87 research outputs found
Isovector part of nuclear energy density functional from chiral two- and three-nucleon forces
A recent calculation of the nuclear energy density functional from chiral
two- and three-nucleon forces is extended to the isovector terms pertaining to
different proton and neutron densities. An improved density-matrix expansion is
adapted to the situation of small isospin-asymmetries and used to calculate in
the Hartree-Fock approximation the density-dependent strength functions
associated with the isovector terms. The two-body interaction comprises of
long-range multi-pion exchange contributions and a set of contact terms
contributing up to fourth power in momenta. In addition, the leading order
chiral three-nucleon interaction is employed with its parameters fixed in
computations of nuclear few-body systems. With this input one finds for the
asymmetry energy of nuclear matter the value MeV,
compatible with existing semi-empirical determinations. The strength functions
of the isovector surface and spin-orbit coupling terms come out much smaller
than those of the analogous isoscalar coupling terms and in the relevant
density range one finds agreement with phenomenological Skyrme forces. The
specific isospin- and density-dependences arising from the chiral two- and
three-nucleon interactions can be explored and tested in neutron-rich systems.Comment: 14 pages, 7 figures, to be published in European Physical Journal
Nature of Sonoluminescence: Noble Gas Radiation Excited by Hot Electrons in "Cold" Water
We show that strong electric fields occurring in water near the surface of
collapsing gas bubbles because of the flexoelectric effect can provoke dynamic
electric breakdown in a micron-size region near the bubble and consider the
scenario of the SBSL. The scenario is: (i) at the last stage of incomplete
collapse of the bubble the gradient of pressure in water near the bubble
surface has such a value and sign that the electric field arising from the
flexoelectric effect exceeds the threshold field of the dynamic electrical
breakdown of water and is directed to the bubble center; (ii) mobile electrons
are generated because of thermal ionization of water molecules near the bubble
surface; (iii) these electrons are accelerated in ''cold'' water by the strong
electric fields; (iv) these hot electrons transfer noble gas atoms dissolved in
water to high-energy excited states and optical transitions between these
states produce SBSL UV flashes in the trasparency window of water; (v) the
breakdown can be repeated several times and the power and duration of the UV
flash are determined by the multiplicity of the breakdowns. The SBSL spectrum
is found to resemble a black-body spectrum where temperature is given by the
effective temperature of the hot electrons. The pulse energy and some other
characteristics of the SBSL are found to be in agreement with the experimental
data when realistic estimations are made.Comment: 11 pages (RevTex), 1 figure (.ps
The three-dimensional Anderson model of localization with binary random potential
We study the three-dimensional two-band Anderson model of localization and
compare our results to experimental results for amorphous metallic alloys
(AMA). Using the transfer-matrix method, we identify and characterize the
metal-insulator transitions as functions of Fermi level position, band
broadening due to disorder and concentration of alloy composition. The
appropriate phase diagrams of regions of extended and localized electronic
states are studied and qualitative agreement with AMA such as Ti-Ni and Ti-Cu
metallic glasses is found. We estimate the critical exponents nu_W, nu_E and
nu_x when either disorder W, energy E or concentration x is varied,
respectively. All our results are compatible with the universal value nu ~ 1.6
obtained in the single-band Anderson model.Comment: 9 RevTeX4 pages with 11 .eps figures included, submitted to PR
The Role of Radioactivities in Astrophysics
I present both a history of radioactivity in astrophysics and an introduction
to the major applications of radioactive abundances to astronomy
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MLNSC instrument design and simulation package, task order 57 (modified). Final report, September 30, 1997
The objectives of this task as described in Statement of Work have been met and the documents required as Deliverables have been prepared and submitted to the requester. Specifically, a document titled ``The MCLIB Library: Monte Carlo Simulation of Neutron Scattering Instruments,`` revised September 23, 1997, includes documentation of new standards, code revisions and additions, and some improved efficiency due to improved optimization strategies. The procedures for user implementation of new optical devices, and information on using the package and reading and viewing the output have also been included. Second, a new document entitled ``MCLIB Element Definitions and Help`` was written and revised through the duration of the task, to supply the needed input to group CIC-15 for the purpose of integrating the MCLIB package with a web-based user interface. Finally, an application of the package was presented and a (successful) demonstration of the new user interface was given at a workshop at Argonne National Laboratory, August 24--26, 1997, as described in the modification to the Statement of Work
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The MCLIB library: Monte Carlo simulation of neutron scattering instruments
Monte Carlo is a method to integrate over a large number of variables. Random numbers are used to select a value for each variable, and the integrand is evaluated. The process is repeated a large number of times and the resulting values are averaged. For a neutron transport problem, first select a neutron from the source distribution, and project it through the instrument using either deterministic or probabilistic algorithms to describe its interaction whenever it hits something, and then (if it hits the detector) tally it in a histogram representing where and when it was detected. This is intended to simulate the process of running an actual experiment (but it is much slower). This report describes the philosophy and structure of MCLIB, a Fortran library of Monte Carlo subroutines which has been developed for design of neutron scattering instruments. A pair of programs (LQDGEOM and MC{_}RUN) which use the library are shown as an example
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The MCLIB library: New features
This report describes the philosophy and structure of MCLIB, A Fortran library of Monte Carlo subroutines which has been developed to test designs of neutron scattering instruments. Emphasis is placed on new features added to the library since the previous presentation of MCLIB at ICANS-XIII in October, 1995. These new features include toroidal mirrors, writing and reading source files, splitting and banking of histories, and a Maxwellian probability distribution. The only change of a program structure has been to include charge and polarization vector in the description of a particle. The latest release of the source code and documentation may be obtained by anonymous ftp. Work is also continuing on a more friendly web-based user interface, and user input is requested for additional features to be added to the library
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