324 research outputs found
Linear response theory in the continuum for deformed nuclei: Green's function vs. time-dependent Hartree-Fock with the absorbing-boundary condition
The continuum random-phase approximation is extended to the one applicable to
deformed nuclei. We propose two different approaches. One is based on the use
of the three dimensional (3D) Green's function and the other is the
small-amplitude TDHF with the absorbing-boundary condition. Both methods are
based on the 3D Cartesian grid representation and applicable to systems without
any symmetry on nuclear shape. The accuracy and identity of these two methods
are examined with the BKN interaction. Using the full Skyrme energy functional
in the small-amplitude TDHF approach, we study the isovector giant dipole
states in the continuum for O-16 and for even-even Be isotopes.Comment: 15 pages, 8 figure
Nuclear Excitations Described by Randomly Selected Multiple Slater Determinants
We propose a new stochastic method to describe low-lying excited states of
finite nuclei superposing multiple Slater determinants without assuming
generator coordinates a priori. We examine accuracy of our method by using
simple BKN interaction.Comment: Talk at International Symposium on Correlation Dynamics in Nuclei,
Tokyo, Japan, 31 Jan.-- 4 Feb. 200
Continuum QRPA response for deformed neutron-rich nuclei
We discuss properties of the quadrupole collective excitation of the deformed
neutron-rich nucleus Mg within the framework of quasi-particle random
phase approximation (QRPA). We first solve the coupled-channels equations to
obtain the single-particle levels, and construct the ground state by treating
the pairing correlations in the BCS approximation. We then solve the QRPA
equation using the response function formalism, by including the continuum
spectra with the box dicscretization method. We show that the collectivity of
the gamma vibration (the lowest mode) is significantly enhanced if
protons and neutrons have different deformations. We also discuss an attempt
towards full continuum QRPA calculations for deformed nuclei.Comment: 8 pages, 2 eps figures. Use espcrc1.sty. A talk given at the
International Conference on Collective Motion in Nuclei Under Extreme
Conditions (COMEX1), June 10 - 13, 2003, Paris, France. To be published in
the proceedings (Nucl. Phys. A
Microscopic Structure of High-Spin Vibrational Excitations in Superdeformed 190,192,194Hg
Microscopic RPA calculations based on the cranked shell model are performed
to investigate the quadrupole and octupole correlations for excited
superdeformed bands in 190Hg, 192Hg, and 194Hg. The K=2 octupole vibrations are
predicted to be the lowest excitation modes at zero rotational frequency. At
finite frequency, however, the interplay between rotation and vibrations
produces different effects depending on neutron number: The lowest octupole
phonon is rotationally aligned in 190Hg, is crossed by the aligned
two-quasiparticle bands in 192Hg, and retains the K=2 octupole vibrational
character up to the highest frequency in 194Hg. The gamma vibrations are
predicted to be higher in energy and less collective than the octupole
vibrations. From a comparison with the experimental dynamic moments of inertia,
a new interpretation of the observed excited bands invoking the K=2 octupole
vibrations is proposed, which suggests those octupole vibrations may be
prevalent in SD Hg nuclei.Comment: 22 pages, REVTeX, 12 postscript figures are available on reques
Nuclear charge-exchange excitations in localized covariant density functional theory
The recent progress in the studies of nuclear charge-exchange excitations
with localized covariant density functional theory is briefly presented, by
taking the fine structure of spin-dipole excitations in 16O as an example. It
is shown that the constraints introduced by the Fock terms of the relativistic
Hartree-Fock scheme into the particle-hole residual interactions are
straightforward and robust.Comment: 4 pages, 1 figure, Proceedings of INPC2013, Florence, Italy, 2-7 June
201
Self-consistent calculation of nuclear photoabsorption cross section: Finite amplitude method with Skyrme functionals in the three-dimensional real space
The finite amplitude method (FAM), which we have recently proposed (T.
