6,319 research outputs found
Using datasets from the Internet for hydrological modeling: an example from the Kntnk Menderes Basin, Turkey
River basin development / Water resources / Data collection / Models / Hydrology / Land classification / Water management / Water scarcity / Water allocation / Stream flow / Water demand / Turkey / Kntnk Menderes Basin
Functional approach for pairing in finite systems: How to define restoration of broken symmetries in Energy Density Functional theory ?
The Multi-Reference Energy Density Functional (MR-EDF) approach (also called
configuration mixing or Generator Coordinate Method), that is commonly used to
treat pairing in finite nuclei and project onto particle number, is
re-analyzed. It is shown that, under certain conditions, the MR-EDF energy can
be interpreted as a functional of the one-body density matrix of the projected
state with good particle number. Based on this observation, we propose a new
approach, called Symmetry-Conserving EDF (SC-EDF), where the breaking and
restoration of symmetry are accounted for simultaneously. We show, that such an
approach is free from pathologies recently observed in MR-EDF and can be used
with a large flexibility on the density dependence of the functional.Comment: proceeding of the conference "Many body correlations from dilute to
dense Nuclear systems", Paris, February 201
Pairing dynamics in particle transport
We analyze the effect of pairing on particle transport in time-dependent
theories based on the Hartree-Fock-Bogoliubov (HFB) or BCS approximations. The
equations of motion for the HFB density matrices are unique and the theory
respects the usual conservation laws defined by commutators of the conserved
quantity with the Hamiltonian. In contrast, the theories based on the BCS
approximation are more problematic. In the usual formulation of TDHF+BCS, the
equation of continuity is violated and one sees unphysical oscillations in
particle densities. This can be ameliorated by freezing the occupation numbers
during the evolution in TDHF+BCS, but there are other problems with the BCS
that make it doubtful for reaction dynamics. We also compare different
numerical implementations of the time-dependent HFB equations. The equations of
motion for the and Bogoliubov transformations are not unique, but it
appears that the usual formulation is also the most efficient. Finally, we
compare the time-dependent HFB solutions with numerically exact solutions of
the two-particle Schrodinger equation. Depending on the treatment of the
initial state, the HFB dynamics produces a particle emission rate at short
times similar to that of the Schrodinger equation. At long times, the total
particle emission can be quite different, due to inherent mean-field
approximation of the HFB theory.Comment: 11 pages, 9 figure
Chiral two-dimensional electron gas in a periodic magnetic field
We study the energy spectrum and electronic properties of two-dimensional
electron gas in a periodic magnetic field of zero average with a symmetry of
triangular lattice. We demonstrate how the structure of electron energy bands
can be changed with the variation of the field strength, so that we can start
from nearly free electron gas and then transform it continuously to a system of
essentially localized chiral electron states. We find that the electrons near
some minima of the effective potential are responsible for occurrence of
dissipationless persistent currents creating a lattice of current contours. The
topological properties of the electron energy bands are also varied with the
intensity of periodic field. We calculated the topological Chern numbers of
several lower energy bands as a function of the field. The corresponding Hall
conductivity is nonzero and, when the Fermi level lies in the gap, it is
quantized.Comment: 10 pages;9 figures;42 reference
Transport Model Simulations of Projectile Fragmentation Reactions at 140 MeV/nucleon
The collisions in four different reaction systems using Ca and
Ni isotope beams and a Be target have been simulated using the Heavy
Ion Phase Space Exploration and the Antisymmetrized Molecular Dynamics models.
The present study mainly focuses on the model predictions for the excitation
energies of the hot fragments and the cross sections of the final fragments
produced in these reactions. The effects of various factors influencing the
final fragment cross sections, such as the choice of the statistical decay code
and its parameters have been explored. The predicted fragment cross sections
are compared to the projectile fragmentation cross sections measured with the
A1900 mass separator. At MeV, reaction dynamics can significantly
modify the detection efficiencies for the fragments and make them different
from the efficiencies applied to the measured data reported in the previous
work. The effects of efficiency corrections on the validation of event
generator codes are discussed in the context of the two models.Comment: 28 pages, 13 figure
On radiative transfer in water spray curtains using the discrete ordinates method
International audienc
Description of Pairing correlation in Many-Body finite systems with density functional theory
Different steps leading to the new functional for pairing based on natural
orbitals and occupancies proposed in ref. [D. Lacroix and G. Hupin,
arXiv:1003.2860] are carefully analyzed. Properties of quasi-particle states
projected onto good particle number are first reviewed. These properties are
used (i) to prove the existence of such a functional (ii) to provide an
explicit functional through a 1/N expansion starting from the BCS approach
(iii) to give a compact form of the functional summing up all orders in the
expansion. The functional is benchmarked in the case of the picked fence
pairing Hamiltonian where even and odd systems, using blocking technique are
studied, at various particle number and coupling strength, with uniform and
random single-particle level spacing. In all cases, a very good agreement is
found with a deviation inferior to 1% compared to the exact energy.Comment: 14 pages, 9 figure
Ordering in the pyrochlore antiferromagnet due to Dzyaloshinsky-Moriya interactions
The Heisenberg nearest neighbour antiferromagnet on the pyrochlore (3D)
lattice is highly frustrated and does not order at low temperature where
spin-spin correlations remain short ranged. Dzyaloshinsky-Moriya interactions
(DMI) may be present in pyrochlore compounds as is shown, and the consequences
of such interactions on the magnetic properties are investigated through mean
field approximation and monte carlo simulations. It is found that DMI (if
present) tremendously change the low temperature behaviour of the system. At a
temperature of the order of the DMI a phase transition to a long range ordered
state takes place. The ordered magnetic structures are explicited for the
different possible DMI which are introduced on the basis of symmetry arguments.
The relevance of such a scenario for pyrochlore compounds in which an ordered
magnetic structure is observed experimentally is dicussed
Particle-Number Restoration within the Energy Density Functional Formalism
We give a detailed analysis of the origin of spurious divergences and finite
steps that have been recently identified in particle-number restoration
calculations within the nuclear energy density functional framework. We isolate
two distinct levels of spurious contributions to the energy. The first one is
encoded in the definition of the basic energy density functional itself whereas
the second one relates to the canonical procedure followed to extend the use of
the energy density functional to multi-reference calculations. The first level
of spuriosity relates to the long-known self-interaction problem and to the
newly discussed self-pairing interaction process which might appear when
describing paired systems with energy functional methods using auxiliary
reference states of Bogoliubov or BCS type. A minimal correction to the second
level of spuriosity to the multi-reference nuclear energy density functional
proposed in [D. Lacroix, T. Duguet, M. Bender, arXiv:0809.2041] is shown to
remove completely the anomalies encountered in particle-number restored
calculations. In particular, it restores sum-rules over (positive) particle
numbers that are to be fulfilled by the particle-number-restored formalism. The
correction is found to be on the order of several hundreds of keVs up to about
1 MeV in realistic calculations, which is small compared to the total binding
energy, but often accounts for a substantial percentage of the energy gain from
particle-number restoration and is on the same energy scale as the excitations
one addresses with multi-reference energy density functional methods.Comment: 37 pages, 14 figures, accepted for publication in PR
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