Modelling structural zeros in compositional data

This analysis was stimulated by the real data analysis problem of household expenditure data. The full dataset contains expenditure data for a sample of 1224 households. The expenditure is broken down at 2 hierarchical levels: 9 major levels (e.g. housing, food, utilities etc.) and 92 minor levels. There are also 5 factors and 5 covariates at the household level. Not surprisingly, there are a small number of zeros at the major level, but many zeros at the minor level. The question is how best to model the zeros. Clearly, models that try to add a small amount to the zero terms are not appropriate in general as at least some of the zeros are clearly structural, e.g. alcohol/tobacco for households that are teetotal. The key question then is how to build suitable conditional models. For example, is the sub-composition of spending excluding alcohol/tobacco similar for teetotal and non-teetotal households? In other words, we are looking for sub-compositional independence. Also, what determines whether a household is teetotal? Can we assume that it is independent of the composition? In general, whether teetotal will clearly depend on the household level variables, so we need to be able to model this dependence. The other tricky question is that with zeros on more than one component, we need to be able to model dependence and independence of zeros on the different components. Lastly, while some zeros are structural, others may not be, for example, for expenditure on durables, it may be chance as to whether a particular household spends money on durables within the sample period. This would clearly be distinguishable if we had longitudinal data, but may still be distinguishable by looking at the distribution, on the assumption that random zeros will usually be for situations where any non-zero expenditure is not small. While this analysis is based on around economic data, the ideas carry over to many other situations, including geological data, where minerals may be missing for structural reasons (similar to alcohol), or missing because they occur only in random regions which may be missed in a sample (similar to the durables)

Statistical evidences of cyclic changes in volcanic gas chemistry composition by inverse modelling

The identification of compositional changes in fumarolic gases of active and quiescent volcanoes is one of the most important targets in monitoring programs. From a general point of view, many systematic (often cyclic) and random processes control the chemistry of gas discharges, making difficult to produce a convincing mathematical-statistical modelling. Changes in the chemical composition of volcanic gases sampled at Vulcano Island (Aeolian Arc, Sicily, Italy) from eight different fumaroles located in the northern sector of the summit crater (La Fossa) have been analysed by considering their dependence from time in the period 2000-2007. Each intermediate chemical composition has been considered as potentially derived from the contribution of the two temporal extremes represented by the 2000 and 2007 samples, respectively, by using inverse modelling methodologies for compositional data. Data pertaining to fumaroles F5 and F27, located on the rim and in the inner part of La Fossa crater, respectively, have been used to achieve the proposed aim. The statistical approach has allowed us to highlight the presence of random and not random fluctuations, features useful to understand how the volcanic system works, opening new perspectives in sampling strategies and in the evaluation of the natural risk related to a quiescent volcano

Modelling of Mercury’s surface composition and remote detection from the orbit with the BepiColombo Mercury Planetary Orbiter

It can be assumed that the composition of Mercury’s thin gas envelope (exosphere) is related to the composition of the planets crustal materials. If this relationship is true, then inferences regarding the bulk chemistry of the planet might be made from a thorough exospheric study. The most vexing of all unsolved problems is the uncertainty in the source of each component. Historically, it has been believed that H and He come primarily from the solar wind, while Na and K originate from volatilized materials partitioned between Mercury’s crust and meteoritic impactors. The processes that eject atoms and molecules into the exosphere of Mercury are generally considered to be thermal vaporization, photonstimulated desorption (PSD), impact vaporization, and ion sputtering. Each of these processes has its own temporal and spatial dependence. The exosphere is strongly influenced by Mercury’s highly elliptical orbit and rapid orbital speed. As a consequence the surface undergoes large fluctuations in temperature and experiences differences of insolation with longitude. We will discuss these processes but focus more on the expected surface composition and solar wind particle sputtering which releases material like Ca and other elements from the surface minerals and discuss the relevance of composition modelling

Implantación de un SIG basado en software libre para el estudio de recursos hídricos y procesos hidrológicos

En este trabajo se describe la solución ideada para la implantación de un Sistema de Información Geográfica que debe dar servicio al Instituto Universitario del Agua y del Medio Ambiente de la Universidad de Murcia y al Instituto Euromediterráneo del Agua. Dada la naturaleza de ambas instituciones, se trata de una herramienta orientada fundamentalmente al estudio de recursos hídricos y procesos hidrológicos. El proceso se inició con una identificación de las necesidades de los usuarios (con perfiles y requerimiento diferentes) y el posterior desarrollo del diseño conceptual que pudiera asegurar la satisfacción de estas necesidades. Debido a que los requerimientos de los usuarios así lo demandaban, se ha tenido en cuenta tanto a usuarios que trabajan en entorno linux como a otros que lo hacen en entorno windows. Se ha optado por un sistema basado en software libre utilizando GRASS para el manejo de información raster y modelización; postgis (sobre postgreSQL) y GRASS para la gestión de información vectorial; y QGIS, gvSIG y Kosmo como interfaces gráficas de usuario. Otros programas utilizados para propósitos específicos han sido R, Mapserver o GMT

