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Dielectric Properties of Microwave Processed CaCu3Ti4O12 - Based Ceramics and Related (0-3) Epoxy-composites
No full textCaCu3Ti4O12 (CCTO) based ceramics are technologically important due to large frequency and temperature independent dielectric constant [104-105 at room temperature (RT)]. This material has drawbacks in terms of high ‘tan δ’, low dielectric break down strength (Ebd) and low volumetric energy density (Uvol). In this present work, high ‘tan δ’ value is utilized for synthesis by adopting microwave assisted solid state reaction (MASSR) and an attempt has been initiated towards the improvement of ‘tan δ’, ‘Ebd’ and ‘Uvol’ of CCTO based ceramics by incorporating Al3+, Nb5+, and (Nb5+0.5Al3+0.5) as substitutes of Ti4+site; therefore perturbing the TiO6 octahedron. Ceramics are synthesized via microwave assisted solid state reaction [MASSR] synthesis route. Ceramics used for this work are: (1) CaCu3Ti4O12, (2) CaCu3Ti4-xAlxO12 [CCTAxO], (3) CaCu3Ti4-xNbxO12 [CCTNxO], (4) CaCu3Ti4-x(Nb0.5Al0.5)xO12 [CCT(NA)xO]; x = 0.025, 0.05, 0.075, 0.1. Starting with single phase CCTO calcined powder; effect of sintering temperature in between 1000 to 1075 °C (with a step size of 25 ° and ceramics are assigned as CCTO1, CCTO2, CCTO3, and CCTO4 respectively) was investigated. CuO melted phase increases with increasing temperature. Maximum ‘εr’ found in CCTO3 (sintered at 1050 °C) is ~ 15,000 with tan δ ~ 0.15 at 100 Hz and amount of CuO secondary phase ~ 16 % (estimated from Rietveld analysis). In addition, non-ohmic voltage exponent (‘α’), breakdown field strength (‘Ebd’), volumetric energy density (Uvol), Shottky barrier height (ϕB) and barrier width related parameter (β) of CCTO3 are ~ 3.72, 9.7 kV/cm, 0.062 J/cm3, 0.836 eV and 2.4×10-3 (eV) V-1/2 cm-1/2 respectively. In modified CCTO ceramics, CuO secondary phase also appeared during sintering at 1050 °C. Variations of CuO phase with guest atom and ‘x’ are quite anomalous. Rietveld analysis has been performed to quantify the amount of monoclinic CuO phase. Microstructure evolution reveals the presence of melted phase and its Cu-rich nature has been confirmed through selective area EDX. Distinct variations in microstructure in terms of grain size, amount of melted phase, density are observed in this work. Dielectric, modulus, impedance, ac conductivity are studied as functions of frequency and temperature. CCTA0.05O, CCTN0.075O, and CCT(NA)0.075O are showing improved dielectric properties among individual batch of modified CCTO ceramics. Amount of CuO is found in between 10-16 % for the above mentioned composition. CCTN0.075O shows highest ‘εr (100 Hz)’ ∼ 37,239 with ‘tan δ’ ∼ 0.37 among all CCTNxO ceramics as well as other batches at RT. CuO secondary phase is ~ 10.5 %. ‘εr’ rapidly drops to ∼ 23,889 with ‘tan δ’ ∼ 0.223 and ∼ 5,708 with ‘tan δ’ ∼ 0.55 at 1 kHz and 1 MHz respectively. Lower ‘Ebd’∼ 4.58 kV/cm and ‘Uvol’ ∼ 0.035 J/cm3 are