Reversible click chemistry at the service of macromolecular materials

The application of the reversible Diels-Alder (DA) reaction to the realm of furan polymers has recently bloomed, because of its potential for the preparation of a wide variety of novel macromolecular materials based on renewable resources, possessing, among other properties, thermoreversible, mendable and recycling features. In this study, the synthesis and characterisation of novel furan-maleimide monomers, viz. AB-type molecules, and their polycondensation by means of the DA reaction, are presented. These systems represent an interesting alternative to the traditional linear DA polycondensations, because they ensure the ideal initial stoichiometry. The behaviour of two A-B monomers was investigated with the maleimide group protected in the form of a furan-DA adduct in order to obtain a stable monomer and thus avoid premature polymerization. Their polycondensation was then followed after the in situ deprotection at high temperature, followed by the cooling to the appropriate temperature for the DA polymerization to occur.FCT - SFRH/BD/ 28271/2006REEQ/515/CTM/2005POCI 2010FEDE

Researching YouTube

‘Researching YouTube’ introduces the special issue of Convergence which arose out of an international academic conference on YouTube that was held in London at Middlesex University in September 2016. The conference aimed to generate a robust overview of YouTube’s changing character and significance after its first ten years of development by creating a productive dialogue between speakers from different disciplines and cultures, and between YouTube-specific research and wider debates in media and social research on identity, aesthetics, politics, celebrity, production practices, business models, and research methods in digital culture. This introduction is structured around four themes that help to contextualise the papers that were selected from the many submitted for inclusion in the special issue and offers a substantial overview of the field of research: Participatory Culture and User-Generated Content; YouTube as a Hybrid Commercial Space; Vlogging and YouTube Celebrity; The ‘Mystery’ of the Algorithm and Digital Methods of Research

Regular functions on spherical nilpotent orbits in complex symmetric pairs: Exceptional cases

Given an exceptional simple complex algebraic group G and a symmetric pair (G, K), we study the spherical nilpotent K-orbit closures in the isotropy representation of K. We show that they are all normal except in one case in type G(2), and we compute the K-module structure of the ring of regular functions on their normalizations

The costs of breed reconstruction from cryopreserved material in mammalian livestock species

The aim of this work was to compare costs, in the horse, cattle, sheep, swine, and rabbit species, for the creation of gene banks for reconstruction of an extinct breed, using different strategies: embryos-only, embryos in combination with semen, and semen-only. Three cost measures were used: time required for population reconstruction, cost for creation of the gene bank, number of years-keeping-female to reach reconstruction. Semen costs were estimated across four scenarios: the presence or absence of a commercial market for semen, purchase of semen donors, and semen extracted from the epididymus. The number of cells were doubled to take into account the creation of two storage sites. The strategy embryos-only required the shortest time to reach reconstruction. With the strategy embryos + semen, time increased with decreasing proportions of embryos. With semen-only, reconstruction time varied from 2 to 21 years. A high variation of costs was observed across species and strategies, from 360 Euros in the rabbit to 1 092 300 in the horse. In all species, the embryos-only strategy was about 10% more expensive than using 90% embryos + semen. Decreasing the percentage of embryos further diminished costs. The number of years-keeping-female ranged across strategies, from 2 in the rabbit, to a maximum of 12 878 in the horse

Cambios en la estructura de la comunidad y contenido de carbono orgánico del meio- y macrobentos entre las áreas de planicies de marea y marismas colonizadas por Spartina alterniflora en el Estuario de Bahía Blanca (Atlántico SO)

