Controle biológico de insetos-praga em frutíferas de Clima Temperado: uma opção viável, mas desafiadora.

bitstream/item/33948/1/documento-208.pd

Exact ground state Monte Carlo method for Bosons without importance sampling

Generally ``exact'' Quantum Monte Carlo computations for the ground state of many Bosons make use of importance sampling. The importance sampling is based, either on a guiding function or on an initial variational wave function. Here we investigate the need of importance sampling in the case of Path Integral Ground State (PIGS) Monte Carlo. PIGS is based on a discrete imaginary time evolution of an initial wave function with a non zero overlap with the ground state, that gives rise to a discrete path which is sampled via a Metropolis like algorithm. In principle the exact ground state is reached in the limit of an infinite imaginary time evolution, but actual computations are based on finite time evolutions and the question is whether such computations give unbiased exact results. We have studied bulk liquid and solid 4He with PIGS by considering as initial wave function a constant, i.e. the ground state of an ideal Bose gas. This implies that the evolution toward the ground state is driven only by the imaginary time propagator, i.e. there is no importance sampling. For both the phases we obtain results converging to those obtained by considering the best available variational wave function (the Shadow wave function) as initial wave function. Moreover we obtain the same results even by considering wave functions with the wrong correlations, for instance a wave function of a strongly localized Einstein crystal for the liquid phase. This convergence is true not only for diagonal properties such as the energy, the radial distribution function and the static structure factor, but also for off-diagonal ones, such as the one--body density matrix. From this analysis we conclude that zero temperature PIGS calculations can be as unbiased as those of finite temperature Path Integral Monte Carlo.Comment: 11 pages, 10 figure

Dynamic structure factor for 3He in two-dimensions

Recent neutron scattering experiments on 3He films have observed a zero-sound mode, its dispersion relation and its merging with -and possibly emerging from- the particle-hole continuum. Here we address the study of the excitations in the system via quantum Monte Carlo methods: we suggest a practical scheme to calculate imaginary time correlation functions for moderate-size fermionic systems. Combined with an efficient method for analytic continuation, this scheme affords an extremely convincing description of the experimental findings.Comment: 5 pages, 5 figure

Ocorrência da mosca dos favos Pseudohpocera kerteszi (Diptera: Phoridae) em colméias de abelhas melíferas africanizadas no Rio Grande do Sul.

bitstream/item/31359/1/comunicado-178.pdfMeta: 2008

Ocorrência de tefritídeos em Passiflora caerulea em Pelotas e Capão do Leão, RS, Brasil.

O objetivo do estudo foi determinar a(s) espécie(s) de tefritídeo(s) coletado(s) em P. caerulea

Primeiro relato de Drosophila suzukii (Diptera: Drosophilidae) em frutos de araçá e pitanga em municípios da região sul do Rio Grande do Sul, Brasil.

O objetivo do estudo foi relatar a ocorrência de D. suzukii em frutíferas mirtáceas em municípios da região sul do Rio Grande do Sul, Brasil

Ocorrência de Diaphorina citri Kuwayama (Hemiptera: Liviidae) no Estado do Rio Grande do Sul.

O objetivo do trabalho foi determinar os locais de ocorrência de D. citri no Estado do RS e estudar a flutuação populacional da praga no município de Rosário do Sul

Novel substrates for Helium adsorption: Graphane and Graphene-Fluoride

The discovery of fullerenes has stimulated extensive exploration of the resulting behavior of adsorbed films. Our study addresses the planar substrates graphene-fluoride (GF) and graphane (GH) in comparison to graphene. We present initial results concerning the potential energy, energy bands and low density behavior of 4He and 3He films on such different surfaces. For example, while graphene presents an adsorption potential that is qualitatively similar to that on graphite, GF and GH yield potentials with different symmetry, a number of adsorption sites double that on graphene/graphite and a larger corrugation for the adatom. In the case of GF, the lowest energy band width is similar to that on graphite but the He atom has a significantly larger effective mass and the adsorption energy is about three time that on graphite. Implications concerning the monolayer phase diagram of 4He are explored with the exact path integral ground state method. A commensurate ordered state similar to the sqrt{3} x sqrt{3} R30^o state on graphite is found the be unstable both on GF and on GH. The ground states of submonolayer 4He on both GF and GH are superfluids with a Bose Einstein condensate fraction of about 10%.Comment: 6 pages, 3 figures, LT26 proceedings, accepted for publication in Journal of Physics: Conference Serie