Dispersion of passive particles by a quasi-two-dimensional turbulent flow

Using the experimental data of Paret and Tabeling [Phys. Rev. Lett. 79, 4162 (1997)] we consider in detail the dispersion of particle pairs by a two-dimensional turbulent flow and its relation to the kinematic properties of the velocity field. We show that the mean square separation of a pair of particles is governed by rather rare, extreme events and that the majority of initially close pairs are not dispersed by the flow. Another manifestation of the same effect is the fact that the dispersion of an initially dense cluster is not the result of homogeneously spreading the particles within the whole system. Instead it proceeds through a splitting into smaller but also dense clusters. The statistical nature of this effect is discussed.

Sobre el area de dispersion de Artemisia tournefortiana Reich. en la Peninsula Iberica

Al consultar los pliegos de Artemisia L. contenidos en el Herbario BCF, con motivo de la revisión de dicho género en la Península Ibérica, que estamos realizando como tesis doctoral, hemos hallado dos de ellos (BCF n.° 7473 y n.° 7475) recolectados por don Salvador Rivas Goday, el 17 de septiembre de 1948, en Titulcia (MADRID) y determinados como Artemisia variabilis Ten.

A proposito de la dispersion de Verbascum boerhavii L. var. bicolor (Bad.) Arcang. en Catalunya

A propósito de la dispersión de Verbascum boerhavii var. bicolor (Bad.) Arcang. en Catalunya. Verbascum boerhavii L. var. bicolor (Bad.) Arcang., Comp. Fl. Ital. 505 (1882). = V. bicolor Bad., Osserv., 3 (1824) = V. boerhavii L. fma. bicolor (Bad.) Murb., Lunds. Univ. Arssk, 29 (2): 159 (1933). = V. maiale DC. var. bicolor (Bad.) Rouy, Fl. Fr. 9:9 (1909).

Experimental investigation of the initial regime in fingering electrodeposition: Dispersion relation and velocity measurements.

Recently a fingering morphology, resembling the hydrodynamic Saffman-Taylor instability, was identified in the quasi-two-dimensional electrodeposition of copper. We present here measurements of the dispersion relation of the growing front. The instability is accompanied by gravity-driven convection rolls at the electrodes, which are examined using particle image velocimetry. While at the anode the theory presented by Chazalviel et al. [J. Electroanal. Chem. 407, 61 (1996)] describes the convection roll, the flow field at the cathode is more complicated because of the growing deposit. In particular, the analysis of the orientation of the velocity vectors reveals some lag of the development of the convection roll compared to the finger envelope.

Fluid flow and dispersion predictions in porous media by utilizing advanced numerical methods

Diplomityön tavoitteena oli tarkastella numeerisen virtauslaskennan avulla virtaukseen liittyviä ilmiöitä ja kaasun dispersiota. Diplomityön sisältö on jaettu viiteen osaan; johdantoon, teoriaan, katsaukseen virtauksen mallinnukseen huokoisessa materiaalissa liittyviin tutkimusselvityksiin, numeeriseen mallinnukseen sekä tulosten esittämiseen ja johtopäätöksiin. Diplomityön alussa kiinnitettiin huomiota erilaisiin kokeellisiin, numeerisiin ja teoreettisiin mallinnusmenetelmiin, joilla voidaan mallintaa virtausta huokoisessa materiaalissa. Kirjallisuusosassa tehtiin katsaus aikaisemmin julkaistuihin puoliempiirisiin ja empiirisiin tutkimusselvityksiin, jotka liittyvät huokoisen materiaalin aiheuttamaan painehäviöön. Numeerisessa virtauslaskenta osassa rakennettiin ja esitettiin huokoista materiaalia kuvaavat numeeriset mallit käyttäen kaupallista FLUENT -ohjelmistoa. Työn lopussa arvioitiin teorian, numeerisen virtauslaskennan ja kokeellisten tutkimusselvitysten tuloksia. Kolmiulotteisen huokoisen materiaalinnumeerisessa mallinnuksesta saadut tulokset vaikuttivat lupaavilta. Näiden tulosten perusteella tehtiin suosituksia ajatellen tulevaa virtauksen mallinnusta huokoisessa materiaalissa. Osa tässä diplomityössä esitetyistä tuloksista tullaan esittämään 55. Kanadan Kemiantekniikan konferenssissa Torontossa 1619 Lokakuussa 2005. ASME :n kansainvälisessä tekniikan alan julkaisussa. Työ on hyväksytty esitettäväksi esitettäväksi laskennallisen virtausmekaniikan (CFD) aihealueessa 'Peruskäsitteet'. Lisäksi työn yksityiskohtaiset tulokset tullaan lähettämään myös CES:n julkaisuun.

Networks of noisy oscillators with correlated degree and frequency dispersion

We investigate how correlations between the diversity of the connectivity of networks and the dynamics at their nodes affect the macroscopic behavior. In particular, we study the synchronization transition of coupled stochastic phase oscillators that represent the node dynamics. Crucially in our work, the variability in the number of connections of the nodes is correlated with the width of the frequency distribution of the oscillators. By numerical simulations on Erdös-Rényi networks, where the frequencies of the oscillators are Gaussian distributed, we make the counterintuitive observation that an increase in the strength of the correlation is accompanied by an increase in the critical coupling strength for the onset of synchronization. We further observe that the critical coupling can solely depend on the average number of connections or even completely lose its dependence on the network connectivity. Only beyond this state, a weighted mean-field approximation breaks down. If noise is present, the correlations have to be stronger to yield similar observations.

