1,720,991 research outputs found
Belousov-Zhabotinsky type reactions: the non-linear behavior of chemical systems
Full text linkChemical oscillators are open systems characterized by periodic variations of some reaction species concentration due to complex physico-chemical phenomena that may cause bistability, rise of limit cycle attractors, birth of spiral waves and Turing patterns and finally deterministic chaos. Specifically, the Belousov-Zhabotinsky reaction is a noteworthy example of non-linear behavior of chemical systems occurring in homogenous media. This reaction can take place in several variants and may offer an overview on chemical oscillators, owing to its simplicity of mathematical handling and several more complex deriving phenomena. This work provides an overview of Belousov-Zhabotinsky-type reactions, focusing on modeling under different operating conditions, from the most simple to the most widely applicable models presented during the years. In particular, the stability of simplified models as a function of bifurcation parameters is studied as causes of several complex behaviors. Rise of waves and fronts is mathematically explained as well as birth and evolution issues of the chaotic ODEs system describing the Györgyi-Field model of the Belousov-Zhabotinsky reaction. This review provides not only the general information about oscillatory reactions, but also provides the mathematical solutions in order to be used in future biochemical reactions and reactor designs
Heterogeneous mechanism of NOx-assisted soot oxidation in the passive regeneration of a bench-scale diesel particulate filter catalyzed with nanostructured equimolar ceria-praseodymia
No full textFundamental properties and sustainable applications of the natural zeolite clinoptilolite
Full text linkThis review explores a set of sustainable applications of clinoptilolite, a natural zeolite abundant around the world in different localities. Thanks to its physico-chemical properties this material is extremely versatile for several applications, ranging from environmental catalysis and CO2 removal to industrial and agricultural wastewater purification, aquaculture, animal feeding, and food industry but also medical applications and energy storage systems. Due to the presence of cations in its framework, it is possible to tune the material’s features making it suitable for adsorbing specific compounds. Thus, this review aims to provide insight into developing new technologies based on the use of this material that is sustainable, not harmful for humans and animals, naturally abundant, and above all cost-effective. Furthermore, it is intended to promote the use of natural materials in various areas with a view to sustainability and to reduce as far as possible the use of chemicals or other materials whose synthesis process can have a polluting effect on the environment
Catalytic Activity of Nanostructured Ceria-Based Materials Prepared by Different Synthesis Conditions
No full textCO oxidation on ceria-based nanocatalysts: Cooperative and non-cooperative behavior for a structure-sensitive reaction
No full textCeria-based catalysts (namely, CeO2, CePrOx and CePrZrOx) have been prepared to investigate the structuredependency for the CO oxidation. Then, it has been proved that the CO oxidation over ceria nanocatalysts depends on the presence of highly reactive (100) and (110)-type planes. The best performance has been achieved for the Ce-NC catalyst because of the higher amount of low-index surfaces on the CeO2-nanocubes. For catalysts prepared by the Solution Combustion Synthesis (SCS), higher CO conversion values have been reached with ternary and binary oxides rather than with pure ceria, and the following activity order can be drawn: Ce-SCS < CePr-SCS < CePrZr-SCS. Therefore, the presence of Zr and Pr species into the ceria framework improves the catalytic performance, showing a cooperative behavior among the Ce/Pr/Zr/O sites. On the other hand, the oxidation activity with the nanocubic structures increases as follows: CePrZr-NC < CePr-NC < Ce- NC. This means that the presence of Pr/Zr species into the ceria lattice does not have a beneficial effect on the activity (non-cooperative behavior). These findings further confirm that the surface properties of solid catalysts depend on both the electronic and geometric factors. Moreover, CO oxidation is highly sensitive to the electronic and geometric structures of ceria-based catalysts and it appears as a “ill-conditioned system,” since small variations in the catalyst properties give rise to large effects on the activity
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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