RD-flatness and RD-injectivity

It is proved that every commutative ring whose RD-injective modules are $\Sigma$-RD-injective is the product of a pure semi-simple ring and a finite ring. A complete characterization of commutative rings for which each artinian (respectively simple) module is RD-injective, is given. These results can be obtained by using the properties of RD-flat modules and RD-coflat modules which are respectively the RD-relativization of flat modules and fp-injective modules. It is also shown that a commutative ring is perfect if and only if each RD-flat module is RD-projective.Comment: A new section is added to the version published in Communications in Algebra where a complete proof of Theorem 3.1 is give

Wind Forced Variability in Eddy Formation, Eddy Shedding, and the Separation of the East Australian Current

The East Australian Current (EAC), like many other subtropical western boundary currents, is believed to be penetrating further poleward in recent decades. Previous observational and model studies have used steady state dynamics to relate changes in the westerly winds to changes in the separation behavior of the EAC. As yet, little work has been undertaken on the impact of forcing variability on the EAC and Tasman Sea circulation. Here using an eddy‐permitting regional ocean model, we present a suite of simulations forced by the same time‐mean fields, but with different atmospheric and remote ocean variability. These eddy‐permitting results demonstrate the nonlinear response of the EAC to variable, nonstationary inhomogeneous forcing. These simulations show an EAC with high intrinsic variability and stochastic eddy shedding. We show that wind stress variability on time scales shorter than 56 days leads to increases in eddy shedding rates and southward eddy propagation, producing an increased transport and southward reach of the mean EAC extension. We adopt an energetics framework that shows the EAC extension changes to be coincident with an increase in offshore, upstream eddy variance (via increased barotropic instability) and increase in subsurface mean kinetic energy along the length of the EAC. The response of EAC separation to regional variable wind stress has important implications for both past and future climate change studies

Coexpression, copurification, crystallization and preliminary X-ray analysis of a complex of ARL2-GTP and PDE delta

The small GTPase ARL2 (from Mus musculus) and an effector protein, the δ subunit of human cGMP phosphodiesterase (hPDE δ), were coexpressed and copurified from Escherichia coli as a stable complex. Coexpression significantly increased the otherwise low yield of PDE δ production in E. coli. The complex, which contains ARL2 in the activated GTP-bound form, was crystallized in two forms. The first belongs to the monoclinic space group P21, with unit-cell parameters a = 48.1, b = 45.7, c = 74.7 Å, β = 94.0° and one complex (39 kDa) in the asymmetric unit. Cryocooled crystals diffract to 2.3 Å using synchrotron radiation. The micro-focused X-­ray beam at beamline ID13 (ESRF) allowed the use of very small crystals, which helped to overcome twinning and enabled the identification of a molecular-replacement solution. The second form recrystallized from the first one after several months. These crystals belong to the orthorhombic space group P212121, with unit-cell parameters a = 44.5, b = 65.4, c = 104.4 Å and one complex in the asymmetric unit. They diffracted to 1.8 Å using synchrotron radiation

An Empirical Investigation in Credit Spread Indices

We study the dynamics of the spread between U.S. corporate and Treasury bonds. We focus on Aaa and Baa corporate yield indices and estimate nonparametrically the dynamics of the spreads assuming that they follow a univariate diffusion process. Using techniques developed for interest rate processes we try to infer from the data what acceptable process can be used to model aggregate credit spreads for option pricing or risk management purposes. We find that there is significant evidence of mean reversion especially for higher rated spreads and that the volatility of Aaa spreads exhibit a U-shape while the volatility of Baa spreads is monotonically increasing in the level of spreads. Based on these observations and on the evidence of jumps in the series, we propose a new model for credit spread indices (an Ornstein-Uhlenbeck with jumps) and estimate it by maximum likelihood.Credit spread; risk management; jump diffusion; volatility; nonparametric

Non-Hausdorff Symmetries of C*-algebras

Symmetry groups or groupoids of C*-algebras associated to non-Hausdorff spaces are often non-Hausdorff as well. We describe such symmetries using crossed modules of groupoids. We define actions of crossed modules on C*-algebras and crossed products for such actions, and justify these definitions with some basic general results and examples.Comment: very minor changes. To appear in Math. An

A New Channel for the Detection of Planetary Systems Through Microlensing: II. Repeating Events

In the companion paper we began the task of systematically studying the detection of planets in wide orbits ($a > 1.5 R_E$) via microlensing surveys. In this paper we continue, focusing on repeating events. We find that, if all planetary systems are similar to our own Solar System, reasonable extensions of the present observing strategies would allow us to detect 3-6 repeating events per year along the direction to the Bulge. Indeed, if planetary systems with multiple planets are common, then future monitoring programs which lead to the discovery of thousands of stellar-lens events will likely discover events in which several different planets within a single system serve as lenses, with light curves exhibiting multiple repetitions. In this paper we discuss observing strategies to maximize the discovery of all wide-orbit planet-lens events. We also compare the likely detection rates of planets in wide orbits to those of planets located in the zone for resonant lensing. We find that, depending on the values of the planet masses and stellar radii of the lensed sources (which determine whether or not finite source size is important), and also on the sensitivity of the photometry used by observers, the detection of planets in wide orbits may be the primary route to the discovery of planets via microlensing. We also discuss how the combination of resonant and wide-orbit events can help us to learn about the distribution of planetary system properties (S 6.1). In addition, by determining the fraction of short-duration events due to planets, we indirectly derive information about the fraction of all short-duration events that may be due to low-mass MACHOs (S 6.2).Comment: 51 pages, 7 figures. To be published in the Astrophysical Journal, 20 February 1999. This completes the introduction to the discovery of planets in wide orbits begun in astro-ph/9808075, also to appear in ApJ on 20 February 199

