1,720,954 research outputs found
Cloning, purification and characterisation of human and mouse ADAM 8 sheddase activity
Full text linkAl-Riyami H. Cloning, purification and characterisation of human and mouse ADAM 8 sheddase activity. Bielefeld (Germany): Bielefeld University; 2006
Investigation into the effect of temperature on nitrogen foam behavior
No full textIncludes bibliographical references.2022 Spring.Thermal enhanced oil recovery is touted as the most effective recovery method for heavy oil with steam being the most common injectant, but unfortunately, conformance issues such as gravity override and channeling are rife in steam injection processes. Foam has been used to mitigate conformance issues in gas injection processes, however, at high temperatures these issues return due to the rapid decay of foams and degradation of surfactants.
Literature reports many investigations of the formulation of surfactants and additives to improve the stability of foams. However, the study of foam behavior at higher temperatures is lacking as most studies aim to understand foam decay at ambient temperatures for dry foams. This work aims to shine some light on the issues of studying foam behavior at lower temperature for high temperature applications and to generate better insight into the decay behavior of foams at higher temperatures in closed environments.
Established foam decay analysis methods such as test tubes and dynamic foam column tests were employed to highlight the dependance of foamability and stability of surfactant foams on temperature and the inadequacy of low temperature analysis to predict high temperature foam performance. It was found that some surfactants perform comparatively better than others when stabilizing foams at high temperatures, even when their low-temperature performance was worse. It was also shown that foamability was differently sensitive to temperature for the different surfactants.
This work introduces a methodology to visually analyze foams in a sealed high-pressure high-temperature cell. Using three different surfactants, foam was visually analyzed at different temperatures, and it was found that the decay behavior of foams tends to split around the 40 °C mark. Below that temperature, a dry polyhedral foam is observed for most of the decay that is primarily driven by drainage and evaporation, while at temperatures above 40 ºC, a wet spherical foam is observed for most of the decay and the mechanisms governing the decay depend on the surfactant being used.
For anionic surfactants, it was found that wet foams decay through the Marangoni flow induced by temperature fluctuations across the bubbles’ surfaces, which are exacerbated at higher temperatures. When a lamella ruptures, if the adjacent bubbles are sufficiently different in size, the gas influx from the smaller bubble to the larger one combined with the liquid in the lamella and the bubbles themselves causes new bubbles to be formed due to the shearing of the liquid.
The results also showed that at temperatures above 120 °C the decay of the foams was primarily occurring at a middle layer within the foam structure rather than the top layer that is exposed to the gas phase. The decay occurred in the form of splitting, where large bubbles burst and form smaller ones, that shifts the foam downwards making it appear as if the top layer is exhibiting the bulk of the decay.
For nonionic surfactants, the decay is more complex and depends on the phase behavior of the surfactant molecule with temperature. As the temperature increases, the aggregation of the monomers into larger structures such as micellar, lamellar, and isotropic structures, changes the way foam decays. It was found that at 90 °C, the decay of the foam occurred primarily at the liquid-foam interface which is attributed to the preferential aggregation of the monomers into larger structures in the liquid phase, as opposed to adsorption to the gas-liquid interface.
Overall, this work showed that foam behavior can either be independent of the surfactant behavior with temperatures, as is the case with anionic surfactants, or coupled to the thermodynamic behavior of the surfactant molecule, as in the nonionic surfactant, and is significantly different between low and high temperatures
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Full text link“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
Full text linkWe 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
Full text linkWe 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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