1,403 research outputs found
Prolate spheroidal slosh model for fluid motion
Mathematical model, designed for zero gravity conditions, analyzes dynamic effects of large amplitude fluid motion interior to a rigid body. It has two advantages over other mathematical models: (1) constrains slosh motion to given region in natural manner, and (2) allows equilibrium position of slosh mass to be anywhere on slosh surface
RMS massless arm dynamics capability in the SVDS
The equations of motion for the remote manipulator system, assuming that the masses and inertias of the arm can be neglected, are developed for implementation into the space vehicle dynamics simulation (SVDS) program for the Orbiter payload system. The arm flexibility is incorporated into the equations by the computation of flexibility terms for use in the joint servo model. The approach developed in this report is based on using the Jacobian transformation matrix to transform force and velocity terms between the configuration space and the task space to simplify the form of the equations
Kinematic capability in the SVDS
The details of the Remote Manipulator System kinematic model implemented into the Space Vehicle Dynamics Simulation are given. Detailed engineering flow diagrams and definitions of terms are included
On the Theory of Superfluidity in Two Dimensions
The superfluid phase transition of the general vortex gas, in which the
circulations may be any non-zero integer, is studied. When the net circulation
of the system is not zero the absence of a superfluid phase is shown. When the
net circulation of the vortices vanishes, the presence of off-diagonal long
range order is demonstrated and the existence of an order parameter is
proposed. The transition temperature for the general vortex gas is shown to be
the Kosterlitz---Thouless temperature. An upper bound for the average vortex
number density is established for the general vortex gas and an exact
expression is derived for the Kosterlitz---Thouless ensemble.Comment: 22 pages, one figure, written in plain TeX, published in J. Phys. A24
(1991) 502
Microscopic Structure of the Calcium Isotopes
This research was sponsored by the National Science Foundation Grant NSF PHY-931478
On the shopfloor: exploring the impact of teacher trade unions on school-based industrial relations
Teachers are highly unionised workers and their trade unions exert an important influence on the shaping and implementation of educational policy. Despite this importance there is relatively little analysis of the impact of teacher trade unions in educational management literature. Very little empirical research has sought to establish the impact of teacher unions at school level. In an era of devolved management and quasi-markets this omission is significant. New personnel issues continue to emerge at school level and this may well generate increased trade union activity at the workplace. This article explores the extent to which devolved management is drawing school-based union representation into a more prominent role. It argues that whilst there can be significant differences between individual schools, increased school autonomy is raising the profile of trade union activity in the workplace, and this needs to be better reflected in educational management research
Electrodynamics with Lorentz-violating operators of arbitrary dimension
The behavior of photons in the presence of Lorentz and CPT violation is
studied. Allowing for operators of arbitrary mass dimension, we classify all
gauge-invariant Lorentz- and CPT-violating terms in the quadratic Lagrange
density associated with the effective photon propagator. The covariant
dispersion relation is obtained, and conditions for birefringence are
discussed. We provide a complete characterization of the coefficients for
Lorentz violation for all mass dimensions via a decomposition using
spin-weighted spherical harmonics. The resulting nine independent sets of
spherical coefficients control birefringence, dispersion, and anisotropy. We
discuss the restriction of the general theory to various special models,
including among others the minimal Standard-Model Extension, the isotropic
limit, the case of vacuum propagation, the nonbirefringent limit, and the
vacuum-orthogonal model. The transformation of the spherical coefficients for
Lorentz violation between the laboratory frame and the standard Sun-centered
frame is provided. We apply the results to various astrophysical observations
and laboratory experiments. Astrophysical searches of relevance include studies
of birefringence and of dispersion. We use polarimetric and dispersive data
from gamma-ray bursts to set constraints on coefficients for Lorentz violation
involving operators of dimensions four through nine, and we describe the mixing
of polarizations induced by Lorentz and CPT violation in the cosmic-microwave
background. Laboratory searches of interest include cavity experiments. We
present the theory for searches with cavities, derive the experiment-dependent
factors for coefficients in the vacuum-orthogonal model, and predict the
corresponding frequency shift for a circular-cylindrical cavity.Comment: 58 pages two-column REVTeX, accepted in Physical Review
Cosmological quantum entanglement
We review recent literature on the connection between quantum entanglement
and cosmology, with an emphasis on the context of expanding universes. We
discuss recent theoretical results reporting on the production of entanglement
in quantum fields due to the expansion of the underlying spacetime. We explore
how these results are affected by the statistics of the field (bosonic or
fermionic), the type of expansion (de Sitter or asymptotically stationary), and
the coupling to spacetime curvature (conformal or minimal). We then consider
the extraction of entanglement from a quantum field by coupling to local
detectors and how this procedure can be used to distinguish curvature from
heating by their entanglement signature. We review the role played by quantum
fluctuations in the early universe in nucleating the formation of galaxies and
other cosmic structures through their conversion into classical density
anisotropies during and after inflation. We report on current literature
attempting to account for this transition in a rigorous way and discuss the
importance of entanglement and decoherence in this process. We conclude with
some prospects for further theoretical and experimental research in this area.
These include extensions of current theoretical efforts, possible future
observational pursuits, and experimental analogues that emulate these cosmic
effects in a laboratory setting.Comment: 23 pages, 2 figures. v2 Added journal reference and minor changes to
match the published versio
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Evaluation of seismic interactions: Guidelines and application
It is readily recognized that a significant source of damage from earthquakes is due to interactions between structures and components, such as the fall of a masonry wall or a ceiling on equipment, or the impact of a valve on a wall or structure. There are also other significant, while less intuitively evident, sources of seismic interaction damage, such as flooding, spraying, fires, or electrical shorts. The understanding of all these sources of interaction damage and their evaluation in the field can easily turn into a significant effort. Yet, it is the opinion of the Senior Seismic Review and Advisory Panel (SSRAP) that the evaluation of interactions, in a commercial nuclear power plant, should account for about 10 to 20% of the seismic walkdown'' devoted to equipment seismic qualification. To this end, SSRAP recognizes the need for exercising of considerable judgement and experience -- so that the program remains cost effective.'
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