160,899 research outputs found
PlasMOStor: A metal-oxide-Si field effect plasmonic modulator
Realization of chip-based all-optical and optoelectronic computational networks will require ultracompact Si-compatible modulators, ideally comprising dimensions, materials, and functionality similar to electronic complementary metal−oxide−semiconductor (CMOS) components. Here we demonstrate such a modulator, based on field-effect modulation of plasmon waveguide modes in a MOS geometry. Near-infrared transmission between an optical source and drain is controlled by a gate voltage that drives the MOS into accumulation. Using the gate oxide as an optical channel, electro-optic modulation is achieved in device volumes of half of a cubic wavelength with femtojoule switching energies and the potential for gigahertz modulation frequencies
Computation of Electromagnetic Fields Scattered From Objects With Uncertain Shapes Using Multilevel Monte Carlo Method
Computational tools for characterizing electromagnetic scattering from
objects with uncertain shapes are needed in various applications ranging from
remote sensing at microwave frequencies to Raman spectroscopy at optical
frequencies. Often, such computational tools use the Monte Carlo (MC) method to
sample a parametric space describing geometric uncertainties. For each sample,
which corresponds to a realization of the geometry, a deterministic
electromagnetic solver computes the scattered fields. However, for an accurate
statistical characterization the number of MC samples has to be large. In this
work, to address this challenge, the continuation multilevel Monte Carlo
(CMLMC) method is used together with a surface integral equation solver. The
CMLMC method optimally balances statistical errors due to sampling of the
parametric space, and numerical errors due to the discretization of the
geometry using a hierarchy of discretizations, from coarse to fine. The number
of realizations of finer discretizations can be kept low, with most samples
computed on coarser discretizations to minimize computational cost.
Consequently, the total execution time is significantly reduced, in comparison
to the standard MC scheme.Comment: 25 pages, 10 Figure
Computational interferometric description of nested flow fields
Computer graphics and theoretical descriptions of density are used to obtain computer generated flow visualizations called computational interferograms. Computational interferograms are pictorially analogous to optical interferograms, and examples showing the fringe pattern for the flow about a sharp tip cone in a supersonic air stream are presented. To ascertain the effect of unsteady behavior, local density disturbances are added to the steady state flow field. This introduces irregularities to the computational interferogram like those seen in the optical interferograms. These theoretical disturbances can be varied in geometry, density description, translated with time, and strengthened or dissipated. The accuracy of computational interferometry relies on the accuracy of the theoretical density descriptions and therefore, it provides a way of verifying existing models of flow fields, especially those containing unsteady or turbulent behavior. In addition to being a unique method of flow visualization, computational interferometry can be used to develop and modify theories or numerical solutions to both simple and complex flow fields. The presented research is a general description of this process
Inverse Mapping of Polarised Optical Emission from Pulsars : Basic Formulation and Determination of Emission Altitude
We present an inverse mapping approach to determining the emission height of
the optical photons from pulsars, which is directly constrained by empirical
data. The model discussed is for the case of the Crab pulsar. Our method, using
the optical Stokes parameters, determines the most likely geometry for emission
including magnetic field inclination angle (), observers line of sight
angle () and emission height. We discuss the computational implementation
of the approach, along with any physical assumptions made. We find that the
most likely emission altitude is at 20% of the light cylinder radius above the
stellar surface, in the open field region. We also present a general treatment
of the expected polarisation from synchrotron source with a truncated power law
spectrum of particles.Comment: 17 pages 16 figures; accepted for publication in MNRA
Perception of Motion and Architectural Form: Computational Relationships between Optical Flow and Perspective
Perceptual geometry refers to the interdisciplinary research whose objectives
focuses on study of geometry from the perspective of visual perception, and in
turn, applies such geometric findings to the ecological study of vision.
Perceptual geometry attempts to answer fundamental questions in perception of
form and representation of space through synthesis of cognitive and biological
theories of visual perception with geometric theories of the physical world.
Perception of form, space and motion are among fundamental problems in vision
science. In cognitive and computational models of human perception, the
theories for modeling motion are treated separately from models for perception
of form.Comment: 10 pages, 13 figures, submitted and accepted in DoCEIS'2012
Conference: http://www.uninova.pt/doceis/doceis12/home/home.ph
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