Disorder and the effective Mn-Mn exchange interaction in Ga1−x_{1-x}Mnx_xAs diluted magnetic semiconductors

We perform a theoretical study, using {\it ab initio} total energy density-functional calculations, of the effects of disorder on the $Mn-Mn$ exchange interactions for $Ga_{1-x}Mn_xAs$ diluted semiconductors. For a 128 atoms supercell, we consider a variety of configurations with 2, 3 and 4 Mn atoms, which correspond to concentrations of 3.1%, 4.7%, and 6.3%, respectively. In this way, the disorder is intrinsically considered in the calculations. Using a Heisenberg Hamiltonian to map the magnetic excitations, and {\it ab initio} total energy calculations, we obtain the effective \JMn, from first ($n=1$) all the way up to sixth ($n=6$) neighbors. Calculated results show a clear dependence in the magnitudes of the \JMn with the Mn concentration $x$. Also, configurational disorder and/or clustering effects lead to large dispersions in the Mn-Mn exchange interactions, in the case of fixed Mn concentration. Moreover, theoretical results for the ground-state total energies for several configurations indicate the importance of a proper consideration of disorder in treating temperature and annealing effects

A numerical study of non structural masonry walls with bed joint reinforcement subject to flexure

This paper presents a numerical investigation of a non structural small masonry wall submitted to a flexion effort in its plan and constructed with ceramic blocks. The effort is due to an excessive deformation of the structural elements. The small walls of ceramic blocks (named here mini-walls) were analyzed under two different situations: without bed joint reinforcement (for reference) and with bed joint reinforcement. In order to evaluate the improvement of structural performance with the proposed strengthening (reinforcement masonry walls) the arrows were measured in the middle of the mini-walls, cracking degree and the steel bars deformation. The program employed to carry out the numerical analyses was DIANA (version 9.1), that uses Finet Element Method (FEM). The strategy adopted was macromodelling and non linear phisical behaviour. The results obtained from the numerical research proved that masonry walls with bed joint showed an increased load at first cracking, better performance in service, increased capacity and more resistant arrow at break. Improvements also in relation to the ultimate limit state, which indicates that it is profit and that bed joint reinforcement can be used in non structural and structural mansory walls

O portal da tecnologia da informação para o agronegócio.

Objetivo: Reunir informações atualizadas sobre os softwares disponíveis, para o agronegócio, empresas desenvolvedoras e distribuidoras, dados do mercado ofertante e demandas em tecnologias da informação para o setor rural.Poster. Trabalho apresentado na V Mostra de Trabalhos de Estagiários e Bolsistas, Campinas, out. 2009