3,231 research outputs found
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 He
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 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
Índices de frutificação em variedades de Malpighia emarginata DC. (Malpighiaceae), em cultivo irrigado, no Vale do Submédio São Francisco.
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