56,749 research outputs found
Shape matching by curve modelling and alignment
Automatic information retrieval in the eld of shape recognition has been widely covered by many
research elds. Various techniques have been developed using different approaches such as intensity-based, modelbased
and shape-based methods. Whichever is the way to represent the objects in images, a recognition method
should be robust in the presence of scale change, translation and rotation. In this paper we present a new recognition
method based on a curve alignment technique, for planar image contours. The method consists of various phases
including extracting outlines of images, detecting signicant points and aligning curves. The dominant points can
be manually or automatically detected. The matching phase uses the idea of calculating the overlapping indices
between shapes as similarity measures. To evaluate the effectiveness of the algorithm, two databases of 216 and
99 images have been used. A performance analysis and comparison is provided by precision-recall curves
Holographic Holes and Differential Entropy
Recently, it has been shown by Balasubramanian et al. and Myers et al. that
the Bekenstein-Hawking entropy formula evaluated on certain closed surfaces in
the bulk of a holographic spacetime has an interpretation as the differential
entropy of a particular family of intervals (or strips) in the boundary theory.
We first extend this construction to bulk surfaces which vary in time. We then
give a general proof of the equality between the gravitational entropy and the
differential entropy. This proof applies to a broad class of holographic
backgrounds possessing a generalized planar symmetry and to certain classes of
higher-curvature theories of gravity. To apply this theorem, one can begin with
a bulk surface and determine the appropriate family of boundary intervals by
considering extremal surfaces tangent to the given surface in the bulk.
Alternatively, one can begin with a family of boundary intervals; as we show,
the differential entropy then equals the gravitational entropy of a bulk
surface that emerges from the intersection of the neighboring entanglement
wedges, in a continuum limit.Comment: 62 pages; v2: minor improvements to presentation, references adde
Liquid crystal anchoring transitions on aligning substrates processed by plasma beam
We observe a sequence of the anchoring transitions in nematic liquid crystals
(NLC) sandwiched between the hydrophobic polyimide substrates treated with the
plasma beam. There is a pronounced continuous transition from homeotropic to
low tilted (nearly planar) alignment with the easy axis parallel to the
incidence plane of the plasma beam (the zenithal transition) that takes place
as the exposure dose increases. In NLC with positive dielectric anisotropy, a
further increase in the exposure dose results in in-plane reorientation of the
easy axis by 90 degrees (the azimuthal transition). This transition occurs
through the two-fold degenerated alignment characteristic for the second order
anchoring transitions. In contrast to critical behavior of anchoring, the
contact angle of NLC and water on the treated substrates monotonically declines
with the exposure dose. It follows that the surface concentration of
hydrophobic chains decreases continuously. The anchoring transitions under
consideration are qualitatively interpreted by using a simple phenomenological
model of competing easy axes which is studied by analyzing anchoring diagrams
of the generalized polar and non-polar anchoring models.Comment: revtex4, 18 pages, 10 figure
Shear banding in nematogenic fluids with oscillating orientational dynamics
We investigate the occurrence of shear banding in nematogenic fluids under
planar Couette flow, based on mesoscopic dynamical equations for the
orientational order parameter and the shear stress. We focus on parameter
values where the sheared homogeneous system exhibits regular oscillatory
orientational dynamics, whereas the equilibrium system is either isotropic
(albeit close to the isotropic--nematic transition) or deep in its nematic
phase. The numerical calculations are restricted to spatial variations in shear
gradient direction. We find several new types of shear banded states
characterized by regions with regular oscillatory orientational dynamics. In
all cases shear banding is accompanied by a non--monotonicity of the flow curve
of the homogeneous system; however, only in the case of the initially isotropic
system this curve has the typical --like shape. We also analyze the
influence of different orientational boundary conditions and of the spatial
correlation length.Comment: 12 pages, 10 figure
Chromatic dispersion of liquid crystal infiltrated capillary tubes and photonic crystal fibers
We consider chromatic dispersion of capillary tubes and photonic crystal
fibers infiltrated with liquid crystals. A perturbative scheme for inclusion of
material dispersion of both liquid crystal and the surrounding waveguide
material is derived. The method is used to calculate the chromatic dispersion
at different temperatures.Comment: 18 pages, 8 figures. Manuscript layout changed Feb. 10th 200
Image based visual servoing using algebraic curves applied to shape alignment
Visual servoing schemes generally employ various image features (points, lines, moments etc.) in their control formulation. This paper presents a novel method for using boundary information in visual servoing. Object boundaries are
modeled by algebraic equations and decomposed as a unique sum of product of lines. We propose that these lines can be used to extract useful features for visual servoing purposes. In this paper, intersection of these lines are used as point features in visual servoing. Simulations are performed with a 6 DOF Puma
560 robot using Matlab Robotics Toolbox for the alignment of a free-form object. Also, experiments are realized with a 2 DOF SCARA direct drive robot. Both simulation and experimental results are quite promising and show potential of our new method
Image based visual servoing using bitangent points applied to planar shape alignment
We present visual servoing strategies based on bitangents for aligning planar shapes. In order to acquire bitangents we use convex-hull of a curve. Bitangent points are employed in the construction of a feature vector to be used in visual control. Experimental results obtained on a 7 DOF Mitsubishi PA10 robot, verifies the proposed method
Spin-polarized currents in superconducting films
We present a microscopic theory of coherent quantum transport through a
superconducting film between two ferromagnetic electrodes. The scattering
problem is solved for the general case of
ferromagnet/superconductor/ferromagnet (FSF) double-barrier junction, including
the interface transparency from metallic to tunnel limit, and the Fermi
velocity mismatch. Charge and spin conductance spectra of FSF junctions are
calculated for parallel (P) and antiparallel (AP) alignment of the electrode
magnetization. Limiting cases of nonmagnetic normal-metal electrodes (NSN) and
of incoherent transport are also presented. We focus on two characteristic
features of finite size and coherency: subgap tunneling of electrons, and
oscillations of the differential conductance. Periodic vanishing of the Andreev
reflection at the energies of geometrical resonances above the superconducting
gap is a striking consequence of the quasiparticle interference. Also, the
non-trivial spin-polarization of the current is found for FSF junctions in AP
alignment. This is in contrast with the incoherent transport, where the
unpolarized current is accompanied by excess spin accumulation and destruction
of superconductivity. Application to spectroscopic measurements of the
superconducting gap and the Fermi velocity is also discussed.Comment: 11 pages, 11 figure
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