Correlation between SERS of Pyridine and Electrochemical Response of Silver Electrodes in Halide-Free Alkaline Solutions

Surface-enhanced Raman scattering (SERS) of pyridine (Py) on Ag electrodes in alkaline solutions free of halide ions was obtained at 25°C as a function of the applied potential. The Ag surface was activated for SERS through repetitive oxidation-reduction cycles (ORC), the effect being dependent on the electrochemical electrode history. The SERS effect was correlated to the activation for the hydrogen evolution reaction (HER), which can be obtained by means of potentiodynamic as well as potentiostatic procedures. The maximum SERS activity was achieved at potentials near the potential of zero charge (pzc) of polycrystalline Ag and appeared to be related to the maximum observed in the roughness factor vs potential curve. These results can be interpreted through the formation of a new uniform globular overlayer structure on the electroreduced Ag surface, which apparently exhibits a certain degree of preferred crystallographic orientation. Three well-defined potential regions can be distinguished for the complex competitive interactions between H2O, OH- ion, and Py with the new Ag electrode surface.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

The contribution of meteorological parameters and the COVID-19 partial lockdown on air quality in Rio de Janeiro, Brazil

This study evaluated the pollutant levels (NO2, SO2, CO, and O3), air quality index (AQI) and the influence of meteorological variables and coronavirus disease (COVID-19) pandemic on the air quality in Rio de Janeiro. The data set used comprises periods before (March-April, 2019) and during pandemic (March-April, 2020). According to the AQI results, on most days, the air quality was ranked as “good”. Brazilian air quality standards for SO2, O3, and NO2 were not exceeded in any of the monitoring stations during partial lockdown, while CO exceeded in all periods in one site due to industrial emission. Comparing both periods, descriptive statistics for the meteorological parameters presented no differences, which suggests similar conditions. However, when evaluated week by week in 2020, weather conditions presented some differences that probably affected pollutant concentrations. The correlations between O3 and NO2 and some meteorological parameters indicate that variations in both favored ozone formation, since it is a photochemical process favored by temperature and solar radiation and that, in Rio de Janeiro, low NO2 concentrations lead to increased O3. The improvements on air quality during the partial lockdown may be attributed mainly to a reduction on emission sources rather than weather conditions.Campus Lima Centr

Viscous behaviour around an underground opening in a two-phase medium

the results of a numerical study are presented for an unlined circular opening in a homogeueous, isotropic, two-phase medium. The solid phase is assumed to behave according to a visco-plastic rheological model which allows for primary, secondary and tertiary creep behaviour. For the liquid phase the classical diffusion (consolidation) equations based on Darcy's law are considered

Finite element analysis of free surface seepage flows

The analysis of unconfined seepage flows is often required in geotechnical engineering, for instance when dealing with the design of earth dams, with the stability analysis of natural slopes, etc. They belong to the class of boundary value problems involving differential equations on a domain part of whose boundaries is unknown and has to be determined, together with the distribution of hydraulic head, as part of the solution. In the paper the equations governing the seepage flows, and the relevant boundary conditions, are first recalled both for the continuum problem and for its finite element discretization. Then, some variable and fixed mesh procedures for steady state and transient analyses are outlined. Some comments are also presented on solution approaches based on the so called "conformal mapping" technique. Finally the sources of instability which might affect the variable mesh approaches are discussed and a procedure is discussed aimed at avoiding these negative effects

Back analysis of geotechnical problems

Some back analysis techniques applicable in geotechnical engineering are summarised, considering both their deterministic and probabilistic aspects. The discussion is limited to static conditions. First, two alternative back analysis approaches are described, in a deterministic context, referred to as "direct" and "inverse" techniques. Subsequently, a probabilistic Bayesian technique is discussed which aims at investigating the influence of the experimental errors on the results of back calculations. Finally, two appli-cations to actual tunnelling problems are summarised

Gallerie in roccia spingente: effetto del fronte sulla ridistribuzione tensionale

Nel seguito vengono illustrati alcuni aspetti dell'analisi a ritroso in ingegneria geotecnica basando la discussione suI metoda degli elementi finiti e limitandola a problemi in regime statico