767 research outputs found
Microscopic Theory of Damon-Eshbach Modes in Ferromagnetic Films
The surface spin wave branches in ferromagnetic films are studied using a
microscopic theory which considers both magnetic dipole-dipole and Heisenberg
exchange interactions. The dipole terms are expressed in a Hamiltonian
formalism, and the dipole sums are calculated in a rapidly convergent form. The
Damon-Eshbach surface modes are analyzed for different directions of the
spin-wave propagation and also for different ratios of the strength of the
dipole interactions relative to the exchange interactions. Numerical results
are presented using parameters for Fe and GdCl.Comment: 9 pages including figures, Revtex, to appear in the proceedings of
the ICM 200
Brazilian elections: voting for a scaling democracy
The proportional elections held in Brazil in 1998 and 2002 display identical
statistical signatures. In particular, the distribution of votes among
candidates includes a power-law regimen. We suggest that the rationale behind
this robust scaling invariance is a multiplicative process in which the voter's
choice for a candidate is governed by a product of probabilities.Comment: 4 pages, 2 figure
Spatial correlations in vote statistics: a diffusive field model for decision-making
We study the statistics of turnout rates and results of the French elections
since 1992. We find that the distribution of turnout rates across towns is
surprisingly stable over time. The spatial correlation of the turnout rates, or
of the fraction of winning votes, is found to decay logarithmically with the
distance between towns. Based on these empirical observations and on the
analogy with a two-dimensional random diffusion equation, we propose that
individual decisions can be rationalised in terms of an underlying "cultural"
field, that locally biases the decision of the population of a given region, on
top of an idiosyncratic, town-dependent field, with short range correlations.
Using symmetry considerations and a set of plausible assumptions, we suggest
that this cultural field obeys a random diffusion equation.Comment: 18 pages, 5 figures; added sociophysics references
Levantamento das patologias e monitorização do Arco-Cruzeiro da Igreja da Misericórdia de Aveiro
O estado de conservação das construções tradicionais motiva para um crescente interesse na recuperação e manutenção do património construído. Antes de mais, é importante obter uma visão geral da evolução temporal das construções permitindo assim a caracterização dos diversos aspectos estruturais e construtivos. Este trabalho foi desenvolvido com o objectivo de estudar as patologias associadas à nave principal da Igreja da Misericórdia de Aveiro e em particular as patologias associadas ao Arco-Cruzeiro que se encontra no interior desta, com o intuito de se estabelecer a melhor estratégia de monitorização dos danos estruturais a aplicar. Como resultado desta análise foi proposto e implementado um plano de monitorização, com o desenvolvimento de meios de instrumentação, que permitem monitorizar o comportamento estrutural do arco, de forma não intrusiva, garantindo a reversibilidade e a eventual futura extensão da instrumentação. Foi ainda desenvolvido um modelo numérico em elementos finitos que serviu de apoio à interpretação das causas dos danos estruturais encontrados
Antisymmetric Tensor Fields in Randall Sundrum Thick Branes
In this article we study the issue of localization of the three-form field in
a Randall-Sundrum-like scenario. We simulate our membrane by kinks embedded in
D=5, describing the usual case (not deformed) and new models coming from a
specific deformation procedure. The gravitational background regarded includes
the dilaton contribution. We show that we can only localize the zero-mode of
this field for a specific range of the dilaton coupling, even in the deformed
case. A study about resonances is presented. We use a numerical approach for
calculations of the transmission coefficients associated to the quantum
mechanical problem. This gives a clear description of the physics involved in
the model. We find in this way that the appearance of resonances is strongly
dependent on the coupling constant. We study the cases and 5 for
and . The first value of give us one
resonance peak for and no resonances for . The second value of
give us a very rich structure of resonances, with number deppending on
the value of .Comment: 7 pages, 3 figure
Pattern Selection in a Phase Field Model for Directional Solidification
A symmetric phase field model is used to study wavelength selection in two
dimensions. We study the problem in a finite system using a two-pronged
approach. First we construct an action and, minimizing this, we obtain the most
probable configuration of the system, which we identify with the selected
stationary state. The minimization is constrained by the stationary solutions
of stochastic evolution equations and is done numerically. Secondly, additional
support for this selected state is obtained from straightforward simulations of
the dynamics from a variety of initial states.Comment: 7 pages, 6 figures, to appear in Physica
Transforming growth factor-β (TGF-β) maintains follicular ultrastructure and stimulates preantral follicle growth in caprine ovarian tissue cultured in vitro
