Diluted antiferromagnet in a ferromagnetic enviroment

The question of robustness of a network under random ``attacks'' is treated in the framework of critical phenomena. The persistence of spontaneous magnetization of a ferromagnetic system to the random inclusion of antiferromagnetic interactions is investigated. After examing the static properties of the quenched version (in respect to the random antiferromagnetic interactions) of the model, the persistence of the magnetization is analysed also in the annealed approximation, and the difference in the results are discussed

Avaliação de hibridos triplóides de melancia no Vale do Sub-médio São Francisco.

O desempenho agronômico de doze híbridos de melancia sem sementes foi avaliado no município de Petrolina -PE. Foram utilizados os híbridos Tiffany (Asgrow), Nova, AF-180, AF-179, AF-178, AF-177, AF-176 (Sakata-Agroflora), W-691 (Sainoda), Ailet 1, Ailet 2, HLT- 02 e H L T -03 (Embrapa Semi-Árido). O experimento foi realizado no delineamento de blocos ao acaso com três repetições de dez plantas e espaçamento de 3,0 x 1,0 m. Foram avaliados o número de dias para o aparecimento da primeira flor feminina, número de frutos por planta, peso médio de frutos, teor de sólidos solúveis, espessura média da casca, percentual de frutos com sementes e percentual de frutos com ocamento. Todos os híbridos apresentaram produtividade e teor de sólidos solúveis em níveis satisfatórios, no entanto verificou-se elevada ocorrência de frutos com sementes verdadeiras e com problemas de ocamento na polpa. Os altos coeficientes de variação observados na análise de algumas variáveis sugerem a necessidade de realizar novos ensaios, utilizando-se parcelas maiores, a fim de aumentar a precisão do experimento.Suplemento 2. Edição do 42 Congresso Brasileiro de Olericultura; 11 Congresso Latino Americano de Horticultura, Uberlândia, jul. 2002

Spin-glass behaviour on random lattices

The ground-state phase diagram of an Ising spin-glass model on a random graph with an arbitrary fraction $w$ of ferromagnetic interactions is analysed in the presence of an external field. Using the replica method, and performing an analysis of stability of the replica-symmetric solution, it is shown that $w=1/2$, correponding to an unbiased spin glass, is a singular point in the phase diagram, separating a region with a spin-glass phase ($w<1/2$) from a region with spin-glass, ferromagnetic, mixed, and paramagnetic phases ($w>1/2$)

Decoherence of tripartite states - a trapped ion coupled to an optical cavity

We investigate the non-dissipative decoherence of three qubit system obtained by manipulating the state of a trapped two-level ion coupled to an optical cavity. Modelling the environment as a set of noninteracting harmonic oscillators, analytical expressions for the state operator of tripartite composite system, the probability of generating maximally entangled GHZ state, and the population inversion have been obtained. The pointer observable is the energy of the isolated quantum system. Coupling to environment results in exponential decay of off diagonal matrix elements of the state operator with time as well as a phase decoherence of the component states. Numerical calculations to examine the time evolution of GHZ state generation probability and population inversion for different system environment coupling strengths are performed. Using negativity as an entanglement measure and linear entropy as a measure of mixedness, the entanglement dynamics of the tripartite system in the presence of decoherence is analysed.Comment: Revised version, errors corrected and references added. 12 pages, 6 figures, Presented at ICSSUR May 2005, Besancon, Franc

Agrotóxicos em hortaliças: segurança alimentar, riscos socioambientais e políticas públicas para promoção da saúde.

Made available in DSpace on 2011-04-09T16:10:18Z (GMT). No. of bitstreams: 1 almeidaagrotoxicos.pdf: 159523 bytes, checksum: 9bd99532d3c206f5143d94335bd0d706 (MD5) Previous issue date: 2010-03-0

Magnetic phases evolution in the LaMn1-xFexO3+y system

We have investigated the crystal structure and magnetic properties for polycrystalline samples of LaMn1-xFexO3+y, in the whole range x=0.0 to x=1.0, prepared by solid state reaction in air. All samples show the ORT-2 orthorhombic structure that suppresses the Jahn-Teller distortion, thus favoring a ferromagnetic (FM) superexchange (SE) interaction between Mn^{3+}-O-Mn^{3+}. For x=0.0 the oxygen excess (y ~ 0.09) produces vacancies in the La and Mn sites and generates a fraction around 18% of Mn^{4+} ions and 82% of the usual Mn^{3+} ions, with possible double exchange interaction between them. The Fe doping in this system is known to produce only stable Fe^{3+} ions. We find an evolution from a fairly strong FM phase with a Curie temperature T_{C} ~ 160 K, for x=0.0, to an antiferromagnetic (AFM) phase with T_{N} = 790 K, for x=1.0, accompanied by clear signatures of a cluster-glass behavior. For intermediate Fe contents a mixed-phase state occurs, with a gradual decrease (increase) of the FM (AFM) phase, accompanied by a systematic transition broadening for 0.2 < x < 0.7. A model based on the expected exchange interaction among the various magnetic-ion types, accounts very well for the saturation-magnetization dependence on Fe doping.Comment: 27 pages, 9 figure

Efeito dos sistemas de produção na qualidade do solo e na produtividade de soja no Oeste Paulista.

A adoção de rotação de culturas e ausência de revolvimento de solo pode interferir na qualidade química, física e estrutural do solo. O objetivo desse estudo foi avaliar qualidade do solo e produtividade de soja em diferentes sistemas de produção. O experimento foi conduzido no Campus II da UNOESTE em Presidente Prudente (SP), entre maio de 2010 e março de 2012. Foram testados cinco diferentes sistemas separados em talhões. Os sistemas foram: 1)Integração Lavoura Pecuária Floresta; 2)Integração Lavoura Pecuária; 3)Sucessão braquiária/soja em área anteriormente cultivada com amendoim em preparo convencional; 4)Pastagem irrigada; 5)Testemunha com pastagem degradada. Os resultados foram submetidas á analise estatistica pelo teste de Tukey, à 5 % de probabilidade. A produtividade de soja foi maior no sistema de sucessão braquiária/soja por dois anos, em área de reforma de pastagem com preparo convencional e cultivo de amendoim. O sistema de iLPF aumenta a densidade do solo em subsuperfície

Is the droplet theory for the Ising spin glass inconsistent with replica field theory?

Symmetry arguments are used to derive a set of exact identities between irreducible vertex functions for the replica symmetric field theory of the Ising spin glass in zero magnetic field. Their range of applicability spans from mean field to short ranged systems in physical dimensions. The replica symmetric theory is unstable for d>8, just like in mean field theory. For 6<d<8 and d<6 the resummation of an infinite number of terms is necessary to settle the problem. When d<8, these Ward-like identities must be used to distinguish an Almeida-Thouless line from the replica symmetric droplet phase.Comment: 4 pages. Accepted for publication in J.Phys.A. This is the accepted version with the following minor changes: one extra sentence in the abstract; footnote 2 slightly extended; last paragraph somewhat reformulate