31,596 research outputs found
Exchange coupling between magnetic layers across non-magnetic superlattices
The oscillation periods of the interlayer exchange coupling are investigated
when two magnetic layers are separated by a metallic superlattice of two
distinct non-magnetic materials. In spite of the conventional behaviour of the
coupling as a function of the spacer thickness, new periods arise when the
coupling is looked upon as a function of the number of cells of the
superlattice. The new periodicity results from the deformation of the
corresponding Fermi surface, which is explicitly related to a few controllable
parameters, allowing the oscillation periods to be tuned.Comment: 13 pages; 5 figures; To appear in J. Phys.: Cond. Matte
A model for Hopfions on the space-time S^3 x R
We construct static and time dependent exact soliton solutions for a theory
of scalar fields taking values on a wide class of two dimensional target
spaces, and defined on the four dimensional space-time S^3 x R. The
construction is based on an ansatz built out of special coordinates on S^3. The
requirement for finite energy introduces boundary conditions that determine an
infinite discrete spectrum of frequencies for the oscillating solutions. For
the case where the target space is the sphere S^2, we obtain static soliton
solutions with non-trivial Hopf topological charges. In addition, such hopfions
can oscillate in time, preserving their topological Hopf charge, with any of
the frequencies belonging to that infinite discrete spectrum.Comment: Enlarged version with the time-dependent solutions explicitly given.
One reference and two eps figures added. 14 pages, late
ECOFISIOLOGIA DE MILLETTIA STUHLMANNII TAUB EM DIFERENTES DEMANDAS ATMOSFÉRICAS E DISPONIBILIDADES HÍDRICAS NO SOLO
No cenário florestal moçambicano diversas espécies nativas tem revelado potencial para a expansão silvicultural. Entre as espécies destaca-se a Millettia stuhlmannii (conhecida vulgarmente por panga-panga) com alto valor comercial e que tem contribuído para a economia do país. Contudo, há carência de estudos sobre o comportamento ecofisiológico desta espécie frente às condições edafoclimáticas, fato que pode comprometer o sucesso de novos projetos. Assim, o presente trabalho teve como objetivo investigar a ecofisiologia de Millettia stuhlmannii em diferentes demandas atmosféricas e disponibilidades hídricas no solo. O estudo foi realizado em casas de vegetação climatizadas, localizadas na área experimental do Departamento de Ciências Florestais e da Madeira, no Centro de Ciências Agrárias da Universidade Federal do Espírito Santo, situado no município de Jerônimo Monteiro ES, utilizando delineamento experimental inteiramente casualizado em esquema fatorial 2x4, sendo o fator demanda atmosférica em dois níveis (Alta e Baixa) e o fator disponibilidade hídrica no solo em quatro níveis da água disponível (100, 80, 60 e 40%), com cinco repetições. No final do experimento foram avaliadas as seguintes variáveis morfológicas: massa seca total, massa seca da parte aérea, massa seca radicular, área foliar, área foliar especifica, fração de massa foliar, fração de massa radicular, fração de massa da parte aérea, razão da área foliar, relação massa seca radicular por massa seca da parte aérea e eficiência do uso da água de produtividade; variáveis fisiológicas: taxa fotossintética líquida, condutância estomática, concentração interna de CO2 e transpiração e teores dos pigmentos fotossintéticos: clorofila a, clorofila b, clorofila a+b, carotenóides, razão clorofila a/clorofila b e clorofila a+b por carotenóides. Os dados foram comparados através do modelo de regressão por meio de teste de identidade de modelos, de acordo com Chow (1960) para crescimento. Para as trocas gasosas e pigmentos fotossintéticos, foi realizado teste de Tukey (P≤0,05) usando software SISVAR 5.1 de Furtado (2011). A espécie apresentou diminuição da massa seca total, massa seca da parte aérea, área foliar, fração de massa foliar, razão de área foliar, fração de massa da parte aérea com a redução da disponibilidade hídrica no solo independente da demanda atmosférica; e aumento da massa seca radicular, razão massa seca radicular por massa seca da parte aérea, área foliar específica, fração de massa radicular, eficiência do uso da água de produtividade com a redução da disponibilidade hídrica no solo independente da demanda atmosférica. Porém, o maior acúmulo de massa seca total, maior área foliar e eficiência do uso da água de produtividade foi observado na alta demanda atmosférica. Para as trocas gasosas, a taxa fotossintética líquida, condutância estomática e transpiração foram maiores sob alta demanda atmosférica e o contrário foi observado para a concentração interna de CO2. Nos pigmentos fotossintéticos, houve a diminuição do teor com a redução da disponibilidade hídrica no solo independente da demanda atmosférica na clorofila a, b, clorofila a+b, carotenóides, relação clorofila a/b e clorofila a+b/Carot. Assim, a espécie teve maior desempenho na alta demanda atmosférica, o que revela se adequar as condições de clima tropical
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
Aggregation in a mixture of Brownian and ballistic wandering particles
In this paper, we analyze the scaling properties of a model that has as
limiting cases the diffusion-limited aggregation (DLA) and the ballistic
aggregation (BA) models. This model allows us to control the radial and angular
scaling of the patterns, as well as, their gap distributions. The particles
added to the cluster can follow either ballistic trajectories, with probability
, or random ones, with probability . The patterns were
characterized through several quantities, including those related to the radial
and angular scaling. The fractal dimension as a function of
continuously increases from (DLA dimensionality) for
to (BA dimensionality) for . However, the
lacunarity and the active zone width exhibt a distinct behavior: they are
convex functions of with a maximum at . Through the
analysis of the angular correlation function, we found that the difference
between the radial and angular exponents decreases continuously with increasing
and rapidly vanishes for , in agreement with recent
results concerning the asymptotic scaling of DLA clusters.Comment: 7 pages, 6 figures. accepted for publication on PR
Integrable theories and loop spaces: fundamentals, applications and new developments
We review our proposal to generalize the standard two-dimensional flatness
construction of Lax-Zakharov-Shabat to relativistic field theories in d+1
dimensions. The fundamentals from the theory of connections on loop spaces are
presented and clarified. These ideas are exposed using mathematical tools
familiar to physicists. We exhibit recent and new results that relate the
locality of the loop space curvature to the diffeomorphism invariance of the
loop space holonomy. These result are used to show that the holonomy is abelian
if the holonomy is diffeomorphism invariant.
