Spiral Disk Instability Can Drive Thermonuclear Explosions in Binary White Dwarf Mergers

Thermonuclear, or Type Ia supernovae (SNe Ia), originate from the explosion of carbon--oxygen white dwarfs, and serve as standardizable cosmological candles. However, despite their importance, the nature of the progenitor systems that give rise to SNe Ia has not been hitherto elucidated. Observational evidence favors the double-degenerate channel in which merging white dwarf binaries lead to SNe Ia. Furthermore, significant discrepancies exist between observations and theory, and to date, there has been no self-consistent merger model that yields a SNe Ia. Here we show that a spiral mode instability in the accretion disk formed during a binary white dwarf merger leads to a detonation on a dynamical timescale. This mechanism sheds light on how white dwarf mergers may frequently yield SNe Ia.Comment: Final version (as in ApJL) with minor edit

The evolution of GX 339-4 in the low-hard state as seen by NuSTAR and Swift

We analyze eleven NuSTAR and Swift observations of the black hole X-ray binary GX 339-4 in the hard state, six of which were taken during the end of the 2015 outburst, five during a failed outburst in 2013. These observations cover luminosities from 0.5%-5% of the Eddington luminosity. Implementing the most recent version of the reflection model relxillCp, we perform simultaneous spectral fits on both datasets to track the evolution of the properties in the accretion disk including the inner edge radius, the ionization, and temperature of the thermal emission. We also constrain the photon index and electron temperature of the primary source (the "corona"). We find the disk becomes more truncated when the luminosity decreases, and observe a maximum truncation radius of $37R_g$. We also explore a self-consistent model under the framework of coronal Comptonization, and find consistent results regarding the disk truncation in the 2015 data, providing a more physical preferred fit for the 2013 observations.Comment: 15 pages, 8 figures, 6 tables, accepted for publication in The Astrophysical Journa

RkNN Query Processing in Distributed Spatial Infrastructures: A Performance Study

The Reverse k-Nearest Neighbor (RkNN) problem, i.e. finding all objects in a dataset that have a given query point among their corresponding k-nearest neighbors, has received increasing attention in the past years. RkNN queries are of particular interest in a wide range of applications such as decision support systems, resource allocation, profile-based marketing, location-based services, etc. With the current increasing volume of spatial data, it is difficult to perform RkNN queries efficiently in spatial data-intensive applications, because of the limited computational capability and storage resources. In this paper, we investigate how to design and implement distributed RkNN query algorithms using shared-nothing spatial cloud infrastructures as SpatialHadoop and LocationSpark. SpatialHadoop is a framework that inherently supports spatial indexing on top of Hadoop to perform efficiently spatial queries. LocationSpark is a recent spatial data processing system built on top of Spark. We have evaluated the performance of the distributed RkNN query algorithms on both SpatialHadoop and LocationSpark with big real-world datasets. The experiments have demonstrated the efficiency and scalability of our proposal in both distributed spatial data management systems, showing the performance advantages of LocationSpark

El pretérito perfecto compuesto en el español andino peruano: usos innovadores y extensión a contextos de aoristo

El presente trabajo tiene como objetivo analizar los valores del pretérito perfecto compuesto (PPC) en el español andino peruano. El estudio se basa en un corpus oral formado por 28 entrevistas de 30 a 60 minutos de duración, recopilado en la ciudad de Cuzco y en el distrito de Chinchero. El foco de nuestro estudio se centra en la extensión del PPC a ámbitos de pasado perfectivo que no tienen conexión con el presente, esto es, en contextos del pretérito perfecto simple (PPS), así como en la identificación de sus valores evidenciales y discursivos del PPC en el corpus. Planteamos la hipótesis de que la adquisición de estos nuevos valores del PPC está motivada por el contacto con el quechua, que se constituye como un disparador del cambio lingüístico y acelera su evolución en el proceso de la gramaticalización de las formas de perfecto hacia la evidencialidad.The objective of this paper is to analyze the values of the past perfect tense (PP) in Peruvian Andean Spanish. The study is based on an oral corpus consisting of 28 30-to-60 minute interviews regarding life stories and personal experiences, collected in Cusco and the district of Chinchero. The study focuses on the extension of the PP to areas of perfective past that have no connection with the present, that is, to past simple tense (PS) contexts, as well as on the identification of the evidential and discursive values of the PP in the corpus. Our hypothesis is that the acquisition of these new values of the PP is motivated by contact with Quechua, which triggers linguistic change and accelerates its evolution in the process of grammaticalization of forms of the perfect towards evidentiality.Este trabalho tem como objetivo analisar os valores do pretérito perfeito composto (PPC) no espanhol andino peruano. O estudo baseia-se num corpus oral formado por 28 entrevistas de 30 a 60 minutos de duração, recopilado na cidade de Cuzco e no distrito de Chinchero. O foco deste estudo está na extensão do PPC a âmbitos de pasado perfectivo que não têm conexão com o presente, isto é, em contextos do pretérito perfeito simples (PPS), bem como na identificação de seus valores evidenciais e discursivos do PPC no corpus. Levantamos a hipótese de que a aquisição desses novos valores do PPC está motivada pelo contato com o quechua, que se constitui como disparador da mudança linguística e acelerador de sua evolução no processo da gramaticalização das formas de perfeito à evidencialidade

