1,720,958 research outputs found
Contrôle quantique des dynamiques couplées électrons-noyaux
No full textLes processus ultra rapides comme le transfert non-radiatif et la photodissociation ont un fort impact sur la redistribution de l'énergie dans les molécules après irradiation par la lumière. Ces processus d'une importance fondamentale impliquent souvent une intersection conique (le cas extrême de la situation hors Born-Oppenheimer), comme dans le système qui nous intéresse, la pyrazine, une molécule complexe avec 24 modes de vibration. Ainsi, le paquet d'ondes une fois excité se scinde en deux (ou plus) composantes selon le nombre d'états électroniques impliqués dans cette intersection (ici deux). Notre objectif dans cette étude donc est d'utiliser des lasers pour guider et même visualiser les paquets d'ondes, c'est-à-dire l'évolution quantique du système, dans les directions préférentielles. L'impact de l'intersection conique est également très important en chimie traditionnelle et dans les réactions biologiques pour déclencher des processus très importants tels que la vision ou la photosynthèse. Nous utilisons une approche variationnelle basée sur des paquets d'ondes implémentée dans le logiciel appelé MCTDH (Multi Configuration Time Dependent Hartree) que nous utilisons. Cet algorithme, développé par nos collègues allemands, peut servir d'outil essentiel pour comprendre la dynamique moléculaire sous-jacente à de nombreux phénomènes physiques se produisant à une échelle de temps ultra-rapide. Partant d'un simple hamiltonien impliquant 2 modes normaux, la robustesse et l'efficacité de différentes stratégies de contrôle du transfert d'énergie à travers l'intersection conique ont été vérifiées par une augmentation systématique de la dimension: 4 modes normaux et une comparaison finale avec des simulations à 24 modes normaux. Nous simulons les populations et les cohérences électroniques.The ultra fast processes like radiation-less transfer and photo dissociation have a very strong impact on energy redistribution after the molecules being irradiated by light. These processes of fundamental importance often involve, what we call, a conical intersection (the extreme case of non Born-Oppenheimer situation), like in our system of interest, pyrazine, a complex molecule with 24 vibrational modes. Thus, the wave packet once excited is bifurcated into two (or more) components depending on the number of electronic states involved in this intersection (here two). Our goal is thus, to use time delayed laser pulses to guide, and indeed, visualize the wave packets, i.e. the quantum evolution of the system, in the preferred directions. The impact of conical intersection is also very important in traditional chemistry and also in biological reactions to trigger very important processes such as vision or photosynthesis. We use a variational approach of wavepackets implemented in the software called MCTDH (Multi Configuration Time Dependent Hartree) we are using. This algorithm, developed by our colleagues in Germany, could serve as an essential tool for understanding the molecular dynamics underlying many physical phenomena occurring in an ultrafast time scale. Starting with a simple Hamiltonian involving 2 normal modes, the robustness and efficiency of different strategies of control of the energy transfer through the conical intersection have been verified by a systematic increase of dimensions to 4 normal modes. Finally, for the sake of completeness, a comparison is made including all the 24 normal modes in our Hamiltonian. We simulate the electronic populations and coherences
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
Laser control strategies in full dimensional funneling dynamics: The case of pyrazine
No full textInternational audienceMotivated by the major role funneling dynamics plays in light-harvesting processes, we built some laser control strategies inspired from basic mechanisms such as interference and kicks, and apply them to the case of pyrazine. We are studying the internal conversion between the two excited states, the highest and directly reachable from the initial ground state being considered as a donor, and the lowest as an acceptor. The ultimate control objective is the maximum population deposit in the otherwise dark acceptor, from a two-step process: radiative excitation of the donor, followed by a conical-intersection-mediated funneling towards the acceptor. The overall idea is to first obtain the control field parameters (individual pulses leading frequency and intensity, duration and inter-pulse time delay) for tractable reduced dimensional models basically describing the conical intersection branching space. Once these parameters are optimized, they are fixed and used in full dimensional dynamics describing the electronic population transfer. In the case of pyrazine, the reduced model is 4 dimensional, whereas the full dynamics involve 24 vibrational modes. Within experimentally achievable electromagnetic field requirements, we obtain a robust control with about 60% of the ground state population deposited in the acceptor state, while about 16% remains in the donor. Moreover, we anticipate a possible transposition to the control of even larger molecular systems, for which only a small number of normal modes are active, among all the others acting as spectators in the dynamics
Laser control strategies in full dimensional funneling dynamics: The case of pyrazine
Full text linkMotivated by the major role funneling dynamics plays in light-harvesting
processes, we built some laser control strategies inspired from basic
mechanisms such as interference and kicks, and apply them to the case of
pyrazine. We are studying the internal conversion between the two excited
states, the highest and directly reachable from the initial ground state being
considered as a donor, and the lowest as an acceptor. The ultimate control
objective is the maximum population deposit in the otherwise dark acceptor,
from a two-step process: radiative excitation of the donor, followed by a
conical-intersection-mediated funneling towards the acceptor. The overall idea
is to first obtain the control field parameters (individual pulses leading
frequency and intensity, duration and inter-pulse time delay) for tractable
reduced dimensional models basically describing the conical intersection
branching space. Once these parameters are optimized, they are fixed and used
in full dimensional dynamics describing the electronic population transfer. In
the case of pyrazine, the reduced model is 4 dimensional, whereas the full
dynamics involve 24 vibrational modes. Within experimentally achievable
electromagnetic field requirements, we obtain a robust control with about 60 %
of the ground state population deposited in the acceptor state, while about 16
% remains in the donor. Moreover, we anticipate a possible transposition to the
control of even larger molecular systems, for which only a small number of
normal modes are active, among all the others acting as spectators in the
dynamics.Comment: 12 pages, 12 figure
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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