1,721,026 research outputs found
Combined Use of Scanning Electron Microscopy-Energy-Dispersive X-ray Spectroscopy and Fourier Transform Infrared Imaging Coupled with Principal Component Analysis in the Study of Ancient Egyptian Papyri
No full textThis paper reports the results of a spectroscopic study on the chemistry of some small papyrus fragments arising from three Egyptian excavation sites. The aim of this investigation was to verify the possibility to identify significant differences in ancient Egyptian papyri using noninvasive analytical methods, that is, ATR (attenuated total reflection)-FTIR (Fourier transform infrared) spectroscopic imaging and scanning electron microscopy-energy-dispersive X-ray spectroscopy. Differences in both lignin and cellulose compositions, which are difficult to detect with traditional FTIR and FTIR imaging spectral analysis, were revealed by the multivariate approach, and the second derivative spectroscopy was applied to enhance the spectrum resolution. Thus, it has been possible to recognize a fragment characterized by the presence of lead and of long chain aliphatic organic compound, which are not present in the other fragments, in the ink region. These data show not only that the combination of these techniques can provide important chemical information, such as to evidence the different compositions and manufacture of each papyrus, but also that metal inks were probably used also in ancient Egyptian papyri
Bromination of Alkynes in Ionic Liquids - A Kinetic Investigation
No full textThe kinetic behaviour and the product distributions of brominations of several arylalkynes with Br2 in the room-temperature ionic liquids (ILs) 1-butyl-3-methylimidazolium hexafluorophosphate [bmim][PF6] and 1-butyl-3-methylimidazolium bromide [bmim][Br], have been investigated at different temperatures. In [bmim][Br], alkynes stereospecifically gave the anty addition products, the reactions following a second-order rate law.In [bmim][PF6], mixtures of syn and anti addition products were obtained, and the reaction followed a second- or third-order rate law, depending on the structure of the alkyne and the concentration of Br2. The data obtained for the reactions in [bmim][Br] are interpreted on the basis of a mechanism involving a product- and a rate-determining nucleophilic attack by bromide on the alkyne-Br2 Π complex. The data relating to the electrophilic addition in [bmim][PF6] are explained in terms of the initial 1:1 alkyne-Br2 Π complex, the ionisation of which, probably catalysed either by a second halogen molecule or by the imidazolium cation, gives a bromirenium (or β-bromovynil cation) Br- or [Br3]- intermediate. Such intermediates then collapse to give the corresponding dibromo adduct(s). The kinetic constants and the activation parameters for the reaction in [bmim][Br] are compared with those relating to the second-order reaction of the same alkynes with tetrabutylammonium tribromide ([NBu4][Br3]) in 1,2-dichloroethane (DCE). On the basis of the kinetic data, a significant role for solvent viscosity in determining the reaction rate may be envisaged
Thermal behavior analysis as a valuable tool for comparing ionic liquids of different classes
No full textIonic liquids (ILs) are neoteric solvents characterized by unique physicochemical properties and considerable structural variability. The thermal behavior of 24 ILs, belonging to two structurally related families with either bromide or Tf2N as counteranion, was analyzed. For bromide mono- and dicationic ionic liquids (DILs), thermal gravimetric analysis showed similar decomposition events, with only small gain in stability for a few members of the latter class. Conversely, all Tf2N DILs displayed higher stabilities (up to 34 K) than the corresponding monocations, thus highlighting the different role played by the two counteranions. Mono- and dicationic ILs bearing a reactive group on the imidazolium substituent resulted instead the least stable ILs studied. Differential scanning calorimetry analyses of most of the (D)ILs only showed glass transition temperatures, a behavior in agreement with the broad liquid range of ILs. The impact of the cationic structure and/or of the type of anion on the above-mentioned transition temperatures has been studied. The apparent activation energy (Ea) and the fragility index (m) for some (D)ILs have also been obtained. Finally, a few bromide (D)ILs presented peculiar thermal events
Theoretical descriptor for the correlation of aquatic toxicity of ionic liquids by quantitative structure–toxicity relationships
No full textQuantitative structure–toxicity relationships were developed for the prediction of toxicity to Vibrio fischeri
using the CODESSA treatment. A four-parameter correlation was found for a class of ionic liquids
based on halide. All the descriptors utilized are calculated only from the structures of the molecules,
which makes it possible to predict unavailable or unknown ILs, in gas phase and in water (PCM treatment).
Satisfactory correlations with the same descriptors were found for both cases but the employment
of descriptors calculated in solvent assure a better correlation and a bigger reliability on the foresight
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
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