Light curves and spectra from a thermonuclear explosion of a white dwarf merger

This is the final version of the article. Available from the publisher via the DOI in this record.Double-degenerate (DD) mergers of carbon-oxygen white dwarfs have recently emerged as a leading candidate for normal Type Ia supernovae (SNe Ia). However, many outstanding questions surround DD mergers, including the characteristics of their light curves and spectra. We have recently identified a spiral instability in the post-merger phase of DD mergers and demonstrated that this instability self-consistently leads to detonation in some cases. We call this the spiral merger SN Ia model. Here, we utilize the SuperNu radiative transfer software to calculate three-dimensional synthetic light curves and spectra of the spiral merger simulation with a system mass of 2.1 from Kashyap et al. Because of their large system masses, both violent and spiral merger light curves are slowly declining. The spiral merger resembles very slowly declining SNe Ia, including SN 2001ay, and provides a more natural explanation for its observed properties than other SN Ia explosion models. Previous synthetic light curves and spectra of violent DD mergers demonstrate a strong dependence on viewing angle, which is in conflict with observations. Here, we demonstrate that the light curves and spectra of the spiral merger are less sensitive to the viewing angle than violent mergers, in closer agreement with observation. We find that the spatial distribution of 56Ni and IMEs follows a characteristic hourglass shape. We discuss the implications of the asymmetric distribution of 56Ni for the early-time gamma-ray observations of 56Ni from SN 2014J. We suggest that DD mergers that agree with the light curves and spectra of normal SNe Ia will likely require a lower system mass.This work is supported in part at the University of Chicago by the National Science Foundation under grants AST-0909132, PHY-0822648 (JINA, Joint Institute for Nuclear Astrophysics), and PHY–1430152 (JINA-CEE, Joint Institute for Nuclear Astrophysics). This work used the Extreme Science and Engineering Discovery Environment (XSEDE), which is supported by National Science Foundation grant number ACI-1053575. Simulations at UMass Dartmouth were performed on a computer cluster supported by NSF grant CNS-0959382 and AFOSR DURIP grant FA9550-10-1-0354. The work of E.G.-B., G.A.-S., and P. L.-A. was partially funded by the MINECO AYA2014-59084- P grant and by the AGAUR. This research has made use of NASA’s Astrophysics Data System and the yt astrophysics analysis software suit

PÉRDIDAS DE CARBONO EN SUELOS DE LA LLANURA COSTERA DE NAYARIT, MÉXICO

Se analizaron las pérdidas de carbono orgánico en suelos a partir de 12 perfiles localizados en el delta del río San Pedro y distribuidos por nivel geomorfológico en la llanura costera del estado de Nayarit, México. El estudio se realizó comparando el contenido de carbono de los suelos con mayor conservación bajo bosque y cultivados. Los niveles considerados para este análisis fueron llanura alta, llanura media y sus depresiones, llanura baja y barras costeras. Las reservas de carbono (RCO) se determinaron teniendo en cuenta la densidad aparente (Da), el espesor de cada horizonte y el contenido de carbono. Los resultados se ponderaron para las profundidades 0-20, 0-50 y 0-100 cm. Las pérdidas de carbono identificadas fueron del 36 % para suelos Cambisoles de la llanura alta, 40 % para Feozem y Cambisoles de la llanura media, 60 % en suelos Feozem y Solonetz de las depresiones de la llanura media, 67 % para Cambisoles de la llanura baja y 90 % para Arenosoles de las barras costeras. Se demostró que la actividad agrícola intensiva y continuada, ha ocasionado pérdidas en el contenido de carbono; así mismo, la capa agrícola (20 cm) resulta la más afectada por esta actividad antropogénica

Gramaticalización inducida por contacto en español en contacto con la lengua maya tzutujil: el sistema pronominal átono de tercera persona

The goal of this study is to analyse both the use of lo and null object to refer to third person direct objects in an oral corpus of Tzutujil-Spanish bilinguals from the village of Chicacao, Guatemala. The corpus’s direct object marking system is characterized by two variants: a) the use of lo as the only third person direct object pronoun, i.e. as an invariable morph; b) its omission, i.e., the production of a zero morph. We put forward that these changes belong to a pronominal system reorganization process caused by the bilingual situation of the region, and an intense contact with Tzutujil, that has caused an acceleration of the grammaticalization process of the Spanish pronominal system of direct object to an object concordance.El objetivo del presente estudio es analizar la tendencia al empleo de lo o un cero fonético para la marcación del objeto directo de tercera persona en un corpus oral de bilingües tzutujil-español recogido en Chicacao, Guatemala. El sistema de marcación del objeto analizado se caracterizaría básicamente por dos fenómenos: a) el empleo de una única forma lo invariable que ha perdido la morfología de género y número; b) la omisión de esta, esto es, un cero fonético. A través de su análisis, mostraremos que estos cambios se enmarcan dentro de un proceso de reorganización del sistema pronominal que se ha producido debido a la situación de bilingüismo y contacto intenso con el tzutujil, y que se manifiesta en una aceleración del proceso de gramaticalización del sistema pronominal de objeto directo del español hacia una concordancia de objeto