Time filter

Source Type

Arroyo D.,Northern Catholic University | Emery X.,University of Chile | Pelaez M.,Northern Catholic University
Computers and Geosciences | Year: 2012

This paper addresses the problem of simulating a Gaussian random vector with zero mean and given variance-covariance matrix, without conditioning constraints. Variants of the Gibbs sampler algorithm are presented, based on the proposal by Galli and Gao, which do not require inverting the variance-covariance matrix and therefore allow considerable time savings. Numerical experiments are performed to check the accuracy of the algorithm and to determine implementation parameters (in particular, the updating and blocking strategies) that increase the rates of convergence and mixing. © 2012 Elsevier Ltd.

Emery X.,University of Chile | Pelaez M.,Northern Catholic University
Computers and Geosciences | Year: 2012

The simulation of vector random fields whose spatial correlation structure is represented by a linear coregionalization model can be performed by decomposing the vector components into spatially orthogonal factors and by simulating each factor separately. However, when the number of basic nested structures is large, so is the number of factors, making simulation computationally demanding.This paper proposes a methodology to construct linear coregionalization models with as many nested structures as desired, together with as few orthogonal factors as possible. The construction rests on the decomposition of the model coregionalization matrices into pairwise commuting matrices, followed by a factorization by principal component analysis. The proposed approach is illustrated through a case study in mineral resources evaluation and compared to the traditional fitting procedure, obtaining an equally good fit of the direct and cross variograms but with significantly less factors. © 2012 Elsevier Ltd.

Kapstein Lopez P.,Technical University of Madrid | Kapstein Lopez P.,Northern Catholic University | Aranda Dioses E.,Peruvian National University of Engineering
Revista INVI | Year: 2014

A system of inner peripheries has been identified in downtown Lima, comprising a series of old slums that makes up an urban entity with its own characteristics and problems.These slumswere part of the northern periphery of Lima until the 1950s and extended along the course of the Rimac River, the then-border between the district of Lima and the emerging northern extension of the urban area.The objective of this paper is to demarcate the system of inner peripheries and identify the neighborhoods that act as focal points of vulnerability within the system.The methodology used by this research is based both on a cartographic analysis of the growth experienced by Lima from 1940 to 1981 and the study of the urban and social conditions of neighborhoods that act as focal points of vulnerability. This research describes the case of San Cosme, which by reasons of its age and its geomorphological and urban characteristics is one of the paradigmatic slums of Lima. The findings of this paper support the need to generate a Master Plan on Rehabilitation Strategies aimed at the inner peripheries of Lima. © 2014, Instituto de la Vivienda. All rights reserved.

News Article | December 10, 2015
Site: phys.org

Globular clusters are spherical-shaped or globular stellar groupings—hence its name- which can contain millions of stars. There are about 200 of them in the Milky Way, but few are as intriguing to astronomers as the E 3 cluster. It is situated around 30,000 light years away, in the southern constellation of Chameleon. A team of Spanish and Italian astronomers have named it "a ghost from the Milky Way's past" in an article published recently in the Astronomy & Astrophysics journal. "This globular cluster, and a few similar ones—such as Palomar 5 or Palomar 14—are `ghosts´ because they appear to be in the last stages of their existence, and we say ´from the past´ because they are very old. They were formed when our galaxy was virtually new-born, 13,000 million years ago," says one of the authors, Carlos de la Fuente Marcos. E 3 is hidden behind younger and brighter objects located between the cluster and Earth, but it has been possible to analyse it thanks to the Very Large Telescope (VLT) held in the European Southern Observatory (ESO) in Cerro Paranal, Chile. The data obtained revealed some surprises. "Unlike typical globular clusters, which contain hundreds of thousands and in some cases millions of stars, the object studied only has a few tens of thousands of them," says De la Fuente Marcos. "Additionally, it doesn't have the typical circular symmetry, but a much distorted, almost ghostly, rhomboidal shape, contorted by the galactic gravitational waves". According to another study on E 3 by Michigan State University (USA) researchers, published in The Astrophysical Journal, this cluster is chemically homogeneous, that is, it doesn't have several star populations in its interior. "This is characteristic of an object that was created in block, in one single episode, like what is supposed to have happened when our galaxy was born: very large star clusters (containing millions of stars) were formed, but what remains of them today are objects like E 3, ghosts from a distant past," says De la Fuente Marcos. He explains that the study of these objects "enables us to gain insight into the infancy of the Milky Way". Despite the recently published new data on this strange globular cluster, astronomers still have to clarify if it was really formed in our galaxy or not. It is known that some of its clusters are not native to the Milky Way, but were captured, even though they can currently be seen in its interior. Thousands of millions of years ago, our galaxy cannibalised other smaller galaxies and kept their globular clusters. The rest were formed in-situ. In the article, it is suggested that the object analysed could be dynamically related to other clusters, such as 47 Tucanae, one of the richest and largest of the Milky Way. They could even share the same stream of stars. If this were the case, it would support the hypothesis that E 3 was captured in the distant past. "We hope to obtain new data in 2016, thanks to more spectroscopic observations, and perhaps we will be able to give answers to these questions," says De la Fuente Marcos, an independent astronomer who collaborates with colleagues from the Northern Catholic University and ESO in Chile, and the University of Padua, Italy. Explore further: Image: Hubble looks into Terzan 7 More information: R. de la Fuente Marcos et al. Ghosts of Milky Way's past: the globular cluster ESO 37-1 (E 3), Astronomy & Astrophysics (2015). DOI: 10.1051/0004-6361/201526580

Loading Northern Catholic University collaborators
Loading Northern Catholic University collaborators