Four-dimensional electrical resistivity imaging for monitoring pumping-induced saltwater intrusion in a coastal aquifer.

Conventional views of saltwater intrusion (SWI), where a basal saline wedge extends inland below fresh groundwater, can be complicated by the influence of saltwater cells in the upper part of aquifers in areas affected by tidal cycles. Distinguishing the contribution of each saltwater source may prove fundamental for well design and resource management. Application of time-lapse electrical resistivity imaging (ERI) during a 32-h pumping test in a pristine unconfined coastal sand aquifer, affected by strong tidal ranges (>2 m), aimed to evaluate the potential of the method to characterize the source of induced SWI in four dimensions (three dimensions and time). Water level monitoring during the test revealed that at the end of pumping, the upper 2 m of the aquifer had dewatered in the vicinity of the well field, reversing hydraulic gradients between the aquifer and the sea. This induced SI, with mixing models of well head water quality suggesting that saline water contributions to total discharge rose from 4 % to 8 %. ERI results reflected dewatering through an increase in resistivity in the upper 2-6 m of the aquifer, while a decline in resistivity, relative to background conditions, occurred immediately below this, reflecting the migration of saline water through the upper layers of the aquifer to the pumping well. By contrast no change in resistivity occurred at depth, indicating no significant change in contribution from the basal saline water to discharge. Test findings suggest that future water resource development at the site should focus on close monitoring of shallow pumping, or pumping from deeper parts of the aquifer, while more generally demonstrating the value of time-lapse geophysical methods in informing coastal water resource management.

Atomic-Scale Model and Electronic Structure of Cu2O/CH3NH3PbI3 Interfaces in Perovskite Solar Cells.

Cuprous oxide has been conceived as a potential alternative to traditional organic hole-transport layers in hybrid halide perovskite-based solar cells. Device simulations predict record efficiencies using this semiconductor, but experimental results do not yet show this trend. More detailed knowledge about the Cu2O/perovskite interface is mandatory to improve the photoconversion efficiency. Using density functional theory calculations, here, we study the interfaces of CH3NH3PbI3 with Cu2O to assess their influence on device performance. Several atomistic models of these interfaces are provided for the first time, considering different compositions of the interface atomic planes. The interface electronic properties are discussed on the basis of the optimal theoretical situation, but in connection with the experimental realizations and device simulations. It is shown that the formation of vacancies in the Cu2O terminating planes is essential to eliminate dangling bonds and trap states. The four interface models that fulfill this condition present a band alignment favorable for photovoltaic conversion. Energy of adhesion and charge transfer across the interfaces are also studied. The termination of CH3NH3PbI3 in PbI2 atomic planes seems optimal to maximize the photoconversion efficiency.

Band Alignment of the CuGaS2 Chalcopyrite Interfaces Studied by First-Principles Calculations.

The valence and conduction band offsets for both polar and nonpolar CuGaS2/CuAlSe2 and CuGaS2/ZnSe interfaces were studied here by the state-of-the-art first-principles calculations. Using the hybrid functional calculations, we show that the CuGaS2/CuAlSe2 and CuGaS2/ZnSe heterostructures in all interfaces form type II band alignment. The difference of valence and conduction band offsets is mainly due to lattice mismatch, generating stress in the interface and affecting the electronic properties of each material; meanwhile, the polarity configuration does not play an important role in these values. From the local density of states and the charge density, we can determine how the nature of the band alignments changes when the semiconductor conforms to each interface. This allows us to localize the electrons and holes at different sites of the interface.

Técnicas de imagen para el estudio de la recuperación funcional tras el ictus: I. Aspectos metodológicos / Imaging techniques for studying functional recovery following a stroke: I. Methodological aspects

Resumen. Muchos pacientes que sobreviven a un ictus se enfrentan a serias discapacidades funcionales durante el resto de sus vidas, lo que supone un drama personal para sí mismos y para sus allegados, y un elevado coste para la sociedad. Por ello, la recuperación funcional del sujeto tras el ictus debería ser un objetivo esencial que se debería considerar en el desarrollo de nuevas aproximaciones terapéuticas. En esta serie de dos trabajos, revisamos las estrategias y herramientas disponibles hoy en día para la evaluación de múltiples aspectos relacionados con la función cerebral (tanto en humanos como en animales de experimentación), y que están ayudando a los neurocientíficos a entender mejor los procesos de restauración y reorganización de la función cerebral que se inician tras un ictus. Hemos puesto especial énfasis en las aplicaciones de la resonancia magnética, probablemente la técnica de neuroimagen más versátil disponible hoy en día, y que aún no ha dejado de evolucionar y proporcionar nuevas y excitantes aplicaciones. Pero también abordamos otras técnicas alternativas y complementarias, puesto que una aproximación multidisciplinar proporciona una perspectiva más completa de los mecanismos que subyacen bajo los mecanismos de reparación tisular, de reorganización plástica del cerebro, y de los compensatorios que se desencadenan tras un ictus. El primer trabajo de esta serie se centra en aspectos metodológicos que nos ayudarán a comprender cómo es posible caracterizar la función cerebral basándonos en diferentes principios físicos y fisiológicos. El segundo trabajo se centrará en técnicas complementarias y en diversos aspectos prácticos relacionados con la aplicación de las técnicas aquí comentadas (AU)

Summary. Many patients that survive stroke have to face serious functional disabilities for the rest of their lives, which is a personal drama for themselves and their relatives, and an elevated charge for society. Thus functional recovery following stroke should be a key objective for the development of new therapeutic approaches. In this series of two works we review the strategies and tools available nowadays for the evaluation of multiple aspects related to brain function (both in humans and research animals), and how they are helping neuroscientist to better understand the processes of restoration and reorganization of brain function that are triggered following stroke. We have mainly focused on magnetic resonance applications, probably the most versatile neuroimaging technique available nowadays, and that everyday surprises us with new and exciting applications. But we tackle other alternative and complementary techniques, since a multidisciplinary approach allows a wider perspective over the underlying mechanisms behind tissue repair, plastic reorganization of the brain and compensatory mechanisms that are triggered after stroke. The first of the works of this series is focused on methodological aspects that will help us to understand how it is possible to assess brain function based on different physical and physiological principles. In the second work we will focus on different practical issues related to the application of the techniques here discussed (AU)