Squeezing generation and revivals in a cavity-ion system in contact with a reservoir

We consider a system consisting of a single two-level ion in a harmonic trap, which is localized inside a non-ideal optical cavity at zero temperature and subjected to the action of two external lasers. We are able to obtain an analytical solution for the total density operator of the system and show that squeezing in the motion of the ion and in the cavity field is generated. We also show that complete revivals of the states of the motion of the ion and of the cavity field occur periodically.Comment: 9 pages, 3 figure

X-ray spectral modelling of the AGN obscuring region in the CDFS: Bayesian model selection and catalogue

AGN are known to have complex X-ray spectra that depend on both the properties of the accreting SMBH (e.g. mass, accretion rate) and the distribution of obscuring material in its vicinity ("torus"). Often however, simple and even unphysical models are adopted to represent the X-ray spectra of AGN. In the case of blank field surveys in particular, this should have an impact on e.g. the determination of the AGN luminosity function, the inferred accretion history of the Universe and also on our understanding of the relation between AGN and their host galaxies. We develop a Bayesian framework for model comparison and parameter estimation of X-ray spectra. We take into account uncertainties associated with X-ray data and photometric redshifts. We also demonstrate how Bayesian model comparison can be used to select among ten different physically motivated X-ray spectral models the one that provides a better representation of the observations. Despite the use of low-count spectra, our methodology is able to draw strong inferences on the geometry of the torus. For a sample of 350 AGN in the 4 Ms Chandra Deep Field South field, our analysis identifies four components needed to represent the diversity of the observed X-ray spectra: (abridged). Simpler models are ruled out with decisive evidence in favour of a geometrically extended structure with significant Compton scattering. Regarding the geometry of the obscurer, there is strong evidence against both a completely closed or entirely open toroidal geometry, in favour of an intermediate case. The additional Compton reflection required by data over that predicted by toroidal geometry models, may be a sign of a density gradient in the torus or reflection off the accretion disk. Finally, we release a catalogue with estimated parameters such as the accretion luminosity in the 2-10 keV band and the column density, $N_{H}$, of the obscurer.Comment: 28 pages, 18 figures, catalogue available from https://www.mpe.mpg.de/~jbuchner/agn_torus/analysis/cdfs4Ms_cat/, software available from https://github.com/JohannesBuchner/BX

Regeneração de espécies silvestres brasileiras de arroz através do cultivo de embrião.

O objetivo deste trabalho foi regenerar os acessos das espécies silvestres de arroz brasileiras através do cultivo de embriões

Low load Pt catalyst with surface functionalised carbon supports for PEM fuel cells: half and full cell asssessments

ABSTRACT: Current US DOE 2020 targets for electrocatalysts aim for a total platinum group metals (PGM) loading of 0.125 mgcm-2 on membrane-electrode assemblies. The catalysts are expected to endure an elevated number of load cycles in order to comply with the expected 5000 h stack lifetime. At the stated PGM low loading attributes of performance, power and durability, as well as costs, are simultaneously required. The present paper deals with performance assessment of new catalyst using Pt nanoparticles and a surface functionalized carbon support. Due to its relevance to fuel cell operation, the stability and durability were assessed in half cell mode, through the application of demanding aging cycling protocols (30000 cycles). Full fuel cell assessments were also conducted entailing power density curves and cell electrochemical impedance. Results denote significant improvements in cell performance as well as in catalyst stability, regarding a commercial catalyst tested in the same conditions, at Pt loadings of 0.1 mgcm-2.N/

Implantação de desenvolvimento da produção integrada de mandioca em cinco regiões produtoras do Brasil.

Publicado também na: RAT: Revista Raízes e Amidos Tropicais, v. 3, 2007. (SEP 040)