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Instituto Superior Técnico
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About: Instituto Superior Técnico is a based out in . It is known for research contribution in the topics: Catalysis & Finite element method. The organization has 10085 authors who have published 30226 publications receiving 667524 citations. The organization is also known as: IST & Instituto Superior Tecnico.
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12 May 2008TL;DR: This work proposes iterative methods in which each step is obtained by solving an optimization subproblem involving a quadratic term with diagonal Hessian plus the original sparsity-inducing regularizer, and proves convergence of the proposed iterative algorithm to a minimum of the objective function.
Abstract: Finding sparse approximate solutions to large underdetermined linear systems of equations is a common problem in signal/image processing and statistics. Basis pursuit, the least absolute shrinkage and selection operator (LASSO), wavelet-based deconvolution and reconstruction, and compressed sensing (CS) are a few well-known areas in which problems of this type appear. One standard approach is to minimize an objective function that includes a quadratic (pound 2) error term added to a sparsity-inducing (usually pound 1) regularizer. We present an algorithmic framework for the more general problem of minimizing the sum of a smooth convex function and a nonsmooth, possibly nonconvex, sparsity-inducing function. We propose iterative methods in which each step is an optimization subproblem involving a separable quadratic term (diagonal Hessian) plus the original sparsity-inducing term. Our approach is suitable for cases in which this subproblem can be solved much more rapidly than the original problem. In addition to solving the standard pound 2 - pound 1 case, our approach handles other problems, e.g., pound p regularizers with p ne 1, or group-separable (GS) regularizers. Experiments with CS problems show that our approach provides state-of-the-art speed for the standard pound 2 - pound 1 problem, and is also efficient on problems with GS regularizers.
1,154 citations
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Spanish National Research Council1, University of Cambridge2, Complutense University of Madrid3, Max Planck Society4, Leibniz Institute for Astrophysics Potsdam5, University of La Laguna6, University of Zaragoza7, University of Vienna8, Masaryk University9, University of Sydney10, Centre national de la recherche scientifique11, Ruhr University Bochum12, Autonomous University of Madrid13, Australian Astronomical Observatory14, Paris Diderot University15, University of Copenhagen16, University of Missouri–Kansas City17, Tianjin Normal University18, Institut d'Astrophysique de Paris19, Academy of Sciences of the Czech Republic20, Charles University in Prague21, Macquarie University22, Instituto Superior Técnico23, University of Porto24, Heidelberg University25, University of Granada26, Kapteyn Astronomical Institute27, University of Edinburgh28
TL;DR: The Calar Alto Legacy Integral Field Area (CALIFA) survey as discussed by the authors was designed to provide a first step in this direction by obtaining spatially resolved spectroscopic information of a diameter selected sample of similar to 600 galaxies in the Local Universe.
Abstract: The final product of galaxy evolution through cosmic time is the population of galaxies in the local universe. These galaxies are also those that can be studied in most detail, thus providing a stringent benchmark for our understanding of galaxy evolution. Through the huge success of spectroscopic single-fiber, statistical surveys of the Local Universe in the last decade, it has become clear, however, that an authoritative observational description of galaxies will involve measuring their spatially resolved properties over their full optical extent for a statistically significant sample. We present here the Calar Alto Legacy Integral Field Area (CALIFA) survey, which has been designed to provide a first step in this direction. We summarize the survey goals and design, including sample selection and observational strategy. We also showcase the data taken during the first observing runs (June/July 2010) and outline the reduction pipeline, quality control schemes and general characteristics of the reduced data. This survey is obtaining spatially resolved spectroscopic information of a diameter selected sample of similar to 600 galaxies in the Local Universe (0.005 < z < 0.03). CALIFA has been designed to allow the building of two-dimensional maps of the following quantities: (a) stellar populations: ages and metallicities; (b) ionized gas: distribution, excitation mechanism and chemical abundances; and (c) kinematic properties: both from stellar and ionized gas components. CALIFA uses the PPAK integral field unit (IFU), with a hexagonal field-of-view of similar to 1.3 square', with a 100% covering factor by adopting a three-pointing dithering scheme. The optical wavelength range is covered from 3700 to 7000 angstrom, using two overlapping setups (V500 and V1200), with different resolutions: R similar to 850 and R similar to 1650, respectively. CALIFA is a legacy survey, intended for the community. The reduced data will be released, once the quality has been guaranteed. The analyzed data fulfill the expectations of the original observing proposal, on the basis of a set of quality checks and exploratory analysis: (i) the final datacubes reach a 3 sigma limiting surface brightness depth of similar to 23.0 mag/arcsec(2) for the V500 grating data (similar to 22.8 mag/arcsec(2) for V1200); (ii) about similar to 70% of the covered field-of-view is above this 3 sigma limit; (iii) the data have a blue-to-red relative flux calibration within a few percent in most of the wavelength range; (iv) the absolute flux calibration is accurate within similar to 8% with respect to SDSS; (v) the measured spectral resolution is similar to 85 km s(-1) for V1200 (similar to 150 km s(-1) for V500); (vi) the estimated accuracy of the wavelength calibration is similar to 5 km s(-1) for the V1200 data (similar to 10 km s(-1) for the V500 data); (vii) the aperture matched CALIFA and SDSS spectra are qualitatively and quantitatively similar. Finally, we show that we are able to carry out all measurements indicated above, recovering the properties of the stellar populations, the ionized gas and the kinematics of both components. The associated maps illustrate the spatial variation of these parameters across the field, reemphasizing the redshift dependence of single aperture spectroscopic measurements. We conclude from this first look at the data that CALIFA will be an important resource for archaeological studies of galaxies in the Local Universe.
