1,720,962 research outputs found
Fine-Tuning the Electrostatic Properties of an Alkali-Linked Organic Adlayer on a Metal Substrate
Full text linkThe performance of modern organic electronic devices is often determined by the electronic level alignment at a metal–organic interface. This property can be controlled by introducing an interfacial electrostatic dipole via the insertion of a stable interlayer between the metallic and the organic phases. Here, we use density functional theory to investigate the electrostatic properties of an assembled structure formed by alkali metals coadsorbed with 7,7,8,8-tetracyanoquinodimethane (TCNQ) molecules on a Ag(100) substrate. We find that the interfacial dipole buildup is regulated by the interplay of adsorption energetics, steric constraints and charge transfer effects, so that choosing chemical substitutions within TCNQ and different alkali metals provides a rich playground to control the systems’ electrostatics and in particular fine-tune its work-function shift
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
MODELLING THE SELF-ASSEMBLY OF SUPRAMOLECULAR NANOSTRUCTURES ADSORBED ON METALLIC SUBSTRATES
Full text link2005/2006The term Nanotechnology is used to describe a variety of techniques to
fabricate materials and devices at the nanoscale. Nano-techniques include
those used for fabrication of nanowires, those used in semiconductor fabrication
such as deep ultraviolet and electron beam lithography, focused ion beam
machining, nanoimprint lithography, atomic layer deposition, molecular vapor
deposition, and the ones including molecular self-assembly techniques.
All these methods are still being developed and not all of them were devised
with the sole purpose of creating devices for nanotechnology.
A number of physical phenomena become noticeably pronounced as the
system size decreases. These include statistical effects, as well as quantum
effects, where the electronic properties of solids are altered if the particle
size is greatly reduced. There are also effects which never come into play by
going from macro to micro dimensions, while they become dominant when
the nanometer scale is reached. Furthermore nanotechnology can be thought
of as extensions of traditional disciplines towards the explicit consideration
of all these effects. Traditional disciplines can be re-interpreted as specific
applications of nanotechnology. Broadly speaking, nanotechnology is the
synthesis and application of ideas from science and engineering towards the
understanding and production of novel materials and devices with atomicscale
control.
Modern synthetic chemistry has reached the point where it is possible
to prepare small molecules of almost any (stable) structure. Methods exist
today to produce a wide variety of useful chemicals. A branch of nanotechnology,
relevant to the present thesis work, is looking for methods to assemble
single molecules into supramolecular assemblies arranged in a well defined
manner. These approaches use molecular self-assembly and supramolecular
chemistry to automatically arrange the single molecules into interesting and
potentially useful structures. The scanning tunneling microscope (STM) is
a non-optical microscope that scans an electrical probe (the tip) over a conductive
surface to be imaged. It allows scientists to visualize regions of high
electron density at the atomic scale, and hence infer the position of individual
atoms and molecules on a material surface. STM is specially suited for the
study of the self-assembly of molecules deposited on conductive substrates
because it provides direct insight into the assembled structures. However,
the STM images are often insufficient for a complete description of the phenomena,
and computer simulations offer a complementary approach that can
effectively integrate the experiments .
The theoretical investigation of the molecular self-assembly aims at the
understanding of the mechanisms that are involved in the assemblies formatiom.
In particular the atomistic simulation can provide information on the
geometry of the stable structures, the nature and the intensity of the interactions
as well as on the dynamical processes. In this thesis, a combination of
first principles and classical molecular dynamics simulations is used to shed
light on the self-assembly of some organic molecules deposited on noble metal
substrates. Three cases are discussed, the self-assembly of TMA and BTA
molecules on Ag(111) and the self-assembly of an oxalic amide derivative on
Au(111).
When TMA and BTA molecules are deposited onto a silver surface at a
temperature lower than room temperature they form a regular 2D honeycomb
network featuring double hydrogen bonds between carboxylic groups.
Even if this bonding makes the network very stable, when these systems are
annealed to higher temperatures they undergo some irreversible phase transition
into closer-packed supramolecular arrangements. Namely, the TMA
has a transition from honeycomb to a high coverage “quartet” structure and
the BTA has two transtions: from honeycomb to unidimensional stripes and
from here to a closed-packed monolayer. A combination of experimental and
theoretical techniques allowed us to identify the stepwise deprotonation of
the carboxylic acid groups as the driving force driving the phase transitions.
Our theoretical investigation targeted the electrostatic interaction involved
in the formation of the various phases revealing that a depolarisation
of the molecular ions occurs as a consequence of the deprotonation process.
Therefore, the repulsive contribution arising from the interaction of negatively
charged molecules can be overcome by the attractive hydrogen bond
interaction involving the deprotonated carboxylic groups, thus resulting in a
stable closed-packed arrangement. Rather remarkably, this exemplifies how
higher-coverage phases can be obtained at each step of a series of phase transitions
in a supramolecular assembled system, despite the increasing temperature
and the increasing electrostatic repulsive energy cost accompanying
deprotonation.
The oxalic amide derivative molecules arranges themselves in linear chains
both in the molecular solid and when adsorbed on a gold surface. However
the intermolecular distance and the geometry of the chains are different in
these two cases. Various relaxed bonding structure between molecules in the
chains have been calculated from first principles in the present work.
The rationale of the different linkage behaviour between molecules in the
two situations described have also been investigated: the interaction with
the substrate appears to be the main cause for the particular rearrangement
observed in the chains. Both experimental observations and theoretical predictions
indicate that a conformational change involving the rotation of the
phenyl rings of the monomers is necessary for chain formation
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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