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Search Results: 1 - 10 of 20613 matches for " James;Corney "
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Virtual Assembly Rapid Prototyping of Near Net Shapes
Lim, Theodore;Medellin, Hugo;Sung, Raymond;Ritchie, James;Corney, Jonathan;
Ingeniería mecánica, tecnología y desarrollo , 2009,
Abstract: virtual reality (vr) provides another dimension to many engineering applications. its immersive and interactive nature allows an intuitive approach to study both cognitive activities and performance evaluation. market competitiveness means having products meet form, fit and function quickly. rapid prototyping and manufacturing (rp&m) technologies are increasingly being applied to produce functional prototypes and the direct manufacturing of small components. despite its flexibility, these systems have common drawbacks such as slow build rates, a limited number of build axes (typically one) and the need for post processing. this paper presents a virtual assembly rapid prototyping (varp) project which involves evaluating cognitive activities in assembly tasks based on the adoption of immersive virtual reality along with a novel non-layered rapid prototyping for near net shape (nns) manufacturing of components. it is envisaged that this integrated project will facilitate a better understanding of design for manufacture and assembly by utilising equivalent scale digital and physical prototyping in one rapid prototyping system. the state of the art of the varp project is also presented in this paper.
What Are Lightness Illusions and Why Do We See Them?
David Corney,R. Beau Lotto
PLOS Computational Biology , 2007, DOI: 10.1371/journal.pcbi.0030180
Abstract: Lightness illusions are fundamental to human perception, and yet why we see them is still the focus of much research. Here we address the question by modelling not human physiology or perception directly as is typically the case but our natural visual world and the need for robust behaviour. Artificial neural networks were trained to predict the reflectance of surfaces in a synthetic ecology consisting of 3-D “dead-leaves” scenes under non-uniform illumination. The networks learned to solve this task accurately and robustly given only ambiguous sense data. In addition—and as a direct consequence of their experience—the networks also made systematic “errors” in their behaviour commensurate with human illusions, which includes brightness contrast and assimilation—although assimilation (specifically White's illusion) only emerged when the virtual ecology included 3-D, as opposed to 2-D scenes. Subtle variations in these illusions, also found in human perception, were observed, such as the asymmetry of brightness contrast. These data suggest that “illusions” arise in humans because (i) natural stimuli are ambiguous, and (ii) this ambiguity is resolved empirically by encoding the statistical relationship between images and scenes in past visual experience. Since resolving stimulus ambiguity is a challenge faced by all visual systems, a corollary of these findings is that human illusions must be experienced by all visual animals regardless of their particular neural machinery. The data also provide a more formal definition of illusion: the condition in which the true source of a stimulus differs from what is its most likely (and thus perceived) source. As such, illusions are not fundamentally different from non-illusory percepts, all being direct manifestations of the statistical relationship between images and scenes.
Modulational instability in periodic quadratic nonlinear materials
J. F. Corney,Ole Bang
Physics , 2001, DOI: 10.1103/PhysRevLett.87.133901
Abstract: We investigate the modulational instability of plane waves in quadratic nonlinear materials with linear and nonlinear quasi-phase-matching gratings. Exact Floquet calculations, confirmed by numerical simulations, show that the periodicity can drastically alter the gain spectrum but never completely removes the instability. The low-frequency part of the gain spectrum is accurately predicted by an averaged theory and disappears for certain gratings. The high-frequency part is related to the inherent gain of the homogeneous non-phase-matched material and is a consistent spectral feature.
Plane waves in periodic, quadratically nonlinear slab waveguides: stability and exact Fourier structure
J. F. Corney,O. Bang
Physics , 2001, DOI: 10.1364/JOSAB.19.000812
Abstract: We consider the propagation of broad optical beams through slab waveguides with a purely quadratic nonlinearity and containing linear and nonlinear long-period quasi-phase-matching gratings. An exact Floquet analysis on the periodic, plane-wave solution shows that the periodicity can drastically alter the growth rate of the modulational instability but that it never completely removes the instability. The results are confirmed by direct numerical simulation, as well as through a simpler, approximate theory for the averaged fields that accurately predicts the low-frequency part of the spectrum.
