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Combining Valence to Core X ray Emission and Cu K edge X ray Absorption Spectroscopies to Experimentally Assess Oxidation State in Organometallic Cu I II III Complexes
No full textA series of organometallic copper complexes in formal oxidation states ranging from 1 to 3 have been characterized by a combination of Cu K edge X ray absorption XAS and Cu K amp; 946; valence to core X ray emission spectroscopies VtC XES . Each formal oxidation state exhibits distinctly different XAS and VtC XES transition energies due to the differences in the Cu Zeff, concomitant with changes in physical oxidation state from 1 to 2 to 3. Herein, we demonstrate the sensitivity of XAS and VtC XES to the physical oxidation states of a series of N heterocyclic carbene NHC ligated organocopper complexes. We then extend these methods to the study of the [Cu CF3 4] amp; 8722; ion. Complemented by computational methods, the observed spectral transitions are correlated with the electronic structure of the complexes and the Cu Zeff. These calculations demonstrate that a contraction of the Cu 1s orbitals to deeper binding energy upon oxidation of the Cu center manifests spectroscopically as a stepped increase in the energy of both XAS and K amp; 946;2,5 emission features with increasing formal oxidation state within the [Cun NHC2 ]n series. The newly synthesized Cu III cation [CuIII NHC4 ]3 exhibits spectroscopic features and an electronic structure remarkably similar to [Cu CF3 4] amp; 8722;, supporting a physical oxidation state assignment of low spin d8 Cu III for [Cu CF3 4] amp; 8722;. Combining XAS and VtC XES further demonstrates the necessity of combining multiple spectroscopies when investigating the electronic structures of highly covalent copper complexes, providing a template for future investigations into both synthetic and biological metal center
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
Free Clusters Studied by Synchrotron-Based X-ray Spectroscopy: From Rare Gases to Metals
No full textThe main topic of this Thesis is the x-ray spectroscopic studies of free nano-clusters with size more than 10^3 atoms. The photoelectron spectroscopy experiments on rare gas and metal clusters were performed at beamline I411 at MAX-lab National Swedish synchrotron radiation facility. Free rare-gas clusters are simplest objects in cluster research. However their electronic structure springs a lot of surprises. In the x-ray absorption spectra of free Kr clusters the positions of the related cluster and atomic states of the higher 3d^{-1}6p and 3d^{-1}7p excited states in bulk and surface atoms are reversed compared to the 3d^{-1}5p state. The energy shifts of the higher core-excited states in cluster atoms grow towards the limiting values of the core-ionized states. The knowledge of the final cluster states reached after Auger decay of the resonantly excited core states threw a new light on this phenomenon. We explain these experimental findings by a spatial spread of the excited orbitals over the cluster lattice. The interplay of the two main effects - confinement and polarization - leads to qualitatively different situations. When the excited orbital radius is less than the interatomic distance in clusters (3d^{-1}5p state in Kr), confinement dominates. If the excited orbital radius exceeds the nearest neighbour distance (3d^{-1}np, n>5 states in Kr), polarization takes over and the energy-level structure becomes ion-like. Interest in studies of more complex than rare gas clusters systems determined the construction of the gas-aggregation metal cluster source. For the vaporisation of low melting point metals (Na) an oven was used. Vapours of higher melting point metals (Ag, Cu, Pb) were produced with a magnetron sputtering source. The design of the gas-aggregation source and description of the experimental setup are presented in this Thesis. Using this source we performed the first core-level photoemission (XPS) experiments on free metal clusters. The recorded spectra have shown that synchrotron-based x-ray core-level photoelectron spectroscopy can be efficiently implemented to free metal clusters. The evolution of the electronic structure with size has been studied by valence ionization, XPS and Auger techniques. These measurements have shown a close similarity between large clusters and solids. The difference between the established ionization potential of metal clusters and the solid has been used for the cluster size estimation for Na, Cu and Ag clusters. The presence of neutral and charged metal clusters in the Pb cluster beam created by magnetron-based source has offered an independent method for estimating cluster dimensions from core-level spectra, in which the charge states are resolved
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
Cu4S Cluster in "0-Hole" and "1-Hole" States: Geometric and Electronic Structure Variations for the Active Cu-Z* Site of N2O Reductase
No full textThe active site of nitrous oxide reductase N2OR , a key enzyme in denitrification, features a unique ?4 sulfido bridged tetranuclear Cu cluster the so called CuZ or CuZ site . Details of the catalytic mechanism have remained under debate and, to date, synthetic model complexes of the CuZ CuZ sites are extremely rare due to the difficulty in building the unique Cu4 ?4 S core structure. Herein, we report the synthesis and characterization of [Cu4 ?4 S ]n n 2, 2; n 3, 3 clusters, supported by a macrocyclic py2NHC4 ligand py pyridine, NHC N heterocyclic carbene , in both their 0 hole 2 and 1 hole 3 states, thus mimicking the two active states of the CuZ site during enzymatic N2O reduction. Structural and electronic properties of these Cu4 ?4 S clusters are elucidated by employing multiple methods, including X ray diffraction XRD , nuclear magnetic resonance NMR , UV vis, electron paramagnetic resonance EPR , Cu S K edge X ray emission spectroscopy XES , and Cu K edge X ray absorption spectroscopy XAS in combination with time dependent density functional theory TD DFT calculations. A significant geometry change of the Cu4 ?4 S core occurs upon oxidation from 2 ?4 S 0.46, seesaw to 3 ?4 S 0.03, square planar , which has not been observed so far for the biological CuZ site and is unprecedented for known model complexes. The single electron of the 1 hole species 3 is predominantly delocalized over two opposite Cu ions via the central S atom, mediated by a ? ? superexchange pathway. Cu K edge XAS and Cu S K edge XES corroborate a mixed Cu S based oxidation event in which the lowest unoccupied molecular orbital LUMO has a significant S character. Furthermore, preliminary reactivity studies evidence a nucleophilic character of the central ?4 S in the fully reduced 0 hole stat
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
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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