Statistical characterization of sedimentation velocity of natural particles

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Statistical characterization of sedimentation velocity of natural particles

Aeolian sediment transport has major repercussions for global climatic variations, air quality, human health, agricultural areas, air and ground transportation, civil structures and infrastructures. This led to the development of models to understand the involved physical process, and to predict the dynamics of aeolian sediment transport. The sedimentation velocity is one of the key model parameters characterizing sediment behavior. It allows the prediction of the mode of transport, the distribution of particles above the ground, and the sediment transport rate. Despite its importance, there is substantial discrepancy among the sedimentation velocity laws for natural particles, also due to the large dispersion of experimental data. This study proposes the statistical characterization of the experimental measurements of sedimentation velocity available from the literature. 1812 experimental measurements were recovered from 11 studies. Their variability was discussed, providing an aerodynamic reading. Nonlinear regression was carried out on the consolidated dataset in order to assess the average value. Two well-known laws initially conceived for spheres were refitted to natural particles providing high coefficients of determination equal to 0.90 and 0.93. Then, copula-based regression was performed in order to seize the variability of sedimentation velocity. Finally, the results from the two approaches were compared and critically discussed

Living on the Edge: An Unified Approach to Antithetic Sampling

We identify recurrent ingredients in the antithetic sampling literature leading to a unified sampling framework. We introduce a new class of antithetic schemes that includes the most used antithetic proposals. This perspective enables the derivation of new properties of the sampling schemes: i) optimality in the Kullback--Leibler sense; ii) closed-form multivariate Kendall's $\tau$ and Spearman's $\rho$; iii) ranking in concordance order and iv) a central limit theorem that characterizes stochastic behaviour of Monte Carlo estimators when the sample size tends to infinity. The proposed simulation framework inherits the simplicity of the standard antithetic sampling method, requiring the definition of a set of reference points in the sampling space and the generation of uniform numbers on the segments joining the points. We provide applications to Monte Carlo integration and Markov Chain Monte Carlo Bayesian estimation

Transformations of Copulas and Measures of Concordance

Copulas are real functions representing the dependence structure of the distribution of a random vector, and measures of concordance associate with every copula a numerical value in order to allow for the comparison of different degrees of dependence. We first introduce and study a group of transformations mapping the collection of all copulas of fixed but arbitrary dimension into itself. These transformations may be used to construct new copulas from a given one or to prove that certain real functions on the unit cube are indeed copulas. It turns out that certain transformations of a symmetric copula may be asymmetric, and vice versa. Applying this group, we then propose a concise definition of a measure of concordance for copulas. This definition, in which the properties of a measure of concordance are defined in terms of two particular subgroups of the group, provides an easy access to the investigation of invariance properties of a measure of concordance. In particular, it turns out that for copulas which are invariant under a certain subgroup the value of every measure of concordance is equal to zero. We also show that the collections of all transformations which preserve symmetry or the concordance order or the value of every measure of concordance each form a subgroup and that these three subgroups are identical. Finally, we discuss a class of measures of concordance in which every element is defined as the expectation with respect to the probability measure induced by a fixed copula having an invariance property with respect to two subgroups of the group. This class is rich and includes the well-known examples Spearman's rho and Gini's gamma

