Luis Alvarez - Academia.edu (original) (raw)
Papers by Luis Alvarez
Alfred Loomis
Physics Today, 1975
National Academy
Physics Today, 1949
Meson Physics
Physics Today, 1953
Excerpts from a RUSSIAN DIARY
Physics Today, 1957
Alvarez: Adventures of a Physicist
Physics Today, 1987
Alvarez: Adventures of a Physicist. [Physics Today 40, 83 (1987)]. Luis W. Alvarez, Richard L. Ga... more Alvarez: Adventures of a Physicist. [Physics Today 40, 83 (1987)]. Luis W. Alvarez, Richard L. Garwin Reviewer. Keywords. Publications of lectures (advanced institutes, summer schools, etc.). Careers in physics and science.
Photooxidative bleaching of chlorophyllin
Free Radical Research, 1999
Chlorophyllin, a water-soluble, copper-containing porphyrin, can be bleached rapidly in the light... more Chlorophyllin, a water-soluble, copper-containing porphyrin, can be bleached rapidly in the light or slowly in the dark in a reaction which is oxygen dependent. Both the photo and the dark bleaching reactions are temperature dependent. Cyclic voltammetry measurements show that the copper in the bleached and nonbleached state remains in the +2 redox state and could be readily reduced. This would imply that there is no net oxidative change to the copper during the bleaching process. FT-IR absorption spectroscopy showed vibrations characteristic of a vinyl functionality disappeared upon bleaching. Aqueous solutions of chlorophyllin were not dialyzable through dialysis tubing of molecular weight cut-off, 6000-8000 molecular weight, indicative of an aggregate chlorophyllin micelle. Analysis of products by high performance liquid chromatography showed that the chlorophyllin mixture was more complex than originally anticipated and that two components were lost from the mixture upon photobleaching. One compound that is preferentially lost upon photobleaching has been identified by mass spectral analysis as Cu(II) chlorin e6.
Biophysical Journal, 2009
The modifications induced by reactive oxygen species (ROS) on fluorescent proteins (FPs) may have... more The modifications induced by reactive oxygen species (ROS) on fluorescent proteins (FPs) may have important implications for live cell fluorescence imaging. Using quantitative c-radiolysis, we have studied the ROS-induced biochemical and photophysical perturbations on recombinant cyan fluorescent protein (CFP). After oxidation by the • OH radical, the protein displays a modified RP-HPLC elution profile, while the CFP fluorescence undergoes pronounced decreases in intensity and lifetime, without changes in its excitation and emission spectra. Meanwhile, the Fo¨rster resonant energy transfer (FRET) between the single W 57 and the chromophore remains unperturbed. These results rule out a direct oxidation of the CFP chromophore and of W 57 as well as major changes in the protein 3D structure, but show that new fluorescent forms associated to a higher level of dynamic quenching have been generated. Thus, strict in situ controls are required when CFP is to be used for FRET studies in situations of oxidative activity, or under strong illumination.
Alvarez: Adventures of a Physicist
American Journal of Physics, 1989
Journal of Mathematical Imaging and Vision, 2009
A very important property of the usual pinhole model for camera projection is that 3D lines in th... more A very important property of the usual pinhole model for camera projection is that 3D lines in the scene are projected in 2D lines. Unfortunately, wide-angle lenses (specially lowcost lenses) may introduce a strong barrel distortion which makes the usual pinhole model fail. Lens distortion models try to correct such distortion. In this paper, we propose an algebraic approach to the estimation of the lens distortion parameters based on the rectification of lines in the image. Using the proposed method, the lens distortion parameters are obtained by minimizing a 4 total-degree polynomial in several variables. We perform numerical experiments using calibration patterns and real scenes to show the performance of the proposed method.
Lecture Notes in Computer Science, 1997
We use an optimum quantizer according to an energy criterion to divide the histogram of the image... more We use an optimum quantizer according to an energy criterion to divide the histogram of the image into subintervals whose sizes are inversely proportional to the number of pixels affected. By establishing a correspondence between this quantizer and the evenly distributed one, we obtain a new image where the most frequent grey levels are expanded whereas those grey levels with less number of pixels are compressed.
