Studies in stoichiometry with compositional data

Geochemical data that is derived from the whole or partial analysis of various geologic materials represent a composition of mineralogies or solute species. Minerals are composed of structured relationships between cations and anions which, through atomic and molecular forces, keep the elements bound in specific configurations. The chemical compositions of minerals have specific relationships that are governed by these molecular controls. In the case of olivine, there is a well-defined relationship between Mn-Fe-Mg with Si. Balances between the principal elements defining olivine composition and other significant constituents in the composition (Al, Ti) have been defined, resulting in a near-linear relationship between the logarithmic relative proportion of Si versus (MgMnFe) and Mg versus (MnFe), which is typically described but poorly illustrated in the simplex. The present contribution corresponds to ongoing research, which attempts to relate stoichiometry and geochemical data using compositional geometry. We describe here the approach by which stoichiometric relationships based on mineralogical constraints can be accounted for in the space of simplicial coordinates using olivines as an example. Further examples for other mineral types (plagioclases and more complex minerals such as clays) are needed. Issues that remain to be dealt with include the reduction of a bulk chemical composition of a rock comprised of several minerals from which appropriate balances can be used to describe the composition in a realistic mineralogical framework. The overall objective of our research is to answer the question: In the cases where the mineralogy is unknown, are there suitable proxies that can be substituted? Kew words: Aitchison geometry, balances, mineral composition, oxides

Comparing meta-analysis and ecological-longitudinal analysis in time-series studies: a case study of the effects of air pollution on mortality in three Spanish cities

The objective of this paper is to introduce a diVerent approach, called the ecological-longitudinal, to carrying out pooled analysis in time series ecological studies. Because it gives a larger number of data points and, hence, increases the statistical power of the analysis, this approach, unlike conventional ones, allows the complementation of aspects such as accommodation of random effect models, of lags, of interaction between pollutants and between pollutants and meteorological variables, that are hardly implemented in conventional approaches. Design—The approach is illustrated by providing quantitative estimates of the short-termeVects of air pollution on mortality in three Spanish cities, Barcelona,Valencia and Vigo, for the period 1992–1994. Because the dependent variable was a count, a Poisson generalised linear model was first specified. Several modelling issues are worth mentioning. Firstly, because the relations between mortality and explanatory variables were nonlinear, cubic splines were used for covariate control, leading to a generalised additive model, GAM. Secondly, the effects of the predictors on the response were allowed to occur with some lag. Thirdly, the residual autocorrelation, because of imperfect control, was controlled for by means of an autoregressive Poisson GAM. Finally, the longitudinal design demanded the consideration of the existence of individual heterogeneity, requiring the consideration of mixed models. Main results—The estimates of the relative risks obtained from the individual analyses varied across cities, particularly those associated with sulphur dioxide. The highest relative risks corresponded to black smoke in Valencia. These estimates were higher than those obtained from the ecological-longitudinal analysis. Relative risks estimated from this latter analysis were practically identical across cities, 1.00638 (95% confidence intervals 1.0002, 1.0011) for a black smoke increase of 10 μg/m3 and 1.00415 (95% CI 1.0001, 1.0007) for a increase of 10 μg/m3 of sulphur dioxide. Because the statistical power is higher than in the individual analysis more interactions were statistically significant,especially those among air pollutants and meteorological variables. Conclusions—Air pollutant levels were related to mortality in the three cities of the study, Barcelona, Valencia and Vigo. These results were consistent with similar studies in other cities, with other multicentric studies and coherent with both, previous individual, for each city, and multicentric studies for all three cities

Recerca versus docència en una experiència d'internalització dels estudis de Geografia a la Universitat de Girona: The faces of landscape, Catalonia and North Karelia = Research versus teaching in one experience of internationalization of the Geography degree studies in the University of Girona: The faces of landscape, Catalonia and North Karelia

Un dels reptes cabdals de la Universitat és enllaçar l’experiència de recerca amb la docència, així com promoure la internacionalització dels estudis, especialment a escala europea, tenint present que ambdues poden actuar com a catalitzadores de la millora de la qualitat docent. Una de les fórmules d’internacionalització és la realització d’assignatures compartides entre universitats de diferents països, fet que suposa l’oportunitat d’implementar noves metodologies docents. En aquesta comunicació es presenta una experiència en aquesta línia desenvolupada entre la Universitat de Girona i la Universitat de Joensuu (Finlàndia) en el marc dels estudis de Geografia amb la realització de l’assignatura 'The faces of landscape: Catalonia and North Karelia'. Aquesta es desenvolupa al llarg de dues setmanes intensives, una en cadascuna de les Universitats. L’objectiu és presentar i analitzar diferents significats del concepte paisatge aportant també metodologies d’estudi tant dels aspectes físics i ecològics com culturals que s’hi poden vincular i que són les que empren els grups de recerca dels professors responsables de l’assignatura. Aquesta part teòrica es completa amb una presentació de les característiques i dinàmiques pròpies dels paisatges finlandesos i catalans i una sortida de camp. Per a la part pràctica es constitueixen grups d’estudi multinacionals que treballen a escala local algun dels aspectes en els dos països, es comparen i es realitza una presentació i defensa davant del conjunt d’estudiants i professorat. La llengua vehicular de l’assignatura és l’anglès

Internal test sets studies in a group of antimalarials

Topological indices have been applied to build QSAR models for a set of 20 antimalarial cyclic peroxy cetals. In order to evaluate the reliability of the proposed linear models leave-n-out and Internal Test Sets (ITS) approaches have been considered. The proposed procedure resulted in a robust and consensued prediction equation and here it is shown why it is superior to the employed standard cross-validation algorithms involving multilinear regression models