572 research outputs found
Validation of a multi-scale simulation strategy based on the Pointwise Strain Superposition Method
This paper details the experimental validation of a multi-scale simulation strategy that we developed for predicting the stresses and distortions induced by Powder Bed Fusion processes. The strategy comprises a meso-scale model, a macro-scale model, and a scaling method named Pointwise Strain Superposition. The first model evaluates the temperature, stress, and strain fields produced by a single scan line. The scaling method transfers the meso-scale results to the macro-scale model, which is then able to simulate the entire manufacturing process with a reasonable computational cost. The simulation strategy was validated by comparing its results with the stresses and distortions measured on several specimens made of selective laser melted Inconel 718. Stresses were measured through the blind hole drilling method on a cylindrical specimen printed with two different scanning strategies, while distortions were measured on a hollow cylinder and on a cantilever-shaped specimen after removing its supports. In both cases, the simulation showed first- or higher-order accuracy despite the significant uncertainties regarding the input parameters and material properties. This robustness, coupled with its computational efficiency, leads us to believe that our simulation strategy could enhance the process optimization and provide a better understanding of the underlying physical phenomena along with their effects on the manufactured parts
Modificações ambientais causadas pela implantação de Sistemas Agroflorestais em Áreas de Preservação Permanente: marco zero.
Sistemas agroflorestais (SAF) são alternativa para recuperação de Áreas de Preservação Permanente, mantendo-se a área produtiva do ponto de vista ecológico e agrícola. Está sendo feito um estudo, sob princípios da pesquisa-ação participativa, para acompanhamento e avaliação da evolução de SAF sucessionais na APA da Serra da Esperança e caracterização do efeito dos mesmos sobre o ecossistema, bem como sua inserção nos sistemas de produção locais. O objetivo deste trabalho é caracterizar as parcelas anteriormente à implantação dos SAF. Em cada parcela de estudo, em três propriedades de agricultores familiares de Inácio Martins/PR, Brasil, fez-se análises química e física do solo e levantamento florístico. Os solos apresentam baixa fertilidade natural e elevada acidez. O conteúdo de matéria orgânica é elevado e a estrutura apresenta excelentes condições. As parcelas experimentais tem semelhanças quanto à vegetação, entretanto há diferenças em função das práticas agrícolas associadas.Edição dos resumos do 7º Congresso Brasileiro de Agroecologia, 2013, Porto Alegre
On the role of Eurasian autumn snow cover in dynamical seasonal predictions
Seasonal predictions leverage on predictable or persistent components of the Earth system that can modify the state of the atmosphere. The land surface provides predictability through various mechanisms, including snow cover, with particular reference to Autumn snow cover over the Eurasian continent. The snow cover alters the energy exchange between surface and atmosphere and induces a diabatic cooling that in turn can affect the atmosphere locally and remotely. Lagged relationships between snow cover in Eurasia and atmospheric modes of variability in the Northern Hemisphere have been documented but are deemed to be non-stationary and climate models typically do not reproduce observed relationships with consensus. The role of the snow in recent dynamical seasonal forecasts is therefore unclear. Here we assess the role of Autumn Eurasian snow cover in a set of five operational seasonal forecasts with large ensemble size and high resolution and with the help of targeted idealised simulations. Forecast systems reproduce realistically regional changes of the surface energy balance. Retrospective forecasts and idealised sensitivity experiments identify a coherent change of the circulation in the Northern Hemisphere. The main features of the atmospheric response are a wave-train downstream over the Pacific and North America and a signal in the Arctic. The latter does not emerge in reanalysis data but is compatible with a lagged but weak and fast feedback from the snow to the Arctic Oscillation
Size quantization effects in thin film Casimir interaction
We investigate the role of size quantization in the vacuum force between
metallic films of nanometric thickness. The force is calculated by the Lifshitz
formula with the film dielectric tensor derived from the one-electron energies
and wavefunctions under the assumption of a constant potential inside the film
and a uniform distribution of the positive ion charge. The results show that
quantization effects tend to reduce the force with respect to the continuum
plasma model. The reduction is more significant at low electron densities and
for film size of the order of few nanometers and persists for separation
distances up to 10 nm. Comparison with previous work indicates that the
softening of the boundary potential is important in determining the amount of
the reduction. The calculations are extended to treat Drude intraband
absorption. It is shown that the inclusion of relaxation time enhances the size
quantization effects in the force calculations
Analysis of Diterpens in Green and Roasted Coffee of Coffea arabica Cultivars Growing in the Same Edapho-Climatic Conditions.
