130,700 research outputs found
Seeing and knowing: Story and plot in '5x2'
No full textRecounting a couple's doomed marriage in reverse, Francois Ozon's unsettling representation of romantic incompatibility both manipulates traditional narrative conventions and allows key events to remain ambiguous. As Dennis Bruining contends, the film presents a useful case study in the distinctions between story and plot, and the difficulties that viewers may face in attempting to reconcile them
On the Riemann solutions of the balance equations for steam and water flow in a porous medium
No full textConservation laws have been used to model a variety of physical phenomena and therefore the theory for this class of equations is well developed. However, in many problems, such as transport of hot fluids and gases undergoing mass transfer, balance laws are required to describe the flow. As an example, in this work we obtain the solutions for the basic one-dimensional profiles that appear in the clean up problem or in recovery of geothermal energy. We consider the injection of a mixture of steam and water in several proportions in a porous rock filled with a different mixture of water and steam. We neglect compressibility, heat conductivity and capillarity and present a physical model for steam injection based on the mass balance and energy conservation equations. We describe completely all possible solutions of the Riemann problem. We find several types of shock between regions and develop a scheme to find the solution from these shocks. A new type of shock, the evaporation shock, is identified in the Riemann solution. This work generalizes the work of Bruining et. al., where the condensation shock appears. It is a step towards obtaining a general method for solving Riemann problems for a wide class of balance equations with phase changes.GeotechnologyCivil Engineering and Geoscience
Automated rock mass characterisation using 3-D terrestrial laser scanning
No full textThe research investigates the possibility of using point cloud data from 3-D terrestrial laser scanning as a basis to characterise discontinuities in exposed rock massed in an automated way. Examples of discontinuities in rock are bedding planes, joints, fractures and schistocity. The characterisation of discontinuities is of importance, since they determine to a large extend the geotechnical behaviour of the entire rock mass. The conventional way of characterising discontinuities is by manual geological survey using geological compass and measuring tape. A logical alternative to the conventional methods for surveying rock faces is the use of 3-D terrestrial laser scanning. A 3-D terrestrial laser scanning survey yield a 3-D point cloud but this data does not yet provide the information on the character of the discontinuities that can be seen in the rock exposure. In this research two different approaches are followed: the first approach uses surface reconstruction through interpolation of the point cloud and the second approach makes use of direct segmentation of the original point cloud. The main conclusion of this research is that it is possible to automate the derivation of discontinuity orientation and spacing information with both methods. Point cloud segmentation is however, the most preferred approach, since it does not require prior surface reconstruction, is therefore faster, and is not strongly influenced by vegetation and other noise in the data. Point cloud segmentation uses the original point cloud, so there is no data loss, which is unavoidable with a surface reconstruction approach.GeotechnologyCivil Engineering and Geoscience
Combustion for Enhanced Recovery of Light Oil at Medium Pressures
No full textUsing conventional production methods, recovery percentages from oil reservoirs range from 5% for difficult oil to 50% for light oil in highly permeable homogeneous reservoirs. To increase the oil recovery factor, enhanced oil recovery (EOR) methods are used. We distinguish EOR that uses chemical methods, (partially) miscible methods and thermal methods. Air injection is categorized as a thermal recovery method as it leads to combustion and therefore high temperature in the reservoir. However, many oil recovery mechanisms are involved in air injection process, including sweeping by flue gases, field re-pressurization by the injected gas, oil swelling, oil viscosity reduction, stripping off light components in the oil by flue gas and thermal effects generated by the oxidation reactions. Our interest is in recovering light oil from low permeability heterogeneous reservoirs using air injection leading to oil combustion, as the heated oil vaporizes away from the lower permeability parts to be collected in the higher permeability streaks. Due to simultaneous vaporization, the combustion at medium pressures, i.e., at medium depth, occurs at medium temperatures. Our focus is on air injection at medium pressures (? 