Normalization and feature extraction on ear images
2012 IEEE International Carnahan Conference on Security Technology (ICCST), 2012
ABSTRACT Ear image analysis is an emerging biometrie application. A method for normalizing ear im... more ABSTRACT Ear image analysis is an emerging biometrie application. A method for normalizing ear images and extracting from them a set of measurable features (feature vector) that can be used to identify its owner is proposed. The identification would be made based on the comparison between the feature vector of the input image and all feature vectors of the images in the database we work with. The feature vector is based on the ear contours. One important goal of this paper is to identify the most significant areas in the ear contour for human being identification purpose. Another important contribution of the paper is the combination of active contours techniques and ovoid model ear fitting (used to normalize ear features) and a high accurate invariant approach of internal and external ear contours. Ear geometry is characterized using a set of distances to external and internal contours points. This set of distances, along with six ovoid parameters is considered as the feature vector of the image. To test the method a new ear images database has been created. The proposed method identifies front-parallel views pretty good, even when varying the distance of the individual to the camera or the camera lens.
Morphological snakes
2010 IEEE Computer Society Conference on Computer Vision and Pattern Recognition, 2010
Page 1. Morphological Snakes Luis Álvarez Luis Baumela Pedro Henríquez Pablo Márquez-Neila D... more Page 1. Morphological Snakes Luis Álvarez Luis Baumela Pedro Henríquez Pablo Márquez-Neila Dep. Informática y Sistemas Universidad de las Palmas de Gran Canaria http://ami.dis.ulpgc.es/ Dep. Inteligencia Artificial ...
Image Processing On Line, 2012
Active contours, or snakes, are computer-generated curves that move within images to find out sal... more Active contours, or snakes, are computer-generated curves that move within images to find out salient image structures like object boundaries. Energy based formulations using a level set approach have been successfully used to model the snake evolution. The Euler-Lagrange equation associated to such energies yields to partial differential equations (PDE) which are usually solved using level set methods which involve contour distance function estimation and standard methods to discretize the PDE. Recently we have proposed a morphological approach to snake evolution. First, we observe that the differential operators used in the standard PDE snake models can be approached using morphological operations. By combining the morphological operators associated to the PDE components we achieve a new morphological approach to the PDE snakes evolution. This new approach is based on numerical methods which are very simple and fast. Moreover, since the level set is just a binary piecewise constant function, this approach does not require to estimate a contour distance function to define the level set. In this paper we present an algorithm to compute morphological snake evolution in real time.
Image Processing On Line, 2010
Communicated by Pascal Monasse monasse@imagine.enpc.fr, IMAGINE, ENPC ParisTech Edited by Nicolas... more Communicated by Pascal Monasse monasse@imagine.enpc.fr, IMAGINE, ENPC ParisTech Edited by Nicolas Limare nicolas.limare@cmla.ens-cachan.fr, CMLA, ENS Cachan Overview A very important property of the usual pinhole model for camera projection is that 3D lines in the scene are projected to 2D lines. Unfortunately, wide-angle lenses (specially low-cost lenses) may introduce a strong barrel distortion, which makes the usual pinhole model fail. Lens distortion models try to correct such distortion. In reference 1., we propose an algebraic approach to the estimation of the lens distortion parameters based on the rectification of lines in the image.
Image Processing On Line, 2014
We present a method to automatically correct the radial distortion caused by wide-angle lenses us... more We present a method to automatically correct the radial distortion caused by wide-angle lenses using the distorted lines generated by the projection on the image of 3D straight lines. Lens distortion is estimated by the division model using one parameter, which allows to state the problem into the Hough transform scheme by adding a distortion parameter to better extract straight lines from the image. This paper describes an algorithm which applies this technique, providing all the details of the design of an improved Hough transform. We perform experiments using calibration patterns and real scenes showing a strong distortion to illustrate the performance of the proposed method.