Agglomeration vs. dispersion of economic activities in the districts of Paris

The spatial distribution of economic activity has often been analysed for wide geographical areas such as regions or metropolitan areas, but it has rarely been subject to microanalysis, especially outside the U.S. In this paper we focus on what happens within a large European city (Par is), and analyse how the industrial composition of its districts differs and how these districts evolve. We also analyse suburbanization process for both residents and the workforce and provide empirical evidence about the changing roles of the core and intramuros periphery. Keywords: agglomeration, suburbanization, Paris, micropolitan analysis

Quantification of the bond-angle dispersion by Raman spectroscopy and the strain energy of amorphous silicon

A thorough critical analysis of the theoretical relationships between the bond-angle dispersion in a-Si, Δθ, and the width of the transverse optical Raman peak, Γ, is presented. It is shown that the discrepancies between them are drastically reduced when unified definitions for Δθ and Γ are used. This reduced dispersion in the predicted values of Δθ together with the broad agreement with the scarce direct determinations of Δθ is then used to analyze the strain energy in partially relaxed pure a-Si. It is concluded that defect annihilation does not contribute appreciably to the reduction of the a-Si energy during structural relaxation. In contrast, it can account for half of the crystallization energy, which can be as low as 7 kJ/mol in defect-free a-Si

EVALUATION OF A BUFFERED SOLID PHASE DISPERSION PROCEDURE ADAPTED FOR PESTICIDE ANALYSES IN THE SOIL MATRIX

An evaluation of the pesticides extracted from the soil matrix was conducted using a citrate-buffered solid phase dispersion sample preparation method (QuEChERS). The identification and quantitation of pesticide compounds was performed using gas chromatography-mass spectrometry. Because of the occurrence of the matrix effect in 87% of the analyzed pesticides, the quantification was performed using matrix-matched calibration. The method's quantification limits were between 0.01 and 0.5 mg kg-1. Repeatability and intermediate precision, expressed as a relative standard deviation percentage, were less than 20%. The recoveries in general ranged between 62% and 99%, with a relative standard deviation < 20%. All the responses were linear, with a correlation coefficient (r) ≥0.99.

Dispersion of Hybrid Electromagnetic-Spin Waves in the Slotline

The presented thesis is devoted to investigation of wave processes in hybrid ferrite / ferroelectric structures. Spin wave devices based on ferrite films have such disadvantages, as huge size of the magnetic systems, low tuning velocity, considerable power inputs for parameters control that limits possible device applications. The considered layered structures allow to overcome the disadvantages mentioned and to promote the development of novel class of tunable microwave devices. The proposed theoretical analysis is intended to construct a model of hybrid electromagnetic-spin waves. Based on the theoretical analysis the experimental investigations were carried out. The experimental resonance characteristics of ferrite / ferroelectric resonator were obtained and their tunability by means of magnetic and electric field was demonstrated.

Warning system based on theoretical-experimental study of dispersion of soluble pollutants in rivers

Information about capacity of transport and dispersion of soluble pollutants in natural streams are important in the management of water resources, especially in planning preventive measures to minimize the problems caused by accidental or intentional waste, in public health and economic activities that depend on the use of water. Considering this importance, this study aimed to develop a warning system for rivers, based on experimental techniques using tracers and analytical equations of one-dimensional transport of soluble pollutants conservative, to subsidizing the decision-making in the management of water resources. The system was development in JAVA programming language and MySQL database can predict the travel time of pollutants clouds from a point of eviction and graphically displays the temporal distribution of concentrations of passage clouds, in a particular location, downstream from the point of its launch.

Application of a non isotropic turbulence model to stable atmospheric flows and dispersion over 3D topography

A non isotropic turbulence model is extended and applied to three dimensional stably stratified flows and dispersion calculations. The model is derived from the algebraic stress model (including wall proximity effects), but it retains the simplicity of the "eddy viscosity" concept of first order models. The "modified k-epsilon" is implemented in a three dimensional numerical code. Once the flow is resolved, the predicted velocity and turbulence fields are interpolated into a second grid and used to solve the concentration equation. To evaluate the model, various steady state numerical solutions are compared with small scale dispersion experiments which were conducted at the wind tunnel of Mitsubishi Heavy Industries, in Japan. Stably stratified flows and plume dispersion over three distinct idealized complex topographies (flat and hilly terrain) are studied. Vertical profiles of velocity and pollutant concentration are shown and discussed. Also, comparisons are made against the results obtained with the standard k-epsilon model.

Do We Understand Hydrodynamic Dispersion in Sedimenting Suspensions?

Microstructural changes, that is an important feature for the understanding of the velocity variance in sedimentation is investigated with numerical simulations. The simulations are used to describe velocity fluctuations and hydrodynamic dispersion in a suspension of interacting point-particles sedimenting in a rectangular box with periodic sides and impenetrable bottom and top. It is observed how the positions of the particles evolve in a finite container. The suspension that was initially random in the gravity direction only, tends to be fully randomized as a result of the relative arrangements of the particles and the hydrodynamic interactions between them. The computer simulations, based on statistics over a significant number of particle configurations, suggest velocity variances and diffusivities dependent on the size of the simulated system but with anisotropy in velocity fluctuations and diffusion coefficients nearly independent of the box size.