1,280 research outputs found
Influence of the disorder on tracer dispersion in a flow channel
Tracer dispersion is studied experimentally in periodic or disordered arrays
of beads in a capillary tube. Dispersion is measured from light absorption
variations near the outlet following a steplike injection of dye at the inlet.
Visualizations using dye and pure glycerol are also performed in similar
geometries. Taylor dispersion is dominant both in an empty tube and for a
periodic array of beads: the dispersivity increases with the P\'eclet
number respectively as and and is larger by a factor of 8
in the second case. In a disordered packing of smaller beads (1/3 of the tube
diameter) geometrical dispersion associated to the disorder of the flow field
is dominant with a constant value of reached at high P\'eclet numbers.
The minimum dispersivity is slightly higher than in homogeneous nonconsolidated
packings of small grains, likely due heterogeneities resulting from wall
effects. In a disordered packing with the same beads as in the periodic
configuration, is up to 20 times lower than in the latter and varies as
with or (depending on the fluid viscosity).
A simple model accounting for this latter result is suggested.Comment: available online at
http://www.edpsciences.org/journal/index.cfm?edpsname=epjap&niv1=contents&niv2=archive
Quantum and random walks as universal generators of probability distributions
Quantum walks and random walks bear similarities and divergences. One of the
most remarkable disparities affects the probability of finding the particle at
a given location: typically, almost a flat function in the first case and a
bell-shaped one in the second case. Here I show how one can impose any desired
stochastic behavior (compatible with the continuity equation for the
probability function) on both systems by the appropriate choice of time- and
site-dependent coins. This implies, in particular, that one can devise quantum
walks that show diffusive spreading without loosing coherence, as well as
random walks that exhibit the characteristic fast propagation of a quantum
particle driven by a Hadamard coin.Comment: 8 pages, 2 figures; revised and enlarged versio
Correct quantum chemistry in a minimal basis from effective Hamiltonians
We describe how to create ab-initio effective Hamiltonians that qualitatively
describe correct chemistry even when used with a minimal basis. The
Hamiltonians are obtained by folding correlation down from a large parent basis
into a small, or minimal, target basis, using the machinery of canonical
transformations. We demonstrate the quality of these effective Hamiltonians to
correctly capture a wide range of excited states in water, nitrogen, and
ethylene, and to describe ground and excited state bond-breaking in nitrogen
and the chromium dimer, all in small or minimal basis sets
Um estudo de caso do diagnose virtual na web 2.0.
Neste trabalho são apresentados os resultados obtidos na integração do módulo produtor do Diagnose Virtual ao portal WebAgritec visando garantir a interoperabilidade do mesmo. O projeto WebAgritec tem como objetivo desenvolver uma infra-estrutura, concretizada na forma de um website, que integrará vários sistemas desenvolvidos na Embrapa Informática Agropecuária. Um dos principais requisitos deste projeto é interface baseada nos conceitos de interatividade da Web 2.0. Além desse conceito, tecnologias e padrões de projeto próprios para o desenvolvimento de aplicações web e plataformas, bem como comunicação entre seus componentes são investigados. Outros requisitos não funcionais como desempenho e escalabilidade também devem ser analisados.SBIAgro 2009
Study of the reaction pbar p -> phi phi from 1.1 to 2.0 GeV/c
A study has been performed of the reaction pbar p -> 4K using in-flight
antiprotons from 1.1 to 2.0 GeV/c incident momentum interacting with a hydrogen
jet target. The reaction is dominated by the production of a pair of phi
mesons. The pbar p -> phi phi cross section rises sharply above threshold and
then falls continuously as a function of increasing antiproton momentum. The
overall magnitude of the cross section exceeds expectations from a simple
application of the OZI rule by two orders of magnitude. In a fine scan around
the xi/f_J(2230) resonance, no structure is observed. A limit is set for the
double branching ratio B(xi -> pbar p) * B(xi -> phi phi) < 6e-5 for a spin 2
resonance of M = 2.235 GeV and Width = 15 MeV.Comment: 13 pages, 13 figures, 2 tables, Latex. To be published in Phys. Rev.
