Estadías Hospitalarias Inadecuadas: Aspectos Metodológicos para su Detección, Estimación y Predicción

Estadías Hospitalarias Inadecuadas: Aspectos Metodológicos para su Detección, Estimación y Predicció

Abdala, M y Spiller, P. Instituciones, Contratos y Regulación en Argentina, Buenos Aires

Abdala, M y Spiller, P. Instituciones, Contratos y Regulación en Argentina, Buenos Aire

Order Reduction of the Chemical Master Equation via Balanced Realisation

We consider a Markov process in continuous time with a finite number of discrete states. The time-dependent probabilities of being in any state of the Markov chain are governed by a set of ordinary differential equations, whose dimension might be large even for trivial systems. Here, we derive a reduced ODE set that accurately approximates the probabilities of subspaces of interest with a known error bound. Our methodology is based on model reduction by balanced truncation and can be considerably more computationally efficient than the Finite State Projection Algorithm (FSP) when used for obtaining transient responses. We show the applicability of our method by analysing stochastic chemical reactions. First, we obtain a reduced order model for the infinitesimal generator of a Markov chain that models a reversible, monomolecular reaction. In such an example, we obtain an approximation of the output of a model with 301 states by a reduced model with 10 states. Later, we obtain a reduced order model for a catalytic conversion of substrate to a product; and compare its dynamics with a stochastic Michaelis-Menten representation. For this example, we highlight the savings on the computational load obtained by means of the reduced-order model. Finally, we revisit the substrate catalytic conversion by obtaining a lower-order model that approximates the probability of having predefined ranges of product molecules.Comment: 12 pages, 6 figure

Conflictos y lealtades en el Reino de Galicia (1700-1714)

La entrada de Portugal en la alianza contra los Borbones durante la Guerra de Sucesión de España (1700-1714) abrió un frente militar en el sur de Galicia que exigió la movilización de hombres y recursos y la implicación de todas las instituciones gallegas, empezando por el arzobispo de Santiago, fray Antonio de Monroy, que desde 1691 mantenía correspondencia con el rey Pedro II. Esta situación provocó que portugueses residentes en Galicia fuesen objeto de sospecha y acusados por su supuesto apoyo al enemigo. Este artículo se centra en el estudio de la participación y la actitud de los portugueses en Galicia durante el conflicto, la visión que se tenía de ellos, el posicionamiento de las diferentes instituciones y las repercusiones de la guerra con Portugal en el plano simbólico y político.Ministerio de Ciencia e Innovación del Gobierno de España a través del proyecto de investigación Cultura e identidades urbanas en la Castilla Moderna, su producción y proyecciones (HAR2009-13508-C02-02, subproyecto HIST.)Consejo de Administración de Patrimonio Naciona

Normality-based validation for crisp clustering

This is the author’s version of a work that was accepted for publication in Pattern Recognition. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Pattern Recognition, 43, 36, (2010) DOI 10.1016/j.patcog.2009.09.018We introduce a new validity index for crisp clustering that is based on the average normality of the clusters. Unlike methods based on inter-cluster and intra-cluster distances, this index emphasizes the cluster shape by using a high order characterization of its probability distribution. The normality of a cluster is characterized by its negentropy, a standard measure of the distance to normality which evaluates the difference between the cluster's entropy and the entropy of a normal distribution with the same covariance matrix. The definition of the negentropy involves the distribution's differential entropy. However, we show that it is possible to avoid its explicit computation by considering only negentropy increments with respect to the initial data distribution, where all the points are assumed to belong to the same cluster. The resulting negentropy increment validity index only requires the computation of covariance matrices. We have applied the new index to an extensive set of artificial and real problems where it provides, in general, better results than other indices, both with respect to the prediction of the correct number of clusters and to the similarity among the real clusters and those inferred.This work has been partially supported with funds from MEC BFU2006-07902/BFI, CAM S-SEM-0255-2006 and CAM/UAM CCG08-UAM/TIC-442

Abdala, M y Spiller, P. Instituciones, Contratos y Regulación en Argentina, Buenos Aires

Abdala, M y Spiller, P. Instituciones, Contratos y Regulación en Argentina, Buenos Aire

Crisis gemelas, régimen cambiario e información de mercado

En este trabajo se investiga cómo el régimen cambiario y la existencia de información imperfecta respecto de los fundamentals de la economía afecta la probabilidad de ocurrencia de una crisis gemela. Se demuestra que una crisis bancaria es más probable cuanto menor sea la calidad de la información de mercado disponible. Si las reservas con que cuenta el banco central son escasas, una crisis bancaria puede desembocar en una crisis cambiaria al aumentar el volumen de la salida de capitales, si bien la posibilidad de crisis es menor con un tipo de cambio flexible que con uno fijo.In this paper I analyze how the exchange rate regime and imperfect information about the quality of the fundamentals of the economy may affect the likelihood of a twin crisis. I prove that bank runs are more probable when the quality of market information available to investors is poor. A banking crisis can lead to a currency crisis if the amount of reserves held by the central bank is low. Finally, I compare the likelihood of crisis under two alternative exchange rate regimes (fixed rate and flexible rate), concluding that financial fragility is higher under a fixed rate regime.Departamento de Economí