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In this paper, we revisit level-dependent quasi-birth-death processes with finitely many possible values of the level and phase variables by complementing the work of Gaver, Jacobs, and Latouche (Adv. Appl. Probab. 1984), where the emphasis is upon obtaining numerical methods for evaluating stationary probabilities and moments of first-passage times to higher and lower levels. We provide a matrix-analytic scheme for numerically computing hitting probabilities, the number of upcrossings, sojourn time analysis, and the random area under the level trajectory. Our algorithmic solution is inspired from Gaussian elimination, which is applicable in all our descriptors since the underlying rate matrices have a block-structured form. Using the results obtained, numerical examples are given in the context of varicella-zoster virus infections., Depto. de Estadística y Ciencia de los Datos, Fac. de Estudios Estadísticos, TRUE, pub

We aim to quantify the spread of a direct contact infectious disease that confers permanent immunity after recovery, within a non-isolated finite and homogeneous population. Prior to the onset of the infection and to prevent the spread of this disease, a proportion of individuals was vaccinated. But the administered vaccine is imperfect and can fail, which implies that some vaccinated individuals get the infection when being in contact with infectious individuals. We study the evolution of the epidemic process over time in terms of a continuous-time Markov chain, which represents a general SIR model with an additional compartment for vaccinated individuals. In our stochastic framework, we study two bi-dimensional variables recording infection events, produced by a single infectious individual or by the whole infected group, taking into account if the newly infected individual was previously vaccinated or not. Theoretical schemes and recursive algorithms are derived in order to compute joint probability mass functions and factorial moments for these random variables. We illustrate the applicability of our techniques by means of a set of numerical experiments., Ministerio de Ciencia, Innovación y Universidades (España), British Spanish Society, Universidad Complutense de Madrid, Depto. de Estadística y Ciencia de los Datos, Fac. de Estudios Estadísticos, TRUE, pub

La familia de estándares ISO/IEEE 11073 (X73) tiene como objetivo garantizar la interoperabilidad entre los dispositivos de salud personal. A pesar de la popularidad de Bluetooth Low Energy (BLE) como tecnología de comunicación en dispositivos biomédicos, no existe una propuesta consensuada que permita la compatibilidad entre ambos estándares. En este trabajo se propone la encapsulación de datos X73 para su envío a través de BLE como forma de facilitar la interoperabilidad. Se presentan dos alternativas que han sido evaluadas en el contexto de la especialización 11073-10420 e implementadas sobre la placa evaluación de un dispositivo BLE comercial. Los resultados muestran la viabilidad de ambas alternativas y se discuten en términos del volumen de información que es necesario transmitir y el consumo que representa para la interfaz radio.

This article belongs to the Special Issue Stochastic Processes with Applications, We propose a stochastic model for the development of gastrointestinal nematode infection in growing lambs under the assumption that nonhomogeneous Poisson processes govern the acquisition of parasites, the parasite-induced host mortality, the natural (no parasite-induced) host mortality and the death of parasites within the host. By means of considering a number of age-dependent birth and death processes with killing, we analyse the impact of grazing strategies that are defined in terms of an intervention instant t0, which might imply a move of the host to safe pasture and/or anthelmintic treatment. The efficacy and cost of each grazing strategy are defined in terms of the transient probabilities of the underlying stochastic processes, which are computed by means of Strang–Marchuk splitting techniques. Our model, calibrated with empirical data from Uriarte et al. and Nasreen et al., regarding the seasonal presence of nematodes on pasture in temperate zones and anthelmintic efficacy, supports the use of dose-and-move strategies in temperate zones during summer and provides stochastic criteria for selecting the exact optimum time instant t (sub index 0) when these strategies should be applied., Ministerio de Economía y Competitividad (MINECO), Depto. de Estadística e Investigación Operativa, Fac. de Ciencias Matemáticas, TRUE, pub

