Singular random matrix decompositions: distributions.

Assuming that Y has a singular matrix variate elliptically contoured distribution with respect to the Hausdorff measure, the distributions of several matrices associated to QR, modified QR, SV and Polar decompositions of matrix Y are determined, for central and non-central, non-singular and singular cases, as well as their relationship to the Wishart and Pseudo-Wishart generalized singular and non-singular distributions. We present a particular example for the Karhunen-Lòeve decomposition. Some of these results are also applied to two particular subfamilies of elliptical distributions, the singular matrix variate normal distribution and the singular matrix variate symmetric Pearson type VII distribution

Singular random matrix decompositions: Jacobians.

For a singular random matrix Y, we find the Jacobians associated with the following decompositions; QR, Polar, Singular Value (SVD), L'U, L'DM and modified QR (QDR). Similarly, we find the Jacobinas of the following decompositions: Spectral, Cholesky's, L'DL and symmetric non-negative definite square root, of the cross-product matrix S = Y'Y

Vertical segregation among pathways mediating nitrogen loss (N2 and N2O production) across the oxygen gradient in a coastal upwelling ecosystem

Indexación: ScopusThe upwelling system off central Chile (36.5 S) is seasonally subjected to oxygen (O2)-deficient waters, with a strong vertical gradient in O2 (from oxic to anoxic conditions) that spans a few metres (30-50€m interval) over the shelf. This condition inhibits and/or stimulates processes involved in nitrogen (N) removal (e.g. anammox, denitrification, and nitrification). During austral spring (September 2013) and summer (January 2014), the main pathways involved in N loss and its speciation, in the form of N2 and/or N2O, were studied using 15N-tracer incubations, inhibitor assays, and the natural abundance of nitrate isotopes along with hydrographic information. Incubations were developed using water retrieved from the oxycline (25€m depth) and bottom waters (85€m depth) over the continental shelf off Concepción, Chile. Results of 15N-labelled incubations revealed higher N removal activity during the austral summer, with denitrification as the dominant N2-producing pathway, which occurred together with anammox at all times. Interestingly, in both spring and summer maximum potential N removal rates were observed in the oxycline, where a greater availability of oxygen was observed (maximum O2 fluctuation between 270 and 40€μmol€L'1) relative to the hypoxic bottom waters ( < €20€μmol€O2€L'1). Different pathways were responsible for N2O produced in the oxycline and bottom waters, with ammonium oxidation and dissimilatory nitrite reduction, respectively, as the main source processes. Ammonium produced by dissimilatory nitrite reduction to ammonium (DNiRA) could sustain both anammox and nitrification rates, including the ammonium utilized for N2O production. The temporal and vertical variability of /15N-NO3' confirms that multiple N-cycling processes are modulating the isotopic nitrate composition over the shelf off central Chile during spring and summer. N removal processes in this coastal system appear to be related to the availability and distribution of oxygen and particles, which are a source of organic matter and the fuel for the production of other electron donors (i.e. ammonium) and acceptors (i.e. nitrate and nitrite) after its remineralization. These results highlight the links between several pathways involved in N loss. They also establish that different mechanisms supported by alternative N substrates are responsible for substantial accumulation of N2O, which are frequently observed as hotspots in the oxycline and bottom waters. Considering the extreme variation in oxygen observed in several coastal upwelling systems, these findings could help to understand the ecological and biogeochemical implications due to global warming where intensification and/or expansion of the oceanic OMZs is projected.https://www.biogeosciences.net/14/4795/2017

El Trabajo Social y los Campos Disciplinarios de las Ciencias Sociales en Chile

The paper aims to review critically the concept of discipline and observe from it the classifications have been proposed to organize the subfields belonging to social sciences in Chile. Reflection begins by reviewing the concept of discipline, from its different meanings it has had to its current use in the academic world as a field or area of knowledge. Under the latter sense can be seen that there are two disputing senses, one with emphasis on epistemic order, and other on factors of socio-historical nature. It analyses the different taxonomic proposals used to group and classify subdisciplines is social sciences by governmental institutions, as well as the Faculties of Social Sciences. Finally a review is made to studies on the development and establishment of social sciences in Chile, while excluding social work discipline.El artículo tiene como propósito hacer una revisión crítica en torno al concepto de disciplina y a partir de éste observar las clasificaciones que se han propuesto para organizar las subdisciplinas pertenecientes al campo de las ciencias sociales en Chile. Se inicia la reflexión revisando el concepto de disciplina, a partir de sus diferentes acepciones que ha tenido hasta su actual uso en el mundo académico, como campo o área del conocimiento. Bajo esta última acepción se aprecia la existencia de dos metasignificados que disputan su sentido, uno con énfasis en cuestiones de orden epistémico, y otro, en factores de naturaleza sociohistóricos. Se analiza las diferentes propuestas taxonómicas  que se utilizan para agrupar y clasificar las subdiciplinas del área de las ciencias sociales por parte de instituciones gubernamentales encargadas del desarrollo de la educación y las ciencias del país, así como de las Facultades Universitarias de Ciencias Sociales. Finalmente se elabora una crítica a los estudios realizados sobre el desarrollo y constitución de las ciencias sociales en el Chile, en tanto se excluye al Trabajo Social como disciplina

