Continuous autonomous measurement of total dissolved inorganic carbon (TCO2) in the oceans is critical for climate change modelling and ocean acidification measurement. A microfluidic conductivity-based approach will permit integration of miniaturised chemical analysis systems into Argo ocean floats, for long-term, high-accuracy depth profiling of dissolved CO2 with minimal reagent payload. Precise metering, suitable for sample acidification and CO2 liberation, is addressed. Laser etched microfluidic snake channel restrictors and asymmetric Y-meters were fabricated, with channel dimensions down to ∼75 μm, to adjust metering ratios between seawater and acid simulants. Hydrodynamic resistances, from flow versus pressure measurements, were compared with finite element simulations for various cross-section profiles and areas. Microfluidic metering circuits were constructed from various resistance snake channels and Y-junction components. Sample to acid volume ratios (meter ratio) up to 100:1 have been achieved with 300 μm wide snake channels for lengths >m. At highest resolution, the footprint would be >600 mm2. Circuits based solely on asymmetric Y-junctions gave maximum meter ratios of 16:1 with a footprint of <40 mm2 and ∼0.2% precision. Further refinement is required to ensure the integrity of such small channels in integration of metering units into full TCO2 analysis microfluidic circuits.

A B S T R A C TThe objective of this research was to identify and quantify the primary processes responsible for the increase in salinity observed in the alluvial aquifer during the dry season. Multivariate statistical analysis and inverse geochemical modeling were used to simulate possible salinization mechanisms in the alluvial aquifer. For this, by quantifying electrical conductivity and the concentrations of the ions Ca 2+ , Mg 2+ , Na + , K + , Cl -, HCO 3 -and SO 4 2-in waters from the crystalline basement near the study area, water reservoirs near the alluvial aquifer and the studied alluvial aquifer, groups were formed and discriminant analysis was applied. Significance tests showed that direct evaporation has not only an influence on the alluvial aquifer, but also a mean volumetric contribution of 15.8% from waters of the crystalline basement, accompanied by processes of salt dissolution and precipitation, which would also justify the increase in salinity observed in the alluvial aquifer in the dry period.Mecanismos de salinização de um pequeno aquífero aluvial localizado no semiárido do Nordeste brasileiro R E S U M O Com o objetivo de identificar e quantificar os principais processos responsáveis pelo aumento da salinidade observada durante o período não chuvoso em um pequeno aquífero aluvial localizado no semiárido do Nordeste brasileiro utilizaram-se a análise estatística multivariada e a modelagem geoquímica inversa para simular prováveis mecanismos de salinização no aquífero; para isto e por meio da quantificação da condutividade elétrica e dos íons Ca 2+ , Mg 2+ , Na + , K + , Cl -, HCO 3 -e SO 4 2-em amostras de águas do embasamento cristalino próximo à área de estudo, nos reservatórios próximos ao aquífero aluvial e do aquífero aluvial estudado, foram formados grupos e aplicada a análise discriminante. Testes de significância dos resultados demonstraram que a evaporação direta não apenas exerce influência sobre o aquífero aluvial mas ainda tem uma contribuição volumétrica média de 15,8% de águas do cristalino acompanhada de processos de dissolução e precipitação de sais, o que também justificaria o aumento da salinidade no aquífero aluvial no período seco.

The use of windmills for the pumping of well water has appeared economically feasible in regions with average winds above 5 m/s, and when the water is used for human consumption and irrigation in arid rural zones, the importance of extracting the water from these wells efficiently and sustainably becomes more evident. However, concerning the state of Ceará/Brazil, only 18% of the drilled wells are freshwater wells, thus requiring additional energy for the utilization of desalination systems such as reverse osmosis. For that, the correct sizing of the pumping system associated with water desalination systems is essential, bearing in mind that the knowledge of the performance curves of the windmills, usually associated with piston pumps, is the "key factor" of the project. A brief analysis of the literature and websites of windmill suppliers shows that the performance curves of windmills associated with piston pumps are scarce, and the procedure to obtain them is not clear. This work's novelty is to use the windmill's power coefficient curve in association with the piston pumps to obtain the windpump performance curves, as pressure head versus volumetric flow rate in different wind conditions and sizes of windmills. The obtained curves were compared with other two curves found in the literature: one in a supplier's catalog and another from the "rule of thumb". The results showed a considerable divergence when calculating the root mean square deviation: 43.73% in relation to the supplier data average, and 125.76% in relation to the rule of thumb average results; however, the model proposed herein presented a limited operational range, which was not verified in the other two curves, which reproduced unlimited machines in terms of provided pressure head and flow rate. The unreal and asymptotic characteristics are more evident in the curves obtained by the rule of thumb, where the differences are also greater (125.76%) in relation to the proposed model. In terms of freshwater production, the model proposed herein reached, with an average wind speed of 6.5 m/s, and with a windmill of 6.1 m in diameter, a flow rate of up to 9.1 m 3 /day, after going through the reverse osmosis system. The same condition with the rule of thumb's model reached a flow rate of up to 11.3 m 3 /day. Finally, the model proposed herein for obtaining windmill's performance curves proved to be easy to implement and with realistic results, becoming an important design tool.

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