1,720,986 research outputs found
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
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
Modeling of the Cryogenic Liquid Pool Evaporation and the Effect of the Convective Heat Transfer from Atmosphere
Get PDFLiquefied Natural Gas (LNG) has recently known significant development worldwide. The assessment and the control of the risks associated to the production, storage and transportation of LNG is of paramount importance to ensure the sustainability of this activity. This includes the prediction of the consequences of potential loss of containment of LNG, which requires the modelling of the vaporization rate of LNG resulting from the heat transfer between the pool and surroundings. The present work focuses on the role of evaporation and convection phenomena on the cryogenic pool temperature and its vaporization rate. Various models describing heat transfer by evaporation were compared. The models differ from each other in terms of mass transfer coefficient and saturation vapor pressure (i.e. linear versus logarithmic expression). Simulations were performed to observe the temperature and vaporization rate of cryogenic liquid pool (methane/nitrogen) under known atmospheric conditions. The results show that the pool initially stays at its boiling temperature, for models using linear driving force, such indicating the prevalence of boiling on the overall vaporization rate. Subsequently, the temperature of the cryogenic pool drops down, as the heat taken by evaporation exceeds the heat transfer by convection or conduction whereas, models adopting logarithmic driving force show drop in temperature from the beginning of simulation. The results of these models were compared to existing experimental data for cryogenic liquid vaporization rate to assess their accuracy and clarify the role of evaporation in the vaporization of a cryogenic liquid pool
Modeling of a Gas Release from Underground Pipeline
Get PDFThe underground gas releases from buried pipelines can cause serious damage to the environment, properties, and population. This work aims at modelling the underground gas releases using a computational fluid dynamics numerical tool to allow the user to obtain a desired property (velocity, release rate, etc.) and visualize the behavior of a release. This was done through performing a sensitivity analysis on five crucial parameters that affect the results significantly, namely, the meshing size, soil particle diameter, turbulence model and the granular viscosity characterizing the soil. The resulting model was validated and used to delineate the boundaries between the different regimes corresponding to various release forces. The regimes are the resulting outcomes of the methane���s flow which vary according to its release force ranging from migration through the soil, to uplift visible on the ground, till a crater formation. The pipeline burial depth was changed to investigate the effect of the change of burial height on the regime. The result was presented on a nomograph that allows to identify the regime corresponding to a given inlet force and pipeline burial depth, for an upward release orientation. The effect of the release orientation on the outcome was investigated for given pressures
Modeling and Evaluating the Dispersion of a Underwater Sour Gas Release in Shallow Waters
Get PDFIn the ocean, at offshore production facilities, subsea gas releases can occur from the rupture of subsea pipelines, failure in flow lines, gas export lines and subsea equipment. There have been many subsea gas release incidents in the oil and gas industry, where natural gas is released. An increasing numbers of sour gas reserves are being found, with a high number within the Middle East. The release of sour gas can cause toxic exposure, fire and explosion issues, leading to major environmental and safety impacts. Therefore it is important to understand the phenomena of subsea gas release as it will aid in controlling and quantifying the risks associated with it. From literature it is found that CFD models are developed to quantify the severity of risks associated with subsea releases of natural gas. The usage of CFD models is expensive and time consuming hence in this project a nomograph was generated in order to extract data for risk assessment in an easier and more efficient way. In order to do so a transient, Eulerian-Eulerian CFD model was developed to model the release of sour gas in shallow waters to obtain simulation results to construct the nomograph. The model was validated against Engebretsen���s 1997 experiment. The simulation results showed excellent agreement with the experimental data. The validated model was expanded to predict the behavior of the bubble plume for several scenarios for Qatar���s industry, for release depths between 25 and 100 m, release mass flow rates between 20 and 80 kg/s, release hole diameters between 0.05 and 0.25 m and sour gases with H2S compositions of 11 and 22 % by mass. A sensitivity analysis was performed that indicated high concentrations of CH4 and H2S on the surface, suggesting that dispersion modeling be carried out to determine what offshore facilities are within the vicinity of flammable and toxic clouds. The results obtained from the expanded CFD model include surface mass flux, rise time and surface gas concentrations. Using the results a nomograph was generated in order to extract data for risk assessment
Rigorous Simulation of Accidental Leaks from High-Pressure Storage Vessels
Get PDFSeveral major industrial disasters involve accidental releases of hazardous chemicals from ruptured vessels or pipelines as consequence of equipment failures, maintenance errors, operational errors, cracks, corrosion, ruptures, or also by acts of nature. The released chemical can form and disperse as vapor cloud leading to fire, explosion, or toxic exposure. The resulting leak could be single phase or multiphase release, choked or non-choked. These releases could result in liquid spills, vapor cloud formation, explosion, toxic dispersion and flashing liquids. The impact of the release depends on the properties of the fluid and the exit conditions. Often the leak goes unnoticed and also it becomes hard to estimate the leak flow rate. When a leak occurs, it is very important to have an idea of the leak flow rate and the fluid properties. This helps in assessing the hazards posed by the leak and also predict the consequences.
