1,720,961 research outputs found
Selective energy dispersive diffraction peak fitting by using genetic algorithm RID F-3370-2011
No full textAccurate and precise estimates of X-Ray diffraction peak parameters is mandatory, when small dynamic changes of lattice parameters have to be quantitatively analyzed. To follow in real time such changes, a large set of patterns must be usually collected, so that the position of certain peaks of interest can be tracked. To calculate the positions, a fitting procedure of the peaks is required and several algorithms are reported in the literature for this purpose. However, these algorithms are mainly focused on the determination of parameters based on a model of the cell geometry. Here, we present a new algorithm allowing to carry out the fitting procedure on a portion only of the pattern, with neither tight constraints on the dataset, nor restrictive hypotheses on the sample structure. In our case, a coarse estimate of the detector resolution and of the positions of the peaks to fit are the only initial conditions required. This method can be regarded as a hybrid technique, as it makes use of a genetic algorithm approach, mixed with an intensive multiple random generation of the population, that makes it similar to a Monte Carlo technique. Moreover, adaptive genetic operators have been implemented in the data processing code. These properties result in a fast and efficient algorithm, a fundamental requirement when, as in the present case, the Energy Dispersive X-ray Diffraction method is applied to observe structural changes, which implies the acquisition of many patterns in a relatively short time. The result of this application is shown by some practical examples
Angular calibration in energy dispersive X-Ray diffraction by using genetic algorithms
No full textIn Energy Dispersive X-Ray diffraction measurements, the estimate of momentum transfer q, on which the diffracted intensity depends, should be as accurate as possible. Since q, in turn, depends on both the energy and the scattering angle, an error on the latter due to an incorrect positioning of the sample, to the asymmetric angular spread induced by the collimation slits or, in general, to any uncertainty on the geometric setup, results in an uncertainty on the q value. Here, a new self calibration method to correct such errors, based on a genetic algorithm is presented. It is robust, fast and completely automatic. Results obtained by carrying out Energy Dispersive X-Ray Diffraction measurements on reference samples are reported and discussed. They show how the application of such genetic algorithm may provide a fast esteem of the two parameters required when multiple angle pattern collection is performed, namely the effective starting angle and the angular step. In this way, reliable q-values of all the diffraction pattern features (Bragg peaks for crystalline, and diffused bumps for non-crystalline samples) are obtained
Effect of disturbance induced by the electronic noise on the Energy Dispersive X-ray Diffraction patterns collection RID F-3370-2011
No full textThe Energy Dispersive X-ray Diffraction (EDXD) proved to be an interesting alternative to its conventional Angular Dispersive counterpart (ADXD) each time the in situ measurements are of concern. Indeed, although its resolution is lower than that of ADXD, nevertheless it may allow a very accurate determination of even minimal changes of crystalline powders lattice parameters, thanks to several advantages it exhibits with respect to ADXD. Among these advantages, discussed in the paper, the main is that no motion is required upon diffraction pattern collection. However, the reliability of EDXD results may be compromised by the presence of an electronic noise that, along with a broadening of the Bragg peaks, may induce a shift of their positions. To evaluate the magnitude of such shift and, therefore, the level of confidence in determining the lattice parameters, a systematic study of the disturbance due to the electronic noise is reported. (C) 2009 Elsevier B.V. All rights reserved
Evidence of a rearrangement of the surface structure in titanium phthalocyanine sensors induced by the interaction with nitrogen oxides molecules
No full textThin-film samples of titanium phthalocyanine, a sensor of environmental pollutants, were studied by time resolved energy-dispersive x-ray reflectivity (EDXR). This original method demonstrated to be an ideal tool to follow the evolution of the films morphology upon gas exposure, in situ, also allowing an unexpected response of the sensors to be detected. Indeed, while the increase in thickness showed the characteristic feature of a "breathing-like" expansion, already observed in other metal-Pc, the curve of roughness versus exposure time exhibited a peak. This effect, in some cases evident by observation with the naked eye the EDXR data, was attributed to a surface structure rearrangement process
From chemical to structural order of electrodeposited Ni22P alloy: An XPS and EDXD study
No full textAmorphous electrodeposited Ni-22 at.% P alloys were analyzed in the amorphous and re-crystd. state by EDXD and XPS surface anal. The re-crystn. kinetics were detd. following in situ structural changes by EDXD. Distinct diffraction patterns indicating the presence of Ni3P confirm alloy re-crystn. at 645. The XPS results show that all the core level binding energies of nickel such as Ni2p3/2 and Ni2p1/2 and phosphorus (P2p, P2s) remained const. after the change from x-ray amorphous to cryst. structure of the Ni-P alloy. Differences obsd. were as follows: (a) the binding energy difference between the Ni2p main lines and the satellite, (b) the fine structure of the NiLMM Auger lines, and (c) the d. of states in the valence band in the region of the Ni3d electrons. On the basis of these results from EDXD and XPS, the change in alloy structure from x-ray amorphous to cryst. influences the electronic structure of the Ni-P alloy but not the chem. state of phosphorus. An explanation based on the screening model proposed in the literature is discussed
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
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
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