1,721,018 research outputs found
Nanomaterials in sun-care products
No full textThe increased incidence of melanoma and other skin diseases induced by excessive sun exposure has led dermatologists to recommend a daily use of sunscreens to consumers. Interestingly, in the last few years, the formulation technology of these products has begun to employ nanomaterials to improve photoprotection and esthetic pleasantness. So, this chapter, among sunscreens, focuses the attention on the use of nanosunscreens, in particular, toward nano-TiO2 and nano-ZnO, taking into consideration their effectiveness and safety. In the first section of this chapter, an overview about sunscreens opens the discussion presenting their role, distinguishing them as organic and inorganic filters, giving information about their regulatory status. The sun protection factor and the characteristic of light are also defined. In the second section, the definition and use of nanomaterials in cosmetics, especially in sun-care products, their regulatory status, and nanotoxicology are deeply discussed
The Suzuki-Heck polymerisation as a tool for the straightforward obtainment of poly(fluorenylene-vinylene) sensitisers for DSSCs
No full textThis article describes the synthesis and properties
of the first poly(arylene-vinylene)-based sensitizers for application
in dye-sensitized solar cells (DSSC). The polymers were
prepared by the Suzuki–Heck copolymerization of potassium
vinyltrifluoroborate (PVTB) with a mixture of dibromoaryl
comonomers designed to obtain macromolecules able to bind
onto the photoelectrode by means of carboxyphenylene units.
The copolymerization reactions were carried out in the presence
of an excess of PVTB to lower the molecular weights of
the polymers, which were obtained as soluble materials. The
polymers poly[(9,9-didodecyl-2,7-fluorenylene)-vinylene-co-(carboxy-
2,5-phenylene)-vinylene] (P1), poly[(9,9-didodecyl-2,7-fluorenylene)-
vinylene-co-(carboxy-2,5-phenylene)-vinylene-co-(4,7-
benzothiadiazolylene)-vinylene] (P2), and poly[(9,9-didodecyl-
2,7-fluorenylene)-vinylene-co-(carboxy-2,5-phenylene)-vinyleneco-
2,5-thienylene-vinylene] (P3) were used in DSSC devices,
obtaining conversion efficiencies up to 0.88% (P3)
Random Poly(fluorenylene-vinylene)s Containing 3,7-Dibenzothiophene-5,5-dioxide Units: Synthesis, Photophysical, and Electroluminescence Properties
No full textThe synthesis of new random poly(arylene-vinylene)s containing the electron withdrawing 3,7-dibenzothiophene-5,5-dioxide unit was achieved by the Suzuki-Heck cascade polymerization reaction. The properties of poly[9,9-bis(2-ethylhexyl)-2,7-fluorenylene-vinylene-co-3,7-dibenzothiophene-5,5-dioxide-vinylene] (50/50 mol/mol, P1) and poly[1,4-bis(2-ethylhexyloxy)-2,5-phenylene-vinylene-co-3,7-dibenzothiophene-5,5-dioxide-vinylene] (50/50 mol/mol, P2) were compared with those of terpolymers obtained by combining the fluorene, dibenzothiophene, and 1,4-bis(2-ethylexyloxy)benzene in 20/40/40 (P3), 50/25/25 (P4), and 80/10/10 (P5) molar ratios. The polymers were characterized by (1)H NMR and IR, whereas their thermal properties were investigated by TGA and DSC. Polymers P1-5 are blue-green emitters in solution (lambda(em) between 481 and 521 nm) whereas a profound red shift observed in the solid state is emission (lambda(em) from 578 to 608 nm) that can be attributed both to the charge transfer stabilization exerted by the polar medium and to intermolecular interactions occurring in the solid state. Cyclic voltammetry permitted the evaluation of the ionization potentials and also revealed a quasi-reversible behavior in the reduction scans for the polymers (P1-4) containing the higher amounts of 3,7-dibenzothiophene-5,5-dioxide units. Electroluminescent devices with both ITO/PEDOT-PSS/P1-5/Ca/Al (Type 1) and ITO/PEDOT-PSS/P1-5/Alq(3)/Ca/Al (Type 11) configuration were fabricated showing a yellow to yellow-green emission. In the case of P4, a luminance of 1835 cd/m(2) and an efficiency of 0.25 cd/A at 14 V were obtained for the Type II devices. (C) 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2093-2104, 200
Single Step Plasma Deposition of Platinum-Fluorocarbon Nanocomposite Films as Electrocatalysts of Interest for Micro Fuel Cells Technology
No full textIn this paper, we present a one step plasma based approach for the deposition of Pt-fluorocarbon nanocomposite films as electrocatalysts in hydrogen-based micro fuel cells. Results show that the chemical and morphological structure of the film can be tuned by controlling the power delivered to the plasma, and the gas feed composition. Platinum is included in the film in metallic form and its content can be continuously varied from a few atomic percent to 86%. The metal is embedded in the film as crystalline nanoclusters of size below 10 nm, uniformly distributed across the sample. Film catalytic activity, in terms of hydrogen oxidation reaction, has been tested by cyclovoltammetry and it increases with the Pt loading, with a maximum specific electrochemical surface area of 94cm2 · mg-1, for film deposited on flat glassy carbon
Chlorophyll a/fullerene C60 blends assembled at the air-water interface as artificial photosynthetic systems
No full text
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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