1,395 research outputs found
Large-scale deformed quasiparticle random-phase approximation calculations of the -ray strength function using the Gogny force
Valuable theoretical predictions of nuclear dipole excitations in the whole
chart are of great interest for different nuclear applications, including in
particular nuclear astrophysics. Here we present large-scale calculations of
the -ray strength function obtained in the framework of the
axially-symmetric deformed QRPA based on the finite-range Gogny force. This
approach is applied to even-even nuclei, the strength function for odd nuclei
being derived by interpolation. The convergence with respect to the adopted
number of harmonic oscillator shells and the cut-off energy introduced in the
2-quasiparticle (2-) excitation space is analyzed. The calculations
performed with two different Gogny interactions, namely D1S and D1M, are
compared. A systematic energy shift of the strength is found for D1M
relative to D1S, leading to a lower energy centroid and a smaller
energy-weighted sum rule for D1M. When comparing with experimental
photoabsorption data, the Gogny-QRPA predictions are found to overestimate the
giant dipole energy by typically 2 MeV. Despite the microscopic nature of
our self-consistent Hartree-Fock-Bogoliubov plus QRPA calculation, some
phenomenological corrections need to be included to take into account the
effects beyond the standard 2- QRPA excitations and the coupling between
the single-particle and low-lying collective phonon degrees of freedom. For
this purpose, three prescriptions of folding procedure are considered and
adjusted to reproduce experimental photoabsorption data at best. All of them
are shown to lead to rather similar predictions of the strength, both at
low energies and for exotic neutron-rich nuclei. Predictions of -ray
strength functions and Maxwellian-averaged neutron capture rates for the whole
Sn isotopic chain are also discussed and compared with previous theoretical
calculations
A new inverse quasifission mechanism to produce neutron-rich transfermium nuclei
Based on time-dependent Hartree-Fock theory, a new inverse quasifission
mechanism is proposed to produce neutron-rich transfermium nuclei, in collision
of prolate deformed actinides. Calculations show that collision of the tip of
one nucleus with the side of the other results in a nucleon flux toward the
latter. The role of nucleon evaporation and impact parameter, as well as the
collision time are discussed.Comment: 8 pages, 7 figure
Glasgow University at TRECVID 2006
In the first part of this paper we describe our experiments in the automatic and interactive search tasks of TRECVID 2006. We submitted five fully automatic runs, including a text baseline, two runs based on visual features, and two runs that combine textual and visual features in a graph model. For the interactive search, we have implemented a new video search interface with relevance feedback facilities, based on both textual and visual features.
The second part is concerned with our approach to the high-level feature extraction task, based on textual information extracted from speech recogniser and machine translation outputs. They were aligned with shots and associated with high-level feature references. A list of significant words was created for each feature, and it was in turn utilised for identification of a feature during the evaluation
Global Properties of Spherical Nuclei Obtained from Hartree-Fock-Bogoliubov Calculations with the Gogny Force
Selfconsistent Hartree-Fock-Bogoliubov (HFB) calculations have been performed
with the Gogny force for nuclei along several constant Z and constant N chains,
with the purpose of extracting the macroscopic part of the binding energy using
the Strutinsky prescription. The macroscopic energy obtained in this way is
compared to current liquid drop formulas. The evolution of the single particle
levels derived from the HFB calculations along the constant Z and constant N
chains and the variations of the different kinds of nuclear radii are also
analysed. Those radii are shown to follow isospin-dependent three parameter
laws close to the phenomenological formulas which reproduce experimental data.Comment: 17 pages in LaTeX and 17 figures in eps. Phys. Rev. C, accepted for
publicatio
Structure of even-even nuclei using a mapped collective Hamiltonian and the D1S Gogny interaction
A systematic study of low energy nuclear structure at normal deformation is
carried out using the Hartree-Fock-Bogoliubov theory extended by the Generator
Coordinate Method and mapped onto a 5-dimensional collective quadrupole
Hamiltonian. Results obtained with the Gogny D1S interaction are presented from
dripline to dripline for even-even nuclei with proton numbers Z=10 to Z=110 and
neutron numbers N less than 200. The properties calculated for the ground
states are their charge radii, 2-particle separation energies, correlation
energies, and the intrinsic quadrupole shape parameters. For the excited
spectroscopy, the observables calculated are the excitation energies and
quadrupole as well as monopole transition matrix elements. We examine in this
work the yrast levels up to J=6, the lowest excited 0^+ states, and the two
next yrare 2^+ states. The theory is applicable to more than 90% of the nuclei
which have tabulated measurements. The data set of the calculated properties of
1712 even-even nuclei, including spectroscopic properties for 1693 of them, are
provided in CEA website and EPAPS repository with this article \cite{epaps}.Comment: 51 pages with 26 Figures and 4 internal tables; this version is
accepted by Physical Review
Helioseismic and Magnetic Imager observations of linear polarization from a loop prominence system
White-light observations by the Solar Dynamics Observatory's Helioseismic and
Magnetic Imager of a loop-prominence system occurring in the aftermath of an
X-class flare on 2013 May 13 near the eastern solar limb show a linearly
polarized component, reaching up to 20% at an altitude of 33 Mm,
about the maximal amount expected if the emission were due solely to Thomson
scattering of photospheric light by the coronal material. The mass associated
with the polarized component was 8.210 g. At 15 Mm altitude, the
brightest part of the loop was 3(+/-0.5)% linearly polarized, only about 20% of
that expected from pure Thomson scattering, indicating the presence of an
additional unpolarized component at wavelengths near Fe I (617.33 nm), probably
thermal emission. We estimated the free electron density of the white-light
loop system to possibly be as high as 1.810 cm.Comment: 9 pages, 5 figure
Sea lice exposure to non-lethal levels of emamectin benzoate after treatments: a potential risk factor for drug resistance
The avermectin derivative emamectin benzoate (EMB) has been widely used by salmon industries around the world to control sea lice infestations. Resistance to this anti-parasitic drug is also commonly reported in these industries. The objective of this study was to quantify the number of sea lice potentially exposed to sub-lethal concentrations of EMB while fish clear the drug after treatments. We assessed juvenile sea lice abundance after 38 EMB treatments on six Atlantic salmon farms, in a small archipelago in British Colombia, Canada, between 2007 and 2018. We fitted a standard EMB pharmacokinetic curve to determine the time when fish treated with this product would have EMB tissue concentrations below the recommended target therapeutic level. During the study, we estimated that for each sea lice treatment there was, on average, an abundance of 0.12 juvenile sea lice per fish during the time period when the concentrations of EMB would have been lower than 60ppb, the recommended therapeutic treatment level for sea lice. The findings from this study on metaphylactic anti-parasitic treatments identify a potential driver for drug resistance in sea lice that should be further explored
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