Self-dual Hopfions

We construct static and time-dependent exact soliton solutions with non-trivial Hopf topological charge for a field theory in 3+1 dimensions with the target space being the two dimensional sphere S**2. The model considered is a reduction of the so-called extended Skyrme-Faddeev theory by the removal of the quadratic term in derivatives of the fields. The solutions are constructed using an ansatz based on the conformal and target space symmetries. The solutions are said self-dual because they solve first order differential equations which together with some conditions on the coupling constants, imply the second order equations of motion. The solutions belong to a sub-sector of the theory with an infinite number of local conserved currents. The equation for the profile function of the ansatz corresponds to the Bogomolny equation for the sine-Gordon model.Comment: plain latex, no figures, 23 page

Plasma Processing of Large Curved Surfaces for SRF Cavity Modification

Plasma based surface modification of niobium is a promising alternative to wet etching of superconducting radio frequency (SRF) cavities. The development of the technology based on Cl2/Ar plasma etching has to address several crucial parameters which influence the etching rate and surface roughness, and eventually, determine cavity performance. This includes dependence of the process on the frequency of the RF generator, gas pressure, power level, the driven (inner) electrode configuration, and the chlorine concentration in the gas mixture during plasma processing. To demonstrate surface layer removal in the asymmetric non-planar geometry, we are using a simple cylindrical cavity with 8 ports symmetrically distributed over the cylinder. The ports are used for diagnosing the plasma parameters and as holders for the samples to be etched. The etching rate is highly correlated with the shape of the inner electrode, radio-frequency (RF) circuit elements, chlorine concentration in the Cl2/Ar gas mixtures, residence time of reactive species and temperature of the cavity. Using cylindrical electrodes with variable radius, large-surface ring-shaped samples and d.c. bias implementation in the external circuit we have demonstrated substantial average etching rates and outlined the possibility to optimize plasma properties with respect to maximum surface processing effect

Conservação de pólen de cana-de-açúcar.

A conservação de pólen tem aplicações importantes no melhoramento genético de cana-de-açúcar. Entre as diversas aplicações, a realização de cruzamentos entre variedades assincrônicas no florescimento possibilita a exploração de novas combinações genéticas, isoladas pelas diferentes épocas de floração. Com o objetivo de viabilizar a realização de cruzamentos entre variedades assincrônicas no florescimento foi desenvolvida metodologia para coleta e conservação de pólen de cana-de-açúcar. A pesquisa foi conduzida em parceria entre Embrapa-Ridesa na Estação de Floração e Cruzamento Serra do Ouro, em Murici (AL) e em laboratórios, pertencentes à Embrapa Tabuleiros Costeiros e ao Programa de Melhoramento Genético de Cana-de-açúcar, localizado no Centro de Ciências Agrárias da Universidade Federal de Alagoas. Os grãos-de pólen foram conservados com controle de temperatura (Freezer a -18°C) e com redução de umidade (20% de teor de água). Quando analisada a viabilidade in vivo, através de cruzamentos com pólen armazenado por 30-60 dias, foram obtidas mais de uma centena de plantas (139). Parte destas plantas foram submetidas a Teste de Paternidade (19) e confirmaram a origem de pólen conservado (6). Estes resultados demonstram que é possível armazenar e manter viável o pólen de cana-de-açúcar para realizar cruzamentos entre variedades assincrônicas no florescimento em Alagoas/Brasil

Adaptive Optics Observations of the Galactic Center Young Stars

Adaptive Optics observations have dramatically improved the quality and versatility of high angular resolution measurements of the center of our Galaxy. In this paper, we quantify the quality of our Adaptive Optics observations and report on the astrometric precision for the young stellar population that appears to reside in a stellar disk structure in the central parsec. We show that with our improved astrometry and a 16 year baseline, including 10 years of speckle and 6 years of laser guide star AO imaging, we reliably detect accelerations in the plane of the sky as small as 70 microarcsec/yr/yr (~2.5 km/s/yr) and out to a projected radius from the supermassive black hole of 1.5" (~0.06 pc). With an increase in sensitivity to accelerations by a factor of ~6 over our previous efforts, we are able to directly probe the kinematic structure of the young stellar disk, which appears to have an inner radius of 0.8". We find that candidate disk members are on eccentric orbits, with a mean eccentricity of = 0.30 +/- 0.07. Such eccentricities cannot be explained by the relaxation of a circular disk with a normal initial mass function, which suggests the existence of a top-heavy IMF or formation in an initially eccentric disk.Comment: 7 pages, 4 figures, SPIE Astronomical Telescopes and Instrumentation 201