Entrepreneuriat et création d’entreprises : un aperçu des différentes approches

Afin de mieux comprendre le débat historique autour de l’entrepreneur et l’entrepreneuriat, il est nécessaire de commencer par se demander « qu’est ce que l’entrepreneuriat ? ». Bien que l’entrepreneuriat a été largement étudié. La réponse à cette question n’est pas une tâche facile. Car il n’y a pas de définition universellement accepté du terme. Cet article présente une synthèse de la recherche en entrepreneuriat et l’entrepreneur. Tout d'abord, nous opter pour des lectures historiques. L'origine de ce concept remonte aux économistes classiques Cantillon et Say, puis redéfini avec la disparition de Smith, Ricardo, Marshall et Marx, et repositionné avec Schumpeter, qui a restauré la réputation des entrepreneurs. Une multitude de figures ont été plaquées sur l’entrepreneur, depuis les économistes classiques jusqu’aux auteurs contemporains, ce qui a montre qu'il n'y a pas de définition unanime des entrepreneurs. Ensuite nous allons essayer de révéler le pluralisme théorique de l'entrepreneuriat. Chaque théorie tente d'imaginer ce qu'elle peut apporter à la recherche dans le domaine de l'entrepreneuriat

Influence of gold particle size in Au/C catalysts for base-free oxidation of glucose

A series of gold colloids were prepared and immobilized on commercial activated carbon. The influence of the colloid preparation and stability were studied and related to the gold particle size in the final catalyst. The catalysts show an important activity in the glucose to gluconic acid oxidation reaction, leading to gluconic acid yield close to 90% in base free mild conditions (0.1 MPa O2 and 40 ◦C). The size-activity correlation and probable mechanism were also discussed. Finally, the viability of the catalyst was tested by recycling it up to four times. © 2017 Elsevier B.V. All rights reserved. 1. Introduction Biorefinery, defined as the efficient transformation of renew- able materials to fuels and intermediate chemicals, and associated to environmental and economic benefits, has driven the research in this area to notable increase in the last decades [1–4]. Within the renewable materials the vegetal biomass, mostly constituted by carbohydrates, represents around 75% of the total renewable biomass [5]. Among the carbohydrates represented in this biomass the cellulose remains the most attractive fuel precursor, mainly due to its low price, chemical purity and because it is formed only by one monomer – glucose [6]. After cellulose depolimerazion the subse- quent transformation of glucose to valuable compounds involves a variety of processes such as hydrogenation [7], isomerization [8], dehydration [9] and oxidation [10]. Every single mentioned pro- cess or a combination of them lead to the formation of different ‘platform chemicals’. As an example, the D-Gluconic acid, derived from the oxidation of glucose at anomeric position, results to be an useful food additive and raw material for drugs and biodegradable polymers manufacturing [11,12]. Industrially D-Gluconic acid is ∗ Corresponding author. E-mail address: [email protected] (C. Megías-Sayago). produced by enzymatic fermentation process [13,14] for which the principal inconvenient for sustainable large-scale production is the necessity of a neutralization step in order to avoid enzymes deac- tivation by the produced acid [15]. This problem could be solved either by using a base or by the substitution of the enzymes with a heterogeneous catalyst able to oxidize glucose under mild base-free conditions by using either O2 or H2O2 as oxidants [16–19]. Although the use of base (NaOH and a relatively high pH of around 9-9.5) results in increase of heterogeneous catalyst’s activ- ity due to particle size stabilization and metal leaching suppression [20–22], a decrease in the selectivity to gluconic acid is often observed caused by the glucose to fructose isomerization process [23]. In addition, the formation of gluconate salt instead of pure glu- conic acid occurs and entails the need of cost effective post-reaction treatment to obtain the target acid. Therefore, a simple base-free heterogeneously catalyzed process able to produce selectively glu- conic acid and avoiding the problems of particle size sintering and metal leaching is highly desirable. Within the catalyst’s candidates for such a process, the most promising alternative is nanometric gold. Glucose oxidation has been carried out over both unsupported [24,25] and supported [20,26] gold catalysts with good results in activity and selectiv- ity; however, some issues must be addressed in order to improve the catalytic system. Various studies reported the base-free aero- https://doi.org/10.1016/j.cattod.2017.01.007 0920-5861/© 2017 Elsevier B.V. All rights reserved.Ministerio de Economía y Competitividad de España (MINECO) y fondos FEDER de la Unión Europea-ENE2013-47880-C3-2-

