670 research outputs found
Large-space shell-model calculations for light nuclei
An effective two-body interaction is constructed from a new Reid-like
potential for a large no-core space consisting of six major shells and is used
to generate the shell-model properties for light nuclei from =2 to 6. (For
practical reasons, the model space is partially truncated for =6.) Binding
energies and other physical observables are calculated and compare favorably
with experiment.Comment: prepared using LaTex, 21 manuscript pages, no figure
Nuclear shell-model calculations for 6Li and 14N with different NN potentials
Two ``phase-shift equivalent'' local NN potentials with different
parametrizations, Reid93 and NijmII, which were found to give nearly identical
results for the triton by Friar et al, are shown to yield remarkably similar
results for 6Li and 14N in a (0+2)hw no-core space shell-model calculation. The
results are compared with those for the widely used Hamada-Johnson hard-core
and the original Reid soft-core potentials, which have larger deuteron D-state
percentages. The strong correlation between the tensor strength and the nuclear
binding energy is confirmed. However, many nuclear-structure properties seem to
be rather insensitive to the details of the NN potential and, therefore, cannot
be used to test various NN potentials. (Submitted to Phys. Rev. C on Nov. 9,
1993 as a Brief Report.)Comment: 12 text pages and 1 figure (Figure available upon request),
University of Arizona Physics Preprint (Number not yet assigned
Simple approximation for the starting-energy-independent two-body effective interaction with applications to 6Li
We apply the Lee-Suzuki iteration method to calculate the linked-folded
diagram series for a new Nijmegen local NN potential. We obtain an exact
starting-energy-independent effective two-body interaction for a multi-shell,
no-core, harmonic-oscillator model space. It is found that the resulting
effective-interaction matrix elements can be well approximated by the Brueckner
G-matrix elements evaluated at starting energies selected in a simple way.
These starting energies are closely related to the energies of the initial
two-particle states in the ladder diagrams. The ``exact'' and approximate
effective interactions are used to calculate the energy spectrum of 6Li in
order to test the utility of the approximate form.Comment: 15 text pages and 2 PostScript figures (available upon request).
University of Arizona preprint, Number unassigne
Chemistry and structure of BaTiO3 ultra-thin films grown by different O2 plasma power
International audienceWe present a study of the chemical and atomic properties of 5 nm TiO2-terminated BaTiO3 (001) epitaxialfilms on Nb-doped SrTiO3, as a function of the atomic oxygen plasma power for film growth. Lowerplasma power produces non-stoichiometric films with oxygen vacancies and Ti3+ ions. The larger Ti3+ion radius and the in-plane clamping gives rise to an increase in the out-of-plane lattice parameter.XPS measures the Ti3+ concentration and the concomitant increase in dissociative water uptake in thefilm, giving rise to on-top OH adsorption on surface Ti, proton adsorption on surface oxygen, and a nearsurface Ba-OH environment
The alpha-particle based on modern nuclear forces
The Faddeev-Yakubovsky equations for the alpha-particle are solved. Accurate
results are obtained for several modern NN interaction models, which include
charge-symmetry breaking effects in the NN force, nucleon mass dependences as
well as the Coulomb interaction. These models are augmented by three-nucleon
forces of different types and adjusted to the 3N binding energy. Our results
are close to the experimental binding energy with a slight overbinding. Thus
there is only little room left for the contribution of possible 4N interactions
to the alpha-particle binding energy. We also discuss model dependences of the
binding energies and the wave functions.Comment: 22 pages REVTeX 4, 12 figures, table with TM parameters added, typos
corrected, version as published in PR
Spurious states in the Faddeev formalism for few-body systems
We discuss the appearance of spurious solutions of few-body equations for
Faddeev amplitudes. The identification of spurious states, i.e., states that
lack the symmetry required for solutions of the Schroedinger equation, as well
as the symmetrization of the Faddeev equations is investigated. As an example,
systems of three and four electrons, bound in a harmonic-oscillator potential
and interacting by the Coulomb potential, are presented.Comment: 11 pages. REVTE
An evaluation of the stimulants and impediments to innovation within PFI/PPP projects
