Non-paraxial Talbot effect in one-dimensional gratings with period comparable to the wavelength

The Talbot effect is a diffractive phenomenon which was found since its inception in the Gaussian optics, but when the period of the object is comparable with the wavelength is considered entering its non-paraxial regime. There, it has attracted interest for its applications related to the design of objects and their restorative effects posing in damaged gratings on this scale. In this contribution a study of this phenomenon at level non-paraxial (metaxial) is presented by using scalar diffraction theory in plane waves representation for periodic transversal fields. To this end, a one-dimensional amplitude grating of period p is used which is illuminated by a monochromatic plane wave of wavelength λ where p ranges between 1,5 λ and 4,2 λ.Fil: Arrieta, E.. Universidad Popular del Cesar; ColombiaFil: Bolognini, Nestor Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigaciones Ópticas. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Centro de Investigaciones Ópticas. Universidad Nacional de La Plata. Centro de Investigaciones Ópticas; ArgentinaFil: Torres, C.O.. Universidad Popular del Cesar; Colombi

Latin America's "New Open Regionalism" and WTO Negotiations: the case of agriculture

This article analyses past trade trends and agricultural protectionism in Latin American agriculture, by examining observed changes in Latin American agriculture and trade policies over the last 20 years that have led to what the authors call the "New Open Regionalism". It also discussed the conflicting interests and various trading positions taken up by Latin American countries in multilateral trade talks, as a result of the strong heterogeneity between net agricultural exporters and importers. The authors show that the repeated failure of the Doha round of trade talks opens the door for bilateral or sub-regional free trade agreements, concluding with the prediction that regional integration in Latin America will come about as a result of agreements between various sub-regional trade blocs. The weakness of internal demand makes the development of the region's agri-food sector highly dependent on exports, the growth of which is one of the main economic drivers in these countries, particularly net exporters. In addressing the issue of the distribution of profits from trade liberalization, the authors propose a variety of schemes that have already proved their effectiveness in countries such as Mexico, Turkey, Brazil, Colombia, Nicaragua and Honduras Nuevos acuerdos regionales de comercio en Latinoamérica y disposición a negociar: el caso de la agricultura Resumen Este artículo analiza las tendencias del comercio agrario y el proteccionismo de la agricultura en Latinoamérica, examinando los cambios observados en la agricultura y la política comercial en los últimos 20 años, denominados por los autores como "nuevos acuerdos regionales de comercio". También se discuten el conflicto de intereses y las variadas posiciones comerciales desarrolladas por los distintos países de América Latina, como resultado de una fuerte heterogeneidad entre los exportadores y los importadores agrarios netos. Los autores muestran que los reiterados fallos de las negociaciones comerciales de la ronda Doha abrieron las puertas para acuerdos comerciales libres bilaterales o sub-regionales, concluyendo con la predicción de que la integración regional traerá como resultado un acuerdo entre varios bloques de comercio sub-regionales. La debilidad de la demanda interna hace que el desarrollo del sector agroalimentario dependa fuertemente de las exportaciones, especialmente de los exportadores netos. En la dirección de los resultados de la distribución de beneficios de los acuerdos de liberalización, los autores proponen una variedad de esquemas que han tenido su efectividad en países como México, Turquía, Brasil, Colombia, Nicaragua y Honduras. Palabras clave: acuerdos libre de comercio, nuevos acuerdos regionales de comercio y agricultura.Free Trade Agreements, New Open Regionalism and Agriculture, International Relations/Trade, Q17,

An Overlapping Generations Model of Electoral Competition

This paper presents a dynamic model of political competition between two "parties" with different policy preferences. A "party" is explicitly modeled as a sequence of overlapping generations of candidates, all of whom face finite decision horizons. In general, there is a conflict between the interests of the individual policymakers and those of the "party" , which includes subsequent generations of candidates. We characterize this conflict and suggest a scheme of "intergenerational transfers" within the party which can resolve or mitigate this conflict. The paper shows how the "overlapping generations" model can be usefully applied to the political arena.

FIGHTING RURAL POVERTY IN LATIN AMERICA: NEW EVIDENCE AND POLICY

We synthesize recent case studies on rural poverty in six Latin American countries, plus two thematic studies. We find that the return to education in farming is surprisingly small; land redistribution increases total farm output, but has mixed effects on income; and urban economic growth significantly reduces rural poverty.Community/Rural/Urban Development, Food Security and Poverty,

Frictional dynamics of viscoelastic solids driven on a rough surface

We study the effect of viscoelastic dynamics on the frictional properties of a (mean field) spring-block system pulled on a rough surface by an external drive. When the drive moves at constant velocity V, two dynamical regimes are observed: at fast driving, above a critical threshold Vc, the system slides at the drive velocity and displays a friction force with velocity weakening. Below Vc the steady sliding becomes unstable and a stick-slip regime sets in. In the slide-hold-slide driving protocol, a peak of the friction force appears after the hold time and its amplitude increases with the hold duration. These observations are consistent with the frictional force encoded phenomenologically in the rate-and-state equations. Our model gives a microscopical basis for such macroscopic description.Comment: 10 figures, 7 pages, +4 pages of appendi