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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
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
An automatic algorithm for the estimation of in situ contact angle from X-ray micro-scale imaging of two-phase flow in porous media
No full textLAUREA MAGISTRALELa presente tesi si focalizza sullo studio e la quantificazione della bagnabilità dei mezzi porosi. Questa è una proprietà fondamentale per la comprensione dell'arrangiamento dei diversi fluidi nel caso di flussi multifase. Infatti, la bagnabilità influenza importanti quantità, come ad esempio il salto di pressione fra diverse fasi, la permeabilità del mezzo e le relazioni di queste grandezze con la saturazione dei diversi fluidi.
La metrica che viene universalmente usata per quantificare il grado di bagnabilità di un mezzo è l'angolo di contatto. Storicamente, questo è misurato adagiando gocce di fluido su superfici piane, e misurando l'angolo di contatto con il metodo della goccia sessile. Il limite fondamentale di questo metodo consiste nel fatto che, pur essendo in grado di fornire accurate e valide misure di angoli di contatto per superfici piane, non fornisce indicazoni rispetto a quanto questa misura cambi nel caso di fluidi risiedenti in pori di forma, rugosità e composizione mineralogica variabile. Il recente sviluppo di microscopi a raggi X, in grado di ottenere immagini tridimensionali (3D) dello spazio poroso saturo di fluidi multifase, ad una scala di qualche micrometro. Da queste immagini è possibile ottenere misure dirette, i.e. in situ, degli angoli di contatto.
Recentemente, l'angolo di contatto in situ è stato stimato dalle immagini 3D precedentemente citate con un metodo manuale, con cui si riesce ad ottenere solo un numero limitato di stime, che possono essere influenzate da pregiudizio e soggette ad errori da parte dell'operatore. Il cuore di questa tesi consiste nello sviluppo e l'implementazione in codice di un algoritmo automatico, in grado di ottenere migliaia di oggettive stime dell'angolo di contatto da immagini 3D di un singolo campione di mezzo poroso.
Il corretto funzionamento di questo innovativo algoritmo è stato verificato mediante la sua applicazione ad immagini sintetiche, costruite in modo che il valore dell'angolo di contatto sia noto analiticamente. Successivamente, si è effettuato un confronto con il metodo manuale di cui sopra, applicando entrambi i metodi alle immagini ottenute sezionando le rappresentazioni 3D nei medesimi punti. Infine, il metodo è stato applicato ad immagini 3D prodotte con la scansione mediante microscopi a raggi X di due campioni di rocce Ketton sature di due fluidi immiscibili, caratterizzati da differenti condizioni di bagnabilità.
I risultati ottenuti sono stati studiati in un contesto probabilistico ed alcune equazioni di Gaussiane troncate sono proposte per interpretare le funzioni di densità di probabilità dell'angolo di contatto, per sistemi caratterizzati da diversi gradi di bagnabilità. I parametri di queste equazioni sono stimati per modellizzare correttamente i casi di studio mediante il metodo della massima verosimiglianza.
Alcune parti di questa tesi sono state inviate per la pubblicazione al giornale Journal of Colloids and Interface Science.This thesis is focused on the study of the wettability of porous media, and its measurement. This property is fundamental in multi-phase flow for the understanding of the arrangement of the different phases in the pore space. In turn, it influences key quantities like capillary pressure and permeability, and their relationship with the saturation of the different fluids.
The universally acknowledged direct metric for the quantification of wettability is the contact angle. Measurements of contact angles have been typically performed on flat surfaces at ambient conditions through sessile drop and/or captive bubble approaches. While these methods yield valuable information, they do not give indication about the in situ contact angle within a porous medium, as roughness and the irregular shape of pores and the complex mineralogy of the rocks are not taken into account. The recent advent of X-ray micro computed tomography (micro-CT) technologies allows the direct visualization of three-dimensional (3D) images of micron-scale pore space saturated with different fluids, that allow to obtain direct, i.e. in situ, measurements of contact angle.
