45,545 research outputs found
Reverse Engineering from Assembler to Formal Specifications via Program Transformations
The FermaT transformation system, based on research carried out over the last
sixteen years at Durham University, De Montfort University and Software
Migrations Ltd., is an industrial-strength formal transformation engine with
many applications in program comprehension and language migration. This paper
is a case study which uses automated plus manually-directed transformations and
abstractions to convert an IBM 370 Assembler code program into a very
high-level abstract specification.Comment: 10 page
First Observations of the Magnetic Field Geometry in Pre-stellar Cores
We present the first published maps of magnetic fields in pre-stellar cores,
to test theoretical ideas about the way in which the magnetic field geometry
affects the star formation process. The observations are JCMT-SCUBA maps of 850
micron thermal emission from dust. Linear polarizations at typically ten or
more independent positions in each of three objects, L1544, L183 and L43 were
measured, and the geometries of the magnetic fields in the plane of the sky
were mapped from the polarization directions. The observed polarizations in all
three objects appear smooth and fairly uniform. In L1544 and L183 the mean
magnetic fields are at an angle of around 30 degrees to the minor axes of the
cores. The L43 B-field appears to have been influenced in its southern half,
such that it is parallel to the wall of a cavity produced by a CO outflow from
a nearby T Tauri star, whilst in the northern half the field appears less
disturbed and has an angle of 44 degrees to the core minor axis. We briefly
compare our results with published models of magnetized cloud cores and
conclude that no current model can explain these observations simultaneously
with previous ISOCAM data.Comment: 13 pages, 3 figs, to appear in ApJ Letter
Infrared Observations of AGN
We present results from an imaging and spectroscopic study of the dust
properties of Seyfert galaxies in the 1-10um range. The data are compared to
state of the art models of torus emission to constrain geometrical and physical
properties of the obscuring medium.Comment: 2 pages, to appear in the IAU Symp.No.222 proceedings:"The Interplay
among Black Holes, Stars and ISM in Galactic Nuclei", Gramado, Brazil, March
1-5, 200
Psychological Issues in Online Adaptive Task Allocation
Adaptive aiding is an idea that offers potential for improvement over many current approaches to aiding in human-computer systems. The expected return of tailoring the system to fit the user could be in the form of improved system performance and/or increased user satisfaction. Issues such as the manner in which information is shared between human and computer, the appropriate division of labor between them, and the level of autonomy of the aid are explored. A simulated visual search task was developed. Subjects are required to identify targets in a moving display while performing a compensatory sub-critical tracking task. By manipulating characteristics of the situation such as imposed task-related workload and effort required to communicate with the computer, it is possible to create conditions in which interaction with the computer would be more or less desirable. The results of preliminary research using this experimental scenario are presented, and future directions for this research effort are discussed
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Leveraging legacy codes to distributed problem solving environments: A web service approach
This paper describes techniques used to leverage high performance legacy codes as CORBA components to a distributed problem solving environment. It first briefly introduces the software architecture adopted by the environment. Then it presents a CORBA oriented wrapper generator (COWG) which can be used to automatically wrap high performance legacy codes as CORBA components. Two legacy codes have been wrapped with COWG. One is an MPI-based molecular dynamic simulation (MDS) code, the other is a finite element based computational fluid dynamics (CFD) code for simulating incompressible Navier-Stokes flows. Performance comparisons between runs of the MDS CORBA component and the original MDS legacy code on a cluster of workstations and on a parallel computer are also presented. Wrapped as CORBA components, these legacy codes can be reused in a distributed computing environment. The first case shows that high performance can be maintained with the wrapped MDS component. The second case shows that a Web user can submit a task to the wrapped CFD component through a Web page without knowing the exact implementation of the component. In this way, a userâs desktop computing environment can be extended to a high performance computing environment using a cluster of workstations or a parallel computer
Anti-self-dual conformal structures with null Killing vectors from projective structures
Using twistor methods, we explicitly construct all local forms of
four--dimensional real analytic neutral signature anti--self--dual conformal
structures with a null conformal Killing vector. We show that is
foliated by anti-self-dual null surfaces, and the two-dimensional leaf space
inherits a natural projective structure. The twistor space of this projective
structure is the quotient of the twistor space of by the group action
induced by the conformal Killing vector.
We obtain a local classification which branches according to whether or not
the conformal Killing vector is hyper-surface orthogonal in . We give
examples of conformal classes which contain Ricci--flat metrics on compact
complex surfaces and discuss other conformal classes with no Ricci--flat
metrics.Comment: 43 pages, 4 figures. Theorem 2 has been improved: ASD metrics are
given in terms of general projective structures without needing to choose
special representatives of the projective connection. More examples (primary
Kodaira surface, neutral Fefferman structure) have been included. Algebraic
type of the Weyl tensor has been clarified. Final version, to appear in
Commun Math Phy
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