1,721,009 research outputs found
Orientation and Order of Xanthene Dyes in the One-Dimensional Channels of Zeolite L: Bridging the Gap between Experimental Data and Molecular Behavior
No full textSupramolecular organization in nanochannels is governed by both the nature of the channels and the size, shape, and charge of the guests, and may also depend on the cosolvent in the host. Oxonine (Ox+) and pyronine (Py+) cationic dyes in zeolite L (ZL) could provide important insight on this issue, but their orientation in the composite materials is not understood yet. Theoretical modeling of Ox+/ZL and Py+/ZL composites indicates that the 70–80° orientation, deduced from optical microscopy data but incompatible with host–guest geometry contraints, is not stable and reveals two possible orientations for these dyes in ZL nanochannels: perpendicular or parallel to the channel axis. In the hydrated composite, corresponding to optical microscopy experiments conditions, perpendicular Ox+/Py+ is the favored orientation, suggesting a larger portion of perpendicularly oriented dye molecules and a smaller fraction aligned. Optical microscopy data might therefore be reinterpreted as the vector sum of components arising from a population of molecules with nonuniform orientation. The stability order is reversed at dry conditions, indicating that the organization of xanthene dyes in ZL channels is governed by water. Our study explains this cosolvent-driven supramolecular organization regime, here unraveled for the first time, and highlights the role of molecular flexibility in switching the dye orientation
Interactions, Behavior, And Stability of Fluorenone inside Zeolite Nanochannels
No full textThe development of functional materials based on the supramolecular organization of photoactive species in nanosized porous matrices requires a deep knowledge of host−guest interactions and of their influence on material properties and stability. Extensive first-principles investigations on the fluorescent dye fluorenone inside zeolite L, both at dry conditions and in the presence of water, have unraveled the molecular origin of the peculiar stability of this composite in humid environments, a fundamental prerequisite for practical applications. Results of first-principles molecular dynamics simulations, structural optimizations, and TDDFT calculations, validated by comparison with experimental data, provide a comprehensive picture of the structure, energetics, electronic excitation properties, and room-temperature behavior of the fluorenone/zeolite L composite and predict a substantial optical anisotropy for this material also maintained upon contact with water. The interaction of the fluorenone carbonyl group with the zeolite extraframework potassium cations is responsible for the dye stabilization in zeolite L nanochannels and features itself as a general leitmotiv regarding important properties of carbonyl functionalized photoactive species in hydrophilic matrices
COMPORTAMENTO DEI LIVELLI DI ALLUMINIO PLASMATICO E URINARIO IN SOGGETTI PROFESSIONALMENTE ESPOSTI
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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
First-Principles Simulation of Absorption Bands of Fluorenone in Zeolite L
Full text linkThe absorption spectrum of fluorenone in zeolite L is calculated from first-principles simulations. The broadening of each band is
obtained from the explicit treatment of the interactions between the chromophore and its environment in the statistical ensemble.
The comparison between the simulated and measured spectra reveals the main factors affecting the spectrum of the chromophore
in hydrated zeolite L. Whereas each distinguishable band is found to originate from a single electronic transition, the bandwidth
is determined by the statistical nature of the environment of the fluorenone molecule. The K
+
...O=C motif is retained in all
conformations. Although the interactions between K
+
and the fluorenone carbonyl group result in an average lengthening of the
C=O bond and in a redshift of the lowest energy absorption band compared to gas phase or non-polar solvents, the magnitude of
this shift is noticeably smaller than the total shift. An important factor affecting the shape of the band is fluorenone’s orientation,
which is strongly affected by the presence of water. The effect of direct interactions between fluorenone and water is, however,
negligible
Cadmium concentrations in blood and urine of pregnant women at delivery and their offspring
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