1,721,019 research outputs found
Influence of monolayer state on spectroscopy and photoisomerization of an amphiphilic styryl-pyridinium dye on a solid substrate
No full textThe spectroscopy and photochromic properties of transferred monolayers of the amphiphilic styryl-pyridinium dye 4-(3',4'-dimethoxystyryl)-N-octadecylpyridinium perchlorate (DMPOP) were studied at different conditions during their transfer. The emission maxima of the monolayers transferred from the air-water interface in the liquid-expanded phase are strongly dependent on the surface pressure applied during the transfer process, even at values when the area per molecule is 2-3 times larger than the area occupied by a chromophore. In monolayers transferred from the liquid-condensed phase, the presence of a different kind of aggregates was observed. The fluorescence emission properties of the monolayers can be reversibly modulated by photoinduced E-Z isomerization. A blue shift up to 72 nm in the emission maximum, depending on the transfer conditions of the films, can be obtained by irradiation with blue light, and partially recovered (a red shift of up to 26 nm) with UV radiation. The rate at which the first process (E -> Z) takes place is drastically reduced in monolayers transferred from the liquid-condensed phase as compared to those transferred from the liquid-expanded one. However, the rate of the reverse reaction (Z -> E) is not significantly altered. These properties make DMPOP a promising material for the preparation of Langmuir-Blodgett films, whose properties can be effectively controlled by the transfer conditions and subsequently optically modulated, for potential applications as photonics devices for data storage
Molecular organization of an amphiphilic styryl pyridinium dye in monolayers at the air/water interface in the presence of various anions
No full textAmphiphilic 4-(3',4'-dimethoxystyryl)-N-octadecylpyridinium perchlorate and bromide form stable monolayers at the air/water interface. Small differences in the surface pressure-area and Surface potential-area isotherms depending on the anion indicate interactions between the chromophore and the anions on the pure water subphase. The monolayer behavior is considerably modified on 10 mM aqueous solutions of KI, KClO4, KCl, and KF as revealed by isotherm measurements, reflection spectroscopy, and Brewster angle microscopy. The phase transition observed in the isotherms is shifted to higher surface pressure because of variation of the salt according to the Hofmeister series. Upon monolayer compression, the chromophores are increasingly tilted, and a shift of the band to longer wavelengths is attributed to the environment becoming less polar. However, in the case of KCl at small areas per molecule, relaxation is observed at constant area with the appearance of a new band shifted to shorter wavelengths. This band is assigned to small associates of about four chromophores (H aggregates). In the case of KI, a new band shifted to longer wavelengths is found. Theoretical calculations did not yield a transition in the observed range, even for large aggregates (J aggregates). Therefore, other interactions may be responsible for the appearance of this band
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Spectroscopic properties of an amphiphilic styryl pyridinium dye in Langmuir-Blodgett films
No full textSurface pressure-molecular area and surface potential-molecular area isotherms of the recently synthesized amphiphilic dye 1 indicate that it forms monolayers on distilled water. A shift of the fluorescence maximum from 505 up to 570 nm was measured upon increasing the surface pressure applied during the Langmuir-Blodgett transfer from 7 up to 20 mN/m, and a slight red shift in the absorption. The increase of the surface pressure also produces a new blue-shifted band only present in the p-polarized component of the absorption spectra under oblique incidence of light. The results were interpreted as reorientation and association of the chromophores in the monolayer, according to the extended dipole model
Variations on the Author
Get PDF“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
Get PDFWe 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
Get PDFWe 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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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