Dynamics of liquid nanofilms

The van der Waals forces across a very thin liquid layer (nanofilm) in contact with a plane solid wall make the liquid nonhomogeneous. The dynamics of such flat liquid nanofilms is studied in isothermal case. The Navier-Stokes equations are unable to describe fluid motions in very thin films. The notion of surface free energy of a sharp interface separating gas and liquid layer is disqualified. The concept of disjoining pressure replaces the model of surface energy. In the nanofilm a supplementary free energy must be considered as a functional of the density. The equation of fluid motions along the nanofilm is obtained through the Hamilton variational principle by adding, to the conservative forces, the forces of viscosity in lubrication approximation. The evolution equation of the film thickness is deduced and takes into account the variation of the disjoining pressure along the layer.Comment: 13 pages. International Journal of Engineering Science / International Journal of Engineering Sciences 46 (2008) to appea

Természettudományos nevelés ma: megújult pedagógia Európa jövőjéért. Vezetői összefoglaló

Az utóbbi években több tanulmány rámutatott, hogy aggasztóan visszaesett a fiatalság érdeklődése a kulcsfontosságú természettudományok (2) és a matematika iránt. Annak ellenére, hogy számos projekt és kezdeményezés van folyamatban a trend megfordítására, egyelőre csak a fejlődés visszafogott jelei mutatkoznak. Ha nem kerül sor hatékonyabb fellépésre, Európa hosszú távú kapacitásai az innováció, valamint az innovációhoz szükséges kutatások terén hanyatlani fognak. Ezen felül a népesség egészét nézve, egy olyan társadalomban, amely egyre nagyobb mértékben támaszkodik a tudás felhasználására, a mindennapi élethez szükséges készségek megszerzését is egyre nagyobb veszélyben látjuk

Természettudományos nevelés ma: megújult pedagógia Európa jövőjéért. Vezetői összefoglaló

Formación militar a un costado del Capitolio Nacional, durante la ceremonia de trasmisión de mando.Enrique Olaya Herrera (Guateque, noviembre 12 de 1880 - Roma, febrero 18 de 1937) ocupó la presidencia de Colombia en el periodo 1930-1934. Sucedió en el cargo al conservador Miguel Abadía Méndez. La elección presidencial de Olaya significó la caída de la hegemonía conservadora y el inició de la llamada República Liberal (1930-1946). Gumersindo Cuéllar registro la trasmisión del mando, llevada a cabo el 7 de agosto de 1930. Durante el gobierno de Olaya, se adelantaron reformas sociales, en especial relacionadas con la protección a los sectores obreros y campesinos; se fomentó la industria nacional; se adelantaron importantes obras públicas; se apoyó el desarrollo de la infraestructura de transporte, por medio de la construcción de carreteras, fomento del sistema de ferrocarriles, y el impulso a la infraestructura portuaria; también se estimuló la educación pública; entre otros aspectos. Reformas que luego se adelantaría, de manera más radical, durante la llamada “Revolución en marcha”, nombre con el que se conoció el primer periodo presidencial de Alfonso López Pumarejo (1934-1938)

Investigating participation in Advanced level mathematics: a study of student drop out

There has for some years been a growing concern about participation in university-entrance level mathematics in England and across the developed world. Extensive statistical analyses present the decline but offer little to help us understand the causes. In this paper we explore a concern which cannot be explored through national datasets, namely the retention of mathematics students on Advanced level mathematics courses. Drawing on survey data from fifteen secondary schools in the Midlands of England, we examine subject differences in decisions to study, withdraw from, and continue in a range of A level subjects. Not only is the rate of attrition from mathematics higher than most other subjects, but there are substantial differences between schools. In order to explore this high rate of attrition further we consider one school – Queensbury Park - in which a large proportion of students decided not to continue with their study of mathematics from year 12 to 13. Drawing on performance data and focus group interviews we explore some of the reasons for the students’ decisions

