2,209 research outputs found
Dynamical approach to heavy-ion induced fission using actinide target nuclei at energies around the Coulomb barrier
In order to describe heavy-ion fusion reactions around the Coulomb barrier
with an actinide target nucleus, we propose a model which combines the
coupled-channels approach and a fluctuation-dissipation model for dynamical
calculations. This model takes into account couplings to the collective states
of the interacting nuclei in the penetration of the Coulomb barrier and the
subsequent dynamical evolution of a nuclear shape from the contact
configuration. In the fluctuation-dissipation model with a Langevin equation,
the effect of nuclear orientation at the initial impact on the prolately
deformed target nucleus is considered. Fusion-fission, quasi-fission and deep
quasi-fission are separated as different Langevin trajectories on the potential
energy surface. Using this model, we analyze the experimental data for the mass
distribution of fission fragments (MDFF) in the reactions of
S+U and Si+U at several incident energies
around the Coulomb barrier. We find that the time scale in the quasi-fission as
well as the deformation of fission fragments at the scission point are
different between the Si+U and S+U systems,
causing different mass asymmetries of the quasi-fission.Comment: 11 figure
The effect of downstream turbulent region on the spiral vortex structures of a rotating-disk flow
Attempt to Suppress Numerical Viscosity in Incompressible SPH Method
In this study, attempts to suppress numerical viscosity in incompressible smoothed particle hydrodynamics (SPH) computations are reported. Two-dimensional computations are performed for inviscid and viscous flows to evaluate the effects of numerical viscosity suppression. The first approach is to reduce numerical viscosity at the wall by considering only the wall-normal components of the forces between fluid particles and wall particles. The second approach is to reduce numerical viscosity within the flow field by employing elliptic kernel functions whose major axes are aligned with the local mean flow direction. It is found that special treatment of the wall radically reduces the numerical wall friction. Using an elliptic kernel function is found to work reasonably well in reducing numerical viscosity
Electric-field-induced lifting of the valley degeneracy in alpha-(BEDT-TTF)_2I_3 Dirac-like Landau levels
The relativistic Landau levels in the layered organic material
alpha-(BEDT-TTF)_2I_3 [BEDT-TTF=bis(ethylenedithio)tetrathiafulvalene] are
sensitive to the tilt of the Dirac cones, which, as in the case of graphene,
determine the low-energy electronic properties under appropriate pressure. We
show that an applied inplane electric field, which happens to be in competition
with the tilt of the cones, lifts the twofold valley degeneracy due to a
different level spacing. The scenario may be tested in infrared transmission
spectroscopy.Comment: 4 pages, 1 figure; version with minor corrections published in EP
The 95zr(n, gamma)96zr cross section from the surrogate ratio method and its effect on the s-process nucleosynthesis
The 95Zr(n,gamma)96Zr reaction cross section is crucial in the modelling of
s-process nucleosynthesis in asymptotic giant branch stars because it controls
the operation of the branching point at the unstable 95Zr and the subsequent
production of 96Zr. We have carried out the measurement of the 94Zr(18O,16O)
and 90Zr(18O,16O) reactions and obtained the gamma-decay probability ratio of
96Zr* and 92Zr* to determine the 95Zr(n,gamma)96Zr reaction cross sections with
the surrogate ratio method. Our deduced maxwellian-averaged cross section of
66+-16 mb at 30 keV is close to the value recommended by Bao et al. (2000), but
30% and more than a factor of two larger than the values proposed by Toukan &
Kappeler (1990) and Lugaro et al. (2014), respectively, and routinely used in
s-process models. We tested the new rate in stellar models with masses between
2 and 6 Msun and metallicities 0.014 and 0.03. The largest changes - up 80%
variations in 96Zr - are seen in models of mass 3-4 Msun, where the 22Ne
neutron source is mildly activated. The new rate can still provide a match to
data from meteoritic stardust silicon carbide grains, provided the maximum mass
of the parent stars is below 4 Msun, for a metallicity of 0.03.Comment: 10 pages, 6 figures, accepted for publication in Ap
Genetic analysis of hybrid seed formation ability of Brassica rapa in intergeneric crossings with Raphanus sativus
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