457 research outputs found
Solution of the Nuclear Shell Model by Symmetry-Dictated Truncation
The dynamical symmetries of the Fermion Dynamical Symmetry Model are used as
a principle of truncation for the spherical shell model. Utilizing the usual
principle of energy-dictated truncation to select a valence space, and
symmetry-dictated truncation to select a collective subspace of that valence
space, we are able to reduce the full shell model space to one of manageable
dimensions with modern supercomputers, even for the heaviest nuclei. The
resulting shell model then consists of diagonalizing an effective Hamiltonian
within the restricted subspace. This theory is not confined to any symmetry
limits, and represents a full solution of the original shell model if the
appropriate effective interaction of the truncated space can be determined. As
a first step in constructing that interaction, we present an empirical
determination of its matrix elements for the collective subspace with no broken
pairs in a representative set of nuclei with . We demonstrate
that this effective interaction can be parameterized in terms of a few
quantities varying slowly with particle number, and is capable of describing a
broad range of low-energy observables for these nuclei. Finally we give a brief
discussion of extending these methods to include a single broken collective
pair.Comment: invited paper for J. Phys. G, 57 pages, Latex, 18 figures a macro are
available under request at [email protected]
Neutrino-driven supernovae: Boltzmann neutrino transport and the explosion mechanism
Core-collapse supernovae are, despite their spectacular visual display,
neutrino events. Virtually all of the 10^53 ergs of gravitational binding
energy released in the formation of the nascent neutron star is carried away in
the form of neutrinos and antineutrinos of all three flavors, and these
neutrinos are primarily responsible for powering the explosion. This mechanism
depends sensitively on the neutrino transport between the neutrinospheres and
the shock. In light of this, we have performed a comparison of multigroup
Boltzmann neutrino transport (MGBT) and multigroup flux-limited diffusion
(MGFLD) in post-core bounce environments. Differences in the mean inverse flux
factors, luminosities, and RMS energies translate to heating rates that are up
to 2 times larger for Boltzmann transport, with net cooling rates below the
gain radius that are typically 0.8 times the MGFLD rates. These differences are
greatest at earlier postbounce times for a given progenitor mass, and for a
given postbounce time, greater for greater progenitor mass. The increased
differences with increased progenitor mass suggest that the net heating
enhancement from MGBT is potentially robust and self-regulated.Comment: 7 pages, 2 figures, 1 table; LaTex using iopconf.sty; To appear in:
Proceedings of The Second Oak Ridge Symposium on Atomic & Nuclear
Astrophysic
SU(3) Richardson-Gaudin models: three level systems
We present the exact solution of the Richardson-Gaudin models associated with
the SU(3) Lie algebra. The derivation is based on a Gaudin algebra valid for
any simple Lie algebra in the rational, trigonometric and hyperbolic cases. For
the rational case additional cubic integrals of motion are obtained, whose
number is added to that of the quadratic ones to match, as required from the
integrability condition, the number of quantum degrees of freedom of the model.
We discuss different SU(3) physical representations and elucidate the meaning
of the parameters entering in the formalism. By considering a bosonic mapping
limit of one of the SU(3) copies, we derive new integrable models for three
level systems interacting with two bosons. These models include a generalized
Tavis-Cummings model for three level atoms interacting with two modes of the
quantized electric field.Comment: Revised version. To appear in Jour. Phys. A: Math. and Theo
Universality of Symmetry and Mixed-symmetry Collective Nuclear States
The global correlation in the observed variation with mass number of the
and summed transition strengths is examined for rare earth nuclei. It is
shown that a theory of correlated and fermion pairs with a simple
pairing plus quadrupole interaction leads naturally to this universality. Thus
a unified and quantitative description emerges for low-lying quadrupole and
dipole strengths.Comment: In press, Phys. Rev. Lett. 199
Ways to Reduce Peak Electrical Demand in South Louisiana
This study analyses alternatives for coping with the peak electrical demand of hot summer afternoons. Economic and Political aspects, as well as technical feasibility, are included. It is concluded that South Louisiana may indeed be able to trim peak demand to 5% below what is anticipated by 1980 , thus making one of the coal fired stations scheduled then unnecessary. However, the contingencies (Natural Gas Shortage, Another Oil Embargo) would make a coal-fired station very desirable
Association Analysis of Reported Attitudes and Culturally Competent Behavior Engagement among Public Health Department Employees
Objective: The purpose of this research is to analyze the association of attitudes and beliefs on engaging in culturally competent behavior.
