5,813 research outputs found
Position-dependent mass models and their nonlinear characterization
We consider the specific models of Zhu-Kroemer and BenDaniel-Duke in a
sech-mass background and point out interesting correspondences with the
stationary 1-soliton and 2-soliton solutions of the KdV equation in a
supersymmetric framework.Comment: 8 Pages, Latex version, Two new references are added, To appear in
J.Phys.A (Fast Track Communication
Source of acetylcholine in the frog's heart on stimulation of the vagus nerve
This article does not have an abstract
Escoliose: triagem em escolares de 10 a 15 anos
O proposito deste estudo foi o de verificar a prevalência de casos suspeitos de escoliose e sua associação com peso do material escolar e em alunos de uma escola pública do município de Jequié - BA. Fizeram parte deste estudo descritivo e transversal, 143 escolares (13,26 ± 1,52 anos), 40 meninos e 103 meninas. A triagem dos casos suspeitos de escoliose foi feita através do teste de Adam: presença de gibosidade (suspeita de escoliose); ausência de gibosidade. A verificação da adequação do peso do material escolar (PME) foi feita a partir da relação entre PME e massa corporal (MC), utilizando-se a seguinte classificação: 10 % da MC = adequado e; > 10% da MC = inadequado. As associações foram feitas com teste qui-quadrado. Foram detectados 71 (49,7%) casos suspeitos de escoliose, 40 do sexo masculino e 103 do sexo feminino. Em ambos os sexos, a freqüência de casos suspeitos foi maior no grupo etário de 13-15 anos. O peso de material adequado foi observado em 91,6% dos escolares. Foram observadas associações estatisticamente significativas entre suspeita de escoliose e PME para meninos de 10-12 anos e meninas de 10-12 e 13-15 anos. Os resultados do permitem concluir, para este grupo de escolares, que a prevalência de casos suspeitos de escoliose é maior no sexo feminino, no grupo etário mais velho e nos indivíduos com peso do material escolar inadequado
Lattice-Boltzmann Method for Geophysical Plastic Flows
We explore possible applications of the Lattice-Boltzmann Method for the
simulation of geophysical flows. This fluid solver, while successful in other
fields, is still rarely used for geotechnical applications. We show how the
standard method can be modified to represent free-surface realization of
mudflows, debris flows, and in general any plastic flow, through the
implementation of a Bingham constitutive model. The chapter is completed by an
example of a full-scale simulation of a plastic fluid flowing down an inclined
channel and depositing on a flat surface. An application is given, where the
fluid interacts with a vertical obstacle in the channel.Comment: in W. Wu, R.I. Borja (Edts.) Recent advances in modelling landslides
and debris flow, Springer Series in Geomechanics and Geoengineering (2014),
ISBN 978-3-319-11052-3, pp. 131-14
Multi-component lattice-Boltzmann model with interparticle interaction
A previously proposed [X. Shan and H. Chen, Phys. Rev. E {\bf 47}, 1815,
(1993)] lattice Boltzmann model for simulating fluids with multiple components
and interparticle forces is described in detail. Macroscopic equations
governing the motion of each component are derived by using Chapman-Enskog
method. The mutual diffusivity in a binary mixture is calculated analytically
and confirmed by numerical simulation. The diffusivity is generally a function
of the concentrations of the two components but independent of the fluid
velocity so that the diffusion is Galilean invariant. The analytically
calculated shear kinematic viscosity of this model is also confirmed
numerically.Comment: 18 pages, compressed and uuencoded postscript fil
Monitoring environmental supporting conditions of a raised bog using remote sensing techniques
Conventional methods of monitoring wetlands and detecting changes
over time can be time-consuming and costly. Inaccessibility and remoteness of
many wetlands is also a limiting factor. Hence, there is a growing
recognition of remote sensing techniques as a viable and cost-effective
alternative to field-based ecosystem monitoring. Wetlands encompass a diverse
array of habitats, for example, fens, bogs, marshes, and swamps. In this
study, we concentrate on a natural wetland – Clara Bog, Co. Offaly, a raised
bog situated in the Irish midlands. The aim of the study is to identify and
monitor the environmental conditions of the bog using remote sensing
techniques. Environmental conditions in this study refer to the vegetation
composition of the bog and whether it is in an intact (peat-forming) or
degraded state. It can be described using vegetation, the presence of water
(soil moisture) and topography. Vegetation indices (VIs) derived from
satellite data have been widely used to assess variations in properties of
vegetation. This study uses mid-resolution data from Sentinel-2 MSI, Landsat
8 OLI for VI analysis. An initial study to delineate the boundary of the bog
using the combination of edge detection and segmentation techniques namely,
entropy filtering, canny edge detection, and graph-cut segmentation is
performed. Once the bog boundary is defined, spectra of the delineated area
are studied. VIs like NDVI, ARVI, SAVI, NDWI, derived using Sentinel-2 MSI
and Landsat 8 OLI are analysed. A digital elevation model (DEM) was also used
for better classification. All of these characteristics (features) serve as a
basis for classifying the bog into broad vegetation communities (termed
ecotopes) that indicate the quality of raised bog habitat. This analysis
is validated using field derived ecotopes. The results show that, by using
spectral information and vegetation index clustering, an additional linkage
can be established between spectral RS signatures and wetland ecotopes.
Hence, the benefit of the study is in understanding ecosystem (bog)
environmental conditions and in defining appropriate metrics by which changes
in the conditions can be monitored.</p
Diffusion in a multi-component Lattice Boltzmann Equation model
Diffusion phenomena in a multiple component lattice Boltzmann Equation (LBE)
model are discussed in detail. The mass fluxes associated with different
mechanical driving forces are obtained using a Chapman-Enskog analysis. This
model is found to have correct diffusion behavior and the multiple diffusion
coefficients are obtained analytically. The analytical results are further
confirmed by numerical simulations in a few solvable limiting cases. The LBE
model is established as a useful computational tool for the simulation of mass
transfer in fluid systems with external forces.Comment: To appear in Aug 1 issue of PR
Leveraging the performance of LBM-HPC for large sizes on GPUs using ghost cells
Today, we are living a growing demand of larger and more efficient computational resources from the scientific community. On the other hand, the appearance of GPUs for general purpose computing supposed an important advance for covering such demand. These devices offer an impressive computational capacity at low cost and an efficient power consumption. However, the memory available in these devices is (sometimes) not enough, and so it is necessary computationally expensive memory transfers from (to) CPU to (from) GPU, causing a dramatic fall in performance. Recently, the Lattice-Boltzmann Method has positioned as an efficient methodology for fluid simulations. Although this method presents some interesting features particularly amenable to be efficiently exploited on parallel computers, it requires a considerable memory capacity, which can suppose an important drawback, in particular, on GPUs. In the present paper, it is proposed a new GPU-based implementation, which minimizes such requirements with respect to other state-of-the-art implementations. It allows us to execute almost 2 bigger problems without additional memory transfers, achieving faster executions when dealing with large problems
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