1,720,972 research outputs found
Thermally stable hybrid foams based on cyclophosphazenes and polyurethanes
No full textTwo cyclotriphosphazenes, containing OH groups, have been synthesized: hexakis[p-(hydroxymethyl)phenoxy]cyclotriphosphazene (PN6), with six hydroxyl groups, and 2,2-di-[p-(hydroxymethyl)phenoxy]-4,4,6,6,-bis[spiro(2',2" -dioxy-1',1"-biphenyl)cyclotriphosphazene (PN2) with two hydroxyl groups. They were used in the preparation of modified rigid polyurethane foams as OH containing compounds, alone or in mixtures with polyol components. The thermal stabilities of the resultant hybrid foams were analysed using thermogravimetric analysis (TGA), in inert (nitrogen) and oxidizing (air) atmosphere. The fire behaviour has been investigated by means of oxygen index (LOI) tests. The results showed that the introduction of increasing amount of cyclotriphosphazene in foams leads to a significant improvement of the thermal stability, both in nitrogen and in air. Improvement has also been observed in the fire behaviour of modified foams, particularly for the foams containing cyclotriphosphazene PN2
The Thermally-Induced Bulk Polymerization of Hexachlorocyclotriphosphazene to Polydichlorophosphazene by First-Principles Simulations
No full textIn this paper we report first principles calculations using the Car-Parrinello molecular dynamics approach in order to clarify the mechanism of the ring-opening polymerization of hexachlorocyclotriphosphazene, N3P3Cl6 to polydichlorophosphazene (NPCl2) (n) . In particular, we highlight the key role played by the cyclophosphazene phosphorus cation N3P3Cl5 (+) generated from the heterolytic cleavage of the P-Cl bond as the main component in the polymerization process. Moreover, the generation of the maximally localized Wannier functions, together with the Mulliken population analysis, allows us to clarify some basic issues of the investigated reaction. The activation energy, mainly due to the formation of phosphazenium cation, is found to be in good agreement with experiments. Structural and electronic analysis of the molecules involved is also reported
Surface Functionalization with Phosphazene Substrates. Part II. Theoretical and Experimental Investigations of the Interactions of Hexachlorocyclophosphazene with Hydroxylated Silicon-based Surfaces
No full textThe interaction of hexachlorocyclophosphazene (HCCP) with the hydroxylated silicon-based surfaces is studied by a combination of XPS experimental analysis and theoretical ab initio simulations, including the estimate of the energy barriers via CI-NEB method to determine the minimum energy reaction paths. Several possible, stable chemisorbed configurations are found to exist, whose structural, energetic, and electronic properties have been analyzed in detail. The theoretical results are in good qualitative agreement with available experimental data. In particular, we get indications that water plays a crucial role in the surface functionalization with HCCP, although the presence of a suitable solvent (e.g. tetrahydrofuran, THF) seems to be essential
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
- …