Spatial distributed modelling of erosion and sediment transport in mountain catchments in the Pyrenees: challenges for calibration and validation

28 p., 10 Figs., 5 Tabls.Publicado inicialmente por la Universidad de La Rioja (España) en: Cuadernos de Investigación Geográfica 39(2) (2013)[EN] Most erosion models applied at basin scale are based on spatially aggregated representation, for example, in a space subdivision of the surfaces to which behavior is assumed homogeneous (sub-basins, hydrological units, etc.). This approach leads to a desirable simplification of the calculations, but presents difficulties in addressing problems related to sediment transport and identification of sediment source areas, which should be treated by a continuous spatial representation. Spatially distributed models, however, allow a more accurate approach to this problem, at the cost of an increased computational complexity. The objective of this work is the calibration and validation of the model WATEM/SEDEM, an empirical-conceptual spatially distributed model, to predict erosion and sediment yield in two watersheds in the Central Spanish Pyrenees: i) the watershed of the Barasona Reservoir (1504 km2), which is drained by the Esera and Isabena Rivers, the model calibration and validation was based on the depositional history of the Barasona Reservoir and suspended sediment records over 3 years (May 2005–May 2008) at the outlet of the Isabena River; ii) the experimental Arnas catchment (2.84 km2), the model calibration was performed based on a dataset of soil redistribution rates derived from point 137Cs inventories, allowing capture differences per land use in the main model parameters. The validation process was carried with the registration of six years of suspended sediment at the outlet of the Arnas catchment. The calibration process for watershed of the Barasona Reservoir showed the problem you have when trying to calibrate the parameters of transport capacity with a single variable (the export of sediment to the basin outlet), making impossible to find a single set of parameters that optimize the error function, making it necessary to adopt a compromise solution. For the experimental Arnas catchment the model calibration processes using spatially distributed sediment yield derived from 137Cs inventories allowed calibrating the empirical parameters of transport capacity in a satisfactory way, finding a single combination of values that optimizes the error function. These results show that the calibration parameters of transport capacity are a fundamental aspect of the model WATEM/SEDEM and other similar models. To obtain a reliable estimate of the spatial distribution of erosion and sediment transport requires a calibration and validation by means of spatially distributed data of soil loss, which in turn allows a calibration of spatially distributed parameters concerning transport capacity.[ES] Una gran parte de los modelos de erosion aplicados a escala de cuenca se basan en una representacion espacialmente agregada, es decir en la subdivision del espacio en superficies a las que se supone un comportamiento homogeneo (subcuencas, unidades hidrologicas, etc.). Esta aproximacion conlleva una deseable simplificacion de los calculos, pero presenta dificultades para abordar problemas relacionados con el transporte de sedimentos y la identificacion de areas fuente de sedimento, que deben tratarse mediante una representacion espacial continua. Los modelos espacialmente distribuidos, en cambio, permiten una aproximacion mas precisa a este problema, a costa de una mayor complejidad de calculo. El objetivo de este trabajo es la calibracion y validacion del modelo WATEM/SEDEM, un modelo empirico-conceptual espacialmente distribuido, para predecir erosion y la produccion de sedimentos en dos cuencas del Pirineo aragones: i) la cuenca del embalse de Barasona (1504 km2), drenada por los rios Esera e Isabena, donde la base de datos para el proceso de calibracion fue el registro de 3 anos de sedimentos en suspension (mayo 2005-mayo 2008) a la salida de la subcuenca del Rio Isabena y para la validacion se utilizo el registro historico de sedimentacion del embalse de Barasona; y, ii) la cuenca experimental de Arnas (2.84 km2), donde se conto para la calibracion con datos espacialmente distribuidos de tasas de erosion y sedimentacion derivadas de inventarios de Cs137, mas el registro de seis anos de sedimento en suspension a la salida de la cuenca de Arnas para el proceso de validacion. El proceso de calibracion para el embalse de Barasona mostro el problema que se tiene al intentar calibrar los parametros de capacidad de transporte con una sola variable (la exportacion de sedimento a la salida de la cuenca), haciendo imposible encontrar un solo conjunto de parametros que optimicen la funcion de error y obligando a adoptar una solucion de compromiso. En la cuenca de Arnas el uso de datos espacialmente distribuidos de produccion de sedimentos derivados de inventarios de Cs137 permitio calibrar los parametros empiricos de capacidad de transporte de una forma satisfactoria, encontrando una sola combinacion de valores que optimiza la funcion de error. Con los resultados obtenidos se demuestra que la calibracion de los parametros de capacidad de transporte es un aspecto fundamental de WATEM/SEDEM y de otros modelos similares. Para obtener una estimacion fiable de la distribucion espacial de los procesos de erosion y transporte de sedimento se requiere de una calibracion y validacion con datos espacialmente distribuidos de perdida o ganancia de suelo que permita a su vez realizar una calibracion espacialmente distribuida de los parametros relativos a la capacidad de transporte.Este trabajo se ha llevado a cabo con el apoyo del proyecto INDICA (CGL2011- 27753-C02-01 y -02), financiado por el Ministerio de Economia y Competitividad, el proyecto ACQWA (FP7-ENV-2007-1-212250), financiado por la Comision Europea y un acuerdo entre el CSIC y el Ministerio de Medio Ambiente (RESEL). N. Lana-Renault ha disfrutado de un contrato de investigacion en el Programa Juan de la Cierva (Ministerio de Economia y Competitividad). En este articulo han participado numerosos colegas del Departamento de Procesos Geoambientales y Cambio Global del Instituto Pirenaico de Ecologia (IPE), asi como del Departamento de Suelo y Agua de la Est. Exp. Aula Dei (EEAD-CSIC).Peer reviewe