10?90 bars) to reduce the high compression costs and to avoid fracturing at shallower depth. We study this process at low air injection rates to mimic the processes in the main reaction zone (away from the injection well) in an oil reservoir, which provides a long residence time for the oxygen to be in contact with the oil. The main recovery mechanism that we consider for medium pressures is the interaction between vaporization and combustion of light oil. In the thesis, we consider exclusively modeling and simulation of air injection in light oil leading to medium temperature oxidation (MTO). In MTO, all physical processes, reaction, vaporization, condensation and filtration, are active. The main purpose of the thesis is to elucidate the prevailing mechanisms in MTO. Therefore we developed a 1-D model considering light oil recovery through displacement by air at medium pressures and low injection rates and performed both numerical and laboratory experiments to validate the MTO concept. The presence of liquid fuel, which is mobile and can vaporize or condense, is a challenge for modeling of the combustion process. We only consider the one dimensional flow problem, expecting that its solution contributes to understanding the MTO process and determine the displacement efficiency. The detailed mechanism depends on diffusive processes (capillary, molecular diffusion and heat conductivity), oil composition, air injection rate, pressure, and the presence of reaction water and initial water saturation. Each chapter is summarized as follows: In Chapter 2, the modeling and simulation of the MTO process are exclusively studied including mass-, thermal and capillary-diffusion for air injection in light oil reservoirs. In this case, we consider only single pseudo-component oil, e.g., heptane as liquid fuel in dry porous rock, to improve the understanding of the oxidation/vaporization/condensation mechanisms. It turns out that the oxidation, vaporization and condensation often occur close to each other and move with the same speed in the porous medium (resonant structure). The temperature variation is bounded by the oil boiling temperature and thus not very large. We analyze the effect of capillary pressure, heat conductivity and diffusion and compare the results with the analytical solution in the absence of diffusion processes. The numerical simulation results and the analytical results with zero diffusion processes show qualitatively similar behavior. The solution consists of three types of waves, i.e., a thermal wave, an MTO wave and saturation waves separated by constant state regions. The effect of the diffusive terms is as follows. Molecular diffusion lowers the temperature in the MTO region, but creates a small peak in the vaporization region. Capillary diffusion increases the temperature upstream of the MTO region. Higher capillary diffusion increases the recovery by gas displacement and leaves less oil for combustion. The analytical solution, without diffusive terms, and the numerical solution become qualitatively different at very high capillary diffusion coefficients. The effect of thermal diffusion smoothes the thermal wave and widens the hydrocarbon vapour region. In Chapter 3, we extended 1-D model involving a two-component oil mixture, e.g., light and medium oils as pseudo-components in dry porous rock. The light component (heptane) both vaporizes and combusts, whereas medium fraction in the oil mixture only reacts with oxygen, but its vaporization is disregarded. It was anticipated that at increasing medium oil content the nature of the combustion process would change from MTO to high temperature oxidation (HTO). The main discerning factor in the MTO combustion process is the ratio between vaporization and combustion in the low injection rate regime. It turns out that also with the two-component mixture, oxidation, vaporization and condensation often occur close to each other in the MTO wave. The character of the MTO wave changes by altering the composition of the oil. Vaporization occurs upstream of the combustion process when oil mixture is composed of a higher fraction of light component. This fact confirms previously obtained analytical and numerical solutions for one component volatile oil. The combustion front velocity is high as less oil remains behind in the combustion zone. Whereas, for a predominantly medium oil mixture (0.8 of medium component fraction in volume fraction), the vaporization moves downstream of the combustion zone in the MTO wave. As more oil stays behind in the combustion zone, the velocity of the combustion zone is slower, albeit that the temperatures are much higher. Due to high temperatures, we conjecture a transition to the HTO process in this case. To summarize, numerical calculations establish a range of parameters for the bifurcation point between MTO and HTO in a two-component oil mixture. Indeed, the bifurcation point is mainly determined by the fraction of the non-volatile component. At the bifurcation the character of the combustion process changes from a vaporization-dominated (MTO) to a combustion-dominated process (HTO). In Chapter 4, we investigate the effects of water on the oxidation/vaporization/ condensation mechanisms in the MTO wave by considering a simple three phase model involving a one-component oil (e.g., heptane, pentane or dodecane) and water in porous rock. The single pseudo-component oil vaporizes/condenses as well as combusts, whereas water only vaporizes and condenses. It was anticipated that only if the boiling point of oil is around or modestly higher (below 200oC) than the boiling point of water, the presence of water is conducive to higher and faster oil recovery. The main emphasis of this Chapter is to investigate the relative importance of steam condensation, vaporization/condensation of oil and combustion in the low injection rate regime. The numerical solution consists of a thermal wave, a steam condensation front coinciding with or downstream of the medium temperature oxidation (MTO) wave (oil vaporization and combustion), and a three-phase saturation wave region involving oil, gas and water. Numerical calculations show that the presence of water makes the light oil recovery more efficient and faster and diminishes the adverse effect of high oil boiling points. When the boiling point of the volatile oil is about or slightly higher than the boiling point of water, the speed of the MTO wave (oil vaporization/combustion front) is equal to the