Search results for "optical"
showing 10 items of 7671 documents
Real And Positive Filter Based On Circular Harmonic Expansion
1989
A real and positive filter for pattern recognition is presented. The filter, based on the circular harmonic (CH) expansion of a real function, is partially rotation invariant. As it is real and positive, the filter can be recorded on a transparency as an amplitude filter. Computer simulations of character recognition show a partial rotation invariance of about 40°. Optical experiments agree with these results and with acceptable discrimination between different characters. Nevertheless, due to experimental difficulties, the method is onerous for use in general pattern recognition problems.
Perceptually weighted optical flow for motion-based segmentation in MPEG-4 paradigm
2000
In the MPEG-4 paradigm, the sequence must be described in terms of meaningful objects. This meaningful, high-level representation should emerge from low-level primitives such as optical flow and prediction error which are the basic elements of previous-generation video coders. The accuracy of the high-level models strongly depends on the robustness of the primitives used. It is shown how perceptual weighting in optical flow computation gives rise to better motion estimates which consistently improve motion-based segmentation compared to equivalent unweighted motion estimates.
Development of a multispectral imagery device devoted to weed detection
2003
Multispectral imagery is a large domain with number of practical applications: thermography, quality control in industry, food science and agronomy, etc. The main interest is to obtain spectral information of the objects for which reflectance signal can be associated with physical, chemical and/or biological properties. Agronomic applications of multispectral imagery generally involve the acquisition of several images in the wavelengths of visible and near infrared. This paper will first present different kind of multispectral devices used for agronomic issues and will secondly introduce an original multispectral design based on a single CCD. Third, early results obtained for weed detection…
Optical flow estimation from multichannel spherical image decomposition
2011
The problem of optical flow estimation is largely discussed in computer vision domain for perspective images. It was also proven that, in terms of optical flow analysis from these images, we have difficulty distinguishing between some motion fields obtained with little camera motion. The omnidirectional cameras provided images with large filed of view. These images contain global information about motion and allow to remove the ambiguity present in perspective case. Nevertheless, these images contain significant radial distortions that is necessary to take into account when treating these images to estimate the motion. In this paper, we shall describe new way to compute efficient optical fl…
Bottle microresonator with actively stabilized evanescent coupling
2011
The evanescent coupling of light between a whispering-gallery-mode bottle microresonator and a sub-wavelength-diameter coupling fiber is actively stabilized by means of a Pound-Drever-Hall technique. We demonstrate the stabilization of a critically coupled resonator with a control bandwidth of 0.1 Hz, yielding a residual transmission of (9 \pm 3) \times 10^-3 for more than an hour. Simultaneously, the frequency of the resonator mode is actively stabilized.
Third-harmonic generation in optical microfibers: From silica experiments to highly nonlinear glass prospects
2012
International audience; Using optical microfibers, phase matching between different propagation modes allows for third-harmonic generation (THG). After detailing the relevant phase matching conditions and overlap integrals, we provide a comparison between THG effective efficiencies in silica and tellurite glasses. We also explain the relatively easy, wideband, conversion that we observe experimentally in silica glass microfibers, from 155 mu m to the green, by the geometry of the tapering region.
Influence of M23C6 carbides on the heterogeneous strain development in annealed 420 stainless steel
2020
Understanding the local strain enhancement and lattice distortion resulting from different microstructure features in metal alloys is crucial in many engineering processes. The development of heterogeneous strain not only plays an important role in the work hardening of the material but also in other processes such as recrystallization and damage inheritance and fracture. Isolating the contribution of precipitates to the development of heterogeneous strain can be challenging due to the presence of grain boundaries or other microstructure features that might cause ambiguous interpretation. In this work a statistical analysis of local strains measured by electron back scatter diffraction and …
Density Functional Theory Investigation on the Nucleation and Growth of Small Palladium Clusters on a Hyper-Cross-Linked Polystyrene Matrix
2014
Density functional theory calculations were employed to investigate the nucleation and growth of small palladium clusters, up to Pd9, into a microcavity of the porous hyper-cross-linked polystyrene (HPS). The geometries and the electronic structures of the palladium clusters inside the HPS cavity, following the one-by-one atom addition, are affected by a counterbalance between the Pd–phenyl (Pd−Φ) and Pd–Pd interactions. The analysis performed on energetics, cavity distortions, and cluster geometries indeed suggest that the cluster growth is dominated by the Pd−Φ interactions up to the formation of Pd4 aggregates, whereas the metal–metal interactions actually rule the growth of the larger c…
A general diastereoselective synthesis of highly functionalized ferrocenyl ambiphiles enabled on a large scale by electrochemical purification
2017
International audience; A general synthesis of highly functionalized ferrocenes, which include (P,B)- and (N,B)-ambiphiles, has been developed at a multigram scale. Diastereoselective stepwise modification of di-tert-butylated ferrocenes included the unprecedented separation of electroactive species. Bulky alkyl groups on ferrocenes ensure planar chirality of ambiphiles and enforce closer proximity of antagonist Lewis functions.
Airy-function approach to binary black hole merger waveforms: The fold-caustic diffraction model
2022
From numerical simulations of the Einstein equations, and also from gravitational wave observations, the gravitational wave signal from a binary black hole merger is seen to be simple and to possess certain universal features. The simplicity is somewhat surprising given that non-linearities of general relativity are thought to play an important role at the merger. The universal features include an increasing amplitude as we approach the merger, where transition from an oscillatory to a damped regime occurs in a pattern apparently oblivious to the initial conditions. We propose an Airy-function pattern to model the binary black hole (BBH) merger waveform, focusing on accounting for its simpl…