How to use the Kohonen algorithm to simultaneously analyse individuals in a survey

The Kohonen algorithm (SOM, Kohonen,1984, 1995) is a very powerful tool for data analysis. It was originally designed to model organized connections between some biological neural networks. It was also immediately considered as a very good algorithm to realize vectorial quantization, and at the same time pertinent classification, with nice properties for visualization. If the individuals are described by quantitative variables (ratios, frequencies, measurements, amounts, etc.), the straightforward application of the original algorithm leads to build code vectors and to associate to each of them the class of all the individuals which are more similar to this code-vector than to the others. But, in case of individuals described by categorical (qualitative) variables having a finite number of modalities (like in a survey), it is necessary to define a specific algorithm. In this paper, we present a new algorithm inspired by the SOM algorithm, which provides a simultaneous classification of the individuals and of their modalities.Comment: Special issue ESANN 0

Les archives du ciel

Défi technique et esthétique, le ciel est un sujet canonique de l'histoire de la photographie ancienne. Alors que la question de sa représentation a retenu l'attention, celle qui concerne les usages et les pratiques de la photographie en météorologie a été délaissée et mérite d'être mise à jour. Préoccupation ancienne, la météorologie est une discipline scientifique relativement jeune, comparée à l'astronomie, la physique, ou la botanique. En France, c'est en 1834, date de la publicati..

Pyrénées, voyages photographiques de 1839 à nos jours, Pau, Éditions du pin à crochets, 1998, 318 p., ill. coul. et NB.

" La montagne n'a pas toujours été un paysage ", constatait Alain Roger dans un des premiers ouvrages français consacrés à la photographie de montagne, tous massifs confondus (Françoise Guichon, Montagne, photographies de 1845 à 1914, 1984). Associée à la peinture et à la littérature, la photographie contribue à l'édification de cette notion de paysage, renouvelant nos regards, nos perceptions, bref notre imaginaire de la montagne. Dans un premier ouvrage (1995) consacré à la photogra..

La "restauration" des montagnes

Dans la seconde moitié du XIXe siècle, de nombreuses institutions françaises constituent des collections de photographies : l'École des ponts et chaussées, l'École des beaux-arts, la Bibliothèque historique de la Ville de Paris, le musée des Arts décoratifs, le musée de Sculpture comparée, etc. Mais aucune d'entre elles n'a déployé un programme photographique comparable à celui organisé par l'Administration des forêts, qui, dans le dernier tiers du XIXe siècle, incorpora la pratique ph..

La "restauration" des montagnes

Dans la seconde moitié du XIXe siècle, de nombreuses institutions françaises constituent des collections de photographies : l'École des ponts et chaussées, l'École des beaux-arts, la Bibliothèque historique de la Ville de Paris, le musée des Arts décoratifs, le musée de Sculpture comparée, etc. Mais aucune d'entre elles n'a déployé un programme photographique comparable à celui organisé par l'Administration des forêts, qui, dans le dernier tiers du XIXe siècle, incorpora la pratique ph..

Predictors and outcome impact of perioperative serum sodium changes in a high-risk population.

BACKGROUND: The perioperative period may be associated with a marked neurohumoral stress response, significant fluid losses, and varied fluid replacement regimes. Acute changes in serum sodium concentration are therefore common, but predictors and outcomes of these changes have not been investigated in a large surgical population. METHODS: We carried out a retrospective cohort analysis of 27 068 in-patient non-cardiac surgical procedures in a tertiary teaching hospital setting. Data on preoperative conditions, perioperative events, hospital length of stay, and mortality were collected, along with preoperative and postoperative serum sodium measurements up to 7 days after surgery. Logistic regression was used to investigate the association between sodium changes and mortality, and to identify clinical characteristics associated with a deviation from baseline sodium >5 mmol litre(-1). RESULTS: Changes in sodium concentration >5 mmol litre(-1) were associated with increased mortality risk (adjusted odds ratio 1.49 for a decrease, 3.02 for an increase). Factors independently associated with a perioperative decrease in serum sodium concentration >5 mmol litre(-1) included age >60, diabetes mellitus, and the use of patient-controlled opioid analgesia. Factors associated with a similar increase were preoperative oxygen dependency, mechanical ventilation, central nervous system depression, non-elective surgery, and major operative haemorrhage. CONCLUSIONS: Maximum deviation from preoperative serum sodium value is associated with increased hospital mortality in patients undergoing in-patient non-cardiac surgery. Specific preoperative and perioperative factors are associated with significant serum sodium changes.This work was supported by the Cambridge University Division of Anaesthesia.This is the author accepted manuscript. The final version is available from Oxford University Press via http://dx.doi.org/10.1093/bja/aeu40

Recurrence Quantification Analysis and Principal Components in the Detection of Short Complex Signals

Recurrence plots were introduced to help aid the detection of signals in complicated data series. This effort was furthered by the quantification of recurrence plot elements. We now demonstrate the utility of combining recurrence quantification analysis with principal components analysis to allow for a probabilistic evaluation for the presence of deterministic signals in relatively short data lengths.Comment: 10 pages, 3 figures; Elsevier preprint, elsart style; programs used for analysis available for download at http://homepages.luc.edu/~cwebbe