L’évaluation des coûts de changement de fournisseur sur le marché résidentiel de l’énergie

Le coût de changement (ou coût de switching) supporté par le consommateur qui change de fournisseurs est un concept récent mais qui a connu sur la dernière décennie des développements méthodologiques importants, comme en témoignent les nombreux articles publiés sur ce sujet. L’évaluation des coûts de changement demeure toutefois un exercice délicat du fait des difficultés liées à l’observation des choix du consommateur et à la mesure de la désutilité liée au changement de fournisseur. Cet article traite du cadre et des fondements théoriques sous-jacents à l’évaluation et des principales méthodes d’estimation disponibles. Les modèles économétriques qui permettent de reconstituer soit une fonction de demande (méthodes indirectes), soit l’impact du changement sur le bien-être du consommateur (méthodes directes) sont également présentés. L’application d’un modèle de choix discret au comportement du consommateur sur le marché du gaz en Grande-Bretagne réalisée par Giuletti, Waddams Price et Paterson en 2003 illustre les possibilités offertes par les méthodes directes d’évaluation.The switching costs perceived by the residential consumer who has to choose between suppliers is a recent concept. Nevertheless, it has led to important methodological and empirical developments in economic literature over the past decade. The valuation of switching costs is still fragile due to two difficulties : i) observation of consumer’s choices and ii) measure of utility variation. This paper discusses the framework and theoretical bases of valuation and the principal methods available. We also discuss the econometric models which reconstitute either a demand function (indirect methods) or the impact of change on the consumer’s surplus (direct methods). The application of the direct valuation method is illustrated by an implementation by Giuletti, Waddams Price and Paterson in 2003, namely a discrete choice model of the consumer’s behavior in the United Kingdom natural gas supply market

Evaluation of urinary hydrogen peroxide as an oxidative stress biomarker in a healthy Japanese population

The usefulness of urinary hydrogen peroxide (H2O2) as an oxidative stress biomarker was evaluated in 766 healthy Japanese. The mean level of urinary concentrations of H2O2 was 5.66 +/- 8.27 mu mol/g creatinine, and was significantly higher in females than in males. Significant correlations of H2O2 were observed with age, aspartate aminotransferase (AST), alanine aminotransferase (ALT), total cholesterol (TC), low-density lipoprotein cholesterol (LDL-c), insulin, 8-hydroxy-2'-deoxyguanosine (8-OHdG), and exercise habit in females. In both sexes, H2O2 showed a significant correlation with 8-OHdG. By a multiple logistic regression analysis, urinary H2O2 was positively associated with urinary 8-OHdG and TC and was inversely associated with insulin. By stratification of sex and age, the association of urinary H2O2 with TC was positive in both sexes under 50 years old and was inverse in males over 50 years old, and that with insulin was inverse in males over 50 years old and in females under 50 years old. Moreover, by stratification of sex and age, a positive association of H2O2 with exercise and an inverse association of H2O2 with alcohol consumption became clear in males under 50 years old, although there were no significant odds for H2O2 after adjustment for covariates. In conclusion, the present results suggest that urinary H2O2 is a useful biomarker for oxidative stress, showing an association with 8-OHdG, TC, and insulin independently

Supplemental Information 3: Dataset including repeated measures for the carotenoid-supplement experiment. The dataset excludes birds receiving diquat (see Methods). Description of variables inserted as comments on variable names.

