1,720,967 research outputs found
Direct measurements of electrostatic potentials at grain boundaries: mechanism for current improvement in high-T-c superconductors
No full textGrain boundaries (GBs) in high-temperature superconductors represent the major factor limiting high current applications. Via magneto-optical imaging and direct transport measurements, we observed an increase of the intergranular J(c) in 4degrees and 8degrees [001] low-angle grain boundaries via substitution of Y by Ca in YBa2Cu3O7-x by up to 100%. Since Ca substitution leads to hole overdoping, these results suggest that charge depletion and band bending may be responsible for the suppression of superconductivity in GBs. By using electron holography, we directly observe ail electrostatic potential at the dislocation cores. The radius as well as the value of the potential are reduced in Ca-doped grain boundaries, directly reflecting the improved transport properties. (C) 2004 Elsevier B.V. All rights reserved
On the transport of intensity technique for phase retrieval
No full textThe Transport of Intensity technique is becoming a viable alternative to electron holography for phase retrieval in Transmission Electron Microscopy. However, several issues are still to be clarified in order to ascertain the applicability of the technique; among them, the controversy regarding its geometrical or wave-optical nature, as related to the phase detection limit. We show here that the Transport of Intensity is a wave-optical technique that works in a special regime of small defocus where the image intensity is linear with the defocus parameter. By a simple analytical example we show that the Transport of Intensity correctly reconstructs the electron optical phase shift even when the phase is smaller than pi, a value defining the boundary between the geometrical and wave approaches. Another example is given, the reconstruction of a phase jump, accompanied with experimental support showing that phase retrieval by Electron Holography and Transport of Intensity techniques yields results in good agreement. (C) 2004 Elsevier B.V. All rights reserved
Quantitative domain wall width measurement with coherent electrons
No full textQuantitative measurements of domain wall widths in a magnetic thin foil of Nd2Fe14B are obtained by the analysis of coherent shadow deformation of the biprism in an electron microscope. Information related to the phase gradient in the direction, perpendicular to the biprism is extracted by comparing recorded images and simulations computed according to the experimental electron-optical configuration and by varying the domain wall width w. We demonstrate the usefulness of the technique for extraction of magnetic information at the nanometer scale. (c) 2006 Elsevier B.V. All rights reserved
Direct correlation of reversal rate dynamics to domain configurations in micron-sized permalloy elements
No full textThe distribution of states upon the removal of applied magnetic field in an array of 7.5 X 7.5 mu m(2) permalloy square elements, as observed by transmission electron microscopy in Lorentz mode, shows a predominance of two states: the vortex state and the seven-domain state. The distributional dependence of these two states on the rate of change of the reversal field is established. Micromagnetic simulations suggest that vortex nucleation and the subsequent domain-wall propagation are the two primary mechanisms for magnetization reversal. The kinetics of the two pathways is examined in a manner that conforms to the observed distribution of states. (c) 2005 American Institute of Physics
Quantitative shadow technique for the investigation of magnetic domain wall widths
No full textQuantitative measurement of domain wall widths in a magnetic thin foil of Nd2Fe14B and a patterned Ni88Fe12 Permalloy element is obtained by the analysis of coherent shadow deformation of an electrostatic biprism in an electron microscope. Information related to the phase gradient in the direction perpendicular to the biprism is extracted by comparing the recorded shadow images with simulations computed according to the experimental electron optical configuration and by varying a single free parameter: the domain wall width. We demonstrate the feasibility of such experiments and the usefulness of the technique for characterization of magnetic features at different length scales
Direct evidence for negative grain boundary potential in Ca-doped and undoped YBa2Cu3O7-x
No full textUsing electron holography in a transmission electron microscope, we obtained direct evidence for the reduction of negative charge at grain boundary dislocations in Ca-doped YBa2Cu3O7 (YBCO) when compared to undoped YBCO. Because of the finite width of the valence band in the superconducting CuO2 planes, the negative grain boundary charge can lead to a depletion of electron holes available for superconductivity. A significant reduction in the size of the perturbed region in the Ca-doped samples appears to be the principal mechanism for the improved interfacial superconductivity
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
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