33,027 research outputs found
A New Perspective and Extension of the Gaussian Filter
The Gaussian Filter (GF) is one of the most widely used filtering algorithms;
instances are the Extended Kalman Filter, the Unscented Kalman Filter and the
Divided Difference Filter. GFs represent the belief of the current state by a
Gaussian with the mean being an affine function of the measurement. We show
that this representation can be too restrictive to accurately capture the
dependences in systems with nonlinear observation models, and we investigate
how the GF can be generalized to alleviate this problem. To this end, we view
the GF from a variational-inference perspective. We analyse how restrictions on
the form of the belief can be relaxed while maintaining simplicity and
efficiency. This analysis provides a basis for generalizations of the GF. We
propose one such generalization which coincides with a GF using a virtual
measurement, obtained by applying a nonlinear function to the actual
measurement. Numerical experiments show that the proposed Feature Gaussian
Filter (FGF) can have a substantial performance advantage over the standard GF
for systems with nonlinear observation models.Comment: Will appear in Robotics: Science and Systems (R:SS) 201
Photon pair-state preparation with tailored spectral properties by spontaneous four-wave mixing in photonic-crystal fiber
We study theoretically the generation of photon pairs by spontaneous
four-wave mixing (SFWM) in photonic crystal optical fiber. We show that it is
possible to engineer two-photon states with specific spectral correlation
(``entanglement'') properties suitable for quantum information processing
applications. We focus on the case exhibiting no spectral correlations in the
two-photon component of the state, which we call factorability, and which
allows heralding of single-photon pure-state wave packets without the need for
spectral post filtering. We show that spontaneous four wave mixing exhibits a
remarkable flexibility, permitting a wider class of two-photon states,
including ultra-broadband, highly-anticorrelated states.Comment: 17 pages, 7 figures, submitte
A Generic Framework for Tracking Using Particle Filter With Dynamic Shape Prior
©2007 IEEE. Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or distribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE. This material is presented to ensure timely dissemination of scholarly and technical work. Copyright and all rights therein are retained by authors or by other copyright holders. All persons copying this information are expected to adhere to the terms and constraints invoked by each author's copyright. In most cases, these works may not be reposted without the explicit permission of the copyright holder.DOI: 10.1109/TIP.2007.894244Tracking deforming objects involves estimating the global motion of the object and its local deformations as functions of time. Tracking algorithms using Kalman filters or particle filters (PFs) have been proposed for tracking such objects, but these have limitations due to the lack of dynamic shape information. In this paper, we propose a novel method based on employing a locally linear embedding in order to incorporate dynamic shape information into the particle filtering framework for tracking highly deformable objects in the presence of noise and clutter. The PF also models image statistics such as mean and variance of the given data which can be useful in obtaining proper separation of object and backgroun
Feedrate planning for machining with industrial six-axis robots
The authors want to thank Stäubli for providing the necessary information of the controller, Dynalog for its contribution to the experimental validations and X. Helle for its material contributions.Nowadays, the adaptation of industrial robots to carry out high-speed machining operations is strongly required by the manufacturing industry. This new technology machining process demands the improvement of the overall performances of robots to achieve an accuracy level close to that realized by machine-tools. This paper presents a method of trajectory planning adapted for continuous machining by robot. The methodology used is based on a parametric interpolation of the geometry in the operational space. FIR filters properties are exploited to generate the tool feedrate with limited jerk. This planning method is validated experimentally on an industrial robot
Theoretical optimal modulation frequencies for scattering parameter estimation and ballistic photon filtering in diffusive media
The efficiency of using intensity modulated light for estimation of
scattering properties of a turbid medium and for ballistic photon
discrimination is theoretically quantified in this article. Using the diffusion
model for modulated photon transport and considering a noisy quadrature
demodulation scheme, the minimum-variance bounds on estimation of parameters of
interest are analytically derived and analyzed. The existence of a
variance-minimizing optimal modulation frequency is shown and its evolution
with the properties of the intervening medium is derived and studied.
Furthermore, a metric is defined to quantify the efficiency of ballistic photon
filtering which may be sought when imaging through turbid media. The analytical
derivation of this metric shows that the minimum modulation frequency required
to attain significant ballistic discrimination depends only on the reduced
scattering coefficient of the medium in a linear fashion for a highly
scattering medium
On the non-local geometry of turbulence
A multi-scale methodology for the study of the non-local geometry of eddy structures in turbulence is developed. Starting from a given three-dimensional field, this consists of three main steps: extraction, characterization and classification of structures. The extraction step is done in two stages. First, a multi-scale decomposition based on the curvelet transform is applied to the full three-dimensional field, resulting in a finite set of component three-dimensional fields, one per scale. Second, by iso-contouring each component field at one or more iso-contour levels, a set of closed iso-surfaces is obtained that represents the structures at that scale. The characterization stage is based on the joint probability density function (p.d.f.), in terms of area coverage on each individual iso-surface, of two differential-geometry properties, the shape index and curvedness, plus the stretching parameter, a dimensionless global invariant of the surface. Taken together, this defines the geometrical signature of the iso-surface. The classification step is based on the construction of a finite set of parameters, obtained from algebraic functions of moments of the joint p.d.f. of each structure, that specify its location as a point in a multi-dimensional ‘feature space’. At each scale the set of points in feature space represents all structures at that scale, for the specified iso-contour value. This then allows the application, to the set, of clustering techniques that search for groups of structures with a common geometry. Results are presented of a first application of this technique to a passive scalar field obtained from 5123 direct numerical simulation of scalar mixing by forced, isotropic turbulence (Reλ = 265). These show transition, with decreasing scale, from blob-like structures in the larger scales to blob- and tube-like structures with small or moderate stretching in the inertial range of scales, and then toward tube and, predominantly, sheet-like structures with high level of stretching in the dissipation range of scales. Implications of these results for the dynamical behaviour of passive scalar stirring and mixing by turbulence are discussed
Photon engineering for quantum information processing
We study distinguishing information in the context of quantum interference
involving more than one parametric downconversion (PDC) source and in the
context of polarization-entangled photon pairs based on PDC. We arrive at
specific design criteria for two-photon sources so that when used as part of
complex optical systems, such as photon-based quantum information processing
schemes, distinguishing information between the photons is eliminated
guaranteeing high visibility interference. We propose practical techniques
which lead to suitably engineered two-photon states that can be realistically
implemented with available technology. Finally, we study an implementation of
the nonlinear-sign shift (NS) logic gate with PDC sources and show the effect
of distinguishing information on the performance of the gate.Comment: 23 pages, 13 figures. submitted to Quantum Information & Computatio
Accessing the purity of a single photon by the width of the Hong-Ou-Mandel interference
We demonstrate a method to determine the spectral purity of single photons.
The technique is based on the Hong-Ou-Mandel (HOM) interference between a
single photon state and a suitably prepared coherent field. We show that the
temporal width of the HOM dip is not only related to reciprocal of the spectral
width but also to the underlying quantum coherence. Therefore, by measuring the
width of both the HOM dip and the spectrum one can directly quantify the degree
of spectral purity. The distinct advantage of our proposal is that it obviates
the need for perfect mode matching, since it does not rely on the visibility of
the interference. Our method is particularly useful for characterizing the
purity of heralded single photon states.Comment: Extended version, 16 pages, 9 figure
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