociated operators, one for the normal and one
for the deformed phase. While the Lipkin Hamiltonian is hermitian and has a
second order phase transition in finite dimensions (finite particle number),
both properties seem to be destroyed in the thermodynamic limit.Comment: 9 pages, 3 figures to appear in JPhys
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