1,721,005 research outputs found
Caratteri di base e tipologia degli insediamenti
No full textIl testo presenta gli obiettivi e il possibile quadro delle ricerche per la conoscenza di base del patrimonio edilizio storico, al fine di impostare metodi e tecniche di protezione sismic
Experimental investigation of highly exergonic outer-sphere electron-transfer reactions
No full textSome 20 rate constants of highly exergonic thermal electron-transfer reactions between reduced metal-polypyridine complexes and radical cations of aromatic molecules have been measured by laser and flash photolysis techniques. The rate constant values remain at diffusion-controlled levels up to free energy changes of -58 kcal/mol. Such exergonicity values are more than twice the value at which the classical Marcus theory, under the most favorable assumption, predicts the onset of the inverted behavior to occur. In the reactions studied, the energetics of the products (which are molecules in their standard oxidation states) is well-known, and the formation of electronically excited states can be very safely ruled out. Among the possible reasons for the failure to observe the inverted behavior, quantum effects (nuclear tunneling) are believed to play the major role in these systems. Measurements of the yields of formation of the reactants in the flash photolysis experiments also point toward the lack of any inverted behavior in these reactions. © 1984 American Chemical Society
Phosphorescent 8- Quinolinol Metal Chelates. Excited-State Properties and Redox Behavior
No full textA number of metal complexes of 8-quinolinol (QOH) of general formula M(QO)n(n = 3, M = Al(III), Bi(III), Rh(III), Ir(III); n = 2, M = Pt(II), Pb(II)) have been synthesized and characterized. The heavy-metal complexes (M = Pt(II), Pb(II), Bi(III), Ir(III)) exhibit long-lived (τ ≃ 2–4 μs) phosphorescence and excited-state absorption (ESA) in fluid solution. The photophysics of these complexes (emission spectra and lifetimes, ESA spectra and lifetimes, emission quantum yields, efficiencies of formation of the long-lived state) has been studied in some detail. The long-lived emitting state is assigned as a metal-perturbed triplet state of the 8-quinolinol ligand. On the basis of their ground-state redox potentials and on their excited-state properties, the heavy-metal 8-quinolinol complexes are predicted to behave as powerful excited-state reductants (potentials in the-0.8 to-1.3 V range vs. SCE). Quenching studies verify these expectations. © 1986, American Chemical Society. All rights re..
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
Doublet-doublet annihilation in chromium(III) polypyridine complexes
No full textUnder high-intensity pulsed laser excitation, the doublet states of Cr(4,7-Me2phen)33+ and Cr(phen)33+ decay with mixed first- and second-order kinetics. The dependence of the kinetics on laser intensity, presence of quenchers, and ionic strength demonstrates the occurrence of a doublet-doublet annihilation process in competition with the unimolecular doublet decay. The bimolecular rate constants for the annihilation process have been determined and found to be substantially lower than those for diffusion. Both energy-transfer and electron-transfer mechanisms for the annihilation process are discussed. © 1982 American Chemical Society
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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