Order and Disorder in AKLT Antiferromagnets in Three Dimensions

The models constructed by Affleck, Kennedy, Lieb, and Tasaki describe a family of quantum antiferromagnets on arbitrary lattices, where the local spin S is an integer multiple M of half the lattice coordination number. The equal time quantum correlations in their ground states may be computed as finite temperature correlations of a classical O(3) model on the same lattice, where the temperature is given by T=1/M. In dimensions d=1 and d=2 this mapping implies that all AKLT states are quantum disordered. We consider AKLT states in d=3 where the nature of the AKLT states is now a question of detail depending upon the choice of lattice and spin; for sufficiently large S some form of Neel order is almost inevitable. On the unfrustrated cubic lattice, we find that all AKLT states are ordered while for the unfrustrated diamond lattice the minimal S=2 state is disordered while all other states are ordered. On the frustrated pyrochlore lattice, we find (conservatively) that several states starting with the minimal S=3 state are disordered. The disordered AKLT models we report here are a significant addition to the catalog of magnetic Hamiltonians in d=3 with ground states known to lack order on account of strong quantum fluctuations.Comment: 7 pages, 2 figure

Optical doping and damage formation in AIN by Eu implantation

AlN films grown on sapphire were implanted with 300 keV Eu ions to fluences from 3×1014 to 1.4×1017 atoms/cm2 in two different geometries: “channeled” along the c-axis and “random” with a 10° angle between the ion beam and the surface normal. A detailed study of implantation damage accumulation is presented. Strong ion channeling effects are observed leading to significantly decreased damage levels for the channeled implantation within the entire fluence range. For random implantation, a buried amorphous layer is formed at the highest fluences. Red Eu-related photoluminescence at room temperature is observed in all samples with highest intensities for low damage samples (low fluence and channeled implantation) after annealing. Implantation damage, once formed, is shown to be stable up to very high temperatures.FCT - POCI/FIS/57550/2004FCT - PTDC/FIS/66262/2006FCT - PTDC/CTM/100756/200

Variação da alogamia em população recorrente para o desenvolvimento de genitores de híbridos em arroz.

O objetivo deste trabalho foi verificar tendências na variação em alogamia, de uma população desenvolvida para a criação de linhagens genitoras de híbridos, do Programa Arroz Híbrido Embrapa-Cirad

Coleta de forrageiras nativas na Ilha de Marajó, Pará.

bitstream/item/57580/1/CPATU-PA122.pd

The mass of the graviton and the cosmological constant

We show that the graviton acquires a mass in a de Sitter background given by $m_{g}^{2}=-{2/3}\Lambda.$ This is precisely the fine-tuning value required for the perturbed gravitational field to mantain its two degrees of freedom.Comment: Title changed and few details added, without any changes in the conclusio

Variação da habilidade combinatória em população restauradora para o desenvolvimento de genitores de híbridos de arroz.

Baseia-se na exploração da macho-esterilidade genética utilizada na população restauradora em processo de seleção recorrente

Variação da habilidade combinatória em população restauradora para o desenvolvimento de linhagens R em arroz.

O objetivo deste trabalho foi avaliar test crosses de uma população desenvolvida para a criação de linhagens R genitoras de híbridos, do Programa Arroz Híbrido Embrapa-Cirad

Macho-esterilidade monogênica e recessiva: ferramenta de seleção para a criação genitores de arroz híbrido.

Objetivando selecionar eficazmente as linhagens genitoras de híbridos, é necessário selecionar em gerações precoces: 1) aptidão à combinação, para obter híbridos produtivos com elevado valor tecnológico; e 2) aptidão à alogamia, para obter híbridos cujas sementes são fáceis de produzir e, conseqüentemente, mais baratas