Scale Factor Self-Dual Cosmological Models

We implement a conformal time scale factor duality for Friedmann-Robertson-Walker cosmological models, which is consistent with the weak energy condition. The requirement for self-duality determines the equations of state for a broad class of barotropic fluids. We study the example of a universe filled with two interacting fluids, presenting an accelerated and a decelerated period, with manifest UV/IR duality. The associated self-dual scalar field interaction turns out to coincide with the "radiation-like" modified Chaplygin gas models. We present an equivalent realization of them as gauged K\"ahler sigma models (minimally coupled to gravity) with very specific and interrelated K\"ahler- and super-potentials. Their applications in the description of hilltop inflation and also as quintessence models for the late universe are discussed.Comment: v3, improved and extended version to be published in JHEP; new results added to sect.2; 4 figures; 17pg

COMPARING THE PROFITABILITY OF CASSAVA-BASED PRODUCTION SYSTEMS IN THREE WEST AFRICAN COUNTRIES: COTE D'IVOIRE, GHANA AND NIGERIA

Sub-Saharan Africa (SSA) cassava-producing countries such as Nigeria, Ghana, and Côte d'Ivoire have developed, in recent years, a renewed interest in cassava as an alternative food crop. This has led to a major expansion in cassava-based production systems in Nigeria and Ghana, whereas there has been a slower growth in Côte d'Ivoire (Nweke et al., 1998). This paper is based on the argument that the difference in various factors such as agricultural policies (i.e., trade and price policies, domestic production taxes or subsidies), location and technologies (production and processing) between Nigeria, Ghana and Côte d'Ivoire the difference in the level of growth in cassava-based production systems. The paper examines, using the Policy Analysis Matrix (PAM), the magnitude of the impact of these factors on the private and social profitability of cassava production and post-production processing in Côte d'Ivoire, Ghana and Nigeria. The topic has not been examined in previous studies. The paper relies primarily on data for Côte d'Ivoire, Ghana and Nigeria from the Collaborative Study of Cassava in Africa (COSCA) survey. The baseline results demonstrate the similarity in efficiencies of production in these West African countries. The simulation findings indicated that, in Côte d'Ivoire, farmers benefited from the depreciation of the equilibrium exchange rate while farmers in Ghana and Nigeria suffered losses. Simulation results also indicated that Ivorian and Ghanaian cassava/maize farmers could benefit from growing IITA's improved variety and adopting mechanized processing methods.Crop Production/Industries,

Cultura do sorgo sacarino.

Só existe crise para usineiro quando a usina está parada. Esta foi a frase que ouvi outro dia de um encarregado de campo em uma usina. A entressafra de cana-de-açúcar em Alagoas está chegando ao fim. Depois de um período que se estendeu desde março/abril, usinas como Santo Antonio e Camaragibe já anunciam o início da safra para os próximos dias.bitstream/item/123122/1/17-cultura-do-sorgo.pd

THE ROLE OF ENVIRONMENTAL EDUCATION IN PREDICTING ADOPTION OF WIND EROSION CONTROL PRACTICES

Logit and ordered probit analyses were used to identify factors associated with reduced tillage adoption, continuous spring cropping, and the number of changes made in response to wind erosion. Contrary to previous results for water erosion control, simple perception of a wind erosion problem or membership in a particular socioeconomic category did not significantly explain adoption of wind erosion control practices, but participating in a targeted educational program did. This educational program: (a) highlighted the threats of wind erosion to human health and to soil productivity, and (b) described specific potentially profitable farming practices for solving the wind erosion problem.Environmental Economics and Policy,