1,721,096 research outputs found
PORE-SCALE MODELING OF FLOW AND REACTIVE TRANSPORT IN POROUS MEDIA
No full textFlow and reactive transport of fluids in porous media are observed in a wide variety of fields and applications such as hydrology, contaminated site remediation and petroleum engineering. Concerning the environmental issues, fate and transport of dissolved contaminants in natural porous media is a fundamental aspect to understand pollutants migration in groundwater and to identify the most appropriate technologies to remove these compounds from subsurface (i.e. the vadose zone and the groundwater). The traditional approach used to study the motion of fluids (single or multi-phase) and transport of dissolved substances within porous media is based on a macroscopic representation, founded on the continuum hypothesis (Bear, 1972). At this scale, pore-scale effects are embedded into the model through a set of constitutive equations such as the phenomenological Darcy’s law for flow in saturated porous media (Hubbert, 1956; Bear, 1972), Richard’s equation in variable saturated media (Richards, 1931; Van Genuchten, 1980) and the advection-dispersion equation for solute transport (Bear, 1972). When the continuum description breaks down, the need to investigate a more detailed scale as the pore-scale brings to use the Navier-Stokes equations (NSE) and the advection-diffusion (and reaction) equation (ADE), able to capture microscopic-scale gradients in concentration resulting from transport and a non-uniform distribution of reactive material (Steefel et al., 2005; Blunt et al., 2013).
Pore-scale modeling has developed rapidly over the last decades, thanks to the development of both direct 3D imaging of the pore space and faster and more efficiency computing tools. It can be used to predict macroscopic properties of porous media that are difficult to obtain experimentally and provides the opportunity to investigate phenomena impossible to be obtained by laboratory experiments for single and multi-phase fluids. In the framework of pore-scale modeling, the lattice Boltzmann method (LBM) is able to solve the NSE for incompressible fluids and ADE in porous media, which is emerged over the last decades as an alternative approach for computational fluid dynamics (CFD) (Chen and Doolen, 1998; Succi, 2001; Aidun and Clausen, 2010).
Unlike the conventional CFD schemes based on discretization of macroscopic continuum equations, the LBM is based on microscopic models and mesoscopic kinetic equation. The main features are the relatively ease to code, versatility to model different process, handle complex boundary conditions and its efficiency for parallel platforms (Latt, 2009, Coon et al., 2014).
For the above-mentioned reasons, the goal of my research is the study of pore-scale effects on different flow and transport processes, which have a close relationship with contaminant dynamics at a macroscopic scale (i.e. laboratory and field scale). Each of these processes is addressed in the following chapters of the thesis. The thesis consists of a collection of scientific papers, except for the first chapter, submitted to or already published in international journals and is organized as follows.
In chapter I, the basics of the LB algorithm are introduced. The numerical schemes for the simulation of fluid flow and transport process of a concentration field are described.
In chapter II, the effects of the pore spatial distribution on seepage velocity through numerical simulations of 3D fluid flow performed by the lattice Boltzmann method are investigated. The goal of this work is to evaluate the sensitivity of the flow, through the seepage velocity, inside a porous medium to the spatial distribution of the pores size and to address the uncertainty associated to the sample size and resolution. To this scope, we generate 3D porous media using a geostatistical method based on random spatially correlated fields applied at the pore-scale (typically from tens to hundreds μm).
The use of 3D domains allows handling porous media with realistic porosity compared to 2D structures. Finally, a sensitivity analysis of the macroscopic velocity is carried out in relation to two semi-variograms models (or correlation functions) and different spatial resolutions.
In Chapter III, the impact of heterogeneity through pore-scale flux and transport LBM simulations are carried out. One of the effects that heterogeneities produce in the framework of contaminated sites remediation is associated with the retention of pollutants in the finest (or less mobile for an effective transport) regions of the porous media, where contaminants are released by diffusion to more mobile zones after the concentration in the latter is significantly reduced because of efficient transport. Despite its microscopic nature, it may have important implications for macroscale pollutants transport. The process of mass transfer from low to high mobility regions at the back end of a contaminant plume has referred to back diffusion (also defined as matrix diffusion). The main question that we address in this study is the extent to which spatial heterogeneities in the structure (porosity and permeability) of the host porous medium influences the rate of migration of dissolved species (e.g. contaminants).
Chapter IV is dedicated to reactive transport at the pore-scale. A lattice Boltzmann model is developed for surface reaction taking place at the interface between solid-fluids and multiphase fluids (Di Palma et al., 2015). The phase-field approach is used to identify the interface and its orientation, the concentration of reactant at the interface is then calculated iteratively to impose the correct reactive flux condition. The main advantages of the model is that interfaces are considered part of the bulk dynamics and the reactive scheme is introduced in the classical LBM algorithm; as a consequence, the model’s implementation and performance is independent of the interface geometry and orientation. Results obtained with the developed model are compared to analytical solution for three different benchmark tests
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Women’s Ways to Nature: Steinbeck’s (Mock)Pastoral Diptych of Gardening (& Childless) Wives in The Long Valley
Full text linkThe essay is an ecocritical reading of the two short stories that open John Steinbeck’s The Long Valley (1938), “The Chrysanthemums” and “The White Quail.” It maintains that Steinbeck’s pastoral diptych seems to restage the coming of age of an American biocentric consciousness. Moreover, by depicting two opposite female figures of eros and frigidity, and of fertility and barrenness, Steinbeck explores a way out of the decadence of the ideal of westering in his times into the idea of a civilizing art. This art should go back to its roots in the territory by coming close again to the earth, the body, and a holistic view of life. Mary and Elisa are both figures of the artist, but while Mary uses nature as a means of self-expression, Elisa is a means for nature to express itself. They face each other as portraits of the egocentric versus the ecocentric artist
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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