Lipids are important components of coffee beverage flavor and aroma. Coffee oil is rich in diterpens of the kaurane family, mainly cafestol (C20H28O3) and kahweol (C20H26O3), which have increasingly received attention in recent years due to their physiological effects in human health. However, few studies have been conducted on the effects of the genetic variability for those lipids in Coffea arabica. In this work we initiate the characterization of cafestol and kahweol in different cultivars of Coffea arabica, growing in the same edaphoclimatic conditions. Mature coffee fruits from cultivars Catuaí, Icatu and three Catucaí derived the cultivars IPR 100, IPR 102 and IPR 106. They were harvested at the Agricultural Field Station of the Coop COCARI, Mandaguari, Paraná, Brazil, from May to July 2009. Although the time of harvesting was according to the maturation of each cultivar, harvesting and post-harvesting conditions were the same for all cultivars. The five samples were subjected to medium roasting for 8 to 11 minutes at 200-210 °C, until the degree of roasting light/media (L* around 28). The extraction of diterpens was carried out in green or roasted coffee by direct saponification with KOH, extraction with terc-butyl methyl ether, and clean up with water. A reverse-phase HPLC column with isocratic elution with acetonitrile/water (55/45 v/v) was used for detection and quantification of kahweol at 290 nm and cafestol at 220 nm. In green beans, the level of kahweol was higher than cafestol, for all three IPR cultivars. Meanwhile, the inverse was observed for green beans cultivars Catuaí and Icatu, where cafestol levels were higher than kahweol. The higher levels of kahweol in relation to cafestol were again observed in roasted coffee of the three IPR cultivars. In cultivars Icatu the values for kahweol and cafestol were similar (635 and 683 mg/100 g, respectively). The highest levels of kahweol were observed in cultivar IPR 106 (1096 mg/100 g). The cultivar IPR 102 showed the highest level of cafestol (394 mg/100g). Association of this data with gene expression profile can be useful to find genes involved in cafestol and kahweol metabolism as well as to develop molecular markers for diterpens in coffee
The nature of the short wavelength excitations in vitreous silica: X-Rays Brillouin scattering study
The dynamical structure factor (S(Q,E)) of vitreous silica has been measured
by Inelastic X-ray Scattering varying the exchanged wavevector (Q) at fixed
exchanged energy (E) - an experimental procedure that, contrary to the usual
one at constant Q, provides spectra with much better identified inelastic
features. This allows the first direct evidence of Brillouin peaks in the
S(Q,E) of SiO_2 at energies above the Boson Peak (BP) energy, a finding that
excludes the possibility that the BP marks the transition from propagating to
localised dynamics in glasses.Comment: 4 pages, 3 Postscript figures. To appear in Physical Review Letter
Graph Regionalization with Clustering and Partitioning: an Application for Daily Commuting Flows in Albania
The paper presents an original application of the recently proposed spatial data mining
method named GraphRECAP on daily commuting flows using 2011 Albanian census data.
Its aim is to identify several clusters of Albanian municipalities/communes; propose a
classification of the Albanian territory based on daily commuting flows among
municipalities/communes. Starting from 373 local units, we first applied a spatial
clustering technique without imposing any constraining strategy. Based on the input
variables, we obtained 16 clusters. In the second step of our analysis, we impose a set of
constraining parameters to identify intermediate areas between the local level
(municipality/commune) and the national one. We have defined 12 derived regions (same
number as the actual Albanian prefectures but with different geographies). These derived
regions are quite different from the traditional ones in terms of both geographical
dimensions and boundarie
Resummation of the Divergent Perturbation Series for a Hydrogen Atom in an Electric Field
We consider the resummation of the perturbation series describing the energy
displacement of a hydrogenic bound state in an electric field (known as the
Stark effect or the LoSurdo-Stark effect), which constitutes a divergent formal
power series in the electric field strength. The perturbation series exhibits a
rich singularity structure in the Borel plane. Resummation methods are
presented which appear to lead to consistent results even in problematic cases
where isolated singularities or branch cuts are present on the positive and
negative real axis in the Borel plane. Two resummation prescriptions are
compared: (i) a variant of the Borel-Pade resummation method, with an
additional improvement due to utilization of the leading renormalon poles (for
a comprehensive discussion of renormalons see [M. Beneke, Phys. Rep. vol. 317,
p. 1 (1999)]), and (ii) a contour-improved combination of the Borel method with
an analytic continuation by conformal mapping, and Pade approximations in the
conformal variable. The singularity structure in the case of the LoSurdo-Stark
effect in the complex Borel plane is shown to be similar to (divergent)
perturbative expansions in quantum chromodynamics.Comment: 14 pages, RevTeX, 3 tables, 1 figure; numerical accuracy of results
enhanced; one section and one appendix added and some minor changes and
additions; to appear in phys. rev.
Elastic constant dishomogeneity and dependence of the broadening of the dynamical structure factor in disordered systems
We propose an explanation for the quadratic dependence on the momentum ,
of the broadening of the acoustic excitation peak recently found in the study
of the dynamic structure factor of many real and simulated glasses. We ascribe
the observed law to the spatial fluctuations of the local wavelength of
the collective vibrational modes, in turn produced by the dishomegeneity of the
inter-particle elastic constants. This explanation is analitically shown to
hold for 1-dimensional disordered chains and satisfatorily numerically tested
in both 1 and 3 dimensions.Comment: 4 pages, RevTeX, 5 postscript figure
Tipificação do café conilon produzido no Estado do Espírito Santo - safra 98/99.
O Espírito Santo cultiva as espécies de café arábica e conilon, sendo a altitude de 450m o seu divisor. O conilon é utilizado, além da exportação como café verde, para a indústria do solúvel e para o mercado interno. Visando monitorar a qualidade do café conilon no estado, foram amostrados 13 municípios, em março/2000, sendo as amostras referentes à safra 98/99, realizadas no café em estoque na propriedade rural. Quantificou-se o número de grãos sadios, pretos, verdes, ardidos, brocados e quebrados, calculando-se o tipo e a freqüência de ocorrência dos defeitos, por região. Observou-se que os maiores índices de defeitos foram observados na região Centro-Serrana, seguida de Cachoeiro de Itapemirim, Vitória e Colatina. Os defeitos mais freqüentes foram grãos ardidos, brocados, quebrados, verdes e pretos, em ordem decrescente. 17% das amostras apresentaram tipo 6 e superiores. A maior incidência foi de amostras tipo 7 e 7/8
- …