1,720,970 research outputs found
Ionic adsorption on bulk nanobubble interfaces and its uncertain role in diffusive stability
No full textHypothesis: Bulk nanobubbles have been proposed to improve gas exchange in a variety of applications, such as in water treatment, theragnostics, and microfluidic surface cleaning. However, there is currently no consensus regarding the mechanism responsible for their reportedly long lifetimes, which contradicts classical understanding of diffusive bubble dynamics. Recently, there has been increasing support for an electrostatic stability mechanism, following from experiments that observe negatively charged zeta potentials around nanobubbles.
Simulations: We use high-fidelity Molecular Dynamics simulations to model bulk nanobubbles under mechanical equilibrium in a sodium iodide electrolyte solution, to investigate ionic adsorption on the liquid-gas interface, and resulting zeta potential. We critically examine the hypothesised electrostatic stress underpinning this previously suggested stability mechanism, which is theorised to stabilise the nanobubbles against dissolution by counteracting the otherwise dominant effects of surface tension, however, has been too difficult to directly measure in experiments.
Findings: Ions adsorb onto the liquid-gas interface, confirming an Electric Double Layer (EDL) distribution around the nanobubble with an estimated ζ0 ∼ −10mV zeta potential, in accordance with experiments. However, we find no significant electrostatic stress exerted on the nanobubble surface, as any ion charge density in the EDL is completely neutralised by the rearrangement of the water molecules. As a result, the internal gas pressure is still well predicted by the standard Laplace pressure equation (with a fitted Tolman length correction λ = 0.31 nm), challenging an essential assumption underlying the previously proposed theories, and we instead speculate on alternative mechanisms for electrostatic-based stability
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
Cavitation dynamics of surface nanobubbles
Full text linkCavitation is the fluid phenomenon where a bubble of gas or vapour can spontaneously form in a liquid in response to a local drop or variation in pressure. Unlike bubbles formed from other types of processes such as boiling, cavitation bubbles can become highly unstable due to their sensitivity to fluctuations in pressure. These cavitation bubbles can very rapidly expand many orders of magnitude in size, in what is sometimes referred to as “explosive” growth; when they collapse, they often release a high-speed liquid jet, which can lead to pitting and erosion if directed onto a solid surface. Cavitation is a problem often encountered in engineering, such as in turbomachinery, where the repeated formation and collapse of these bubbles can cause major structural damage. More recently, engineers have aimed to exploit the high-speed jet dynamics during cavitation bubble collapse for novel applications at the nano to microscale, such as in surface cleaning, diagnostics and cancer treatment.
Around 20 years ago, spherical-cap shaped nanoscale bubbles were found to be able to exist long-term on solid substrates under certain experimental conditions. These newly discovered “surface nanobubbles” were of scientific interest as their resistance to dissolution seemed to contradict previous Epstein-Plesset theory on the general unstable diffusive equilibrium of bubbles. They were confirmed to be diffusively stable if the surrounding liquid was supersaturated with dissolved gas, and the substrate had surface heterogeneities, such as roughness or chemical patterning, such that the bubble’s three-phase contact line was pinned to the substrate. This contact line pinning resulted in a constant contact radius (CCR) mode of growth unique to surface nanobubbles, where the radius of curvature would begin to decrease during expansion, contrary to the radial growth typically found in spherical bubbles.
Surface nanobubbles initially seemed to provide a convenient explanation for the heterogeneous nucleation of cavitation bubbles. However, early experiments found that they did not respond as expected to pressure drops intended to induce cavitation growth. Most of the classical analyses for cavitation assume a spherical bubble immersed in an infinite liquid. This results in models which are mathematically simple and usually suitable for most applications, however, surface nanobubbles have a spherical cap shape and typically grow with a pinned contact line, and so the classical spherical bubble models were found not to be suitable for these cases.
The research in this thesis investigates the cavitation dynamics of pinned surface nanobubbles using Molecular Dynamics (MD) simulations. The cavitation threshold for unstable growth, the growth rate and oscillation dynamics, and finally the collapse of pinned surface nanobubbles are simulated and investigated further here. Results are compared to the corresponding classical spherical bubble equations, and improved models are proposed, where appropriate, to account for their different observed cavitation dynamics.
Most of the surface nanobubbles’ unique behaviour arises from their pinned mode of growth. The surface tension contribution across the liquid-gas interface (the Laplace pressure) is found to increase during growth of the surface nanobubble due to the CCR mode of growth, which is the opposite effect to spherical bubbles. Surface nanobubbles are found to be able to resist pressures many mega-Pascals (MPa) lower than that predicted by the classical Blake threshold equation for unstable growth of spherical bubbles. A new model is derived to more accurately predict this cavitation threshold for surface nanobubbles, which captures their spherical cap shape and pinned growth. The proposed model suggests that the smallest surface nanobubbles can be resistant to pressures as low as −28 MPa. Critical discussions are also made on experimental findings that suggested that 300 nm bubbles were resistant to pressures of −6 MPa.
The classical Rayleigh-Plesset equation for spherical bubbles is modified to be more suitable for surface nanobubbles, accounting for their spherical cap shape and Laplace pressure variation, which could accurately predict their growth rate and oscillation dynamics. The natural frequency of surface nanobubbles is also found through linearised analyses of this newly derived growth rate model. The proposed natural frequency is compared to other models for bubbles, such as the classical Minnaert frequency, and was found to be better at capturing the surface nanobubble’s oscillation dynamics. The MD simulation set-up is also critically examined for accurately modelling the pressure variations acting on the surface nanobubbles.
The surface nanobubbles are found to collapse less violently than spherical bubbles, since the cavitation jets have less time to develop before impacting the solid surface. Despite the collapsing surface nanobubbles causing less damage, the resulting pit shapes were found to be similar to the pit shapes from spherical bubble collapse, with the perimeters of the pits typically scaling with the maximum bubble size before collapse. The internal gas phase is found to decelerate the jet formation, and reduce the resulting damage, through comparisons to the collapse of vapour bubbles. No toroidal rebounding bubbles were observed in the collapsing surface nanobubbles, which is a common occurrence in spherical bubble collapse, as the jets do not flow outward from the impact centre after impact on the substrates.
The findings presented here should provide an improved understanding for the design of microfluidic engineering processes where the cavitation dynamics of pinned surface nanobubbles are to be utilised
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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