A linear nonequilibrium thermodynamics approach to optimization of thermoelectric devices

Improvement of thermoelectric systems in terms of performance and range of applications relies on progress in materials science and optimization of device operation. In this chapter, we focuse on optimization by taking into account the interaction of the system with its environment. For this purpose, we consider the illustrative case of a thermoelectric generator coupled to two temperature baths via heat exchangers characterized by a thermal resistance, and we analyze its working conditions. Our main message is that both electrical and thermal impedance matching conditions must be met for optimal device performance. Our analysis is fundamentally based on linear nonequilibrium thermodynamics using the force-flux formalism. An outlook on mesoscopic systems is also given.Comment: Chapter 14 in "Thermoelectric Nanomaterials", Editors Kunihito Koumoto and Takao Mori, Springer Series in Materials Science Volume 182 (2013

Mixture of Fluids involving Entropy Gradients and Acceleration Waves in Interfacial Layers

Through an Hamiltonian action we write down the system of equations of motions for a mixture of thermocapillary fluids under the assumption that the internal energy is a function not only of the gradient of the densities but also of the gradient of the entropies of each component. A Lagrangian associated with the kinetic energy and the internal energy allows to obtain the equations of momentum for each component and for the barycentric motion of the mixture. We obtain also the balance of energy and we prove that the equations are compatible with the second law of thermodynamics. Though the system is of parabolic type, we prove that there exist two tangential acceleration waves that characterize the interfacial motion. The dependence of the internal energy of the entropy gradients is mandatory for the existence of this kind of waves. The differential system is non-linear but the waves propagate without distortion due to the fact that they are linearly degenerate (exceptional waves).Comment: 30 page

Governance traditions and narratives of public sector reform in contemporary France.

This article explores the basic traditions of governance in contemporary France and the narratives of public sector reform associated with them. It should be stressed right from the outset that this article does not aim to describe the set of public sector reforms that have been implemented in France in the last ten years or so. Instead, the aim is to demonstrate the similarities and differences between the narratives of the left and the right with regard to these reforms and to show how these narratives help to explain the types of reform that have been enacted. The basic argument is that there is a certain commonality to both the left and the right with regard to their narratives of public sector reform. At the same time, though, there are differences of emphasis both within each tradition and between the two main traditions themselves. Except where indicated, all translations are the author's own

A new approach for the limit to tree height using a liquid nanolayer model

Liquids in contact with solids are submitted to intermolecular forces inferring density gradients at the walls. The van der Waals forces make liquid heterogeneous, the stress tensor is not any more spherical as in homogeneous bulks and it is possible to obtain stable thin liquid films wetting vertical walls up to altitudes that incompressible fluid models are not forecasting. Application to micro tubes of xylem enables to understand why the ascent of sap is possible for very high trees like sequoias or giant eucalyptus.Comment: In the conclusion is a complementary comment to the Continuum Mechanics and Thermodynamics paper. 21 pages, 4 figures. Continuum Mechanics and Thermodynamics 20, 5 (2008) to appea

