8,061 research outputs found
Influência das variáveis meteorológicas na temperatura da superfície da Caatinga em Petrolina, PE.
A análise da temperatura de um organismo compreende a principal variável utilizada para a compreensão de sua termorregulação. Esta por sua vez, pode variar em função de elementos meteorológicos e principalmente da disponibilidade hídrica do local, sendo um indicador do grau de estresse hídrico da vegetação. O objetivo deste trabalho foi analisar a influencia de variáveis ambientais nos valores da temperatura da superfície da caatinga em Petrolina, PE. Para tanto, realizou-se um experimento em uma área de caatinga preservada pertencente à Embrapa Semiárido, Petrolina ? PE. As medições foram realizadas durante o ano de 2012 por meio de uma torre micrometeorológica de 16m de altura equipada com um sistema de aquisição de dados datalogger. Para determinação da temperatura da superfície utilizou-se o termômetro infravermelho (SI111) instalado a 13,9 metros de altura da superfície do solo. Concomitantemente, foram realizadas medidas dos elementos meteorológicos: temperatura do ar, déficit de pressão de vapor, radiação solar e umidade relativa do ar. Procedeu-se realizando correlações para analisar a influencia de cada variável nos valores médios da temperatura da superfície por meio de regressões e do coeficiente de determinação. Com os resultados observou-se que as variáveis que melhor representaram a temperatura da superfície foram a temperatura do ar e o déficit de pressão de vapor com r² iguais a 0,856 e 0,6327. Essas informações podem ser utilizadas para melhor compreender as respostas dessa área de Caatinga às condições do ambiente, bem como para subsidiar estudos de fluxos de carbono e modelagem climática no Bioma Caatinga
Group Theory analysis of phonons in two-dimensional Transition Metal Dichalcogenides
Transition metal dichalcogenides (TMDCs) have emerged as a new two
dimensional materials field since the monolayer and few-layer limits show
different properties when compared to each other and to their respective bulk
materials. For example, in some cases when the bulk material is exfoliated down
to a monolayer, an indirect-to-direct band gap in the visible range is
observed. The number of layers ( even or odd) drives changes in space
group symmetry that are reflected in the optical properties. The understanding
of the space group symmetry as a function of the number of layers is therefore
important for the correct interpretation of the experimental data. Here we
present a thorough group theory study of the symmetry aspects relevant to
optical and spectroscopic analysis, for the most common polytypes of TMDCs,
i.e. , and , as a function of the number of layers. Real space
symmetries, the group of the wave vectors, the relevance of inversion symmetry,
irreducible representations of the vibrational modes, optical selection rules
and Raman tensors are discussed.Comment: 32 pages, 4 figure
A model to simulate the contribution of fibre reinforcement for the punching resistance of RC slabs
In this paper analytical formulations are developed for the prediction of the punching resistance of flat slabs
17 of steel fibre reinforced concrete (SFRC) flexurally reinforced with steel bars. By performing statistical
18 analysis with a database that collects experimental results on the characterization of the post-cracking
19 behaviour of SFRC, equations are determined for the evaluation of the residual flexural tensile strength
20 parameters (fRi) from fundamental data that characterize steel fibres. The fRi strength parameters proposed by
21 CEB-FIP 2010 were used for the definition of the stress-crack width law (s-w) that simulates the fibre
22 reinforcement mechanisms in cement based materials. In the second part of the paper is described an
2
analytical formulation based on the concepts proposed by Muttoni and Ruiz, where 23 the s-w law is
24 conveniently integrated for the simulation of the contribution of steel fibres for the punching resistance of
25 SFRC slabs. By using a database composed of 154 punching tests with SFRC slabs, the good predictive
26 performance of the developed proposal is demonstrated. The good performance of this model is also
27 evidenced by comparing its predictions to those from other models.Fundação para a Ciência e a Tecnologia (FCT
The predictive performance of design models for the punching resistance of SFRC slabs in inner column loading conditions
In the recent years steel fibre reinforced concrete (SFRC), in a volume percentage between 0.75
and 1.25, is being proposed to build slabs supported on piles and slabs supported on columns, where the unique
conventional reinforcement is composed of some steel bars in the alignments of the columns/piles, designated as
anti-progressive collapse bars.
Punching resistance, however, can be a concern in this structural system. In fact, punching has a brittle failure
character, and the prediction of the punching resistance is still a challenge, even in concrete slabs with
traditional reinforcement systems. The difficulties on assessing the contribution of the reinforcement
mechanisms of steel fibres for the flexural and shear resistance in the critical punching perimeter increase this
complexity.
The research carried out in this paper has the purpose of assessing the reliability of existing analytical models
for the prediction of the punching resistance of SFRC slabs. For this purpose, a data-base of experimental tests
with SFRC slabs failing in punching was built and the predictive performance of four analytical available
models was assessed. In order to turn more practical the model that is more reliable from physical and
mechanical point of views, the concepts proposed by Model Code 2010 for the characterization of the postcracking behaviour of FRC were introduced in this model
Análise comparativa da eficácia de dois tipos de fibras de aço no reforço de elementos de betão
Duas extensas campanhas de ensaios experimentais foram efectuadas no sentido de se avaliar o
desempenho de dois tipos de fibras de aço no comportamento à flexão e à compressão de betões
de custo competitivo reforçados com fibras de aço para pavimentos de edifícios industriais. Os
resultados obtidos são apresentados e analisados
Gaussian superpositions in scalar-tensor quantum cosmological models
A free scalar field minimally coupled to gravity model is quantized and the
Wheeler-DeWitt equation in minisuperspace is solved analytically, exhibiting
positive and negative frequency modes. The analysis is performed for positive,
negative and zero values of the curvature of the spatial section. Gaussian
superpositions of the modes are constructed, and the quantum bohmian
trajectories are determined in the framework of the Bohm-de Broglie
interpretation of quantum cosmology. Oscillating universes appear in all cases,
but with a characteristic scale of the order of the Planck scale. Bouncing
regular solutions emerge for the flat curvature case. They contract classically
from infinity until a minimum size, where quantum effects become important
acting as repulsive forces avoiding the singularity and creating an
inflationary phase, expanding afterwards to an infinite size, approaching the
classical expansion as long as the scale factor increases. These are
non-singular solutions which are viable models to describe the early Universe.Comment: 14 pages, LaTeX, 3 Postscript figures, uses graficx.st
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