The Effect of Hepatitis C on Humans

The aim of the study is to know the effect of the hepatitis C virus on humans, how the virus is transmitted, what is the method of preventing it, and what treatment is used to alleviate the severity of the disease. The questionnaire was designed via the Google Drive application and distributed via the social networking application (WhatsApp), with complete transparency to the population targeted by the research. The city of Mecca, from the age of (25-55 years), where 600 questionnaires were distributed via social media application groups (WhatsApp) according to available conditions (distancing), and answers to 580 questionnaires were obtained

Worldwide trends in underweight and obesity from 1990 to 2022: a pooled analysis of 3663 population-representative studies with 222 million children, adolescents, and adults

Background Underweight and obesity are associated with adverse health outcomes throughout the life course. We estimated the individual and combined prevalence of underweight or thinness and obesity, and their changes, from 1990 to 2022 for adults and school-aged children and adolescents in 200 countries and territories. Methods We used data from 3663 population-based studies with 222 million participants that measured height and weight in representative samples of the general population. We used a Bayesian hierarchical model to estimate trends in the prevalence of different BMI categories, separately for adults (age ≥20 years) and school-aged children and adolescents (age 5–19 years), from 1990 to 2022 for 200 countries and territories. For adults, we report the individual and combined prevalence of underweight (BMI <18·5 kg/m2) and obesity (BMI ≥30 kg/m2). For schoolaged children and adolescents, we report thinness (BMI <2 SD below the median of the WHO growth reference) and obesity (BMI >2 SD above the median). Findings From 1990 to 2022, the combined prevalence of underweight and obesity in adults decreased in 11 countries (6%) for women and 17 (9%) for men with a posterior probability of at least 0·80 that the observed changes were true decreases. The combined prevalence increased in 162 countries (81%) for women and 140 countries (70%) for men with a posterior probability of at least 0·80. In 2022, the combined prevalence of underweight and obesity was highest in island nations in the Caribbean and Polynesia and Micronesia, and countries in the Middle East and north Africa. Obesity prevalence was higher than underweight with posterior probability of at least 0·80 in 177 countries (89%) for women and 145 (73%) for men in 2022, whereas the converse was true in 16 countries (8%) for women, and 39 (20%) for men. From 1990 to 2022, the combined prevalence of thinness and obesity decreased among girls in five countries (3%) and among boys in 15 countries (8%) with a posterior probability of at least 0·80, and increased among girls in 140 countries (70%) and boys in 137 countries (69%) with a posterior probability of at least 0·80. The countries with highest combined prevalence of thinness and obesity in school-aged children and adolescents in 2022 were in Polynesia and Micronesia and the Caribbean for both sexes, and Chile and Qatar for boys. Combined prevalence was also high in some countries in south Asia, such as India and Pakistan, where thinness remained prevalent despite having declined. In 2022, obesity in school-aged children and adolescents was more prevalent than thinness with a posterior probability of at least 0·80 among girls in 133 countries (67%) and boys in 125 countries (63%), whereas the converse was true in 35 countries (18%) and 42 countries (21%), respectively. In almost all countries for both adults and school-aged children and adolescents, the increases in double burden were driven by increases in obesity, and decreases in double burden by declining underweight or thinness. Interpretation The combined burden of underweight and obesity has increased in most countries, driven by an increase in obesity, while underweight and thinness remain prevalent in south Asia and parts of Africa. A healthy nutrition transition that enhances access to nutritious foods is needed to address the remaining burden of underweight while curbing and reversing the increase in obesit

Worldwide trends in underweight and obesity from 1990 to 2022 : a pooled analysis of 3663 population-representative studies with 222 million children, adolescents, and adults

