Examinando por Autor "Contreras, C."
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Ítem Automatically Generated Algorithms for the Vertex Coloring Problem(Public Library of Science, 2013) Contreras, C.; Gatica, G.; Parada, V.The vertex coloring problem is a classical problem in combinatorial optimization that consists of assigning a color to each vertex of a graph such that no adjacent vertices share the same color, minimizing the number of colors used. Despite the various practical applications that exist for this problem, its NP-hardness still represents a computational challenge. Some of the best computational results obtained for this problem are consequences of hybridizing the various known heuristics. Automatically revising the space constituted by combining these techniques to find the most adequate combination has received less attention. In this paper, we propose exploring the heuristics space for the vertex coloring problem using evolutionary algorithms. We automatically generate three new algorithms by combining elementary heuristics. To evaluate the new algorithms, a computational experiment was performed that allowed comparing them numerically with existing heuristics. The obtained algorithms present an average 29.97% relative error, while four other heuristics selected from the literature present a 59.73% error, considering 29 of the more difficult instances in the DIMACS benchmark.Ítem Luminous Type II supernovae for their low expansion velocities(Oxford University Press, 2020-05) Rodríguez, O.; Pignata, G.; Anderson, J.P.; Moriya, T.J.; Clocchiatti, A.; Forster, F.; Prieto, J.L.; Phillips, M.M.; Burns, C.R.; Contreras, C.; Folatelli, G.; Gutierrez, C.P.; Hamuy, M.; Morrell, N.I.; Stritzinger, M.D.; Suntzeff, N.B.; Benetti, S.; Cappellaro, E.; Elias-Rosa, N.; Pastorello, A.; Turatto, M.; Maza, J.; Antezana, R.; Cartier, R.; Gonzalez, L.; Haislip, J.B.; Kouprianov, V.; Lopez, P.; Marchi-Lasch, S.; Reichart, D.We present optical and near-infrared data of three Type II supernovae (SNe II), SN 2008bm, SN 2009aj, and SN 2009au. These SNe display the following common characteristics: signs of early interaction of the ejecta with circumstellar material (CSM), blue B - V colours, weakness of metal lines, low expansion velocities, and V-band absolute magnitudes 2-3 mag brighter than those expected for normal SNe II based on their expansion velocities. Two more SNe reported in the literature (SN 1983K and LSQ13fn) share properties similar to our sample. Analysing this set of five SNe II, which are luminous for their low expansion velocities (LLEV), we find that their properties can be reproduced assuming ejecta-CSM interaction that lasts between 4 and 11 weeks post-explosion. The contribution of this interaction to the radiation field seems to be the dominant component determining the observed weakness of metal lines in the spectra rather than the progenitor metallicity. Based on hydrodynamic simulations, we find that the interaction of the ejecta with a CSM of ∼3.6 M⊙ can reproduce the light curves and expansion velocities of SN 2009aj. Using data collected by the Chilean Automatic Supernova Search, we estimate an upper limit for the LLEV SNe II fraction to be 2-4 per cent of all normal SNe II. With the current data set, it is not clear whether the LLEV events are a separated class of SNe II with a different progenitor system, or whether they are the extreme of a continuum mediated by CSM interaction with the rest of the normal SN II population. © 2020 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society.