Lecture Notes in Computer Science, 2010
Thick line center and width estimation are important problems in computer vision. In this paper, ... more Thick line center and width estimation are important problems in computer vision. In this paper, we analyze this issue in real situations where we have to deal with some additional difficulties, such as the thick line distortion produced by interlaced broadcast video cameras or large shaded areas in the scene. We propose a technique to properly extract the thick lines and their centers using mathematical morphological operators. In order to illustrate the performance of the method, we present some numerical experiments in real images.
Pattern Recognition, 2014
Journal of Mathematical Imaging and Vision, 2012
We propose new mathematical models to study the variation of lens distortion models when we chang... more We propose new mathematical models to study the variation of lens distortion models when we change zoom setting in the case of zoom lenses. The new models are based on a polynomial approximation to account for the variation of the radial distortion parameters through the range of zoom lens settings and the minimization of a global error energy measuring the distance between sequences of distorted aligned points and straight lines after lens distortion correction. To validate the performance of the method we present experimental results on calibration pa-ttern images and on sport event scenarios using broadcast video cameras. We obtain, experimentally, that using just a second order polynomial approximation of lens distortion parameter zoom variation, the quality of lens distortion correction is as good as the one obtained individually frame by frame using independent lens distortion model for each frame.
Differential Equations & Applications, 2011
In this paper we study a variational problem derived from a computer vision application: video ca... more In this paper we study a variational problem derived from a computer vision application: video camera calibration with smoothing constraint. By video camera calibration we mean to estimate the location, orientation and lens zoom-setting of the camera for each video frame taking into account image visible features. To simplify the problem we assume that the camera is mounted on a tripod, in such case, for each frame captured at time t , the calibration is provided by 3 parameters : (1) P(t) (PAN) which represents the tripod vertical axis rotation, (2) T (t) (TILT) which represents the tripod horizontal axis rotation and (3) Z(t) (CAMERA ZOOM) the camera lens zoom setting. The calibration function t → u(t) = (P(t),T (t),Z(t)) is obtained as the minima of an energy function I [u] . In this paper we study the existence of minima of such energy function as well as the solutions of the associated Euler-Lagrange equations.
Alfred Loomis
Physics Today, 1975
National Academy
Physics Today, 1949
Meson Physics
Physics Today, 1953
Excerpts from a RUSSIAN DIARY
Physics Today, 1957
Alvarez: Adventures of a Physicist
Physics Today, 1987
Alvarez: Adventures of a Physicist. [Physics Today 40, 83 (1987)]. Luis W. Alvarez, Richard L. Ga... more Alvarez: Adventures of a Physicist. [Physics Today 40, 83 (1987)]. Luis W. Alvarez, Richard L. Garwin Reviewer. Keywords. Publications of lectures (advanced institutes, summer schools, etc.). Careers in physics and science.
Photooxidative bleaching of chlorophyllin
Free Radical Research, 1999
Chlorophyllin, a water-soluble, copper-containing porphyrin, can be bleached rapidly in the light... more Chlorophyllin, a water-soluble, copper-containing porphyrin, can be bleached rapidly in the light or slowly in the dark in a reaction which is oxygen dependent. Both the photo and the dark bleaching reactions are temperature dependent. Cyclic voltammetry measurements show that the copper in the bleached and nonbleached state remains in the +2 redox state and could be readily reduced. This would imply that there is no net oxidative change to the copper during the bleaching process. FT-IR absorption spectroscopy showed vibrations characteristic of a vinyl functionality disappeared upon bleaching. Aqueous solutions of chlorophyllin were not dialyzable through dialysis tubing of molecular weight cut-off, 6000-8000 molecular weight, indicative of an aggregate chlorophyllin micelle. Analysis of products by high performance liquid chromatography showed that the chlorophyllin mixture was more complex than originally anticipated and that two components were lost from the mixture upon photobleaching. One compound that is preferentially lost upon photobleaching has been identified by mass spectral analysis as Cu(II) chlorin e6.
