24,300 research outputs found
A longitudinal analysis of the decision to drop out of post-compulsory education
In this paper we analyse the magnitude, timing, determinants and outcomes of dropping out of post-compulsory education over the period 1985-94. We use data from the Youth Cohort Surveys for England and Wales to estimate non-parametric single and competing risks duration models allowing for the effects of unobserved heterogeneity and time varying covariates. By the mid-1990s approximately 1 in 10 young people dropped out of post-compulsory education, especially in April and July. Dropouts were more likely to get jobs rather than become unemployed and the most important predictor of the likelihood of dropping out was prior attainment.
Energy spectra of vortex distributions in two-dimensional quantum turbulence
We theoretically explore key concepts of two-dimensional turbulence in a
homogeneous compressible superfluid described by a dissipative two-dimensional
Gross-Pitaeveskii equation. Such a fluid supports quantized vortices that have
a size characterized by the healing length . We show that for the
divergence-free portion of the superfluid velocity field, the kinetic energy
spectrum over wavenumber may be decomposed into an ultraviolet regime
() having a universal scaling arising from the vortex
core structure, and an infrared regime () with a spectrum that
arises purely from the configuration of the vortices. The Novikov power-law
distribution of intervortex distances with exponent -1/3 for vortices of the
same sign of circulation leads to an infrared kinetic energy spectrum with a
Kolmogorov power law, consistent with the existence of an inertial
range. The presence of these and power laws, together with
the constraint of continuity at the smallest configurational scale
, allows us to derive a new analytical expression for the
Kolmogorov constant that we test against a numerical simulation of a forced
homogeneous compressible two-dimensional superfluid. The numerical simulation
corroborates our analysis of the spectral features of the kinetic energy
distribution, once we introduce the concept of a {\em clustered fraction}
consisting of the fraction of vortices that have the same sign of circulation
as their nearest neighboring vortices. Our analysis presents a new approach to
understanding two-dimensional quantum turbulence and interpreting similarities
and differences with classical two-dimensional turbulence, and suggests new
methods to characterize vortex turbulence in two-dimensional quantum fluids via
vortex position and circulation measurements.Comment: 19 pages, 8 figure
Deploying expert systems in Ada
As the Department of Defense Ada mandate begins to be enforced actively, interest in deploying expert systems in Ada has increased. A prototype Ada based expert system tool is introduced called ART/Ada. This prototype was built to support research into the language and operational issues of expert systems in Ada. ART/Ada allows applications of a conventional expert system tool called ART-IM (Automated Reasoning Tool for Information Management) to be deployed in various Ada environments with efficient use of time and space. ART-IM, a C-based expert system tool, is used to generate Ada source code which is compiled and linked with an Ada base inference engine to produce an Ada executable image. ART/Ada will be used to implement several prototype expert systems for the Space Station Freedom Program testbeds
ART-Ada: An Ada-based expert system tool
The Department of Defense mandate to standardize on Ada as the language for software systems development has resulted in increased interest in making expert systems technology readily available in Ada environments. NASA's Space Station Freedom is an example of the large Ada software development projects that will require expert systems in the 1990's. Another large scale application that can benefit from Ada based expert system tool technology is the Pilot's Associate (PA) expert system project for military combat aircraft. Automated Reasoning Tool (ART) Ada, an Ada Expert system tool is described. ART-Ada allow applications of a C-based expert system tool called ART-IM to be deployed in various Ada environments. ART-Ada is being used to implement several prototype expert systems for NASA's Space Station Freedom Program and the U.S. Air Force
The Quantum de Laval Nozzle: stability and quantum dynamics of sonic horizons in a toroidally trapped Bose gas containing a superflow
We study an experimentally realizable system containing stable black
hole-white hole acoustic horizons in toroidally trapped Bose-Einstein
condensates - the quantum de Laval nozzle. We numerically obtain stationary
flow configurations and assess their stability using Bogoliubov theory, finding
both in hydrodynamic and non-hydrodynamic regimes there exist dynamically
unstable regions associated with the creation of positive and negative energy
quasiparticle pairs in analogy with the gravitational Hawking effect. The
dynamical instability takes the form of a two mode squeezing interaction
between resonant pairs of Bogoliubov modes. We study the evolution of
dynamically unstable flows using the truncated Wigner method, which confirms
the two mode squeezed state picture of the analogue Hawking effect for low
winding number.Comment: 12 pages, 10 figure
ART-Ada design project, phase 2
Interest in deploying expert systems in Ada has increased. An Ada based expert system tool is described called ART-Ada, which was built to support research into the language and methodological issues of expert systems in Ada. ART-Ada allows applications of an existing expert system tool called ART-IM (Automated Reasoning Tool for Information Management) to be deployed in various Ada environments. ART-IM, a C-based expert system tool, is used to generate Ada source code which is compiled and linked with an Ada based inference engine to produce an Ada executable image. ART-Ada is being used to implement several expert systems for NASA's Space Station Freedom Program and the U.S. Air Force
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