Temperature oscillations of magnetization observed in nanofluid ferromagnetic graphite

We report on unusual magnetic properties observed in the nanofluid room-temperature ferromagnetic graphite (with an average particle size of l=10nm). More precisely, the measured magnetization exhibits a low-temperature anomaly (attributed to manifestation of finite size effects below the quantum temperature) as well as pronounced temperature oscillations above T=50K (attributed to manifestation of the hard-sphere type pair correlations between ferromagnetic particles in the nanofluid)

Screening effects in flow through rough channels

A surprising similarity is found between the distribution of hydrodynamic stress on the wall of an irregular channel and the distribution of flux from a purely Laplacian field on the same geometry. This finding is a direct outcome from numerical simulations of the Navier-Stokes equations for flow at low Reynolds numbers in two-dimensional channels with rough walls presenting either deterministic or random self-similar geometries. For high Reynolds numbers, when inertial effects become relevant, the distribution of wall stresses on deterministic and random fractal rough channels becomes substantially dependent on the microscopic details of the walls geometry. In addition, we find that, while the permeability of the random channel follows the usual decrease with Reynolds, our results indicate an unexpected permeability increase for the deterministic case, i.e., ``the rougher the better''. We show that this complex behavior is closely related with the presence and relative intensity of recirculation zones in the reentrant regions of the rough channel.Comment: 4 pages, 5 figure

Invasion Percolation Between two Sites

We investigate the process of invasion percolation between two sites (injection and extraction sites) separated by a distance r in two-dimensional lattices of size L. Our results for the non-trapping invasion percolation model indicate that the statistics of the mass of invaded clusters is significantly dependent on the local occupation probability (pressure) Pe at the extraction site. For Pe=0, we show that the mass distribution of invaded clusters P(M) follows a power-law P(M) ~ M^{-\alpha} for intermediate values of the mass M, with an exponent \alpha=1.39. When the local pressure is set to Pe=Pc, where Pc corresponds to the site percolation threshold of the lattice topology, the distribution P(M) still displays a scaling region, but with an exponent \alpha=1.02. This last behavior is consistent with previous results for the cluster statistics in standard percolation. In spite of these discrepancies, the results of our simulations indicate that the fractal dimension of the invaded cluster does not depends significantly on the local pressure Pe and it is consistent with the fractal dimension values reported for standard invasion percolation. Finally, we perform extensive numerical simulations to determine the effect of the lattice borders on the statistics of the invaded clusters and also to characterize the self-organized critical behavior of the invasion percolation process.Comment: 7 pages, 11 figures, submited for PR

Gravity with extra dimensions and dark matter interpretation: Phenomenological example via Miyamoto-Nagai galaxy

A configuration whose density profile coincides with the Newtonian potential for spiral galaxies is constructed from a 4D isotropic metric plus extra dimensional components. A Miyamoto-Nagai ansatz is used to solve Einstein equations. The stable rotation curves of such system are computed and, without fitting techniques, we recover with accuracy the observational data for flat or not asymptotically flat galaxy rotation curves. The density profiles are reconstructed and compared to that obtained from the Newtonian potential.Comment: 10 pages, 10 figures, submitted to Brazilian Journal of Physic

Bearing capacity of spread foundations on rock masses according to EC7

O Eurocódigo 7 (EC7) define diretivas para o projeto de fundações superficiais assentes em maciços rochosos e apresenta o exemplo de um método para estimar a capacidade resistente presumida deste tipo de fundação. Contudo, o mesmo não tem em conta importantes fatores que influenciam a capacidade de carga da fundação, o que pode ser considerado como uma importante limitação. Neste trabalho, o método recomendado pelo EC7 é comparado com dois métodos existentes na literatura. São utilizados dois casos de estudo simples e os resultados são comparados. Da análise dos resultados detetou-se que a capacidade resistente obtida utilizando o método do EC7 é a menos conservativa num dos casos analisados e a mais conservativa, conjuntamente com um dos métodos alternativos, no outro caso estudado. Isto revela que o método preconizado pelo EC7 deve ser usado com precaução mesmo em casos muito simples.In Eurocode 7 (EC7), some guidelines are provided for the design of spread foundations built on rock masses and a method for the calculation of the bearing capacity for this type of foundations is suggested. However, this method does not take into account important factors that influence the bearing capacity of the foundation, which can be an important limitation of the method. In this work, the EC7 method is compared with two other methods that can be found in literature. They are applied to two simple examples and the results are compared. The results revealed the EC7 method as the least conservative in one of the analysed cases and the greatest conservative, jointly with other used method, in the other studied case. This means that the EC7 method should be used with caution even for very simple cases

Application of RIAM to the environmental impact assessment of hydroelectric installations

This paper evaluates an Environmental Impact Assessment (EIA) using the Rapid Impact Assessment Matrix (RIAM). It analyses and presents in a structured, friendly and transparent environment the numerous parameters and alternatives of an EIA. It considers all 4 components: physical / chemical, biological / ecological, social / cultural, economic / operational. These are then evaluated using universal criteria common to all impact consideration. Figures and tables made comparisons much easier. This Matrix was applied to the EIA of the future Vale de Madeira Hydroelectric Installation that will be situated on the River Côa of the Douro River Basin in the Municipalities of Pinhel and Figueira de Castelo Rodrigo, North of Portugal. It will be shown that such a project will be positive economically but negative otherwise (as related to the other three components evaluated in RIAM)