1,720,964 research outputs found
Luce e molecole in regime di accoppiamento forte: un approccio Quantum Chemistry.
Full text linkQuando luce e molecole organiche interagiscono confinati in un volume nanometrico, si scambiano energia coerentemente su scale di tempi dell’ordine di decine di femtosecondi. Se la velocità di scambio di energia risulta maggiore delle velocità di decadimento del sistema, si raggiunge il regime di accoppiamento forte. In questo regime, i gradi di libertà di luce e molecole si mescolano ed il sistema è caratterizzato da una reattività chimica modificate. Un modo semplice di descrivere luce e molecole in accoppiamento forte è quello di trattare gli autostati del sistemi come ibridi fra luce e materia: i polaritoni. I primi esperimenti in questo ambito hanno utilizzato i polaritoni per modificare sensibilmente le velocità di processi fotochimici. Inoltre, i polaritoni sono stati osservati a temperatura ambiente con una risoluzione fino alla singola molecola. Parallelamente, i modelli teorici sviluppati forniscono uno schema concettuale semplice per descrivere una nuova e ricca chimica polaritonica. Tuttavia, descrivere teoricamente e simulare sistemi polaritonici realistici si è rivelato arduo per le dimensioni e la complessità del sistema. In questa tesi, viene presentato un metodo in grado di simulare sistemi polaritonici simulando esperimenti realistici. Il metodo si basa su un approccio Quantum Chemistry ed estende i tipici oggetti presenti in chimica quantistica al caso polaritonico. Gli stessi concetti trovano successivamente impiego nell’estensione ai polaritoni di un metodo semiclassico QM/MM basato sulla tecnica Surface Hopping e nella simulazione un’intera reazione fotochimica in condizioni di accoppiamento forte. Il metodo sviluppato permette di caratterizzare il meccanismo di reazione e di prevedere la possibilità di aumentare o sopprimere selettivamente le rese quantiche di reazione.When light and organic molecules interact in confined nanometric volumes, their exchange of energy becomes coherent over a few tens of femtoseconds. As the rate of such exchange becomes quicker than the decay of the system, the so-called strong coupling regime is achieved. In strong coupling, the degrees of freedom of light and molecule mix, offering a brand-new way to modify chemical processes. A straightforward description of molecules in strong coupling is promptly obtained by describing the eigenstates state of the system as hybrids between light and matter: the polaritons. The experiments driving this field exploited polaritons to modify the rate of photochemical processes and observed polaritons down to the single molecule level at room temperature. In parallel, the theoretical models developed a simple interpretative framework to polaritons, pioneering a new, rich polaritonic chemistry. However, the complexity of real-life polaritonic systems can quickly become cumbersome to describe theoretically, resulting detrimental for the predictive power of such models. In this thesis, the typical quantum chemistry concepts are revised for the polaritonic case. The same concepts are then exploited to extend a QM/MM surface hopping method to polaritons. In the end, the developed method is successfully applied to the study of a complete polaritonic photochemical reaction, allowing to predict a remarkable enhancement of the quantum yields and explain its mechanism
Influence of the nature of the electrode material and process variables on the kinetics of the chlorine evolution reaction. (I) The case of IrO2-based electrocatalysts
No full textKinetic studies on the chlorine evolution reaction (ChlER) on oxide-based materials have been the subject of a number of papers since the seventies, following the introduction of DSAs (Dimensionally Stable Anodes) in chlor-alkali plants. On the basis of experimental data, different pathways have been proposed for the reaction over the years. Actually, specific experimental conditions and different approaches in sample preparation may lead to conflicting explanations. In the present paper, the ChlER kinetics has been studied at four electrode materials based on iridium and titanium oxides (with a 1:2 molar ratio). Electrodes were synthetized at two temperatures (350 and 450 °C) and by two different preparation methods: physical vapor deposition (rf-magnetron sputtering) and a conventional sol-gel technique, using special precursors developed in our laboratory. Both methodologies guarantee a high level of reproducibility. As