1,143 citations
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University of California, Berkeley1, University of Minnesota2, Queen Mary University of London3, Lawrence Berkeley National Laboratory4, California Institute of Technology5, Sapienza University of Rome6, University of Oxford7, Instituto Superior Técnico8, Cardiff University9, University of Toronto10
TL;DR: In this article, the authors presented a map and an angular power spectrum of the anisotropy of the cosmic microwave background (CMB) from the first flight of MAXIMA.
Abstract: We present a map and an angular power spectrum of the anisotropy of the cosmic microwave background (CMB) from the first flight of MAXIMA. MAXIMA is a balloon-borne experiment with an array of 16 bolometric photometers operated at 100 mK. MAXIMA observed a 124 deg region of the sky with 10' resolution at frequencies of 150, 240 and 410 GHz. The data were calibrated using in-flight measurements of the CMB dipole anisotropy. A map of the CMB anisotropy was produced from three 150 and one 240 GHz photometer without need for foreground subtractions. Analysis of this CMB map yields a power spectrum for the CMB anisotropy over the range 36 {le} {ell} {le} 785. The spectrum shows a peak with an amplitude of 78 {+-} 6 {mu}K at {ell} {approx_equal} 220 and an amplitude varying between {approx} 40 {mu}K and {approx} 50 {mu}K for 400 {approx}< {ell} {approx}< 785.
1,134 citations
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TL;DR: In this paper, the theoretical and phenomenological aspects of the Next-to-Minimal Supersymmetric Standard Model (NMSSM) were reviewed, including the Higgs sector including radiative corrections and the 2-loop β -functions for all parameters of the general NMSSM.
1,019 citations
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TL;DR: Current and future increase in food production must go along with production of food with better quality and with less toxic contaminants, which requires more cautious use of agrochemical through prior testing, careful risk assessment, and licensing.
Abstract: Agrochemicals have enabled to more than duplicate food production during the last century, and the current need to increase food production to feed a rapid growing human population maintains pressure on the intensive use of pesticides and fertilizers. However, worldwide surveys have documented the contamination and impact of agrochemical residues in soils, and terrestrial and aquatic ecosystems including coastal marine systems, and their toxic effects on humans and nonhuman biota. Although persistent organic chemicals have been phased out and replaced by more biodegradable chemicals, contamination by legacy residues and recent residues still impacts on the quality of human food, water, and environment. Current and future increase in food production must go along with production of food with better quality and with less toxic contaminants. Alternative paths to the intensive use of crop protection chemicals are open, such as genetically engineered organisms, organic farming, change of dietary habits, and development of food technologies. Agro industries need to further develop advanced practices to protect public health, which requires more cautious use of agrochemicals through prior testing, careful risk assessment, and licensing, but also through education of farmers and users in general, measures for better protection of ecosystems, and good practices for sustainable development of agriculture, fisheries, and aquaculture. Enhanced scientific research for new developments in food production and food safety, as well as for environmental protection, is a necessary part of this endeavor. Furthermore, worldwide agreement on good agriculture practices, including development of genetically modified organisms (GMOs) and their release for international agriculture, may be urgent to ensure the success of safe food production.
918 citations
Authors
Showing all 10288 results
Name | H-index | Papers | Citations |
---|---|---|---|
Joao Seixas | 153 | 1538 | 115070 |
A. Gomes | 150 | 1862 | 113951 |
Amartya Sen | 149 | 689 | 141907 |
António Amorim | 136 | 1477 | 96519 |
Joao Varela | 133 | 1411 | 92438 |
Pietro Faccioli | 132 | 1378 | 89795 |
João Carvalho | 126 | 1278 | 77017 |
Pedro Jorge | 124 | 776 | 68658 |
Pedro Silva | 124 | 961 | 74015 |
A. De Angelis | 118 | 534 | 54469 |
Hermine Katharina Wöhri | 116 | 629 | 55540 |
Helena Santos | 114 | 1058 | 54286 |
P. Conde Muiño | 109 | 558 | 56133 |
Joao Saraiva | 107 | 519 | 53340 |
J. N. Reddy | 106 | 926 | 66940 |