1,720,973 research outputs found
Eco-Friendly Aliphatic Polyesters Containing 1,4-Cyclohexane Dicarboxylate Units: Effect of Diol Chain Length on Thermo-Mechanical Properties
No full textAliphatic polyesters containing 1,4-cyclohexylene rings are an interesting class of materials, not yet fully investigated. They potentially have the good characteristics typical of biopolyesters (for example, polyalkylene dicarboxylates and polyhydroxy alkanoates), such as sustainability and biodegradability. Indeed, renewable biomass resources can be used as feedstock to prepare the monomers and some preliminary tests of biodegradation suggest that the aliphatic rings do not hinder the microorganism attack.1 Moreover, the presence of cyclohexyl groups into the main chain provides rigidity to macromolecular chains, raises Tg, and imparts desirable physical-mechanical properties. In this way, the problem of the poor mechanical properties generally found in aliphatic polyesters can be solved. Finally, the 1,4-cyclohexylene unit shows the other remarkable peculiarity that it can have two possible configurations, cis and trans. In a polymer containing the 1,4-cyclohexylene rings, it will suffice to slightly modify the cis/trans isomeric ratio to obtain materials whose phase behavior changes from fully amorphous to semicrystalline.2 Therefore, the final properties of these materials can be easily tailored according to the specific applications.
In this work diols with different chain length were tested as monomers for novel polyesters and the effects of the molecular characteristics on final properties were analyzed
Photodegradation of aliphatic polyesters and their composites with TiO2
No full textDegradability or, on the contrary, durability of polymers are very important features affecting the performances of the materials in their shelf-life and their impact on the environment. The degradation can be due to different environmental factors, including light exposure, very important for polymers used in outdoor applications.
The knowledge of the photo-degradation mechanisms and the possibility to modify them is a very important topic, especially for the novel biopolymers, as their durability with respect to the petro-plastics is yet an open question.
Among the biopolymers aliphatic polyesters are an emerging class of materials, thanks to the possibility of preparing them from renewable resources and their potential environmental degradability. In this study two aliphatic molecular structures, containing 1,4-cyclohexylene units, have been analysed and used as matrixes for composites.
PBCHD and PCCD were exposed to UV irradiation in an accelerated photo-ageing device and the modifications in their chemical structures were analysed by rheology, UV and IR spectroscopies. It results that the photo durability of PBCHD, containing only one cycle per monomeric unit, is higher than that of PCCD.
Moreover, in order to increase the durability, substances can be incorporated into the polymer. Among all the particles and nanoparticles which can be used, titanium dioxide (TiO2) is known for its capability of absorbing UV radiation. This photo-catalytic effect is strictly connected to its crystalline phases.
Therefore, composites containing different amount of TiO2, in the anatase and rutile crystalline phases separately, have been prepared by using a Brabender mixer. The well dispersion of the particles and the good adhesion between TiO2 and polymer have been checked by SEM observations.
The composites result to have a photo stability higher than those of the homopolymers. The protection of TiO2 against the photo-oxidation increases with the particle content and results higher for the anatase crystalline phase.
As a conclusion, a good increment of the photo-durability of the studied aliphatic polyesters has been obtained by preparing composites with titanium oxide. This result could be particularly significant for outdoor applications of these polymers
Photodegradation of aliphatic polyesters and their composites with TiO2
No full textDegradability or, on the contrary, durability of polymers are very important features affecting the performances of the materials in their shelf-life and their impact on the environment. The degradation can be due to different environmental factors, including light exposure, very important for polymers used in outdoor applications.
The knowledge of the photo-degradation mechanisms and the possibility to modify them is a very important topic, especially for the novel biopolymers, as their durability with respect to the petro-plastics is yet an open question.
Among the biopolymers aliphatic polyesters are an emerging class of materials, thanks to the possibility of preparing them from renewable resources and their potential environmental degradability. In this study two aliphatic molecular structures, containing 1,4-cyclohexylene units, have been analysed and used as matrixes for composites.
PBCHD and PCCD were exposed to UV irradiation in an accelerated photo-ageing device and the modifications in their chemical structures were analysed by rheology, UV and IR spectroscopies. It results that the photo durability of PBCHD, containing only one cycle per monomeric unit, is higher than that of PCCD.
Moreover, in order to increase the durability, substances can be incorporated into the polymer. Among all the particles and nanoparticles which can be used, titanium dioxide (TiO2) is known for its capability of absorbing UV radiation. This photo-catalytic effect is strictly connected to its crystalline phases.
Therefore, composites containing different amount of TiO2, in the anatase and rutile crystalline phases separately, have been prepared by using a Brabender mixer. The well dispersion of the particles and the good adhesion between TiO2 and polymer have been checked by SEM observations.
The composites result to have a photo stability higher than those of the homopolymers. The protection of TiO2 against the photo-oxidation increases with the particle content and results higher for the anatase crystalline phase.
As a conclusion, a good increment of the photo-durability of the studied aliphatic polyesters has been obtained by preparing composites with titanium oxide. This result could be particularly significant for outdoor applications of these polymers
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
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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