also observed by other authors, experimental data have shown a lack of linearity in Tafel plots, high b slopes and reaction orders with respect to chloride ≤ 1, which have been justified on the basis of a Volmer-Heyrovsky pathway, by considering a model proposed by Tilak and Conway in 1992. This approach highlighted the role of the adsorbed intermediates, also at low overpotentials, for all electrode materials. To analyze further the kinetics, Langmuir and Frumkin models for intermediates adsorption were considered. Values for the lateral interaction parameter g were estimated, which ranged between 1 and 10, in all cases. Concerning the effect of pH, its influence on the ChlER rate seems to be related only with electrode surface modifications, without any involvement of protons in the rate determining step of the process. A slight inhibiting effect was assessed, by increasing the protons concentration. Eventually, impedance spectroscopy analysis did not appear sensitive to intermediate adsorption, plausibly because of the low variation of the coverage within the Tafel region; a poorly resolved contribution related to porosity was found in the case of samples prepared at 350 °C.Kinetic studies on the chlorine evolution reaction (ChlER) on oxide-based materials have been the subject of a number of papers since the seventies, following the introduction of DSAs (Dimensionally Stable Anodes) in chlor-alkali plants. On the basis of experimental data, different pathways have been proposed for the reaction over the years. Actually, specific experimental conditions and different approaches in sample preparation may lead to conflicting explanations. In the present paper, the ChlER kinetics has been studied at four electrode materials based on iridium and titanium oxides (with a 1:2 molar ratio). Electrodes were synthetized at two temperatures (350 and 450 °C) and by two different preparation methods: physical vapor deposition (rf-magnetron sputtering) and a conventional sol-gel technique, using special precursors developed in our laboratory. Both methodologies guarantee a high level of reproducibility. As also observed by other authors, experimental data have shown a ..
Photoprotecting uracil by coupling with lossy nanocavities
Full text linkWe analyze how the photorelaxation dynamics of a molecule can be controlled by modifying its electromagnetic environment using a nanocavity mode. In particular, we consider the photorelaxation of the RNA nucleobase uracil, which is the natural mechanism to prevent photodamage. In our theoretical work, we identify the operative conditions in which strong coupling with the cavity mode can open an efficient photoprotective channel, resulting in a relaxation dynamics twice as fast as the natural one. We rely on a state-of-the-art chemically detailed molecular model and a non-Hermitian Hamiltonian propagation approach to perform full-quantum simulations of the system dissipative dynamics. By focusing on the photon decay, our analysis unveils the active role played by cavity-induced dissipative processes in modifying chemical reaction rates, in the context of molecular polaritonics. Remarkably, we find that the photorelaxation efficiency is maximized when an optimal trade-off between light-matter coupling strength and photon decay rate is satisfied. This result is in contrast with the common intuition that increasing the quality factor of nanocavities and plasmonic devices improves their performance. Finally, we use a detailed model of a metal nanoparticle to show that the speedup of the uracil relaxation could be observed via coupling with a nanosphere pseudomode, without requiring the implementation of complex nanophotonic structuresThis work has been funded by the
European Research Council through Grants ERC-2016-StG-
714870 (S. Felicetti, J. Feist, and J. Fregoni) and ERC-2015-
CoG-681285 (J. Fregoni, PI Stefano Corni) and by the
Spanish Ministry for Science, Innovation, and Universities -
Agencia Estatal de Investigación through Grants RTI2018-
099737-B-I00, PCI2018-093145 (through the QuantERA
program of the European Commission), and MDM-2014-
0377 (through the Marıá de Maeztu program for Units of
Excellence in R&D). T. Schnappinger and R. de Vivie-Riedle
gratefully acknowledge the DFG Normalverfahren. S. Reiter
gratefully acknowledges financial support by the International Max Planck Research School of Advanced Photon Science
(IMPRS-APS
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
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