3,467 research outputs found
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 scale as and where
and , independently of the growth
temperature.Comment: 15 pages, 7 figure
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 .
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
Superpulsed low-level laser therapy protects skeletal muscle of mdx mice against damage, inflammation and morphological changes delaying dystrophy progression.
Aim: To evaluate the effects of preventive treatment with low-level laser therapy (LLLT) on progression of dystrophy in mdx mice. Methods: Ten animals were randomly divided into 2 experimental groups treated with superpulsed LLLT (904 nm, 15 mW, 700 Hz, 1 J) or placebo-LLLT at one point overlying the tibialis anterior muscle (bilaterally) 5 times per week for 14 weeks (from 6th to 20th week of age). Morphological changes, creatine kinase (CK) activity and mRNA gene expression were assessed in animals at 20th week of age. Results: Animals treated with LLLT showed very few morphological changes in skeletal muscle, with less atrophy and fibrosis than animals treated with placebo-LLLT. CK was significantly lower (p = 0.0203) in animals treated with LLLT (864.70 U.lâ1, SEM 226.10) than placebo (1708.00 U.lâ1, SEM 184.60). mRNA gene expression of inflammatory markers was significantly decreased by treatment with LLLT (p<0.05): TNF-α (placebo-control = 0.51 ”g/”l [SEM 0.12], - LLLT = 0.048 ”g/”l [SEM 0.01]), IL-1ÎČ (placebo-control = 2.292 ”g/”l [SEM 0.74], - LLLT = 0.12 ”g/”l [SEM 0.03]), IL-6 (placebo-control = 3.946 ”g/”l [SEM 0.98], - LLLT = 0.854 ”g/”l [SEM 0.33]), IL-10 (placebo-control = 1.116 ”g/”l [SEM 0.22], - LLLT = 0.352 ”g/”l [SEM 0.15]), and COX-2 (placebo-control = 4.984 ”g/”l [SEM 1.18], LLLT = 1.470 ”g/”l [SEM 0.73]). Conclusion: Irradiation of superpulsed LLLT on successive days five times per week for 14 weeks decreased morphological changes, skeletal muscle damage and inflammation in mdx mice. This indicates that LLLT has potential to decrease progression of Duchenne muscular dystrophy
An Investigation of the -type Lorentz-Symmetry Breaking Gauge Models in -Supersymmetric Scenario
In this work, we present two possible venues to accomodate the -type
Lorentz-symmetry violating Electrodynamics in an -supersymmetric
framework. A chiral and a vector superfield are chosen to describe the
background that signals Lorentz-symmetry breaking. In each case, the -tensor is expressed in terms of the components of the
background superfield that we choose to describe the breaking. We also present
in detail the actions with all fermionic partners of the background that
determine .Comment: 10 page
The apparent roughness of a sand surface blown by wind from an analytical model of saltation
We present an analytical model of aeolian sand transport. The model
quantifies the momentum transfer from the wind to the transported sand by
providing expressions for the thickness of the saltation layer and the apparent
surface roughness. These expressions are derived from basic physical principles
and a small number of assumptions. The model further predicts the sand
transport rate (mass flux) and the impact threshold (the smallest value of the
wind shear velocity at which saltation can be sustained). We show that, in
contrast to previous studies, the present model's predictions are in very good
agreement with a range of experiments, as well as with numerical simulations of
aeolian saltation. Because of its physical basis, we anticipate that our model
will find application in studies of aeolian sand transport on both Earth and
Mars
Bioatividade de extratos de sisal (Agave Sisalana Perrine ex Engelm) sobre a oviposição de Ceratitis Capitata (Wiedemann, 1824) (DĂpTERA: Tephritidae).
O Brasil Ă© terceiro maior produtor de frutas do mundo, perdendo apenas para a China e Ăndia, produz frutas tropicais, subtropicais e temperadas. Um dos maiores problemas encontrados pela fruticultura internacional, sĂŁo espĂ©cies de praga s pertencentes Ă famĂlia dos tefritĂdeos
Uso de biofertilizante lĂquido na produção de alfafa
bitstream/CNPAB-2010/27430/1/doc151.pd
Soft lubrication: the elastohydrodynamics of non-conforming and conforming contacts
We study the lubrication of fluid-immersed soft interfaces and show that
elastic deformation couples tangential and normal forces and thus generates
lift. We consider materials that deform easily, due to either geometry (e.g. a
shell) or constitutive properties (e.g. a gel or a rubber), so that the effects
of pressure and temperature on the fluid properties may be neglected. Four
different system geometries are considered: a rigid cylinder moving parallel to
a soft layer coating a rigid substrate; a soft cylinder moving parallel to a
rigid substrate; a cylindrical shell moving parallel to a rigid substrate; and
finally a cylindrical conforming journal bearing coated with a thin soft layer.
In addition, for the particular case of a soft layer coating a rigid substrate
we consider both elastic and poroelastic material responses. For all these
cases we find the same generic behavior: there is an optimal combination of
geometric and material parameters that maximizes the dimensionless normal force
as a function of the softness parameter = hydrodynamic pressure/elastic
stiffness = surface deflection/gap thickness which characterizes the
fluid-induced deformation of the interface. The corresponding cases for a
spherical slider are treated using scaling concepts.Comment: 61 pages, 20 figures, 2 tables, submitted to Physics of Fluid
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