O objetivo desse estudo foi investigar se o TGF-β afeta a sobrevivência, ativação e crescimento de folículos primordiais caprinos inclusos no córtex ovariano após o cultivo in vitro. Ovários de cabras foram coletados em abatedouro e fragmentos de tecido ovariano foram cultivados por um e sete dias em meio essencial mínimo alfa (α-MEM+) sozinho ou suplementado com TGF-β (1, 5, 10 ou 50ng/mL). Fragmentos ovarianos não cultivados e cultivados foram processados para análise histológica e ultraestrutural. Os resultados mostraram que, comparado ao controle fresco, houve diminuição no percentual de folículos morfologicamente normais em todos os tratamentos somente após sete dias de cultivo. O TGF-β não afetou a ativação folicular independente da concentração testada, contudo, o diâmetro folicular foi superior (P<0.05) no tratamento com 10ng/mL de TGF-β quando comparado ao controle fresco e aos demais tratamentos. Além disso, essa mesma concentração manteve a ultraestrutura normal dos folículos após sete dias de cultivo. Em conclusão, o TGF-β apresentou efeito adicional no crescimento folicular e na manutenção da integridade ultraestrutural de folículos pré-antrais caprinos inclusos no tecido ovariano quando utilizado na concentração de 10ng/mL durante sete dias de cultivo.The objectives of this study were to investigate whether TGF-β affect the survival, activation and further growth of goat primordial follicles enclosed in ovarian cortex after in vitro culture. Goat ovaries were collected from an abattoir and pieces of ovarian tissues were cultured for one or seven days in a supplemented alpha Minimum Essential Medium, alone or containing TGF-β (1, 5, 10 or 50ng/mL). Ovarian tissues from the fresh control as well as those cultured were processed for histological and ultrastructural studies. The results showed that when compared with fresh control, there was decrease in the percentages of histologically normal follicles in all treatments only after seven days culture. TGF-β did not affect the activation of preantral follicles regardless of its concentration, however, larger follicles diameter (P<0.05) was observed using 10ng/mL TGF-β than in the fresh control and other treatments. Moreover, this concentration maintained the normal ultrastructure after seven days of culture. In conclusion, TGF-β showed additional effect on the follicle growth and the maintenance of ultrastructural integrity of goat preantral follicles enclosed in ovarian tissue when used at 10ng/mL during seven days of culture
Holocene Critical Zone dynamics in an Alpine catchment inferred from a speleothem multiproxy record : disentangling climate and human influences
Disentangling the effects of climate and human impact on the long-term evolution of the Earth CriticalZone is crucial to understand the array of its potential responses to the ongoing Global Change. This task requires natural archives from which local information about soil and vegetation can be linked directly to climate parameters. Here we present a high-resolution, well-dated, speleothem multiproxy record from the SW Italian Alps, spanning the last ~10,000 years of the present interglacial (Holocene). We correlate magnetic properties and the carbon stable isotope ratio to soil stability and pedogenesis, whereas the oxygen isotope composition is interpreted as primarily related to precipitation amount, modulated at different timescales by changes in precipitation source and seasonality. During the 9.7-2.8 ka period, when anthropic pressure over the catchment was scarce, intervals of enhanced soil erosion are related to climate-driven vegetation contractions and occurred during drier periods. Immediately following the onset of the Iron Age (ca. 2.8 ka), by contrast, periods of enhanced soil erosion coincided with a wetter climate. We propose that the observed changes in the soil response to climate forcing were related to early anthropogenic manipulations of Earth\u2019s surface, which made the ECZ more sensitive to climate oscillations
Variational Principle underlying Scale Invariant Social Systems
MaxEnt's variational principle, in conjunction with Shannon's logarithmic
information measure, yields only exponential functional forms in
straightforward fashion. In this communication we show how to overcome this
limitation via the incorporation, into the variational process, of suitable
dynamical information. As a consequence, we are able to formulate a somewhat
generalized Shannonian Maximum Entropy approach which provides a unifying
"thermodynamic-like" explanation for the scale-invariant phenomena observed in
social contexts, as city-population distributions. We confirm the MaxEnt
predictions by means of numerical experiments with random walkers, and compare
them with some empirical data
Proton Decay in a Minimal SUSY SO(10) Model for Neutrino Mixings
A minimal renormalizable SUSY SO(10) model with B-L symmetry broken by {\bf
126} Higgs field has recently been shown to predict all neutrino mixings and
the ratio in agreement with observations.
Unlike models where B-L is broken by {\bf 16} Higgs, this model guarantees
automatic R-parity conservation and hence a stable dark matter as well as the
absence of dim=4 baryon violating operator without any additional symmetry
assumptions. In this paper, we discuss the predictions of the model for proton
decay induced at the GUT scale. We scan over the parameter space of the model
allowed by neutrino data and find upper bounds on the partial lifetime for the
modes yrs and yrs for the
average squark mass of a TeV and wino mass of 200 GeV, when the parameters
satisfy the present lower limits on mode. These
results can be used to test the model.Comment: 17 pages, 6 figures; Minor corrections with improved predictions;
references update
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