1,721,033 research outputs found
Rapid Desorption of Polyelectrolytes from Solid Surfaces Induced by Changes of Aqueous Chemistry
Full text linkThe short-term desorption
induced by changes of aqueous chemistry
of predeposited polyelectrolyte layers on solid surfaces was studied
with reflectometry. The behavior of a strong polycation, polydiallydimethylammonium
chloride (PDADMAC), interacting with flat silica was investigated
in detail. Results showed that partial desorption of preadsorbed polymer
chains can be quickly triggered by changes in ionic strength and pH.
When lowering these parameters in the PDADMAC–silica system,
the increased lateral repulsive potential of neighboring chains drove
the desorption of some of the polymer. Furthermore, layer desorption
was favored when electrostatic interactions between a polyelectrolyte
and the underlying surface became less attractive or switched to being
repulsive. At the investigated timescales (<1 h), adlayer desorption
was always partial and often incomplete. When initiating desorption
from a condition of large adsorbed mass, desorption effects did not
result in the plateau mass obtained by adsorption on a clean surface:
an excess mass remained deposited. The results thus suggest that a
relatively large energy barrier needs to be overcome to induce redissolution
of predeposited chains and that this barrier may be a function of
the number of polymer–surface interactions, which are in turn
correlated with polymer molecular mass. These mechanisms have important
implications for environmental processes and colloidal systems because
they imply that, once adsorbed, polymeric chains may be redissolved
but only to a limited degree at typical engineering timescales
Bond- and mode-specific reactivity of methane on Ni(100)
No full textIn this work, the state-resolved reactivity of methane excited to different C-H stretch vibrations have been measured on a Ni(100) surface. Two kinds of experiments have been performed. In the first series of experiments, we have measured the reactivity of dideutero methane (CD2H2) excited in two different C-H stretch vibrational states which are nearly iso-energetic, but have different vibrational amplitudes. We observed that CD2H2 excited with two quanta of vibrational energy in one C-H bond were more reactive (by as much as a factor 5) than molecules excited with one quantum in each of two C-H bonds. This was the first time that state specificity has been observed in a gas-surface reaction. Our results clearly exclude the possibility of statistical models correctly describing the mechanisms of the methane chemisorption and highlight the importance of the dynamical calculations. We rationalize our results in terms of a spectator model and bond-specific reactivity, where the laser excited bond is broken in the reaction with the surface and the difference in reactivity of the two vibrational states is explained in terms of vibrational energy localized in a single C-H bond. Additionally, we have measured the state-resolved reactivity of CH4 in its totally symmetric C-H stretch vibration (ν1) on Ni(100). The methane molecules were excited to ν1 by stimulated Raman pumping prior the collision with the surface. We observed that the reactivity of the ν1 excited CH4 is about an order of magnitude higher than that of methane excited to the isoenergetic antisymmetric stretch (ν3) reported by Juurlink et al. [Phys. Rev. Lett. 83, 868 (1999)] and is similar to that we have previously observed for the excitation of the first overtone (2ν3). Since all four bonds initially carry vibrational amplitude for both ν1 and ν3, the difference in reactivity between the symmetric and antisymmetric vibrations cannot simply be explained in terms of bond-specific laser excitation. We refer to this reactivity difference as mode-specific. In this case, the relative reactivity between two different vibrational states does not only depend on the quantity of vibrational energy contained in each bond, but it is also influenced by the symmetry of the vibrational state excited. Our results are consistent with predictions of a vibrationally adiabatic model of the methane reaction dynamics [Halonen et al., J. Chem. Phys. 115, 5611 (2001)].LCP
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
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