No abstract

Magnetic resonance imaging (MRI) has proven to be a powerful tool for the characterization and investigation of in situ chemical reactions. This is more relevant when dealing with complex systems, where the spatial distribution of the species, partition equilibrium, flow patterns, among other factors have a determining effect over mass transport and therefore over the reaction rate. The advantage of MRI is that it provides spatial information in a noninvasive way and does not require any molecular sensor or sample extraction. In this work, MRI is used to fully characterize an electrochemical reaction under forced hydrodynamic conditions. Reaction rates, flow patterns, and quantitative concentration of the chemical species involved are spatially monitored in situ in a complex system that involves metallic pieces and a heterogeneous cementation reaction. Experimental data are compared with numerical simulations.

In this paper, multiannual periodicities in the historical time-series average annual streamflows discharges of 14 rivers of Argentina and in ten macroclimatic indicators are identified using spectral analysis. The estimation of dominant frequencies of the analyzed time series allows to understand the time scale of the processes involved in the hydrological cycles. The spectral analysis found that high, low and medium frequency fluctuations contribute, in different percentages, to the flow variability. Then, this results have been compared with results of similar analysis performed on time series of macro-climatic indicators to calculate the relation of the evolution of these indicators with streamflows discharge series. These results constitute an important step toward implementing conceptual and forecasting models of deficit and excess of surface water in fluvial system for planning and management of the water resources.