Essays on trade policies and poverty in developing countries

[ommerciales et d’intégration sur la pauvreté dans les pays en développement. Elle analyse plus spécifiquement l’effet de l’adhésion au GATT et à l’OMC et des politiques tarifaires sur la pauvreté dans les pays en développement.] Dans le premier chapitre nous avons développé un modèle théorique basé sur le modèle Heckscher-Ohlin comportant une segmentation urbaine-rurale, avec des facteurs de production et des produits spécifiques à une région, pour expliquer le rôle de l’avantage comparatif dans la relation entre l’accession au GATT et à l’OMC et la pauvreté. Empiriquement, nous avons recouru aux méthodes économétriques d’appariement pour identifier les effets de l’adhésion au GATT et à l’OMC sur la pauvreté en utilisant un échantillon de 125 pays sur la période1980-2012. Nos résultats montrent que l’adhésion au GATT et à l’OMC a réduit la pauvreté dans les pays membres qui sont des exportateurs nets de produits agricoles et plus spécifiquement d’exportations de produits agricoles à forte intensité de main-d’œuvre. A l’inverse, l’adhésion au GATT et à l’OMC a accru la pauvreté dans les pays en développement qui sont des importateurs nets de produits agricoles. Dans le deuxième chapitre, nous examinons les effets hétérogènes de l’adhésion au GATT et à l’OMC sur la pauvreté. Nous utilisons un modèle Heckscher-Ohlin avec une dimension régionale et des différences de productivité entre pays pour montrer les effets de l’accession au GATT et à l’OMC sur la pauvreté peuvent varier considérablement d’un pays à l’autre en fonction de leur productivité et de leurs dotations factorielles et par conséquent de leur niveau initial de pauvreté. En conséquence, nous utilisons la régression quantile pour tester que l’adhésion a des répercussions différentes pour des pays regroupés dans différents quantiles de pauvreté. Nos résultats révèlent que l’adhésion au GATT et à l’OMC augmente considérablement la pauvreté dans tous les quantiles. L’augmentation de la pauvreté est plus élevée dans les pays les plus pauvres (quantiles supérieurs) que dans les pays les moins pauvres (quantiles inférieurs). Enfin, dans le troisième chapitre, nous évaluons les effets des politiques tarifaires consistant à réduire la taxe sur le commerce international couplé de l’augmentation des taxes domestiques sur la pauvreté dans les pays en développement. Nous modélisons le lien entre les réformes tarifaires et la pauvreté comme hétérogène entre les pays en utilisant un échantillon de 91 pays en développement sur la période 1980-2016. Nos résultats montrent que le passage des taxes sur le commerce international aux taxes nationales avec neutralité des recettes fiscales réduit la pauvreté dans les pays qui ont consolidé en moyenne leur avantage comparatif dans le secteur agricole ; par contre la pauvreté augmente dans les pays qui sont passés d’exportateurs nets à des importateurs nets de produits agricoles.This thesis investigates theoretically and empirically the effects of trade policies and trade integration on poverty in developing countries. More specifically, we are interested in the effects of GATT/WTO membership on poverty and the effects of trade tax reforms on poverty in developing countries. In the first chapter, we develop a Heckscher-Ohlin framework featuring an urban-rural segmentation, with region-specific and product-specific factors and goods to explain the role of comparative advantage in how GATT/WTO accession impacts on poverty. We rely on matching econometrics to identify the effects of GATT/WTO membership on poverty using a sample of 125 countries over the 1980-2012 period. Our results show that the GATT/WTO membership decreased poverty in member countries that are net exporters of agricultural products and more specifically of labor-intensive agricultural exports. In contrast, GATT/WTO accession increased poverty in developing countries that are net importers of agricultural products. In the second chapter, we we develop a Heckscher-Ohlin model with a regional segmentation and country-specific productivity shifters to show that the incidence of GATT/WTO adhesion generally depends on productivity and endowment differences and hence on the level of poverty prior to adhesion. This justifies an empirical model featuring a quantile regression approach. This approach allows us to test that the effects of GATT/WTO on poverty vary across countries belonging to different poverty quantiles. Our results reveal that GATT/WTO membership increases significantly poverty across the entire conditional poverty distribution. Countries with high initial poverty rates suffer higher poverty increases than countries with lower poverty rates. Finally, in the third chapter, we assess trade-tax reforms induced by the reduction in trade taxes that typically accompany participation in multilateral and regional trade agreements in terms of their effects on poverty in developing countries. We model the trade tax reforms poverty nexus as heterogeneous across countries with cross-sectionally dependent errors usinga sample of 91 developing countries over 1980-2016 period. We find that a shift from taxeson international trade towards domestic taxes under revenue-neutrality reduces poverty in the countries that have consolidated on average over time their comparative advantage in agriculture while it increases poverty in countries that moved from being net exporters to net importers of agricultural products