J.A.G. Orza

Mesoscopic theory of granular fluids

Using fluctuating hydrodynamics we describe the slow buildup of long range spatial correlations in a freely evolving fluid of inelastic hard spheres. In the incompressible limit, the behavior of spatial velocity correlations (including r^(-d) behavior) is governed by vorticity fluctuations only and agrees well with two-dimensional simulations up to 50 to 100 collisions per particle. The incompressibility assumption breaks down beyond a distance that diverges in the elastic limit.

Patterns and long range correlations in idealized granular flows

An initially homogeneous freely evolving fluid of inelastic hard spheres develops inhomogeneities in the flow field u(r, t) (vortices) and in the density field n (r, t)(clusters), driven by unstable fluctuations, δa = {δn, δu}. Their spatial correlations, , as measured in molecular dynamics simulations, exhibit long range correlations; the mean vortex diameter grows as

Simple estimates of vehicle-induced resuspension rates

\xi(t)\propto\sqrt{\ln t}

The association between the North Atlantic oscillation and the interannual variability of the tropospheric transport pathways in Western Europe

; there occur transitions to macroscopic shearing states, etc.The Cahn–Hilliard theory of spinodal decomposition offers a qualitative understanding and quantitative estimates of the observed phenomena. When intrinsic length scales are of the order of the system size, effects of physical boundaries and periodic boundaries (finite size effects in simulations) are important.

Air mass origin and its influence on radionuclide activities (7Be and 210Pb) in aerosol particles at a coastal site in the western Mediterranean

Road dust emissions are considered to be a major source of airborne particulate matter (PM). This is particularly true for industrial environments, where there are high resuspension rates of deposited dust. The calculation of roads as PM emission sources has mostly focused on the consequences of this emission, viz. the increase in PM concentrations. That approach addresses the atmospheric transport of the emitted dust, and not its primary origin. In contrast, this paper examines the causes of the emission. The study is based on mass conservation of the dust deposited on the road surface. On the basis of this premise, estimates of emission rates were calculated from experimental data obtained in a road in a ceramic industrial area.

Wind speed analysis in the province of Alicante, Spain. Potential for small-scale wind turbines

The variations in tropospheric transport pathways over a 20 year period, 1990-2009, are studied at six locations in Europe. Three Atlantic (Lisbon, Mace Head, and Cabauw) and three Mediterranean sites (Malaga and Elche in the western part and Lecce in the central Mediterranean) are considered. The work is based on the identification of flow types at each location by robust cluster analysis of the trajectories, the assessment of temporal trends for each advection pattern, and subsequent quantification of the association, at the monthly scale, between the North Atlantic Oscillation (NAO) index (NAOi) and the frequency of occurrence of the identified flows. This exploratory study demonstrates the usefulness of the approach for specific locations in a context where synoptic circulation/weather-type classifications are usually used. A different number of advection pathways were identified at each location. Common features to all the sites were prevalence of westerly flows, strong seasonal variability, and association of the air flow types to known synoptic situations in both phases of the NAO. The degree of association varies strongly with latitude, location within the Mediterranean basin, and closeness to the action centers. Overall, flows reaching Mace Head and Cabauw present stronger association to the NAO, which is substantially reduced at lower latitudes and is not significant at Lisbon. Significant temporal trends are found for northerly flows at Mace Head and Malaga, associated to changes at the beginning of the study period that are also present in the NAOi time series. WSW flows at Mace Head exhibit a steady decreasing trend over the whole period.