222 research outputs found
BRST Treatment of the Bohr Collective Hamiltonian at High Spins
The BRST treatment of triaxial systems rotating at high spins is used to
solve perturbatively the -independent Bohr collective hamiltonian.Comment: 10 pages in LaTeX using Esp-LaTeX and Feynman package
Dynamical moment of inertia and quadrupole vibrations in rotating nuclei
The contribution of quantum shape fluctuations to inertial properties of
rotating nuclei has been analysed within the self-consistent one-dimensional
cranking oscillator model. It is shown that in even-even nuclei the dynamical
moment of inertia calculated in the mean field approximation is equivalent to
the Thouless-Valatin moment of inertia calculated in the random phase
approximation if and only if the self-consistent conditions for the mean field
are fulfilled.Comment: 4 pages, 2 figure
Microwave vs optical crosslink study
The intersatellite links (ISL's) at geostationary orbit is currently a missing link in commercial satellite services. Prior studies have found that potential application of ISL's to domestic, regional, and global satellites will provide more cost-effective services than the non-ISL's systems (i.e., multiple-hop systems). In addition, ISL's can improve and expand the existing satellite services in several aspects. For example, ISL's can conserve the scarce spectrum allocated for fixed satellite services (FSS) by avoiding multiple hopping of the relay stations. ISL's can also conserve prime orbit slot by effectively expanding the geostationary arc. As a result of the coverage extension by using ISL's more users will have direct access to the satellite network, thus providing reduced signal propagation delay and improved signal quality. Given the potential benefits of ISL's system, it is of interest to determine the appropriate implementations for some potential ISL architectures. Summary of the selected ISL network architecture as supplied by NASA are listed. The projected high data rate requirements (greater than 400 Mbps) suggest that high frequency RF or optical implementations are natural approaches. Both RF and optical systems have their own merits and weaknesses which make the choice between them dependent on the specific application. Due to its relatively mature technology base, the implementation risk associated with RF (at least 32 GHz) is lower than that of the optical ISL's. However, the relatively large antenna size required by RF ISL's payload may cause real-estate problems on the host spacecraft. In addition, because of the frequency sharing (for duplex multiple channels communications) within the limited bandwidth allocated, RF ISL's are more susceptible to inter-system and inter-channel interferences. On the other hand, optical ISL's can offer interference-free transmission and compact sized payload. However, the extremely narrow beam widths (on the order of 10 micro-rad) associated with optical ISL's impose very stringent pointing, acquisition, and tracking requirements on the system. Even if the RF and optical systems are considered separately, questions still remain as to selection of RF frequency, direct versus coherent optical detection, etc. in implementing an ISL for a particular network architecture. These and other issues are studied
Kamlah Expansion and Gauge Theories
In Yang-Mills theories, variational calculations of the Rayleigh-Ritz type
face the problem that on the one hand, calculability puts severe constraints on
the space of test wave functionals; on the other hand, the test wave
functionals have to be gauge invariant. The conflict between the two
requirements can be resolved by introducing a projector. In this paper we
present an approach to approximating the projector in a way known and
successfully employed in nuclear physics: the Kamlah expansion. We discuss it
both for electrodynamics and for Yang-Mills theories to leading order in a
perturbative expansion, and demonstrate that the results are compatible with
what one would expect from perturbation theory.Comment: 26 pages, REVTeX4, uses amsfonts and package longtabl
Wobbling excitations at high spins in A~160
We found that in 156Dy and 162Yb the lowest odd spin gamma-vibrational states
transform to the wobbling excitations after the backbending, associated with
the transition from axially-symmetric to nonaxial shapes. The analysis of
quadrupole electric transitions determines uniquely the sign of the
gamma-deformation in both nuclei after the transition point.Comment: 6 pages, 4 figure
Quadrupole correlations and inertial properties of rotating nuclei
The contribution of quantum shape fluctuations to inertial properties of
rotating nuclei has been analyzed for QQ-nuclear interaction using the random
phase approximation (RPA). The different recipes to treat the cranking mean
field plus RPA problem are considered. The effects of the dN=2 quadrupole
matrix elements and the role of the volume conservation condition are
discussed.Comment: 14 pages, 7 figures, To be published in J. Phys. G: Nucl. Phy
Description of Multi Quasi Particle Bands by the Tilted Axis Cranking Model
The selfconsistent cranking approach is extended to the case of rotation
about an axis which is tilted with respect to the principal axes of the
deformed potential (Tilted Axis Cranking). Expressions for the energies and the
intra bands electromagnetic transition probabilities are given.
The mean field solutions are interpreted in terms of quantal rotational
states. The construction of the quasiparticle configurations and the
elimination of spurious states is discussed. The application of the theory to
high spin data is demonstrated by analyzing the multi quasiparticle bands in
the nuclide-s with and .Comment: 23 pages 27 figure
Single Boson Images Via an Extended Holstein Primakoff Mapping
The Holstein-Primakoff mapping for pairs of bosons is extended in order to
accommodate single boson mapping. The proposed extension allows a variety of
applications and especially puts the formalism at finite temperature on firm
grounds. The new mapping is applied to the O(N+1) anharmonic oscillator with
global symmetry broken down to O(N). It is explicitly demonstrated that
N-Goldstone modes appear. This result generalizes the Holstein-Primakoff
mapping for interacting boson as developed in ref.[1].Comment: 9 pages, LaTeX. Physical content unchanged. Unnecessary figure
remove
Recommended from our members
Theoretical studies in nuclear structure
In this period, the work has centered on two topics. The first is the study of a novel type of collective rotation in which an atomic nucleus with an inversion-symmetric shape rotates uniformly about an axis that is not a principal axis of the quadrupole tensor of the density distribution. This mode is referred to as tilted rotation. By using the cranking model together with higher-order corrections, it was shown that tilted rotation is indeed possible, not only within a microscopic framework, but also within the framework of collective models such as the IBM. The maximum tilt angle of {pi}/4 is realized for a certain class of states in the U(5) limit. The second topic, which actually was suggested during the course of the first investigation, is concerned with a new way of representing collective harmonic-oscillator algebras using boson-mapping techniques. In this approach, the many-phonon eigenvectors of a 2{lambda}+1-dimensional oscillator having good angular momentum are represented by simple products of boson operators acting on a vacuum. This representation may simplify the calculation of reduced matrix elements of arbitrary operators in collective models, but more work needs to be done
- âŠ