Dreta i esquerra: les molècules quirals

Molècules de dretes i d'esquerres? Una història científica amb contribució de la UdG: investigadors de l'Institut de Química Computacional de la UdG van participar en una recerca que amb posterioritat va ser premiada amb el Nobel de química del 2001

Benvinguda als becaris de recerca

"La recerca és l'anima de la UdG, i els becaris de recerca els vivificadors d'aquesta ànima". Amb aquestes paraules la rectora Anna Maria Geli va donar la benvinguda als nous becaris de la Universitat de Girona en un acte que es va realitzar el 23 de maig a la sala de graus de la Facultat de Lletres

A la recerca d'un perfecte equilibri acústic

Avui un gran nombre de propostes musicals tenen lloc fora dels recintes dissenyats expressament per a això. Es vol afegir valor a l'experiència musical associant-la a elements arquitectònics de prestigi, malgrat el risc que això comporta de deteriorar la qualitat amb què els assistents a aquestes representacions escolten en la música, que, per la realitat física de l'espai, acostuma a dispersar-se de manerea deficient. Joventuts Musicals, conscients d'aquest problema en el seu festival de Torroella de Montgrí, es va posar en contacte amb el Grup de Recerca en Enginyeria de Fluids, Energia i Medi Ambient (GREFEMA) de la Universitat de Girona per estudiar una solució satisfactòria que permetés conjugar la bona música amb un entorn de gran bellesa

Avaluació de la recerca en humanitats. Una qüestió controvertida

La comunitat universitària és el motor de la recerca que es fa a l'Estat espanyol. Docents i investigadors són, gairebé sempre, una mateixa cosa. La seva contribució s'acosta al 70% de tota la recerca que es fa. Incentivar-los adequament és assegurar el progrés d'un sector estratègic com la R+D, i més enllà del país. La retribució econòmica que perceben per aquest esforç es quantifica a través de l'assignació dels anomenats trams de recerca. Es podria deduir que, com més treball de recerca, més retribució, però la realitat porta a creure que al darrere d'aquest sistema s'amguen alguns paranys que condicionen la manera com s'investiga, l'objecte de la recerca i fins i tot la llengua que s'utilitza per fer-la

Història urbana de Girona: una història dibuixada

El Dr. Josep Maria Nolla ha contribuït de manera decisiva al coneixement dels orígens de la ciutat de Girona. El seu treball i el dels seus companys en aquesta aventura de recerca és a l'abast de tothom en la col·lecció "Història urbana de Girona", que ha tingut, la tardor del 2007, una traducció brillant en l'exposició "De Kerunta a Gerunda. Els orígens de la ciutat"

Biotech Girona: l'espai de la biotecnologia

Espais a mida, tota mena de facilitats i bona companyia. Sembla l'anunci d'una promoció immobiliària, però això és el que ofereix el Biogech Girona, un lloc dins el Parc Científic i Tecnològic que proposa espais a mida per establir-se en un entorn d'excel·lència en la recerca. El Parc acaba d'obrir la convocatòria per seleccionar les empreses interessades

Batxillerat: camins cap a la Universitat

El batxillerat és un intens camí que recorre l'estudiant i que en bona part dels casos té com a meta la universitat. En el trajecte hi ha uns quants esculls, com el treball de recerca i la selectivitat. Els joves han de prémer fort l'accelerador si volen assolir la fita consignada. El suport de la família i els professors els pot fer el viatge una mica més fàcil

Medicina a Girona

La Universitat de Girona impartirà la titulació de Medicina en una facultat pròpia a partir del curs 2008-2009. Es proposa un pla d'estudis innovador que la convertirà en un centre pioner a Catalunya, elaborat en complicitat amb els diversos agents clínics i assistencials de la demarcació, per garantir la màxima qualitat de la docència i la recerca

Compositional data analysis: where we are and where should we be heading?

We take stock of the present position of compositional data analysis, of what has been achieved in the last 20 years, and then make suggestions as to what may be sensible avenues of future research. We take an uncompromisingly applied mathematical view, that the challenge of solving practical problems should motivate our theoretical research; and that any new theory should be thoroughly investigated to see if it may provide answers to previously abandoned practical considerations. Indeed a main theme of this lecture will be to demonstrate this applied mathematical approach by a number of challenging examples

Statistical modeling on coordinates

This paper is a first draft of the principle of statistical modelling on coordinates. Several causes —which would be long to detail—have led to this situation close to the deadline for submitting papers to CODAWORK’03. The main of them is the fast development of the approach along the last months, which let appear previous drafts as obsolete. The present paper contains the essential parts of the state of the art of this approach from my point of view. I would like to acknowledge many clarifying discussions with the group of people working in this field in Girona, Barcelona, Carrick Castle, Firenze, Berlin, G¨ottingen, and Freiberg. They have given a lot of suggestions and ideas. Nevertheless, there might be still errors or unclear aspects which are exclusively my fault. I hope this contribution serves as a basis for further discussions and new developments

Hilbert space on probability density functions with Aitchison geometry

Compositional data analysis motivated the introduction of a complete Euclidean structure in the simplex of D parts. This was based on the early work of J. Aitchison (1986) and completed recently when Aitchinson distance in the simplex was associated with an inner product and orthonormal bases were identified (Aitchison and others, 2002; Egozcue and others, 2003). A partition of the support of a random variable generates a composition by assigning the probability of each interval to a part of the composition. One can imagine that the partition can be refined and the probability density would represent a kind of continuous composition of probabilities in a simplex of infinitely many parts. This intuitive idea would lead to a Hilbert-space of probability densities by generalizing the Aitchison geometry for compositions in the simplex into the set probability densities

Distributions on the simplex

The simplex, the sample space of compositional data, can be structured as a real Euclidean space. This fact allows to work with the coefficients with respect to an orthonormal basis. Over these coefficients we apply standard real analysis, inparticular, we define two different laws of probability trought the density function and we study their main properties

When a data set can be considered compositional?

Traditionally, compositional data has been identified with closed data, and the simplex has been considered as the natural sample space of this kind of data. In our opinion, the emphasis on the constrained nature of compositional data has contributed to mask its real nature. More crucial than the constraining property of compositional data is the scale-invariant property of this kind of data. Indeed, when we are considering only few parts of a full composition we are not working with constrained data but our data are still compositional. We believe that it is necessary to give a more precise definition of composition. This is the aim of this oral contribution

Possible solution of some essential zero problems in compositional data analysis

One of the tantalising remaining problems in compositional data analysis lies in how to deal with data sets in which there are components which are essential zeros. By an essential zero we mean a component which is truly zero, not something recorded as zero simply because the experimental design or the measuring instrument has not been sufficiently sensitive to detect a trace of the part. Such essential zeros occur in many compositional situations, such as household budget patterns, time budgets, palaeontological zonation studies, ecological abundance studies. Devices such as nonzero replacement and amalgamation are almost invariably ad hoc and unsuccessful in such situations. From consideration of such examples it seems sensible to build up a model in two stages, the first determining where the zeros will occur and the second how the unit available is distributed among the non-zero parts. In this paper we suggest two such models, an independent binomial conditional logistic normal model and a hierarchical dependent binomial conditional logistic normal model. The compositional data in such modelling consist of an incidence matrix and a conditional compositional matrix. Interesting statistical problems arise, such as the question of estimability of parameters, the nature of the computational process for the estimation of both the incidence and compositional parameters caused by the complexity of the subcompositional structure, the formation of meaningful hypotheses, and the devising of suitable testing methodology within a lattice of such essential zero-compositional hypotheses. The methodology is illustrated by application to both simulated and real compositional data

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)