1,720,957 research outputs found
Untangling the physics of water transport in boron nitride nanotubes
No full textLAMMPS data file and input script required to setup and run simulations carried out in the paper: Mistry, Pillai, Mattia and Borg, 'Untangling the physics of water transport in boron nitride nanotubes', Nanoscale
Transport, selectivity and antifouling in nanoscale membranes
Full text linkDesalination of seawater has been pursued since ancient times, first being recorded around 300
BC, largely to provide drinking water in ocean-going vessels. The primitive means used then
depended on distilling seawater, which is an energy intensive process. In the late 1950s, reverse
osmosis (RO) was demonstrated to be capable of desalinating seawater without vaporizing it.
RO accounts for nearly 60% of all major desalination plants in operation today due to its
lower energy consumption. The need for freshwater, however, has increased significantly in
the last few decades, in towns and cities where populations have grown and water bodies
diminished. Despite lower energy consumption, RO remains too energy-intensive to supply
fresh water at city-scale cheaply, driving research into new RO membranes that can reduce
energy consumption. A large number of new nanomaterials have emerged as a result, including
carbon nanotubes (CNTs), boron nitride nanotubes (BNNTs), metal-organic framework (MOF)
and zeolite membranes. These materials promise very high water permeance and salt rejection,
which is expected to drive down desalination costs.
Among these materials, CNTs have been considered the forerunner, promising orders of magnitude higher water permeance compared to traditional membranes. Simulations showed BNNTs
could potentially provide higher permeance, but manufacturing difficulties prevented much
experimental research on BNNTs. These have been recently overcome, and BNNTs once
again appear as a promising membrane candidate. Molecular dynamics (MD) based simulation
studies of BNNTs, however, present a few discrepancies. While some earlier studies showed
permeance higher than CNTs, later studies showed CNTs had higher permeance than BNNTs.
In this thesis, the analysis of the membrane transport resistance allowed the resolution of this
discrepancy. Simulations studies were found to be largely conducted by modelling membranes
having short nanotube lengths, where the flow resistance due to effects at the entrance and
exit of the nanotubes dominates, hiding the behaviour inside the nanotubes. As the nanotube
lengths are increased, the transport resistance within the nanotubes starts to increase, and in
this regime, CNTs are found to have a lower transport resistance compared to BNNTs. The
transport resistance within BNNTs is also found to be largely dependent on the partial charge
chosen for the BN atoms in the simulation. Experimental evidence concurred with the higher
resistance for BNNTs, supporting the hypothesis of a high partial charge on BN atoms, which
is known to retard water flow.
The high partial charge of BNNTs, while reducing water flow, provides BNNT membranes
with the advantage of high selectivity. Traditional RO membranes are already operating near
the thermodynamic limit of energy utilisation, indicating massive increases in permeability is
unlikely to drive down energy use, and therefore costs. Instead, high selectivity is one avenue
that could reduce the cost of post-treatment, where clean water from the RO membrane needs
to undergo additional steps due to the inability of the membrane to selectively remove solutes.
These include boron removal from desalinated seawater, and remineralization of drinking water
to make up for essential minerals removed by the membrane. BNNT membranes in water have
a charged surface, allowing the membrane to discriminate between cations and anions and repel
anions. In this thesis, using both simulations and experiments, this charge-based rejection was
shown to work alongside the size-based rejection of traditional membranes where particles
are only rejected because they are too large for the membrane pores. As a result, BNNT
membranes could be manufactured with larger pores, allowing up to 70% higher water flow
rates for comparable rejection with reference to CNTs.
The second avenue where cost reductions may be found lie in membrane cleaning. Membrane
fouling and cleaning costs could nearly equal the energy costs and also result in reduced
membrane life. The dominant method of membrane cleaning is through the use of chemicals,
which requires the desalination plant to be put offline and creates a chemical-laden wastewater
disposal problem. Chemical cleaning is therefore done infrequently, while foulant build-up
on membranes is a continuous process. Physical methods of cleaning, such as by heating the
membrane, appear promising and can be applied frequently without stopping the desalination
process. Heating has been shown to act through biological means (by denaturing proteins) and
physical means (causing shear flows and vapour expansion within pores), promising cleaning
ability against a wide range of foulants. In this thesis, direct heating of membranes was found to
be capable of removing nanoparticles from the membrane surface. Heating was shown to work
through a mixture of bubble formation and increased Brownian motion of the nanoparticle
to displace it away from the membrane surface. The large role played by Brownian forces,
however, prevents a deterministic prediction of whether a particle will be removed or not when
heat is applied to the surface.
This work therefore deals with the three avenues of improvement in filtration and desalination
membranes, i.e., permeability, selectivity and antifouling. This work resolves the question of
permeability in BNNT membranes, established charge based rejection in BNNTs as the basis of
a membrane capable of high selectivity and finally explores membrane heating as a promising
candidate mechanism for the cleaning of membranes
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
- …
