1,720,999 research outputs found
Ionic liquids as solvents for rare-earth metals: a combined XAS and Molecular Dynamics study
Full text linkIn this work a detailed investigation of the structural organization of ILs, both monocationic and dicationic, and their water mixtures has been carried out by combining XAS spectroscopy and Classical MD simulations. The same joint XAS-MD approach has been also applied to the study of the solvation properties of Ln(III) salts dissolved in ILs. The original application of EXAFS and MD simulations paves the route for the systematic use of an integrated approach, with increased reliability, in the structural investigation of ILs. All together these issues are expected to be of great help in the systematic design of IL systems to meet the requirements of key applications
Unveiling the complex network of interactions in Ionic Liquids: A combined EXAFS and Molecular Dynamics approach
No full textHow Does CeIII Nitrate Dissolve in a Protic Ionic Liquid? A Combined Molecular Dynamics and EXAFS Study
No full text
Local order and long range correlations in imidazolium halide ionic liquids: a combined molecular dynamics and XAS study
No full textA thorough characterization of the structural properties of alkylimidazolium halides ionic liquids (ILs), namely 1-alkyl-3-methylimidazolium bromide ([Cn mim]Br with n = 5, 6, 8, 10) and iodide ([C6 mim]I), has been carried out by combining Molecular Dynamics simulations and the EXAFS spectroscopy. The existence of a local order in [Cn mim]Br ILs has been evidenced, with anions and imidazolium head groups forming a local three-dimensional bonding pattern that is common to all the [Cn mim]Br IL family, regardless the length of the alkyl chain attached to the cation. On the other hand, upon alkyl chain elongation significant differences have been highlighted in the long-range structure of these ILs. Theoretical X-ray structure
factors have been calculated starting from the MD simulations and a low q peak has been found for all [Cn mim]Br ILs, indicating the existence of long-range structural correlations. The low q peak moves to longer distances, increases in intensity and sharpens with increasing alkyl chain length on the cation. Similarities and differences between the ion three-dimensional arrangements
in [C6 mim]Br and [C6 mim]I were highlighted and the structural arrangement of Br− and I− was found to be different in the
proximity of the most acidic hydrogen atom of the imidazolium ring: the I− ion is preferentially located above and below the
ring plane, while the Br− ion has a high probability also to be coplanar with the imidazolium ring. A quantitative analysis of the
Br and I K-edge EXAFS spectra of alkylimidazolium halides ILs has been carried out starting from the microscopic description
of the systems derived from MD simulations. A very good agreement between theoretical and experimental EXAFS signals has
been obtained, allowing us to assess the reliability of the MD structural result for all the alkylimidazolium halides ILs investigated
in this work
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
Influence of Counterions on the Hydration Structure of Lanthanide Ions in Dilute Aqueous Solutions
No full textA synergic
approach combining molecular dynamics (MD) simulations
and X-ray absorption spectroscopy (XAS) has been used to investigate
diluted (0.1 M) aqueous solutions of two lanthanide ions (Ln3+), namely, La3+ and Dy3+, with triflate, nitrate,
and bis(trifluoromethylsulfonyl)imide (Tf2N–) as counterions. The different complexing ability of the three anions
has been highlighted by the analysis of the MD simulations: Tf2N– does not form inner-sphere complexes,
while a small amount of triflate coordinates both the La3+ and Dy3+ cations in their first solvation shell. On the
other hand, the nitrate ion is almost absent in the La3+ first coordination sphere, while forming contact ion pairs with
Dy3+. Both lanthanide ions are found to preferentially
interact with the water molecules, and the total number of oxygen
atoms coordinating the Ln3+ cations in their first solvation
sphere is the same in all of the solutions, regardless of whether
they belong to water molecules or to the counterion. The presence
of counterions in the cation first or second shell changes neither
the first shell distance nor the symmetry of the hydration complex
formed in solution. The MD results have been confirmed by comparison
with the Ln K-edge XAS experimental data, and the quantitative analysis
of the extended X-ray absorption fine structure (EXAFS) spectra of
the three salt solutions has provided a definite proof of the accuracy
of the force field employed in the simulations and of the MD structural
result. The anion–water and water–water hydrogen bond
lifetimes have been analyzed highlighting the slow down effect of
the triflate, nitrate, and Tf2N– anions
on the hydrogen bond dynamics in the Ln3+ first solvation
shell, with the effect being stronger in the Dy3+ solutions,
due to the higher charge density of the Dy3+ ion as compared
to La3+
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