9,344 research outputs found
Coherent state triplets and their inner products
It is shown that if H is a Hilbert space for a representation of a group G,
then there are triplets of spaces F_H, H, F^H, in which F^H is a space of
coherent state or vector coherent state wave functions and F_H is its dual
relative to a conveniently defined measure. It is shown also that there is a
sequence of maps F_H -> H -> F^H which facilitates the construction of the
corresponding inner products. After completion if necessary, the F_H, H, and
F^H, become isomorphic Hilbert spaces. It is shown that the inner product for H
is often easier to evaluate in F_H than F^H. Thus, we obtain integral
expressions for the inner products of coherent state and vector coherent state
representations. These expressions are equivalent to the algebraic expressions
of K-matrix theory, but they are frequently more efficient to apply. The
construction is illustrated by many examples.Comment: 33 pages, RevTex (Latex2.09) This paper is withdrawn because it
contained errors that are being correcte
Integrating case-based reasoning and hypermedia documentation: an application for the diagnosis of a welding robot at Odense steel shipyard
Reliable and effective maintenance support is a vital consideration for the management within today's manufacturing environment. This paper discusses the development of a maintenance system for the world's largest robot welding facility. The development system combines a case-based reasoning approach for diagnosis with context information, as electronic on-line manuals, linked using open hypermedia technology. The work discussed in this paper delivers not only a maintenance system for the robot stations under consideration, but also a design framework for developing maintenance systems for other similar applications
Use of Standardized Assessments and Online Resources in Stroke Rehabilitation
Background: The extent to which movement-related standardized assessments and online resources are used in stroke rehabilitation is unclear in the United States.
Method: The researchers used a cross-sectional descriptive survey that examined (a) therapists use of movement-related standardized assessments, (b) factors influencing learning of new assessments, and (c) use of frequency of online resources by occupational therapists and physical therapists in the United States.
Results: Of 151 respondents (46.4% occupational therapists, 53.6% physical therapists), the most frequently used movement-related assessments by occupational and physical therapists were the Berg and Fugl-Meyer Assessment, respectively. More physical therapists use motor-related standardized assessments regularly than occupational therapists, and physical therapists showed more consensus among standardized assessments. Both professions cited quality of patient care for motivating them to integrate outcome measures into practice. Most therapists in stroke rehabilitation used online resources to access movement-related standardized assessment content at least 25% of the time. The Rehabilitation Measures Database was the most frequently used website.
Conclusion: Both occupational and physical therapists use online resources for movement-related standardized assessments on a regular basis. However, occupational therapists do not use standardized assessments as frequently as physical therapists. A systematic study of factors that impact the integration of standardized assessments is needed to further identify barriers and inform clinical practice change
Large-Amplitude, Pair-Creating Oscillations in Pulsar and Black Hole Magnetospheres
A time-dependent model for pair creation in a pulsar magnetosphere is
developed. It is argued that the parallel electric field that develops in a
charge-starved region (a gap) of a pulsar magnetosphere oscillates with large
amplitude. Electrons and positrons are accelerated periodically and the
amplitude of the oscillations is assumed large enough to cause creation of
upgoing and downgoing pairs at different phases of the oscillation. With a
charge-starved initial condition, we find that the oscillations result in
bursts of pair creation in which the pair density rises exponentially with
time. The pair density saturates at , where is the parallel electric field in the
charge-starved initial state, and is the Lorentz factor for
effec tive pair creation. The frequency of oscillations following the pair
creation burst is given roughly by . A positive feedback keeps the system stable, such that the average pair
creation rate balances the loss rate due to pairs escaping the magnetosphere.Comment: 21 pages, 6 figures, ApJ submitte
Reversable heat flow through the carbon nanotube junctions
Microscopic mechanisms of externally controlled reversable heat flow through
the carbon nanotube junctions (NJ) are studied theoretically. Our model
suggests that the heat is transfered along the tube section by
electrons () and holes () moving ballistically in either in parallel or
in opposite directions and accelerated by the bias source-drain voltage (Peltier effect). We compute the Seebeck coefficient , electric
and thermal conductivities and find that their magnitudes
strongly depend on and . The sign reversal of