This paper identifies the theoretical stimulants and impediments associated with the implementation of PFI/PPP (Private Finance Initiative/Public Private Partnership) projects. A current defect of this procurement approach is the unintentional constraint upon the innovations incorporated into the development of PFI projects. A critical evaluation of the published literature has been utilized to synthesize a theoretical model. The paper proposes a theoretical model for the identification of potential innovation stimulants and impediments within this type of procurement. This theoretical model is then utilised to evaluate four previously completed PFI projects. These project case-studies have been examined in detail. The evaluation demonstrates how ineffective current procedures are. The application of this model before project letting could eliminate unintentional constraints and stimulate improved innovation within the process. The implementation of the model could improve the successful delivery of innovation within the entire PFI/PPP procurement process
TomograPy: A Fast, Instrument-Independent, Solar Tomography Software
Solar tomography has progressed rapidly in recent years thanks to the
development of robust algorithms and the availability of more powerful
computers. It can today provide crucial insights in solving issues related to
the line-of-sight integration present in the data of solar imagers and
coronagraphs. However, there remain challenges such as the increase of the
available volume of data, the handling of the temporal evolution of the
observed structures, and the heterogeneity of the data in multi-spacecraft
studies.
We present a generic software package that can perform fast tomographic
inversions that scales linearly with the number of measurements, linearly with
the length of the reconstruction cube (and not the number of voxels) and
linearly with the number of cores and can use data from different sources and
with a variety of physical models: TomograPy
(http://nbarbey.github.com/TomograPy/), an open-source software freely
available on the Python Package Index. For performance, TomograPy uses a
parallelized-projection algorithm. It relies on the World Coordinate System
standard to manage various data sources. A variety of inversion algorithms are
provided to perform the tomographic-map estimation. A test suite is provided
along with the code to ensure software quality. Since it makes use of the
Siddon algorithm it is restricted to rectangular parallelepiped voxels but the
spherical geometry of the corona can be handled through proper use of priors.
We describe the main features of the code and show three practical examples
of multi-spacecraft tomographic inversions using STEREO/EUVI and STEREO/COR1
data. Static and smoothly varying temporal evolution models are presented.Comment: 21 pages, 6 figures, 5 table
Three-dimensional random Voronoi tessellations: From cubic crystal lattices to Poisson point processes
We perturb the SC, BCC, and FCC crystal structures with a spatial Gaussian noise whose adimensional strength is controlled by the parameter a, and analyze the topological and metrical properties of the resulting Voronoi Tessellations (VT). The topological properties of the VT of the SC and FCC crystals are unstable with respect to the introduction of noise, because the corresponding polyhedra are geometrically degenerate, whereas the tessellation of the BCC crystal is topologically stable even against noise of small but finite intensity. For weak noise, the mean area of the perturbed BCC and FCC crystals VT increases quadratically with a. In the case of perturbed SCC crystals, there is an optimal amount of noise that minimizes the mean area of the cells. Already for a moderate noise (a>0.5), the properties of the three perturbed VT are indistinguishable, and for intense noise (a>2), results converge to the Poisson-VT limit. Notably, 2-parameter gamma distributions are an excellent model for the empirical of of all considered properties. The VT of the perturbed BCC and FCC structures are local maxima for the isoperimetric quotient, which measures the degre of sphericity of the cells, among space filling VT. In the BCC case, this suggests a weaker form of the recentluy disproved Kelvin conjecture. Due to the fluctuations of the shape of the cells, anomalous scalings with exponents >3/2 is observed between the area and the volumes of the cells, and, except for the FCC case, also for a->0. In the Poisson-VT limit, the exponent is about 1.67. As the number of faces is positively correlated with the sphericity of the cells, the anomalous scaling is heavily reduced when we perform powerlaw fits separately on cells with a specific number of faces
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