64,448 research outputs found
Diagnostic accuracy of tests based on radiologic measurements of dogs and cats: a systematic review
Structure and dynamics of topological defects in a glassy liquid on a negatively curved manifold
We study the low-temperature regime of an atomic liquid on the hyperbolic
plane by means of molecular dynamics simulation and we compare the results to a
continuum theory of defects in a negatively curved hexagonal background. In
agreement with the theory and previous results on positively curved (spherical)
surfaces, we find that the atomic configurations consist of isolated defect
structures, dubbed "grain boundary scars", that form around an irreducible
density of curvature-induced disclinations in an otherwise hexagonal
background. We investigate the structure and the dynamics of these grain
boundary scars
Quantum Holonomies in (2+1)-Dimensional Gravity
We describe an approach to the quantization of (2+1)--dimensional gravity
with topology R x T^2 and negative cosmological constant, which uses two
quantum holonomy matrices satisfying a q--commutation relation. Solutions of
diagonal and upper--triangular form are constructed, which in the latter case
exhibit additional, non--trivial internal relations for each holonomy matrix.
This leads to the notion of quantum matrix pairs. These are pairs of matrices
with non-commuting entries, which have the same pattern of internal relations,
q-commute with each other under matrix multiplication, and are such that
products of powers of the matrices obey the same pattern of internal relations
as the original pair. This has implications for the classical moduli space,
described by ordered pairs of commuting SL(2,R) matrices modulo simultaneous
conjugation by SL(2,R) matrices.Comment: 5 pages, to appear in the proceedings of 10th Marcel Grossmann
Meeting on Recent Developments in Theoretical and Experimental General
Relativity, Gravitation and Relativistic Field Theories (MG X MMIII), Rio de
Janeiro, Brazil, 20-26 Jul 200
Design and implementation of a medium speed communications interface and protocol for a low cost, refreshed display computer
The design and implementation of hardware and software systems involved in using a 40,000 bit/second communication line as the connecting link between an IMLAC PDS 1-D display computer and a Univac 1108 computer system were described. The IMLAC consists of two independent processors sharing a common memory. The display processor generates the deflection and beam control currents as it interprets a program contained in the memory; the minicomputer has a general instruction set and is responsible for starting and stopping the display processor and for communicating with the outside world through the keyboard, teletype, light pen, and communication line. The processing time associated with each data byte was minimized by designing the input and output processes as finite state machines which automatically sequence from each state to the next. Several tests of the communication link and the IMLAC software were made using a special low capacity computer grade cable between the IMLAC and the Univac
An LQR controller design approach for a Large Gap Magnetic Suspension System (LGMSS)
Two control approaches for a Large Gap Magnetic Suspension System (LGMSS) are investigated and numerical results are presented. The approaches are based on Linear Quadratic Regulator (LQR) control theory and include a nonzero set point regulator with constant disturbance input and an integral feedback regulator. The LGMSS provides five degree of freedom control of a cylindrical suspended element which is composed of permanent magnet material. The magnetic actuators are air core electromagnets mounted in a planar way
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