Biophysical Journal, 2009
The modifications induced by reactive oxygen species (ROS) on fluorescent proteins (FPs) may have... more The modifications induced by reactive oxygen species (ROS) on fluorescent proteins (FPs) may have important implications for live cell fluorescence imaging. Using quantitative c-radiolysis, we have studied the ROS-induced biochemical and photophysical perturbations on recombinant cyan fluorescent protein (CFP). After oxidation by the • OH radical, the protein displays a modified RP-HPLC elution profile, while the CFP fluorescence undergoes pronounced decreases in intensity and lifetime, without changes in its excitation and emission spectra. Meanwhile, the Fo¨rster resonant energy transfer (FRET) between the single W 57 and the chromophore remains unperturbed. These results rule out a direct oxidation of the CFP chromophore and of W 57 as well as major changes in the protein 3D structure, but show that new fluorescent forms associated to a higher level of dynamic quenching have been generated. Thus, strict in situ controls are required when CFP is to be used for FRET studies in situations of oxidative activity, or under strong illumination.
Alvarez: Adventures of a Physicist
American Journal of Physics, 1989
Journal of Mathematical Imaging and Vision, 2009
A very important property of the usual pinhole model for camera projection is that 3D lines in th... more A very important property of the usual pinhole model for camera projection is that 3D lines in the scene are projected in 2D lines. Unfortunately, wide-angle lenses (specially lowcost lenses) may introduce a strong barrel distortion which makes the usual pinhole model fail. Lens distortion models try to correct such distortion. In this paper, we propose an algebraic approach to the estimation of the lens distortion parameters based on the rectification of lines in the image. Using the proposed method, the lens distortion parameters are obtained by minimizing a 4 total-degree polynomial in several variables. We perform numerical experiments using calibration patterns and real scenes to show the performance of the proposed method.
Lecture Notes in Computer Science, 1997
We use an optimum quantizer according to an energy criterion to divide the histogram of the image... more We use an optimum quantizer according to an energy criterion to divide the histogram of the image into subintervals whose sizes are inversely proportional to the number of pixels affected. By establishing a correspondence between this quantizer and the evenly distributed one, we obtain a new image where the most frequent grey levels are expanded whereas those grey levels with less number of pixels are compressed.
Normalization and feature extraction on ear images
2012 IEEE International Carnahan Conference on Security Technology (ICCST), 2012
ABSTRACT Ear image analysis is an emerging biometrie application. A method for normalizing ear im... more ABSTRACT Ear image analysis is an emerging biometrie application. A method for normalizing ear images and extracting from them a set of measurable features (feature vector) that can be used to identify its owner is proposed. The identification would be made based on the comparison between the feature vector of the input image and all feature vectors of the images in the database we work with. The feature vector is based on the ear contours. One important goal of this paper is to identify the most significant areas in the ear contour for human being identification purpose. Another important contribution of the paper is the combination of active contours techniques and ovoid model ear fitting (used to normalize ear features) and a high accurate invariant approach of internal and external ear contours. Ear geometry is characterized using a set of distances to external and internal contours points. This set of distances, along with six ovoid parameters is considered as the feature vector of the image. To test the method a new ear images database has been created. The proposed method identifies front-parallel views pretty good, even when varying the distance of the individual to the camera or the camera lens.
Morphological snakes
2010 IEEE Computer Society Conference on Computer Vision and Pattern Recognition, 2010
Page 1. Morphological Snakes Luis Álvarez Luis Baumela Pedro Henríquez Pablo Márquez-Neila D... more Page 1. Morphological Snakes Luis Álvarez Luis Baumela Pedro Henríquez Pablo Márquez-Neila Dep. Informática y Sistemas Universidad de las Palmas de Gran Canaria http://ami.dis.ulpgc.es/ Dep. Inteligencia Artificial ...
