191 research outputs found
Towards a microscopic description of the fission process
One major issue in nuclear physics is to develop a consistent model able to describe on the same footing the different aspects of the fission process, i.e. properties of the fissioning system, fission dynamics and fragment distributions. Microscopic fission studies based on the mean-field approximation are here presented
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
Structure properties of Th and Fm fission fragments: mean field analysis with the Gogny force
The constrained Hartree-Fock-Bogoliubov method is used with the Gogny
interaction D1S to calculate potential energy surfaces of fissioning nuclei
Th and Fm up to very large deformations. The
constraints employed are the mass quadrupole and octupole moments. In this
subspace of collective coordinates, many scission configurations are identified
ranging from symmetric to highly asymmetric fragmentations. Corresponding
fragment properties at scission are derived yielding fragment deformations,
deformation energies, energy partitioning, neutron binding energies at
scission, neutron multiplicities, charge polarization and total fragment
kinetic energies.Comment: 15 pages, 23 figures, accepted for publication in Phys. Rev. C (2007
Kernel Methods for Document Filtering
This paper describes the algorithms implemented by the KerMIT consortium for its participation in the Trec 2002 Filtering track. The consortium submitted runs for the routing task using a linear SVM, for the batch task using the same SVM in combination with an innovation threshold-selection mechanism, and for the adaptive task using both a second-order perceptron and a combination of SVM and perceptron with uneven margin. Results seem to indicate that these algorithm performed relatively well on the extensive TREC benchmark
Role of deformation on giant resonances within the QRPA approach and the Gogny force
Fully consistent axially-symmetric-deformed Quasi-particle Random Phase
Approximation (QRPA) calculations have been performed, in which the same Gogny
D1S effective force has been used for both the Hartree-Fock-Bogolyubov mean
field and the QRPA approaches. Giant resonances calculated in deformed
Si and Mg nuclei as well as in the spherical Si and
Mg isotopes are presented. Theoretical results for isovector-dipole and
isoscalar monopole, quadrupole, and octupole responses are presented and the
impact of the intrinsic nuclear deformation is discussed.Comment: 12 pages, 6 figures and 4 tables, accepted in PR
Fission Dynamics: The Quest of a Temperature Dependent Nuclear Viscosity
oai:ojs2.jnp.chitkara.edu.in:article/2This paper presents a journey within some open questions about the current use of a temperature dependent nuclear viscosity in models of nuclear fission and proposes an alternative experimental approach by using systems of intermediate fissility. This study is particularly relevant because: i) systems of intermediate fissility offer a suitable frame-work since the intervals between the compound nucleus and scission point temperatures with increasing excitation energy are much smaller than in the case of heavier systems, ii) the dependence of viscosity on the temperature may change with the fissility of the composite system; iii) the opportunity to measure also observables in the evaporation residues channel translates into a larger set of effective constraints for the models
Numerical search of discontinuities in self-consistent potential energy surfaces
Potential energy surfaces calculated with self-consistent mean-field methods
are a very powerful tool, since their solutions are, in theory, global minima
of the non-constrained subspace. However, this minimization leads to an
incertitude concerning the saddle points, that can sometimes be no more saddle
points in bigger constrained subspaces (fake saddle points), or can be missing
on a trajectory (it missing saddle points). These phenomena are the
consequences of discontinuities of the self-consistent potential energy
surfaces (SPES). These discontinuities may have important consequences, since
they can for example hide the real height of an energy barrier, and avoid any
use of a SPES for further dynamical calculations, barrier penetrability
estimations, or trajectory predictions. Discontinuities are not related to the
quality of the production of a SPES, since even a perfectly converged SPES with
an ideally fine mesh can be discontinuous. In this paper we explain what are
the discontinuities, their consequences, and their origins. We then propose a
numerical method to detect and identify discontinuities on a given SPES, and
finally we discuss what are the best ways to transform a discontinuous SPES
into a continuous one.Comment: 14 pages, 9 figure
A Generic Transferable EEG Decoder for Online Detection of Error Potential in Target Selection
Reliable detection of error from electroencephalography (EEG) signals as feedback while performing a discrete target selection task across sessions and subjects has a huge scope in real-time rehabilitative application of Brain-computer Interfacing (BCI). Error Related Potentials (ErrP) are EEG signals which occur when the participant observes an erroneous feedback from the system. ErrP holds significance in such closed-loop system, as BCI is prone to error and we need an effective method of systematic error detection as feedback for correction. In this paper, we have proposed a novel scheme for online detection of error feedback directly from the EEG signal in a transferable environment (i.e., across sessions and across subjects). For this purpose, we have used a P300-speller dataset available on a BCI competition website. The task involves the subject to select a letter of a word which is followed by a feedback period. The feedback period displays the letter selected and, if the selection is wrong, the subject perceives it by the generation of ErrP signal. Our proposed system is designed to detect ErrP present in the EEG from new independent datasets, not involved in its training. Thus, the decoder is trained using EEG features of 16 subjects for single-trial classification and tested on 10 independent subjects. The decoder designed for this task is an ensemble of linear discriminant analysis, quadratic discriminant analysis, and logistic regression classifier. The performance of the decoder is evaluated using accuracy, F1-score, and Area Under the Curve metric and the results obtained is 73.97, 83.53, and 73.18%, respectively
- …