found for this composition. ‘ϕB’ and ‘β’ are ∼ 0.79 eV and ∼ 2.8 ×10-3 (eV) V-1/2 cm-1/2 respectively. CCTA0.05O shows maximum ‘εr (100 Hz)’ ∼ 23,000 with tan δ ∼ 0.08 among all CCTAxO ceramics at RT. The amount of secondary CuO phase is ∼ 12 % and high ‘Ebd’∼ 24.02 kV/cm, along with ‘α’ ∼ 5.13 and Uvol ∼ 0.59 J/cm3 has been found. ‘ϕB’ and ‘β’ are 0.84 eV and 1.5×10-3 (eV) V-1/2 cm-1/2 respectively. Maximum ‘εr (100 Hz)’ ∼ 29,648 with tan δ ∼ 0.2 has been found in CCT(NA)0.075O among all CCT(NA)xO ceramics. ‘εr (1 MHz)’ ∼ 12,995 is quite high with tan δ ∼ 0.45. Amount of CuO phase is ∼ 14.7 %. This composition shows ‘εr’ ∼ 24,173 at 1 kHz with ‘tan δ’ ∼ 0.15, and ‘εr’ remains highest throughout the frequency range between 1 kHz to 1 MHz. Maximum ‘Ebd’~ 28.8 kV/cm (at 1 mA/cm2 current density), along with ‘α’∼5.51 and highest energy density Uvol ∼ 1 J/cm3 has been achieved in CCT(NA)0.075O ceramic. Formation of ‘Shottky barrier’ is verified and maximum ‘ϕB’ ∼ 0.92 eV is observed in CCT(NA)0.075O. Barrier width parameter ‘β’ is ∼ 1.8 ×10-3 (eV) V-1/2 cm-1/2. Improvement in dielectric properties is analyzed on the basis of IBLC model in presence of CuO secondary phase. AC conductivity shows correlated barrier hopping mechanism (CBH). From the above results, CCT(NA)0.075O is considered as the best in terms of ‘εr’, ‘tan δ’, ‘Ebd’, ‘Uvol’ ‘α’, ϕB etc. In addition, an attempt has been initiated to prepare Epoxy-based composites by taking CCT(NA)0.075O (abbreviated as CCTNAO in Chapter 7) and conducting Al particle as fillers. Filler volume is restricted within 40 % in all composites. Composites prepared for the purpose are 1. (1-x) Epoxy – x Al ; x = 0, 0.05,0.1, 0.2, 0.3, 0.4 ,2. (1-x) Epoxy – x CCTNAO ; x = 0, 0.05,0.1, 0.2, 0.3, 0.4, 3. (1-x) [0.8Epoxy – 0.2 CCTNAO] – x Al ; x = 0, 0.05,0.1, 0.15, 0.2 While studying (1-x) Epoxy – x Al composites, maximum ‘εeff’ ∼ 150 achieved for x = 0.4, at 1 kHz, but loss became so high (tan δ > 10). But, the ‘εeff’ ∼ 70 with low loss (∼ 0.5 at 1 kHz) has been found for x = 0.3. At RT, highest ‘εeff’ ∼ 33.37 with tan δ ∼ 0.1 at 1 kHz has been found in 0.6 Epoxy - 0.4 CCTNAO, but ‘tan δ’ reduced to ∼ 0.055 beyond 100 kHz. Maximum ‘εeff’ ∼ 77.5 with tan δ ∼ 0.154 has been found in 0.64 Epoxy – 0.16 CCTNAO – 0.2 Al composite at 1 kHz. ‘εeff’ falls off to ∼ 72.5 with tan δ ∼ 0.1 at 10 kHz. Beyond 10 kHz, ‘tan δ’ is < 0.1. At 1 kHz, ‘εeff’ is ∼ 50 with tan δ ∼ 0.09 observed in 0.68 Epoxy – 0.17 CCTNAO – 0.15 Al composite. At 10 kHz, ‘εr’ is ∼ 47, with tan δ ∼ 0.06. Experimentally measured values of ‘εeff’ is in close agreement with EMT model (η = 0.13) and Yamada Model (η = 7) in (1-x) Epoxy – x CCTNAO composites. Proposed empirical power equation, εeff = εm (1+x)n with n ∼ 10 has a considerable agreement with the experimental data of (1-x) Epoxy – x Al and (1-x) [0.8Epoxy - 0.2 CCTNAO] – x Al composites
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
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