1,720,983 research outputs found
Inelastic neutron scattering investigation of ball-milled FeSiB samples
No full textInelastic neutron scattering measurements have been carried out at T = 300 K on FeSiB samples produced by mechanical milling from a ferromagnetic amorphous Fe80Si7B13 ribbon prepared by melt spinning. We have produced three samples, milled for 10, 20 and 70 hours in a shaker-type milling device under Ar atmosphere (ball to powder weight ratio 4:1); the samples, in form of micrometric powder, were labeled as M10h, M20h and M70h, respectively. The collected neutron spectra have been integrated over all scattering angles, corrected for self-absorption coefficient and finally normalized to the sample mass.
The study of the dynamic structure factor S(E) as a function of energy for the as-cast FeSiB ribbon and for the milled samples reveals a depletion of the energy region around 10 meV with increasing the milling time, corresponding to the suppression of vibrational modes proper of the amorphous FeSiB alloy. This behavior is consistent with X-ray diffraction and Mössbauer spectroscopy analyses on the same samples indicating that the milling process induces the formation of a minor fraction of bcc Fe nanocrystallites (in M70h, the resonant area ascribed to bcc Fe is about 7% of the total Mössbauer spectrum). The inelastic area of the S(E) spectra decreases upon milling over 10 hours; the elastic area decreases as well passing from 10 to 20 hours milling, in an amount larger than 3%.
This reduction of the elastic scattering intensity can be accounted for considering that the milling process, prolonged for 20 hours, brings about a decrease in the magnetic cross section of the FeSiB powders, with respect to the as-cast ribbon. In M70h, the elastic region area is slightly larger than in M20h, likely because of the more relevant presence of bcc Fe nanocrystallites, but it remains definitely smaller than in the as-cast and M10h samples.
Measurements of the saturation magnetization of the samples by SQUID magnetometer fully support this description. On the other hand, the Mössbauer analysis indicates that the averaged hyperfine field relative to the amorphous component does not change upon milling compared to the as-cast ribbon, suggesting that the value of the magnetic moment per Fe atom remains constant.
We discuss these results by the light of previous magnetic studies revealing a peculiar magnetic behavior of milled FeSiB powder, featuring a transition at T ~ 50 K from a frozen collective state, similar to a cluster-glass, to a ferromagnetic regime (reentrant ferromagnet transition) [1]. The explanation for this effect was based on the existence of a magnetic phase showing spin-glass like properties (speromagnetism), dispersed into the ferromagnetic FeSiB matrix and coexisting with the bcc Fe nanocrystallites. Hence, although ferromagnetism predominates at T = 300 K, we propose that antiferromagnetic interactions and imperfect magnetic moments alignment persist in the regions showing spin-glass like behavior at low temperature, which causes the decrease in the magnetic cross section.
[1] L. Del Bianco et al., J. Phys.: Condens. Matter 22, 296010 (2010
Combined Mössbauer and neutron scattering investigation of ball-milled FeSiB samples
No full textFerromagnetic amorphous alloys are very intriguing systems, combining a long range ferromagnetic (FM) order with the absence of long range crystalline order. In spite of that, the actual atoms disposition may have a remarkable effect on the alloy properties. Indeed, we observed that submitting Fe80Si7B13 ribbons prepared by melt spinning to mechanical milling, a transition at T ~ 50 K from a low temperature frozen collective state, similar to a cluster-glass, to a high temperature ferromagnetic regime (reentrant ferromagnet transition) was observed [1].
To investigate this result, we performed Mössbauer and inelastic neutron scattering measurements. We produced three samples, milled for 10, 20 and 70 hours in a shaker-type milling device under Ar atmosphere (ball to powder weight ratio 4:1); the samples, in form of micrometric powder, were labeled as M10h, M20h and M70h, respectively. Transmission Mössbauer spectra were collected at room temperature using a 57Co in Rh source, and the spectrometer was calibrated using an α-Fe foil. The neutron spectra were recorded at the same temperature and were integrated over all scattering angles, corrected for self-absorption coefficient and finally normalized to the sample mass.
Mössbauer investigation as a function of milling time features the progressive precipitation of a minor fraction of bcc Fe nanocrystallites, also displayed by X-Ray diffraction measurements. The Mössbauer analysis indicates that, during this process, the averaged hyperfine field relative to the amorphous component does not change upon milling compared to the as-cast ribbon, suggesting that the value of the magnetic moment per Fe atom remains constant. In parallel, the comparison between the dynamic structure factor S(E) as a function of energy for the as-cast FeSiB ribbon and for the milled samples reveals a depletion of the energy region around 10 meV with increasing the milling time, corresponding to the suppression of vibrational modes proper of the amorphous FeSiB alloy. This behavior is consistent with the formation of bcc Fe nanocrystallites. The inelastic area of the S(E) spectra decreases upon milling over 10 hours; the elastic area decreases as well passing from 10 to 20 hours milling, in an amount larger than 3%.
This reduction of the elastic scattering intensity may be accounted for considering that the milling process, prolonged for 20 hours, brings about a decrease in the magnetic cross section of the FeSiB powders, with respect to the as-cast ribbon. Measurements of the saturation magnetization of the samples by SQUID magnetometer fully support this description.
As the Mössbauer analysis suggest that the magnetic moment per Fe atom remains constant, to discuss these results we resort to the peculiar magnetic properties of the ball milled ribbons. Indeed, the magnetic properties of the ball milled samples were explained in terms of the existence of a magnetic phase showing spin-glass like properties (speromagnetism), dispersed into the ferromagnetic FeSiB matrix and coexisting with the bcc Fe nanocrystallites. Hence, although ferromagnetism predominates at T = 300 K, we propose that antiferromagnetic interactions and imperfect magnetic moments alignment persist in the regions showing spin-glass like behavior at low temperature, which causes the decrease in the magnetic cross section.
[1] L. Del Bianco, F. Spizzo, M. Tamisari, E. Bonetti, F. Ronconi, D. Fiorani, J. Phys.: Condens. Matter 22 (2010) 296010
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
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
- …
