1,721,002 research outputs found
Energy Transfer Processes in NaBiF4 Nanocrystals Co‐Doped with Tb3+ and Eu3+ Dispersed in Aqueous Solution
No full textThe synthesis of hexagonal NaBiF4 co-doped with Tb3+ and Eu3+(NaBi0.75-xTb0.25EuxF4; with x=0, 5, 10, 20 and 30) was achieved via a facile and fast precipitation route at 35 degrees C. Powder X-ray diffraction (PXRD) and luminescence spectroscopy have been employed to characterize and investigate the materials. The study of luminescence spectroscopy and decay kinetics of the D-5(4) excited state of Tb3+ provides the evidence of a Tb3+-> Eu3+ energy transfer process. Sodium citrate has been adopted as capping agent to promote a homogeneous dispersion of the materials into water and to protect the inorganic host, which is water sensitive, from direct contact with this molecule. The comparison of luminescence properties between bare and citrate-capped samples of NaBiF4 co-doped with Tb3+ and Eu3+ reveals a marked difference in the Tb3+-> Eu3+ energy transfer efficiency, which has been tentatively explained on the basis of a different environment surrounding the lanthanide ions in the two families of compounds
Synthesis, characterization and molecular structures of the new [Bi@Rh12(CO)27]3–, [(Bi@Rh12(CO)26)2Bi]5–, [Bi@Rh14(CO)27Bi2]3– and [Bi@Rh17(CO)33Bi2]4– carbonyl clusters
No full textCircularly Polarized Luminescence from Pure and Eu-Doped Trigonal TbPO4·nH2O Nanocrystals
No full textIn this contribution, we describe the preparation, by means of a precipitation reaction from aqueous solution at 40 degrees C, and the structural characterization of nanocrystalline powders of trigonal Tb1-xEuxPO4nH(2)O (with x = 0, 0.005, 0.01, 0.05, and 0.1; n tentatively assigned as 0.67) which crystallize in the two possible P3(1)21 or P3(2)21 enantiomorphic space groups. While the volume of the crystal lattice is not significantly affected by the Tb3+/Eu3+ substitution, the average crystallite size seems to depend on the Eu3+ dopant concentration and ranges from 13 to 30 nm. The desired handedness of the crystals has been induced by using, during the synthesis, one of the two possible enantiomers of tartaric acid (l or d). The analysis of the luminescence excitation and emission spectra, together with the decay kinetics of the D-5(4) Tb3+ excited state, suggests the presence of a very efficient Tb3+ -> Eu3+ energy transfer process in the Eu3+-doped orthophosphates. Upon excitation of Tb3+ ions at 368 nm, the enantiomorphic powders grown with l- or d-tartaric acid (i.e., l-TbPO40.67H(2)O/d-TbPO40.67H(2)O, l-Tb0.995Eu0.005PO40.67H(2)O/d-Tb0.995Eu0.005PO40.67H(2)O, and l-Tb0.9Eu0.1PO40.67H(2)O/d-Tb0.9Eu0.1PO40.67H(2)O) exhibited mirror circularly polarized luminescence signals in the visible spectral region (in the green and/or in the red)
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
Highly Active Catalysts Based on the Rh4(CO)12 Cluster Supported on Ce0.5Zr0.5 and Zr Oxides for Low-Temperature Methane Steam Reforming
No full textSyngas and Hydrogen productions from methane are industrially carried out at high temperatures (900 ◦C). Nevertheless, low-temperature steam reforming can be an alternative for small-scale plants. In these conditions, the process can also be coupled with systems that increase the overall efficiency such as hydrogen purification with membranes, microreactors or enhanced reforming with CO2 capture. However, at low temperature, in order to get conversion values close to the equilibrium ones, very active catalysts are needed. For this purpose, the Rh4(CO)12 cluster was synthetized and deposited over Ce0.5Zr0.5O2 and ZrO2 supports, prepared by microemulsion, and tested in low-temperature steam methane reforming reactions under different conditions. The catalysts were active at 750 ◦C at low Rh loadings (0.05%) and outperformed an analogous Rh-impregnated catalyst. At higher Rh concentrations (0.6%), the Rh cluster deposited on Ce0.5Zr0.5 oxide reached conversions close to the equilibrium values and good stability over long reaction time, demonstrating that active phases derived from Rh carbonyl clusters can be used to catalyze steam reforming reactions. Conversely, the same catalyst suffered from a fast deactivation at 500 ◦C, likely related to the oxidation of the Rh phase due to the oxygen-mobility properties of Ce. Indeed, at 500 ◦C the Rh-based ZrO2-supported catalyst was able to provide stable results with higher conversions. The effects of different pretreatments were also investigated: at 500 ◦C, the catalysts subjected to thermal treatment, both under N2 and H2, proved to be more active than those without the H2 treatment. In general, this work highlights the possibility of using Rh carbonyl-cluster-derived supported catalysts in methane reforming reactions and, at low temperature, it showed deactivation phenomena related to the presence of reducible supports
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
- …
