Regression analysis of compositional data when both the dependent variable and independent variable are components

It is well known that regression analyses involving compositional data need special attention because the data are not of full rank. For a regression analysis where both the dependent and independent variable are components we propose a transformation of the components emphasizing their role as dependent and independent variables. A simple linear regression can be performed on the transformed components. The regression line can be depicted in a ternary diagram facilitating the interpretation of the analysis in terms of components. An exemple with time-budgets illustrates the method and the graphical features

Interactions between grain size and composition of sediments: two examples

Two contrasting case studies of sediment and detrital mineral composition are investigated in order to outline interactions between chemical composition and grain size. Modern glacial sediments exhibit a strong dependence of the two parameters due to the preferential enrichment of mafic minerals, especially biotite, in the fine-grained fractions. On the other hand, the composition of detrital heavy minerals (here: rutile) appears to be not systematically related to grain-size, but is strongly controlled by location, i.e. the petrology of the source rocks of detrital grains. This supports the use of rutile as a well-suited tracer mineral for provenance studies. The results further suggest that (i) interpretations derived from whole-rock sediment geochemistry should be flanked by grain-size observations, and (ii) a more sound statistical evaluation of these interactions require the development of new tailor-made statistical tools to deal with such so-called two-way compositions

Comparison studies of tin deposits (Priamurye, Russia) using the Aitchison’s methodology

A study of tin deposits from Priamurye (Russia) is performed to analyze the differences between them based on their origin and also on commercial criteria. A particular analysis based on their vertical zonality is also given for samples from Solnechnoe deposit. All the statistical analysis are made on the subcomposition formed by seven trace elements in cassiterite (In, Sc, Be, W, Nb, Ti and V) using the Aitchison’ methodology of analysis of compositional data

The chemical variability at the surface of Mars: implications for exogenic processes

The chemical composition of sediments and rocks, as well as their distribution at the Martian surface, represent a long term archive of processes, which have formed the planetary surface. A survey of chemical compositions by means of Compositional Data Analysis represents a valuable tool to extract direct evidence for weathering processes and allows to quantify weathering and sedimentation rates. clr-biplot techniques are applied for visualization of chemical relationships across the surface (“chemical maps”). The variability among individual suites of data is further analyzed by means of clr-PCA, in order to extract chemical alteration vectors between fresh rocks and their crusts and for an assessment of different source reservoirs accessible to soil formation. Both techniques are applied to elucidate the influence of remote weathering by combined analysis of several soil forming branches. Vector analysis in the Simplex provides the opportunity to study atmosphere surface interactions, including the role and composition of volcanic gases

Application of discriminant function analysis and change-point problem in dating volcanic ashes

The application of Discriminant function analysis (DFA) is not a new idea in the study of tephrochrology. In this paper, DFA is applied to compositional datasets of two different types of tephras from Mountain Ruapehu in New Zealand and Mountain Rainier in USA. The canonical variables from the analysis are further investigated with a statistical methodology of change-point problems in order to gain a better understanding of the change in compositional pattern over time. Finally, a special case of segmented regression has been proposed to model both the time of change and the change in pattern. This model can be used to estimate the age for the unknown tephras using Bayesian statistical calibration

Statistical Analysis of Eco-Toxicologic Data of Mammals from a Polluted Area

Several eco-toxicological studies have shown that insectivorous mammals, due to their feeding habits, easily accumulate high amounts of pollutants in relation to other mammal species. To assess the bio-accumulation levels of toxic metals and their in°uence on essential metals, we quantified the concentration of 19 elements (Ca, K, Fe, B, P, S, Na, Al, Zn, Ba, Rb, Sr, Cu, Mn, Hg, Cd, Mo, Cr and Pb) in bones of 105 greater white-toothed shrews (Crocidura russula) from a polluted (Ebro Delta) and a control (Medas Islands) area. Since chemical contents of a bio-indicator are mainly compositional data, conventional statistical analyses currently used in eco-toxicology can give misleading results. Therefore, to improve the interpretation of the data obtained, we used statistical techniques for compositional data analysis to define groups of metals and to evaluate the relationships between them, from an inter-population viewpoint. Hypothesis testing on the adequate balance-coordinates allow us to confirm intuition based hypothesis and some previous results. The main statistical goal was to test equal means of balance-coordinates for the two defined populations. After checking normality, one-way ANOVA or Mann-Whitney tests were carried out for the inter-group balances

