Interatomic potentials for atomistic simulations of the Ti-Al system

Semi-empirical interatomic potentials have been developed for Al, alpha-Ti, and gamma-TiAl within the embedded atomic method (EAM) by fitting to a large database of experimental as well as ab-initio data. The ab-initio calculations were performed by the linear augmented plane wave (LAPW) method within the density functional theory to obtain the equations of state for a number of crystal structures of the Ti-Al system. Some of the calculated LAPW energies were used for fitting the potentials while others for examining their quality. The potentials correctly predict the equilibrium crystal structures of the phases and accurately reproduce their basic lattice properties. The potentials are applied to calculate the energies of point defects, surfaces, planar faults in the equilibrium structures. Unlike earlier EAM potentials for the Ti-Al system, the proposed potentials provide reasonable description of the lattice thermal expansion, demonstrating their usefulness in the molecular dynamics or Monte Carlo studies at high temperatures. The energy along the tetragonal deformation path (Bain transformation) in gamma-TiAl calculated with the EAM potential is in a fairly good agreement with LAPW calculations. Equilibrium point defect concentrations in gamma-TiAl are studied using the EAM potential. It is found that antisite defects strongly dominate over vacancies at all compositions around stoichiometry, indicating that gamm-TiAl is an antisite disorder compound in agreement with experimental data.Comment: 46 pages, 6 figures (Physical Review B, in press

Maíz para pan en agricultura ecológica

Maize (Zea mays L.) bread is increasingly appreciated by consumers from the northwest of the Iberian Peninsula. However, the ancient maize varieties specifically selected for those uses have been replaced by hybrids with higher yield and lower flour quality. Besides, maize available comes from intensive agriculture, involving herbicides, insecticides and other potentially dangerous products. Organic production of traditional maize varieties for human consumption could be valuable for raising the returns of small local farmers in the northwest of Spain and the north of Portugal, and for matching the demands of consumers. Autochthonous varieties have been evaluated under organic farming and the quality of those with higher yield for bakery. Four autochthonous varieties were identified with the best performance under organic conditions and adequate quality for making bread and other traditional maize foods. Those varieties are "Tuy" (yellow kernel and medium growing cycle), "Sarreaus" (yellow kernel and early cycle), "Meiro" (black kernel and late cycle), and "Rebordanes" (white kernel and medium-early cycle). Traditional white, yellow and black maize varieties have been identified, and a selection program for increasing yield and quality is being performed for each.El pan de maíz (Zea mays L.) es cada vez más apreciado por los consumidores del noroeste de la Península Ibérica. Sin embargo, las antiguas variedades de maíz específicamente seleccionadas para esos usos han sido reemplazadas por híbridos con mayor rendimiento y menor calidad harinera. Además, el maíz disponible procede de agricultura intensiva, donde se usan herbicidas, insecticidas y otros productos potencialmente peligrosos para la salud. La producción ecológica de variedades tradicionales de maíz para consumo humano puede ser útil para aumentar los beneficios de los pequeños agricultores locales en el noroeste de España y norte de Portugal, así como para satisfacer las demandas de los consumidores. En este trabajo hemos evaluado variedades autóctonas en condiciones de agricultura ecológica y la calidad panificable de las variedades con mayores rendimientos. Hemos identificado cuatro variedades autóctonas con el mayor valor agronómico en condiciones de agricultura ecológica y calidad satisfactoria para hacer pan de maíz y otros alimentos tradicionales de maíz. Estas variedades son "Tuy" (grano amarillo y ciclo medio), "Sarreaus" (grano amarillo y temprana), "Meiro" (grano negro y tardía), y "Rebordanes" (grano blanco y ciclo medio). Estas variedades tradicionales de maíz blanco, amarillo y negro están siendo mejoradas para aumentar el rendimiento harinero

Is group selection necessary? An alternative interpretation of homogeneous Middleman groups: Comments on Janet Landa’s paper

Clubs, Group selection, Inclusive fitness, Social networks and norms, D71, Z13,

Convergent cultural evolution and multilevel selection: Reply to comments on Janet Landa’s ‘The bioeconomics of homogenous middleman groups as adaptive units: Theory and empirical evidence viewed from a group selection framework’

Cultural diversity, Group selection, Proximate and ultimate causation, Fitness differences, The Law Merchant, K12, P51, Q57, Z1, Z12,