1,720,968 research outputs found
Physical genetics: Cross-breeding density functional theory and X-ray photoelectron spectroscopy to rationalize chemical shifts of binding energies in solid compounds
Full text linkLike other spectroscopic methods XPS and AES show characteristic chemical shifts depending on the elemental matrix of a compound, however, a satisfactory rationalization of the variance of such values is often difficult. By an extension of a previous approach we present a theory in a unifying equation which combines several parameters - some of them resulting from DFT calculations - which influence the energy of the outgoing electrons and thereby seemingly the binding energy. By calculating Bader charges, atomic volumes and site potentials we have produced a data basis for a set of chalcogenides and halides of Ba, Zn, Pb and Cu to rationalize the spread of measured binding energies and Auger energies. It has thereby become possible to quantify different factors separately which bias the measurement of the kinetic energies of the outgoing core electrons, both the photo-emitted and the Auger electrons. Such an analysis can also trace special features of an open-shell configuration and even show up effects of a semiconductor-type
Relationship between the Auger parameter and the ground state valence charge at the core-ionized site
Full text linkA simple semi-empirical model that correlates the Auger parameter to the ground state valence charge of the core-ionized atom with closed valence shell configuration, and which was previously applied to Cu(I) (3d10) compounds, is extended to Ba (II) (5d10), Pb (II) (5d104s2), and Zn (II) (3d10) compounds (halides and chalcogenides). Until now, the Auger parameter was employed to separate initial and final state effects that influence the core electron binding energy. In agreement with our model, a linear relationship is found between the Auger parameter shift and the ground state Bader valence charge obtained by density functional theory (DFT) calculations
Relationship between the Auger parameter and the ground state valence charge of the core-ionized atom: the case of Cu(I) and Cu (II) compounds
No full textWe develop a simple semiempirical model that correlates the Auger parameter to the ground state valence charge of the core-ionized atom with closed shell electron configuration. Until now, the Auger parameter was employed to separate initial and final state effects that influence the core electron binding energy. The model is applied to Cu(I) and Cu (II) compounds with the Auger parameter defined as α' = Eb FL (2p3/2) + Ek FL (L3M45M45;1G). The Auger parameter shift for Cu(I) ion in CuI, CuBr, CuFeS2, Cu2S, and Cu2O compounds—with respect to the copper free atom—increases with the electronic polarizability of the nearest-neighbour ligands suggesting a nonlocal screening mechanism. This relaxation process is interpreted as due to an electron transfer from the nearest-neighbour ligands toward the spatially extended 4sp valence orbitals of the core-ionized Cu(I) ion. In agreement with our model, a linear relationship is found between the Auger parameter shift and the ground state Bader valence charge obtained by density functional theory calculations. The Auger parameter shift for the Cu (II) ion in CuF2, CuCl2, CuBr2, CuSO4, Cu (NO3)2•3H2O, Cu3(PO4)2, Cu (OH)2, and CuO compounds is very close to the Auger parameter of metallic copper, and therefore, it is not related to the calculated ground state Bader valence charge. The relaxation process in the final state is dominated by the local screening mechanism, which involves an electron transfer from the nearest-neighbour ligands toward the spatially contracted 3d orbitals of the core-ionized Cu (II) ion. © 2019 John Wiley & Sons, Ltd
A New, Facile Route to 2âAzaallenium SaltsâBis(2âadamantylidene)ammonium Hexachloroantimonate
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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
Synthetical and structural studies with the purpose of exploring new pigments
No full textGegenstand dieser Arbeit war die Untersuchung von Verbindungen unterschiedlicher Substanzklassen und deren mögliche Anwendung als Pigment, um toxikologisch bedenkliche Farbmittel zu ersetzen. Die meisten der betrachteten Stoffe waren bereits aus der Literatur bekannt, die farblichen Eigenschaften jedoch nicht näher erforscht. Ziel war eine saubere, präparativ leicht zugängliche Synthese der Verbindungen mittels Festkörperreaktion und deren farbmetrische Analyse. Die Proben wurden mit Hilfe von Röntgenbeugung und Reflexionspektroskopie untersucht. Anhand der bestimmten Farbparametern des CIELab-Systems konnte ein erster Eindruck der optischen Eigenschaften der Produkte gewonnen werden. Bei dem ersten Themengebiet handelte es sich um Sn-haltige oxidische Pigmente, die eine Vielzahl auch strukturell unterschiedlicher Substanzen umfassten und deren Produkte im orange-roten Farbbereich zu finden waren. Untersucht wurden die Verbindungen M2-xBixSn2O7 (M=Y, La), Sn2TiWO7, Sn2-xMxTiNbO6-xF1+x (M=Na, K) und xZnO*ySnO*zTiO2 von denen vor allem die letzten beiden gute Farbwerte lieferten. Des Weiteren wurden Versuche zur Stabilisierung von Bi2O3-Modifikationen bei Raumtemperatur durch Dotierung durchgeführt. Als substituierende