To assess the consequences of a leak, it is important to estimate its flow rate and properties of the discharged fluid, but both change with time during the leaking process. Several models and programs exist to simulate accidental releases, often based on assumptions that increase the uncertainty of their predictions when applied to high-pressure vessels. This thesis takes a different approach by using rigorous calculation procedures and a cubic equation of state to: (1) find the state of fluid within the vessel using a flash algorithm for systems of specified internal energy (U), volume (V), and mole numbers of each component (N); (2) track phase appearance and disappearance in the vessel; (3) find the state of fluid as it exits the vessel, assuming the leaking point is the throat of an adiabatic, converging nozzle that operates isentropically; (4) compute sound speeds in multiphase systems to establish whether the leak flow is choked. The code that implements these steps has been validated against ideal gas state for single component data and against experimental data for leaks from vessels containing mixtures
Assessment of Maximum Gas Production Rate of an Untempered System Under Runaway Conditions
Get PDFRunaway reactions are characterized by the exponential increase of the temperature and pressure of a chemical system that could potentially lead to the explosion of the reactor or storage vessel of concern. The consequences of a runaway reaction may be very severe in terms of life, economic and environmental losses.
Emergency relief systems (ERS) are the ultimate mitigation method to prevent vessel explosion following the runaway reaction. In the case of the runaway of gas producing chemical systems, ERS sizing requires the assessment of the maximum gas production rates. Significant work was performed in the 1980���s by the Design Institute for Emergency Relief Systems to develop vent sizing methods for runaway reaction cases. While vent sizing methods developed for vapor systems provided relatively good results, those developed for gas generating systems (hybrid or gassy) tend to be oversized and still need to be improved. A very significant part of this work includes the improvement of the current methods for the measurements of the maximum gas production rate for such systems.
The objective of this thesis work is to experimentally study the decomposition of a gas generating system under runaway condition using adiabatic calorimetry and assess the maximum gas production rate corresponding to the runaway. A critical analysis of the current methodologies to interpret experimental data to compute the maximum gas production rate was done. The decomposition of Cumene Hydroperoxide (CHP) in Cumene was chosen for the study
ANALYSIS AND VALIDATION OF INTEGRAL POOL SPREADING MODELS OF LNG SPILLS ON CONCRETE
Get PDFWhen a loss of primary containment of liquefied natural gas (LNG) occurs on the ground, a pool, that simultaneously spreads and vaporizes, is formed posing cryogenic, asphyxiating, and flammable hazards to its surrounding. Determining the pool size and vapor generation upon release play key roles in the accuracy of dispersion and consequence models. This work focuses on expanding the available data to be used for LNG source term model validation through the evaluation of an existing model.
A field-scale experimental setup was designed to study the pool temperature, pool spreading and heat flux under the concrete, after a release. In this work, liquid nitrogen (LNv2) was used as a safer analogue to LNG as it is a non-toxic non-flammable cryogen. The experiments were carried out inside a 6��5��1.2 m pit. A vaporizing pool spreading model based on Gas Accumulation over a Spreading Pool (GASP) was then implemented and used to predict the vaporization and pool spreading rates of the spill. Finally, the model predictions were compared to the experimental data.
The results of this work gave insight to the validity of two existing source term models, the coupling of a pool spreading model with Fourier���s one-dimensional conduction heat transfer model. While the first model assumes that heat flux is uniform across the pool, the second model takes into account higher heat transfer due to exposure time difference between the outer rings of the pool to the center of the pool during pool spreading. Both models assume that the pool boils until it completely vaporizes. Experimental results indicate that the pool does boil until it completely vaporizes, and that the temperature at the center of the substrate was cooler than its outer parts. It was found that the model which accounts for higher heat transfer in the pool outer rings tends to underestimate pool size. Both models, however, overestimate the pool size at the early stages of the spill. As both models incorporate a solution of Fourier���s one-dimensional conduction equation, a comparison was also done between the predicted and experimental temperature
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