1,720,982 research outputs found
Catalytic properties on the hydrogen desorption process of metallic additives dispersed in the MgH2 matrix
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Mixed gas diffusion and permeation of ternary and quaternary CO2/CO/N2/O2 gas mixtures in Matrimid®, polyetherimide and poly(lactic acid) membranes for CO2/CO separation
Full text linkThe CO2/CO mixed-gas separation performance of a polyimide (Matrimid®), polyetherimide (PEI) and polylactic
acid (PLA) membrane, were characterized in the presence of CO2- rich ternary (CO2/ CO/ O2) and quaternary
(CO2/ CO/ O2/ N2) feed gas mixtures mimicking the products of CO2 reforming conversion reactions. The
membrane-based separation of this mixture is poorly characterized and original data were obtained in a novel
mass spectrometric apparatus that permits to monitor the instantaneous permeate composition, thus allowing to
evaluate both mixed gas diffusion and permeability coefficients of all gases. CO2, CO, O2 and N2 permeability
and diffusivity in single gas tests were measured between 298 and 353 K up to 1 atm feed pressure and relevant
activation energies were evaluated. At 298 K Matrimid® exhibits CO permeability of 0.50 ± 0.03 Barrer and an
ideal CO2/ CO selectivity of 16 ± 1. PEI and PLA exhibit similar ideal selectivity values but lower CO transport
rates. In all examined polymer films the CO2/ CO selectivity has absorption-selective character that favours the
permeation of CO2. The ideal CO2/ CO selectivity of all membrane samples decreases with temperature, reaching
values of 10 ± 1 at 335 K in Matrimid®. The CO2/ CO selective performances of all examined membrane do not
show markable variations exposing the membrane samples to CO2- rich gas mixtures as feed gas. The upper
bound correlation among selectivity and permeability for the CO2/ CO gas couple is here for the first time
proposed
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
Poly(vinyl chloride) Coupling with UV Laser Radiation: Comparison between Polymer Absorbers and Nanoparticles to Increase Efficiency for Laser Ablation Propulsion
No full textAmong the wide variety of applications of polymers, their use as targets for laser ablation propulsion has recently gained interest. Poly(vinyl chloride) (PVC) showed promising propulsion properties that can be related to its well-defined thermal decomposition path. However, strategies are needed to increase the momentum generation efficiency with laser radiation. To increase the energetic efficiency in the laser generation of a mechanical impulse, optical and thermodynamic properties must be properly tuned so that the ablation threshold fluence (Fth) is reduced. In this work, we compare two strategies to increase the optical absorption of PVC in the UV region. One is based on embedding carbon nanoparticles (CNPs) in the PVC matrix, whereas the other relies on mixing PVC with poly(styrene sulfonate) acting as a chromophore. Uniform polymer films of 50 μm thickness are fabricated using a multilayer spin-coating technique. Samples are then tested by measuring the laser-generated impulse using a ballistic pendulum under the fluence range from 0.2 to 3 J/cm2 and values of Fth are extracted. These results are discussed from the point of view of optical and thermodynamic properties of the modified PVC, concluding that the localized optical absorption given by CNP is the most efficient strategy in the optical-to-mechanical energy conversion via laser-induced ablation of the polymer film
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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