7,686 research outputs found
Human Activity Recognition using Max-Min Skeleton-based Features and Key Poses
Human activity recognition is still a very challenging research area, due to the inherently complex temporal and spatial patterns that characterize most human activities. This paper proposes a human activity recognition framework based on random forests, where each activity is classified requiring few training examples (i.e. no frame-by-frame activity classification). In a first approach, a simple mechanism that divides each action sequence into a fixed-size window is employed, where max-min skeleton-based features are extracted. In the second approach, each window is delimited by a pair of automatically detected key poses, where static and max-min dynamic features are extracted, based on the determined activity example. Both approaches are evaluated using the Cornell Activity Dataset [1], obtaining relevant overall average results, considering that these approaches are fast to train and require just a few training examples. These characteristics suggest that the proposed framework can beuseful for real-time applications, where the activities are typicallywell distinctive and little training time is required, or to be integrated in larger and sophisticated systems, for a first quick impression/learning of certain activitie
Geometric Aspects of the Dipolar Interaction in Lattices of Small Particles
The hysteresis curves of systems composed of small interacting magnetic
particles, regularly placed on stacked layers, are obtained with Monte Carlo
simulations. The remanence as a function of temperature, in interacting
systems, presents a peak that separates two different magnetic states. At low
temperatures, small values of remanence are a consequence of antiferromagnetic
order due to the dipolar interaction. At higher values of temperature the
increase of the component normal to the lattice plane is responsible for the
small values of remanence. The effect of the number of layers, coordination
number and distance between particles are investigated.Comment: 5 pages, 7 figure
Reheating induced by competing decay modes
We address the problem of studying the decay of the inflaton field to
another scalar field through parametric resonance in the case of a
coupling that involves several decay modes. This amounts to the presence of
extra harmonic terms in the perturbation of the field dynamics. For the
case of two frequencies we compute the geometry of the resonance regions, which
is significantly altered due to the presence of non-cuspidal resonance regions
associated to higher harmonics and to the emergence of instability `pockets'.
We discuss the effect of this change in the efficiency of the energy transfer
process for the simplest case of a coupling given by a combination of the two
interaction terms of homogeneous degree usually considered in the literature.
We find that the presence of higher harmonics has limited cosmological
implications.Comment: 14 pages, 4 figures Added references. Corrected typo
Influence of linseed oil on the microstructure and composition of lime and lime-metakaolin pastes after a long curing time
This study investigates the effect of linseed oil on the microstructure of lime and lime-metakaolin pastes after 68 months of curing under controlled conditions. The hydrophobicity imparted by linseed oil to the pastes’ bulk was confirmed by measuring water drops’ contact angle. The results of thermal analysis, X-ray powder diffraction, and Fourier transform infrared spectroscopy showed that linseed oil significantly hindered the carbonation reaction in both lime and lime-metakaolin pastes and promoted the development of amorphous phases. The obtained results also indicated that linseed oil could foster the pozzolanic reaction in the lime-metakaolin system by stabilizing and/or promoting the development of hydration products resulting in reduced shrinkage in comparison with the reference
Density-functional theory of polar insulators
We examine the density-functional theory of macroscopic insulators, obtained in the large-cluster limit or under periodic boundary conditions. For polar crystals, we find that the two procedures are not equivalent. In a large-cluster case, the exact exchange-correlation potential acquires a homogeneous ``electric field'' which is absent from the usual local approximations, and the Kohn-Sham electronic system becomes metallic. With periodic boundary conditions, such a field is forbidden, and the polarization deduced from Kohn-Sham wavefunctions is incorrect even if the exact functional is used
Ocorrência de carvão-da-folha (Etyloma oryzae) na cultura do arroz irrigado no Rio Grande do Sul.
bitstream/item/36421/1/comunicado-237.pd
Study of quasimonoenergetic electron bunch generation in self-modulated laser wakefield acceleration using TW or sub-TW ultrashort laser pulses
This work presents a study on laser wakefield electron acceleration in the self-modulated regime (SM-LWFA) using 50-fs laser pulses with energy on the mJ scale, at λ = 0.8 μm, impinging on a thin H2 gas jet. Particle-in-cell simulations were performed using laser peak powers ranging from sub-terawatt to a few terawatts and plasma densities varying from the relativistic self-focusing threshold up to values close to the critical density. The differences in the obtained acceleration processes are discussed. Results show that bunched electron beams with full charge on the nC scale and kinetic energy in the MeV range can be produced and configurations with peak density in the range 0.5–5 × 1020 atoms/cm3 generate electrons with maximum energies. In this range, some simulations generated quasimonoenergetic bunches with ∼0.5% of the total accelerated charge and we show that the beam characteristics, process dynamics, and operational parameters are close to those expected for the blowout regime. The configurations that led to quasimonoenergetic bunches from the sub-TW SM-LWFA regime allow the use of laser systems with repetition rates in the kHz range, which can be beneficial for practical applications
Possibilidade de seleção de linhagens de caupi mais eficientes na fixação simbiótica de nitrogênio.
RESUMO - 0 comportamento de caracteres presumivelmente relacionados com a fixação simbiótica de nitrogênio foi estudado em progênies de 75 seleções de cada uma de duas cultivares de caupi, Vigna unguiculata (L.) Walp, em quatro diferentes idades da planta. As cultivares estudadas, Seridó e Pitiúba, diferiram entre si em todas as caracterÃsticas consideradas e observou-se a existência de variação estatisticamente significativa, entre progênies e entre plantas dentro de progênies de ambas as cultivares, sugerindo a possibilidade de identificação, nessas cultivares, de linhagens ou genótipos mais eficientes com respeito à simbiose de que resulta a fixação biológica de nitrogênio. No que respeita ao peso dos nódulos, foi possÃvel a formação de grupos de plantas de comportamento caracterÃstico, o que indica que, em uma mesma variedade, podem ser identificados genótipos diferentes e que esse caráter é geneticamente controlado. ABSTRACT - Several characters assumed to be related to symbiotic fixation of nitrogen were studied in progenies of 75 selections of two cowpea cultivars, Vigna unguiculata (L.) Walp, in four developmental plant stages. The two cultivars, Seridó and Pitiúba were found to be statistically different to all characters studied. The variation observed arnong plants in both cultivars suggests that it is possible to select lines within each cultivar for a better efficiency in nitrogen fixation through symbiotic activity, in relation to nodule weight it was possible to identify genotypes of similar behavior and to gather them into groups of the sarne characteristic pattern. It is suggested that nodule weight is a character of the plant and geneticaliy controlled by it.TÃtulo em inglês: Selection possibility for more efficient nitrogen fixation in cowpea
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