Institution

# Instituto Superior Técnico

About: Instituto Superior Técnico is a(n) based out in . It is known for research contribution in the topic(s): Catalysis & Finite element method. The organization has 10085 authors who have published 30226 publication(s) receiving 667524 citation(s). The organization is also known as: IST & Instituto Superior Tecnico.

##### Papers
More filters
Journal ArticleDOI
TL;DR: In this paper, the mass density, Omega_M, and cosmological-constant energy density of the universe were measured using the analysis of 42 Type Ia supernovae discovered by the Supernova Cosmology project.
Abstract: We report measurements of the mass density, Omega_M, and cosmological-constant energy density, Omega_Lambda, of the universe based on the analysis of 42 Type Ia supernovae discovered by the Supernova Cosmology Project. The magnitude-redshift data for these SNe, at redshifts between 0.18 and 0.83, are fit jointly with a set of SNe from the Calan/Tololo Supernova Survey, at redshifts below 0.1, to yield values for the cosmological parameters. All SN peak magnitudes are standardized using a SN Ia lightcurve width-luminosity relation. The measurement yields a joint probability distribution of the cosmological parameters that is approximated by the relation 0.8 Omega_M - 0.6 Omega_Lambda ~= -0.2 +/- 0.1 in the region of interest (Omega_M <~ 1.5). For a flat (Omega_M + Omega_Lambda = 1) cosmology we find Omega_M = 0.28{+0.09,-0.08} (1 sigma statistical) {+0.05,-0.04} (identified systematics). The data are strongly inconsistent with a Lambda = 0 flat cosmology, the simplest inflationary universe model. An open, Lambda = 0 cosmology also does not fit the data well: the data indicate that the cosmological constant is non-zero and positive, with a confidence of P(Lambda > 0) = 99%, including the identified systematic uncertainties. The best-fit age of the universe relative to the Hubble time is t_0 = 14.9{+1.4,-1.1} (0.63/h) Gyr for a flat cosmology. The size of our sample allows us to perform a variety of statistical tests to check for possible systematic errors and biases. We find no significant differences in either the host reddening distribution or Malmquist bias between the low-redshift Calan/Tololo sample and our high-redshift sample. The conclusions are robust whether or not a width-luminosity relation is used to standardize the SN peak magnitudes.

15,392 citations

Journal ArticleDOI
José M. P. Nascimento
TL;DR: A new method for unsupervised endmember extraction from hyperspectral data, termed vertex component analysis (VCA), which competes with state-of-the-art methods, with a computational complexity between one and two orders of magnitude lower than the best available method.
Abstract: Given a set of mixed spectral (multispectral or hyperspectral) vectors, linear spectral mixture analysis, or linear unmixing, aims at estimating the number of reference substances, also called endmembers, their spectral signatures, and their abundance fractions. This paper presents a new method for unsupervised endmember extraction from hyperspectral data, termed vertex component analysis (VCA). The algorithm exploits two facts: (1) the endmembers are the vertices of a simplex and (2) the affine transformation of a simplex is also a simplex. In a series of experiments using simulated and real data, the VCA algorithm competes with state-of-the-art methods, with a computational complexity between one and two orders of magnitude lower than the best available method.

2,090 citations

Journal ArticleDOI
TL;DR: In this comprehensive survey, a large number of existing approaches to biclustering are analyzed, and they are classified in accordance with the type of biclusters they can find, the patterns of bIClusters that are discovered, the methods used to perform the search, the approaches used to evaluate the solution, and the target applications.
Abstract: A large number of clustering approaches have been proposed for the analysis of gene expression data obtained from microarray experiments. However, the results from the application of standard clustering methods to genes are limited. This limitation is imposed by the existence of a number of experimental conditions where the activity of genes is uncorrelated. A similar limitation exists when clustering of conditions is performed. For this reason, a number of algorithms that perform simultaneous clustering on the row and column dimensions of the data matrix has been proposed. The goal is to find submatrices, that is, subgroups of genes and subgroups of conditions, where the genes exhibit highly correlated activities for every condition. In this paper, we refer to this class of algorithms as biclustering. Biclustering is also referred in the literature as coclustering and direct clustering, among others names, and has also been used in fields such as information retrieval and data mining. In this comprehensive survey, we analyze a large number of existing approaches to biclustering, and classify them in accordance with the type of biclusters they can find, the patterns of biclusters that are discovered, the methods used to perform the search, the approaches used to evaluate the solution, and the target applications.

2,027 citations

Journal ArticleDOI
TL;DR: In this paper, the authors consider the evolution of a universe evolving from a phase dominated by nonrelativistic matter to a cosmological constant via an intermediate period where the effective equation of state is given by $p=\ensuremath{\alpha{-}A/{\ensemath{\rho}}^{\ensemblem{\alpha}},$ where A is a positive constant and $0l √ √ 1/ √ l 1/1. Abstract: We consider the scenario emerging from the dynamics of a generalized Born-Infeld theory. The equation of state describing this system is given in terms of the energy density$\ensuremath{\rho}$and pressure p by the relationship$p=\ensuremath{-}A/{\ensuremath{\rho}}^{\ensuremath{\alpha}},$where A is a positive constant and$0l\ensuremath{\alpha}l~1.$We discuss the conditions under which homogeneity arises and show that this equation of state describes the evolution of a universe evolving from a phase dominated by nonrelativistic matter to a phase dominated by a cosmological constant via an intermediate period where the effective equation of state is given by$p=\ensuremath{\alpha}\ensuremath{\rho}.\$

1,760 citations

Journal ArticleDOI
TL;DR: In this article, the authors presented cosmological constraints from a joint analysis of type Ia supernova (SN Ia) observations obtained by the SDSS-II and SNLS collaborations.
Abstract: Aims. We present cosmological constraints from a joint analysis of type Ia supernova (SN Ia) observations obtained by the SDSS-II and SNLS collaborations. The dataset includes several low-redshift samples (z< 0.1), all three seasons from the SDSS-II (0.05

1,725 citations

##### Authors

Showing all 10085 results

NameH-indexPapersCitations
Joao Seixas1531538115070
A. Gomes1501862113951
Amartya Sen149689141907
António Amorim136147796519
Joao Varela133141192438
Pietro Faccioli132137889795
João Carvalho126127877017
Pedro Jorge12477668658
Pedro Silva12496174015
A. De Angelis11853454469
Hermine Katharina Wöhri11662955540
Helena Santos114105854286
P. Conde Muiño10955856133
Joao Saraiva10751953340
J. N. Reddy10692666940
##### Network Information
###### Related Institutions (5)
Royal Institute of Technology
68.4K papers, 1.9M citations

95% related

École Polytechnique Fédérale de Lausanne
98.2K papers, 4.3M citations

94% related

Karlsruhe Institute of Technology
82.1K papers, 2.1M citations

93% related

Delft University of Technology
94.4K papers, 2.7M citations

93% related

Technical University of Denmark
66.3K papers, 2.4M citations

93% related

##### Performance
###### Metrics
No. of papers from the Institution in previous years
YearPapers
202282
20212,262
20202,432
20192,327
20182,190
20172,193