25,016 research outputs found
Luminosity segregation versus fractal scaling in the galaxy distribution
In this letter I present results from a correlation analysis of three galaxy
redshift catalogs: the SSRS2, the CfA2 and the PSCz. I will focus on the
observation that the amplitude of the two--point correlation function rises if
the depth of the sample is increased. There are two competing explanations for
this observation, one in terms of a fractal scaling, the other based on
luminosity segregation. I will show that there is strong evidence that the
observed growth is due to a luminosity dependent clustering of the galaxies.Comment: 7 pages, EPL in pres
The flow field in the slender combustion chambers of solid propellant rockets
We analyse the near inviscid flow field generated in a slender non-axisymmetric cylindrical cavity by the gasification and combustion reactions of a surrounding solid propellant grain. These reactions are confined to a thin layer adjacent to the surface of the solid propellant, so that the flow is non-reacting in most of the cavity, and of the same form as the flow in slender ducts due to fluid injection through lateral porous walls.
The non-reacting flow can be described in terms of self-similar solutions of the Navier -Stokes equations that we calculate numerically for star-shaped grain configurations, with Reynolds numbers only moderately large for the flow to remain laminar and steady. The self-similar flows for non-axisymmetric configurations show strong axial vortices that we analyze using the Euler simplified form of the flow equations for large Reynolds numbers, and the general solution of the Burgers equation for strained vortices that describes their viscous cores; a logarithmic singularity could then be encountered at their center line
Typical length scales in conducting disorderless networks
We take advantage of a recently established equivalence, between the
intermittent dynamics of a deterministic nonlinear map and the scattering
matrix properties of a disorderless double Cayley tree lattice of connectivity
, to obtain general electronic transport expressions and expand our
knowledge of the scattering properties at the mobility edge. From this we
provide a physical interpretation of the generalized localization length.Comment: 12 pages, 3 figure
Directed Random Markets: Connectivity determines Money
Boltzmann-Gibbs distribution arises as the statistical equilibrium
probability distribution of money among the agents of a closed economic system
where random and undirected exchanges are allowed. When considering a model
with uniform savings in the exchanges, the final distribution is close to the
gamma family. In this work, we implement these exchange rules on networks and
we find that these stationary probability distributions are robust and they are
not affected by the topology of the underlying network. We introduce a new
family of interactions: random but directed ones. In this case, it is found the
topology to be determinant and the mean money per economic agent is related to
the degree of the node representing the agent in the network. The relation
between the mean money per economic agent and its degree is shown to be linear.Comment: 14 pages, 6 figure
‘Not as Bad as…’ The Concept of Disadvantage in the Justification of Positive Action under UK Anti-Discrimination Law
An essential goal of anti-discrimination law is to break the connection between disadvantage and group membership. There should not be a predictable link between being a member of a group with a protected characteristic and being disadvantaged in society. Positive action is the ultimate tool to achieve this aim, however, its application in the UK has been scarce. In this paper, I argue that the relevant concept of disadvantage in discrimination claims is different from the one used to justify positive action. This distinction impacts on the proportionality test and allows clarification of the potentialities and limitations of positive action to redress inequality. This attempt stands from a theoretical point of view but also highlights the reasoning behind recent cases under UK and EU anti-discrimination law
Wetland restoration and nitrate reduction: the example of the periurban wetland of Vitoria-Gasteiz (Basque Country, North Spain)
Changes in land use and agricultural intensification caused wetlands on the quaternary aquifer of Vitoria-Gasteiz (Basque Country) to disappear some years ago and nitrate concentration in groundwaters increased very quickly. The Basque Government recently declared the East Sector of this aquifer a Vulnerable Zone according to the 91/676/CEE European Directive. Recently, the wetlands have been restored through the closure of the main drainage ditches, the consequent elevation of the water table and the abondonment of agricultural practices near the wetlands. This is the case of the Zurbano wetland. Restoration has allowed the recovery of its biogeochemical function, which has reduced nitrate concentrations in waters. Nitrate concentrations which exceed 50 mg l–1 in groundwaters entering into the wetland are less than 10 mg l–1 at the outlet. Conditions in the wetland are conducive to the loss of nitrates: organic matter rich wetted soils, clay presence allowing a local semiconfined flow and very low hydraulic gradient. Water quality monitoring at several points around the wetland showed the processes involved in nitrate loss, although some aspects still remain unresolved. However, during storm events, the wetland effectively reduces the nitrate concentration entering the Alegria River, the most important river on the quaternary aquifer
On the use of the Bingham statistical distribution in microsphere-based constitutive models for arterial tissue
Constitutive models for arterial tissue have been an active research field during the last years. The main micro-constituents of blood vessels are different types of cells and the extra-cellular matrix formed by an isotropic high water content ground substance and a network composed of elastin and collagen fibres. Usually the arterial tissue has been modelled as a hyperelastic material within the framework of continuum mechanics, whereas inclusion of structural tensors into constitutive laws is the most widely used technique to introduce the anisotropy induced by the fibres. Though the different existing fibre bundles present a clear preferential direction, the dispersion inherent to biological tissue advices using of constitutive models including representative structural information associated to the spatial probabilistic distribution of the fibres. Lately, microsphere-based models have demonstrated to be a powerful tool to incorporate this information. The fibre dispersion is incorporated by means of an Orientation Density Function (ODF) that weights the contribution of each fibre in each direction of the micro-sphere. In previous works the rotationally symmetric von Mises ODF was successfully applied to the modelling of blood vessels. In this study, the inclusion of the Bingham ODF into microsphere-based model is analysed. This ODF exhibits some advantages with respect to the von Mises one, like a greater versatility and a comparable response to simple tension and equibiaxial tension tests.Peer ReviewedPostprint (author's final draft
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