Colorful ornaments have been the focus of sexual selection studies since the work of Darwin. Yellow to red coloration is often produced by carotenoid pigments. Different hypotheses have been formulated to explain the evolution of these traits as signals of individual quality. Many of these hypotheses involve the existence of a signal production cost. The carotenoids necessary for signaling can only be obtained from food. In this line, carotenoid-based signals could reveal an individual's capacity to find sufficient dietary pigments. However, the ingested carotenoids are often yellow and became transformed by the organism to produce pigments of more intense color (red ketocarotenoids). Biotransformation should involve oxidation reactions, although the exact mechanism is poorly known. We tested the hypothesis that carotenoid biotransformation could be costly because a certain level of oxidative stress is required to correctly perform the conversion. The carotenoid-based signals could thus reveal the efficiency of the owner in successfully managing this challenge. In a bird with ketocarotenoid-based ornaments (the red-legged partridge Alectoris rufa), the availability of different carotenoids in the diet (i.e. astaxanthin, zeaxanthin and lutein) and oxidative stress were manipulated. The carotenoid composition was analyzed and quantified in the ornaments, blood, liver and fat. A number of oxidative stress biomarkers were also measured in the same tissues. First, we found that color and pigment levels in the ornaments depended on food levels of those carotenoids used as substrates in biotransformation. Second, we found that birds exposed to mild levels of a free radical generator (diquat) developed redder bills and deposited higher amounts of ketocarotenoids (astaxanthin) in ornaments. Moreover, the same diquat-exposed birds also showed a weaker resistance to hemolysis when their erythrocytes were exposed to free radicals, with females also enduring higher oxidative damage in plasma lipids. Thus, higher color production would be linked to higher oxidative stress, supporting the biotransformation hypothesis. The recent discovery of an avian oxygenase enzyme involved in converting yellow to red carotenoids may support our results. Nonetheless, the effect could also depend on the abundance of specific substrate carotenoids in the diet. Birds fed with proportionally higher levels of zeaxanthin showed the reddest ornaments with the highest astaxanthin concentrations. Moreover, these birds tended to show the strongest diquat-mediated effect. Therefore, in the evolution of carotenoid-based sexual signals, a biotransformation cost derived from maintaining a well-adjusted redox machinery could coexist with a cost linked to carotenoid acquisition and allocation (i.e. a resource allocation trade-off).Esther García-de Blas was supported by a predoctoral grant (JAE-PRE) from the Consejo Superior de Investigaciones Científicas (CSIC) co-financed by Fondo Social Europeo (EU). This study was funded by Consejería de Educación y Ciencia, Junta de Comunidades de Castilla la Mancha (project ref.: PII1I09-0271-5037) and Ministerio de Economía y Competitividad (CGL2009-10883-C02-02 and CGL2015-69338-C2-2-P) from the Spanish Government.Peer Reviewe

Benefits of Whey Proteins on Type 2 Diabetes Mellitus Parameters and Prevention of Cardiovascular Diseases

Type 2 diabetes mellitus (T2DM) is a major cause of morbidity and mortality, and it is a major risk factor for the early onset of cardiovascular diseases (CVDs). More than genetics, food, physical activity, walkability, and air pollution are lifestyle factors, which have the greatest impact on T2DM. Certain diets have been shown to be associated with lower T2DM and cardiovascular risk. Diminishing added sugar and processed fats and increasing antioxidant-rich vegetable and fruit intake has often been highlighted, as in the Mediterranean diet. However, less is known about the interest of proteins in low-fat dairy and whey in particular, which have great potential to improve T2DM and could be used safely as a part of a multi-target strategy. This review discusses all the biochemical and clinical aspects of the benefits of high-quality whey, which is now considered a functional food, for prevention and improvement of T2DM and CVDs by insulin- and non-insulin-dependent mechanisms

Étude potentiométrique de la neutralisation de solutions aqueuses d'éthylènediaminotétraacétato mercurate (II) de sodium par la soude à 25 °C

L'étude potentiométrique de la neutralisation du complexe éthylènediaminotétraacétatomercurate (II) de sodium Na2HgY par la soude, à 25 ± 0,1 °C, a été réalisée dans trois milieux différents à concentration cationique constante : milieux aqueux [math]et [math] et milieu mixte eau-ethanol [math] avec une concentration constante de 6,75 M en alcool.L'existence de phénomènes d'isopolycondensation est mise en évidence dans chaque cas. L'interprétation des résultats qui utilise la méthode de la surface potentiométrique conduit à admettre l'existence d'équilibres entre formes monomères HgY2-, Hg(OH)Y3-, dimère (HgY)2(OH)5- et trimère [math] dont on a calculé les constantes