23,376 research outputs found
In Search of the Vortex Loop Blowout Transition for a type-II Superconductor in a Finite Magnetic Field
The 3D uniformly frustrated XY model is simulated to search for a predicted
"vortex loop blowout" transition within the vortex line liquid phase of a
strongly type-II superconductor in an applied magnetic field. Results are shown
to strongly depend on the precise scheme used to trace out vortex line paths.
While we find evidence for a transverse vortex path percolation transition, no
signal of this transition is found in the specific heat.Comment: 11 pages, 17 figure
Developments in GRworkbench
The software tool GRworkbench is an ongoing project in visual, numerical
General Relativity at The Australian National University. Recently, GRworkbench
has been significantly extended to facilitate numerical experimentation in
analytically-defined space-times. The numerical differential geometric engine
has been rewritten using functional programming techniques, enabling objects
which are normally defined as functions in the formalism of differential
geometry and General Relativity to be directly represented as function
variables in the C++ code of GRworkbench. The new functional differential
geometric engine allows for more accurate and efficient visualisation of
objects in space-times and makes new, efficient computational techniques
available. Motivated by the desire to investigate a recent scientific claim
using GRworkbench, new tools for numerical experimentation have been
implemented, allowing for the simulation of complex physical situations.Comment: 14 pages. To appear A. Moylan, S.M. Scott and A.C. Searle,
Developments in GRworkbench. Proceedings of the Tenth Marcel Grossmann
Meeting on General Relativity, editors M. Novello, S. Perez-Bergliaffa and R.
Ruffini. Singapore: World Scientific 200
Intersection of three-dimensional geometric surfaces
Calculating the line of intersection between two three-dimensional objects and using the information to generate a third object is a key element in a geometry development system. Techniques are presented for the generation of three-dimensional objects, the calculation of a line of intersection between two objects, and the construction of a resultant third object. The objects are closed surfaces consisting of adjacent bicubic parametric patches using Bezier basis functions. The intersection determination involves subdividing the patches that make up the objects until they are approximately planar and then calculating the intersection between planes. The resulting straight-line segments are connected to form the curve of intersection. The polygons in the neighborhood of the intersection are reconstructed and put back into the Bezier representation. A third object can be generated using various combinations of the original two. Several examples are presented. Special cases and problems were encountered, and the method for handling them is discussed. The special cases and problems included intersection of patch edges, gaps between adjacent patches because of unequal subdivision, holes, or islands within patches, and computer round-off error
Improving Pulsar Distances by Modelling Interstellar Scattering
We present here a method to study the distribution of electron density
fluctuations in pulsar directions as well as to estimate pulsar distances. The
method, based on a simple two-component model of the scattering medium
discussed by Gwinn et al. (1993), uses scintillation & proper motion data in
addition to the measurements of angular broadening & temporal broadening to
solve for the model parameters, namely, the fractional distance to a discrete
scatterer and the ascociated relative scattering strength. We show how this
method can be used to estimate pulsar distances reliably, when the location of
a discrete scatterer (e.g. an HII region), if any, is known. Considering the
specific example of PSR B0736-40, we illustrate how a simple characterization
of the Gum nebula region (using the data on the Vela pulsar) is possible and
can be used along with the temporal broadening measurements to estimate pulsar
distances.Comment: To be published in MNRAS, 7 pages, 3 figure
Research study of an aircraft-contained radar zero-zero landing system, volume 1 Final report, Jan. - Dec. 1967
Two rapid scan radar/display techniques evaluated for use in aircraft-contained zero-zero landing syste
Computer-aided analysis and design of the shape rolling process for producing turbine engine airfoils
Mild steel (AISI 1018) was selected as model cold rolling material and Ti-6A1-4V and Inconel 718 were selected as typical hot rolling and cold rolling alloys, respectively. The flow stress and workability of these alloys were characterized and friction factor at the roll/workpiece interface was determined at their respective working conditions by conducting ring tests. Computer-aided mathematical models for predicting metal flow and stresses, and for simulating the shape rolling process were developed. These models utilized the upper bound and the slab methods of analysis, and were capable of predicting the lateral spread, roll separating force, roll torque, and local stresses, strains and strain rates. This computer-aided design system was also capable of simulating the actual rolling process, and thereby designing the roll pass schedule in rolling of an airfoil or a similar shape
A study of charged particle motion in magnetic radiation shielding fields Final technical report
Charged particle motion in magnetic radiation shielding field
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