A compositional approach to stable isotope data analysis

Isotopic data are currently becoming an important source of information regarding sources, evolution and mixing processes of water in hydrogeologic systems. However, it is not clear how to treat with statistics the geochemical data and the isotopic data together. We propose to introduce the isotopic information as new parts, and apply compositional data analysis with the resulting increased composition. Results are equivalent to downscale the classical isotopic delta variables, because they are already relative (as needed in the compositional framework) and isotopic variations are almost always very small. This methodology is illustrated and tested with the study of the Llobregat River Basin (Barcelona, NE Spain), where it is shown that, though very small, isotopic variations comp lement geochemical principal components, and help in the better identification of pollution sources

Introducció al dret administratiu = Introducción al derecho administrativo [versió html]

Aquesta publicació virtual és el recull adaptat de les unitats didàctiques corresponents a les assignatures “Introducció al Dret Administratiu I” (mòdul I) i “Introducció al Dret Administratiu II” (mòdul II) impartides, des del curs acadèmic 2004-2005, com a complements de formació dels Estudis de segon grau de Crimonologia de la Facultat de Dret de la Universitat de Girona. Esta publicación virtual es la recopilación adaptada de las unidades didácticas correspondientes a las assignaturas "Introducción al Derecho Administrativo I" (módulo I) y "Introducción al Derecho Administrativo II" (módulo II) impartidas, desde el curso académico 2004-2005, como complemento de formación de los Estudios de segundo grado de Criminologia de la Facultad de Derecho de la Universidad de Girona

Hebreu bíblic [Versió comprimida]

Manual pensat per a servir de guia per als alumnes dels curs Hebreu Bíblic de la Universitat de Girona. Hebreu Bíblic conté una descripció de la gramàtica fonamental de la llengua hebrea bíblica en 54 lliçons. Cada lliçó presenta sols els continguts essencials de la gramàtica, que en el treball de classe és ampliat i matisat. La segona part del manual consta de 24 vocabularis i exercicis formats exclusivament per frases tretes del text de la Bíblia

Hebreu: llengua, literatura, gramàtica [versió comprimida]

El llibre Hebreu: llengua, literatura i gramàtica conté una síntesi breu de la història de la llengua hebrea, un resum de la història de la literatura escrita en hebreu i una descripció panoràmica dels trets gramaticals més significatius de la llengua hebrea contemporània. Aquestes pàgines han estat pensades per a servir de complement als cursos d'hebreu de la Universitat de Girona

Introducció al dret administratiu = Introducción al derecho administrativo [versió comprimida]

Aquesta publicació virtual és el recull adaptat de les unitats didàctiques corresponents a les assignatures “Introducció al Dret Administratiu I” (mòdul I) i “Introducció al Dret Administratiu II” (mòdul II) impartides, des del curs acadèmic 2004-2005, com a complements de formació dels Estudis de segon grau de Crimonologia de la Facultat de Dret de la Universitat de Girona. Esta publicación virtual es la recopilación adaptada de las unidades didácticas correspondientes a las assignaturas "Introducción al Derecho Administrativo I" (módulo I) y "Introducción al Derecho Administrativo II" (módulo II) impartidas, desde el curso académico 2004-2005, como complemento de formación de los Estudios de segundo grado de Criminologia de la Facultad de Derecho de la Universidad de Girona

Tres honoris causa

El 28 d'abril, a l'auditori del Centre Cultural la Mercè, es va dur a terme la quarta cerimònia d'investidura de Doctors Honoris Causa des de la creació de la Universitat de Girona

Treballar més per consumir millor

La Universitat de Girona ha posat en marxa la Càtedra de Processos Industrials Sostenibles. El projecte busca proporcionar instruments per ajudar a difondre la cultura de l'optimització dels recursos. En definitiva, es tracta de formar tècnics que ajudin la indústria a consumir millor

Aromaticitat molecular: una recerca d'èxit amb gust d'UdG

Diu el diccionari que l'aromaticitat molecular és un conjunt de propietats essencials que posseeixen certes substàncies orgàniques cícliques que les distingeixen de les substàncies alifàtiques o alicícliques. Però mesurar aquestes propietats ha resultat, fins ara, difícil. Un equip de la Universitat de Girona ha fet una contribució destacable per fixar un mètode de mesura fiable i acceptat per la comunitat científica internacional

Creativitat industrial: quinze anys de projectes

L'exposició Creativitat industrial vol ser un reconeixement a la tasca de les persones que han participat en els estudis de Disseny Industrial: estudiants, professors i empreses. Els estudis de Disseny Industrial i Desenvolupament de Producte de la Universitat de Girona fan quinze anys i, en aquest temps, han estat molts els projectes que s’han convertit en realitat