A list of authors and their affiliations appears online. A supplementary appendix is herewith attached.Background: Underweight and obesity are associated with adverse health outcomes throughout the life course. We estimated the individual and combined prevalence of underweight or thinness and obesity, and their changes, from 1990 to 2022 for adults and school-aged children and adolescents in 200 countries and territories. Methods: We used data from 3663 population-based studies with 222 million participants that measured height and weight in representative samples of the general population. We used a Bayesian hierarchical model to estimate trends in the prevalence of different BMI categories, separately for adults (age ≥20 years) and school-aged children and adolescents (age 5–19 years), from 1990 to 2022 for 200 countries and territories. For adults, we report the individual and combined prevalence of underweight (BMI 2 SD above the median). Findings: From 1990 to 2022, the combined prevalence of underweight and obesity in adults decreased in 11 countries (6%) for women and 17 (9%) for men with a posterior probability of at least 0·80 that the observed changes were true decreases. The combined prevalence increased in 162 countries (81%) for women and 140 countries (70%) for men with a posterior probability of at least 0·80. In 2022, the combined prevalence of underweight and obesity was highest in island nations in the Caribbean and Polynesia and Micronesia, and countries in the Middle East and north Africa. Obesity prevalence was higher than underweight with posterior probability of at least 0·80 in 177 countries (89%) for women and 145 (73%) for men in 2022, whereas the converse was true in 16 countries (8%) for women, and 39 (20%) for men. From 1990 to 2022, the combined prevalence of thinness and obesity decreased among girls in five countries (3%) and among boys in 15 countries (8%) with a posterior probability of at least 0·80, and increased among girls in 140 countries (70%) and boys in 137 countries (69%) with a posterior probability of at least 0·80. The countries with highest combined prevalence of thinness and obesity in school-aged children and adolescents in 2022 were in Polynesia and Micronesia and the Caribbean for both sexes, and Chile and Qatar for boys. Combined prevalence was also high in some countries in south Asia, such as India and Pakistan, where thinness remained prevalent despite having declined. In 2022, obesity in school-aged children and adolescents was more prevalent than thinness with a posterior probability of at least 0·80 among girls in 133 countries (67%) and boys in 125 countries (63%), whereas the converse was true in 35 countries (18%) and 42 countries (21%), respectively. In almost all countries for both adults and school-aged children and adolescents, the increases in double burden were driven by increases in obesity, and decreases in double burden by declining underweight or thinness. Interpretation: The combined burden of underweight and obesity has increased in most countries, driven by an increase in obesity, while underweight and thinness remain prevalent in south Asia and parts of Africa. A healthy nutrition transition that enhances access to nutritious foods is needed to address the remaining burden of underweight while curbing and reversing the increase in obesity.peer-reviewe

Hydrogénation du crotonaldéhyde en phase gaz sur catalyseurs au platine ou au palladium supporté sur oxyde de zinc ou chlorure de zinc déposé sur silice (corrélation réactivité-structure)

