1,720,981 research outputs found
Magnetic correlations in Fe<sub>80</sub>B<sub>20</sub> studied by magnetic small angle neutron scattering
No full textFe80B20 alloys with different degrees of crystallization were investigated by small angle neutron scattering. From the analysis of the obtained scattering patterns with and without magnetic field, we were able to separate the magnetic and the nuclear scattering contributions and to study the evolution of both structural and magnetic parameters of the iron particles in the various steps of the crystallization process
Crystal Structures of Ziegler-Natta Catalyst Supports
No full textThe crystal structures of three MgCl2·nEtOH complexes with n=1.5, 2.8, and 3.3 have been fully determined.
Such complexes are the fundamental precursors for Ziegler–Natta
polymerization catalysts used to produce polyolefins on a multimillion-ton scale worldwide. The ab initio structure
solution showed that the structure of MgCl2·nEtOH complexes with n=1.5 and 2.8 are based on ribbons of metalcentered
octahedra, whereas for n=3.3 this chainlike arrangement breaks into a threadlike structure of isolated octahedra linked by hydrogen bonds. A clear correlation between catalyst performance and the crystal structure of precursors has been found, and reveals the fundamental role of the latter in determining catalyst properties. The direct knowledge of building blocks in the precursor structures will help to develop more accurate models for activated catalysts. These models will not require the arbitrary and oversimplified assumption of locating the catalyst active sites on selected cut surfaces of
the a-MgCl2 crystal lattice
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
The influence of temperature fluctuations on hot-wire measurements in wall-bounded turbulence
No full textThere are no measurement techniques for turbulent flows capable of reaching the versatility of hot-wire probes and their frequency response. Nevertheless, the issue of their spatial resolution is still a matter of debate when it comes to high Reynolds number near-wall turbulence. Another, so far unattended, issue is the effect of temperature fluctuations - as they are, e.g. encountered in non-isothermal flows - on the low and higher-order moments in wall-bounded turbulent flows obtained through hot-wire anemometry. The present investigation is dedicated to document, understand, and ultimately correct these effects. For this purpose, the response of a hot-wire is simulated through the use of velocity and temperature data from a turbulent channel flow generated by means of direct numerical simulations. Results show that ignoring the effect of temperature fluctuations, caused by temperature gradients along the wall-normal direction, introduces - despite a local mean temperature compensation of the velocity reading - significant errors. The results serve as a note of caution for hot-wire measurements in wall-bounded turbulence, and also where temperature gradients are more prevalent, such as heat transfer measurements or high Mach number flows. A simple correction scheme involving only mean temperature quantities (besides the streamwise velocity information) is finally proposed that leads to a substantial bias error reduction. © 2014 Springer-Verlag Berlin Heidelberg
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
Poly (1-butene-ran-ethylene) monomodal copolymers from metallocene catalysts: Structural and morphological differences with increasing ethylene content
Full text linkSamples of random poly(butene-ran-ethylene) copolymers produced with metallocene catalysts were studied in order to elucidate the different behaviors of this particular class of materials as a function of increasing ethylene (C2) content. The samples cooled down from the melt are semi-crystalline or amorphous and crystallize in different crystal modifications, depending on the amount of C2. Thermal analysis, X-ray diffraction, and microscopic techniques were used to follow the changes of the materials with aging time and to understand the structural and morphological behavior with the aim of highlighting possible peculiar properties, which may be of great interest in the application of such materials in the field of Hot Melt adhesives
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