Mitmemõõtmeliste andmete statistiline analüüs bioinformaatikas

Väitekirja elektrooniline versioon ei sisalda publikatsioone.Valgud on organismide ühed tähtsaimad ehituskivid. Nende kogust ja omavahelisi seoseid uurides on võimalik saada infot organismi seisundi kohta. Tänapäevased seadmed võimaldavad koguda lühikese ajaga palju valkudega seotud andmeid. Nende analüüs on aga suhteliselt keerukas ja on loonud uue teadusharu nimega bioinformaatika. Käesoleva doktoritöö eesmärgiks on kirjeldada mitmemõõtmeliste andmete statistilise analüüsiga seotud probleeme ja nende lahendusi. Näidatakse, kuidas sellised andmed saab esitada maatriksi kujul. Antakse ülevaade andmeallikatest ja analüüsimeetoditest ning näidatakse, kuidas neid saab praktikas kasutada. Kirjeldatakse üleeuroopalist vähiuuringute projekti PREDECT, kus paljud organisatsioonid osalevad vähimudelite täiustamises. Antakse ülevaade metaandmete kogumisest paljudelt partneritelt, samuti veebitööriistadest, mis loodi esmaseks andmeanalüüsiks. Kirjeldatakse uudse rinnavähi mudeliga seotud analüüsi ja koelõikude võrdlust erinevates laboritingimustes. Tutvustatakse vabalt kasutatavat veebitööriista, millega saab teha kirjeldavat andmeanalüüsi. Järgmistes peatükkides kirjeldatakse andmeanalüüsi erinevates uuringutes. Inimese platsentas leiti mitmeid uusi alleelispetsiifilise ekspressiooniga geene. Uuriti atoopilise dermatiidi molekulaarseid mehhanisme, täpsemalt valgu gamma-interferoon mõju sellele haigusele. Leiti mikroRNAsid, mida saab kasutada endometrioosi markeritena, ja loodi klassifitseerija endometrioosihaigete eristamiseks tervetest.Proteins are one of the most important building blocks of an organism. By investigating the abundance and relations between different proteins, it is possible to get information about the current state of the organism. Modern technologies allow to collect a large amount of data related to proteins in a short period of time. This type of analysis is quite complicated and has created a new field of science called bioinformatics. The aim of the dissertation is to describe problems and solutions related to statistical analysis of multivariate data. It is shown how this type of data can be presented as a matrix. An overview of data sources and analysis methods is given and it is shown how they can be used in practice. A pan-European project PREDECT is described where many organizations are contributing to develop better cancer models. An overview is given about collecting metadata from multiple partners, and about web tools created for initial data analysis. An analysis concerning a novel breast cancer model is described, and a comparison of tissue slices in different cultivation conditions is made. A freely available web tool is introduced which allows to perform exploratory data analysis. Next chapters describe data analysis in various projects. Multiple novel genes were found in the human placenta that have an allele-specific expression. Molecular mechanisms of a disease called atopic dermatitis were examined, more specifically the influence of the protein interferon-gamma. MicroRNAs were found that can be used as markers for a disease called endometriosis, and a classifier was built to differentiate people with endometriosis from healthy people

Design of bioinformatic tools for integrative analysis of microRNA-mRNA interactome applied to digestive cancers

[spa] En esta tesis se han desarrollado e implementado distintas herramientas bioinformáticas que permiten el estudio de las interacciones miRNA-mRNA en contextos celulares específicos. oncretamente se ha creado un paquete de R (miRComb) que calcula las interacciones miRNA-mRNA partiendo de expresión de miRNAs y mRNAs, y predicciones bloinformáticas de bases de datos preexistentes. Las interacciones miRNA-mRNA finales son aquellas que muestran una correlación negativa y han estado predichas por al meno una base de datos. Como valor añadido, el paquete miRComb realiza un resumen en pdf con los resultados básicos del análisis (número de interacciones, número de mRNAs target por miRNA, análisis funcional, etc.), que permite comparar los datos de distintos estudios. Hemos aplicado esta metodología en el contexto de cánceres digestivos. En un primer estudio hemos utilizado datos públicos de 5 cánceres digestivos (colon, recto, esófago, stómago e hígado) y hemos determinado las interacciones miRNA-mRNA comunes entre ellos y específicas de cada uno. En un segundo estudio, hemos utilizado la misma metodología para analizar datos de IRNA-mRNA en biopsias de pacientes del Hospital Clínic de Barcelona con cáncer de páncreas. En este estudio hemos descrito interacciones miRNA-mRNA en el contexto de cáncer pancreático y hemos podido validar dos de ellas a nivel experimental. En resumen, podemos concluir que el paquete miRComb es una herramienta útil para el estudio del interactoma de miRNA-mRNA, y que ha servido para establecer hipótesis biológicas que luego se han podido comprobar en el laboratori