Agricultura familiar, multifuncionalidade da agricultura e ruralidade: interfaces de uma realidade complexa.

Nas últimas décadas, assistimos à revitalização do debate em torno da agricultura familiar pela incorporação das discussões sobre as múltiplas funções da agricultura num rural que não pode mais ser visto como domínio exclusivo da atividade agrícola e dos agricultores. No contexto brasileiro, acreditamos que essa discussão deva ser permeada pela análise de como processos diferenciados de distribuição fundiária e desenvolvimento econômico e o tipo de agricultura resultante geram ruralidades específicas com características como, no caso da agricultura familiar, a manutenção de práticas sociais e de trabalho marcadas pelas relações de parentesco e vizinhança presentes numa sociedade de interconhecimento. Partindo desse princípio, este trabalho analisa a agricultura familiar de um bairro rural do município de Ouro Fino - MG, sua herança histórica e sua participação na criação de uma paisagem natural e humana que muito contribui para a atratividade da região

High-Order Coupled Cluster Method (CCM) Calculations for Quantum Magnets with Valence-Bond Ground States

In this article, we prove that exact representations of dimer and plaquette valence-bond ket ground states for quantum Heisenberg antiferromagnets may be formed via the usual coupled cluster method (CCM) from independent-spin product (e.g. N\'eel) model states. We show that we are able to provide good results for both the ground-state energy and the sublattice magnetization for dimer and plaquette valence-bond phases within the CCM. As a first example, we investigate the spin-half $J_1$--$J_2$ model for the linear chain, and we show that we are able to reproduce exactly the dimerized ground (ket) state at $J_2/J_1=0.5$. The dimerized phase is stable over a range of values for $J_2/J_1$ around 0.5. We present evidence of symmetry breaking by considering the ket- and bra-state correlation coefficients as a function of $J_2/J_1$. We then consider the Shastry-Sutherland model and demonstrate that the CCM can span the correct ground states in both the N\'eel and the dimerized phases. Finally, we consider a spin-half system with nearest-neighbor bonds for an underlying lattice corresponding to the magnetic material CaV$_4$O$_9$ (CAVO). We show that we are able to provide excellent results for the ground-state energy in each of the plaquette-ordered, N\'eel-ordered, and dimerized regimes of this model. The exact plaquette and dimer ground states are reproduced by the CCM ket state in their relevant limits.Comment: 34 pages, 13 figures, 2 table

Uma Tipologia Dos Estabelecimentos Agropecuários Do Brasil A Partir Do Censo De 2006

A classification of farms in four types is proposed, according to the composition of the labour force employed: exclusively family farm; land reform settlement ("assentado"); family farm with hired labour; non-family farm. Exclusively family farms are run by the owner and employ exclusively family labour; land reform settlements are also mostly family-run units; mixed family farms are run by the owner and employ predominantly family labour, complemented by hired labour; non-family farms depend mostly on hired labour, with or without the help of the owner's family. Aspects such as area, gross production value, productivity and revenues are analysed. One of the main results is that the family units are largely predominant in number (90% of the total) and employ 80% of the labour force in the agricultural sector, although they contribute with only 50% of the gross production, in virtue of lower productivity. Inequality in land distribution within the groups is extremely high, even among family farms. In Brazil, only 16% of the total inequality of land distribution is due to the inequality between the four categories of farms, while 84% originate from the inequality within groups.511105122Bolliger, F.P., Oliveira, O.C., Brazilian Agriculture: a ChangingStructure (2010), Trabalho preparado para o Encontro Anual da Agricultural and Applied Economics Association, em Denver, Colorado, Julho dePerfil da agricultura familiar no Brasil: dossie estatistico (1996) FAO/INCRA, , Projeto UFT/BRA/036/BRA. Agosto deGuanziroli, C.E., Agricultura familiar e reforma agraria no seculo XXI (2001), p. 288. , Rio de Janeiro: GaramondHoffmann, R., Distribuicao de renda-medidas de desigualdade e pobreza (1998) Sao Paulo: EDUSPKageyama, A.A., Bergamasco, S.M.P.P., A estrutura da producao no campo em 1980 (1989), 12-13, pp. 55-72. , Perspectivas, Sao PauloKageyama, A.A., Bergamasco, S.M.P.P., Oliveira, J.T., A. Novas possibilidades de pesquisa sobre a agricultura familiar no Brasil a partir do Censo de 2006 (2008), pp. 16-27. , www.apta.sp.gov.br, Revista Tecnologia e Inovacao Agropecuaria, dezembro de . Disponivel emKageyama, A.A., Bergamasco, S.M.P.P., Oliveira, J.T.A., Caracterizacao dos estabelecimentos de assentados no Censo Agropecuario de 2006 (2010), 13, p. 320. , Retratos de Assentamentos. Araraquara-SPMarques, V.P.M.A., Os beneficiarios da reforma agraria no Censo Agropecuario de 2006: aspectos metodologicos (2010), Brasilia: Texto para discussao interna. M.D.A., outCenso Agropecuario 2006 - Agricultura Familiar, Primeiros Resultados (2009) MDA/IBGE., p. 267. , Rio de Janeiro: IBGEVeiga, J.E., Delimitando a agricultura familiar (1995), 25 (2-3), pp. 128-141. , Reforma Agraria, mai-dez,d

Excitations in a modified Shastry-Sutherland model

A modified Shastry-Sutherland model with fourth-nearest-neighbor dimerization is studied with strong coupling perturbation theory. One-triplet excitations are calculated up to the second order. Bose-Einstein condensation of one-triplet excitations may induce different ordered states, i.e. collinear antiferromagnetic state, Néel state or incommensurate state when the gap closes by changing the physical parameters or by an external magnetic field. Two-triplet bound states in the S = 1 and S = 2 channels are shown to exist around the symmetric lines of Kx =  ±Ky and Kx ± Ky =  ±π. For ferromagnetic dimer-dimer interaction, the energies of the bound states in the S = 1 (S = 2) channel lie above (below) the two-triplet continuum. By calculating the existence region, the degeneracy, the symmetry and the dispersion relation, a whole image and main features of the bound states are obtained. Experimental results of (CuX)LaNb2O7 with X = Cl, Br are interpreted

Superfluid density and field-induced magnetism in Ba(Fe1-xCox)(2)As-2 and Sr(Fe1-xCox)(2)As-2 measured with muon spin relaxation

We report muon spin rotation (mu SR) measurements of single-crystal Ba(Fe1-xCox)(2)As-2 and Sr(Fe1-xCox)(2)As-2. From measurements of the magnetic field penetration depth lambda we find that for optimally and overdoped samples, 1/lambda(T -> 0)(2) varies monotonically with the superconducting transition temperature T-C. Within the superconducting state we observe a positive shift in the muon precession signal, likely indicating that the applied field induces an internal magnetic field. The size of the induced field decreases with increasing doping but is present for all Co concentrations studied.This article is published as Williams, T. J., A. A. Aczel, E. Baggio-Saitovitch, S. L. Bud’ko, P. C. Canfield, J. P. Carlo, T. Goko et al. "Superfluid density and field-induced magnetism in Ba (Fe 1− x Co x) 2 As 2 and Sr (Fe 1− x Co x) 2 As 2 measured with muon spin relaxation." Physical Review B 82, no. 9 (2010): 094512. DOI: 10.1103/PhysRevB.82.094512. Copyright 2010 American Physical Society. Posted with permission