Design, set-up and utility of the UK facioscapulohumeral muscular dystrophy patient registry
Facioscapulohumeral dystrophy (FSHD) is a rare inherited neuromuscular disease estimated to affect 1/15,000 people. Through basic research, remarkable progress has been made towards the development of targeted therapies. Patient identification, through registries or other means is essential for trial-readiness. The UK FSHD Patient Registry is a patient initiated registry that collects standardised and internationally agreed dataset of self-reported clinical details combined with professionally verified genetic information. It includes four additional questionnaires to capture patient reported outcomes related to pain, quality of life and scapular fixation. Between 2013 and 2015, 518 patients registered 243 males, 241 females with a mean age of 47.8 years. Most of the patients have FSHD type 1 (91.7 %), and weakness of the facial (59.2 %) was the most prevalent symptom at onset, followed by shoulder-girdle muscles (53.3 %) and distal (22.45 %) or proximal lower limb weakness (14.8 %). 85.57 % patients were ambulant or ambulant with assistance at the time of registration, 7.9 % report respiratory insufficiency. The registry has demonstrated utility with the recruitment of patients for a natural history study of infantile onset FSHD, and the longitudinal analysis of patient-related outcomes will provide much-needed baseline information to power future trials. The internationally agreed core dataset enables national registries to participate in a "Global FSHD registry". We suggest that the registry's ability to interoperate with other large datasets will be instrumental for sharing and exploiting data globally
Changes in soil carbon, nitrogen, and phosphorus due to land-use changes in Brazil
In this paper, soil carbon, nitrogen and phosphorus concentrations and stocks were investigated in agricultural and natural areas in 17 plot-level paired sites and in a regional survey encompassing more than 100 pasture soils In the paired sites, elemental soil concentrations and stocks were determined in native vegetation (forests and savannas), pastures and crop-livestock systems (CPSs). Nutrient stocks were calculated for the soil depth intervals 0-10, 0-30, and 0-60 cm for the paired sites and 0-10, and 0-30 cm for the pasture regional survey by sum stocks obtained in each sampling intervals (0-5, 5-10, 10-20, 20-30, 30-40, 40-60 cm). Overall, there were significant differences in soil element concentrations and ratios between different land uses, especially in the surface soil layers. Carbon and nitrogen contents were lower, while phosphorus contents were higher in the pasture and CPS soils than in native vegetation soils. Additionally, soil stoichiometry has changed with changes in land use. The soil C:N ratio was lower in the native vegetation than in the pasture and CPS soils, and the carbon and nitrogen to available phosphorus ratio (P-ME) decreased from the native vegetation to the pasture to the CPS soils. In the plot-level paired sites, the soil nitrogen stocks were lower in all depth intervals in pasture and in the CPS soils when compared with the native vegetation soils. On the other hand, the soil phosphorus stocks were higher in all depth intervals in agricultural soils when compared with the native vegetation soils. For the regional pasture survey, soil nitrogen and phosphorus stocks were lower in all soil intervals in pasture soils than in native vegetation soils. The nitrogen loss with cultivation observed here is in line with other studies and it seems to be a combination of decreasing organic matter inputs, in cases where crops replaced native forests, with an increase in soil organic matter decomposition that leads to a decrease in the long run. The main cause of the increase in soil phosphorus stocks in the CPS and pastures of the plot-level paired site seems to be linked to phosphorus fertilization by mineral and organics fertilizers. The findings of this paper illustrate that land-use changes that are currently common in Brazil alter soil concentrations, stocks and elemental ratios of carbon, nitrogen and phosphorus. These changes could have an impact on the subsequent vegetation, decreasing soil carbon and increasing nitrogen limitation but alleviating soil phosphorus deficiency121547654780British Embass
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