20,979 research outputs found
Texture-based cloud classification
The purpose of the 1988 ASEE Summer Program has been to broaden the application of texture-based cloud classification approaches to lower spatial resolution GOES imagery, and to design texture-based approaches for determining cloud cover over high albedo surfaces
Effects of classical stochastic webs on the quantum dynamics of cold atomic gases in a moving optical lattice
We introduce and investigate a system that uses temporal resonance-induced
phase space pathways to create strong coupling between an atomic Bose-Einstein
condensate and a traveling optical lattice potential. We show that these
pathways thread both the classical and quantum phase space of the atom cloud,
even when the optical lattice potential is arbitrarily weak. The topology of
the pathways, which form web-like patterns, can by controled by changing the
amplitude and period of the optical lattice. In turn, this control can be used
to increase and limit the BEC's center-of-mass kinetic energy to pre-specified
values. Surprisingly, the strength of the atom-lattice interaction and
resulting BEC heating of the center-of-mass motion is enhanced by the repulsive
inter-atomic interactions.Comment: 8 pages, 7 figure
Dynamics of the Young Binary LMC Cluster NGC 1850
In this paper we have examined the age and internal dynamics of the young
binary LMC cluster NGC 1850 using BV CCD images and echelle spectra of 52
supergiants. Isochrone fits to a BV color-magnitude diagram revealed that the
primary cluster has an age of Myr while the secondary member
has Myr. BV surface brightness profiles were constructed out
to R 40 pc, and single-component King-Michie (KM) models were applied. The
total cluster luminosity varied from L = 2.60 - 2.65
L\sol\ and L = 1.25 - 1.35 as the anisotropy radius
varied from infinity to three times the scale radius with the isotropic models
providing the best agreement with the data. Of the 52 stars with echelle
spectra, a subset of 36 were used to study the cluster dynamics. The KM radial
velocity distributions were fitted to these velocities yielding total cluster
masses of 5.4 - 5.9 M\sol\ corresponding to M/L =
0.02 M\sol/L\sol\ or M/L = 0.05 M\sol/L\sol.
A rotational signal in the radial velocities has been detected at the 93\%
confidence level implying a rotation axis at a position angle of 100\deg. A
variety of rotating models were fit to the velocity data assuming cluster
ellipticities of . These models provided slightly better
agreement with the radial velocity data than the KM models and had masses that
were systematically lower by a few percent. The preferred value for the slope
of a power-law IMF is a relatively shallow, x = 0.29 \pmm{+0.3}{-0.8}
assuming the B-band M/L or x = 0.71 \pmm{+0.2}{-0.4} for the V-band.Comment: 41 pages (figures available via anonymous FTP as described below
A Design Strategy for Deadlock-Free Concurrent Systems
When building concurrent systems, it would be useful to have a collection of reusable processes
to perform standard tasks. However, without knowing certain details of the inner workings of
these components, one can never be sure that they will not cause deadlock when connected to
some particular network.
Here we describe a hierarchical method for designing complex networks of communicating
processeswhich are deadlock-free.We use this to define a safe and simple method for specifying
the communication interface to third party software components. This work is presented using
the CSP model of concurrency and the occam2.1 programming language
Adapting to variable prismatic displacement
In each of two studies, subjects were exposed to a continuously changing prismatic displacement with a mean value of 19 prism diopters (variable displacement) and to a fixed 19-diopter displacement (fixed displacement). In Experiment 1, significant adaptation (post-pre shifts in hand-eye coordination) was found for fixed, but not for variable, displacement. Experiment 2 demonstrated that adaptation was obtained for variable displacement, but it was very fragile and is lost if the measures of adaptation are preceded by even a very brief exposure of the hand to normal or near-normal vision. Contrary to the results of some previous studies, an increase in within-S dispersion was not found of target pointing responses as a result of exposure to variable displacement
An adaptive, hanging-node, discontinuous isogeometric analysis method for the first-order form of the neutron transport equation with discrete ordinate (SN) angular discretisation
In this paper a discontinuous, hanging-node, isogeometric analysis (IGA) method is developed and applied to the first-order form of the neutron transport equation with a discrete ordinate (SN) angular discretisation in two-dimensional space. The complexities involved in upwinding across curved element boundaries that contain hanging-nodes have been addressed to ensure that the scheme remains conservative. A robust algorithm for cycle-breaking has also been introduced in order to develop a unique sweep ordering of the elements for each discrete ordinates direction. The convergence rate of the scheme has been verified using the method of manufactured solutions (MMS) with a smooth solution. Heuristic error indicators have been used to drive an adaptive mesh refinement (AMR) algorithm to take advantage of the hanging-node discretisation. The effectiveness of this method is demonstrated for three test cases. The first is a homogeneous square in a vacuum with varying mean free path and a prescribed extraneous unit source. The second test case is a radiation shielding problem and the third is a 3×3 “supercell” featuring a burnable absorber. In the final test case, comparisons are made to the discontinuous Galerkin finite element method (DGFEM) using both straight-sided and curved quadratic finite elements
SSME structural dynamic model development
A mathematical model of the Space Shuttle Main Engine (SSME) as a complete assembly, with detailed emphasis on LOX and High Fuel Turbopumps is developed. The advantages of both complete engine dynamics, and high fidelity modeling are incorporated. Development of this model, some results, and projected applications are discussed
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