Resonances in a trapped 3D Bose-Einstein condensate under periodically varying atomic scattering length

Nonlinear oscillations of a 3D radial symmetric Bose-Einstein condensate under periodic variation in time of the atomic scattering length have been studied. The time-dependent variational approach is used for the analysis of the characteristics of nonlinear resonances in the oscillations of the condensate. The bistability in oscillations of the BEC width is investigated. The dependence of the BEC collapse threshold on the drive amplitude and parameters of the condensate and trap is found. Predictions of the theory are confirmed by numerical simulations of the full Gross-Pitaevskii equation.

Positronium-positronium interaction: resonance, scattering length, and Bose-Einstein condensation

The low-energy scattering of ortho positronium (Ps) by ortho Ps has been studied in a full quantum mechanical coupled-channel approach. In the singlet channel (total spin s(T) = 0) we find S- and P-wave resonances at 3.35 eV (width 0.02 eV) and 5.05 eV (width 0.04 eV), respectively, and a binding of 0.43 eV of Ps(2). The scattering length for s(T) = 0 is 3.95 Angstrom and for s(T) = 2 is 0.83 Angstrom. The small s(T) = 2 scattering length makes the spin-polarized ortho Ps atoms an almost noninteracting ideal gas which may undergo Bose-Einstein condensation. (C) 2002 Elsevier B.V. B.V. All rights reserved.

Bose-Einstein condensates in 2D with time-periodic scattering length

We discuss two-dimensional Bose-Einstein Condensates (BEC) under time-periodic variation of the scattering length. In particular we argue that for high-frequency variation there exist stable self-confined condensates without an external trap, when the do component of the scattering length is negative. Our results are based on a variational approximation, on direct averaging of the Gross-Pitaevskii equation and on numerical simulations.

Macroscopic quantum tunneling and resonances in coupled Bose-Einstein condensates with oscillating atomic scattering length

We study the macroscopic quantum tunneling, self-trapping phenomena in two weakly coupled Bose-Einstein condensates with periodically time-varying atomic scattering length.The resonances in the oscillations of the atomic populations are investigated. We consider oscillations in the cases of macroscopic quantum tunneling and the self-trapping regimes. The existence of chaotic oscillations in the relative atomic population due to overlaps between nonlinear resonances is showed. We derive the whisker-type map for the problem and obtain the estimate for the critical amplitude of modulations leading to chaos. The diffusion coefficient for motion in the stochastic layer near separatrix is calculated. The analysis of the oscillations in the rapidly varying case shows the possibility of stabilization of the unstable pi-mode regime. (C) 2000 Published by Elsevier B.V. B.V. PACS: 03.75.Fi; 05.30.Jp.

Stabilization of bright solitons and vortex solitons in a trapless three-dimensional Bose-Einstein condensate by temporal modulation of the scattering length

Using variational and numerical solutions of the mean-field Gross-Pitaevskii equation we show that a bright soliton can be stabilized in a trapless three-dimensional attractive Bose-Einstein condensate (BEC) by a rapid periodic temporal modulation of scattering length alone by using a Feshbach resonance. This scheme also stabilizes a rotating vortex soliton in two dimensions. Apart from possible experimental application in BEC, the present study suggests that the spatiotemporal solitons of nonlinear optics in three dimensions can also be stabilized in a layered Kerr medium with sign-changing nonlinearity along the propagation direction.

Bose-Einstein condensates with inhomogeneous scattering length in one and two dimensions

We report on investigations of the properties of bright solitons in Bose-Einstein condensates in the presence of point-like spatial inhomogeneities, in one and two dimensions. By considering an analytical variational approach and full numerical simulations, we describe such processes due to interactions between the soliton and the inhomogeneity as the trapping, reflection, and transmission of bright matter solitons. We also study the critical number of particles as a function of the magnitude of the impurity.

Dipolar Bose-Einstein condensates with large scattering length

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Persistence Length, Mass Fractal, and Branching in the Aggregating of Vinyltriethoxysilane-Derived Organic/Silica Hybrids

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Percepção de distância em crianças durante a locomoção

O objetivo do presente estudo foi investigar a percepção de crianças sobre distância na ausência de informação visual durante a locomoção. Ainda, se parâmetros biomecânicos relativos à locomoção são alterados durante a locomoção nas diferentes distâncias. Sete crianças na idade de 6 anos (GC) e 10 adultos (GA) foram convidados a andar vendados até alvos pré-estabelecidos. O expoente da função de potência e parâmetros biomecânicos (Ex.: duração da passada, proporção da passada e velocidade da passada) foram obtidos para cada grupo. Diferenças foram encontradas somente para os valores de distância produzida ao longo das distâncias testadas. Nenhum dos parâmetros biomecânicos diferiu entre GC e GA. Alterações quantitativas foram observadas nos parâmetros biomecânicos para distâncias curtas, embora o padrão do movimento não tenha sido alterado. Crianças desta faixa etária demonstram, em tarefas não usuais (Ex.: locomoção sem visão), adaptabilidade e capacidade de orientar-se no espaço utilizando apenas da sensibilidade háptica e provavelmente da imagem mental-construída da observação feita antes da realização da tarefa sem informação visual.

