José A. Ferrari

Bio: José A. Ferrari is an academic researcher from University of the Republic. The author has contributed to research in topics: Interferometry & Image processing. The author has an hindex of 19, co-authored 132 publications receiving 1297 citations. Previous affiliations of José A. Ferrari include Simón Bolívar University.

Edge enhancement of color images using a digital micromirror device.

Abstract: A method for orientation-selective enhancement of edges in color images is proposed. The method utilizes the capacity of digital micromirror devices to generate a positive and a negative color replica of the image used as input. When both images are slightly displaced and imagined together, one obtains an image with enhanced edges. The proposed technique does not require a coherent light source or precise alignment. The proposed method could be potentially useful for processing large image sequences in real time. Validation experiments are presented.

Space integrating joint transform correlator using a moving grating

Abstract: A new one-step joint transform correlator (JTC) is presented, in which the joint transform of the images to be correlated is filtered by a moving Ronchi ruling. An alternative JTC architecture without moving parts using two Ronchi rulings is also suggested. A lens produces the spatial integral of the product of the joint transform image and the trans- mission factor of the Ronchi ruling, and a single element detector is used to capture the integral. The amplitude of the light modulation on the detector gives the cross-correlation function of the input images at coor- dinates (0,0) without major processing. Therefore, in principle this tech- nique significantly reduces the time required to evaluate the cross- correlation function, compared to that for usual JTCs. Experimental validation of the proposed one-step architecture is presented. © 1999 Society of Photo-Optical Instrumentation Engineers. (S0091-3286(99)01807-3)

Transversal observation of the light-induced color-center concentration in photochromic glasses in stationary state.

Abstract: The aim of the present work is to study the dependence of the light-induced optical density, i.e., the color-center concentration, as a function of the distance traveled inside a photochromic glass body in stationary state. We propose an experimental setup that allows the direct observation of that concentration from a transversal view. In particular, we will see that for activating intensities much higher than certain threshold, the photochromic material saturates between the surface and an inflection point that happens at a constant normalized concentration of 2/3. The width of this region depends logarithmically on the activating light intensity. This fact will allow us to determine one of the photochemical constants of the material. Validation experiments are presented.

Conversion of bright nondiffracting beams into dark nondiffracting beams by use of the topological properties of polarized light.

Abstract: We present a method for the generation of an axial phase dislocation on a wave front, which is induced by topological properties of polarized light This effect is shown to be useful for conversion of bright nondiffracting beams into dark nondiffracting beams Experiments showing the generation of dark nondiffracting beams have been performed

Faraday rotation measurement with photorefractive Bi12TiO20: comment

Abstract: In a recent paper (Opt. Laser Technol. 34 (2002) 605) Anand and Narayanamurthy described a method for measurement of Faraday rotations using a photorefractive Bi 12 TiO 20 . The effects they observed have nothing to do with the source intensity nor with the photorefractive nature of the crystal. The same effect could be obtained without the use of a photorefractive crystal by simple rotation of the analyzer.

The SIESTA method for ab initio order-N materials simulation

Abstract: We have developed and implemented a selfconsistent density functional method using standard norm-conserving pseudopotentials and a flexible, numerical linear combination of atomic orbitals basis set, which includes multiple-zeta and polarization orbitals. Exchange and correlation are treated with the local spin density or generalized gradient approximations. The basis functions and the electron density are projected on a real-space grid, in order to calculate the Hartree and exchange-correlation potentials and matrix elements, with a number of operations that scales linearly with the size of the system. We use a modified energy functional, whose minimization produces orthogonal wavefunctions and the same energy and density as the Kohn-Sham energy functional, without the need for an explicit orthogonalization. Additionally, using localized Wannier-like electron wavefunctions allows the computation time and memory required to minimize the energy to also scale linearly with the size of the system. Forces and stresses are also calculated efficiently and accurately, thus allowing structural relaxation and molecular dynamics simulations.

Medscape

Abstract: Secret History: Return of the Black Death Channel 4, 7-8pm In 1348 the Black Death swept through London, killing people within days of the appearance of their first symptoms. Exactly how many died, and why, has long been a mystery. This Secret History documentary follows experts as they pick through the evidence and reveal why the plague killed on such a scale. And they ask, what might be coming next?

Fourier-transform method of fringe-pattern analysis for computer-based topography and interferometry

Abstract: A fast-Fourier-transform method of topography and interferometry is proposed. By computer processing of a noncontour type of fringe pattern, automatic discrimination is achieved between elevation and depression of the object or wave-front form, which has not been possible by the fringe-contour-generation techniques. The method has advantages over moire topography and conventional fringe-contour interferometry in both accuracy and sensitivity. Unlike fringe-scanning techniques, the method is easy to apply because it uses no moving components.

Digital wavefront measuring interferometer for testing optical surfaces and lenses

Abstract: A self-scanned 1024 element photodiode array and minicomputer are used to measure the phase (wavefront) in the interference pattern of an interferometer to lambda/100. The photodiode array samples intensities over a 32 x 32 matrix in the interference pattern as the length of the reference arm is varied piezoelectrically. Using these data the minicomputer synchronously detects the phase at each of the 1024 points by a Fourier series method and displays the wavefront in contour and perspective plot on a storage oscilloscope in less than 1 min (Bruning et al. Paper WE16, OSA Annual Meeting, Oct. 1972). The array of intensities is sampled and averaged many times in a random fashion so that the effects of air turbulence, vibrations, and thermal drifts are minimized. Very significant is the fact that wavefront errors in the interferometer are easily determined and may be automatically subtracted from current or subsequent wavefrots. Various programs supporting the measurement system include software for determining the aperture boundary, sum and difference of wavefronts, removal or insertion of tilt and focus errors, and routines for spatial manipulation of wavefronts. FFT programs transform wavefront data into point spread function and modulus and phase of the optical transfer function of lenses. Display programs plot these functions in contour and perspective. The system has been designed to optimize the collection of data to give higher than usual accuracy in measuring the individual elements and final performance of assembled diffraction limited optical systems, and furthermore, the short loop time of a few minutes makes the system an attractive alternative to constraints imposed by test glasses in the optical shop.