versus the sign of formerly observed experimentally is interpreted
in this work in terms of so-called chiral tunneling phenomena (Klein paradox)
Hermitian boson mapping and finite truncation
Starting from a general, microscopic fermion-to-boson mapping that preserves
Hermitian conjugation, we discuss truncations of the boson Fock space basis. We
give conditions under which the exact boson images of finite fermion operators
are also finite (e.g., a 1+2-body fermion Hamiltonian is mapped to a 1+2-body
boson Hamiltonian) in the truncated basis. For the most general case, where the
image is not necessarily exactly finite, we discuss how to make practical and
controlled approximations.Comment: 12 pages in RevTex with no figures, Los Alamos preprint #
LA-UR-94-146
An algebraic approach to problems with polynomial Hamiltonians on Euclidean spaces
Explicit expressions are given for the actions and radial matrix elements of
basic radial observables on multi-dimensional spaces in a continuous sequence
of orthonormal bases for unitary SU(1,1) irreps. Explicit expressions are also
given for SO(N)-reduced matrix elements of basic orbital observables. These
developments make it possible to determine the matrix elements of polynomial
and a other Hamiltonians analytically, to within SO(N) Clebsch-Gordan
coefficients, and to select an optimal basis for a particular problem such that
the expansion of eigenfunctions is most rapidly convergent.Comment: 19 pages, 8 figure
Richardson-Gaudin integrability in the contraction limit of the quasispin
Background: The reduced, level-independent, Bardeen-Cooper-Schrieffer
Hamiltonian is exactly diagonalizable by means of a Bethe Ansatz wavefunction,
provided the free variables in the Ansatz are the solutions of the set of
Richardson-Gaudin equations. On the one side, the Bethe Ansatz is a simple
product state of generalised pair operators. On the other hand, the
Richardson-Gaudin equations are strongly coupled in a non-linear way, making
them prone to singularities. Unfortunately, it is non-trivial to give a clear
physical interpretation to the Richardson-Gaudin variables because no physical
operator is directly related to the individual variables. Purpose: The purpose
of this paper is to shed more light on the critical behavior of the
Richardson-Gaudin equations, and how this is related to the product wave
structure of the Bethe Ansatz. Method: A pseudo-deformation of the quasi-spin
algebra is introduced, leading towards a Heisenberg-Weyl algebra in the
contraction limit of the deformation parameter. This enables an adiabatic
connection of the exact Bethe Ansatz eigenstates with pure bosonic multiphonon
states. The physical interpretation of this approach is an adiabatic
suppression of the Pauli exclusion principle. Results: The method is applied to
a so-called "picket-fence" model for the BCS Hamiltonian, displaying a typical
critical behavior in the Richardson-Gaudin variables. It was observed that the
associated bosonic multiphonon states change collective nature at the critical
interaction strengths of the Richardson-Gaudin equations. Conclusions: The
Pauli exclusion principle is the main responsible for the critical behavior of
the Richardson-Gaudin equations, which can be suppressed by means of a pseudo
deformation of the quasispin algebra.Comment: PACS 02.30.Ik, 21.10.Re, 21.60.Ce, 74.20.F
Trends in typologies of concurrent alcohol, marijuana, and cigarette use among US adolescents: An ecological examination by sex and race/ethnicity
Substance use during adolescence is a public health concern due to associated physical and behavioral health consequences. Such consequences are amplified among concurrent substance users. Although sex and racial/ethnic differences in single-substance use have been observed, the current literature is inconclusive as to whether differences exist in the prevalence of concurrent use. The current study used data from the 2011–2014 National Survey on Drug Use and Health to examine typologies (single and concurrent patterns) of alcohol, marijuana, and cigarette use among current adolescent users age 12–18 by sex and race/ethnicity. Participants were 14,667 White, Hispanic, African American, Asian, and Native American adolescents. The most common typology was alcohol only, followed by concurrent use of alcohol and marijuana. Weighted prevalence estimates indicated that adolescent females were more likely to be current users of alcohol only, whereas male adolescents were more likely to belong to all other typologies. Compared to Whites, racial/ethnic minorities had larger proportions of marijuana only users and were generally less likely than or equally likely to be concurrent users. One exception was for African American adolescents, who were more likely to be alcohol and marijuana users than their White counterparts. Results suggest that concurrent substance use is common among U.S. adolescents, making up over 40% of past-month use, but typologies of use vary by sex and race/ethnicity. Preventive interventions should consider all typologies of use rather than only single substance exposures and address patterns of use that are most pertinent to adolescents based on sex and race/ethnicity
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