1,721,031 research outputs found
Crystallization study of Sn additive Se–Te chalcogenide alloys
No full textResults of differential thermal analysis (DTA) under non-isothermal conditions of glasses Se90 − xTe10Snx (x = 0, 2.5, 5 and 7 at.%) are reported and discussed. The glass transition temperature (Tg), the onset crystallization temperature (Tc) and the peak temperature of crystallization (Tp) were found to be dependent on the compositions and the heating rate. Values of various kinetic parameters such as activation energy of glass transition (Eg), activation energy of crystallization (Ec), rate constant (Kp), Hurby number (Hr) and the order parameter (n) were determined. For the present systems, the results indicate that the rate of crystallization is related to thermal stability and glass forming ability (GFA). According to the Avrami exponent (n), the results show a one dimensional growth for the composition Se90Te10 and a three dimensional growth for the three other compositions. The crystalline phases resulting from DTA and (SEM) have been identified using X-ray diffraction
Crystal growth kinetics in Se87.5 Te10 Sn2.5 glass
No full textThe crystallization process of Se87.5 Te10 Sn2.5 glassy was studied by differential thermal analysis (DTA) technique under non-isothermal condition at various heating rates. The crystallization parameters were calculated using different models. The validity of the Johnson–Mehl–Avrami (JMA) model to describe the crystallization process for the studied composition was discussed. Results obtained by directly fitting the experimental DTA data to the calculated DTA curves indicate that the crystallization process of Se87.5 Te10 Sn2.5 glass cannot be satisfactorily described by the JMA model. On the other hand, kinetic parameters of both the peak crystallization temperature Tp and the glass transition temperature Tg are significantly influenced by the heating rate. Simulation results indicate that the Sestak–Berggren (SB) model is more suitable to describe the crystallization kinetics. The crystalline phases were identified by using X-ray diffraction technique (XRD) and scanning electron microscopy (SEM)
Annealing effect on structural and optical properties of Se87.5Te10Sn2.5 thin films
No full textThin films of Se87.5Te10Sn2.5 were prepared by vacuum thermal evaporation technique. Various optical constants were calculated for the studied composition. The mechanism of the optical absorption follows the rule of direct transition. It was found that the optical energy gap (Eg) decreases from 2.26 to 1.79 eV with increasing the annealing temperature from 340 to 450 K. This result can be interpreted by the Davis and Mott model. On the other hand, the maximum value of the refractive index (n) is shifted towards the long wavelength by increasing the annealing temperature. In addition, the high frequency dielectric constant (εL) increased from 31.26 to 48.11 whereas the ratio of the free carriers concentration to its effective of mass N/m⁎ decreased from 4.3 to 2.09 (×1057 (m−3 Kg−1)). The influence of annealed temperature on the structure was studied by using the X-ray diffraction (XRD) and scanning electron microscopy (SEM). The XRD studies show that the as-deposited films are amorphous in nature, but the crystallinity improved with increasing the annealing temperature. Furthermore the particle size and crystallinity increased whereas the dislocation and strains decreased with increasing the annealing temperature. SEM examination showed that the annealing temperature induced changes in the morphology of the as-deposited film
Optical and other physical characteristics of amorphous Se–Te–Sn alloys
No full textThe Effect of Sn addition in the structural and optical properties of Se–Te chalcogenide alloy at the expense of the Se content has been studied. Stoichiometric bulk ingot materials of the Se90−xTe10Snx (x=0, 2.5, 5 and 7.5 at%) were prepared by a melt-quench technique. X-ray diffraction (XRD) studies indicated that the investigated alloys confirmed its amorphous nature. These results were confirmed by scanning electron microscopy (SEM) investigations and correlated to the rigidity percolation threshold of the lattice. Stoichiometric thermally evaporated thin film of the obtained compositions were carefully characterized to establish the interdependence between their chemical composition and some physical parameters, such as the average heat of atomization (Hs), the cohesive energy CE, the average coordination number 〈Z〉 and the optical band gap (Eg). It has been found that all the parameters varied linearly when Sn content was increased. The variation in the optical band gap (Eg) with Sn addition was discussed in terms of the width of localized states (Ee) and a chemical bond approach model (CBA)
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
Determination of activation energy of amorphous to crystalline transformation for Se90Te10 using isoconversional methods
No full textThe activation energies of crystallization of Se90Te10glass were studied at different heating rates (4–50 K/min)under non-isothermal conditions using a differential scanning calorimetric (DSC) technique. The activation ener-gy was determined by analyzing the data using the Matusita et al. method. A strong heating rate dependence ofthe activation energy was observed. The variation of the activation energy was analyzed by the application of thethree isoconversional methods, of Kissinger–Akahira–Sunose (KAS), Flynn–Wall–Ozawa (FWO), and Vyazovkin.These methods confirm that the activation energy of crystallization is not constant but varies with the degree ofcrystallization and hence with temperature. This variation indicates that the transformation from amorphous tocrystalline phase is a complex process involving different mechanisms of nucleation and growth. On the otherhand, the validity of the Johnson–Mehl–Avrami (JMA) model to describe the crystallization process for thestudied composition was discussed. Results obtained by directlyfitting the experimental DSC to the calculatedDSC curve indicate that the crystallization process of the Se90Te10glass cannot be satisfactorily described bythe JMA model. In general, simulation results indicate that the Sestak–Berggren (SB) model is more suitable todescribe the crystallization kinetic
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
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