Solitons in quadratic nonlinear photonic crystals
Joel F. Corney,Ole Bang
Physics , 2000, DOI: 10.1103/PhysRevE.64.047601
Abstract: We study solitons in one-dimensional quadratic nonlinear photonic crystals with modulation of both the linear and nonlinear susceptibilities. We derive averaged equations that include induced cubic nonlinearities and numerically find previously unknown soliton families. The inclusion of the induced cubic terms enables us to show that solitons still exist even when the effective quadratic nonlinearity vanishes and conventional theory predicts that there can be no soliton. We demonstrate that both bright and dark forms of these solitons are stable under propagation.
The complete modulational instability gain spectrum of nonlinear QPM gratings
J. F. Corney,Ole Bang
Physics , 2003, DOI: 10.1364/JOSAB.21.000617
Abstract: We consider plane waves propagating in quadratic nonlinear slab waveguides with nonlinear quasi-phase-matching gratings. We predict analytically and verify numerically the complete gain spectrum for transverse modulational instability, including hitherto undescribed higher order gain bands.
Gaussian quantum operator representation for bosons
Joel F. Corney,Peter D. Drummond
Physics , 2003, DOI: 10.1103/PhysRevA.68.063822
Abstract: We introduce the Gaussian quantum operator representation, using the most general multi-mode Gaussian operator basis. The representation unifies and substantially extends existing phase-space representations of density matrices for Bose systems, and also includes generalized squeezed-state and thermal bases. It enables first-principles dynamical or equilibrium calculations in quantum many-body systems, with quantum uncertainties appearing as dynamical objects. Any quadratic Liouville equation for the density operator results in a purely deterministic time evolution. Any cubic or quartic master equation can be treated using stochastic methods.
Improving Polarisation Squeezing In Sagnac Interferometer Configuration Using Photonic Crystal Fibre
Morgan J. Tacey,Joel F. Corney
Physics , 2013, DOI: 10.1364/OL.38.002991
Abstract: The greater confinement of light that is possible in photonic crystal fibres leads to a greater effective nonlin- earity, which promises to yield greater quantum squeezing than is possible in standard optical fibre. However, experimental work to date has not achieved improvements over standard fibre. We present a comprehensive numerical investigation of polarisation squeezing in photonic crystal fibre in a Sagnac configuration. By including loss, a non-instantaneous Raman response, excess phase-noise, second- and third-order dispersion and self-steepening, the simulations are able to identify the physical factors that limit current photonic crystal fibre squeezing experiments.
Homodyne Measurements on a Bose-Einstein Condensate
J. F. Corney,G. J. Milburn
Physics , 1997, DOI: 10.1103/PhysRevA.58.2399
Abstract: We investigate a non-destructive measurement technique to monitor Josephson-like oscillations between two spatially separated neutral atom Bose-Einstein condensates. One condensate is placed in an optical cavity, which is strongly driven by a coherent optical field. The cavity output field is monitored using a homodyne detection scheme. The cavity field is well detuned from an atomic resonance, and experiences a dispersive phase shift proportional to the number of atoms in the cavity. The detected current is modulated by the coherent tunneling oscillations of the condensate. Even when there is an equal number of atoms in each well initially, a phase is established by the measurement process and Josephson-like oscillations develop due to measurement back-action noise alone.
Quantum noise in optical fibers II: Raman jitter in soliton communications
J. F. Corney,P. D. Drummond
Physics , 1999,
Abstract: The dynamics of a soliton propagating in a single-mode optical fiber with gain, loss, and Raman coupling to thermal phonons is analyzed. Using both soliton perturbation theory and exact numerical techniques, we predict that intrinsic thermal quantum noise from the phonon reservoirs is a larger source of jitter and other perturbations than the gain-related Gordon-Haus noise, for short pulses, assuming typical fiber parameters. The size of the Raman timing jitter is evaluated for both bright and dark (topological) solitons, and is larger for bright solitons. Because Raman thermal quantum noise is a nonlinear, multiplicative noise source, these effects are stronger for the more intense pulses needed to propagate as solitons in the short-pulse regime. Thus Raman noise may place additional limitations on fiber-optical communications and networking using ultrafast (subpicosecond) pulses.
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