Salt marshes are regarded as among the most productive coastal ecosystems, important “blue carbon” sinks and a support for benthic communities with large abundances, whose structure may be strongly influenced by salt marsh vegetation. During the last few decades, Spartina alterniflora has been colonizing bare mudflats in the Bahía Blanca estuary, and a large increase in the area covered by salt marshes has been reported. This colonization can strongly influence the structure of benthic fauna and its role in the carbon cycle. The hypothesis of this study was that the community structure and the organic carbon contained in the meio- and macrobenthos change between tidal flats and salt marshes recently colonized by S. alterniflora. Response variables studied to compare the tidal flat and salt marsh were density, biomass and production to biomass (P/B) ratio of macro- and meiobenthos. Density and biomass of Gastropoda and P/B ratio of Nematoda were higher on the salt marsh than on the tidal flat. By contrast, density and biomass of Polychaeta were higher on the tidal flat. These results suggest that the expansion of S. alterniflora marshes on tidal flats produces changes in the structure of the macro- and meiobenthos community (taxonomic composition and biomass) that have an influence on carbon cycling.Las marismas son consideradas uno de los ecosistemas costeros más productivos, importantes sumideros de “carbono azul” y soporte para comunidades bentónicas con grandes abundancias, cuya estructura puede estar fuertemente influenciada por la vegetación de las marismas. Durante las últimas décadas, Spartina alterniflora ha estado colonizando las planicies de mareas sin vegetación en el estuario de Bahía Blanca, reportándose un gran incremento del área cubierta por las marismas. Esta colonización puede influir fuertemente en la estructura de la fauna bentónica y en su rol en el ciclo de carbono. La hipótesis de este estudio fue que la estructura de la comunidad y el carbono orgánico contenido en el meiobentos y macrobentos cambian entre las planicies de marea y las marismas recientemente colonizadas por S. alterniflora. Las variables de respuesta estudiadas para comparar la planicie de marea y la marisma fueron la densidad, biomasa y la relación producción/biomasa (P/B) del macrobentos y meiobentos. La densidad y biomasa de Gastropoda y la relación P/B de Nematoda fueron mayores en la marisma que en la planicie de marea. Por el contrario, la densidad y biomasa de Polychaeta fueron mayores en la planicie de marea. Estos resultados sugieren que la expansión de las marismas de S. alterniflora sobre las planicies de marea genera cambios en la estructura de la comunidad del macrobentos y meiobentos (composición taxonómica y biomasa) que influyen en el ciclo del carbono

Determination of the Hydroxy and Carboxylic Acid Groups in Natural Complex Mixtures of Hydroxy Fatty Acids by (1)H Nuclear Magnetic Resonance Spectroscopy

The use of trichloroacetyl isocyanate (TAI) to mark both hydroxyl and carboxyl groups borne by the hydrolysis or methanolysis of suberin fragments (a complex mixture of hydroxy fatty acids), allowed the quantitative assessment of the ratio between carboxyl and hydroxy groups, as well as the ratio between primary and secondary hydroxy groups, to be carried out reliably by (1)H nuclear magnetic resonance (NMR) spectroscopy. All the samples thus analyzed displayed an excess of CO(2)H (or CO(2)CH(3)) functions with respect to the OH counterparts, albeit to a variable extent, depending on the procedure adopted to isolate the suberin fragments. The precise knowledge of the molar ratio of these two reactive moieties is fundamental for the correct utilization of suberin monomers in polymerization reactions leading to aliphatic polyesters.FCT - SFRH/ BD/38890/200

Progress in the synthesis of sustainable polymers from terpenes and terpenoids

The imminent depletion of resources derived from fossil fuels is a major concern for today’s society. 300 Mt of polymers are used every year in the form of plastics, most commonly derived from fossil fuels, hence the necessity to find new materials based on renewable resources. This review explores the utilisation of monoterpenes and terpenoids – a family of abundant and inexpensive natural products – as promising renewable monomers. Terpenes can be directly used in polymerisations or converted into bespoke monomers through organic transformations. The use of terpenes for the production of renewable plastics has been a prevalent topic of research for the past few decades. Early research focused on cationic polymerisation of terpenes by way of their alkene moieties; however, more recently terpenes are being functionalised to incorporate handles for a larger range of polymerisation techniques. Herein an assessment of the future prospects for the use of these small functional molecules to synthesise novel and valuable renewable materials is presented

Spherical orbit closures in simple projective spaces and their normalizations

Let G be a simply connected semisimple algebraic group over an algebraically closed field k of characteristic 0 and let V be a rational simple G-module of finite dimension. If G/H \subset P(V) is a spherical orbit and if X is its closure, then we describe the orbits of X and those of its normalization. If moreover the wonderful completion of G/H is strict, then we give necessary and sufficient combinatorial conditions so that the normalization morphism is a homeomorphism. Such conditions are trivially fulfilled if G is simply laced or if H is a symmetric subgroup.Comment: 24 pages, LaTeX. v4: Final version, to appear in Transformation Groups. Simplified some proofs and corrected minor mistakes, added references. v3: major changes due to a mistake in previous version

Cork suberin as an additive in offset lithographic printing inks

Suberin oligomers, isolated from cork (Quercus suber L.), were used as additives in ‘Waterless’ and vegetable-oil ink formulations, in the range of 2–10% w/w. The rheological behaviour of the suberin oligomers as well as of the inks, with and without suberin, were investigated as a function of temperature. It was shown that the addition of suberin induces a decrease of viscosity of both inks. The tack of pristine inks, suberin oligomers and their mixtures were determined at different temperatures: the variation of this parameter as a function of time provided information about the drying kinetics of these formulations. The tack of the ‘Waterless’ ink was found to increase with the introduction of suberin, whereas that of vegetable-oil based counterparts decreased. All the trends observed were interpreted in terms of the differences in composition between the two types of inks. Preliminary printing tests were carried out with the various suberin-containing inks.info:eu-repo/semantics/publishedVersio