20,412 research outputs found
Selective excitation of plasmons superlocalized at sharp perturbations of metal nanoparticles
Sharp metal corners and tips support plasmons localized on the scale of the
curvature radius -- superlocalized plasmons. We analyze plasmonic properties of
nanoparticles with small and sharp corner- and tip-shaped surface perturbations
in terms of hybridization of the superlocalized plasmons, which frequencies are
determined by the perturbations shape, and the ordinary plasmons localized on
the whole particle. When the frequency of a superlocalized plasmon gets close
to that of the ordinary plasmon, their strong hybridization occurs and
facilitates excitation of an optical hot-spot near the corresponding
perturbation apex. The particle is then employed as a nano-antenna that
selectively couples the free-space light to the nanoscale vicinity of the apex
providing precise local light enhancement by several orders of magnitude
The Local Structure of Space-Variant Images
Local image structure is widely used in theories of both machine and biological vision. The form of the differential operators describing this structure for space-invariant images has been well documented (e.g. Koenderink, 1984). Although space-variant coordinates are universally used in mammalian visual systems, the form of the operators in the space-variant domain has received little attention. In this report we derive the form of the most common differential operators and surface characteristics in the space-variant domain and show examples of their use. The operators include the Laplacian, the gradient and the divergence, as well as the fundamental forms of the image treated as a surface. We illustrate the use of these results by deriving the space-variant form of corner detection and image enhancement algorithms. The latter is shown to have interesting properties in the complex log domain, implicitly encoding a variable grid-size integration of the underlying PDE, allowing rapid enhancement of large scale peripheral features while preserving high spatial frequencies in the fovea.Office of Naval Research (N00014-95-I-0409
Modeling of Polymer Clay Nanocomposite for a Multiscale Approach
The mechanical property enhancement of polymer reinforced with nano-thin clay
platelets (of high aspect ratio) is associated with a high polymer-filler
interfacial area per unit volume. The ideal case of fully separated
(exfoliated) platelets is generally difficult to achieve in practice: a typical
nanocomposite also contains multilayer stacks of intercalated platelets. Here
we use numerical modelling to investigate how the platelet properties affect
the overall mechanical properties. The configuration of platelets is modelled
using a statistical interpretation of the Representative Volume Element (RVE)
approach, in which an ensemble of "sample" heterogeneous material is generated
(with periodic boundary conditions). A simple Monte Carlo algorithm is used to
place non-intersecting platelets in the RVE according to a specified set of
statistical distributions. The effective stiffness of the platelet-matrix
system is determined by measuring the stress (using standard Finite Element
analysis) produced as a result of applying a small deformation to the
boundaries, and averaging over the entire statistical ensemble. In this work we
determine the way in which the platelet properties (curvature, filling
fraction, stiffness, aspect ratio) and the number of layers in the stack affect
the overall stiffness enhancement of the nanocomposite. Thus, we bridge the gap
between behaviour on the macroscopic scale with that on the scale of the
nano-reinforcement, forming part of a multi-scale modelling framework.Comment: 39 pages, 19 figure
The Physics of Unbounded, Broadband Absorption/Gain Efficiency in Plasmonic Nanoparticles
Anomalous resonances in properly shaped plasmonic nanostructures can in
principle lead to infinite absorption/gain efficiencies over broad bandwidths.
By developing a closed-form analytical solution for the fields scattered by
conjoined semicircles, we outline the fundamental physics behind these
phenomena, associated with broadband adiabatic focusing of surface plasmons at
the nanoscale. We are able to justify the apparent paradox of finite
absorption/gain in the limit of infinitesimally small material loss/gain, and
we explore the potential of these phenomena in nonlinear optics, spasing,
energy-harvesting and sensing.Comment: 19 pages, 7figure
Adaptive Nonlocal Filtering: A Fast Alternative to Anisotropic Diffusion for Image Enhancement
The goal of many early visual filtering processes is to remove noise while at the same time sharpening contrast. An historical succession of approaches to this problem, starting with the use of simple derivative and smoothing operators, and the subsequent realization of the relationship between scale-space and the isotropic dfffusion equation, has recently resulted in the development of "geometry-driven" dfffusion. Nonlinear and anisotropic diffusion methods, as well as image-driven nonlinear filtering, have provided improved performance relative to the older isotropic and linear diffusion techniques. These techniques, which either explicitly or implicitly make use of kernels whose shape and center are functions of local image structure are too computationally expensive for use in real-time vision applications. In this paper, we show that results which are largely equivalent to those obtained from geometry-driven diffusion can be achieved by a process which is conceptually separated info two very different functions. The first involves the construction of a vector~field of "offsets", defined on a subset of the original image, at which to apply a filter. The offsets are used to displace filters away from boundaries to prevent edge blurring and destruction. The second is the (straightforward) application of the filter itself. The former function is a kind generalized image skeletonization; the latter is conventional image filtering. This formulation leads to results which are qualitatively similar to contemporary nonlinear diffusion methods, but at computation times that are roughly two orders of magnitude faster; allowing applications of this technique to real-time imaging. An additional advantage of this formulation is that it allows existing filter hardware and software implementations to be applied with no modification, since the offset step reduces to an image pixel permutation, or look-up table operation, after application of the filter
A new Edge Detector Based on Parametric Surface Model: Regression Surface Descriptor
In this paper we present a new methodology for edge detection in digital
images. The first originality of the proposed method is to consider image
content as a parametric surface. Then, an original parametric local model of
this surface representing image content is proposed. The few parameters
involved in the proposed model are shown to be very sensitive to
discontinuities in surface which correspond to edges in image content. This
naturally leads to the design of an efficient edge detector. Moreover, a
thorough analysis of the proposed model also allows us to explain how these
parameters can be used to obtain edge descriptors such as orientations and
curvatures.
In practice, the proposed methodology offers two main advantages. First, it
has high customization possibilities in order to be adjusted to a wide range of
different problems, from coarse to fine scale edge detection. Second, it is
very robust to blurring process and additive noise. Numerical results are
presented to emphasis these properties and to confirm efficiency of the
proposed method through a comparative study with other edge detectors.Comment: 21 pages, 13 figures and 2 table
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