Design: Explorational case study of individuals employed within an urban public health department.
Participants: Employees (n=90) from four metropolitan clinical sites of an urban public health department located in the southwest region of the United States were solicited and recruited during a monthly staff meeting. This sample is representative of 84% of the total employees which is comprised of 107 individuals.
Main Outcome Measures: The Cultural Competence Assessment is designed to explore individual knowledge, feelings and actions of respondents when interacting with clients in health service environments. The instrument is based on the cultural competence model, and measures cultural awareness and sensitivity; cultural competence behaviors and cultural diversity experience and training. For reporting purposes, participants were divided into subgroups, clinical and non-clinical. This was completed to account for the variation in respondents’ level of education, type of client/patient interaction and opportunities for professional development engagement.
Results: Respondents with increased levels of knowledge possessed attitudes which encompass dignity and respect of minority groups, potentially improving clinical interactions. African Americans and Hispanic/Latinos within the non-clinical subgroup displayed more culturally sensitive attitudes compared to their clinical peers within the same race/ethnicity classification. Non-clinical workers with Associate and Bachelors degrees displayed more culturally sensitive attitudes than their clinical counterparts. Clinical staff with graduate or professional degrees scored higher in the culturally sensitive attitudes analysis than non-clinical peers.
Conclusions: Knowledgeable individuals have the necessary foundation to develop beliefs and attitudes conducive to creating an effective clinical encounter. Educational programs must include components which increase participant awareness of diversity. In addition, training should encompass lessons to foster self-reflection of one’s own bias and beliefs, and its effect on how workers provide health services
Microscopic Description of Band Structure at Very Extended Shapes in the A ~ 110 Mass Region
Recent experiments have confirmed the existence of rotational bands in the A
\~ 110 mass region with very extended shapes lying between super- and
hyper-deformation. Using the projected shell model, we make a first attempt to
describe quantitatively such a band structure in 108Cd. Excellent agreement is
achieved in the dynamic moment of inertia J(2) calculation. This allows us to
suggest the spin values for the energy levels, which are experimentally
unknown. It is found that at this large deformation, the sharply down-sloping
orbitals in the proton i_{13/2} subshell are responsible for the irregularity
in the experimental J(2), and the wave functions of the observed states have a
dominant component of two-quasiparticles from these orbitals. Measurement of
transition quadrupole moments and g-factors will test these findings, and thus
can provide a deeper understanding of the band structure at very extended
shapes.Comment: 4 pages, 3 eps figures, final version accepted by Phys. Rev. C as a
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Passive Detection of Narrowband Sources Using a Sensor Array
In this report we derive a model for a highly scattering medium, implemented as a set of MATLAB functions. This model is used to analyze an approach for using time-reversal to enhance the detection of a single frequency source in a highly scattering medium. The basic approach is to apply the singular value decomposition to the multistatic response matrix for a time-reversal array system. We then use the array in a purely passive mode, measuring the response to the presence of a source. The measured response is projected onto the singular vectors, creating a time-reversal pseudo-spectrum. We can then apply standard detection techniques to the pseudo-spectrum to determine the presence of a source. If the source is close to a particular scatterer in the medium, then we would expect an enhancement of the inner product between the array response to the source with the singular vector associated with that scatterer. In this note we begin by deriving the Foldy-Lax model of a highly scattering medium, calculate both the field emitted by the source and the multistatic response matrix of a time-reversal array system in the medium, then describe the initial analysis approach
Bayesian Processing for the Detection of Radioactive Contraband from Uncertain Measurements
With the increase in terrorist activities throughout the world, the need to develop techniques capable of detecting radioactive contraband in a timely manner is a critical requirement. The development of Bayesian processors for the detection of contraband stems from the fact that the posterior distribution is clearly multimodal eliminating the usual Gaussian-based processors. The development of a sequential bootstrap processor for this problem is discussed and shown how it is capable of providing an enhanced signal for eventual detection
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