Nakatsukasa, T. Inakura, and K. Yabana, Phys. Rev. C 76, 024318 (2007)),
simplifies significantly the fully self-consistent RPA calculation. Employing
the FAM, we are conducting systematic, fully self-consistent response
calculations for a wide mass region. This paper is intended to present a
computational scheme to be used in the systematic investigation and to show the
performance of the FAM for a realistic Skyrme energy functional. We implemented
the method in the mixed representation in which the forward and backward RPA
amplitudes are represented by indices of single-particle orbitals for occupied
states and the spatial grid points for unoccupied states. We solve the linear
response equation for a given frequency. The equation is a linear algebraic
problem with a sparse non-hermitian matrix, which is solved with an iterative
method. We show results of the dipole response for selected spherical and
deformed nuclei. The peak energies of the giant dipole resonance agree well
with measurements for heavy nuclei, while they are systematically
underestimated for light nuclei. We also discuss the width of the giant dipole
resonance in the fully self-consistent RPA calculation.Comment: 11 pages, 10 figure
Cytosolic chaperones influence the fate of a toxin dislocated from the endoplasmic reticulum
The plant cytotoxin ricin enters target mammalian cells by receptor-mediated endocytosis and undergoes retrograde transport to the endoplasmic reticulum (ER). Here, its catalytic A chain (RTA) is reductively separated from the cell-binding B chain, and free RTA enters the cytosol where it inactivates ribosomes. Cytosolic entry requires unfolding of RTA and dislocation across the ER membrane such that it arrives in the cytosol in a vulnerable, nonnative conformation. Clearly, for such a dislocated toxin to become active, it must avoid degradation and fold to a catalytic conformation. Here, we show that, in vitro, Hsc70 prevents aggregation of heat-treated RTA, and that RTA catalytic activity is recovered after chaperone treatment. A combination of pharmacological inhibition and cochaperone expression reveals that, in vivo, cytosolic RTA is scrutinized sequentially by the Hsc70 and Hsp90 cytosolic chaperone machineries, and that its eventual fate is determined by the balance of activities of cochaperones that regulate Hsc70 and Hsp90 functions. Cytotoxic activity follows Hsc70-mediated escape of RTA from an otherwise destructive pathway facilitated by Hsp90. We demonstrate a role for cytosolic chaperones, proteins typically associated with folding nascent proteins, assembling multimolecular protein complexes and degrading cytosolic and stalled, cotranslocational clients, in a toxin triage, in which both toxin folding and degradation are initiated from chaperone-bound states
Cytosolic chaperones influence the fate of a toxin dislocated from the endoplasmic reticulum
The plant cytotoxin ricin enters target mammalian cells by receptor-mediated endocytosis and undergoes retrograde transport to the endoplasmic reticulum (ER). Here, its catalytic A chain (RTA) is reductively separated from the cell-binding B chain, and free RTA enters the cytosol where it inactivates ribosomes. Cytosolic entry requires unfolding of RTA and dislocation across the ER membrane such that it arrives in the cytosol in a vulnerable, nonnative conformation. Clearly, for such a dislocated toxin to become active, it must avoid degradation and fold to a catalytic conformation. Here, we show that, in vitro, Hsc70 prevents aggregation of heat-treated RTA, and that RTA catalytic activity is recovered after chaperone treatment. A combination of pharmacological inhibition and cochaperone expression reveals that, in vivo, cytosolic RTA is scrutinized sequentially by the Hsc70 and Hsp90 cytosolic chaperone machineries, and that its eventual fate is determined by the balance of activities of cochaperones that regulate Hsc70 and Hsp90 functions. Cytotoxic activity follows Hsc70-mediated escape of RTA from an otherwise destructive pathway facilitated by Hsp90. We demonstrate a role for cytosolic chaperones, proteins typically associated with folding nascent proteins, assembling multimolecular protein complexes and degrading cytosolic and stalled, cotranslocational clients, in a toxin triage, in which both toxin folding and degradation are initiated from chaperone-bound states
RPA calculations with Gaussian expansion method
The Gaussian expansion method (GEM) is extensively applied to the
calculations in the random-phase approximation (RPA). We adopt the
mass-independent basis-set that has been tested in the mean-field calculations.
By comparing the RPA results with those obtained by several other available
methods for Ca isotopes, using a density-dependent contact interaction and the
Woods-Saxon single-particle states, we confirm that energies, transition
strengths and widths of their distribution are described by the GEM bases to
good precision, for the , and collective states. The GEM is
then applied to the self-consistent RPA calculations with the finite-range
Gogny D1S interaction. The spurious center-of-mass motion is well separated
from the physical states in the response, and the energy-weighted sum
rules for the isoscalar transitions are fulfilled reasonably well. Properties
of low-energy transitions in Ca are argued in some detail.Comment: 30 pages including 12 figure
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