131 research outputs found

    Short-time critical dynamics of the Baxter-Wu model

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    We study the early time behavior of the Baxter-Wu model, an Ising model with three-spin interactions on a triangular lattice. Our estimates for the dynamic exponent zz are compatible with results recently obtained for two models which belong to the same universality class of the Baxter-Wu model: the two-dimensional four-state Potts model and the Ising model with three-spin interactions in one direction. However, our estimates for the dynamic exponent θ\theta of the Baxter-Wu model are completely different from the values obtained for those models. This discrepancy could be related to the absence of a marginal operator in the Baxter-Wu model.Comment: 7 pages, 11 figures, accepted for publication in Phys. Rev.

    Novo ensaio de combate químico ao ácaro da leprose dos citros Brevipalpus phoenicis (Geijskes, 1939) em laranjeiras

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    In order to evaluate the performance of several chemicals to control the citrus leprosis mite on orange-trees a test was performed in Rio das Pedras, State of São Paulo, Brazil. The treatments were as follows: A) control; B) fenpropathrin, 13.5g; C) clofentezine, 20.0g; D) biphenthrin, 5.6g: E) binapacryl, 50.0g; F) flubenzimine 60,0g; G) ciexathin, 20.0g. The amounts above are in active ingredients per 100 liters of water. Each orange-tree received 4.0 liters of liquid (1332 liters/hectare). Seven evaluations of the mite infestation were made on fruits: the first, one day before and 02, 15, 30, 44, 65 and 79 days after spray. The best results were obtained in the treatments with ciexathin, binapacryl and biphenthrin.O ácaro da leprose Brevipalpus phoenicis (Geijskes, 1939) é o vetor responsável pela transmissão do agente causador da leprose em laranjeiras, possivelmente um vírus. A doença é grave, responsável por grandes perdas nos laranjais paulistas. Este trabalho foi realizado com o objetivo de combate a esse ácaro com a aplicação de defensivos químicos. Tratamentos: A) testemunha; B) fempropatrina (13,5g); C) clofentezina (20,0g); D) bifentrina (5,6g); E) binapacril (50,0g); F) flubenzimina (60,0g); G) ciexatina (20,0g). As quantidades entre parênteses sao de ingrediente ativo para 100 litros de água. Gastaram-se 4 litros de calda por árvore e 1.332 litros por hectare. A ciexatina, binapacril e bifentrina foram os tratamentos mais eficientes, principalmente a ciexatina

    On universality in aging ferromagnets

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    This work is a contribution to the study of universality in out-of-equilibrium lattice models undergoing a second-order phase transition at equilibrium. The experimental protocol that we have chosen is the following: the system is prepared in its high-temperature phase and then quenched at the critical temperature TcT_c. We investigated by mean of Monte Carlo simulations two quantities that are believed to take universal values: the exponent λ/z\lambda/z obtained from the decay of autocorrelation functions and the asymptotic value XX_\infty of the fluctuation-dissipation ratio X(t,s)X(t,s). This protocol was applied to the Ising model, the 3-state clock model and the 4-state Potts model on square, triangular and honeycomb lattices and to the Ashkin-Teller model at the point belonging at equilibrium to the 3-state Potts model universality class and to a multispin Ising model and the Baxter-Wu model both belonging to the 4-state Potts model universality class at equilibrium.Comment: 17 page

    Global persistence exponent of the two-dimensional Blume-Capel model

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    The global persistence exponent θg\theta_g is calculated for the two-dimensional Blume-Capel model following a quench to the critical point from both disordered states and such with small initial magnetizations. Estimates are obtained for the nonequilibrium critical dynamics on the critical line and at the tricritical point. Ising-like universality is observed along the critical line and a different value θg=1.080(4)\theta_g =1.080(4) is found at the tricritical point.Comment: 7 pages with 3 figure

    Ensaio de combate a ninhos do cupim Cornitermes cumulans (Kollar, 1832)

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    Five different insecticides were applied into the mounds of a termite C. cumulans. Fifty mounds were measured, divided in 5 groups (10 nests each) and had pesticide applied. Insecticides were introduced into the center of the nests through a 50-60 cm long canal made from the top to the nucleus with a steel bar. The treatments were as follows: A) 5% granular aldoxicarb (1g); B) 10% EC biphenthrin (0.2g); C) 50% EC profenophos (1g); D) 0.45% granular dodecachlor (0,18g); E)50% EC fenthion (1g). The quantities between parenthesis are of active ingredients introduced per nest. Five months after the application mounds were completely opened. The mortality was: A) 40%; B) 70%; C) 80%; D) 100%; E) 100%.O presente trabalho foi realizado com a finalidade de reiniciar pesquisas de com bate químico ao cupim de monte Cornitermes cumulans em pastagem. Cinco produtos foram testados com tal objetivo, totalizando cinco tratamentos: A) aldoxicarbe 1,0g; B) bifentrina 0,2g; C) profenofós 1,0g; D) dodecacloro 0,18 g; E) fentiom 1,0g. As quantidades são de ingrediente ativo aplicado por cupinzeiro. A análise dos resultados mostrou que o dodecacloro e o fentiom foram os melhores tratamentos dessa seleção, com 100% de mortalidade dos ninhos
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