Search results for "Dispersion"

Axial dispersion model for solid flow in liquid suspension in system of two mixers in total recycle

2006

The measurement of residence time distribution of solid particles in solid-liquid suspension is experimentally difficult. However, the twin system approach is particularly suited for the assessment of particle RTD in flow systems as it allows overcoming some of the usual difficulties generally encountered in this kind of measurement. Twin system consists of two vessels and external piping in total recycle. Experimental results from this system can be evaluated using Z-transforms to derive particle RTD for subsequent testing of alternative flow models. Recently, the axial dispersion model was applied using the "advection diffusion equation" (sometimes called the"diffusion with bulk flow equa…

Oblique surface waves at an interface between a metal–dielectric superlattice and an isotropic dielectric

2012

We investigate the existence and dispersion characteristics of surface waves that propagate at an interface between a metal–dielectric superlattice and an isotropic dielectric. Within the long-wavelength limit, when the effective-medium (EM) approximation is valid, the superlattice behaves like a uniaxial plasmonic crystal with the main optical axes perpendicular to the metal–dielectric interfaces. We demonstrate that if such a semi-infinite plasmonic crystal is cut normally to the layer interfaces and brought into contact with a semi-infinite dielectric, a new type of surface mode can appear. Such modes can propagate obliquely to the optical axes if favorable conditions regarding the thick…

I popolamenti faunistici pleistocenici della Sicilia.

2008

Macroecological properties of ammonites : spatial distribution, phylogeny, and faunal similarity

2016

The present work, which lies between macroecology and macroevolution, focuses on the spatio-temporal dynamics of early Pliensbachian ammonites of the western Tethys. Two main questions are addressed: how does inter-assemblage compositional similarity decrease with geographical distance? What is the relationship between species range size and phylogeny, species duration and latitudinal position?Ammonite dispersal dynamics are studied through a multi-scale Similarity Distance Decay analysis. We show that their long-distance dispersal is facilitated when the environment is more homogeneous and that it is not related to their morphology. This suggests that their long-distance dispersal occurred…

Gas—liquid chromatographic analyses

1989

Abstract The retention (I), dispersion (IM) and selectivity (I*) indices of sixteen polychlorinated dibenzo-p-dioxins and fourteen polychlorinated dibenzofurans were determined on a low-polarity HP-5 capillary column using a gas chromatograph connected with an ion-selective detector. IM and I* values were also calculated for all 73 dibenzo-p-dioxins from the di- to the octachloro isomer and for all possible 135 chlorinated dibenzofurans based on the predicted retention index data reported earlier. The effect of the position of chlorination is shown and the results are compared with those for several series of chlorinated aromatics.

All-optical regeneration of polarization of a 40 Gbit/s return-to-zero telecommunication signal

2013

International audience; We report all-optical regeneration of the state of polarization of a 40 Gbit/s return-to-zero telecommunication signal. The device discussed here consists of a 6.2-km-long nonzero dispersion-shifted fiber, with low polarization mode dispersion, pumped from the output end by a backward propagating wave coming from either an external continuous source or a reflection of the signal. An initially scrambled signal acquires a degree of polarization close to 100% toward the polarization generator output. All-optical regeneration is confirmed by means of polarization and bit-error-rate measurements as well as real-time observation of the eye diagrams. We show that the physic…

Numerical simulations of air pollutant dispersion in a stratified planetary boundary layer

1978

Abstract A numerical model is described for computing pollutant concentration distributions downwind from a source. It is based on the three-dimensional dispersion equation governing the time-dependent advective and diffusive transport of air pollutants and is solved numerically by a mixed Lagrangian-Eulerian finite-difference scheme. The model includes the vertical wind shear, the turning of the actual wind, and vertical variations of the vertical eddy diffusivity. In this paper the model is used to simulate the pollutant dispersion process in a stratified planetary boundary layer. The vertical profiles of horizontal mean wind and vertical eddy diffusivities are calculated numerically from…

Dispersion models and air quality data for population exposure assessment to air pollution

2014

Evaluating the extent of exposure to chemicals in absence of continuous measurements of their concentration in air and direct measures of personal exposure is crucial for epidemiological studies. Dispersion models can be a useful tool for reproducing spatio-temporal distribution of contaminants emitted by a specific source. However, they cannot easily be applied to short-term epidemiological studies because they require precise information on daily emission scenarios for a long time, which are generally not available. The aim of this study was to better assess the exposure in the industrial area of Brindisi, which suffers from various critical epidemiological situations, by integrating air …

A new approach for modeling dry deposition velocity of particles

2018

Abstract The dry deposition process is recognized as an important pathway among the various removal processes of pollutants in the atmosphere. In this field, there are several models reported in the literature useful to predict the dry deposition velocity of particles of different diameters but many of them are not capable of representing dry deposition phenomena for several categories of pollutants and deposition surfaces. Moreover, their applications is valid for specific conditions and if the data in that application meet all of the assumptions required of the data used to define the model. In this paper a new dry deposition velocity model based on an electrical analogy schema is propose…

A more cost-effective geomatic approach to modelling PM10 dispersion across Europe

2014

International audience; PM10 concentrations in most major European cities exceed the limits set by the European Directive and are expected to continue to do so in the coming years. Moreover, PM10s can be transported over long distances impacting air quality, public health and ecosystem functionality far from their sources of emission. Modelling remains one of the only options for tracking PM10 deposition in remote areas with no monitoring stations. Even so, air pollution models based on atmospheric physics usually imply substantial economic, logistical and computational investment. In this work, we present a new geomatic approach to modelling mean annual PM10 concentrations across Europe. O…