Ítem PESSTO: Survey description and products from the first data release by the Public ESO Spectroscopic Survey of Transient Objects(EDP Sciences, 2015-07) Smartt, S.J.; Valenti, S.; Fraser, M.; Inserra, C.; Young, D.R.; Sullivan, M.; Pastorello, A.; Benetti, S.; Gal-Yam, A.; Knapic, C.; Molinaro, M.; Smareglia, R.; Smith, K.W.; Taubenberger, S.; Yaron, O.; Anderson, J.P.; Ashall, C.; Balland, C.; Baltay, C.; Barbarino, C.; Bauer, F.E.; Baumont, S.; Bersier, D.; Blagorodnova, N.; Bongard, S.; Botticella, M.T.; Bufano, F.; Bulla, M.; Cappellaro, E.; Campbell, H.; Cellier-Holzem, F.; Chen, T.-W.; Childress, M.J.; Clocchiatti, A.; Contreras, C.; Dall'Ora, M.; Danziger, J.; De Jaeger, T.; De Cia, A.; Della Valle, M.; Dennefeld, M.; Elias-Rosa, N.; Elman, N.; Feindt, U.; Fleury, M.; Gall, E.; Gonzalez-Gaitan, S.; Galbany, L.; Morales Garoffolo, A.; Greggio, L.; Guillou, L.L.; Hachinger, S.; Hadjiyska, E.; Hage, P.E.; Hillebrandt, W.; Hodgkin, S.; Hsiao, E.Y.; James, P.A.; Jerkstrand, A.; Kangas, T.; Kankare, E.; Kotak, R.; Kromer, M.; Kuncarayakti, H.; Leloudas, G.; Lundqvist, P.; Lyman, J.D.; Hook, I.M.; Maguire, K.; Manulis, I.; Margheim, S.J.; Mattila, S.; Maund, J.R.; Mazzali, P.A.; McCrum, M.; McKinnon, R.; Moreno-Raya, M.E.; Nicholl, M.; Nugent, P.; Pain, R.; Pignata, G.; Phillips, M.M.; Polshaw, J.; Pumo, M.; Rabinowitz, D.; Reilly, E.; Romero-Cañizales, C.; Scalzo, R.; Schmidt, B.; Schulze, S.; Sim, S.; Sollerman, J.; Taddia, F.; Tartaglia, L.; Terreran, G.; Tomasella, L.; Turatto, M.; Walker, E.; Walton, N.A.; Wyrzykowski, L.; Yuan, F.; Zampieri, L.Context. The Public European Southern Observatory Spectroscopic Survey of Transient Objects (PESSTO) began as a public spectroscopic survey in April 2012. PESSTO classifies transients from publicly available sources and wide-field surveys, and selects science targets for detailed spectroscopic and photometric follow-up. PESSTO runs for nine months of the year, January - April and August - December inclusive, and typically has allocations of 10 nights per month. Aims. We describe the data reduction strategy and data products that are publicly available through the ESO archive as the Spectroscopic Survey data release 1 (SSDR1). Methods. PESSTO uses the New Technology Telescope with the instruments EFOSC2 and SOFI to provide optical and NIR spectroscopy and imaging. We target supernovae and optical transients brighter than 20.5m for classification. Science targets are selected for follow-up based on the PESSTO science goal of extending knowledge of the extremes of the supernova population. We use standard EFOSC2 set-ups providing spectra with resolutions of 13-18 Å between 3345-9995 Å. A subset of the brighter science targets are selected for SOFI spectroscopy with the blue and red grisms (0.935-2.53 μm and resolutions 23-33 Å) and imaging with broadband JHKs filters. Results. This first data release (SSDR1) contains flux calibrated spectra from the first year (April 2012-2013). A total of 221 confirmed supernovae were classified, and we released calibrated optical spectra and classifications publicly within 24 h of the data being taken (via WISeREP). The data in SSDR1 replace those released spectra. They have more reliable and quantifiable flux calibrations, correction for telluric absorption, and are made available in standard ESO Phase 3 formats. We estimate the absolute accuracy of the flux calibrations for EFOSC2 across the whole survey in SSDR1 to be typically ∼15%, although a number of spectra will have less reliable absolute flux calibration because of weather and slit losses. Acquisition images for each spectrum are available which, in principle, can allow the user to refine the absolute flux calibration. The standard NIR reduction process does not produce high accuracy absolute spectrophotometry but synthetic photometry with accompanying JHKs imaging can improve this. Whenever possible, reduced SOFI images are provided to allow this. Conclusions. Future data releases will focus on improving the automated flux calibration of the data products. The rapid turnaround between discovery and classification and access to reliable pipeline processed data products has allowed early science papers in the first few months of the survey. © ESO, 2015.