speed of the steam condensation front. The volatile oil condenses at the same location as the steam, which leads to complete oil recovery. However, when the boiling point of the oil is much higher than the boiling point of water, the steam condensation front moves ahead of the MTO wave. Numerical calculations make it possible to estimate the bifurcation point (oil boiling point) at which a solution for which steam condensation and combustion occur simultaneously changes to a solution where the steam condenses downstream of the combustion zone. We show that replacing the medium boiling volatile oil by a high boiling point oil (e.g., dodecane) decreases the MTO wave speed with respect to the steam condensation front and leads to delayed recovery. In Chapter 5, a set of experiments have been designed that enables investigation of the medium pressure air injection process at low injection rate in consolidated porous media saturated with one-component oil in a ramped temperature reactor. The initial aim of the laboratory experiments was to validate various aspects considered in Chapters 2-4. The experiments were carried out to evaluate the mechanisms of the combustion reaction at different pressures and injection rates. At slower rates we expect to see details that are not visible for the experiments operating at high rates and high pressures. The most important aspect in this Chapter was to observe that an oxygen sorption step takes place at low temperatures prior to the full combustion reaction. The mechanism of initial uptake of oxygen for later release was established in this work. The sorbed oxygen bonds with hydrocarbon physically or chemically leading to complete uptake of oxygen from the injected air stream at low temperatures. At a later stage, the compound, which contains the chemically or physically adsorbed oxygen, desorbs the oxygen and further undergoes oxidation reactions to produce CO and CO2. The produced liquid is hexadecane; it is not altered by an oxidation reaction because it has the same viscosity and density, which argues against chemisorption. The laboratory experiments indicate displacement efficiencies between 75?90% of the Oil Initially In Place. The amount of oil burned in the air injection process relative to the amount of oil recovered in our laboratory experiments for hexadecane increased from 2% at 10 bar to 18% at 30 bar, and again decreased to 5% at 45 bar, after which it more or less remained constant. This trend was previously obtained by the analytical results of medium temperature oxidation process. It was also shown that the oil recovery is faster at higher pressures.Petroleum EngineeringGeoscience & EngineeringCivil Engineering and Geoscience
MeSH term explosion and author rank improve expert recommendations
No full textInformation overload is an often-cited phenomenon that reduces the productivity, efficiency and efficacy of scientists. One challenge for scientists is to find appropriate collaborators in their research. The literature describes various solutions to the problem of expertise location, but most current approaches do not appear to be very suitable for expert recommendations in biomedical research. In this study, we present the development and initial evaluation of a vector space model-based algorithm to calculate researcher similarity using four inputs: 1) MeSH terms of publications; 2) MeSH terms and author rank; 3) exploded MeSH terms; and 4) exploded MeSH terms and author rank. We developed and evaluated the algorithm using a data set of 17,525 authors and their 22,542 papers. On average, our algorithms correctly predicted 2.5 of the top 5/10 coauthors of individual scientists. Exploded MeSH and author rank outperformed all other algorithms in accuracy, followed closely by MeSH and author rank. Our results show that the accuracy of MeSH term-based matching can be enhanced with other metadata such as author rank
Successful management buyouts: Are they really more entrepreneurial?
No full textThe paper explores the impact of entrepreneurial management dimensions on post-MBO financial performance. We use Stevenson’s conceptualization of entrepreneurship (1983), empirically validated by Brown, Davidsson and Wiklund (2001), positing that entrepreneurial companies will be involved in recognizing and exploiting opportunity, regardless of the resources controlled. From the literature we hypothesize positive effects of entrepreneurial management dimensions on post-MBO financial performance. We find that successful buyout managers cannot be classified as entrepreneurs on all entrepreneurial dimensions. Instead they ambidextrously combine the pursuit of valuable opportunities with the exploitation and control of their resources. Implications for theory and managerial practice are discussed.Entrepreneurial Management;Financial Performance;Management Buyouts
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe 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
"Closing the R&D Gap, Evaluating the Sources of R&D Spending"
No full textBoth spending and tax policies have been implemented in the United States with the goal of stimulating private sector research and development (R&D). Karier questions whether current R&D policy, especially the research and experimentation tax credit, can contribute to closing the gap between nondefense expenditures on R&D in the United States and such expenditures in other countries, such as Japan and Germany. He also explores possible changes to our current R&D policy to make it more effective.
Dispelling the Myths Behind First-author Citation Counts
No full textWe 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
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