Facultad de Ciencias Físicas y Matemáticas
http://repositorio.uchile.cl/handle/2250/100004
Facultad de Ciencias Físicas y Matemáticas2018-11-16T10:37:35ZThe high cadence transient survey (HITS). Compilation and characterization of light–curve catalogs
http://repositorio.uchile.cl/handle/2250/152644
The high cadence transient survey (HITS). Compilation and characterization of light–curve catalogs
Martínez Palomera, Jorge; Forster, Francisco; Protopapas, Pavlos
The High Cadence Transient Survey (HiTS) aims to discover and study transient objects with characteristic
timescales between hours and days, such as pulsating, eclipsing and exploding stars. This
survey represents a unique laboratory to explore large etendue observations from cadences of about
0.1 days and to test new computational tools for the analysis of large data. This work follows a fully
Data Science approach: from the raw data to the analysis and classification of variable sources. We
compile a catalog of ∼15 million object detections and a catalog of ∼2.5 million light–curves classified
by variability. The typical depth of the survey is 24.2, 24.3, 24.1 and 23.8 in u, g, r and i bands,
respectively. We classified all point–like non–moving sources by first extracting features from their
light–curves and then applying a Random Forest classifier. For the classification, we used a training
set constructed using a combination of cross-matched catalogs, visual inspection, transfer/active
learning and data augmentation. The classification model consists of several Random Forest classifiers
organized in a hierarchical scheme. The classifier accuracy estimated on a test set is approximately
97%. In the unlabeled data, 3 485 sources were classified as variables, of which 1 321 were classified
as periodic. Among the periodic classes we discovered with high confidence, 1 δ–scutti, 39 eclipsing
binaries, 48 rotational variables and 90 RR–Lyrae and for the non–periodic classes we discovered 1
cataclysmic variables, 630 QSO, and 1 supernova candidates. The first data release can be accessed in
the project archive of HiTSa)
2018-01-01T00:00:00ZProx-regularity approach to generalized equations and image projection
http://repositorio.uchile.cl/handle/2250/152638
Prox-regularity approach to generalized equations and image projection
Adly, Samir; Nacry, Florent; Thibault, Lionel
In this paper, we first investigate the prox-regularity behaviour of solution mappings to generalized equations. This study is realized through a nonconvex uniform Robinson Ursescu type theorem. Then, we derive new significant results for the preservation of prox-regularity under various and usual set operations. The role and applications of prox-regularity of solution sets of generalized equations are illustrated with dynamical systems with constraints.
2018-04-01T00:00:00ZOn distance-preserving elimination orderings in graphs: complexity and algorithms
http://repositorio.uchile.cl/handle/2250/152628
On distance-preserving elimination orderings in graphs: complexity and algorithms
Coudert, David; Ducoffe, Guillaume; Nisse, Nicolas; Soto, Mauricio
For every connected graph G, a subgraph H of G is isometric if the distance between any two vertices in H is the same in H as in G. A distance-preserving elimination ordering of G is a total ordering of its vertex-set V (G), denoted (v(1), v(2),....v(n)), such that any subgraph G(i)= G \ (v(1), v(2),, v(i)) with 1 <= i < n is isometric. This kind of ordering has been introduced by Chepoi in his study on weakly modular graphs (Chepoi, 1998). We prove that it is NP complete to decide whether such ordering exists for a given graph even if it has diameter at most 2. Then, we prove on the positive side that the problem of computing a distance preserving ordering when there exists one is fixed-parameter-tractable in the treewidth. Lastly, we describe a heuristic in order to compute a distance-preserving ordering when there exists one that we compare to an exact exponential time algorithm and to an ILP formulation for the problem. (C) 2018 Elsevier B.V. All rights reserved.
2018-07-10T00:00:00ZLoCuSS: the infall of X-ray groups on to massive clusters
http://repositorio.uchile.cl/handle/2250/152623
LoCuSS: the infall of X-ray groups on to massive clusters
Haines, C. P.; Finoguenov, A.; Smith, G. P.; Babul, A.; Egami, E.; Mazzotta, P.; Okabe, N.; Pereira, M. J.; Bianconi, M.; Mcgee, S. L.; Ziparo, F.; Campusano, L. E.; Loyola, C.
Galaxy clusters are expected to form hierarchically in a Lambda cold dark matter (Lambda CDM) universe, growing primarily through mergers with lower mass clusters and the continual accretion of group-mass haloes. Galaxy clusters assemble late, doubling their masses since z similar to 0.5, and so the outer regions of clusters should be replete with accreting group-mass systems. We present an XMM-Newton survey to search for X-ray groups in the infall regions of 23 massive galaxy clusters (< M-200 > similar to 10(15)M(circle dot)) at z similar to 0.2, identifying 39 X-ray groups that have been spectroscopically confirmed to lie at the cluster redshift. These groups have mass estimates in the range 2 x 10(13)-7 x 10(14)M(circle dot), and group-to-cluster mass ratios as low as 0.02. The comoving number density of X-ray groups in the infall regions is similar to 25x higher than that seen for isolated X-ray groups from the XXL survey. The average mass per cluster contained within these X-ray groups is 2.2 x 10(14)M(circle dot), or 19 +/- 5 per cent of the mass within the primary cluster itself. We estimate that similar to 10(15)M(circle dot) clusters increase their masses by 16 +/- 4 per cent between z = 0.223 and the present day due to the accretion of groups with M-200 >= 10(13.2)M(circle dot). This represents about half of the expected mass growth rate of clusters at these late epochs. The other half is likely to come from smooth accretion of matter not bound within haloes. The mass function of the infalling X-ray groups appears significantly top heavy with respect to that of 'field' X-ray systems, consistent with expectations from numerical simulations, and the basic consequences of collapsed massive dark matter haloes being biased tracers of the underlying large-scale density distribution.
2018-07-01T00:00:00Z