1,721,004 research outputs found
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
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Investigation of Filtration Mechanisms Involved in the Removal of Engineering Nanomaterial From Drinking Water
Full text linkThe overarching goal of this study was to systematically investigate how engineered particles behave in engineered filters under a range of relevant solution chemistry conditions. Specifically, the approach was to conduct a combination of fundamental and applied experiments, looking at engineered particles transport in idealized conditions, followed by those simulating actual scenarios in the filtration stage of drinking water treatment. It was confirmed that the leading factors in engineered particles destabilization which leads to their removal include the type and concentrations of salts in solution, and the process operating conditions (ionic strength and coagulant residual). Ultimately, through the systematic variation of these parameters in the proposed micromodel experiments described below, the conditions for optimal engineered particles destabilization and removal was determined. This dissertation work has allowed for the following observations. In the 2D micromodel, the removal efficiency of latex nanoparticles and food grade TiO2 in filtration is sensitive to the particle aggregate size, surface charge, and surface composition. The model was built to show single collector removal efficiency as a function of particle size and ionic strength, as well as predict the behavior or deposition location on collector of any nanoparticles entering the filtration system in order to improve the field of environmental nanotechnology. Furthermore, the predictions generated from the present work parallel those of the constricted 3D model, for instance, the collector size and average velocity. Ultimately, this research could be applied in place of 3D columns when designing filters for water and wastewater treatment.Finally, the role of coagulant residual, TiO2 structure, and solution chemistry on the removal efficiency were studied as well in simulated water (AGW and ASW). Results from this study indicate that for all TiO2 suspensions, the greater coagulant residual concentrations increased the removal efficiency up until 0.5 mg/L alum, above that threshold the effect of coagulant residual were negligible. This collection of studies provides critical insights into the importance of understanding particles size and coagulant residual concentrations more impactful and in realistic environments. These studies demonstrate the need to update more tests such that they moreaccurately reflect real exposure scenarios simulating environmental conditions
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Impact of Fluid and Interaction Forces on the Fate and Transport of Nanomaterials and Bacteria in Aqueous Systems
Full text linkBacteria transport in aqueous environments is heavily influenced by nanoscale forces that govern deposition on and detachment from environmental surfaces. Surface
interaction can prevent these species from being carried long distances by fluid flow.
Nuances in deposition and detachment properties of waterborne pathogenic bacteria can xii
mean the difference between life and death or serious economic losses. In this dissertation,
deposition and detachment properties of the human pathogen Escherichia coli O157:H7
and the plant pathogen Xylella fastidiosa are analyzed using a variety of engineering tools.
Sand column experiments, parallel plate experiments, and thermodynamic surface
interaction predictions are used to study how nanoparticles could affect the transport of E.
coli O157:H7 in agricultural soils. Results indicate that the presence of titanium dioxide
(TiO2) nanoparticles in agricultural waters could increase E. coli O157:H7 soil transport,
especially during rain events. However, the presence of copper oxide (CuO) nanoparticles
may decrease E. coli O157:H7 transport. Xylella fastidiosa transport in an insect-plant
system was studied in silico. Fluid flow fields in this system were simulated and integrated
with custom-made MATLAB code to predict bacteria detachment under relevant
environmental conditions. Results support a model of key fluid dynamic mechanisms
involved in X. fastidiosa spread within plants and between plants. The model can be used
to investigate potential targets for fighting costly crop diseases caused by X. fastidiosa. The
application of computational and experimental tools in this dissertation demonstrate how
engineering methods can enhance analyses of bacterial transport in diverse environmental
systems
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Microbial and Colloidal Deposition to Solid Surfaces: Effect of Heterogeneity
