1,720,984 research outputs found
A novel spectroscopic approach to investigate transport processes in polymers: the case of water-epoxy system
No full textOn the Molecular Mechanism of H2O Diffusion into Polyimides: A Vibrational Spectroscopy Investigation
No full textThe diffusion of water into polyimide films was studied by in situ FTIR spectroscopy using several methods of spectral data anal., namely, difference spectroscopy, least-squares curve fitting, 2D correlation spectroscopy, and normal coordinate anal. The results gave an insight into the mol. mechanism of diffusion in terms of no. and population of penetrant species present in the system and with respect to the nature of the mol. aggregates. In particular, two water species were identified and quantified, i.e., H2O mols. interacting with the carbonyl groups of the polyimide and self-assocd. water. An enthalpy of formation of -0.9 kcal mol-1 was estd. for the H2O-polyimide interaction, which points to a relatively weak H-bonding tendency of the imide carbonyls. Finally, the IR spectrum of the H2O-imide aggregate was calcd. by a quantum mechanic (QM) model chem. to rationalize the effects obsd. in the spectrum of the water satd. films. The results of the computation were in good agreement with the expt., confirming the predictive capabilities of the chosen QM method and supporting the proposed mol. structure of the H-bonding aggregate
A novel spectroscopic approach to investigate transport processes in polymers: the case of water-epoxy system
No full textWater Transport in Densely Crosslinked Networks: a omparison between Epoxy Systems Having Different Interactive Character
No full textWater transport in a densely crosslinked epoxy network, TGDDM-HHPA, was investigated by coupling time-resolved FTIR spectroscopy and gravimetric measurements. Vibrational anal. yielded information on the different water species present in the system and allowed a quant. estn. of their population at sorption equil. The transport of water mols. was found to follow a Fickian behavior characterized by an effective diffusion coeff. which increases with total water concn. The dependence of the effective diffusion coeff., D eff(C), on concn., as obtained from integral sorption curves, was interpreted by introducing a concn. dependent term, D(C), and an "interaction factor", j, which accounts for the effect of the mol. interactions which effectively slow down the diffusion process. The results were compared with those obtained on another epoxy network, TGDDM-DDS, characterized by the presence of stronger interacting sites. Differences and similarities of the spectroscopic and gravimetric results are critically discussed in the light of the structure of the two networks
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
Spectroscopic studies of the diffusion of water and ammonia in polyimide and polyimide-silica hybrids
No full textMass transport of low mol. wt. penetrants in polyimide and silica/polyimide hybrids has been investigated using time-resolved FTIR spectroscopy and gravimetric anal. In particular, transport of reacting (ammonia) and non-reacting (water) penetrants has been studied as a function of penetrant concn., evidencing peculiar features related to the presence of the inorg. phase in the hybrid systems. For the case of water, diffusivity and sorption equil. have been evaluated in an activity range between 0.1 and 0.75. Free water as well as mol. aggregates have been detected in both systems. In the case of ammonia, its reactivity with polyimide has been directly obsd., and the reaction mechanism elucidated. Furthermore, it has been possible to discriminate diffusion and reaction phenomena due to the different time scales of the two processes
Impiego di reflui caseari per la produzione di tea-compost per il controllo di alcuni funghi fitopatogeni
No full textCompost teas are extracts of fermented composted materials used for their ability to control plant diseases. A compost extractor in liquid phase, with a forced air-blowing system, assembled using farmer facilities, was used to produce “on farm” aerated compost teas (ACTs) from five types of compost, in a 14-day fermentation cycle. Solid feedstocks, representing one biowaste compost and four composted tomato or tomato plus escarole residues, were separately extracted in water (waACTs) and whey (whACTs). The ten teas were tested for their ability to inhibit, in vitro, growth of several soil-borne (Fusarium solani, Verticillium dahliae, F. oxysporum f. sp. lycopersici, Rhizoctonia solani, Sclerotinia minor and Sclerotium rolfsii) and air-borne (Alternaria radicina, A. dauci and Colletrichum lindemuthianum) fungal pathogens. All ACTs significantly inhibited the mycelial growth of A. dauci (46-58%), A. radicina (27-66%), F. solani (24-36%) and C. lindemuthianum (31-52%). The other pathogens were affected weakly. The main separation using principal component analysis of inhibition levels of the pathogens could be related to their telluric or aerial nature. Future prospective consists in testing the best ACTs as potential alternatives to the use of synthetic chemical fungicides for disease control in the field
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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