1,720,958 research outputs found
On the preparation of Langmuir-Blodgett films of pyrrole derivatives
No full textIn this paper, we present a study of the preparation of Langmuir-Blodgett films of polymers obtained on a trough from mixtures made by pyrrole derivatives. In particular, the comparison between films obtained by different molar ratios of 3-hexadecyl-pyrrole to pure pyrrole is shown, in terms of the kinetics of the process and of the compressibility of the products obtained.
Depending on the molar ratio in the composition of the mixtures, differences have been found in the structure of the co-polymer obtained and in the behaviour of the resulting film
An on-trough polymerization study of pyrrole derivatives
No full textn this paper, we present a study of the polymerization of 3-hexadecyl-pyrrole (3HP) and 3-decyl-pyrrole (3DP), performed at the air-liquid interface of a Langmuir trough. In particular, we give data on. the kinetics of the process and on the compressibility of the products obtained. The comparison between the two substances has shown that 3HP is the best in terms of stability and of the quality of the layers formed. An estimation of the polymerization efficiency is given in the case of 3HP.
The UV-Vis-NIR analysis made after the polymerization has shown that oligomers have been formed. This result is comparable with that obtained with a traditional ''bulk'' polymerization. Besides, the examination of the isotherm recorded after the polymerization shows that the polymer obtained with this method is more stable and has a better behaviour than that obtained via the traditional ''bulk'' method
Deposition and characterization of Langmuir-Blodgett films of monomeric and polymeric pyrrole derivatives
No full textIn this Paper we report the deposition and characterization of Langmuir-Blodgett multilayers of pyrrole derivatives in monomeric and polymeric form. The influence of monolayer preparation and deposition conditions, the quality and reproducibility of the multilayers were studied by FTIR, Brewster angle and scanning force microscop
Scanning probe characterization of Langmuir-Blodgett and self-assembled films of pyrrole derivatives
No full textAtomic force microscopy was used to investigate the space molecular organization of Langmuir-Blodgett (LB) and self-assembled (SA) films of pyrrole derivatives on different substrates. The LB films were obtained from monomers of 3-hexadecyl-pyrrole (3HP); the polymerization of the film was performed directly at the air-subphase interface, and the films were collected on hydrophilic glass. Very homogeneous polymeric and monomeric LB films were collected on glass with a transfer rate near unity, the typical average roughness range was 0.9 +/- 0.4 nm, and the quality of films was independent of the dipping speed. A functionalized molecule, 11-(3-pyrrolyl) undecyl mercaptane (3UPSH), was used to modify Ti and TiN electrodes by immersing the substrates in a solution containing the redox active molecule. The modification of the metal surfaces was proved by means of time of flight secondary ion mass spectrometry (TOF SIMS) and AFM characterization
Investigation of the conductivity properties of Langmuir-Blodgett films of pyrrole derivatives
No full textIn this paper, we present conductivity measurements made on Langmuir-Blodgett (LB) polymeric films obtained from pyrrole derivatives (3-hexadecyl-pyrrole and mixtures 3-hexadecyl-pyrrole/pyrrole) and deposited onto interdigitated stuctures designed ad hoc for electrical measurements on planar structures, Step response and voltage vs. current characteristics are reported and discussed, with particular attention to linearity and stability; from these data, the resistivity values of both types of film are derived. The results show that monolayers obtained from the mixtures are by far more conductive (four orders of magnitude) than pure 3-hexadecyl-pyrrole (3HP) multilayers, and that their electrical behaviour can be easily related to a pure Ohmic behaviour, while the 3HP multilayers cannot be considered as pure Ohmic components
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
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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