1,721,055 research outputs found
Development of new molecular switches based on Benzazolo-oxazolidine for the visible
No full textDepuis plusieurs années, de nombreuses recherches se sont concentrées sur le développement de matériaux intelligents élaborés à partir d’interrupteurs moléculaires. En effet, lors de l’application d’un stimulus extérieur, ces systèmes peuvent s’interconvertir entre deux états différents métastables présentant des propriétés physico-chimiques différentes. Dans ce contexte, les dérivés à base de benzazolo-oxazolidine ont démontré des propriétés d’interconversion multimodale remarquables. En effet, l’ouverture du cycle oxazolidine des BOX peut être induite de façon indifférenciée par modification du pH, application d’un potentiel électrochimique, ou encore sous irradiation lumineuse. Néanmoins, il est important de noter que la photo-activité de ces systèmes se limite à une irradiation sous lumière UV (254 nm) ce qui limite d’autant leurs champs d’application. Dans ce contexte, l’objectif de cette thèse est d’essayer de décaler la longueur d’activation des BOX de l’UV lointain vers le proche UV voire le domaine visible. Pour atteindre cet objectif, deux approches ont été suivies. La première consiste à modifier directement l’unité indolino-oxazolidine afin d’étendre son système -conjugué et d’induire un effet bathochromique. A l’inverse, la seconde stratégie mise en place repose sur l’association covalente d’une unité BOX et d’un photosensibilisateur capable d’absorber un rayonnement à plus faible énergie, soit en position 2 soit en position 5. Dans ce cadre, l’ouverture photo-induite des BOX reposera sur les propriétés électrochromiques de ces dernières associées à l’existence d’un transfert d’électron photo-induit entre les deux unités lors de l’excitation lumineuse.For several years, much research has focused on the development of smart materials made from molecular switches. Indeed, upon application of an external stimulus, these systems can switch between two different metastable states with different physico-chemical properties. In this context, benzazolo oxazolidine based derivatives demonstrated remarkable multimodal interconversion properties. Indeed, the opening of the oxazolidine ring of BOX can be induced in an undifferentiated way by modification of the pH, application of an electrochemical potential, or even under light irradiation. Nevertheless, it is important to note that the photo-activity of these systems is limited to irradiation under UV light (254 nm), which limits their fields of application. In this context, the objective of this thesis is to try to shift the activation length of the BOX from the far UV to the near UV or even the visible domain. To achieve this objective, two approaches were followed. The first is to directly modify the indolino-oxazolidine unit to extend its -conjugate system and induce a bathochromic effect. Conversely, the second strategy implemented is based on the covalent association of a BOX unit and a photosensitizer capable of absorbing radiation at a lower energy, either in position 2 or in position 5. In this context , the photo-induced opening of the BOX will be based on the electrochromic properties of the latter associated with the existence of a photo-induced electron transfer between the two units during light excitation
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Mise au point d'un test anti-AGE pour le criblage d'extraits végétaux.
No full textDate du colloque : 05/2013</p
Les Benzalo-oxazolidines : nouveaux composés photochimiques dédiés aux applications ONL
Get PDFLa plupart des composés organiques photochromiques sont connus pour présenter deux états stables dont les propriétés physico-chimiques sont très différentes. Nous nous sommes particulièrement intéressés à une nouvelle famille de photochromes : les benzazolooxazolidines. En effet, « la forme colorée » de ces composés possède toutes les caractéristiques (longueur de conjugaison importante, bande à transfert de charge,...) pour en faire un chromophore actif en Optique Non-Linéaire (ONL) quadratique (X²) à l’opposé de l’état initial. L’objectif de cette étude consiste donc à incorporer ces chromophores en forme « incolore » dans une matrice polymère, puis orienter ces derniers par l’application d’un champ électrique statique (« poling ») et ainsi briser l’isotropie du milieu. Enfin une dernière étape consiste à structurer le matériau en photo-générant, par passage de la forme incolore à la forme colorée, des zones très actives en ONL. Afin d’apprécier l’activité de ces chromophores en ONL , nous nous sommes dans un premier temps attachés à déterminer la valeur de l’hyperpolarisabilité quadratique de la plupart d’entre eux par diffusion Hyper-Rayleigh (HRS) et ainsi il nous a été possible d’établir quelques relations structure/activité. Enfin, les chromophores les plus actifs ont été dispersés au sein d’une matrice en PMMA lors d’essais prospectifs afin de mettre en avant le potentiel de nos chromophores.The most of the photochromic organic compounds are known to present two stable states of which physical and/or chemical properties are very different. We are especially interrested of a new family of photochromic compounds particularly the benzazolo-oxazolidines. In fact, the « colored form » of these composits have all characteristics (important conjugaison length, charge transfert band,…) in order to do an active chromophore in nonlinear optic squared to the opposit of the initial state. The purpose of this study will be to incorporate the chromophore into a polymer matrix, then orienting them under an electrostatic field to break environment’s isotropy. Lastly, the final step consists to structure the material by photogenerating some active zones in NLO by transformation from the initial state to the colored state. So to estimate the activity of this new NLO chromophores, we have, in first time, determined their squared hyperpolarisability by Hyper Raleigh Scattering and this we have shown some relationship structure/activity. Lastly, the most active of the chromophores was dispersed into a PMMA matrix during the prospective essays in the purpose to show their potential
The indolino[2,1-b]oxazolidine derivatives for the development of multi-addressable molecular systems
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Dispelling the Myths Behind First-author Citation Counts
Get PDFWe 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
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