7,124 research outputs found
Robust self-trapping of vortex beams in a saturable optical medium
We report the first observation of robust self-trapping of vortex beams
propagating in a uniform condensed medium featuring local saturable
self-focusing nonlinearity. Optical vortices with topological charge m=1, that
remain self-trapped over ~ 5 Rayleigh lengths, are excited in carbon disulfide
using a helical light beam at 532 nm and intensities from 8 to 10 GW/cm^2. At
larger intensities, the vortex beams lose their stability, spontaneously
breaking into two fragments. Numerical simulations based on the nonlinear
Schr\"odinger equation including the three-photon absorption and nonpolynomial
saturation of the refractive nonlinearity demonstrate close agreement with the
experimental findings.Comment: 27 pages, 7 figures,to be published in Phys. Rev. A (2016
Screening effects in flow through rough channels
A surprising similarity is found between the distribution of hydrodynamic
stress on the wall of an irregular channel and the distribution of flux from a
purely Laplacian field on the same geometry. This finding is a direct outcome
from numerical simulations of the Navier-Stokes equations for flow at low
Reynolds numbers in two-dimensional channels with rough walls presenting either
deterministic or random self-similar geometries. For high Reynolds numbers,
when inertial effects become relevant, the distribution of wall stresses on
deterministic and random fractal rough channels becomes substantially dependent
on the microscopic details of the walls geometry. In addition, we find that,
while the permeability of the random channel follows the usual decrease with
Reynolds, our results indicate an unexpected permeability increase for the
deterministic case, i.e., ``the rougher the better''. We show that this complex
behavior is closely related with the presence and relative intensity of
recirculation zones in the reentrant regions of the rough channel.Comment: 4 pages, 5 figure
Improving Whole Slide Segmentation Through Visual Context - A Systematic Study
While challenging, the dense segmentation of histology images is a necessary
first step to assess changes in tissue architecture and cellular morphology.
Although specific convolutional neural network architectures have been applied
with great success to the problem, few effectively incorporate visual context
information from multiple scales. With this paper, we present a systematic
comparison of different architectures to assess how including multi-scale
information affects segmentation performance. A publicly available breast
cancer and a locally collected prostate cancer datasets are being utilised for
this study. The results support our hypothesis that visual context and scale
play a crucial role in histology image classification problems
Avaliação da segurança sísmica de igrejas: aplicação a dois casos de estudo
A conservação de edifícios antigos é um tema que tem suscitado um interesse
crescente na comunidade em geral pela necessidade de preservação do património edificado.
No caso das igrejas, essa conservação atinge interesse acrescido pela carga simbólica e
espiritual que este tipo de edifícios acarreta, para além do seu valor patrimonial e histórico.
Estas construções são particularmente vulneráveis a acções dinâmicas, como os sismos,
tornando-se essencial a avaliação da sua segurança.
O objectivo do estudo apresentado neste artigo é a aplicação de métodos de avaliação da
segurança sísmica distintos a dois monumentos históricos: Igreja de Jesus (Setúbal) e Igreja
de São Jorge dos Latinos (Famagusta, Chipre). No que se refere à Igreja de Jesus, foi
desenvolvido um modelo numérico tridimensional de elementos finitos, validado através de
resultados experimentais de identificação dinâmica. A capacidade resistente a acções
sísmicas foi avaliada através de análises estáticas não-lineares (tipo pushover), procedendose
a uma análise crítica interpretativa dos resultados, assim como à definição do mecanismo
de colapso e determinação do factor de carga associado a esta construção. Relativamente à
Igreja de São Jorge dos Latinos, foram realizadas análises dinâmicas não-lineares para a
avaliação da sua segurança sísmica, fazendo-se, à semelhança do caso anterior, uma análise
interpretativa dos resultados e definição do mecanismo de colapso. Constatou-se que a Igreja
de Jesus, contrariamente à de São Jorge de Latinos, parece ser estruturalmente segura face à
legislação aplicável
Collaboration networks from a large CV database: dynamics, topology and bonus impact
Understanding the dynamics of research production and collaboration may
reveal better strategies for scientific careers, academic institutions and
funding agencies. Here we propose the use of a large and multidisciplinar
database of scientific curricula in Brazil, namely, the Lattes Platform, to
study patterns of scientific production and collaboration. In this database,
detailed information about publications and researchers are made available by
themselves so that coauthorship is unambiguous and individuals can be evaluated
by scientific productivity, geographical location and field of expertise. Our
results show that the collaboration network is growing exponentially for the
last three decades, with a distribution of number of collaborators per
researcher that approaches a power-law as the network gets older. Moreover,
both the distributions of number of collaborators and production per researcher
obey power-law behaviors, regardless of the geographical location or field,
suggesting that the same universal mechanism might be responsible for network
growth and productivity.We also show that the collaboration network under
investigation displays a typical assortative mixing behavior, where teeming
researchers (i.e., with high degree) tend to collaborate with others alike.
Finally, our analysis reveals that the distinctive collaboration profile of
researchers awarded with governmental scholarships suggests a strong bonus
impact on their productivity.Comment: 8 pages, 8 figure
Gravity with extra dimensions and dark matter interpretation: Phenomenological example via Miyamoto-Nagai galaxy
A configuration whose density profile coincides with the Newtonian potential
for spiral galaxies is constructed from a 4D isotropic metric plus extra
dimensional components. A Miyamoto-Nagai ansatz is used to solve Einstein
equations. The stable rotation curves of such system are computed and, without
fitting techniques, we recover with accuracy the observational data for flat or
not asymptotically flat galaxy rotation curves. The density profiles are
reconstructed and compared to that obtained from the Newtonian potential.Comment: 10 pages, 10 figures, submitted to Brazilian Journal of Physic
Comunicação e Transformações Sociais (vol. 3). Economia e Políticas da Comunicação, Estudos Fílmicos, Estudos Televisivos, Género e Sexualidades, Publicidade e Comunicação, Rádio e Meios Sonoros, Retórica, Semiótica
The role of cinema on the tourist destination image formation process
Tourism literature widely acknowledges that images of tourist destinations are a product of all the experiences of an individual, being influenced by a series of information sources. The movies figure amongst this sources, and as an autonomous information agent, which in theory are not associated with the tourist market interests, they transmit information that is perceived as more reliable than conventional publicity. Thus, cinema acts directly on the organic image, creating and perpetuating associations about the places it depicts on the collective imagery. The present article aims to provide a bibliographical state of the art about the influence of films on the tourist destinations’ image, contextualizing the cinema on it’s formation process, as well as the cognitive and phsycological processes involved
- …