La Sociología Chilena en la Década de los Noventa

En el presente estudio se analizó la producción sociológica chilena de los principales géneros documentales socialmente aceptados en la comunidad científica, durante los años 1990-1999, a fin de analizar los siguientes aspectos: productividad, colaboración y campos subdisciplinarios. Se recopiló un total de 1.390 referencias. Su análisis global mostró una actividad ligeramente decreciente que alcanzó alrededor de 139 publicaciones anuales para el periodo en estudio (1990–1999). La distribución de áreas temáticas (subdisciplinas) mostró un aporte mayoritario en Sociología de la Cultura (21.8%), Sociología del Trabajo (14.5%) y la Sociología Política (14.5%); en cambio, las áreas con menor cantidad de trabajos publicados son la Sociología Matemática, Experimental y Problemas Internacionales, todas éstas con un aporte de un 1.4% a la productividad total de publicaciones. Las instituciones más productivas del país son la Facultad Latinoamericana de Ciencias Sociales (FLACSO) con un 26.1%, seguido por la Universidad de Chile (UCH) con un porcentaje de un 26.0% y la Pontificia Universidad Católica de Chile (PUCCH) generó una fracción importante de publicaciones (12.4%). Al analizar, la colaboración de trabajos por autores, se observó una tendencia mayoritaria a publicar trabajos de corte individual, lo cual se refleja en la tasa de colaboración de 1.6 para el decenio en estudio

SINGULAR RANDOM MATRIX DECOMPOSITIONS: DISTRIBUTIONS.

Assuming that Y has a singular matrix variate elliptically contoured distribution with respect to the Hausdorff measure, the distributions of several matrices associated to QR, modified QR, SV and Polar decompositions of matrix Y are determined, for central and non-central, non-singular and singular cases, as well as their relationship to the Wishart and Pseudo-Wishart generalized singular and non-singular distributions. We present a particular example for the Karhunen-Lòeve decomposition. Some of these results are also applied to two particular subfamilies of elliptical distributions, the singular matrix variate normal distribution and the singular matrix variate symmetric Pearson type VII distribution.

SINGULAR RANDOM MATRIX DECOMPOSITIONS: JACOBIANS.

For a singular random matrix Y, we find the Jacobians associated with the following decompositions; QR, Polar, Singular Value (SVD), L´U, L´DM and modified QR (QDR). Similarly, we find the Jacobinas of the following decompositions: Spectral, Cholesky´s, L´DL and symmetric non-negative definite square root, of the cross-product matrix S = Y´Y.

Photoexcitation of graphene with twisted light

We study theoretically the interaction of twisted light with graphene. The light-matter interaction matrix elements between the tight-binding states of electrons in graphene are determined near the Dirac points. We examine the dynamics of the photoexcitation process by posing the equations of motion of the density matrix and working up to second order in the field. The time evolution of the angular momentum of the photoexcited electrons and their associated photocurrents are examined in order to elucidate the mechanisms of angular momentum transfer. We find that the transfer of spin and orbital angular momentum from light to the electrons is more akin here to the case of intraband than of interband transitions in semiconductors, due to the fact that the two relevant energy bands of graphene originate from the same atomic orbitals.Comment: 18 pages, 4 figure

Ensamblajes urbanos: la TAR y el examen de la ciudad

Este artículo presenta nuevas perspectivas de investigación y desafíos analíticos que la teoría del actor-red (TAR) abre para los estudios urbanos. En primer lugar, se revisan cómo los principios de relacionalidad híbrida y asociatividad plana de la TAR están siendo adoptados en los estudios urbanos para ampliar simétricamente la ecología urbana a nohumanos e impugnar concepciones escalares del espacio y economías urbanas. A continuación, se propone que la TAR trae consigo un desafío más fundamental relativo a la concepción de como objeto espacial, entidad político-económica y/o forma sociocultural subraya su carácter singular, estable y delimitado, la TAR permite pensar la ciudad como un objeto múltiple y decentrado. La noción de ensamblajes urbanos se introduce entonces para dar cuenta de la circulación y devenir de la ciudad en múltiples redes híbridas y translocales. El artículo concluye sopesando algunas de las consecuencias de este examen de la ciudad, especialmente el reposicionamiento del problema de la complejidad, urbana en este caso, como punto, si no de partida, entonces al menos de llegada para la TA