Contact angle of a hemispherical bubble: an analytical approach

We have calculated the equilibrium shape of the axially symmetric Plateau border along which a spherical bubble contacts a flat wall, by analytically integrating Laplace’s equation in the presence of gravity, in the limit of small Plateau border sizes. This method has the advantage that it provides closed-form expressions for the positions and orientations of the Plateau border surfaces. Results are in very good overall agreement with those obtained from a numerical solution procedure, and are consistent with experimental data. In particular we find that the effect of gravity on Plateau border shape is relatively small for typical bubble sizes, leading to a widening of the Plateau border for sessile bubbles and to a narrowing for pendant bubbles. The contact angle of the bubble is found to depend even more weakly on gravity

Nonequilibrium stationary states of 3D self-gravitating systems

Three dimensional self-gravitating systems do not evolve to thermodynamic equilibrium, but become trapped in nonequilibrium quasistationary states. In this Letter we present a theory which allows us to a priori predict the particle distribution in a final quasistationary state to which a self-gravitating system will evolve from an initial condition which is isotropic in particle velocities and satisfies a virial constraint 2K=-U, where K is the total kinetic energy and U is the potential energy of the system

Synthesis of new azole phosphonate precursors for fuel cells proton exchange membranes

Herein we present the synthesis and characterization of new phosphonate-, bisphosphonate- and hydroxybisphosphonatebenzimidazole derivatives substituted at the N-1 position and new regioisomers phosphonate-, bisphosphonate-, and hydroxybisphosphonatebenzotriazole derivatives substituted at N-1 or N-2 positions. The compounds were characterized by NMR and IR spectroscopies, and mass spectrometry (low and high resolution) allowing the assignment of their structure, including the identification of regioisomers. These new azole monomers will be precursors for a mesoporous silica host to produce novel membrane materials with high proton conductivity for intermediate temperature proton exchange membrane fuel cells

New proton conductive membranes of indazole- and condensed pyrazolebisphosphonic acid-Nafion membranes for PEMFC

ABSTRACT: The global demands of energy are still increasing alongside many civilizational problems, notably the effects on the environment due to the overuse of traditional energy sources based on fossil fuels. New cleaner, renewable sources for sustainable energy systems are a key challenge of the 21st century society.N/

Chemical stability of new nafion membranes doped with bisphosphonic acids under Fenton oxidative conditions

ABSTRACT: The development of new proton exchange membranes for PEM technology in fuel cells and electrolysers with increased durability is paramount to system's lifetime and scalability. In this work, new modified Nafion membranes doped with bisphosphonic acids are proposed with increased resilience to chemical degradation by H2O2/Fe2+, mimicking ex-situ radical attack to membrane structure. Relevant properties were evaluated throughout Fenton's test using fluoride ion release and gravimetry determinations, and by ATR-FTIR spectros-copy and SEM before and after the chemical degradation. The new membranes showed a very good chemical stability after oxidative degradation under Fenton's test conditions at 80 degrees C, with more durability than Nafion 115 commercial membrane. After chemical degradation, the proton conduction of the membranes was assessed through EIS which reveals a decrease in the proton conductivity of all membranes, with the new modified membranes showing a smaller decrease of their proton conduction properties than Nafion 115 membrane. Fluoride ion release, weight loss measurements and ATR-FTIR spectros-copy data analysis suggest degradation of the side chain of the ionomer.info:eu-repo/semantics/publishedVersio

New proton conductive membranes of indazole- and condensed pyrazolebisphosphonic acid-Nafion membranes for PEMFC

