Green's function approach to the magnetic properties of the kagome antiferromagnet

The $S=1/2$ Heisenberg antiferromagnet is studied on the kagom\'e lattice by using a Green's function method based on an appropriate decoupling of the equations of motion. Thermodynamic properties as well as spin-spin correlation functions are obtained and characterize this system as a two-dimensional quantum spin liquid. Spin-spin correlation functions decay exponentially with distance down to low temperature and the calculated missing entropy at T=0 is found to be $0.46\ln{2}$. Within the present scheme, the specific heat exhibits a single peak structure and a $T^2$ dependence at low temperature.Comment: 6 (two-column revtex4) pages, 5 ps figures. Submitted to Phys. Rev.

Changes in epidemiology of rotavirus in the Triângulo Mineiro region of Brazil: lack of two consecutive rotavirus seasons

Rotaviruses are the main cause of infantile acute diarrhea, and a monovalent (G1P[8]) vaccine against the virus was introduced into the Brazilian National Immunization Program for all infants in March 2006. The objectives of this study were to determine the rate and genotype distribution of rotavirus causing infantile diarrhea in the Triângulo Mineiro region of Brazil during 2011-2012 and to assess the impact of local vaccination. Fecal specimens were analyzed for detection and characterization of rotavirus using polyacrylamide gel electrophoresis, reverse transcription followed by polymerase chain reaction (PCR), and PCR-genotyping assays. Overall, rotavirus was diagnosed in 1.7% (6/348) of cases. Rotavirus positivity rates decreased 88% [95% confidence intervals (CI)=15.2, 98.3%; P=0.026] in 2011 and 78% (95%CI=30.6, 93.0%; P=0.007) in 2012 when compared with available data for baseline years (2005/2006) in Uberaba. In Uberlândia, reductions of 95.3% (95%CI=66.0, 99.4%; P=0.002) in 2011, and 94.2% (95%CI=56.4, 99.2%; P=0.004) in 2012 were also observed compared with data for 2008. The circulation of rotavirus G2P[4] strains decreased during the period under study, and strains related to the P[8] genotype reemerged in the region. This study showed a marked and sustained reduction of rotavirus-related cases, with a lack of rotavirus in the 2011 and 2012 seasons, suggesting a positive impact of the vaccination program

Transgenética computacional: uma aplicação ao problema quadrático de alocação

O presente trabalho apresenta uma nova abordagem, denominada Transgenética Computacional. A metáfora baseia-se na utilização de informações meméticas e no emprego dos fluxos extra e intracelulares para planejar e executar manipulações genéticas no contexto dos algoritmos evolucionários. A pesquisa desenvolve duas linhas de algoritmos: a primeira utilizando-se de ambos os fluxos para informar o processo de busca evolucionária; a segunda utiliza-se exclusivamente da manipulação intracelular. São apresentados os agentes da Transgenética Computacional. São examinadas propriedades resultantes da interação cromossomo x agente de manipulação que se mostram semelhantes às do processo imunológico natural. Ao final são relatados resultados computacionais para o Problema Quadrático de Alocação.<br>This paper introduces the Computational Transgenetic approach. The metaphor is based on the use of memetic pieces of information and on the extra and intracellular flows to design and accomplish genetic manipulation in the chromosomes of a given population of an evolutionary algorithm. The research develops two algorithmic approaches. The first algorithmic approach uses both the intra and extra-cellular flows to guide an evolutionary search process. The second one uses, uniquely, intracellular manipulation. Computational Transgenetic agents are presented. Properties resulting from chromosome x agent interactions, similar to the natural immunologic process, are examined. Finally, the paper reports the results of computational experiments of applying both techniques to the Quadratic Assignment Problem

Algoritmo transgenético aplicado ao problema do caixeiro comprador capacitado simétrico

O presente trabalho apresenta um Algoritmo Transgenético para a solução do Problema do Caixeiro Comprador Capacitado Simétrico. O algoritmo é baseado em endossimbiose e outras transformações do fluxo intracelular. O algoritmo é descrito e experimentos computacionais são relatados no sentido de validar a eficiência da abordagem. São também apresentadas novas melhores soluções para 17 instâncias de um conhecido banco de instâncias para o problema.<br>This paper presents a Transgenetic Algorithm to solve the Symmetric Capacitated Traveling Purchaser Problem. The biological inspiration of the proposed algorithm comes from the endosymbiotic theory of evolution. The algorithm is described and the results of computational experiments are reported. The performance of the algorithm is compared with other recent work presented in the literature. New best solutions for 17 instances of a known benchmark are reported

Algoritmo evolucionário para otimização do plano de tratamento em radioterapia conformal 3D

O planejamento do tratamento por radioterapia tem por objetivo atingir um volume alvo com altas doses de radiação tomando cuidado para não expor órgãos sadios a doses elevadas. É, portanto, muito importante que se encontre um balanço ideal entre esses objetivos conflitantes. O presente trabalho relata um modelo de programação matemática multiobjetivo e introduz um Algoritmo Transgenético para o problema de seleção do direcionamento dos feixes de radiação no planejamento em radioterapia conformal 3D. A seleção das direções dos feixes é feita através de uma técnica denominada de isocentros variáveis. Com a finalidade de testar o potencial do algoritmo desenvolvido, realiza-se um experimento comparativo com um Algoritmo Genético Multiobjetivo. O experimento computacional obtém dados quantitativos e qualitativos que são analisados no trabalho.<br>The radiotherapy treatment planning aims to achieve a target volume with high doses of radiation taking care not to expose healthy organs to high doses. It is therefore very important to find an optimal balance between these conflicting goals. This paper reports a mathematical model of multiobjective programming and presents a Transgenetic Algorithm for the problem of selecting the direction of radiation beams in 3D conformal radiotherapy planning. The selection of beams directions is done with a technique called variable isocenters. In order to test the potential of the developed algorithm, a comparative experiment with a multiobjective genetic algorithm was done. The computational experiment obtains quantitative and qualitative data that are analyzed in this paper