Kinetic modelling of epitaxial film growth with up- and downward step barriers

The formation of three-dimensional structures during the epitaxial growth of films is associated to the reflection of diffusing particles in descending terraces due to the presence of the so-called Ehrlich-Schwoebel (ES) barrier. We generalize this concept in a solid-on-solid growth model, in which a barrier dependent on the particle coordination (number of lateral bonds) exists whenever the particle performs an interlayer diffusion. The rules do not distinguish explicitly if the particle is executing a descending or an ascending interlayer diffusion. We show that the usual model, with a step barrier in descending steps, produces spurious, columnar, and highly unstable morphologies if the growth temperature is varied in a usual range of mound formation experiments. Our model generates well-behaved mounded morphologies for the same ES barriers that produce anomalous morphologies in the standard model. Moreover, mounds are also obtained when the step barrier has an equal value for all particles independently if they are free or bonded. Kinetic roughening is observed at long times, when the surface roughness w and the characteristic length $\xi$ scale as $w ~ t^\beta$ and $\xi ~ t^\zeta$ where $\beta \approx 0.31$ and $\zeta \approx 0.22$, independently of the growth temperature.Comment: 15 pages, 7 figure

Spin-orbit mode transfer via a classical analog of quantum teleportation

We translate the quantum teleportation protocol into a sequence of coherent operations involving three degrees of freedom of a classical laser beam. The protocol, which we demonstrate experimentally, transfers the polarisation state of the input beam to the transverse mode of the output beam. The role of quantum entanglement is played by a non-separable mode describing the path and transverse degrees of freedom. Our protocol illustrates the possibility of new optical applications based on this intriguing classical analogue of quantum entanglement.Comment: 5 pages, 7 figure

Photometric Variability of the Disk Integrated Infrared Emission of the Earth

We present an analysis of the global-integrated mid-infrared emission flux of the Earth based on data derived from satellite measurements. We have studied the photometric annual, seasonal, and rotational variability of the thermal emission of the Earth to determine which properties can be inferred from the point-like signal. We find that the analysis of the time series allows us to determine the 24 hr rotational period of the planet for most observing geometries, due to large warm and cold areas, identified with geographic features, which appear consecutively in the observer's planetary view. However, the effects of global-scale meteorology can effectively mask the rotation for several days at a time. We also find that orbital time series exhibit a seasonal modulation, whose amplitude depends strongly on the latitude of the observer but weakly on its ecliptic longitude. As no systematic difference of brightness temperature is found between the dayside and nightside, the phase variations of the Earth in the infrared range are negligible. Finally, we also conclude that the phase variation of a spatially unresolved Earth-Moon system is dominated by the lunar signal.Comment: 11 pages, 10 figures. Accepted for publication in Ap

Modelling of epitaxial film growth with a Ehrlich-Schwoebel barrier dependent on the step height

The formation of mounded surfaces in epitaxial growth is attributed to the presence of barriers against interlayer diffusion in the terrace edges, known as Ehrlich-Schwoebel (ES) barriers. We investigate a model for epitaxial growth using a ES barrier explicitly dependent on the step height. Our model has an intrinsic topological step barrier even in the absence of an explicit ES barrier. We show that mounded morphologies can be obtained even for a small barrier while a self-affine growth, consistent with the Villain-Lai-Das Sarma equation, is observed in absence of an explicit step barrier. The mounded surfaces are described by a super-roughness dynamical scaling characterized by locally smooth (faceted) surfaces and a global roughness exponent $\alpha>1$. The thin film limit is featured by surfaces with self-assembled three-dimensional structures having an aspect ratio (height/width) that may increase or decrease with temperature depending on the strength of step barrier.Comment: To appear in J. Phys. Cond. Matter; 3 movies as supplementary materia

