Modelisation d'écosystèmes rivières : application à un bief du Lot

Les résultats des premiers essais de modélisation de l'écosystème Lot sont présentés. Cette rivière a un grand intérêt vis-à-vis des problèmes posés par la réponse d'un milieu aux fluctuations, naturelles ou provoquées, des paramètres abiotiques. En effet, le fonctionnement des barrages de l'amont entraîne l'existence d'étiages sévères et, par suite, de longs temps de séjour dans les biefs se succédant sur le cours du Lot moyen et inférieur. Dans ces biefs, l'ensoleillement peut en outre entraîner l'existence de stratifications thermiques. Diverses questions d'intérêt général sont rappelées dans une première partie : 1) schéma classique d'un écosystème aquatique, 2) équations d'échange traduisant les interactions entre les paramètres dynamiques du système ; 3) techniques permettant de définir les moyennes temporelles ou spatio-temporelles, 4) hypothèses phénoménologiques permettant d'aborder le traitement des équations. Dans une deuxième partie sont présentés les premiers résultats d'une tentative de modélisation de la croissance et de la biodégradation des algues dans l'écosystème Lot. Le système général d'équations d'échanges est simplifié en tenant compte 1) des régimes hydrodynamiques, 2) des cycles thermiques d'origine naturelle, 3) de l'influence des deux caractéristiques précédentes sur le fonctionnement de l'écosystème. Deux situations ont été étudiées : - la première correspond à des régimes hydrodynamiques et thermiques pour lesquels chaque section du Lot peut être considérée comme homogène : l'utilisation de moyennes spatiales par section est alors acceptable, - la deuxième correspond à des régimes hydrodynamiques et thermiques qui conduisent à prendre en compte la stratification verticale

Valuations of aircraft noise: experiments in stated preference

The aim of this paper is to report new evidence relating to residents’ valuations of aircraft noise in three countries with an emphasis on a comparison of the valuations obtained using two contrasting approaches. One might be regarded as a standard stated choice approach offering pairwise comparisons of two alternatives characterised by a limited number of attributes. The other choice format adopted is innovative in drawing inspiration from the priority evaluator approach to embed aircraft movements alongside a wide range of other local factors that impact on residents’ quality of life. The paper addresses the differences in the results of the two approaches and explores the possible explanations for these variations. Although not conclusive, there is a suspicion that strategic bias may have influenced the results and we urge further research regarding incentives to such bias

Deterministic Price Setting Rules to Guarantee Profitability of Unbundling in the Airline Industry

Unbundling the traditional airfare is one of the airline industry’s practices to generate ancillary revenue in its struggle for profitability. However, unbundling might just as well negatively affect profit. In this paper deterministic price setting rules are established to guarantee profitability of unbundling irrespective of what product is unbundled. By comparing unbundling to a conventional price change, the least profitable scenarios of unbundling can be solved using the economic principle of price elasticity. The solution can be optimized dichotomously for profitability – profit guaranteed versus not guaranteed – by setting the unbundled prices such that the least profitable scenarios would still be profitable; profitability would then be guaranteed for any other scenario. The price setting rules this method renders are incorporated in a decision tree model and corresponding procedure for airline managers. As opposed to what customer research can produce, the model and corresponding procedure are generally applicable.Control & OperationsAerospace Engineerin

Identifying differences in willingness to pay due to dimensionality in stated choice experiments : a cross country analysis

This paper explores the influence of both cultural and socio-economic characteristics on the perception of complexity and cognitive load associated with stated choice (SC) experiments. Complexity is analysed in terms of five design dimensions which were systematically varied according to a macro experimental design. To study the influence of cross country differences on willingness to pay estimates, we combined datasets collected in Sydney, Santiago de Chile and Taichung city in Taiwan, all of them related to an equivalent route choice experiment. Several mixed logit models were specified and estimated; our results show that design dimensions do have an impact on the behavioural outputs of discrete choice models estimated on SC data. However, these influences seem to be data-specific, suggesting that the impact of design dimensions upon SC outcomes may be local and not necessarily transferable across different countries and cultures.

Genomewide single nucleotide polymorphism discovery in Atlantic salmon (Salmo salar ) : validation in wild and farmed American and European populations

A considerable number of single nucleotide polymorphisms (SNPs) are required to elucidate genotype–phenotype associations and determine the molecular basis of important traits. In this work, we carried out de novo SNP discovery accounting for both genome duplication and genetic variation from American and European salmon populations. A total of 9 736 473 nonredundant SNPs were identified across a set of 20 fish by whole-genome sequencing. After applying six bioinformatic filtering steps, 200 K SNPs were selected to develop an Affymetrix Axiom® myDesign Custom Array. This array was used to genotype 480 fish representing wild and farmed salmon from Europe, North America and Chile. A total of 159 099 (79.6%) SNPs were validated as high quality based on clustering properties. A total of 151 509 validated SNPs showed a unique position in the genome. When comparing these SNPs against 238 572 markers currently available in two other Atlantic salmon arrays, only 4.6% of the SNP overlapped with the panel developed in this study. This novel high-density SNP panel will be very useful for the dissection of economically and ecologically relevant traits, enhancing breeding programmes through genomic selection as well as supporting genetic studies in both wild and farmed populations of Atlantic salmon using high-resolution genomewide information.Keywords : Genomic selection; Next-generation sequencing; Pseudo-tetraploid; Salmo salar; SNP arra

It's not that I don't care, I just don't care very much: confounding between attribute non-attendance and taste heterogeneity

With the growing interest in the topic of attribute non-attendance, there is now widespread use of latent class (LC) structures aimed at capturing such behaviour, across a number of different fields. Specifically, these studies rely on a confirmatory LC model, using two separate values for each coefficient, one of which is fixed to zero while the other is estimated, and then use the obtained class probabilities as an indication of the degree of attribute non-attendance. In the present paper, we argue that this approach is in fact misguided, and that the results are likely to be affected by confounding with regular taste heterogeneity. We contrast the confirmatory model with an exploratory LC structure in which the values in both classes are estimated. We also put forward a combined latent class mixed logit model (LC-MMNL) which allows jointly for attribute non-attendance and for continuous taste heterogeneity. Across three separate case studies, the exploratory LC model clearly rejects the confirmatory LC approach and suggests that rates of non-attendance may be much lower than what is suggested by the standard model, or even zero. The combined LC-MMNL model similarly produces significant improvements in model fit, along with substantial reductions in the implied rate of attribute non-attendance, in some cases even eliminating the phenomena across the sample population. Our results thus call for a reappraisal of the large body of recent work that has implied high rates of attribute non-attendance for some attributes. Finally, we also highlight a number of general issues with attribute non-attendance, in particular relating to the computation of willingness to pay measures