ABSTRACT: In this work, new doped Nafion membranes for PEMFC are prepared by casting with 1 wt% loading of the prepared indazole- and condensed pyrazolebisphosphonic acids (AzBPs). The new membranes were analysed by ATR-FTIR spectroscopy and their morphology was examined by SEM. Membranes were evaluated for water uptake and ion exchange capacity (IEC), and their hydration number was estimated. The proton conduction properties of the modified membranes were evaluated by electrochemical impedance spectroscopy (EIS), at different temperatures (30, 40, 50 and 60 °C) and relative humidity (RH) (40, 60 and 80%). The proton conductivities of all membranes increase with increasing temperature and RH. Also, all new membranes doped with AzBPs exhibited higher proton conductivities than Nafion N-115, used as a reference and tested at the same experimental conditions, with values up to 1.5-fold. Results show that the incorporation of AzBPs dopants on Nafion membranes enhances the proton conduction throughout the modified membranes. The best proton conductivity was observed for membranes with AzBP1 as dopant, with a value of 94 mS cm-1. These results indicate that the Nafion membranes doped with indazole- and condensed pyrazolebisphosphonic acids are a promising approach for new membranes for PEMFC with improved proton conductivity.info:eu-repo/semantics/publishedVersio

Disc Clearing of Young Stellar Objects: Evidence for Fast Inside-out Dispersal

The time-scale over which and the modality by which young stellar objects (YSOs) disperse their circumstellar discs dramatically influences the eventual formation and evolution of planetary systems. By means of extensive radiative transfer (RT) modelling, we have developed a new set of diagnostic diagrams in the infrared colour-colour plane (K-[24] vs. K-[8]), to aid with the classification of the evolutionary stage of YSOs from photometric observations. Our diagrams allow the differentiation of sources with unevolved (primordial) discs from those evolving according to different clearing scenarios (e.g. homologous depletion vs. inside-out dispersal), as well as from sources that have already lost their disc. Classification of over 1500 sources in 15 nearby star-forming regions reveals that approximately 39 % of the sources lie in the primordial disc region, whereas between 31 % and 32 % disperse from the inside-out and up to 22 % of the sources have already lost their disc. Less than 2 % of the objects in our sample lie in the homogeneous draining regime. Time-scales for the transition phase are estimated to be typically a few 10^5 years independent of stellar mass. Therefore, regardless of spectral type, we conclude that currently available infrared photometric surveys point to fast (of order 10 % of the global disc lifetime) inside-out clearing as the preferred mode of disc dispersal.Comment: 31 pages, 21 figures, 6 tables, accepted for publication in MNRA

Determinants of political trust during the early months of the COVID-19 pandemic: Putting policy performance into evidence

Basing on the previous and early months of the Covid-19 pandemic, this article analysis the main determinants of citizens’ trust in the prime minister over this period. Prior research on the political effects of the pandemic has mostly focused on identifying a rally around the flag effect, and little is known about other reasons behind the increase in trust after the outbreak of the pandemic. Based on survey data from February to July 2020 for Spanish citizens, we argue that the reasons for the increased trust in the prime minister after the pandemic outbreak are due more to performance evaluations than to emotional-related factors regarding Covid-19 health issues. We also argue that among performance evaluations, the assessment of policy performance in fighting the Covid-19 crisis is of preeminent relevance in explaining trust in the prime minister during the pandemic period. Findings widely support our argument. By comparing the effects of conventional to emotional-related factors we extend scholarship on political trust in the context of an exogenous crisis.info:eu-repo/semantics/acceptedVersio

Parties and political representation

How has the topic of representation been studied empirically in Portugal? Which main results have been reached? This chapter focuses on the party-voter linkage, and aims at mapping the study of party representation in Portugal. On the one hand, we systematize the most relevant research contributions on the topic; on the other hand, we update and consolidate the findings on the most important trends that have been identified so far. The analysis comprises four main lines of research studies on the subject in Portugal: on political and ideological congruence; on promises fulfilment; on political agendas; and on roles of representation. The general conclusion, aligned with the findings of the international research, is that there is a prevalence of reasonable and quite stable levels of correspondence between parties and electorates.info:eu-repo/semantics/acceptedVersio

Microbiological quality of Portuguese yogurts

The microbiological quality of four brands of natural yogurts and two probiotic yogurts available in the Portuguese market, was evaluated during the shelf-life period. Although the specific flora decreased during storage it was always within the range of recommended values. No coliforms and an insignificant number of fungi were detected