Interacting Particles and Strings in Path and Surface Representations

Non-relativistic charged particles and strings coupled with abelian gauge fields are quantized in a geometric representation that generalizes the Loop Representation. We consider three models: the string in self-interaction through a Kalb-Ramond field in four dimensions, the topological interaction of two particles due to a BF term in 2+1 dimensions, and the string-particle interaction mediated by a BF term in 3+1 dimensions. In the first case one finds that a consistent "surface-representation" can be built provided that the coupling constant is quantized. The geometrical setting that arises corresponds to a generalized version of the Faraday's lines picture: quantum states are labeled by the shape of the string, from which emanate "Faraday`s surfaces". In the other models, the topological interaction can also be described by geometrical means. It is shown that the open-path (or open-surface) dependence carried by the wave functional in these models can be eliminated through an unitary transformation, except by a remaining dependence on the boundary of the path (or surface). These feature is closely related to the presence of anomalous statistics in the 2+1 model, and to a generalized "anyonic behavior" of the string in the other case.Comment: RevTeX 4, 28 page

Qualidade da água subterrânea para fins de irrigação na microrregião de Teresina, Piauí.

O presente estudo teve por objetivo a realização de um levantamento das características físicas, químicas e físico-químicas das águas subterrâneas da Bacia Sedimentar do Rio Parnaíba, em especial aquelas características relevantes para a determinação da qualidade dessas águas para fins de irrigação. Foram coletadas amostras de água em 270 poços georreferenciados localizados em 14 municípios da Microrregião de Teresina-PI. As amostras foram coletadas em duas épocas distintas, ou seja, nas estações secas de 2004 e de 2005. Nessas amostras foram realizadas determinações dos seguintes parâmetros: pH, NH4+, NO3-, Ca2+, Mg2+, CE, RAS, Na+, Cloretos, Bicarbonatos e Carbonatos. Os resultados foram interpolados em um SIG (Sistemas de Informações Geográficas) – SPRING – com o objetivo de constituir mapas temáticos mostrando as classes de restrição das águas para fins de irrigação. Dentre os resultados obtidos, a análise conjunta de RAS e CE revelou potenciais problemas de infiltração da água no solo em mais da metade dos municípios, mostrando a necessidade de um manejo adequado da irrigação com vistas a mitigar os problemas nessas áreas

Delimitação de área para instalação de dessalinizadores no sudeste piauiense.

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Nontyphoidal Salmonella Gastroenteritis in Children: a 10 Year Review

Introdução: A Salmonella não tifoide é o agente mais frequente das toxinfeções alimentares nos países desenvolvidos. Em Portugal, são notificados em média 450 casos por ano, 80% dos quais em crianças. Métodos: Revisão casuística dos casos confirmados por coprocultura, internados num hospital do grupo I, na região de Lisboa e Vale do Tejo, entre 1999 e 2008. Análise estatística no programa SPSS® v16.0, com aplicação do teste de Spearman e significância estatística para p< 0,05. Resultados: Identificaram-se 213 internamentos. A mediana anual foi de 21 internamentos, 39% ocorrendo no verão. A mediana das idades foi de 4,2 anos, com doze casos em lactentes até aos três meses. Houve um predomínio no sexo masculino (57%). A mediana do total de leucócitos foi de 9300/mL e da proteína C reativa de 8,8 mg/dL, não se relacionando com a ocorrência de bacteriemia. A duração média do internamento foi de 5,2 dias. As principais complicações foram desidratação (117/213), bacteriemia (8/213), convulsão febril (6/213), síndrome de Mallory-Weiss (5/213) e apendicite aguda (3/213). Os serotipos mais isolados foram: S. Enteritidis (76%), S. Typhimurium (19%), outros (S. O4,5:i-, S. Derby, S. Hayfa, S. Menden, S. Rissen) (5%). Encontraram-se 27% de resistências à ampicilina e 15% ao trimetoprim-sulfametoxazol, sem resistências ao ceftriaxone. Conclusões: Nos 10 anos estudados, o número de casos manteve-se elevado, com morbilidade relevante e resistências significativas aos antibióticos de primeira linha