1,721,100 research outputs found
Development of new Functional Molecular Spin-Crossover Ceramics by Cool-SPS
No full textLe complexe de [Fe(Htrz)2(trz)] (BF4) est probablement le plus étudié, dans la communauté de SCO, car il présente une bonne stabilité chimique et sa commutation entre les deux états haut et bas spin se fait de manière réversible, avec une large hystérèse aux alentours de l’ambiante. Alors que la structure cristalline de son polymorphe I est déjà connue, nous rapportons, ici, celle de son polymorphe II. Cependant, l’ambition d’utiliser ces composés dans des dispositifs appliqués est liée à leur mise en forme. Parmi celles-ci, l’élaboration de céramiques n’avais jamais été envisagée pour des raisons évidentes de fragilité thermodynamique. Grace au Cool-SPS, nous avons réussi à obtenir les premières céramiques molécules fonctionnelles (SCO). Une optimisation des paramètres expérimentaux de frittage (température, pression, puissance, rampes…) a été faite et leurs influences sur les propriétés structurales et microstructurales et leurs comportements de commutation ont été étudiés. Et dans le but d’élaborer le diagramme de phase (T /P), un suivi fin de la transition de spin, révélant une piezo-hystérèse, a été fait grâce à la diffraction des rayons X sur poudre, sous pression in situ à l’aide du rayonnement synchrotron. Ce travail nous a amené, notamment à effectuer une étude thermodynamique approfondie, basée sur des modèles théoriques existants (Slichter-Drickamer, Sorai-Seki), afin de mieux comprendre les effets provoqués par le frittage de ces composés à conversion de spin.The [Fe(Htrz)2(trz)] (BF4) complex is probably the most studied, in the SCO community, because it exhibits good chemical stability and reversible switching between the two high and low spin states, with large hysteresis around ambient. While the crystal structure of its polymorph I is already known, we report here that of its polymorph II. However, the ambition to use these compounds in applied devices is related to their shaping. Among these, the ceramic aspect had never been studied due to their thermodynamic fragility. Thanks to Cool-SPS, we succeed to obtain the first SCO functional molecular ceramic. An optimization of the experimental sintering parameters (temperature, pressure, power, ramps, etc.) was carried out and their influences on the structural and microstructural properties and their switching behaviors were studied. And in order to develop the phase diagram (T/ P), a fine follow-up of the spin transition, on the powder, with a synchrotron radiation, under high-pressure X-ray diffraction provides a fine track of the pressure-induced SCO and showed a piezo-hysteresis. This work lead us, to a detailed thermodynamic study, based on existing theoretical models (Slichter-Drickamer, Sorai-Seki), in order to better understand the effects caused by the sintering of these spin-conversion compounds
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
Approche structurale du phénomène de transition de spin par diffraction des rayons X sous contraintes (T, P, hv)
No full textThe spin transition phenomenon corresponds to the spin state modification of a transition metal ion under an external perturbation (T, P, B, hv). Some iron (II) complexes, for example, can change from the paramagnetic spin state (S = 2) to the diamagnetic low spin state (S = 0). Before thinking to potential industrial applications, it is necessary to understand and control the differences of magnetic behaviour of such compounds. To this aim, the molecular science group of the ICMCB is studying, for a few years, mononuclear iron (II) complexes, which present very distinct spin transition magnetic features. In this thesis, the structural parameters which govern the behaviour differences from one complex to the other are identified. Moreover, direct correlations between the magnetic features and the structural properties of the [FeL (NCS) ] series of complexes are pointed out. In addition, for the first time, the crystal structures of theses complexes in metastable high spin states obtained by thermal trapping or by light irradiation at very low temperature have been determined.Le phénomène de transition de spin correspond au changement d'état de spin d'un ion de transition sous l'action d'une perturbation extérieure (T, P, B, hv). Dans certains complexes du Fe(II), par exemple, l'ion peut basculer de l'état haut spin paramagnétique (S=2) vers l'état bas spin diamagnétique (S=0). Avant d'envisager des applications industrielles, il est nécessaire de bien comprendre et de maîtriser les différences de comportement magnétique de ces composés. C'est dans ce contexte que l'équipe des sciences moléculaires de l'ICMCB étudie depuis quelques années des complexes mononucléaires du Fe(II) aux caractéristiques magnétiques de transition de spin très variées. Dans ce travail de thèse, les paramètres structuraux à l'origine des différences de comportement d'un complexe à l'autre sont identifiés. De plus, des corrélations directes entre propriétés magnétiques et les propriétés structurales des complexes de la série [FeLn(NCS)2]sont mises en évidence. Par ailleurs, pour la première fois, les structures cristallines de ces complexes dans des états métastables atteints par effet de trempe thermique ou par photo-excitation à très basse température ont été déterminées