Study of the length of the mouthparts of Africanized, Caucasian and Africanized/Caucasian honey bee crosses, and relationships between glossa sizeand food gathering behavior

Os comprimentos das peças que constituem o aparelho bucal, glossa, paraglossa, estipite, gálea, palpo labial, palpo maxilar, cardo, lorum, mento e pré-mento foram estudados a nível unidimensional em abelhas caucasianas, africanizadas e nos descendentes F1. Somente a paraglossa, estipite, gálea, palpo maxilar, mento e pré-mento mostraram ser diferentes entre esses 2 tipos de abelhas. Essas 6 variáveis foram estudadas nos descendentes F1, tendo sido utilizados 2 tipos de cruzamentos: rainhas caucasianas x machos africanizados (cruzamento 1) e rainhas africanizadas x machos caucasianos (cruzamento 2). Análises multidimensionais também foram realizadas, tendo sido obtidas as distâncias generalizadas de Mahalanobis (D2) entre os parentais e os descendentes F1. Tanto nas análises unidimensionais como nas multidimensionais houve aparente dominância das abelhas africanizadas, mas o número de genes não pôde ser conhecido porque só havia a geração F1 e não houve controle da heterozigosidade das 2 colônias parentais. Os cálculos dos coeficientes de correlações de Spearman mostraram que as abelhas com glossae mais longas coletaram mais xarope de açúcar e voaram mais lentamente da colônia para a fonte de alimento.

Effects of age at first calving, gestation length and dry period on milk yield in a Gyr herd

Relationships of several reproductve traits and milk yield were studied in 716 Gyr cows at Sant'Ana da Serra farm, Mococa, State of São Paulo, a humid tropical climate region. Mean age at first calving was 49.8 +/- 0.4 months, with a coeficient of cariation (C. V.) of 20.8%. Only year of parturition significantly affected age at first calving (P < 0.01). Heritability, estimated from paternal half-sib correlations, was 0.91 +/- 0.20, a value considered unrealistically high. Overall mean gestation length was 287.7 +/- 0.5 days (C. V. = 3.3%) for 419 observations, with month and year of parturition having significant effects. Heritability estimate was 0.30 +/- 0.14. Overall mean dry period for 1.276 observations was 238 +/- 3 days (C. V. = 48%); repeatability estimate was 0.19 +/- 0.06. Estimated annual genetic trend for dry period was -0.6 days, phenotypic trend was 11.5 days, and environmental trend, 12.1 days. Month and year of parturition and cow age had no significant effect on dry period. Highest milk yield was obtained at fourth lactation. The gross correlation between milk yield and gestation period was 0.11, and between previous dry period and subsequent milk yield, 0.16. Normal gestations of 285 to 290 days were associated with higher milk yields. Milk yield increased as dry period advanced from 30 to 390 days, and declined as dry period continued beyond 390 days. Delays in first mating and a more extensive dry period decreased reproductive efficiency in the herd studied.

Size and sex compositions, length-weight relationship, and occurrence of the Brazilian sharpnose shark, Rhizoprionodon lalandii, caught by artisanal fishery from southeastern Brazil

Although the Brazilian sharpnose shark, Rhizoprionodon lalandii (Muller and Henle, 1839), is an inshore species widely distributed in the Western Atlantic from Panama to Uruguay, there is little available information on its biology. During a long-term study of small coastal sharks caught by gill net fisheries in southeastern Brazil (PROJETO CACAO), 3643 specimens of R. lalandii were examined, comprising 61.3% of the total sharks,and including all sizes classes, from 30 to 78,5 cm TL., and weights from 100 to 2950 g. The length-weight relationships were not significantly different between sexes, Overall sex ratio favoured the males slightly at the rate of 1.3: 1. Sex ratios, however, did differ significantly between season and size classes. This species occurred in this area all year long. Three seasonal size-class Occurrence patterns were recognized: (1) between October and March, the juveniles were more frequents (2) from April to July, adults were most common, and (3) from August to September, neonates were most numerically abundant. Such patterns we to associated with reproductive tactics that may reduce intra-specific and inter-specific competition with hammerhead shark neonates (Sphyrna lewini). probably result in reduced natural mortality of the offspring during their first few months. (C) 2005 Elsevier B.V. All rights reserved.