Ítem SOAR/Goodman Spectroscopic Assessment of Candidate Counterparts of the LIGO/Virgo Event GW190814(IOP Publishing Ltd, 2022-04-01) Tucker, D.L.; Wiesner, M.P.; Allam, S.S.; Soares-Santos, M.; Bom, C.R.; Butner, M.; Garcia, A.; Morgan, R.; Olivares, E. F.; Palmese, A.; Santana-Silva, L.; Shrivastava, A.; Annis, J.; García-Bellido, J.; Gill, M.S.S.; Herner, K.; Kilpatrick, C.D.; Makler, M.; Sherman, N.; Amara, A.; Lin, H.; Smith, M.; Swann, E.; Arcavi, I.; Bachmann, T.G.; Bechtol, K.; Berlfein, F.; Briceño, C.; Brout, D.; Butler, R.E.; Cartier, R.; Casares, J.; Chen, H.-Y.; Conselice, C.; Contreras, C.; Cook, E.; Cooke, J.; Dage, K.; D'Andrea, C.; Davis, T.M.; De Carvalho, R.; Diehl, H.T.; Dietrich, J.P.; Doctor, Z.; Drlica-Wagner, A.; Drout, M.; Farr, B.; Finley, D.A.; Fishbach, M.; Foley, R.J.; Förster-Burón, F.; Fosalba, P.; Friedel, D.; Frieman, J.; Frohmaier, C.; Gruendl, R.A.; Hartley, W.G.; Hiramatsu, D.; Holz, D.E.; Howell, D.A.; Kawash, A.; Kessler, R.; Kuropatkin, N.; Lahav, O.; Lundgren, A.; Lundquist, M.; Malik, U.; Mann, A.W.; Marriner, J.; Marshall, J.L.; Martínez-Vázquez, C.E.; McCully, C.; Menanteau, F.; Meza, N.; Narayan, G.; Neilsen, E.; Nicolaou, C.; Nichol, R.; Paz-Chinchón, F.; Pereira, M.E.S.; Pineda, J.; Points, S.; Quirola-Vásquez, J.; Rembold, S.; Rest, A.; Rodriguez, Ó.; Romer, A.K.; Sako, M.; Salim, S.; Scolnic, D.; Smith, J.A.; Strader, J.; Sullivan, M.; Swanson, M.E.C.; Thomas, D.; Valenti, S.; Varga, T.N.; Walker, A.R.; Weller, J.; Wood, M.L.; Yanny, B.; Zenteno, A.; Aguena, M.; Andrade-Oliveira, F.; Bertin, E.; Brooks, D.; Burke, D.L.; Rosell, A. Carnero; Kind, M. Carrasco; Carretero, J.; Costanzi, M.; Da Costa, L.N.; De Vicente, J.; Desai, S.; Everett, S.; Ferrero, I.; Flaugher, B.; Gaztanaga, E.; Gerdes, D.W.; Gruen, D.; Gschwend, J.; Gutierrez, G.; Hinton, S.R.; Hollowood, D.L.; Honscheid, K.; James, D.J.; Kuehn, K.; Lima, M.; Maia, M.A.G.; Miquel, R.; Ogando, R.L.C.; Pieres, A.; Plazas Malagón, A.A.; Rodriguez-Monroy, M.; Sanchez, E.; Scarpine, V.; Schubnell, M.; Serrano, S.; Sevilla-Noarbe, I.; Suchyta, E.; Tarle, G.; To, C.; Zhang, Y.On 2019 August 14 at 21:10:39 UTC, the LIGO/Virgo Collaboration (LVC) detected a possible neutron star-black hole merger (NSBH), the first ever identified. An extensive search for an optical counterpart of this event, designated GW190814, was undertaken using the Dark Energy Camera on the 4 m Victor M. Blanco Telescope at the Cerro Tololo Inter-American Observatory. Target of Opportunity interrupts were issued on eight separate nights to observe 11 candidates using the 4.1 m Southern Astrophysical Research (SOAR) telescope's Goodman High Throughput Spectrograph in order to assess whether any of these transients was likely to be an optical counterpart of the possible NSBH merger. Here, we describe the process of observing with SOAR, the analysis of our spectra, our spectroscopic typing methodology, and our resultant conclusion that none of the candidates corresponded to the gravitational wave merger event but were all instead other transients. Finally, we describe the lessons learned from this effort. Application of these lessons will be critical for a successful community spectroscopic follow-up program for LVC observing run 4 (O4) and beyond. © 2022. The Author(s). Published by the American Astronomical Society.