Structural approach of the spin crossover phenomenon by X ray diffraction under constraint (T, P, hv)
No full textLe phénomène de transition de spin correspond au changement d'état de spin d'un ion de transition sous l'action d'une perturbation extérieure (T, P, B, hv). Dans certains complexes du Fe(II), par exemple, l'ion peut basculer de l'état haut spin paramagnétique (S=2) vers l'état bas spin diamagnétique (S=0). Avant d'envisager des applications industrielles, il est nécessaire de bien comprendre et de maîtriser les différences de comportement magnétique de ces composés. C'est dans ce contexte que l'équipe des sciences moléculaires de l'ICMCB étudie depuis quelques années des complexes mononucléaires du Fe(II) aux caractéristiques magnétiques de transition de spin très variées. Dans ce travail de thèse, les paramètres structuraux à l'origine des différences de comportement d'un complexe à l'autre sont identifiés. De plus, des corrélations directes entre propriétés magnétiques et les propriétés structurales des complexes de la série [FeLn(NCS)2]sont mises en évidence. Par ailleurs, pour la première fois, les structures cristallines de ces complexes dans des états métastables atteints par effet de trempe thermique ou par photo-excitation à très basse température ont été déterminées.The spin transition phenomenon corresponds to the spin state modification of a transition metal ion under an external perturbation (T, P, B, hv). Some iron (II) complexes, for example, can change from the paramagnetic spin state (S = 2) to the diamagnetic low spin state (S = 0). Before thinking to potential industrial applications, it is necessary to understand and control the differences of magnetic behaviour of such compounds. To this aim, the molecular science group of the ICMCB is studying, for a few years, mononuclear iron (II) complexes, which present very distinct spin transition magnetic features. In this thesis, the structural parameters which govern the behaviour differences from one complex to the other are identified. Moreover, direct correlations between the magnetic features and the structural properties of the [FeL (NCS) ] series of complexes are pointed out. In addition, for the first time, the crystal structures of theses complexes in metastable high spin states obtained by thermal trapping or by light irradiation at very low temperature have been determined
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
Approche structurale du phénomène de transition de Spin par diffraction des rayons X sous contraintes (T, P, hv)
Full text linkThe spin transition phenomenon corresponds to the spin state modification of a transition metal ion under an external perturbation (T, P, B, hv). Some iron (II) complexes, for example, can change from the paramagnetic spin state (S = 2) to the diamagnetic low spin state (S = 0). Before thinking to potential industrial applications, it is necessary to understand and control the differences of magnetic behaviour of such compounds. To this aim, the molecular science group of the ICMCB is studying, for a few years, mononuclear iron (II) complexes, which present very distinct spin transition magnetic features. In this thesis, the structural parameters which govern the behaviour differences from one complex to the other are identified. Moreover, direct correlations between the magnetic features and the structural properties of the [FeLn(NCS)2] series of complexes are pointed out. In addition, for the first time, the crystal structures of theses complexes in metastable high spin states obtained by thermal trapping or by light irradiation at very low temperature have been determined.The spin transition phenomenon corresponds to the spin state modification of a transition metal ion under an external perturbation (T, P, B, hv). Some iron (II) complexes, for example, can change from the paramagnetic spin state (S = 2) to the diamagnetic low spin state (S = 0). Before thinking to potential industrial applications, it is necessary to understand and control the differences of magnetic behaviour of such compounds. To this aim, the molecular science group of the ICMCB is studying, for a few years, mononuclear iron (II) complexes, which present very distinct spin transition magnetic features. In this thesis, the structural parameters which govern the behaviour differences from one complex to the other are identified. Moreover, direct correlations between the magnetic features and the structural properties of the [FeLn(NCS)2] series of complexes are pointed out. In addition, for the first time, the crystal structures of theses complexes in metastable high spin states obtained by thermal trapping or by light irradiation at very low temperature have been determined
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