122,100 research outputs found
Private Equity Funds Dataset
No full textPreqin on funds (size, crossborder within EU) and fundmanagers and Worldbank on GDP of the memberstates.Merged in Stata on Fundmanagers as common identifier (N=1.630). Independent variable is the implementation of AIMFD in 2013; Dependent variables are PE capital supply (fundsizes) and PE crossborder deals. Control variables: PE firm age and PE experience, and GDP. OLS regression measuring continuous effect size from AIMFD on Fundsize and Binary logistic regression measuring AIMFD effect on cross-border activity.. The outcomes were correlated with the contractual relationships between institutional investors and PE fundmanagers.</div
The impact of business ownership change on employee relations:Buy-outs in the UK and the Netherlands
No full textCombustion 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
A Multi-Language Comparison of Influences on Author Verification using Character N-Grams
No full textWe create a new multi-language corpus for author verification based on Wikipedia talkpages, and evaluate the influence that differences in topic and time have on character n-gram author profiles. Topic alignment between two texts is found to increase author verification precision, and an authors writing style is found to change over time, but not more significantly after 3 years than after 1 year.Information ArchitectureWISElectrical Engineering, Mathematics and Computer Scienc
Appropriate Similarity Measures for Author Cocitation Analysis
No full textWe 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
The vanishing author in computer-generated works: a critical analysis of recent Australian case law
No full textAbstract
The use of software is ubiquitous in the creation of many copyright works, yet the requirement in copyright law that every work have a human author who engages in independent intellectual effort means that its use may prevent copyright subsistence. Several recent Australian cases have refocused attention on authorship as an essential criterion of copyright subsistence, and these cases suggest that much computer-produced output may be authorless and thus lack copyright protection. This article, the first in a two-part series, analyses how each case deals with the question of authorship of computer-produced works and why the use of software diminishes copyright protection for a significant number of computer-generated works. The article critiques the application of conventional notions of human authorship developed in the pre-computer age to modern productions and suggests alternative approaches to authorship that satisfy both the major objectives of copyright policy and the need to adapt to the computer age. The article argues that, without a broader judicial approach to authorship of computer-generated works, Parliament must remedy the lacuna in protection for these ‘authorless’ works. Possible solutions for reform are suggested. In a forthcoming article, the author comprehensively examines those reform proposals
In-Situ Oil Combustion: An Experimental Study Impact of Reactions in the Processes Perpendicular to the Main Gas Flow Direction
No full textThe objective of this thesis is to investigate experimentally the impact of gas phase reactions during a simple ISC process especially the role of heat and oxygen presence in the system. Heat plays an important role in both air and nitrogen injection experiments because the injected gas needs to be heated first to the set temperature before flushing the system. At a certain temperature, heat induces endothermic chemical reactions. Therefore it is also necessary to include precise descriptions of chemical reactions describing ISC process. However, the application of ISC method in the field is still an issue since it is hard to control the process. This can be related to the complexity observed in the experimental results. One of the difficulties encountering in this experiment is to acquire an evenly distributed heat within the reservoir. This needs further investigation in future work. In the work presented here the chemical reactions occurring during ISC are studied using a T-shaped reactor tube. The vertical part of the reactor was filled with an oil-saturated sand column; through the horizontal part of the reactor at top of the vertical part either nitrogen or air is flown. The experiments with air allow the study of the chemical reactions, which are thought to occur during ISC, while the experiments with nitrogen injection allow the study of the influence of heat on the reactions occurring during ISC. Thereby the focus is on the processes occurring perpendicular to the main gas (air or nitrogen) flow direction. The main results of the experiments are the effluent gas composition, the temperature profile within the vertical part of the reactor and the characterization of the sand and the liquid collected in the cooling trap after the experiment.Geoscience & EngineeringCivil Engineering and Geoscience
Quantitative analysis of coronary arteries with computer tomography coronary angiography: Methodology and preliminary results using intracoronary ultrasound as reference standard using a software prototype (QCT)
No full textDiffusive author(s), cohesive author: Analysis of S/N (1994)
No full textThis study indicates the ways in which various aspects of the author(s) are brought forth in Dumb type’s performance art, the S/N production. Previous research has suggested a non-hierarchical organization of Dumb type and the absence of a “privileged author” in Dumb type’s collaborative work, S/N. However, the results that I have investigated from member’s interviews on the creative process of S/N along with my analysis of the recorded images of S/N, indicate a different aspect of the author(s). First, S/N was created through, so to speak, the collective ideas of the members of Dumb type. Further, S/N has at least nine quotations from previous performances, installations, and printed writings, besides the work-in-progress technique. Explicating one of the “author functions” as given by Michel Foucault, each text has plural subjects of the author. However, it has been revealed from members’ interviews that Teiji Furuhashi had a decision-making role in selecting the members’ ideas within the performance. Since then, S/N has had plural subjects of creation; however, Furuhashi is one of the subjects of creation along with the “privileged author.” S/N has plural authors (diffusive authors) yet at the same time, it has a “privileged author,” Teiji Furuhashi (cohesive author)
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