Ítem The unusual acid-accumulating behavior during ripening of cherimoya (Annona cherimola Mill.) is linked to changes in transcription and enzyme activity related to citric and malic acid metabolism(MDPI AG, 2016) González-Agüero, M.; Pardo, L.T.; Zamudio, M.S.; Contreras, C.; Undurraga, P.; Defilippi, B.G.Cherimoya (Annona cherimola Mill.) is a subtropical fruit characterized by a significant increase in organic acid levels during ripening, making it an interesting model for studying the relationship between acidity and fruit flavor. In this work, we focused on understanding the balance between the concentration of organic acids and the gene expression and activity of enzymes involved in the synthesis and degradation of these metabolites during the development and ripening of cherimoya cv. “Concha Lisa”. Our results showed an early accumulation of citric acid and other changes associated with the accumulation of transcripts encoding citrate catabolism enzymes. During ripening, a 2-fold increase in malic acid and a 6-fold increase in citric acid were detected. By comparing the contents of these compounds with gene expression and enzymatic activity levels, we determined that cytoplasmic NAD-dependent malate dehydrogenase (cyNAD-MDH) and mitochondrial citrate synthase (mCS) play important regulatory roles in the malic and citric acid biosynthetic pathways.Ítem Two transitional type Ia supernovae located in the Fornax cluster member NGC 1404: SN 2007on and SN 2011iv(EDP Sciences, 2018-03) Gall, C.; Stritzinger, M.D.; Ashall, C.; Baron, E.; Burns, C.R.; Hoeflich, P.; Hsiao, E.Y.; Mazzali, P.A.; Phillips, M.M.; Filippenko, A.V.; Anderson, J.P.; Benetti, S.; Brown, P.J.; Campillay, A.; Challis, P.; Contreras, C.; Elias De La Rosa, N.; Folatelli, G.; Foley, R.J.; Fraser, M.; Holmbo, S.; Marion, G.H.; Morrell, N.; Pan, Y.-C.; Pignata, G.; Suntzeff, N.B.; Taddia, F.; Robledo, S.T.; Valenti, S.We present an analysis of ultraviolet (UV) to near-infrared observations of the fast-declining Type Ia supernovae (SNe Ia) 2007on and 2011iv, hosted by the Fornax cluster member NGC 1404. The B-band light curves of SN 2007on and SN 2011iv are characterised by Δm 15 (B) decline-rate values of 1.96 mag and 1.77 mag, respectively. Although they have similar decline rates, their peak B- and H-band magnitudes differ by ~ 0.60 mag and ~0.35 mag, respectively. After correcting for the luminosity vs. decline rate and the luminosity vs. colour relations, the peak B-band and H-band light curves provide distances that differ by ~ 14% and ~ 9%, respectively. These findings serve as a cautionary tale for the use of transitional SNe Ia located in early-type hosts in the quest to measure cosmological parameters. Interestingly, even though SN 2011iv is brighter and bluer at early times, by three weeks past maximum and extending over several months, its B - V colour is 0.12 mag redder than that of SN 2007on. To reconcile this unusual behaviour, we turn to guidance from a suite of spherical one-dimensional Chandrasekhar-mass delayed-detonation explosion models. In this context, 56 Ni production depends on both the so-called transition density and the central density of the progenitor white dwarf. To first order, the transition density drives the luminosity-width relation, while the central density is an important second-order parameter. Within this context, the differences in the B - V colour evolution along the Lira regime suggest that the progenitor of SN 2011iv had a higher central density than SN 2007on. © ESO 2018.