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Quantum mechanical calculations coupled with a dynamical continuum model for the description of dielectric relaxation; Time dependent Stokes shift of coumarin C153 in polar solvents
No full textWe present here a study of the time dependent Stokes shift, performing quantum-mechanical calculations on coumarin C153 in polar solvents. The electrostatic interaction between the solute and the solvent is treated within the Polarizable Continuum Model, which allows us to use a molecular shaped cavity for the solute. In order to take into account that the sudden change in the solute electronic density after the S0 → S1 excitation can be accompanied by a non instantaneous rearrangement of a component of the solvent polarization, we use a non-equilibrium representation of the solvent response. We have implemented a procedure to calculate the solvation time correlation function (the theoretical counterpart of the Stokes shift), including experimental data of the complex dielectric permittivity ge(ω). The results that we have obtained are in good agreement with the experimental measurements. We will report the calculations for water, methanol, acetonitrile and dimethyl sulfoxide as solvents, showing that a correct treatment of dielectric relaxation generally needs a more detailed description of the solvent response than diffusive models
Solvation Dynamics by Computer Simulation: Coumarin C153 in 1,4-Dioxane
No full textComputer simulation results are presented for an atomistic pair potential model of 1,4-dioxane which takes into account molecular flexibility. The model has been conceived to be applied to the study of solvatochromism and solvation dynamics in the presence of the polar probe coumarin C153. Computer simulations on the pure liquid have produced thermodynamical, structural, and dynamical data in good agreement with available experimental measures. This constitutes a valuable test of the 1,4-dioxane all-atom model employed. The study of solute-solvent interactions for C153 in 1,4-dioxane has been motivated by the aim of casting light, through simulations, on the interesting experimental findings according to which such a solvent behaves as a "polar" solvent with respect to dynamic solvation properties. Molecular dynamics is particularly suitable to model the process and provides an interpretation of the so-called "dioxane anomaly". An investigation of the structure of the solvation shell and of the dynamics of solvation is presented and discussed. In particular, the satisfactory accordance between simulated and experimental solvation response implies that the simulations give a reliable description of both solute and solvent at a molecular level and reinforces the idea that the explicit inclusion of discrete solvent molecules is needed for a realistic treatment of solvation phenomena in which the local structure of the liquid plays a key role
Solvation response in water: a study based on Molecular Dynamics simulations and Quantum Mechanical calculations
No full textIn this work, we present a way to exploit the data from molecular dynamics (MD) simulations in order to obtain the solvation response in polar solvents. We show how simulations of SPC/E water can be used in combination with a continuum model for solvation dynamics which allows a molecular, quantum mechanical description of the solute. The coupling between different theoretical approaches provides deeper insights into dielectric relaxation: on the one hand, simulations give local information on the solvent, while on the other hand, the continuum-based model enables accurate calculations on the solute. In addition, by using molecular dynamics, we have studied solvation dynamics at three different temperatures. The results that we have obtained even with a simple model for dynamics show a good agreement with experiments, considering that the model used for simulation of water is rigid and nonpolarizable
Solvation of Coumarin 153 in Supercritical Fluoroform
No full textWe present a study of local density augmentation around an attractive solute (i.e., giving rise to more attractive interaction with the solvent than solvent-solvent interactions) in supercritical fluoroform. This work is based on molecular dynamics simulations of coumarin 153 in supercritical fluoroform at densities both above and below the critical density, ranging from dilute gaslike to liquidlike, at a reduced temperature (T/Tc) of 1.03. We focused on studying the structure of the solvation shell and the variation of the solute electronic absorption and emission shifts with density. Quantum calculations at the density functional theory (DFT) level were run on the solute in the ground state, and time-dependent DFT calculations were performed in the solute excited state in order to determine the solute-solvent potential parameters. The results obtained for the Stokes shift are in agreement with the experimental measurements. To evaluate local density augmentation from simulations, we used two different definitions, one based on the solvation number and the other derived from solvatochromic shifts. In the former case, the agreement with experimental results is good, while, in the latter case, better agreement is achieved by perturbatively including the induced-dipole contribution to the solvation energy
A method to estimate the environmental impact of an electric city car during six months of testing in an Italian city
No full textGoing 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
“SIMULAZIONE E SPERIMENTAZIONE DI VEICOLI PLUG-IN ELETTRICI E IBRIDI NELLA REALTÀ LECCESE
No full textVariations 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
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