1,720,990 research outputs found
LaCoO3: Effect of synthesis conditions on properties and reactivity
No full textTwo nanostructured bulk LaCoO3 powders were prepared by co-precipitation and with the citrate gel method and compared with the two
nanocomposites obtained depositing, by wet impregnation, cobalt oxide on the La2O3 surface. All the prepared samples were characterized by
means of X-ray photoelectron (XP) and diffuse reflectance infrared Fourier transform (DRIFT) spectroscopic techniques, X-ray diffraction (XRD),
scanning electron microscopy (SEM) and thermal analysis.
XRD results suggest that only the citrate gel method allows to obtain a single phase lanthanum cobaltite powder having a rhombohedral
perovskite structure. Moreover, SEM images confirm the wide scale homogeneity. In contrast, a lanthanum hydroxide phase (hexagonal) is also
evident in the sample obtained by co-precipitation method. In the nanocomposite richer in cobalt, besides the rhombohedral perovskite, the
hexagonal lanthanum oxide and hydroxide phases are also detectable. Perovskite phase does not form when the amount of deposited cobalt oxide is
too low. Both in the nanostructured sample prepared by citrate gel method and nanocomposite with [Co/La]nominal = 1.0 XPS, DRIFT and TGA
outcomes suggest a lower presence of hydroxyl groups and carbonates species.
The reactivity of the powders with respect to carbon monoxide was studied (at atmospheric pressure, between RT and 573 K) by means of the
diffuse reflectance infrared Fourier transform spectroscopy. A significant signal around 2058 cm1 testifies about the interaction of CO with the
Lewis acidic sites distributed on the surface of all the samples. The two nanostructured bulk LaCoO3 show a high reactivity toward CO oxidation
since 423 K. A similar oxidation capability is observed also for the nanocomposite richer in cobalt. In contrast, a rather low reactivity is displayed
from the nanocomposite with lower Co/La nominal atomic ratio and La2O3
Effects of Agrochemicals on the Mechanical Properties of Plastic Films for Greenhouse Covering
No full textGreenhouse plastic films are subjected to degradation due to their exposure to solar radiation and to agrochemicals used during cultivation. This results in a reduction of life, which ranges from some months to 3–4 years relative to the thickness of the plastic film and to the degree of stabilisation. A research was carried out in order to evaluate the variation of the mechanical properties of 4 different polyethylene-co-vinyl acetate (EVA) films exposed to the climatic agents and to agrochemicals used during cultivation. The test was carried out at the University of Bari (Italy) in 2006. Four EVA films, one without anti-UV additive and three experimental films with different anti-UV additives, were installed on steel arches of four low tunnels. The films were sprayed with agrochemicals containing iron, chlorine and sulphur. The same films, mounted over other four low tunnels, were not sprayed in order to be used as control. Mechanical laboratory tests were carried out on the film samples, taken at fixed time intervals in the field, in order to assess the variations of the stress and strain at break. The different anti-UV stabilizers influenced the behaviour of the films in presence of the sprayed agrochemicals. The tests showed that the highest resistance to the agrochemicals was recorded for the EVA film stabilized with NOR-HALS plus UV filter
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
Reduction of the Environmental Impact of Plastic Films for Greenhouse Covering by Using Fluoropolymeric Materials
No full textGreenhouse plastic films are subjected to degradation due to their exposure to solar radiation and to chemical products used during cultivation. For polyolephinic materials, mainly low density polyethylene, ethylene–butyl acrylate copolymers and ethylene–vinyl acetate copolymers, this results in a service life which ranges from some months up to 3–4 years relative to the thickness of the film and to the degree of stabilisation. Ethylene–tetrafluoroethylene copolymer films show much longer service life, because of the intrinsic UV stability of the polymer without the need of any UV stabilizer and because of the low chemical reactivity vs. the commonly used agrochemicals. A simple model was developed in order to compare ethylene–tetrafluoroethylene copolymer and polyolephinic films in terms of waste generation at the end of their service life. The quantity of waste generated during a period of 15 years by the replacement of the covering sheets for 1 ha of greenhouses was estimated according to the class of duration of the plastic films, in a climatic situation corresponding to Southern Italy. Field and laboratory tests were carried out on ethylene–tetrafluoroethylene copolymers and ethylene–vinyl acetate films in order to assess the film lifetime in real conditions, evaluating the effects of solar radiation and of the agrochemicals in terms of loss of tensile properties and of quantity of contaminants accumulated by the films. The results suggested that the use of ethylene–tetrafluoroethylene copolymer films as covering sheets of greenhouses can reduce the waste of plastic materials in a range from 5 to 10 times, with the further advantage of a significant recovery value for the used sheets
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
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