710 research outputs found
A geometric model of a V-slit Sun sensor correcting for spacecraft wobble
A V-Slit sun sensor is body-mounted on a spin-stabilized spacecraft. During injection from a parking or transfer orbit to some final orbit, the spacecraft may not be dynamically balanced. This may result in wobble about the spacecraft spin axis as the spin axis may not be aligned with the spacecraft's axis of symmetry. While the widely used models in Spacecraft Attitude Determination and Control, edited by Wertz, correct for separation, elevation, and azimuthal mounting biases, spacecraft wobble is not taken into consideration. A geometric approach is used to develop a method for measurement of the sun angle which corrects for the magnitude and phase of spacecraft wobble. The algorithm was implemented using a set of standard mathematical routines for spherical geometry on a unit sphere
Information entropy as a measure of the quality of a nuclear density distribution
The information entropy of a nuclear density distribution is calculated for a
number of nuclei. Various phenomenological models for the density distribution
using different geometry are employed. Nuclear densities calculated within
various microscopic mean field approaches are also employed. It turns out that
the entropy increases on going from crude phenomenological models to more
sophisticated (microscopic) ones. It is concluded that the larger the
information entropy, the better the quality of the nuclear density
distribution. An alternative approach is also examined: the net information
content i.e. the sum of information entropies in position and momentum space
. It is indicated that is a maximum, when the best
fit to experimental data of the density and momentum distributions is attained.Comment: 12 pages, LaTex, no figures, Int. J. of Mod. Phys. E in pres
Temperature induced shell effects in deformed nuclei
The thermal evolution of the shell correction energy is investigated for
deformed nuclei using Strutinsky prescription in a self-consistent relativistic
mean-field framework. For temperature independent single-particle states
corresponding to either spherical or deformed nuclear shapes, the shell
correction energy steadily washes out with temperature. However,
for states pertaining to the self-consistent thermally evolving shapes of
deformed nuclei, the dual role played by the single-particle occupancies in
diluting the fluctuation effects from the single-particle spectra and in
driving the system towards a smaller deformation is crucial in determining
at moderate temperatures. In rare earth nuclei, it is found that
builds up strongly around the shape transition temperature; for
lighter deformed nuclei like and , this is relatively less
prominent.Comment: 6 pages revtex file + 4 ps files for figures, Phys. Rev. C (in press
Relativistic Mean Field Approach and the Pseudo-Spin Symmetry
Based on the Relativistic Mean Field (RMF) approach the existence of the
broken pseudo-spin symmetry is investigated. Both spherical RMF and constrained
deformed RMF calculations are carried out employing realistic Lagrangian
parameters for spherical and for deformed sample nuclei. The quasi - degenerate
pseudo-spin doublets are confirmed to exist near the fermi surface for both
spherical and deformed nuclei.Comment: 9 pages RevTex, 4 p.s figures, to appear in Phys. Rev. C as R.
Alpha-decay chains of and in the Relativistic Mean Field theory
In the recent experiments designed to synthesize the element 115 in the
Am+Ca reaction at Dubna in Russia, three similar decay chains
consisting of five consecutive -decays, and another different decay
chain of four consecutive -decays are detected, and the decay
properties of these synthesized nuclei are claimed to be consistent with
consecutive -decays originating from the parent isotopes of the new
element 115, and , respectively\cite{ogan.03}. Here in
the present work, the recently developed deformed RMF+BCS method with a
density-independent delta-function interaction in the pairing channel is
applied to the analysis of these newly synthesized superheavy nuclei
, , and their -decay daughter nuclei. The
calculated -decay energies and half-lives agree well with the
experimental values and with those of the macroscopic-microscopic FRDM+FY and
YPE+WS models. In the mean field Lagrangian, the TMA parameter set is used.
Particular emphasis is paid on the influence to both the ground-state
properties and energy surfaces introduced by different treatments of pairing.
Two different effective interactions in the particle-particle channel, i.e.,
the constant pairing and the density-independent delta-function interaction,
together with the blocking effect are discussed in detail.Comment: 17 pages, 5 figure
Covariant response theory beyond RPA and its application
The covariant particle-vibration coupling model within the time blocking
approximation is employed to supplement the Relativistic Random Phase
Approximation (RRPA) with coupling to collective vibrations. The Bethe-Salpeter
equation in the particle-hole channel with an energy dependent residual
particle-hole (p-h) interaction is formulated and solved in the shell-model
Dirac basis as well as in the momentum space. The same set of the coupling
constants generates the Dirac-Hartree single-particle spectrum, the static part
of the residual p-h interaction and the particle-phonon coupling amplitudes.
This approach is applied to quantitative description of damping phenomenon in
even-even spherical nuclei with closed shells Pb and Sn. Since
the phonon coupling enriches the RRPA spectrum with a multitude of
phphonon states a noticeable fragmentation of giant monopole and
dipole resonances is obtained in the examined nuclei. The results are compared
with experimental data and with results of the non-relativistic approach.Comment: 12 pages, 4 figures, Proceedings of the NSRT06 Conferenc
Relativistic Hartree-Bogoliubov Approach for Nuclear Matter with Non-Linear Coupling Terms
We investigate the pairing property of nuclear matter with Relativistic
Hartree-Bogoliubov(RHB) approach. Recently, the RHB approach has been widely
applied to nuclear matter and finite nuclei. We have extended the RHB approach
to be able to include non-linear coupling terms of mesons. In this paper we
apply it to nuclear matter and observe the effect of non-linear terms on
pairing gaps.Comment: 13 pages, 5 figure
Generator Coordinate Truncations
We investigate the accuracy of several schemes to calculate ground-state
correlation energies using the generator coordinate technique. Our test-bed for
the study is the interacting boson model, equivalent to a 6-level
Lipkin-type model. We find that the simplified projection of a triaxial
generator coordinate state using the subgroup of the rotation group is
not very accurate in the parameter space of the Hamiltonian of interest. On the
other hand, a full rotational projection of an axial generator coordinate state
gives remarkable accuracy. We also discuss the validity of the simplified
treatment using the extended Gaussian overlap approximation (top-GOA), and show
that it works reasonably well when the number of boson is four or larger.Comment: 19 pages, 6 eps figure
The structure of superheavy elements newly discovered in the reaction of Kr with Pb
The structure of superheavy elements newly discovered in the
Pb(Kr,n) reaction at Berkeley is systematically studied in the
Relativistic Mean Field (RMF) approach. It is shown that various usually
employed RMF forces, which give fair description of normal stable nuclei, give
quite different predictions for superheavy elements. Among the effective forces
we tested, TM1 is found to be the good candidate to describe superheavy
elements. The binding energies of the 118 nucleus and its
decay daughter nuclei obtained using TM1 agree with those of FRDM
within 2 MeV. Similar conclusion that TM1 is the good interaction is also drawn
from the calculated binding energies for Pb isotopes with the Relativistic
Continuum Hartree Bogoliubov (RCHB) theory. Using the pairing gaps obtained
from RCHB, RMF calculations with pairing and deformation are carried out for
the structure of superheavy elements. The binding energy, shape, single
particle levels, and the Q values of the decay are
discussed, and it is shown that both pairing correlation and deformation are
essential to properly understand the structure of superheavy elements. A good
agreement is obtained with experimental data on . %Especially, the
atomic number %dependence of %seems to match with the experimental
observationComment: 19 pages, 5 figure
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