2,181 research outputs found
Structure of the doublet bands in doubly odd nuclei: The case of
The structure of the doublet bands in is
investigated within the framework of the Interacting Vector Boson Fermion Model
(IVBFM). A new, purely collective interpretation of these bands is given on the
basis of the used boson-fermion dynamical symmetry of the model. The energy
levels of the doublet bands as well as the absolute and
transition probabilities between the states of both yrast and yrare bands are
described quite well. The observed odd-even staggering of both and
values is reproduced by the introduction of an appropriate interaction
term of quadrupole type, which produces such a staggering effect in the
transition strengths. The calculations show that the appearance of doublet
bands in certain odd-odd nuclei could be a consequence of the realization of a
larger dynamical symmetry based on the non-compact supersymmetry group
.Comment: 12 pages, 8 figure
Collective excitations in the Unitary Correlation Operator Method and relativistic QRPA studies of exotic nuclei
The collective excitation phenomena in atomic nuclei are studied in two
different formulations of the Random Phase Approximation (RPA): (i) RPA based
on correlated realistic nucleon-nucleon interactions constructed within the
Unitary Correlation Operator Method (UCOM), and (ii) relativistic RPA (RRPA)
derived from effective Lagrangians with density-dependent meson-exchange
interactions. The former includes the dominant interaction-induced short-range
central and tensor correlations by means of an unitary transformation. It is
shown that UCOM-RPA correlations induced by collective nuclear vibrations
recover a part of the residual long-range correlations that are not explicitly
included in the UCOM Hartree-Fock ground state. Both RPA models are employed in
studies of the isoscalar monopole resonance (ISGMR) in closed-shell nuclei
across the nuclide chart, with an emphasis on the sensitivity of its properties
on the constraints for the range of the UCOM correlation functions. Within the
Relativistic Quasiparticle RPA (RQRPA) based on Relativistic Hartree-Bogoliubov
model, the occurrence of pronounced low-lying dipole excitations is predicted
in nuclei towards the proton drip-line. From the analysis of the transition
densities and the structure of the RQRPA amplitudes, it is shown that these
states correspond to the proton pygmy dipole resonance.Comment: 15 pages, 4 figures, submitted to Physics of Atomic Nuclei,
conference proceedings, "Frontiers in the Physics of Nucleus", St.
Petersburg, 28. June-1. July, 200
Nonabelian density functional theory
Given a vector space of microscopic quantum observables, density functional
theory is formulated on its dual space. A generalized Hohenberg-Kohn theorem
and the existence of the universal energy functional in the dual space are
proven. In this context ordinary density functional theory corresponds to the
space of one-body multiplication operators. When the operators close under
commutation to form a Lie algebra, the energy functional defines a Hamiltonian
dynamical system on the coadjoint orbits in the algebra's dual space. The
enhanced density functional theory provides a new method for deriving the group
theoretic Hamiltonian on the coadjoint orbits from the exact microscopic
Hamiltonian.Comment: 1 .eps figur
Excitation of Pygmy Dipole Resonance in neutron-rich nuclei via Coulomb and nuclear fields
We study the nature of the low-lying dipole strength in neutron-rich nuclei,
often associated to the Pygmy Dipole Resonance. The states are described within
the Hartree-Fock plus RPA formalism, using different parametrizations of the
Skyrme interaction. We show how the information from combined reactions
processes involving the Coulomb and different mixtures of isoscalar and
isovector nuclear interactions can provide a clue to reveal the characteristic
features of these states.Comment: 9 Pages, 8 figures, contribution to International Symposium On
Nuclear Physics, December 8-12, 2009,Bhabha Atomic Research Centre, Mumbai,
Indi
Misleading signatures of quantum chaos
The main signature of chaos in a quantum system is provided by spectral
statistical analysis of the nearest neighbor spacing distribution and the
spectral rigidity given by . It is shown that some standard
unfolding procedures, like local unfolding and Gaussian broadening, lead to a
spurious increase of the spectral rigidity that spoils the
relationship with the regular or chaotic motion of the system. This effect can
also be misinterpreted as Berry's saturation.Comment: 4 pages, 5 figures, submitted to Physical Review
Isoscalar dipole coherence at low energies and forbidden E1 strength
In 16O and 40Ca an isoscalar, low-energy dipole transition (IS-LED)
exhausting approximately 4% of the isoscalar dipole (ISD) energy-weighted sum
rule is experimentally known, but conspicuously absent from recent theoretical
investigations of ISD strength. The IS-LED mode coincides with the so-called
isospin-forbidden E1 transition. We report that for N=Z nuclei up to 100Sn the
fully self-consistent Random-Phase-Approximation with finite-range forces,
phenomenological and realistic, yields a collective IS-LED mode, typically
overestimating its excitation energy, but correctly describing its IS strength
and electroexcitation form factor. The presence of E1 strength is solely due to
the Coulomb interaction between the protons and the resulting isospin-symmetry
breaking. The smallness of its value is related to the form of the transition
density, due to translational invariance. The calculated values of E1 and ISD
strength carried by the IS-LED depend on the effective interaction used.
Attention is drawn to the possibility that in N-not-equal-Z nuclei this
distinct mode of IS surface vibration can develop as such or mix strongly with
skin modes and thus influence the pygmy dipole strength as well as the ISD
strength function. In general, theoretical models currently in use may be unfit
to predict its precise position and strength, if at all its existence.Comment: 9 pages, 6 figures, EPJA submitte
Soft Dipole Modes in Neutron-rich Ni-isotopes in QRRPA
The soft dipole modes in neutron rich even-even Ni-isotopes are investigated
in the quasiparticle relativistic random phase approximation. We study the
evolution of strengths distribution, centroid energies of dipole excitation in
low-lying and normal GDR regions with the increase of the neutron excess. It is
found in the present study that the centroid energies of the soft dipole
strengths strongly depend on the thickness of neutron skin along with the
neutron rich even-even Ni-isotopes.Comment: 14 pages, 7 figure
The PanCam instrument on the 2018 Exomars rover: Scientific objectives
Geophysical Research Abstract
The PanCam Instrument for the ExoMars Rover
The scientific objectives of the ExoMars rover are designed to answer several key questions in the search for life on Mars. In particular, the unique subsurface drill will address some of these, such as the possible existence and stability of subsurface organics. PanCam will establish the surface geological and morphological context for the mission, working in collaboration with other context instruments. Here, we describe the PanCam scientific objectives in geology, atmospheric science, and 3-D vision. We discuss the design of PanCam, which includes a stereo pair of Wide Angle Cameras (WACs), each of which has an 11-position filter wheel and a High Resolution Camera (HRC) for high-resolution investigations of rock texture at a distance. The cameras and electronics are housed in an optical bench that provides the mechanical interface to the rover mast and a planetary protection barrier. The electronic interface is via the PanCam Interface Unit (PIU), and power conditioning is via a DC-DC converter. PanCam also includes a calibration target mounted on the rover deck for radiometric calibration, fiducial markers for geometric calibration, and a rover inspection mirror.publishersversionPeer reviewe
Application of PRo3D to Quantitative Analysis of Stereo-Imagery Collected During the Mars Utah Rover Field Investigation (MURFI) Analogue Rover Trials
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