Predicting overall service quality: a structural equation modelling approach

In this article, the results of a modified SERVQUAL questionnaire (Parasuraman et al., 1991) are reported. The modifications consisted in substituting questionnaire items particularly suited to a specific service (banking) and context (county of Girona, Spain) for the original rather general and abstract items. These modifications led to more interpretable factors which accounted for a higher percentage of item variance. The data were submitted to various structural equation models which made it possible to conclude that the questionnaire contains items with a high measurement quality with respect to five identified dimensions of service quality which differ from those specified by Parasuraman et al. And are specific to the banking service. The two dimensions relating to the behaviour of employees have the greatest predictive power on overall quality and satisfaction ratings, which enables managers to use a low-cost reduced version of the questionnaire to monitor quality on a regular basis. It was also found that satisfaction and overall quality were perfectly correlated thus showing that customers do not perceive these concepts as being distinct

Modelling scenarios of diffusion and control of pandemic influenza, italy

En aquest article es resumeixen els resultats publicats en un informe de l' ISS (Istituto Superiore di Sanità) del desembre de 2006, sobre un model matemàtic desenvolupat per un grup de treball que inclou a investigadors de les Universitats de Trento, Pisa i Roma, i els Instituts Nacionals de Salut (Istituto Superiore di Sanità, ISS), per avaluar i mesurar l'impacte de la transmissió i el control de la pandèmia de grip

Disseny conceptual i anàlisi estructural d’una motxilla - cotxet per a transportar de nens en activitats de lleure muntanya

La idea de realitzar aquest projecte sorgeix d’una necessitat en el mercat de productes relacionats amb els nens i nenes petits, dins d’un rang d’edats entre 2 a 5 anys, per poder realitzar activitats de lleure a la muntanya. En ser un producte no existent s’ha hagut de fer el disseny conceptual de tot el producte buscant la solució final adient per a cada part considerada bàsica. Per assegurar-ne la fiabilitat i la seguretat del nen i del pare s’han fet els càlculs pertinents de les seccions més carregades i s’han descrit els processos de fabricació i muntatge de cada peça. La Motxilla – Carretó servirà per circular per pistes de muntanya i forestals. Tindrà dos usos, el primer per quan el nen estigui cansat de caminar i el terreny es poc accidentat,“funció carretó” i el segon ús, per quan el nen està cansat i el terreny és més accidentat, “funció cadireta”. El producte serà transformable en funció d’aquests dos usos principals

Modelling the Human Values Scale from Consumers Transactional Data Bases

The main objective of this paper aims at developing a methodology that takes into account the human factor extracted from the data base used by the recommender systems, and which allow to resolve the specific problems of prediction and recommendation. In this work, we propose to extract the user's human values scale from the data base of the users, to improve their suitability in open environments, such as the recommender systems. For this purpose, the methodology is applied with the data of the user after interacting with the system. The methodology is exemplified with a case study

An Interval Intelligent-based Approach for Fault Detection and Modelling

Not considered in the analytical model of the plant, uncertainties always dramatically decrease the performance of the fault detection task in the practice. To cope better with this prevalent problem, in this paper we develop a methodology using Modal Interval Analysis which takes into account those uncertainties in the plant model. A fault detection method is developed based on this model which is quite robust to uncertainty and results in no false alarm. As soon as a fault is detected, an ANFIS model is trained in online to capture the major behavior of the occurred fault which can be used for fault accommodation. The simulation results understandably demonstrate the capability of the proposed method for accomplishing both tasks appropriately

El Aprendizaje por libre elección en la construcción de conceptos físicos sobre mecánica rotacional por cambio conceptual

El APLE (en inglés se conoce con la sigla FCL: Free-Choice Learning) es un Marco Conceptual Constructivista que explica la forma como se produce la elaboración del conocimiento por parte de los aprendices, cuando se encuentran en espacios de educación informal. En estos escenarios, el control y la dirección del aprendizaje es netamente responsabilidad del individuo, puesto que es él quien decide dónde, cómo, con quién, cuándo y qué quiere aprender. (Falk & Dierking 2002). Según Falk y Dierking estos aprendizajes son más duraderos y significativos para los individuos que los alcanzados a lo largo de los procesos escolares, puesto que son el resultado de los intereses y expectativas del sujeto y ya no obedecen solo a una planeación curricular cerrada y externa a quien aprende