52 research outputs found

    Wide-angle display developments by computer graphics

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    Computer graphics can now expand its new subset, wide-angle projection, to be as significant a generic capability as computer graphics itself. Some prior work in computer graphics is presented which leads to an attractive further subset of wide-angle projection, called hemispheric projection, to be a major communication media. Hemispheric film systems have long been present and such computer graphics systems are in use in simulators. This is the leading edge of capabilities which should ultimately be as ubiquitous as CRTs (cathode-ray tubes). These assertions are not from degrees in science or only from a degree in graphic design, but in a history of computer graphics innovations, laying groundwork by demonstration. The author believes that it is timely to look at several development strategies, since hemispheric projection is now at a point comparable to the early stages of computer graphics, requiring similar patterns of development again

    Exploring the limits of the self consistent Born approximation for inelastic electronic transport

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    The non equilibrium Green function formalism is today the standard computational method for describing elastic transport in molecular devices. This can be extended to include inelastic scattering by the so called self-consistent Born approximation (SCBA), where the interaction of the electrons with the vibrations of the molecule is assumed to be weak and it is treated perturbatively. The validity of such an assumption and therefore of the SCBA is difficult to establish with certainty. In this work we explore the limitations of the SCBA by using a simple tight-binding model with the electron-phonon coupling strength ╬▒\rm{\alpha} chosen as a free parameter. As model devices we consider Au mono-atomic chains and a H2\rm{H_2} molecule sandwiched between Pt electrodes. In both cases our self-consistent calculations demonstrate a breakdown of the SCBA for large ╬▒\rm{\alpha} and we identify a weak and strong coupling regime. For weak coupling our SCBA results compare closely with those obtained with exact scattering theory. However in the strong coupling regime large deviations are found. In particular we demonstrate that there is a critical coupling strength, characteristic of the materials system, beyond which multiple self-consistent solutions can be found depending on the initial conditions in the simulation. We attribute these features to the breakdown of the perturbative expansion leading to the SCBA.Comment: 12 pages, 16 figures, 1 Tabl

    Svortices and the fundamental modes of the "snake instability": Possibility of observation in the gaseous Bose-Einstein Condensate

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    The connection between quantized vortices and dark solitons in a long and thin, waveguide-like trap geometry is explored in the framework of the non-linear Schr\"odinger equation. Variation of the transverse confinement leads from the quasi-1D regime where solitons are stable to 2D (or 3D) confinement where soliton stripes are subject to a transverse modulational instability known as the ``snake instability''. We present numerical evidence of a regime of intermediate confinement where solitons decay into single, deformed vortices with solitonic properties, also called svortices, rather than vortex pairs as associated with the ``snake'' metaphor. Further relaxing the transverse confinement leads to production of 2 and then 3 vortices, which correlates perfectly with a Bogoliubov-de Gennes stability analysis. The decay of a stationary dark soliton (or, planar node) into a single svortex is predicted to be experimentally observable in a 3D harmonically confined dilute gas Bose-Einstein condensate.Comment: 4 pages, 4 figure

    A computer graphics human figure application of bio-stereometrics

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    Structural and geochronological studies of the M├ędio Corea├║ domain, NE Brazil: Constraints on Brasiliano/Pan-African tectonic evolution in the NW part of the Borborema Province

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    Recent structural investigations and geochronological studies of rocks from the M├ędio Corea├║ domain in the NW part of northeast Brazil's Borborema Province provide important constraints on the tectonic evolution of the region both preceeding and during the assembly of West Gondwana. Field observations of structural features and fabrics have revealed the presence of four distinct deformational phases in the MCD: D1, D2, D3 and D4. Only the early Paleoproterozoic gneisses record the D1 tectonic event and its preservation is cryptic owing to strong overprinting by the subsequent tectonic phases. The D2, D3 and D4 events affected younger supracrustal rocks and Neoproterzoic magmatic units, and U-Pb geochronological constraints show that all of these tectonic phases represent deformational events that occurred during Brasiliano collision between the West African craton and the NW part of the Borborema Province. The D2 phase, lasting between ca. 622 and 591 Ma, represents a frontal collision stage, which generated NW verging thrust-nappe systems, low-angle foliation, high-grade metamorphism and crustal anatexis. Transition to a strike-slip regime (D3) occurred at around 591 Ma when the region entered a phase of escape tectonics. During this time, the motion of crustal blocks towards NE and E was accommodated along numerous anastomosing shear zones. Syntectonic emplacement of granitoid plutons took place in transtensional domains of the shear zone system. The intrusion of late tectonic granitoids and rapid uplift and cooling of the orogen around 560 Ma as a result of D4 transpressional movements marked the end of the D3 transcurrent regime. These findings show that only the early Paleoproterozoic gneisses in the M├ędio Corea├║ domain are polycyclic in nature. Rather than representing distinct orogenic events, the D2, D3 and D4 tectonic phases are a manifestation of progressive deformational events that developed in response to changes in the regional stress field during convergence and collision between the Borborema Province and its surrounding cratons
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