Elemente kamen dabei Y3+, Ce4+, Zr4+, Nb5+, Ta5+, V5+, W6+ und Mo6+ zum Einsatz. Speziell die durch Umsetzung mit Cer, Zirkonium und Niob erhaltenen gelb-orangen Produkte der β-Modifikation lieferten farblich interessante Ergebnisse. Zuletzt wurden Dotierungseffekte in dem Mn(V) enthaltenden Grünpigment Ba3Mn2O8 betrachtet. Hierbei wurde versuchsweise sowohl die Ba-Position mit Sr als auch die Mn-Position mit P substituiert. Koloristisch zeigte jedoch die unsubstituierte Verbindung die besten Eigenschaften.The aim of this work was the investigation of compounds from different substance classes and their potential application as pigment to replace colorants which are toxicologically harmful. Most of the observed substances were known from literature. However, the coloristic properties were not explored. The goal was an easily accessible synthesis of the compounds using solid state reactions and their colorimetrical analysis. The samples were analysed by X-ray diffraction and reflexion spectroscopy. The color coordinates of the CIELab system gave a first impression of the optical qualities of the products. The first topic was oxidic pigments containing Sn involving a variety of structurally different substances and with products that can be found in the orange-red color area. The compositions M2-xBixSn2O7 (M=Y, La), Sn2TiWO7, xZnO*ySnO*zTiO2 and Sn2-xMxTiNbO6-xF1+x (M=Na, K) were examined. First of all, the last two compounds have provided excellent color coordinates. Furthermore, experiments were conducted to explore the stabilization of Bi2O3 modifications at room temperature by doping. Y3+, Ce4+, Zr4+, Nb5+, Ta5+, V5+, W6+ and Mo6+ were used as substitutes. In particular, the experiments with cerium, zirconium and niobium to get the β-modification leading to yellow-orange products provided results that were interesting regarding their color properties. Lastly, doping effects in the green pigment Ba3Mn2O8 containing Mn(V) were examined. It was tried to substitute the Ba position with Sr and the Mn position with P. However, the non-substituted compound has shown the best coloristic properties
Synthesis and characterisation of lithium containing transition metal phosphates and vanadates and their mixed crystals
No full textDie Verbindungen LiMXO4 (M = Fe, Mn, Co, Ni; X = P, V) sind potentielle Kandidaten als Kathodenmaterialien für Lithiumionenbatterien. Im Rahmen dieser Arbeit wurden Substitutionsreaktionen innerhalb dieser Verbindungsklassen untersucht. Hier stand insbesondere die Bildung von Phosphat-Vanadat-Mischkristallen im Blickpunkt, aber auch die Substituierbarkeit der Li-Ionen gegen entsprechende Ladungsäquivalente an M-Kationen wurde intensiv erforscht. Im Rahmen dieser Untersuchungen wurden einige neuen Phasen entdeckt und strukturell charakterisiert, darunter die Olivin-Typ-Materialien Li0.42-0.47Co1.29-1.265PO4, Li0.14-0.16Fe1.43-1.42PO4, die Hochtemperaturmodifikation von Mn1.5VO4 (isostrukturell dazu die Verbindungen LixMn1.5-x/2VO4 mit x < 0.22), zwei Modifikationen der Phase Mn20V4O32 und eine bislang unbekannte Verzerrungsvariante der Spinell-Struktur für LixCo1.5-x/2VO4 (0.5 ≤ x ≤ 0.7). Quantenchemische Berechnungen beleuchten elektronische und kristallographische Strukturen ausgewählter Verbindungen und erlauben gleichzeitig die Bestimmung batteriecharakteristischer Kenngrößen (z. B. Zellspannung). EXAFS/XANES-Messungen ermöglichen insbesondere das Verständnis der ablaufenden Redox-Prozesse im Zuge der Syntheseversuche an „LiFeVO4“, und zeigen, warum diese Verbindung als einphasiges Material nicht hergestellt werden kann. Impedanzspektroskopische Untersuchungen zeigten eine Erhöhung der Leitfähigkeit für Vanadat-dotiertes LiMnPO4 gegenüber LiMnPO4 um eine Größenordnung an.The compounds LiMXO4 (M = Fe, Mn, Co, Ni; X = P, V) are candidates for the use as cathode materials in lithium ion batteries. A variety of substitution reactions are under interest for this class of compounds. Among them, especially the formation of mixed crystals between the phosphates and vanadates as well as the substitution of lithium ions by M cations was intensively investigated in this work. A few new phases were found and could be structurally characterized: the olivine type compounds Li0.42-0.47Co1.29-1.265PO4, Li0.14-0.16Fe1.43-1.42PO4, the high temperature modification of Mn1.5VO4 (the compounds LixMn1.5-x/2VO4 with x < 0.22 also crystallize in this structure), two modifications of the compound Mn20V4O32 and a yet unknown monoclinic modification of the spinel structure, which was found for the compounds LixCo1.5-x/2VO4 (0.5 ≤ x ≤ 0.7). Quantumchemical calculations were performed to elucidate the electronic and crystallographic structures of selected compounds and also facilitate the determination of e. g. the voltages of the compounds against Li. Additionally, investigations with EXAFS/XANES help to understand the oxidation state properties of the elements for a synthesis of “LiFeVO4” and explain why this material cannot be prepared as a single phase compound. Furthermore, vanadate doped LiMnPO4 was characterized by impedance spectroscopy and shows an increase of conductivity compared to LiMnPO4 of one order of magnitude
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
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