8,992 research outputs found
Microscopic description of neutron emission rates in compound nuclei
The neutron emission rates in thermal excited nuclei are conventionally
described by statistical models with a phenomenological level density parameter
that depends on excitation energies, deformations and mass regions. In the
microscopic view of hot nuclei, the neutron emission rates can be determined by
the external neutron gas densities without any free parameters. Therefore the
microscopic description of thermal neutron emissions is desirable that can
impact several understandings such as survival probabilities of superheavy
compound nuclei and neutron emissivity in reactors.
To describe the neutron emission rates microscopically, the external thermal
neutron gases are self-consistently obtained based on the Finite-Temperature
Hartree-Fock-Bogoliubov (FT-HFB) approach. The results are compared with the
statistical model to explore the connections between the FT-HFB approach and
the statistical model.
The Skyrme FT-HFB equation is solved by HFB-AX in deformed coordinate spaces.
Based on the FT-HFB approach, the thermal properties and external neutron gas
are properly described with the self-consistent gas substraction procedure.
Then neutron emission rates can be obtained based on the densities of external
neutron gases.
The thermal statistical properties of U and U are studied in
detail in terms of excitation energies. The thermal neutron emission rates in
U and superheavy compound nuclei Cn and
Fl are calculated, which agree well with the statistical model by
adopting an excitation-energy-dependent level density parameter.
The coordinate-space FT-HFB approach can provide reliable microscopic
descriptions of neutron emission rates in hot nuclei, as well as microscopic
constraints on the excitation energy dependence of level density parameters for
statistical models.Comment: 6 pages, 5 figures, revised and accepted for PR
Towards microscopic studies of survival probabilities of compound superheavy nuclei
The microscopic approach of fission rates and neutron emission rates in
compound nuclei have been applied to No and Cn. The microscopic
framework is based on the finite-temperature Skyrme-Hartree-Fock+BCS
calculations, in which the fission barriers and mass parameters are
self-consistently temperature dependent. The fission rates from low to high
temperatures can be obtained based on the imaginary free energy method. The
neutron emission rates are obtained with neutron gases at surfaces. Finally the
survival probabilities of superheavy nuclei can be calculated microscopically.
The microscopic approach has been compared with the widely used statistical
models. Generally, there are still large uncertainties in descriptions of
fission rates.Comment: 9 pages,7 figures, accepted for Physica Scripta Special Issu
A Refined Holographic QCD Model and QCD Phase Structure
We consider the Einstein-Maxwell-dilaton system with an arbitrary kinetic
gauge function and a dilaton potential. A family of analytic solutions is
obtained by the potential reconstruction method. We then study its holographic
dual QCD model. The kinetic gauge function can be fixed by requesting the
linear Regge spectrum of mesons. We calculate the free energy to obtain the
phase diagram of the holographic QCD model.Comment: 21 pages, 17 figures. arXiv admin note: substantial text overlap with
arXiv:1301.038
Confinement-Deconfinment Phase Transition for Heavy Quarks
We study confinement-deconfinement phase transition for heavy quarks in a
bottom-up holographic QCD model. We consider a black hole background in an
Einstein-Maxwell-scalar system and add probe open strings to the background.
Combining the various configurations of the open strings and the phase
structure of the black hole background itself, we obtain the
confinement-deconfinement phase diagram for heavy quarks in the holographic QCD
model.Comment: 23 pages, 14 figures, published in JHEP. arXiv admin note: text
overlap with arXiv:1301.038
Topological phase transition in the quench dynamics of a one-dimensional Fermi gas
We study the quench dynamics of a one-dimensional ultracold Fermi gas in an
optical lattice potential with synthetic spin-orbit coupling. At equilibrium,
the ground state of the system can undergo a topological phase transition and
become a topological superfluid with Majorana edge states. As the interaction
is quenched near the topological phase boundary, we identify an interesting
dynamical phase transition of the quenched state in the long-time limit,
characterized by an abrupt change of the pairing gap at a critical quenched
interaction strength. We further demonstrate the topological nature of this
dynamical phase transition from edge-state analysis of the quenched states. Our
findings provide interesting clues for the understanding of topological phase
transitions in dynamical processes, and can be useful for the dynamical
detection of Majorana edge states in corresponding systems.Comment: 7 pages, 5 figure
Does a change in debt structure matter in earnings management? the application of nonlinear panel threshold test
In this study, we apply Hansen¡¦s (1999) nonlinear panel threshold test, the most powerful test of its kind, to investigate the relationship between debt ratio and earnings management of 474 selected Taiwan-listed companies during the September 2002 - June 2005 period. Rather than a fixed positive relation that is determined from the OLS, our empirical results strongly suggest that when a firm¡¦s debt ratio exceeds 46.79% and 62.17%, its debt structure changes, which in turn leads to changes in earnings management. With an increase in debt ratio, managers tend to manage earnings to a greater extent and at a higher speed. In other words, the threshold effect of debt on the relationship between debt ratio and earnings management generates an increasingly positive impact. These empirical results provide concerned investors and authorities with an enhanced understanding of earnings management, as manipulated by managers confronted with different debt structures.
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