1,721,033 research outputs found
Synthesis of binary and ternary semiconductors by means of microwave irradiation
No full textPure CdTe and CuInSe2 are prepared with high yields and short reaction times starting from metal or binary alloy powders and irradiating the mixture with a microwave radiation of a 2.45 GHz of frequency and 1000 W of power under argon atmosphere. It was possible to successfully synthesize extremely pure CuInSe2 single crystalline phase, differently from a multi-phase mixture as expected from the phase diagram Cu2Se-In2Se3. XRD and SEM analyses, performed for the characterization, have confirmed the success of the process
Microwave-assisted hydrothermal synthesis as a rapid route towards manganite preparation
No full text-In this work attempts to prepare strontium-doped lanthanum manganites La1-xSrxMnO3 using microwave-assisted hydrothermal synthesis were undertaken from a mixture of lanthanum nitrate, strontium nitrate, manganese(II) nitrate, potassium permanganate and potassium hydroxide as a mineralizer. For x = 0.3, and x = 0.5, the perovskite obtained is not defined since both La0.7Sr0.3MnO3 and La0.5Sr0.5MnO3 phases are consistent with XRD spectra. While with x = 1.0, for the first time, hexagonal strontium manganite was prepared as blade-shaped crystallites with a narrow particle length distribution (range 3.75-7.75 μm) at 210°C using a treatment time of only 1 hour. Conventional hydrothermal synthetic routes require at least 24 hrs treatment time
Dielectric characterization of La1-xAgxMnO3+δ (x = 0; 0.2) perovskites in the frequency range 200MHz-3GHz
No full textLa1-xAgxMnO3+δ (x = 0; 0.2) perovskites have been prepared using a microwaves process (MWhyd) by comparing the heating time and reaction temperature with the same factor under conventional thermal process (CHhyd). Experiments have been conducted using hydrothermal method at medium pressure (T = 200°C, P = 2.06 MPa.) followed by a conventional treatment of the precursor at 700°C (10h). While MWhyd and CHhyd powders exhibited the same XRD patterns indexed as pure perovskite structure, their physico-chemical properties were found to be strongly influenced by the preparation method. La1-xAgxMnO3+δ perovskites were characterised using x-ray diffraction (XRD), BET sorption, temperature programmed reduction-mass spectrometry (TPR-MS), x-ray photoelectron spectroscopy (XPS), and dielectric measurements in the frequency range 200 MHz-3GHz
Dehydration, dehydroxylation, densification and deformation during sintering of geopolymers based on the K2O-Al2O3-SiO2 system
No full textBased on the principle of stability of geopolymer gel as refractory binder, a geopolymeric paste in the K2O-Al2O3-SiO2 system was developed and used to produce refractory concretes by adding various amount of α-quartz sand (grain size in the range 0.1μm-1mm) and fine powder alumina (grain size in the range 0.1-100 μm). The consolidated samples were characterized before and after sintering using optical dilatometer, DSC, XRD and SEM. The total shrinkage in the range of 25-900°C was less than 3%, reduced with respect to the most diffused potassium or sodium based systems, which generally records a >5% shrinkage. The maximum shrinkage of the base geopolymer was recorded at 1000°C with a 17% shrinkage which is reduced to 12% by alumina addition. The maximum densification temperature was shifted from 1000°C to 1150°C or 1200°C by adding 75wt% α-quartz sand or fine powder alumina respectively. The sequences of sintering of geopolymer concretes could be resumed as dehydration, dehydroxylation, densification and finally plastic deformation due to liquid phase appearance. The geopolymer formulations developed in this study appeared as promising candidates for high temperature applications. © 2009 Copyrigh
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
Improving the theromchemical water splitting for Hydrogen Production with Magnetic Core-shell Nanoparticles
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