Les alcools a,b insaturés sont des produits très importants en synthèse organique, ils peuvent être obtenu par hydrogénation sélective des aldéhydes a,b insaturés. Dans les dernières années beaucoup d'efforts ont été réalisés pour trouver le catalyseur performant pour l'hydrogénation de la fonction carbonyle dans le crotonaldéhyde (molécules modèle). Mais, jusqu'à présent il n'existe pas de procédé de catalyse hétérogène capable de donner 100% d'alcool crotylique dans l'hydrogénation du crotonaldéhyde.Nous avons étudié l'hydrogénation du crotonaldéhyde en phase gaz, à pression atmosphérique d'hydrogène sur des catalyseurs à base de palladium ou de platine, supporté sur oxyde de zinc ou sur chlorure de zinc déposé sur silice, préparés par la méthode d'imprégnation du support par les sels métalliques. Ces catalyseurs, après avoir été calcinés sous air et réduits sous hydrogène à différentes températures sont testés en réactivité catalytique. Les produits d'hydrogénation sont analysés par chromatographie en phase gaz (CPG) dont les valeurs d'activité et de sélectivité sont déduites. Celles-ci sont étudiées et comparées en fonction de la température de réduction des catalyseurs.Après nous être assurés de l'inactivité de ZnO seul dans l'hydrogénation du crotonaldéhyde à 80ʿC, nous avons étudié les propriétés des catalyseurs Pd/ZnO, puis celles de Pt/ZnO. Seul, le dernier type de catalyseurs nous a permis d'obtenir d'excellentes performances en sélectivité. Plus de 90% de sélectivité en alcool crotylique à été obtenue sur les deux catalyseurs 5%Pt/ZnO et 1%Pt/ZnO ex-chlorure à des conversions importantes après réduction à 400ʿC. Pour ces catalyseurs, nous avons discuté l'effet de la température de réduction, l'effet de la température de réaction et l'effet du nombre de cycles de réduction plus réaction sur l'activité catalytique et sur la sélectivité. La présence de chlore jouant un rôle très important, nous avons étudié des catalyseurs au platine supportés sur chlorure de zinc déposé sur silice de grande surface spécifique. Nous avons fait varier la quantité de ZnCl2 déposé sur la silice. Dans tous les cas nous avons varié la température de réduction afin de jouer sur l'interaction métal-support. Nous avons pu ainsi préciser le rôle du chlore et de l' alliage PtZn. Après une introduction générale et une étude bibliographique dans le deuxième chapitre nous présentons les méthodes utilisées pour la préparation des catalyseurs, la description du test catalytique ainsi que les différentes techniques utilisées pour la caractérisation de nos catalyseurs ; parmi ces méthodes, la diffraction des rayons-X (DRX), la réduction en température programmée (RTP), la spectroscopie d'absorption atomique (AAS), la mesure d'aire spécifique (BET), la spectroscopie de photoélectrons (XPS), la microscopie électronique à transmission (MET) et la spectroscopie infrarouge à transformée de Fourier (FTIR).Unsaturated alcohols constitute very important products for the organic synthesis, it could be produced by selective hydrogenation of a,b unsaturated aldehydes. Since the latter years, a considerable effort have been devoted to develop a catalyst able to hydrogenate the carbonyl function in crotonaldehyde.We have studied a crotonaldehyde hydrogenation in gas-phase at atmospheric pressure of hydrogen on zinc oxide or zinc chloride deposited on silica supported palladium or platinum catalysts, prepared by impregnation of support by metallic salts. These catalysts, precalcined in air and reduced in hydrogen at different temperatures, were tested in catalytic reactivity. The hydrogenation products were analyzed by gas chromatography (CPG) from which activities and selectivities values were deduced. These values were studied and compared as a function of the reduction temperature of catalysts.After checking the no activity of ZnO alone in crotonaldehyde hydrogenation at 80ʿC, we have investigated the properties of Pd/ZnO and Pt/ZnO catalysts. Only the last type of catalysts, gave excellent performance in selectivity. More than 90% crotyl alcohol selectivity was obtained on both 5%Pt/ZnO and 1%Pt/ZnO catalysts prepared from chlorine precursor with a important conversion after 400ʿC reduction. For, these catalysts, we have discussed the effects of the reaction temperature, the reduction temperature and the reduction-reaction cycle numbers on the activity and the selectivity. Because of chlorine important role, we have tested platinum catalysts supported on zinc chloride deposited on silica. We have varied the ZnCl2 quantity. In all these case, we changed the reduction temperature for modulating the interaction metal-support strength. The role of chlorine and the role of alloy were underlined.After a general introduction and bibliographic investigation, the catalysts preparation procedures, a catalytic tests and different methods of catalyst characterization are presented: among these methods, X-ray diffraction (XRD), temperature programmed reduction (TPR), atomic adsorption spectroscopy (AAS), nitrogen adsorption (BET), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and Fourier transformed infra-red spectroscopy (FTIR).STRASBOURG-Sc. et Techniques (674822102) / SudocSudocFranceF

1-(Prop-2-ynyl)indoline-2,3-dione

The structure of the title compound, C11H7NO2, is isotypic to that of its homologue, 1-octylindoline-2,3-dione [Qachchachi et al. (2013). Acta Cryst. E69, o1801]. The indoline ring and the two carbonyl O atoms are approximately coplanar, the largest deviation from the mean plane being 0.021 (1) Å for one of the O atoms. The mean plane through the fused ring system is nearly perpendicular to the propynyl group, as indicated by the N—C—C—C torsion angle of 77.9 (1)°. In the crystal, molecules are linked by C—H...O hydrogen bonds and π–π interactions between benzene rings [intercentroid distance = 3.5630 (10) Å], forming a three-dimensional structure

1-Dodecylindoline-2,3-dione

The structure of the title compound, C20H29NO2, is isotypic to that of its homologue 1-octylindoline-2,3-dione. The indoline ring and the two carbonyl-group O atoms are approximately coplanar, the largest deviation from the mean plane being 0.0760 (10) Å. The mean plane through the fused-ring system is nearly perpendicular to the mean plane passing through the 1-dodecyl chain [dihedral angle = 77.69 (5)°]. All C atoms of the dodecyl group are in an antiperiplanar arrangement. In the crystal, molecules are linked by C—H...O hydrogen bonds, forming a three-dimensional network