These results justify in part and set the limitations of the local
implementations of the approach which has been worked out in the last decade.
We highlight very interesting applications like the construction and the
solution of an integrable four dimensional field theory with Hopf solitons, and
new integrability conditions which generalize BPS equations to systems such as
Skyrme theories. Applications of these ideas leading to new constructions are
implemented in theories that admit volume preserving diffeomorphisms of the
target space as symmetries. Applications to physically relevant systems like
Yang Mills theories are summarized. We also discuss other possibilities that
have not yet been explored.Comment: 64 pages, 8 figure
Social support and mental health of young people in residential care: a qualitative study
The literature suggests the positive role of social support in mental health in residential care. However, most of the studies are focused on psychopathology and fewer on well-being. Also, theoretically-oriented and multidimensional studies on social support are needed. To address these problems, a qualitative study was developed with 29 young people in residential care (76% males), aged from 12 to 19 years old. Data was collected with a semi-structured interview. Results showed young people identify meaningful sources of social support (peers, residential care, and family), considering them available and effective support providers. Social support was also identified as an enhancer of positive psychological functioning and as a buffer of psychological functioning problems. Future research should involve more systematic, multidimensional approaches, both in assessing social support and in mental health. Important implications are recognized for professionals in the justice system.info:eu-repo/semantics/publishedVersio
Local roughness exponent in the nonlinear molecular-beam-epitaxy universality class in one-dimension
We report local roughness exponents, , for three
interface growth models in one dimension which are believed to belong the
non-linear molecular-beam-epitaxy (nMBE) universality class represented by the
Villain-Lais-Das Sarma (VLDS) stochastic equation. We applied an optimum
detrended fluctuation analysis (ODFA) [Luis et al., Phys. Rev. E 95, 042801
(2017)] and compared the outcomes with standard detrending methods. We observe
in all investigated models that ODFA outperforms the standard methods providing
exponents in the narrow interval consistent
with renormalization group predictions for the VLDS equation. In particular,
these exponent values are calculated for the Clarke-Vvdensky and Das
Sarma-Tamborenea models characterized by very strong corrections to the
scaling, for which large deviations of these values had been reported. Our
results strongly support the absence of anomalous scaling in the nMBE
universality class and the existence of corrections in the form
of the one-loop renormalization group analysis
of the VLDS equation
Thermal inactivation of Byssochlamys nivea in pineapple nectar combined with preliminary high pressure treatments
Byssochlamys nivea is a thermal resistant filamentous fungi and potential micotoxin producer. Recent studies have verified the presence of ascospores of such microorganism in samples of pineapple nectars. Although the majority of filamentous fungi have limited heat resistance and are easily destroyed by heat, Byssochlamys nivea ascospores have shown high thermal resistance. The aim of this work was to evaluate the application of linear and Weibull models on thermal inactivation (70, 80 and 90ºC) of Byssochlamys nivea ascospores in pineapple nectar after pretreatment with high pressure (550MPa or 650MPa during 15min). Following the treatments, survival curves were built up for each processing temperature and adjusted for both models. It was observed that survival curves at 90°C after high pressure pretreatment at 550 MPa/15 min did not fit well to linear and Weibull models. For all the other treatments, the Weibull model presented a better fit. At 90ºC without pressure treatment, the Weibull model also showed a better adjustment, having a larger R2 and a smaller RMSE. Regarding the process effectiveness, a 5-log reduction (t5), as recommended for pasteurization, was only achieved for Byssochlamys nivea ascospores presented in pineapple nectar at 90ºC/10.7 min with previous high pressure treatment of 650 MPa for 15 min. Considering the high intensity and energy demanding process with possibly product damage, other preventive and alternative treatments are being investigated
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