1,721,020 research outputs found
Temperature dependence of the structural parameters of gold nanoparticles investigated with EXAFS
No full textThe L3 edge of Au nanoparticles, having sizes ranging from 2.4 to 5.0 nm, have been investigated by x-ray
absorption fine structure spectroscopy in the temperature range of 20–300 K. Data were recorded at the
European Synchrotron Radiation Facility with a very good signal to noise ratio. To achieve a very high
accuracy in the determination of the first shell distance, a very careful data analysis was performed also taking
into account the presence of asymmetry effects. In all samples, the temperature dependence of the first
neighbor distance results is different from that of the macrocrystalline counterpart. In the largest size samples,
a reduction of the thermal expansion was found, whereas in the smallest ones, the presence of a crossover from
an initial thermal expansion to a thermal contraction was observed. Calculations based on a simple model show
that localization effects that increase as the nanoparticle size decreases can explain the reported thermal effects
XANES studies of Fe in pumpellyite-group minerals
No full textA study of the absorption spectra in the Fe K near-edge region of four mineral samples of the pumpellyite-group with different total Fe content was performed. The Fe-rich samples from low-grade metamorphic rocks (Keweenawan basalts, Michigan; porphyrites from Torrente Bulla, Italy) essentially contain all structural Fe in the octahedrally coordinated trivalent state, in contrast to the commonly used crystal-chemistry rules for the computation of the pumpellyite chemical formula. The Fe in an iron-poor sample from high pressure environment (glaucophane-lawsonite bearing rock from Hicks Ranch, California) is shown to be 6-coordinated divalent iron, in agreement with previous structural studies on Al-rich pumpellyites
DEBYE FUNCTION ANALYSIS OF SYNCHROTRON XRD DATA: STACKING FAULTS AND MICROSTRAINS IN SPHERICAL PALLADIUM CRYSTALLITES
No full textthermal evolution of Carbon supported clusters studied by time resolved X-ray diffraction
No full textNanostructure of Pd/SiO2 supported catalysts
No full textPd/SiO2 supported catalysts were investigated using anomalous small-angle X-ray scattering (ASAXS), wide-angle X-ray scattering (WAXS), transmission electron microscopy (TEM) and extended X-ray absorption fine structure spectroscopy (EXAFS). Samples containing about 3 wt.% and 6 wt.% of metal were obtained by impregnation, calcined at 773 K and reduced at 623 K. Two populations of nanoparticles were found in both samples. In the 3 wt.% sample, one population consisted of very small nanoparticles (average 3 nm), and the other of larger ones (average 13 nm). A higher metal load seems to cause a broadening of the size distribution of the first population and a consequent increase in its average dimension (6 nm), rather than to influence the larger nanoparticles. Despite the relatively high metal content and temperatures, the population of small particles was predominant in both samples: 80% in the 3 wt.% sample and 57% in the 6 wt.% one. A large number of the smallest particles (<3 nm) was present in the 6 wt.% sample as well, and the total metal surface available was about the same in the two samples in spite of the different amounts of metal. Anomalous scattering has proven to be essential to quantitative analysis
Amorphous hydrogenated alloys: a comparative EXAFS study of a-Si1-XCX:H, a-SiNX:H and a-Si1-XGeX:H at the Si K-edge
No full textGoing 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
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