We investigate a stochastic model for the competition between two species. Based on percentiles of the maximum number of individuals in the ecosystem, we present an approximating model for which the extinction time can be thought of as a phase-type random variable. We determine formulae for the probabilities of extinction and the moments of the extinction time. We discuss the use of several quasi-stationary assumptions. We include a comparative study between existing asymptotic results, results obtained from a simulation of the process, and our solution., Government of Spain (Ministry of Science and Innovation), European Commission, Depto. de Estadística e Investigación Operativa, Fac. de Ciencias Matemáticas, TRUE, pub

This article has been accepted for publication in Monthly notices of the Royal Astronomical Society © 2013 MNRAS. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved. MAL-G and JL-S acknowledge support by the Spanish Ministerio de Ciencía e Innovación under grant AYA2008-06423-C03-03. JFA-C is a researcher of the CONICET and acknowledges support by grant PICT 2007-02177 (SecyT). PGP-G acknowledges support from the Spanish Programa Nacional de Astronomía y Astrofísica under grants AYA2009-10368 and AYA2009-07723-E. We would like to acknowledge the anonymous referee for a fruitful discussion about the results of this work. His/her comments on the text content have allowed us to notoriously improve this manuscript., Nearby star-forming regions are ideal laboratories to study high-energy emission of different stellar populations, from very massive stars to brown dwarfs. NGC 2023 is a reflection nebula situated to the south of the Flame Nebula (NGC 2024) and at the edge of the H II region IC 434, which also contains the Horsehead Nebula (Barnard 33). NGC 2023, NGC 2024, Barnard 33 and the surroundings of the O-type supergiant star zeta Ori constitute the south part of the Orion B molecular complex. In this work, we present a comprehensive study of X-ray emitters in the region of NGC 2023 and its surroundings. We combine optical and infrared data to determine physical properties (mass, temperature, luminosity and the presence of accretion discs) of the stars detected in an XMM-Newton observation. This study has allowed us to analyse spectral energy distribution of these stars for the first time and determine their evolutionary stage. Properties of the X-ray emitting plasma of these stars are compared to those found in other nearby star-forming regions. The results indicate that the stars that are being formed in this region have characteristics, in terms of physical properties and luminosity function, similar to those found in the Taurus-Auriga molecular complex., Spanish Ministerio de Ciencía e Innovación, SecyT, Spanish Programa Nacional de Astronomía y Astrofísica, Depto. de Física de la Tierra y Astrofísica, Fac. de Ciencias Físicas, TRUE, pub

The interest is in a stochastic model for the competition of two species, which was first introduced by Reuter [18] and Iglehart [11], and then analyzed by Ridler-Rowe [19]. The model is related to the two-species autonomous competitive model (Zeeman [24]), where individuals compete either directly or indirectly for a limited food supply and, consequently, birth and death rates depend on the population size of one or both of the species. The aim is to complement the treatment of the model we started in [8,9] by focusing here on probabilistic descriptors that are inherently linked to an individual: its residual lifetime and the number of direct descendants. We present an approximating model based on the maximum size distribution, and we discuss on various models defined in terms of the underlying killing and reproductive strategies. Numerical examples are presented to show the effects of the killing and reproductive strategies on the behavior of an individual, and how the impact of these strategies on the descriptors vanishes in highly competitive ecosystems., Depto. de Estadística e Investigación Operativa, Fac. de Ciencias Matemáticas, TRUE, pub

Este proyecto complementa el proyecto docente anterior (PIMCD 155) en el que se presentaron un conjunto de ejercicios que ayudan a extraer conclusiones a partir de los datos aportados por diferentes técnicas instrumentales de caracterización de sólidos inorgánicos. Así, en principio se elabora de material docente que implique la interpretación de los datos aportados por cada Técnicas que hemos considerado que todo estudiante de grado debe conocer. Se enfatiza la relevancia de estos resultados en la comprensión de los compuestos inorgánicos. Y en la parte final, hemos elaborado una práctica en la que se manejan los datos aportados por las técnicas y se presenta la complementariedad de todas ellas, y el tipo de información relevante que podemos obtener.