1,720,955 research outputs found
Particle enhanced foam flow in porous media near the critical micelle concentration
No full textThis thesis was performed in the framework of ErasmusMundus EU-INDIA scholarship programme. The main goal is to elucidate particle enhanced foam flow (surfactant water and nitrogen gas) in porous media near the critical micelle concentration. The thesis is divided in four parts: in the first part the modeling of foam flow is investigated, in the second part variables affecting the steady state pressure drop during foam flow are discussed, in the third part the stability of ash particles in the bulk dispersion is tested and in the final part, the effect of the particles on foam flow stability in porous media is experimentally studied. During the period of the study, the set ups for fluid flow and laser scattering of liquids are built and calibrated. We measured pressure drop histories before and after injection of ash particle dispersions with nitrogen gas (N2) across the measurement points in unconsolidated sand packs (1860 and 130 Darcy) and a Bentheimer sand stone core (3 Darcy). This was carried out for various surfactant concentrations (0.0375, 0.075 and 0.15 w/w%), for various gas and surfactant solution velocities (0.27-3.97 m/day), for two salinities (0, 0.5M NaCl) and for two pH values (6.5, 3.0). We used a mathematical formulation with a bubble population function by history matching the experiments. The two-phase flow model that leads to four equations, viz., a pressure equation, a water saturation equation, a bubble density equation and a surfactant transport-adsorption equation can describe the pressure drop during the foam flow experiments. Within the model, the rate of change of bubble density during the transient state can be equated to the bubble density generation function plus the terms accounting for the bubble transport, i.e., by convection and diffusion divided by the porosity saturation product. The effect of the variables (e.g. permeability) on the foam flow is studied by using symbolic regression. We applied a Monte Carlo method (Bootstrap) to calculate the parametric uncertainties. The data driven model obtained without prior knowledge of an underlying physical process can elucidate the general behavior and hierarchy of the variables affecting the steady state pressure drop. The statistical model gives the variable spaces for which more experiments are needed. The trends obtained from the subset of data cannot be derived from the complete data set purely on statistical grounds. To use ash particles in foamflow through porous media we measured their colloidal stability when surfactant is present or absent in the dispersion. We measured properties of dispersions, viz., zeta potential, sedimentation-coagulation behavior, light absorption and particle size for pH values ranging from3 to 11. For the optimal stability of an ash dispersion, we recommend an alkaline mediumwhen surfactant is absent and an acidic medium, when surfactant is present. An ash particle dispersion alone with nitrogen gas cannot generate foamin porous media. The flow of ash particles with foamin porous media (Bentheimer and sandpack) is related to the colloidal stability of the ash dispersion. We observed tiny change in the permeability of the porous media after foam flow experiments with ash particles.Geoscience & EngineeringCivil Engineering and Geoscience
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Foam Flow Experiments. I. Estimation of the Bubble generation-Coalescence Function
No full textGas injection leads to foam formation in porous media in the presence of surfactant solutions, which is used for flow diversion and enhanced oil recovery. We present here laboratory experiments of co-injecting nitrogen and sodium C14?16 alpha olefin sulfonate with two concentrations: 20× the critical micelle concentration (CMC) in an unconsolidated sandpack of 1860 Darcy and at the CMC for a Bentheimer sandstone of 3 Darcy. The steady state profile for the unconsolidated sandpack is achieved after 1.3 pore volumes, whereas for Bentheimer sandstone, steady state is obtained after injection of 12–15 pore volume. A model that leads to four equations, viz., a pressure equation, a water saturation equation, a bubble density equation and a surfactant transport–adsorption equation, is used to explain the experimental pressure drop. It is asserted that the experimental pressure drop across the measurement points can be used to obtain a first estimate of the average bubble density, which can be further used to obtain part of the source term in the bubble density equation. If we consider flowing fraction of foam, the rate of change of bubble density during transient state can be equated to the bubble density generation-coalescence function plus the terms accounted for bubble transport by convection and diffusion divided by porosity and saturation.Geoscience & EngineeringCivil Engineering and Geoscience
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe 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
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe 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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