3,201 research outputs found
Dynamics of many-particle fragmentation in a Cellular Automaton model
A 3D Cellular Automaton model developed by the authors to deal with the
dynamics of N-body interactions has been adapted to investigate the head-on
collision of two identical bound clusters of particles, and the ensuing process
of fragmentation. The range of impact energies is chosen low enough, to secure
that a compound bound cluster can be formed. The model is devised to simulate
the laboratory set-up of fragmentation experiments as monitored by 4pi
detectors. The particles interact via a Lennard-Jones potential. At low impact
energies the numerical experiments following the dynamics of the individual
particles indicate a phase of energy sharing among all the particles of the
compound cluster. Fragments of all sizes are then found to evaporate from the
latter cluster. The cluster sizes, measured in our set-up by simulated 4pi
detectors, conform to a power law of exponent around 2.6.Comment: 27 pages, 10 figures, submitted to Phys. Rev.
Phase space characteristics of fragmenting nuclei described as excited disordered systems
We investigate the thermodynamical content of a cellular model which
describes nuclear fragmentation as a process taking place in an excited
disordered system. The model which reproduces very well the size distribution
of fragments does not show the existence of a first order phase transition.Comment: 14 pages, TeX type, 7 figure
Microscopic three-body force for asymmetric nuclear matter
Brueckner calculations including a microscopic three-body force have been
extended to isospin asymmetric nuclear matter. The effects of the three-body
force on the equation of state and on the single-particle properties of nuclear
matter are discussed with a view to possible applications in nuclear physics
and astrophysics. It is shown that, even in the presence of the three-body
force, the empirical parabolic law of the energy per nucleon vs isospin
asymmetry is fulfilled in the whole asymmetry range
up to high densities. The three-body force provides a strong
enhancement of symmetry energy increasing with the density in good agreement
with relativistic approaches. The Lane's assumption that proton and neutron
mean fields linearly vary vs the isospin parameter is violated at high density
in the presence of the three-body force. Instead the momentum dependence of the
mean fields is rather insensitive to three body force which brings about a
linear isospin deviation of the neutron and proton effective masses. The
isospin effects on multifragmentation events and collective flows in heavy-ion
collisions are briefly discussed along with the conditions for direct URCA
processes to occur in the neutron-star cooling.Comment: 11 pages, 7 figure
Reading bodies: A case study analysis of adolescent girls\u27 experiences in an after school book group
In this study, adolescent female readers participated in an after-school literature based discussion group or Book Group as we came to call it, reading contemporary young adult novels that deal with issues of the body. The purpose of this study was to examine the adolescent girls\u27 experiences within the literature discussions, as most studies relating to literature circle discussions, book clubs, or book groups do not focus on the students\u27 experiences. A related purpose of the study was to investigate how literature based discussion groups reflect and reveal readers\u27 own identities as well as dominant social discourse about issues of femininity. This study was grounded in several areas of research into best practices in adolescent literacy as well as evolving theories on adolescent bodies as sites inscribed by power, culture, and gender. Findings for the study revealed multiple aspects of girls\u27 reading and gendered identities as well as issues of conflict within the readers regarding issues related to the body and their appearance
Nuclear Matter EOS with a Three-body Force
The effect of a microscopic three-body force on the saturation properties of
nuclear matter is studied within the Brueckner-Hartree-Fock approach. The
calculations show a decisive improvement of the saturation density along with
an overall agreement with the empirical saturation point. With the three-body
force the symmetry energy turns more rapidly increasing with density, which
allows for the direct URCA process to occur in -stable neutron star
matter. The influence of the three-body force on the nuclear mean field does
not diminish the role of the ground state correlations.Comment: 10 pages, 2 figure
Automated Determination of Stellar Parameters from Simulated Dispersed Images for DIVA
We have assessed how well stellar parameters (T_eff, logg and [Fe/H]) can be
retrieved from low-resolution dispersed images to be obtained by the DIVA
satellite. Although DIVA is primarily an all-sky astrometric mission, it will
also obtain spectrophotometric information for about 13 million stars
(operational limiting magnitude V ~ 13.5 mag). Constructional studies foresee a
grating system yielding a dispersion of ~200nm/mm on the focal plane (first
spectral order). For astrometric reasons there will be no cross dispersion
which results in the overlapping of the first to third diffraction orders. The
one-dimensional, position related intensity function is called a DISPI
(DISPersed Intensity). We simulated DISPIS from synthetic spectra (...) for a
limited range of metallicites i.e. our results are for [Fe/H] in the range -0.3
to 1 dex. We show that there is no need to deconvolve these low resolution
signals in order to obtain basic stellar parameters. Using neural network
methods and by including simulated data of DIVA's UV telescope, we can
determine T_eff to an average accuracy of about 2% for DISPIS from stars with
2000 K < T_eff < 20000 K and visual magnitudes of V=13 mag (end of mission
data). logg can be determined for all temperatures with an accuracy better than
0.25 dex for magnitudes brighter than V=12 mag. For low temperature stars with
2000 K < T_eff < 5000 K and for metallicities in the range -0.3 to +1 dex a
determination of [Fe/H] is possible (to better than 0.2 dex) for these
magnitudes. Additionally we examined the effects of extinction E(B-V) on DISPIS
and found that it can be determined to better than 0.07 mag for magnitudes
brighter than V=14 mag if the UV information is included.Comment: 12 pages, 8 figures, Accepted for publication in A&
Multi-Objective Probabilistically Constrained Programming with Variable Risk: New Models and Applications
We consider a class of multi-objective probabilistically constrained problems MOPCP with a joint chance constraint, a multi-row random technology matrix, and a risk parameter (i.e., the reliability level) defined as a decision variable. We propose a Boolean modeling framework and derive a series of new equivalent mixed-integer programming formulations. We demonstrate the computational efficiency of the formulations that contain a small number of binary variables. We provide modeling insights pertaining to the most suitable reformulation, to the trade-off between the conflicting cost/revenue and reliability objectives, and to the scalarization parameter determining the relative importance of the objectives. Finally, we propose several MOPCP variants of multi-portfolio financial optimization models that implement a downside risk measure and can be used in a centralized or decentralized investment context. We study the impact of the model parameters on the portfolios, show, via a cross-validation study, the robustness of the proposed models, and perform a comparative analysis of the optimal investment decisions
Interplay of Three-Body Interactions in the EOS of Nuclear Matter
The equation of state of symmetric nuclear matter has been investigated
within Brueckner approach adopting the charge-dependent Argonne
two-body force plus a microscopic three-body force based on a meson-exchange
model. The effects on the equation of state of the individual processes giving
rise to the three-body force are explored up to high baryonic density. It is
found that the major role is played by the competition between the strongly
repulsive exchange term with virtual nucleon-antinucleon
excitation and the large attractive contribution due to
exchange with resonance excitation. The net result is a repulsive
term which shifts the saturation density corresponding to the only two-body
force much closer to the empirical value, while keeping constant the saturation
energy per particle. The contribution from exchange 3BF is shown
to be attractive and rather small. The analysis of the separate three-body
force contributions allows to make a comparison with the prediction of
Dirac-Brueckner approach which is supposed to incorporate via the {\it dressed}
Dirac spinors the same virtual nucleon-antinucleon excitations as in the
present three-body force. The numerical results suggest that the three-body
force components missing from the Dirac-Brueckner approach are not negligible,
especially at high density. The calculation of the nuclear mean field and the
effective mass shows that the three-body force affects to a limited extent such
properties.Comment: 12 pages 7 figure
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