Recently, in situ contact angle has been estimated from X-ray micro-CT images with a manual method. This allows to obtain a limited number of measurements, prone to bias/subjectivity. The main core of this dissertation is the development and the coding of an automatic method, that permits to extract, from 3D images of real rock cores saturated with two phases, thousands of estimates of contact angle in as much locations in the pore space. The new algorithm is first tested on synthetic images, where the actual angle is known analytically and then it is compared on real images with manual measurements in the same points, and its parameters are tuned. Finally, it is applied on 3D images of two micro cores of Ketton limestone, saturated with two immiscible phases, characterized by different grades of wettability.
Results are studied in a probabilistic framework and truncated Gaussian models are proposed to interpret the probability density functions of contact angle for systems characterized by different wettability. The parameters of the models are estimated for the systems considered with the Maximum Likelihood method.
Parts of this thesis have been submitted for publication in Journal of Colloids and Interface Science
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
Immiscible three-phase flow in porous media: dynamics and wettability effects at the pore scale
Get PDFThe simultaneous flow of three phases in porous media is ubiquitous in natural
and engineered processes such as carbon dioxide storage, oil recovery, contaminant
removal, food and drug manufacturing, and chemical reactors. However, only few
studies have been found in the literature on the subject. The recent advent of
non-invasive three-dimensional imaging provided by X-ray microtomography has
yielded a breakthrough in the study of multiphase flow in porous media. We use
these techniques and advanced image analysis methods to provide insights on the
physics of three-phase flow in porous media.
We investigate the mutual arrangement of the phases in the pore space – pore
occupancy –, the types of displacements arising by the simultaneous flow of three
phases, the formation of layers and the mechansims with which one of the fluids
can be trapped inside the pores. We observe that, in general, the wettability of the
system has major effects on these phenomena and hence we perform experiments
at different wettability conditions.
We perform a series of displacement experiments in small rock samples, where
water first displaces oil, followed by gas injection and then secondary waterflooding
to displace gas and oil. We study the amount of trapping of oil and gas, as well
as oil recovery. We perform experiments using laboratory-based X-ray scanners to
image the fluid configurations at the end of each displacement sequence. We also use
time-resolved imaging at a synchrotron to examine the dynamics of displacements,
acquiring pore-scale images approximately every minute.
The results show that pore occupancy is strictly linked to the wettability of the
system, as the water-oil-gas wettability order from the most to the least wetting,
observed in water-wet media, changed as a function of wettability. Mixed-wet
systems are characterised by variable wettability in space and hence lead to nonconstant
wettability orders. Multiple displacements – a chain of displacments
where one phase displaces a second which in turn displaces a third and so on – are
frequently observed in water-wet media but appear to be inhibited in mixed-wet
systems. The formation of oil spreading layers sandwiched between water and gas,
and water wetting layers on the surface of the grains, is favoured in water-wet
systems, while oil spreads in wetting layers in mixed-wet media. The formation of
spreading water or gas layers is not allowed by thermodynamic constraints. Gas
trapping frequently happens in both water- and mixed-wet media, with fundamental
differences caused by the different configurations of the phases in the pore space.
However, in general we measure enhanced trapping of gas in three-phase flow with
respect to two-phase flow and higher amount of trapped gas in mixed-wet systems
with respect to water-wet media, providing for secure gas storage.Using time-resolved imaging we study invasion patterns for two and three-phase
flow in a mixed-wet rock. A distinct flow invasion pattern is observed for two-phase
flow in mixed-wet media, controlled by the thermodynamic contact angle, which
stems from an energy balance at the pore scale. The four Minkowski functionals
– volume, area, total and Gaussian curvatures – are used to provide complete
topological description of the dynamics of three-phase flow in water- and mixed-wet
media. Specifically, the Gaussian curvatures are used to interpret the shape of the
interfaces and the connectivity of the phases, which ultimately strongly influence
the flow and the permeability of each fluid.
This study provides in general an effective and universal methodology to study
three-phase flow at the pore scale, and the results have implications for many
applications, both to storage and recovery in the subsurface, but also for engineered
materials. The findings of this thesis suggest favourable oil recovery with gas
injection in oil fields and augmented trapping of gas with a chase water injection.
This is critical, for example, for safe storage of CO2 underground to mitigate the
climate change.Open Acces
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