Estimation of Poisson parameters: maximum likelihood, Bayes, empirical Bayes or a compromise?

This thesis deals with three point estimation problems where the random variables are assumed to be Poisson with parameters following conjugate prior distributions. In all the three problems, we try to estimate a p-variate Poisson mean;For the first problem, a class of estimators compromising between the maximum likelihood and the Bayes estimators is proposed; the proposed estimators are named limiting translation rule (LTR). In the second problem, we propose the so-called limiting translation compound Bayes rules (LTCBR) which compromise between the maximum likelihood and empirical Bayes estimators. Finally, in the third problem under the assumption that the p-variate mean can be divided into two natural groups, we compare the combined against the separate estimators;We show that the LTRs perform satisfactorily through both the risk criterion and the Bayes risk criterion, the latter measured by what is defined as relative saving loss. With regard to the LTCBRs, it is shown that these estimators have both good componentwise risk and Bayes risk performance, the latter again measured by the relative saving loss. The study of the combined against the separate estimators shows the preference of combined estimators when the scales parameters of the prior distributions assigned to each group are close to each other, otherwise the use of the separate estimators seems more appropriate

Medium dependence of asphaltene agglomeration inhibitor efficiency

Applying chemical additives (molecule inhibitors or dispersants) is one of the common ways to control asphaltene agglomeration and precipitation. However, it is not clear why at some conditions the synthetic flocculation inhibitors as well as resins not only do not inhibit the asphaltene agglomeration,, they may also promote it, and why the increasing of the additive concentration may lead to the diminishing of their efficacy. To clarify this issue, in the present work we have performed a set of vapor preassure osmometry experiments investigating the asphaltene agglomeration inhibition by commercial and new inhibitor molecules in toluene and o-diclorobenzene. Monte Carlo computer modeling has been applied to interpret some unexpected trends of molar mass of the Puerto Ceiba asphaltene clusters at different concentrations of inhibitor, assuming that inhibitors efficiency is directly related to their adsorption on the surface of asphaltene or its complexes. It has been found that a self-assembly of inhibitor molecules, induced by relative lyophilic or lyophobic interactions, may be a reason of the inhibitor efficacy declining.Comment: 21 page

Application of Multifunctional Agents During Enhanced Oil Recovery

During the application of enhanced oil recovery (EOR) processes, complex operational issues, such as the deposition of organic compounds (i.e., wax, resins, and asphaltenes, among others), reservoir formation damage, rock wettability alteration, and high fluids viscosity negatively affect oil recovery. This chapter presents the experimental evaluation of the multifunctional properties of two novel chemical agents recently developed: a zwitterionic surfactant (ZS) and a supramolecular complex (named here as AMESUS) for chemical EOR applications. The performance of the new multifunctional agents and the mechanisms in play on the removal/control of organic compounds deposition oil recovery, asphaltenes inhibition-dispersion activity, reduction in heavy crude oil viscosity, rock wettability modification, and relative permeability are discussed in this chapter

Coordination-driven magnetic-to-nonmagnetic transition in manganese doped silicon clusters

The interaction of a single manganese impurity with silicon is analyzed in a combined experimental and theoretical study of the electronic, magnetic, and structural properties of manganese-doped silicon clusters. The structural transition from exohedral to endohedral doping coincides with a quenching of high-spin states. For all geometric structures investigated, we find a similar dependence of the magnetic moment on the manganese coordination number and nearest neighbor distance. This observation can be generalized to manganese point defects in bulk silicon, whose magnetic moments fall within the observed magnetic-to-nonmagnetic transition, and which therefore react very sensitively to changes in the local geometry. The results indicate that high spin states in manganese-doped silicon could be stabilized by an appropriate lattice expansion

Gene duplication, population genomics, and species-level differentiation within a tropical mountain shrub.

Gene duplication leads to paralogy, which complicates the de novo assembly of genotyping-by-sequencing (GBS) data. The issue of paralogous genes is exacerbated in plants, because they are particularly prone to gene duplication events. Paralogs are normally filtered from GBS data before undertaking population genomics or phylogenetic analyses. However, gene duplication plays an important role in the functional diversification of genes and it can also lead to the formation of postzygotic barriers. Using populations and closely related species of a tropical mountain shrub, we examine 1) the genomic differentiation produced by putative orthologs, and 2) the distribution of recent gene duplication among lineages and geography. We find high differentiation among populations from isolated mountain peaks and species-level differentiation within what is morphologically described as a single species. The inferred distribution of paralogs among populations is congruent with taxonomy and shows that GBS could be used to examine recent gene duplication as a source of genomic differentiation of nonmodel species

Un algoritmo genético para la conformación de grupos de individuos distantes en redes sociales

La conformación de comisiones es una actividad en la que se requiere seleccionar un conjunto de candidatos a partir de una población de individuos. Estos individuos y sus relaciones pueden representarse mediante una red social. Trabajos previos relacionados con el análisis de redes sociales se enfocan en la identificación de la importancia de los nodos que conforman esas redes, o bien en las propiedades estructurales de las mismas. Este trabajo propone una alternativa para la selección de un conjunto de individuos que presenten menor relación entre sí a partir de una red social, considerando esto como un criterio de independencia entre los mismos. El enfoque propuesto es evaluado con un caso de estudio en el cual se propone en primer lugar, la construcción de una red social en base a datos de coautoría de publicaciones de investigadores y mismo lugar de trabajo, la cual es analizada para determinar las distancias entre cada par de individuos de la red, y en segundo lugar, la optimización de las distancias entre los posibles candidatos mediante un algoritmo genético.Sociedad Argentina de Informática e Investigación Operativ

Un algoritmo genético para la conformación de grupos de individuos distantes en redes sociales

La conformación de comisiones es una actividad en la que se requiere seleccionar un conjunto de candidatos a partir de una población de individuos. Estos individuos y sus relaciones pueden representarse mediante una red social. Trabajos previos relacionados con el análisis de redes sociales se enfocan en la identificación de la importancia de los nodos que conforman esas redes, o bien en las propiedades estructurales de las mismas. Este trabajo propone una alternativa para la selección de un conjunto de individuos que presenten menor relación entre sí a partir de una red social, considerando esto como un criterio de independencia entre los mismos. El enfoque propuesto es evaluado con un caso de estudio en el cual se propone en primer lugar, la construcción de una red social en base a datos de coautoría de publicaciones de investigadores y mismo lugar de trabajo, la cual es analizada para determinar las distancias entre cada par de individuos de la red, y en segundo lugar, la optimización de las distancias entre los posibles candidatos mediante un algoritmo genético.Sociedad Argentina de Informática e Investigación Operativ