2008 Inter-laboratory Comparison Study of a Reference Material for Nutrients in Seawater

Autoclaved natural seawater collected in the North Pacific Ocean was used as a reference material for nutrients in seawater (RMNS) during an inter-laboratory comparison (I/C) study conducted in 2008. This study was a follow-up to previous studies conducted in 2003 and 2006. A set of six samples was distributed to each of 58 laboratories in 15 countries around the globe, and results were returned by 54 of those laboratories (15 countries). The homogeneities of samples used in the 2008 I/C study, based on analyses for three determinants, were improved compared to those of samples used in the 2003 and 2006 I/C studies. Results of these I/C studies indicate that most of the participating laboratories have an analytical technique for nutrients that is sufficient to provide data of high comparability. The differences between reported concentrations from the same laboratories in the 2006 and 2008 I/C studies for the same batch of RMNS indicate that most of the laboratories have been maintaining internal comparability for two years. Thus, with the current high level of performance in the participating laboratories, the use of a common reference material and the adaptation of an internationally accepted nutrient scale system would increase comparability among laboratories worldwide, and the use of a certified reference material would establish traceability. In the 2008 I/C study we observed a problem of non-linearity of the instruments of the participating laboratories similar to that observed among the laboratories in the 2006 I/C study. This problem of non-linearity should be investigated and discussed to improve comparability for the full range of nutrient concentrations. For silicate comparability in particular, we see relatively larger consensus standard deviations than those for nitrate and phosphate

Un modèle d'indexation pour les documents textuels structurés

Most indexing models in information retrieval are dedicated to a particular domain or application, and do not exploit the richness of electronic documents. The goal of this work is to define an indexing model for textual documents that includes structure and other complementary information to the discourse. The proposed model consists of two components: the representation language, which defines at a conceptual level the information in the document, including the index themselves, and the derivation rules, which are based on this language and enable to deduce a particular kind of index, the themes. Indexing in our model does not only produce a static representation of documents, but is also dynamically linked to the correspondence process; in this way, selection of themes, as determined by the rules, is a function of the document and the user. Our approach was validated in two steps. First, a questionnaire was submitted to a group of users in order to understand their process of theme derivation. This a priori validation showed the validity of our derivation rules. Then, in an a posteriori validation, the model was implemented and tested on a collection of sgml documents. This experimentation showed the applicability and flexibility of the model.La plupart des modèles d'indexation en recherche d'informations sont spécifiques à une application ou à un domaine particulier, et n'exploitent pas toute la richesse des documents électroniques. Le but de ce travail est de définir un modèle d'indexation pour les documents textuels qui tienne compte de la structure et d'autres informations complémentaires au discours. Le modèle proposé comporte deux composantes : le langage de représentation, qui définit de façon conceptuelle les informations du document, y compris les index eux-mêmes, et les règles de dérivation, qui, reprenant ce langage, permettent de déduire un type particulier d'index, les thèmes. L'indexation dans notre modèle ne se contente pas de produire une représentation statique du document, mais elle est aussi dynamiquement liée au processus de correspondance ; ainsi, le choix des thèmes, tels que déterminés par les règles, est fonction du document et de l'utilisateur. Notre approche a été validée en deux temps. D'abord, un questionnaire a été soumis à un groupe d'utilisateurs afin de cerner leur processus de dérivation de thèmes. Cette validation à priori a permis de démontrer le bien-fondé de nos règles de dérivation. Puis, dans une validation à posteriori, le modèle a été implémenté et testé sur une collection de documents sgml. Cette expérimentation a demontré l'applicabilité et la flexibilité du modèle

Experiments with Theme Extraction in Explanatory Texts

The notion of theme plays a crucial role in topic-based Information Retrieval. We discuss how topics are related to works in linguistic and discourse theories, and according to which rules they can be derived from texts. Two experiments were devised: the first one to validate those rules with users, and the second to implement them with a collection of structured documents. In the first experiment, participants were asked either to choose between possible themes for an expression, or to find relevant themes in a short text. In the second experiment, a prototypal IRS was built to index the TEI Guidelines, a collection of SGML documents. Results for both experiments show the need for a new, more flexible measure of theme representativity that allow different rankings according to user or query types. Keywords: Information Retrieval, Theme extraction, Indexing, Structured documents. 1 Introduction Natural Language Processing techniques have been used for some time in Information Retrie..