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

Loop representation of charged particles interacting with Maxwell and Chern-Simons fields

The loop representation formulation of non-relativistic particles coupled with abelian gauge fields is studied. Both Maxwell and Chern-Simons interactions are separately considered. It is found that the loop-space formulations of these models share significant similarities, although in the Chern-Simons case there exists an unitary transformation that allows to remove the degrees of freedom associated with the paths. The existence of this transformation, which allows to make contact with the anyonic interpretation of the model, is subjected to the fact that the charge of the particles be quantized. On the other hand, in the Maxwell case, we find that charge quantization is necessary in order to the geometric representation be consistent.Comment: 6 pages, improved versio

Orientation dynamics of weakly Brownian particles in periodic viscous flows

Evolution equations for the orientation distribution of axisymmetric particles in periodic flows are derived in the regime of small but non-zero Brownian rotations. The equations are based on a multiple time scale approach that allows fast computation of the relaxation processes leading to statistical equilibrium. The approach has been applied to the calculation of the effective viscosity of a thin disk suspension in gravity waves.Comment: 16 pages, 7 eps figures include

Evaluating recommended audiometric changes to candidacy using the speech intelligibility index

INTRODUCTION: The National Institute of Health and Care Excellence (NICE) has derived candidacy guidelines for cochlear implants in the UK based on audiometric thresholds (90 dB HL or above at 2 and 4 kHz; hereafter referred to as the 90 dB HL criteria). Recent research has proposed that these criteria should be changed to 80 dB HL at 2 and 4 kHz (hereafter referred to as the 80 dB HL criteria) in the ear to be implanted. METHODS: In this study, we analysed aided SII scores derived for different hearing loss profiles falling within the current 90 dB HL criteria and equivalent profiles falling within the new 80 dB HL criteria. RESULTS: The aided SII scores demonstrated that the majority of potential hearing configurations falling within the new proposed 80 dB HL criteria have aided SII values of less than 0.65 (a recommended cut-off point below which there is not sufficient audibility to receive adequate benefit through hearing aids). CONCLUSIONS: This supports the proposed change to the 80 dB HL criterion level and also highlights the additional value of the SII score in supporting candidacy decisions for CI, especially for borderline candidates

A Geometric Approach to Massive p-form Duality

Massive theories of abelian p-forms are quantized in a generalized path-representation that leads to a description of the phase space in terms of a pair of dual non-local operators analogous to the Wilson Loop and the 't Hooft disorder operators. Special atention is devoted to the study of the duality between the Topologically Massive and the Self-Dual models in 2+1 dimensions. It is shown that these models share a geometric representation in which just one non local operator suffices to describe the observables.Comment: 26 pages, LaTeX. The discussion about the equivalence between the Proca model and two seldual models, with opposite spins, was eliminated. Typos correcte

Surface-Invariants in 2D Classical Yang-Mills Theory

We study a method to obtain invariants under area-preserving diffeomorphisms associated to closed curves in the plane from classical Yang-Mills theory in two dimensions. Taking as starting point the Yang-Mills field coupled to non dynamical particles carrying chromo-electric charge, and by means of a perturbative scheme, we obtain the first two contributions to the on shell action, which are area-invariants. A geometrical interpretation of these invariants is given.Comment: 17 pages, 2 figure

The stability of drop shapes for translation at zero Reynolds number through a quiescent fluid

Boundary-integral calculations are used to investigate the evolution of the shape of an initially nonspherical drop that translates at zero Reynolds through a quiescent, unbounded fluid. For finite capillary numbers, it is shown that the drop reverts to a sphere, provided the initial deformation is not too large. However, drops that are initially deformed to a greater extent are shown to deform continuously, forming an elongated shape with a tail when initially prolate, and a flattened shape with a cavity at the rear when initially oblate. The critical degree of deformation decreases as the capillary number increases and appears to be consistent with the results of Kojima et al. [Phys. Fluids 27, 19 (1984)], who showed that the spherical drop is unstable to infinitesimal disturbances in the limit Ca=∞

Efeito da complementação alimentar no pós-parto sobre o desempenho produtivo de cabritos Sem Raça Definida (SRD).

A presente pesquisa foi desenvolvida numa fazenda particular em Pe- trolina- PE, no período de maio a novembro de 1995, e objetivou avaliar o efeito da complementação alimentar de matrizes sem raça definida (SRD) sobre o desem- penho produtivo dos cabritos criados em caatinga não cercada. O delineamento experimental utilizado foi inteiramente casualizado com três tratamentos (T1 : pas- tagem nativa (PN); T2: PN + 25% de NDT e T3 PN + 50% de NDT) e 16 repetições cada. A complementação alimentar foi à base de feno de leucena (Leucaena leu- cocephala (Lam.) de Wit) e raspa de mandioca (Manihot esculenta Crantz.) forne- cida a partir do primeiro dia pós-parto. Para os três tratamentos, os pesos médios observados para os cabritos, do nascimento aos 168 dias de idade, foram estatis- ticamente iguais (P>0,05). A taxa geral de mortalidade de crias aos 112 dias de idade foi de 20,41 %o Não foi possível observar efeito dos tratamentos na taxa de sobrevivência das crias, uma vez que, as causas mais comuns de desaparecimen- to dos animais são roubos e predadores

Caracterização estrutural e paragenética do Campo Pegmatítico do Licungo (Mocuba, Moçambique): identificação de recursos base associados

Publicado em "A engenharia no combate à pobreza, pelo desenvolvimento e competitividade", ISBN 978-972-8826-19-2Geological thematic mapping in Licungo pegmatite field (Mocuba, Mozambique) has clarified the distribution of mineral resources in NYF hyperaluminous pegmatites and revealed its structural control. Two distinct spatial and deformational areas can be distinguished. In the north structural domain, large pegmatites are associated with early tangential tectonic. Besides feldspar with ceramic qualification, industrial beryl and gems are also non-systematic resources. Small pegmatite dykes predominate in the south domain and their emplacement is conditioned by later distensive phases (Dn+1 and Dn+2). Their economic interest comes from gem beryl enrichment and its crystallisation as true-blue varieties