Three-dimensional Dirac oscillator in a thermal bath

The thermal properties of the three-dimensional Dirac oscillator are considered. The canonical partition function is determined, and the high-temperature limit is assessed. The degeneracy of energy levels and their physical implications on the main thermodynamic functions are analyzed, revealing that these functions assume values greater than the one-dimensional case. So that at high temperatures, the limit value of the specific heat is three times bigger.Comment: 9 pages, 4 figures. Text improved, references added. Revised to match accepted version in Europhysics Letters

Relation Discovery from Web Data for Competency Management

This paper describes a technique for automatically discovering associations between people and expertise from an analysis of very large data sources (including web pages, blogs and emails), using a family of algorithms that perform accurate named-entity recognition, assign different weights to terms according to an analysis of document structure, and access distances between terms in a document. My contribution is to add a social networking approach called BuddyFinder which relies on associations within a large enterprise-wide "buddy list" to help delimit the search space and also to provide a form of 'social triangulation' whereby the system can discover documents from your colleagues that contain pertinent information about you. This work has been influential in the information retrieval community generally, as it is the basis of a landmark system that achieved overall first place in every category in the Enterprise Search Track of TREC2006

Adolescent and adult pregnant women: different risk circumstances?

Resumo: Este estudo teve por objectivo caracterizar as circunstâncias em que decorre a gravidez na adolescência e na idade adulta e analisar as principais diferenças, ao nível das condições demográficas, sociais, anteriores de existência e actuais da gravidez. Uma amostra de 130 utentes da Maternidade Júlio Dinis (Porto) (66 grávidas adolescentes e 64 grávidas adultas) foi entrevistada através da Contextual Assessment of the Maternity Experience (CAME, Bernazzani, Marks, Siddle, Asten, Bifulco, et al, 2004), no último trimestre de gravidez. Os resultados mostram que à gravidez na adolescência se associa um elevado número de condições menos favoráveis, que podem comprometer a gestação e os cuidados ao bebé, como por exemplo: desemprego, monoparentalidade, consumo de tabaco, condições anteriores de existência adversas e gravidez não desejada. No entanto, outras circunstâncias adversas estão associadas à gravidez na idade adulta, como seja: história de problemas de fertilidade e de problemas psicológicos com tratamento ou internamento e ausência por morte de pelo menos um dos pais. Conclui-se que um número considerável de grávidas adolescentes vive em condições desfavoráveis, pelo que, não obstante a sua variabilidade, o grupo enquanto um todo pode ser considerado de risco, quando comparado ao grupo de grávidas adultas. Conclui-se ainda que grávidas adolescentes e adultas vivem a gravidez em condições específicas; observam-se diferentes circunstâncias de risco junto de cada um destes dois grupo, que devem ser atendidas na adequação da ajuda prestada pelos técnicos de saúde às reais necessidades das mães.Financiado pela Fundação para a Ciência e Tecnologia (POCTI/S/SAU/14109/98) e Serviço de Saúde e Desenvolvimento Humano da Fundação Calouste Gulbenkian (Proc. 48914/02-04

Combustion behavior of Jet-A1 single droplets and its blends with Hydroprocessed Vegetable Oil in a drop tube furnace

The aeronautical sector contributes significantly to greenhouse gases and pollutant emissions. The negative impact of these emissions in the environment has raised awareness for the introduction of alternative and greener fuels. The implementation of alternative fuels remains one of the main challenges for this sector in the near future. The aeronautical industry is characterized by the dependence on single fossil fuel and by a long service time of its assets. For these reasons, the main research drive has been around the development of “drop-in” fuels, which are alternative fuels that can be used in the already existing fleet without significant modifications. One of the proposed solutions is the blending of biofuels with jet fuel, which would allow the use of greener fuels and a reduction in greenhouse gases and emissions without significant changes in the existing companies’ fleets. In this context, the present work evaluates the ignition and the combustion of single droplets of jet-fuel, hydroprocessed vegetable oil (NExBTL), and their mixtures in a drop tube furnace. The main research focus of this study is to evaluate the influence of the mixture composition in the fuel-burning characteristics. Droplets with diameters of 155 ± 5 μm, produced by a commercial droplet generator, were injected into the top of the drop tube furnace. Three temperatures were investigated 900, 1000, and 1100 °C. The ignition and combustion of the droplets were evaluated through the images obtained with a high-speed camera (CR600x2) coupled with a high magnification lens (Navitar 6000 zoom lens) and treated with an edge detection algorithm. The images allowed for the observation of the burning phenomena, and the data reported the temporal evolution of the droplet sizes and burning rates. The pure fuels and mixtures followed the D2 law, except for the mixture with 75% jet-fuel/ 25% biofuel at 1100 °C that reveals disruptive burning phenomena contributing to the enhancement of the single droplet combustion. The disruptive burning phenomena are related to the appearance of “puffing” and micro-explosions at the end of the droplet lifetime.Fundação para a Ciência e a Tecnologiainfo:eu-repo/semantics/publishedVersio

Direct observation of melting in a 2-D superconducting vortex lattice

Topological defects such as dislocations and disclinations are predicted to determine the twodimensional (2-D) melting transition. In 2-D superconducting vortex lattices, macroscopic measurements evidence melting close to the transition to the normal state. However, the direct observation at the scale of individual vortices of the melting sequence has never been performed. Here we provide step by step imaging through scanning tunneling spectroscopy of a 2-D system of vortices up to the melting transition in a focused-ion-beam nanodeposited W-based superconducting thin film. We show directly the transition into an isotropic liquid below the superconducting critical temperature. Before that, we find a hexatic phase, characterized by the appearance of free dislocations, and a smectic-like phase, possibly originated through partial disclination unbinding. These results represent a significant step in the understanding of melting of 2-D systems, with impact across several research fields, such as liquid crystal molecules, or lipids in membranes.Comment: Submitted to Nature Physic