19,614 research outputs found
Shell-model study of the N=82 isotonic chain with a realistic effective hamiltonian
We have performed shell-model calculations for the even- and odd-mass N=82
isotones, focusing attention on low-energy states. The single-particle energies
and effective two-body interaction have been both determined within the
framework of the time-dependent degenerate linked-diagram perturbation theory,
starting from a low-momentum interaction derived from the CD-Bonn
nucleon-nucleon potential. In this way, no phenomenological input enters our
effective Hamiltonian, whose reliability is evidenced by the good agreement
between theory and experiment.Comment: 7 pages, 11 figures, 3 tables, to be published in Physical Review
Design of a digital controller for spinning flexible spacecraft
An approach to digital control system design is applied to the analysis and design of a practical onboard digital attitude control system for a class of spinning vehicles characterized by a rigid body and two connected flexible appendages. The approach used is to design a continuous-data control system that will provide a satisfactory system response. Then, using the digital redesign method, a digital controller with onboard digital computer is designed to provide a digital control system whose states are similar to those of the continuous system at sampling instants. The simplicity of application of this approach is indicated by example. The example, using spinning Skylab parameters, is used to substantiate the conclusions
Three-body monopole corrections to the realistic interactions
It is shown that a very simple three-body monopole term can solve practically
all the spectroscopic problems--in the , and shells--that were
hitherto assumed to need drastic revisions of the realistic potentials.Comment: 4 pages, 5figure
Low momentum nucleon-nucleon potential and shell model effective interactions
A low momentum nucleon-nucleon (NN) potential V-low-k is derived from meson
exhange potentials by integrating out the model dependent high momentum modes
of V_NN. The smooth and approximately unique V-low-k is used as input for shell
model calculations instead of the usual Brueckner G matrix. Such an approach
eliminates the nuclear mass dependence of the input interaction one finds in
the G matrix approach, allowing the same input interaction to be used in
different nuclear regions. Shell model calculations of 18O, 134Te and 135I
using the same input V-low-k have been performed. For cut-off momentum Lambda
in the vicinity of 2 fm-1, our calculated low-lying spectra for these nuclei
are in good agreement with experiments, and are weakly dependent on Lambda.Comment: 5 pages, 5 figure
Study of the ground-state energy of 40Ca with the CD-Bonn nucleon-nucleon potential
We have calculated the ground-state energy of the doubly-magic nucleus 40Ca
within the framework of the Goldstone expansion using the CD-Bonn
nucleon-nucleon potential. The short-range repulsion of this potential has been
renormalized by integrating out its high-momentum components so as to derive a
low-momentum potential V-low-k defined up to a cutoff momentum Lambda. A simple
criterion has been employed to establish a connection between this cutoff
momentum and the size of the two-nucleon model space in the harmonic oscillator
basis. This model-space truncation approach provides a reliable way to
renormalize the free nucleon-nucleon potential preserving its many-body
physics. The role of the 3p-3h and 4p-4h excitations in the description of the
ground state of 40Ca is discussed.Comment: 4 pages, 1 figure, 1 table, to be published in Physical Review
Variational Principle for Mixed Classical-Quantum Systems
An extended variational principle providing the equations of motion for a
system consisting of interacting classical, quasiclassical and quantum
components is presented, and applied to the model of bilinear coupling. The
relevant dynamical variables are expressed in the form of a quantum state
vector which includes the action of the classical subsystem in its phase
factor. It is shown that the statistical ensemble of Brownian state vectors for
a quantum particle in a classical thermal environment can be described by a
density matrix evolving according to a nonlinear quantum Fokker-Planck
equation. Exact solutions of this equation are obtained for a two-level system
in the limit of high temperatures, considering both stationary and
nonstationary initial states. A treatment of the common time shared by the
quantum system and its classical environment, as a collective variable rather
than as a parameter, is presented in the Appendix.Comment: 16 pages, LaTex; added Figure 2 and Figure
Self-consistent approach for the quantum confined Stark effect in shallow quantum wells
A computationally efficient, self-consistent complex scaling approach to
calculating characteristics of excitons in an external electric field in
quantum wells is introduced. The method allows one to extract the resonance
position as well as the field-induced broadening for the exciton resonance. For
the case of strong confinement the trial function is represented in factorized
form. The corresponding coupled self-consistent equations, which include the
effective complex potentials, are obtained. The method is applied to the
shallow quantum well. It is shown that in this case the real part of the
effective exciton potential is insensitive to changes of external electric
field up to the ionization threshold, while the imaginary part has
non-analytical field dependence and small for moderate electric fields. This
allows one to express the exciton quasi-energy at some field through the
renormalized expression for the zero-field bound state.Comment: 13 pages, RevTeX4, 6 figure
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