1,721,019 research outputs found
Ultrafast vibrational response of activated C–D bonds in a chloroform–platinum(II) complex
Full text link[Image: see text] The vibrational response of the activated C–D bond in the chloroform complex [Pt(C(6)H(5))(2)(btz-N,N′)·CDCl(3), where btz = 2,2′-bi-5,6-dihydro-4H-1,3-thiazine] is studied by linear and nonlinear two-dimensional infrared (2D-IR) spectroscopy. The change of the C–D stretching vibration of metal-coordinated CDCl(3) relative to the free solvent molecule serves as a measure of the non-classical Pt···D–C interaction strength. The stretching absorption band of the activated C–D bond displays a red shift of 119 cm(–1) relative to uncoordinated CDCl(3), a strong broadening, and an 8-fold enhancement of spectrally integrated absorption. The infrared (IR) absorption and 2D-IR line shapes are governed by spectral diffusion on 200 fs and 2 ps time scales, induced by the fluctuating solvent CDCl(3). The enhanced vibrational absorption and coupling to solvent forces are assigned to the enhanced electric polarizability of the activated C–D bond. Density functional theory calculations show a significant increase of C–D bond polarizability of CDCl(3) upon coordination to the 16 valence electron Pt(II) complex
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
On the nature of ligand-induced charge concentrations in molecules and solid-state compounds
Full text linkDie topologische Analyse experimentell und aus quantenchemischen Rechnungen bestimmter Elektronendichteverteilungen nach dem "Atoms in Molecules" Ansatz von R. Bader erlaubt detaillierte Einblicke in die Bindungsverhältnisse und die elektronische Struktur von Molekül- und Festkörperverbindungen. Im Rahmen solcher Studien wurden Orte lokal konzentrierter Elektronendichte in der Valenzschale von Übergangsmetallatomen gefunden und u.A. mit den Vorhersagen des VSEPR-Konzepts in Verbindung gebracht. In der vorliegenden Dissertation wurden die Ursachen und die Auswirkungen solcher Ladungskonzentrationen eingehend untersucht. Dabei konnte gezeigt werden, dass die in der Valenzschale von frühen Übergangsmetallatomen auftretenden ligandeninduzierten Ladungskonzentrationen einen integralen Bestandteil kovalenter Bindungen zu den Liganden darstellen und durch Wechselwirkung mit Bereichen bindender Elektronendichte stereochemisch aktiv sind. Im Gegensatz dazu werden bei Komplexen der späten Übergangsmetalle mit nicht-d0 Konfiguration keine ligandeninduzierten Ladungskonzentrationen gefunden. Die hier auftretenden lokalen Konzentrationen werden durch die ungleichmäßige Besetzung der äußeren d-Schale hervorgerufen. Anhand der Untersuchung des metallorganischen Polymers des Methyltrioxorheniums konnte zusätzlich gezeigt werden, dass sich aus der Analyse des Polarisationsmusters am Übergangsmetallzentrum neben strukturellen Eigenschaften auch ein Maß für Elektronenlokalisierung im Festkörper ableiten lässt. Basierend auf diesen Ergebnissen wurden außerdem die unkonventionellen Bindungen in Nickel-Olefinkomplexen und die Mn...Si-H-Wechselwirkung untersucht. An diesen Beispielen lässt sich auf Grundlage der topologischen Analyse der Elektronendichte und dem Verständnis des Polarisationsmusters am Übergangsmetallzentrum ein detailliertes, über das Dewar-Chatt-Duncanson-Modell hinausgehendes Verständnis der vorliegenden Bindungen erreichen. Des Weiteren wird in dieser Arbeit der Aufbau eines neuen Tieftemperatur-Einkristalldiffraktometers beschrieben, das speziell für die Anforderungen hochauflösender Ladungsdichteexperimente entworfen wurde. Dieser umfasst auch ein modifiziertes closed-cycle 4K-Displex zur untergrundfreien Messung bei tiefen Temperaturen.The topological analysis of electron densities obtained from experiment and from quantum chemical calculations based on the "Atoms in Molecules" approach by R. Bader allows detailed insight into the nature of chemical bonds in molecules and solid-state compounds. In the scope of such studies regions with locally concentrated electron densities were found in the valence shell of transition metal atoms. In earlier studies these were used to find a physical basis for the very successful VSEPR-concept. In this dissertation a detailed study of the nature and the consequences of these charge concentrations was carried out. It revealed, that the ligand induced charge concentrations in the valence shell of early transition metals are an integral part of the covalent bonds formed by the metal and the ligands. Furthermore, these charge concentrations are stereochemically active due to the mutual repulsion with the regions of bonded electron density in the coordination sphere of the central metal atom. In contrast to this, the local charge concentrations in complexes of the late transition metals with non d0-configuration arise from the unequally occupied valence d-shell of the metal. The investigation of the organometallic polymer of Methyltrioxorhenium showed, that by analysing the polarisation pattern at the transition metal centre not only structural properties can be predicted but that it might also offer a measure for electron localization in solid-state compounds. Based on these results, the unconventional chemical bonds in Nickel-olefin complexes and the Mn...Si-H-interaction were investigated. These examples show, that by a topological analysis of the total electron density and an understanding of the polarisation pattern at the metal centre a detailed understanding of the bonding situation is possible, which exceeds the common Dewar-Chatt-Duncanson-model. Furthermore, the setup of a new low-temperature high-resolution single crystal diffractometer is described, which comprises a modified closed-cycle 4K displex which allows for low-temperature measurements without the background from the Be-domes
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
Remanent Si-H interactions in late transition metal silane complexes
No full textIn general, it is assumed that the reaction between silanes and late transition metal fragments yields silyl hydride species as oxidative addition products. However, the silane complex Ni(iPr(2)Im)(2)(SiHMePh2) (iPr(2)Im = 1, 3-diisopropylimidazolin-2-ylidene) (3a), might represent one of the rare systems where a stable (2)-(Si-H)Ni intermediate of the oxidative addition process has been isolated. Indeed, 3a is characterized by an acute [ang]Si-Ni-H angle of 62.0(2)degrees, a rather short Si-H bond length of 1.992(6) angstrom and displays a silicon-hydride cross peak in Si-H-HMQC 2D-NMR studies. We therefore selected the latter system for a combined experimental and theoretical charge density study to explore the electronic prerequisites which hinder the full completion of the oxidative addition step in transition metal silane complexes and cause the presence of remanent Si-H interactions in these species.Deutsche Forschungsgemeinschaft (DFG) [SPP1178
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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