Search results for "Computer Science Application"
showing 10 items of 3998 documents
Experimental Sentinel-2 LAI estimation using parametric, non-parametric and physical retrieval methods – A comparison
2015
Abstract Given the forthcoming availability of Sentinel-2 (S2) images, this paper provides a systematic comparison of retrieval accuracy and processing speed of a multitude of parametric, non-parametric and physically-based retrieval methods using simulated S2 data. An experimental field dataset (SPARC), collected at the agricultural site of Barrax (Spain), was used to evaluate different retrieval methods on their ability to estimate leaf area index (LAI). With regard to parametric methods, all possible band combinations for several two-band and three-band index formulations and a linear regression fitting function have been evaluated. From a set of over ten thousand indices evaluated, the …
Rilievo e ricostruzione virtuale del Ponte Sud di Hierapolis di Frigia (Turchia)
2015
[ES] El artículo se refiere al levantamiento topográfico y la reconstrucción en 3D de un puente-acueducto romano situado inmediatamente al sur de Hierápolis, en Frigia (suroeste de Turquía), a lo largo del antiguo camino dirigido a Colosas, en el interior de Anatolia. Actualmente sólo se conservan su pilar sur y escasos restos del pilar norte. Se encuentra en una situación muy difícil, en el interior de un valle estrecho y profundo, y nunca se ha estudiado antes. Durante la campaña de trabajo de campo de 2011 de la Misión Arqueológica Italiana, fue examinado con un diferencial de alta precisión del sistema GPS (para la documentación del plan y su posicionamiento en el mapa digital arqueológ…
On the Intrinsic Complexity of Learning
1995
AbstractA new view of learning is presented. The basis of this view is a natural notion of reduction. We prove completeness and relative difficulty results. An infinite hierarchy of intrinsically more and more difficult to learn concepts is presented. Our results indicate that the complexity notion captured by our new notion of reduction differs dramatically from the traditional studies of the complexity of the algorithms performing learning tasks.
Measuring dissatisfaction with coauthorship: An empirical approach based on the researchers’ perception
2019
Abstract Increasing levels of collaboration constitute one of the characteristics of science. However, the knowledge production system is based on a fundamental discordance: on the one hand, it is cooperative in nature, with links articulated through coauthorships, and on the other, the systems for assigning merit and distributing rewards function on an individual scale. This contradiction can give rise to dysfunction and inappropriate practices. This study analyses researchers’ perceptions about the problems associated with authorship in scientific publications. We make use of a coauthorship dissatisfaction index that measures the degree of dissatisfaction with the author order on the byli…
Evolution of the surface magnetic field of rotating proto-neutron stars
2017
We study the evolution of the field on the surface of proto-neutron stars in the immediate aftermath of stellar core collapse by analyzing the results of self-consistent, axisymmetric simulations of the cores of rapidly rotating high-mass stars. To this end, we compare the field topology and the angular spectra of the poloidal and toroidal field components over a time of about one seconds for cores. Both components are characterized by a complex geometry with high power at intermediate angular scales. The structure is mostly the result of the accretion of magnetic flux embedded in the matter falling through the turbulent post-shock layer onto the PNS. Our results may help to guide further s…
Numerical simulations of dynamics and emission from relativistic astrophysical jets
2013
Broadband emission from relativistic outflows (jets) of active galactic nuclei (AGN) and gamma-ray bursts (GRBs) contains valuable information about the nature of the jet itself, and about the central engine which launches it. Using special relativistic hydrodynamics and magnetohydronamics simulations we study the dynamics of the jet and its interaction with the surrounding medium. The observational signature of the simulated jets is computed using a radiative transfer code developed specifically for the purpose of computing multi-wavelength, time-dependent, non-thermal emission from astrophysical plasmas. We present results of a series of long-term projects devoted to understanding the dyn…
LOFT - A large observatory for x-ray timing
2010
The high time resolution observations of the X-ray sky hold the key to a number of diagnostics of fundamental physics, some of which are unaccessible to other types of investigations, such as those based on imaging and spectroscopy. Revealing strong gravitational field effects, measuring the mass and spin of black holes and the equation of state of ultradense matter are among the goals of such observations. At present prospects for future, non-focused X-ray timing experiments following the exciting age of RXTE/PCA are uncertain. Technological limitations are unavoidably faced in the conception and development of experiments with effective area of several square meters, as needed in order to…
Cohomology of Filippov algebras and an analogue of Whitehead's lemma
2009
We show that two cohomological properties of semisimple Lie algebras also hold for Filippov (n-Lie) algebras, namely, that semisimple n-Lie algebras do not admit non-trivial central extensions and that they are rigid i.e., cannot be deformed in Gerstenhaber sense. This result is the analogue of Whitehead's Lemma for Filippov algebras. A few comments about the n-Leibniz algebras case are made at the end.
Discrete Abelian gauge symmetries and axions
2015
We combine two popular extensions of beyond the Standard Model physics within the framework of intersecting D6-brane models: discrete Zn symmetries and Peccei-Quinn axions. The underlying natural connection between both extensions is formed by the presence of massive U(1) gauge symmetries in D-brane model building. Global intersecting D6-brane models on toroidal orbifolds of the type T6/Z2N and T6/Z2xZ2M with discrete torsion offer excellent playgrounds for realizing these extensions. A generation-dependent Z2 symmetry is identified in a global Pati-Salam model, while global left-right symmetric models give rise to supersymmetric realizations of the DFSZ axion model. In one class of the lat…
Topics on n-ary algebras
2011
We describe the basic properties of two n-ary algebras, the Generalized Lie Algebras (GLAs) and, particularly, the Filippov (or n-Lie) algebras (FAs), and comment on their n-ary Poisson counterparts, the Generalized Poisson (GP) and Nambu-Poisson (N-P) structures. We describe the Filippov algebra cohomology relevant for the central extensions and infinitesimal deformations of FAs. It is seen that semisimple FAs do not admit central extensions and, moreover, that they are rigid. This extends the familiar Whitehead's lemma to all $n\geq 2$ FAs, n=2 being the standard Lie algebra case. When the n-bracket of the FAs is no longer required to be fully skewsymmetric one is led to the n-Leibniz (or…