24,020 research outputs found
Monte Carlo methods and applications for the nuclear shell model
The shell-model Monte Carlo (SMMC) technique transforms the traditional
nuclear shell-model problem into a path-integral over auxiliary fields. We
describe below the method and its applications to four physics issues:
calculations of sdpf- shell nuclei, a discussion of electron-capture rates in
pf-shell nuclei, exploration of pairing correlations in unstable nuclei, and
level densities in rare earth systems.Comment: Proceedings of the Nuclear Structure '98 conference, Gatlinburg, TN,
10-15 August 199
Tapping Thermodynamics of the One Dimensional Ising Model
We analyse the steady state regime of a one dimensional Ising model under a
tapping dynamics recently introduced by analogy with the dynamics of
mechanically perturbed granular media. The idea that the steady state regime
may be described by a flat measure over metastable states of fixed energy is
tested by comparing various steady state time averaged quantities in extensive
numerical simulations with the corresponding ensemble averages computed
analytically with this flat measure. The agreement between the two averages is
excellent in all the cases examined, showing that a static approach is capable
of predicting certain measurable properties of the steady state regime.Comment: 11 pages, 5 figure
Effective diffusion constant in a two dimensional medium of charged point scatterers
We obtain exact results for the effective diffusion constant of a two
dimensional Langevin tracer particle in the force field generated by charged
point scatterers with quenched positions. We show that if the point scatterers
have a screened Coulomb (Yukawa) potential and are uniformly and independently
distributed then the effective diffusion constant obeys the
Volgel-Fulcher-Tammann law where it vanishes. Exact results are also obtained
for pure Coulomb scatterers frozen in an equilibrium configuration of the same
temperature as that of the tracer.Comment: 9 pages IOP LaTex, no figure
Farming Systems in the Central West of NSW: An Economic Analysis
The objectives of this report have been to describe important farming systems in the Central West of NSW, to gain some insights into current financial performance and to examine in more detail the role of pastures in these farming systems at a time when the profitability of wool growing has been low relative to grain growing. While farms and farming systems vary considerably across the region, a majority can be broadly grouped into a mixed livestock and cropping category. Although there is also significant variability within this category, two representative farms and farming systems were developed for the region with the assistance from a small group of farmers and extension staff from NSW Agriculture. One represents the farms and farming systems east of Condobolin and the other represents the farms and farming systems to the west of Condobolin. Whole-farm budget models have been developed for each to provide a description of the farms in this region and an indication of their current profitability. They are useful to give an indication of how farm income might be altered by the introduction of some new technology, a new enterprise such a pulse crop, or an alternative management practice. This report presents some examples of their application but importantly it has provided a template for the development of additional whole-farm budgets for alternative farming systems in this and other regions. Using the whole-farm budget representing farms east of Condobolin, and a linear programming model, PRISM Condobolin, this report shows that the optimal length of pasture is fairly insensitive to changing market signals for both cropping and livestock commodities. It also shows that although length of pasture is insensitive, the optimal mix of enterprises does change, highlighting the importance of considering the interactions between enterprises in whole-farm analysis.Industrial Organization, Production Economics,
Gamow-Teller GT+ distributions in nuclei with mass A=90-97
We investigate the Gamow-Teller strength distributions in the
electron-capture direction in nuclei having mass A=90-97, assuming a 88Sr core
and using a realistic interaction that reasonably reproduces nuclear
spectroscopy for a wide range of nuclei in the region as well as experimental
data on Gamow-Teller strength distributions. We discuss the systematics of the
distributions and their centroids. We also predict the strength distributions
for several nuclei involving stable isotopes that should be experimentally
accessible for one-particle exchange reactions in the near future.Comment: 9 pages, 10 figures (from 17 eps files), to be submitted to
Phys.Rev.C; corrected typos, minor language change
Perturbation theory for the effective diffusion constant in a medium of random scatterer
We develop perturbation theory and physically motivated resummations of the
perturbation theory for the problem of a tracer particle diffusing in a random
media. The random media contains point scatterers of density uniformly
distributed through out the material. The tracer is a Langevin particle
subjected to the quenched random force generated by the scatterers. Via our
perturbative analysis we determine when the random potential can be
approximated by a Gaussian random potential. We also develop a self-similar
renormalisation group approach based on thinning out the scatterers, this
scheme is similar to that used with success for diffusion in Gaussian random
potentials and agrees with known exact results. To assess the accuracy of this
approximation scheme its predictions are confronted with results obtained by
numerical simulation.Comment: 22 pages, 6 figures, IOP (J. Phys. A. style
Solution of large scale nuclear structure problems by wave function factorization
Low-lying shell model states may be approximated accurately by a sum over
products of proton and neutron states. The optimal factors are determined by a
variational principle and result from the solution of rather low-dimensional
eigenvalue problems. Application of this method to sd-shell nuclei, pf-shell
nuclei, and to no-core shell model problems shows that very accurate
approximations to the exact solutions may be obtained. Their energies, quantum
numbers and overlaps with exact eigenstates converge exponentially fast as the
number of retained factors is increased.Comment: 12 pages, 12 figures (from 15 eps files) include
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