2,830 research outputs found
Texture descriptor combining fractal dimension and artificial crawlers
Texture is an important visual attribute used to describe images. There are
many methods available for texture analysis. However, they do not capture the
details richness of the image surface. In this paper, we propose a new method
to describe textures using the artificial crawler model. This model assumes
that each agent can interact with the environment and each other. Since this
swarm system alone does not achieve a good discrimination, we developed a new
method to increase the discriminatory power of artificial crawlers, together
with the fractal dimension theory. Here, we estimated the fractal dimension by
the Bouligand-Minkowski method due to its precision in quantifying structural
properties of images. We validate our method on two texture datasets and the
experimental results reveal that our method leads to highly discriminative
textural features. The results indicate that our method can be used in
different texture applications.Comment: 12 pages 9 figures. Paper in press: Physica A: Statistical Mechanics
and its Application
How to Answer the Question — Are Drugs Real Threats to Biological Systems or Overrated Innocuous Chemicals?
Complex network classification using partially self-avoiding deterministic walks
Complex networks have attracted increasing interest from various fields of
science. It has been demonstrated that each complex network model presents
specific topological structures which characterize its connectivity and
dynamics. Complex network classification rely on the use of representative
measurements that model topological structures. Although there are a large
number of measurements, most of them are correlated. To overcome this
limitation, this paper presents a new measurement for complex network
classification based on partially self-avoiding walks. We validate the
measurement on a data set composed by 40.000 complex networks of four
well-known models. Our results indicate that the proposed measurement improves
correct classification of networks compared to the traditional ones
Adulterants found in mixtures of illegal psychoactive drugs
Os danos biológicos causados pelo uso de substâncias psicoactivas ilegais podem resultar não só das substâncias
ilegais por si só, mas também da presença de substâncias que os traficantes lhes adicionam no sentido de aumentar
o volume final de droga (substâncias de corte). O objectivo central do presente estudo consistiu na análise de substâncias
psicoactivas ilegais e dos seus contaminantes/adulterantes, pela conjugação de esforços entre CHECK-IN/
APDES e o Instituto Nacional de Medicina Legal do Porto. Esta colaboração permitiu comparar dados portugueses
com os dados gerados pelo projecto Energy Control em Espanha, que se tem dedicado desde há mais de 10 anos à
redução de riscos.
The biological damages caused by the use of illicit psychoactive substances can result not only from the illegal
substances themselves, but can also be due to substances that dealers had to the mixtures in order to increase the
overall volume of drug (cutting substances). The central aim of the present study was analysing illegal psychoactive
substances and their contaminants/adulterants, through the conjugation of efforts by CHECK-IN/APDES and Instituto
Nacional de Medicina Legal do Porto. This cooperation allowed the comparison of Portuguese data with the data that
were collected in Spain by Energy Control, a project that has been working in risk reduction for the past 10 years
Numerical study of the unsteadiness of a ground vortex
Single impinging jets in a crossflow are typical in impingement cooling applications in industry, as well as of the flow beneath a V/STOL aircraft. In this latter application, a primary design consideration is the flow environment induced by the propulsion system during hover with zero or small forward momentum. Ground effect phenomena may occur and change the lift forces on the aircraft, cause re-ingestion of exhaust gases into the engine intake and raise fuselage skin temperatures. An important source of each is the ground vortex which forms far upstream of the impinging jet when the resulting radial wall jet meets a crossflow. Numerical and experimental studies have also been performed in this area. Some were dedicated to the study of the more fundamental configurations: single or multiple impinging jets through a crossflow.
The present thesis extends the analysis of (Pandya, Murman, & Sankaran, 2003) to a wider range of velocity ratios, VR, from 0.065 to 0.2. The impact zone of a wall jet with a boundary layer was studied computationally using a Reynolds Averaged Navier-Stokes (RANS) approach with the “k-ε” turbulence model. The computational domain corresponds to complete experimental rig of (Cimbala, Billet, Gaublomme, & Oefelein, 1991) and the measured boundary conditions were used. It was found that the gross features of the flow are well predicted, and the fluctuations of the flowfield around the ground vortex occur in a very small region near the wall where the impact between each flow occurs. The computational results showed a cyclic formation of two small secondary vortexes that appear and disappear cyclically around the separation and maximum penetration points of the ground vortex. This result confirms the observation of (Pandya, Murman, & Sankaran, 2003). The frequency of the “puffing” was found to compare well with the experimental results for VR=0.1, and the structure of the impact zone is similar. First, the wall jet fluid start to penetrate into the boundary layer side until a very small counterclockwise rotating vortex appears. Then it starts to grow blocking the passage of the clockwise rotating fluid of the wall jet, and a new small vortex appears, but now with clockwise vorticity.
A particular result was obtained for VR=0.175. The flow exhibits a periodic behaviour, but no secondary vortexes are detected. Nevertheless, in this case the frequency was found to correlate well with the values obtained for VR=0.1, 0.125, and 0.15. For the case of very low velocity crossflow (small VR) the computations exhibit a stationary solution, which is in agreement with previous experimental results. For strong crossflows (large VR) the flow is also stationary, although there is a transition region of some unsteadiness without secondary vortexes present. The present work has shown that for a finite interval of velocity ratios between the impinging jet and the crossflow periodic oscillations of the ground vortex are observed. The results indicate a pattern similar to the “puffing” mechanism described by (Cimbala, Billet, Gaublomme, & Oefelein, 1991)
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