Image Processing On Line, 2012
Active contours, or snakes, are computer-generated curves that move within images to find out sal... more Active contours, or snakes, are computer-generated curves that move within images to find out salient image structures like object boundaries. Energy based formulations using a level set approach have been successfully used to model the snake evolution. The Euler-Lagrange equation associated to such energies yields to partial differential equations (PDE) which are usually solved using level set methods which involve contour distance function estimation and standard methods to discretize the PDE. Recently we have proposed a morphological approach to snake evolution. First, we observe that the differential operators used in the standard PDE snake models can be approached using morphological operations. By combining the morphological operators associated to the PDE components we achieve a new morphological approach to the PDE snakes evolution. This new approach is based on numerical methods which are very simple and fast. Moreover, since the level set is just a binary piecewise constant function, this approach does not require to estimate a contour distance function to define the level set. In this paper we present an algorithm to compute morphological snake evolution in real time.
Image Processing On Line, 2010
Communicated by Pascal Monasse monasse@imagine.enpc.fr, IMAGINE, ENPC ParisTech Edited by Nicolas... more Communicated by Pascal Monasse monasse@imagine.enpc.fr, IMAGINE, ENPC ParisTech Edited by Nicolas Limare nicolas.limare@cmla.ens-cachan.fr, CMLA, ENS Cachan Overview A very important property of the usual pinhole model for camera projection is that 3D lines in the scene are projected to 2D lines. Unfortunately, wide-angle lenses (specially low-cost lenses) may introduce a strong barrel distortion, which makes the usual pinhole model fail. Lens distortion models try to correct such distortion. In reference 1., we propose an algebraic approach to the estimation of the lens distortion parameters based on the rectification of lines in the image.
Image Processing On Line, 2014
We present a method to automatically correct the radial distortion caused by wide-angle lenses us... more We present a method to automatically correct the radial distortion caused by wide-angle lenses using the distorted lines generated by the projection on the image of 3D straight lines. Lens distortion is estimated by the division model using one parameter, which allows to state the problem into the Hough transform scheme by adding a distortion parameter to better extract straight lines from the image. This paper describes an algorithm which applies this technique, providing all the details of the design of an improved Hough transform. We perform experiments using calibration patterns and real scenes showing a strong distortion to illustrate the performance of the proposed method.
Lecture Notes in Computer Science, 2010
Thick line center and width estimation are important problems in computer vision. In this paper, ... more Thick line center and width estimation are important problems in computer vision. In this paper, we analyze this issue in real situations where we have to deal with some additional difficulties, such as the thick line distortion produced by interlaced broadcast video cameras or large shaded areas in the scene. We propose a technique to properly extract the thick lines and their centers using mathematical morphological operators. In order to illustrate the performance of the method, we present some numerical experiments in real images.
Pattern Recognition, 2014
Journal of Mathematical Imaging and Vision, 2012
We propose new mathematical models to study the variation of lens distortion models when we chang... more We propose new mathematical models to study the variation of lens distortion models when we change zoom setting in the case of zoom lenses. The new models are based on a polynomial approximation to account for the variation of the radial distortion parameters through the range of zoom lens settings and the minimization of a global error energy measuring the distance between sequences of distorted aligned points and straight lines after lens distortion correction. To validate the performance of the method we present experimental results on calibration pa-ttern images and on sport event scenarios using broadcast video cameras. We obtain, experimentally, that using just a second order polynomial approximation of lens distortion parameter zoom variation, the quality of lens distortion correction is as good as the one obtained individually frame by frame using independent lens distortion model for each frame.
Differential Equations & Applications, 2011
In this paper we study a variational problem derived from a computer vision application: video ca... more In this paper we study a variational problem derived from a computer vision application: video camera calibration with smoothing constraint. By video camera calibration we mean to estimate the location, orientation and lens zoom-setting of the camera for each video frame taking into account image visible features. To simplify the problem we assume that the camera is mounted on a tripod, in such case, for each frame captured at time t , the calibration is provided by 3 parameters : (1) P(t) (PAN) which represents the tripod vertical axis rotation, (2) T (t) (TILT) which represents the tripod horizontal axis rotation and (3) Z(t) (CAMERA ZOOM) the camera lens zoom setting. The calibration function t → u(t) = (P(t),T (t),Z(t)) is obtained as the minima of an energy function I [u] . In this paper we study the existence of minima of such energy function as well as the solutions of the associated Euler-Lagrange equations.