Galerkin-Laguerre Spectral Solution of Self-Similar Boundary Layer Problems

In this work the Laguerre basis for the biharmonic equation introduced by Jie Shen is employed in the spectral solution of self-similar problems of the boundary layer theory. An original Petrov-Galerkin formulation of the Falkner-Skan equation is presented which is based on a judiciously chosen special basis function to capture the asymptotic behaviour of the unknown. A spectral method of remarkable simplicity is obtained for computing Falkner-Skan-Cooke boundary layer flows. The accuracy and efficiency of the Laguerre spectral approximation is illustrated by determining the linear stability of nonseparated and separated flows according to the Orr-Sommerfeld equation. The pentadiagonal matrices representing the derivative operators are explicitly provided in an Appendix to aid an immediate implementation of the spectral solution algorithms

The three-body recombination of a condensed Bose gas near a Feshbach resonance

In this paper, we study the three-body recombination rate of a homogeneous dilute Bose gas with a Feshbach resonance at zero temperature. The ground state and excitations of this system are obtained. The three-body recombination in the ground state is due to the break-up of an atom pair in the quantum depletion and the formation of a molecule by an atom from the broken pair and an atom from the condensate. The rate of this process is in good agreement with the experiment on $^{23}$Na in a wide range of magnetic fields.Comment: 10 pages, 2 figures, to be published in Phys. Rev.

Casimir-like tunneling-induced electronic forces

We study the quantum forces that act between two nearby conductors due to electronic tunneling. We derive an expression for these forces by calculating the flux of momentum arising from the overlap of evanescent electronic fields. Our result is written in terms of the electronic reflection amplitudes of the conductors and it has the same structure as Lifshitz's formula for the electromagnetically mediated Casimir forces. We evaluate the tunneling force between two semiinfinite conductors and between two thin films separated by an insulating gap. We discuss some applications of our results.Comment: 8 pages, 3 figs, submitted to Proc. of QFEXT'05, to be published in J. Phys.

Multiphysics analyses of the effect of package on the performances of PMUT transducers

The paper deals with the multiphysics modeling of piezoelectric micromachined ultrasound transducers (PMUT), that can be used in several practical applications. The model accounts for the multiple couplings between the mechanical fields and the electric and acoustic ones. The numerical solution has been sought by means of the finite element method, for the special case of axial symmetry. The model has been validated with reference to experimental data, that have been obtained by the Authors. The numerical procedure has been applied to carry out a parametric analysis of the effect of package, to extract a set of design guidelines

A 20 GHz bright sample for {\delta} > +72{\deg}: I. Catalogue

During 2010-2011, the Medicina 32-m dish hosted the 7-feed 18-26.5 GHz receiver built for the Sardinia Radio Telescope, with the goal to perform its commissioning. This opportunity was exploited to carry out a pilot survey at 20 GHz over the area for {\delta} > + 72.3{\deg}. This paper describes all the phases of the observations, as they were performed using new hardware and software facilities. The map-making and source extraction procedures are illustrated. A customised data reduction tool was used during the follow-up phase, which produced a list of 73 confirmed sources down to a flux density of 115 mJy. The resulting catalogue, here presented, is complete above 200 mJy. Source counts are in agreement with those provided by the AT20G survey. This pilot activity paves the way to a larger project, the K-band Northern Wide Survey (KNoWS), whose final aim is to survey the whole Northern Hemisphere down to a flux limit of 50 mJy (5{\sigma}).Comment: 10 pages, 10 figures. Accepted by MNRA

Efeito da palhada de trigo na emergência de digitaria insularis (capim-amargoso).

Herbicidas são importantes alternativas de controle, mas devem ser utilizados como parte integrante de um programa de manejo de plantas daninhas. Resultados de pesquisas mostram que o controle químico das plantas daninhas na Soja RR é facilitado ao ser integrado com outras práticas, especialmente como o cultivo de espécies que possibilitem a formação de palhada. Foram conduzidos dois experimentos em casa de vegetação , com o objetivo de avaliar os efeitos da palhada de trigo sobre a emergência de capim-amargoso, uma espécie que está se disseminado nas áreas de produção e apresenta biótipos resistentes ao glifosato. Cinquenta sementes viáveis de capim-amargoso foram semeadas em vasos plásticos com capacidade de 3,5 L, preparado com três partes de terra e uma parte de composto orgânico associado a adubo formulado. No primeiro experimento o solo foi superficialmente coberto com palha de trigo picada, tendo sido estabelecidas oito diferentes quantidades, cada uma representando um tratamento: 1. Sem cobertura ou 0 tonelada/ha; 2. Equivalente a 1 tonelada/ha; 3. Equivalente a 2 toneladas/ha; 4. Equivalente a 3 toneladas/ha; 5. Equivalente a 4 toneladas/ha; 6. O segundo experimento foi instalado com os mesmos tratamentos, adicionando-se mais um com o equivalente a 8 toneladas/há. Foi possível concluir que a palhada de trigo pode ser uma alternativa para compor o manejo integrado em áreas infestadas com capim-amargoso, desde que seja em quantidade igual ou superior a 4 toneladas por hectare