Magnetization plateau in a two-dimensional multiple-spin exchange model

We study a multiple-spin exchange model on a triangular lattice, which is a possible model for low-density solid 3He films. Due to strong competitions between ferromagnetic three-spin exchange and antiferromagnetic four-spin one, the ground states are highly degenerate in the classical limit. At least 2^{L/2}-fold degeneracy exists on the L*L triangular lattice except for the SO(3) symmetry. In the magnetization process, we found a plateau at m/m_{sat}=1/2, in which the ground state is "uuud state" (a collinear state with four sublattices). The 1/2-plateau appears due to the strong four-spin exchange interaction. This plateau survives against both quantum and thermal fluctuations. Under a magnetic field which realizes the "uuud" ordered state, a phase transition occurs at a finite temperature. We predict that low-density solid 3He thin films may show the 1/2-plateau in the magnetization process. Experimental observation of the plateau will verify strength of the four-spin exchange. It is also discussed that this magnetization plateau can be understood as an insulating-conducting transition in a particle picture.Comment: 10 pages, RevTeX, 12 figures, added a reference and corrected typos, to be published in Phys.Rev.B (01 APR 99

Informações sobre polinizadores em maracujazeiro no Vale do São Francisco.

Caracterização da região.; a cultura do maracujazeiro; socioeconômia; floração, morfologia e biologia floral; formação e desenvolvimento dos frutos; polinização do maracujajeiro; visitantes florais na região do Vale do São Francisco; características do comportamento das mamangavas; recomendações de manejo; oferta de recursos alimentares alternativos; oferta de locais para nidificação; alternativa para minimizar o impacto de pilhadores; sensibilização de produtores e técnicos.bitstream/CPATSA-2009-09/40644/1/SDC217.pd

Uma análise das barreiras tarifárias no comércio internacional de lácteos.

bitstream/item/57090/1/BOP-32-Uma-Analise-das-Barreiras-Tarifarias-no-Comercio-Internacional-de-Lacteos.pd

Padronização do preparo de amostras de feijão cozido para teste de dureza instrumental.

O objetivo deste trabalho foi verificar qual o melhor método de cocção de feijão, de forma que os grãos se tornassem cozidos e permitisse a distinção entre amostras recém-colhidas e envelhecidas (hard-to-cook)

Possible chiral phase transition in two-dimensional solid 3^3He

We study a spin system with two- and four-spin exchange interactions on the triangular lattice, which is a possible model for the nuclear magnetism of solid $^3$He layers. It is found that a novel spin structure with scalar chiral order appears if the four-spin interaction is dominant. Ground-state properties are studied using the spin-wave approximation. A phase transition concerning the scalar chirality occurs at a finite temperature, even though the dimensionality of the system is two and the interaction has isotropic spin symmetry. Critical properties of this transition are studied with Monte Carlo simulations in the classical limit.Comment: 4 pages, Revtex, 4 figures, to appear in Phys.Rev.Let

Uso da tomografia de raios-x na determinação de densidade básica da madeira e proporção de lenho inicial e tardio.

Organizado por Patricia Póvoa de Mattos, Celso Garcia Auer, Rejane Stumpf Sberze, Katia Regina Pichelli e Paulo César Botosso