1,721,266 research outputs found
Sol–gel derived silica-based organic–inorganic hybrid materials as “composite precursors” for the synthesis of highly homogeneous nanostructured mixed oxides: an overview
No full textThe present contribution reports on our results concerning the synthesis of different binary and ternary oxide systems by using hybrid materials as “composite” precursors. In the last years, we have developed and explored a valuable strategy to yield a very homogeneous dispersion of nanoparticles of early metal transition oxide, MO2 (M = Zr, Hf) inside a silica matrix. This route is based on the use of the sol–gel process to obtain organic–inorganic hybrid silica-based materials embedding the oxide precursors (Zr and/or Hf oxoclusters), which are then calcined at high (T > 500 °C) temperatures to give the desired oxides. The “precursor” hybrid materials are prepared by a modified sol–gel process, involving the copolymerisation of the organically modified oxozirconium or oxohafnium clusters (M4O2(OMc)12 (M = Zr, Hf and OMc = methacrylate) with (methacryloxymethyl)triethoxysilane (MAMTES) or (methacryloxypropyl)trimethoxysilane (MAPTMS). Free radical copolymerisation of the 12 methacrylate groups of the oxoclusters with the methacrylate-functionalised siloxanes allows a stable anchoring of the oxoclusters to the silica network formed by the hydrolysis and condensation of the alkoxy groups. The sol–gel reactions of the two methacrylate-modified silanes methacryloxymethyltriethoxysilane and methacryloxypropyltrimethoxysilane were followed by using two independent time-resolved spectroscopic methods, viz., IR ATR and NMR with the aim to optimise their pre-hydrolysis times and consequently their use as precursors for hybrid materials. As mentioned, thermal treatment at high temperature of the hybrid yields a very homogeneous dispersion of ZrO2 and/or HfO2 nanoparticles in the silica matrix, since the molecular homogeneity of the starting hybrid is retained in the final mixed oxide. This route was successfully applied both to the synthesis of bulk materials and thin films characterised by different compositions (in term of M/Si molar ratios and M nature), heating route (conventional or microwave-assisted) and final temperature of annealing (from RT to 1,100 °C). The first example of the ZrO2–HfO2–SiO2 ternary oxide system was also prepared by this approach. The prepared systems, both in the form of hybrid materials as well as in the final form of binary or ternary oxides, were thoroughly characterised by a wide variety of analytical tools from a compositional, structural, morphological point of view. Moreover, in the case of the binary ZrO2–SiO2 bulk materials, also the evolution under heating was followed by different methods. In particular, the composition of the hybrid as well as of the final oxidic materials was determined by X-Ray Photoelectron Spectroscopy and elemental analysis, whereas FT-IR and multinuclear solid-state NMR spectroscopies shed light on the changes occurring in the composition upon thermal heating and the degree of condensation of the silica network. The morphology and the microstructure of the hybrids and of the oxides were studied by nitrogen sorption and Scanning Electron Microscopy. X-Ray Diffraction, Transmission Electron Microscopy and X-ray Absorption Fine Structure Spectroscopy X-ray Absorption Fine Structure Spectroscopy were used to follow the conversion of the amorphous oxides to the final materials consisting of crystalline zirconia or hafnia dispersed in amorphous silica. On selected systems, functional properties (surface reactivity, dielectric properties) were furthermore investigated. The obtained binary oxides were also used as substrates for functionalisation experiments with (1) dialkycarbamates and (2) long alkyl chains to produce functional materials for catalysis and HPLC applications, respectively.The present contribution reports on our results concerning the synthesis of different binary and ternary oxide systems by using hybrid materials as “composite” precursors. In the last years, we have developed and explored a valuable strategy to yield a very homogeneous dispersion of nanoparticles of early metal transition oxide, MO2 (M=Zr, Hf) inside a silica matrix. This route is based on the use of the sol-gel process to obtain organic-inorganic hybrid silica-based materials embedding the oxide precursors (Zr and/or Hf oxoclusters), which are then calcined at high (T>500°C) temperatures to give the desired oxides. The “precursor” hybrid materials are prepared by a modified sol-gel process, involving the copolymerisation of the organically modified oxozirconium or oxohafnium clusters (M4O2(OMc)12 (M= Zr, Hf and OMc = methacrylate) with (methacryloxymethyl)triethoxysilane (MAMTES) or (methacryloxypropyl)trimethoxysilane (MAPTMS). Free radical copolymerisation of the 12 methacrylate groups of the oxoclusters with the methacrylate-functionalised siloxanes allows a stable anchoring of the oxoclusters to the silica network formed by the hydrolysis and condensation of the alkoxy groups. The sol-gel reactions of the two methacrylate-modified silanes methacryloxymethyltriethoxysilane and methacryloxypropyltrimethoxysilane were followed by using two independent time-resolved spectroscopic methods, viz., IR ATR and NMR with the aim to optimise their pre-hydrolysis times and consequently their use as precursors for hybrid materials.
As mentioned, thermal treatment at high temperature of the hybrid yields a very homogeneous dispersion of ZrO2 and/or HfO2 nanoparticles in the silica matrix, since the molecular homogeneity of the starting hybrid is retained in the final mixed oxide. This route was successfully applied both to the synthesis of bulk materials and thin films characterised by different compositions (in term of M/Si molar ratios and M nature), heating route (conventional or microwave-assisted) and final temperature of annealing (from RT to 1100°C). The first example of the ZrO2-HfO2-SiO2 ternary oxide system was also prepared by this approach.
The prepared systems, both in the form of hybrid materials as well as in the final form of binary or ternary oxides, were thoroughly characterised by a wide variety of analytical tools from a compositional, structural, morphological point of view. Moreover, in the case of the binary ZrO2- SiO2 bulk materials, also the evolution under heating was followed by different methods. In particular, the composition of the hybrid as well as of the final oxidic materials was determined by X-Ray Photoelectron Spectroscopy (XPS) and elemental analysis (EA), whereas FT-IR and multinuclear solid-state NMR spectroscopies shed light on the changes occurring in the composition upon thermal heating and the degree of condensation of the silica network. The morphology and the microstructure of the hybrids and of the oxides were studied by nitrogen sorption and Scanning Electron Microscopy (SEM). X-Ray Diffraction (XRD), Transmission Electron Microscopy (TEM) and X-ray Absorption Fine Structure Spectroscopy X-ray Absorption Fine Structure Spectroscopy (XAFS) were used to follow the conversion of the amorphous oxides to the final materials consisting of crystalline zirconia or hafnia dispersed in amorphous silica. On selected systems, functional properties (surface reactivity, dielectric properties) were furthermore investigated. The obtained binary oxides were also used as substrates for functionalisation experiments with i) dialkycarbamates and ii) long alkyl chains to produce functional materials for catalysis and HPLC applications, respectively
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
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
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
Author Under Sail The Imagination of Jack London, 1893-1902
No full textIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Intro -- Title Page -- Copyright Page -- Dedication -- Contents -- Acknowledgments -- Introduction -- 1. Spirit Truth -- 2. From Absorption to Theatricality and Back Again -- 3. "I Will Build a New Present" -- 4. Sons as Authors -- 5. Fathers as Publishers -- 6. The Daughter as Author -- 7. Lovers as Authors -- 8. At Sea with the Family -- 9. Yellow News, Yellow Stories -- 10. The Return Home -- Notes -- Bibliography -- Index -- About Jay WilliamsIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Description based on publisher supplied metadata and other sources.Electronic reproduction. Ann Arbor, Michigan : ProQuest Ebook Central, YYYY. Available via World Wide Web. Access may be limited to ProQuest Ebook Central affiliated libraries
- …