Full text linkMicrobial and colloidal particle transport and deposition onto solid surfaces are of great significance to many environmental and technological processes. Initial attachment of particles is governed by the interactions between particles and surfaces. Classic Derjaguin-Landau-Verwey-Overbeek (DLVO) theory is utilized to predict interactions between particles and surfaces. However, discrepancies between experimental observations and theoretical predictions exist and the failure of the predictive model is often attributed to particle and solid collector physical and chemical heterogeneities.This work sought to elucidate the contribution of heterogeneity to the initial particle deposition behavior in a radial stagnation point flow system or a parallel plate flow chamber system by systematically adjusting particle type and size, as well as collector surface chemical and/or physical properties. In Chapter 2 and 3, the role of particle heterogeneity (type and size) was examined. Comparable deposition trends were observed between particles, in this case groundwater and marine bacteria, Burkholderia cepacia G4g and Halomonas pacifica g, respectively. However, the deposition kinetics of H. pacifica g appeared to be more sensitive to solution chemistry than that of B. cepacia G4g. Experimental results also demonstrated that particle size (colloidal and bacterial) had a considerable impact on the transport and interaction with surfaces. In Chapter 4, a method to influence collector surface charge and subsequent colloid deposition was described. Experimental results suggest colloids respond to local variations in surface potential through electrostatic interactions, altering particle streamlines flowing along the surface, and ultimately the extent of deposition. In Chapter 5, cell deposition onto bare and zeolite coated aluminum alloy and stainless steel surfaces was investigated using bacterium H. pacifica g. Collector surface properties found to have the most notable effect on cell attachment were the electrokinetic and hydrophobic nature of the bare metal and zeolite coated surfaces. In Chapter 6, the relative impact of physical roughness on antifouling nature of zeolite surfaces, as compared to these other chemical mechanisms was investigated.This comprehensive dissertation project established both particle and collector surface heterogeneity has a significant effect on particle deposition, which was clearly identified by altering various physical and chemical interaction parameters between particles and surfaces
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Investigation of Titanium Dioxide Engineered Nanomaterials in Microbially Driven Environments
Full text linkThis dissertation characterized two forms of TiO2 engineered nanomaterials (ENMs) to determine the role of solution conditions in mediating differences in the environmental impacts of emerging nanomaterials. In general, ENMs designed for specific product matrices are functionalized to impart distinct characteristics capable of altering the environmental fate and transport (i.e. shape and surface composition). Observations of TiO2 ENM release during product life cycles presents a concern as nanoparticles with unique characteristics begin accumulating in environmental systems. TiO2 nanomaterials were introduced to three consecutive, environmental systems with microbial presence to characterize environmental implications of ENM presence, namely: a model human colon, septic tank, and a quartz sand filtration column. The following critical findings resulted from this dissertation research. Colonic exposure to food (FG) and industrial (IG) grade TiO2 inhibited a natural shift in microbial composition from Proteobacteria to Firmicutes phyla, with FG TiO2 having the greater impact. Colonic pH levels decreased from IG and FG TiO2 exposure where FG TiO2 (pH 4) again had the greatest impact compared to IG TiO2 (pH 5) and the control (pH 6). Therefore, inherent physical and chemical properties of FG and IG TiO2 can produce different microbial responses in the colonic environment. Next, exposure of the septic system to IG TiO2 particles had minimal effect on the composition of the denitrifying-dominant microbial community, while FG exposures resulted in a mixed functionality community less effective at waste treatment. Nano-FG TiO2 exposure in septic systems may facilitate considerable changes in microbial community activity. Lastly, FG TiO2 exhibited a high degree of stability in septic conditions and both monovalent electrolyte suspensions. Elution of FG and IG TiO2 was greatest in septic effluent at the higher nanoparticle concentration (100 ppm); however, FG TiO2 was well retained at the low (2 ppm) concentration suggesting low elution from the drainage field. Valuable insight into the role that inherent physical and chemical properties of emerging ENMs play in environmental systems is gained from this dissertation research. Additionally, the significance of the solution environment at mediating differences observed between uniquely, engineered nanomaterials sheds light on potential mechanisms for minimizing detrimental environmental implications of nanomaterials
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