1,721,026 research outputs found
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
Quantum drude oscillators for accurate many-body intermolecular forces
Get PDFOne of the important early applications of Quantum Mechanics was to explain the
Van-der-Waal’s 1/R6 potential that is observed experimentally between two neutral
species, such as noble gas atoms, in terms of correlated uncertainty between interacting
dipoles, an effect that does not occur in the classical limit [London-Eisenschitz,1930].
When many-body correlations and higher-multipole interactions are taken into account
they yield additional many-body and higher-multipole dispersion terms.
Dispersion energies are closely related to electrostatic interactions and polarisation
[Hirschfelder-Curtiss-Bird,1954]. Hydrogen bonding, the dominant force in water, is an
example of an electrostatic effect, which is also strongly modified by polarisation effects.
The behaviour of ions is also strongly influenced by polarisation. Where hydrogen
bonding is disrupted, dispersion tends to act as a more constant cohesive force. It
is the only attractive force that exists between hydrophobes, for example. Thus all
three are important for understanding the detailed behaviour of water, and effects
that happen in water, such as the solvation of ions, hydrophobic de-wetting, and thus
biological nano-structures.
Current molecular simulation methods rarely go beyond pair-wise potentials, and
so lose the rich detail of many-body polarisation and dispersion that would permit
a force field to be transferable between different environments. Empirical force-fields
fitted in the gas phase, which is dominated by two-body interactions, generally do not
perform well in the condensed (many-body) phases. The leading omitted dispersion
term is the Axilrod-Teller-Muto 3-body potential, which does not feature in standard
biophysical force-fields. Polarization is also usually ommitted, but it is sometimes
included in next-generation force-fields following seminal work by Cochran [1971]. In
practice, many-body forces are approximated using two-body potentials fitted to reflect
bulk behaviour, but these are not transferable because they do not reproduce detailed
behaviour well, resulting in spurious results near inhomogeneities, such as solvated
hydrophobes and ions, surfaces and interfaces.
The Quantum Drude Oscillator model (QDO) unifies many-body, multipole
polarisation and dispersion, intrinsically treating them on an equal footing, potentially leading to simpler, more accurate, and more transferable force fields when it is applied
in molecular simulations. The Drude Oscillator is simply a model atom wherein a
single pseudoelectron is bound harmonically to a single pseudonucleus, that interacts
via damped coulomb interactions [Drude,1900].
Path Integral [Feynman-Hibbs,1965] Molecular Dynamics (PIMD) can, in principle,
provide an exact treatment for moving molecules at finite temperature on the Born-
Oppenheimer surface due to their pseudo-electrons. PIMD can be applied to large
systems, as it scales like N log(N), with multiplicative prefactor P that can be
effectively parallelized away on modern supercomputers. There are other ways to
treat dispersion, but all are computationally intensive and cannot be applied to large
systems. These include, for example, Density Functional Theory provides an existence
proof that a functional exists to include dispersion, but we dont know the functional.
We outline the existing methods, and then present new density matrices to improve
the discretisation of the path integral.
Diffusion Monte Carlo (DMC), first proposed by Fermi, allows the fast computation
of high-accuracy energies for static nuclear configurations, making it a useful method for
model development, such as fitting repulsion potentials, but there is no straightforward
way to generate forces. We derived new methods and trial wavefunctions for DMC,
allowing the computation of energies for much larger systems to high accuracy.
A Quantum Drude model of Xenon, fit in the gas-phase, was simulated in the
condensed-phase using both DMC and PIMD. The new DMC methods allowed for
calculation of the bulk modulus and lattice constant of FCC-solid Xenon. Both were
in excellent agreement with experiment even though this model was fitted in the gasphase,
demonstrating the power of Quantum Drudes to build transferable models by
capturing many-body effects. We also used the Xenon model to test the new PIMD
methods.
Finally, we present the outline of a new QDO model of water, including QDO
parameters fitted to the polarisabilities and dispersion coefficients of water
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
Nonlinear laser microscopy for the study of virus–host interactions
Get PDFBiomedical imaging is a key tool for the study of host-pathogen interactions. New techniques
are enhancing the quality and flexibility of imaging systems, particularly as a result of developments
in laser technologies. This work applies the combination of two advanced laser imaging
methods to study the interactions between a virus and the host cells it infects.
The first part of this work describes the theory and experimental implementation of coherent
anti-Stokes Raman scattering microscopy. This technique—first demonstrated in its current
form in 1999—permits the imaging of microscopic samples without the need for fluorescent
labelling. Chemical contrast in images arises from the excitation of specific vibrations in the
sample molecules themselves. A laser scanning microscope system was set up, based on an
excitation source consisting of two titanium-sapphire lasers synchronized with a commercial
phase-locked loop system. A custom-built microscope was constructed to provide optimal
imaging performance, high detection sensitivity and straightforward adaptation to the specific
requirements of biomedical experiments. The system was fully characterized to determine its
performance.
The second part of this work demonstrates the application of this microscope platform in
virology. The microscope was configured to combine two nonlinear imaging modalities: coherent
anti-Stokes Raman scattering and two-photon excitation. Mouse fibroblast cells were
infected with a genetically modified cytomegalovirus. The modification causes the host cell
to express the green fluorescent protein upon infection. The host cell morphology and lipid
droplet distribution were recorded by imaging with coherent anti-Stokes Raman scattering,
whilst the infection was monitored by imaging the viral protein expression with two-photon
excitation. The cytopathic effects typical of cytomegalovirus infection were observed, including
expansion of the nucleus, rounding of the cell shape, and the appearance of intracellular
viral inclusions. In some cases these effects were accompanied by dense accumulations of lipid
droplets at the nuclear periphery. Imaging was performed both with fixed cells and living. It
was demonstrated that the lipid droplets in a single live cell could be imaged over a period of
7 hours without causing noticeable laser-induced damage. The system is shown to be a flexible
and powerful tool for the investigation of virus replication and its effects on the host cell
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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