1,720,979 research outputs found
Structural, thermal and magnetic characterization of nanocrystalline Co65Ti25W5B5 powders prepared by mechanical alloying
No full textAbstract In this work, nanocrystalline Co65Ti25W5B5 (at.%) powders were prepared by mechanical alloying (MA) of the elemental powder mixture under argon gas atmosphere. The powders were milled during different periods (2.5, 5, 10, 20 and 30 h) using a planetary ball-mill (Retsch PM100 CM) at 400 rpm. The structural, morphological, thermal and magnetic properties of the nanocrystalline Co65Ti25W5B5 powders were studied by means of X-ray diffraction (XRD), scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM/EDX), differential thermal analysis (DTA) and vibrating sample magnetometer (VSM) techniques. Because of its high melting point, hardness and low solubility in the alloy components, a small amount of tungsten remained in the amorphous matrix during MA. By using the Williamson-Hall method, the crystallite size and lattice strain of the tungsten phase were calculated as about 25 nm and 0.48% respectively, for 30 h of milling. The DTA curves of the milled powders demonstrated an exothermic peak at about 600 °C, indicating the crystallization of the amorphous phase. The apparent mean activation energy, 303.5 ± 7 kJ/mol for 20 h milled powders was determined by Kissenger and Ozawa methods. The saturation magnetization (Ms), the coercivity (Hc) and the remanence-to-saturation ratio (Mr/Ms), values were of about 66 emu/g, 11 Oe and 0.012 respectively, after 30 h of milling
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
Influence of mechanical alloying on structural, thermal, and magnetic properties of Fe50Ni10Co10Ti10B20 high entropy soft magnetic alloy
No full textA multicomponent with functional Fe50Ni10Co10Ti10B20 (at.%) high entropy soft magnetic alloy powders were produced from the elemental powders by mechanical alloying (MA). The MA processes were carried out under argon gas atmosphere at a speed of 250 rpm, carrying milling and rest in every 20-min period to prevent the mixture from overheating. Scanning electron microscopy and energy-dispersive X-ray spectroscopy, X-ray diffraction, differential thermal analysis, and vibrating sample magnetometer analysis were utilized to characterize various powdered samples with respect to MA time (0–50 h). The results show that in the first 2.5 h of MA, the mixture of crystalline phases transformed into a nanocrystalline supersaturated α-Fe solid solution phase. With prolonging milling time, the amorphous phase appeared after 20 h of MA. In the final stage of MA (50 h), the saturation magnetization (Ms) and the coercivity (Hc) were 89.7 emu/g and 32.5 Oe, respectively, proposing the alloy as a very good high entropy soft magnet in nature
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe 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
Structural evolutions in Ti and TiO2 powders by ball milling and subsequent heat-treatments
No full textAbstract In this study, nanocrystalline Ti and TiO2 powders were synthesized by wet milling of Ti powder within water and reactive milling of Ti powder under oxygen atmosphere, respectively. The wet milling processes were performed at 300 rpm milling speed for different milling durations (6, 12, 24, and 48 h). Subsequent heat-treatments of the as-milled powders were performed at 200–800 °C for 1 h in an air atmosphere. Structural characteristics of the as-milled and the heat-treated powders were investigated by X-ray diffraction (XRD). The crystallite size, lattice strain and lattice parameters of the powders were also calculated. It has been realized that during the wet milling process, elemental Ti powder undergoes an hcp to fcc polymorphic transformation, which is related to grain refinement and plastic strain. In addition, TiO2 powders are produced after heat-treatments at 600 and 800 °C. Reactive milling of the elemental Ti powder in pressurized oxygen atmosphere leads to nanocrystalline TiO2 powders with an average crystallite size of about 10 nm after 48 h milling time. The subsequent heat-treatments of the as-milled TiO2 powders results in the increase of the crystallite size up to 70–150 nm. In order to understand the thermal behavior of the as-milled powders, thermal analysis (DTA) and thermogravimetric analysis (TGA) were employed. The activation energy of the nanocrystalline TiO2 powders was determined by the Kissinger method is 128±3 kJ/mol
Discrete Element Method Simulation of Filling Level in Planetary Ball Mill
No full textIn this study, DEM (discrete element method) was used to improve our understanding of the fundamental processes involved in the ball milling process, with a particular emphasis on the effect of the many different filling levels in planetary ball mills. This DEM methodology facilitates the simulation of the behavior of balls and powder particles inside the vials, enabling an understanding of the nature of the material milling and the structure of the flow. The major benefit of the DEM technique is the ability to incorporate interrelationships among different milling parameters. The simulations indicate that changing the filling level has a significant effect on the ball milling process.</jats:p
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