LES of turbulent surface shear stress and pressure-gradient-driven flow on shallow continental shelves

Turbulent shear flows on shallow continental shelves (here shallow means that the interaction with the solid, no-slip bottom is important) are of great importance because tide- and wind-driven flows on the shelf are drivers of the transfer of momentum, heat, and mass (gas) across the air–sea interface. These turbulent flows play an important role because vertical mixing and current are vectors for the transport of sediment and bioactive material on continental shelves. Understanding the dynamics of this class of flows presents complications because of the presence of a free surface and also because the flow can be driven by a pressure gradient (a tidal current), a stress at the free surface (a wind-driven current), or a combination of both. In addition, the flow can be modified by the presence of a wave field that can induce Langmuir circulation (Langmuir, Science 87:119–123, 1938). Large eddy simulation is used to quantify the effects of pressure gradient and wind shear on the distinctive structures of the turbulent flow. From these computations, an understanding of the physics governing the turbulence of pressure-driven and wind-driven flows, how they can interact in a normal or a tangential direction, and the effect of wave forcing on these flows is obtained.     

The use of radon as tracer in environmental sciences

Radon can be used as a naturally occurring tracer for environmental processes. By means of grab-sampling or continuous monitoring of radon concentration, it is possible to assess several types of dynamic phenomena in air and water. We present a review of the use of radon and its progeny at the University of Cantabria. Radon can be an atmospheric dynamics indicator related with air mass interchange near land-sea discontinuities as well as for the study of vertical variations of air parameters (average values of different types of stability: 131–580 Bq m^?3). Concerning indoor gas, we present some results obtained at Altamira Cave (Spain): from 222 to 6549 Bq m^?3 (Hall) and from 999 to 6697 Bq m^?3 (Paintings Room). Finally, variations of radon concentration in soil (0.3 to 9.1 kBq m^?3) and underground water (values up to 500 Bq l^?1) provide relevant information about different geophysical phenomena.     

Hybrid Model for Urban Air Pollution Forecasting: A Stochastic Spatio-Temporal Approach

Air pollution is usually driven by a complex combination of factors in which meteorology, physical obstacles, and interactions between pollutants play significant roles. Considering the characteristics of urban atmospheric pollution and its consequent impacts on human health and quality of life, forecasting models have emerged as an effective tool to identify and forecast air pollution episodes. The overall objective of the present work is to produce forecasts of pollutant concentrations with high spatio-temporal resolution and to quantify the uncertainty in those forecasts. Therefore, a new approach was developed based on a two-step methodology. Firstly, neural network models were used to generate short-term temporal forecasts based on air pollution and meteorology data. The accuracy of those forecasts was then evaluated against an independent set of historical data. Secondly, local conditional distributions of the observed values with respect to the predicted values were used to perform spatial stochastic simulations for the entire geographic area of interest. With this approach the spatio-temporal dispersion of a pollutant can be predicted, while accounting for both the temporal uncertainty in the forecast (reflecting the neural networks efficiency at each monitoring station) and the spatial uncertainty as revealed by the spatial variograms. Based on an analysis of the results, our proposed method offers a highly promising alternative for the characterization of urban air quality.     

Deterioration processes affecting prehistoric rock art engravings in granite in NW Spain

Prehistoric rock art sites are endangered despite conservation efforts. The lack of scientific documentation regarding weathering agents affecting rock art and the absence of specific diagnostic protocols hinder the development of conservation strategies. The aim of this research was to investigate active deterioration processes in a granite petroglyph site located in Mougás (Galicia, NW Spain) by characterizing the granite, conducting a geotechnical study of the outcrop and describing and analysing the main weathering processes. Two main deterioration factors were identified. First, water favours block disjunction at the massif scale and causes pitting and surface erosion at the millimetre scale that affects the readability of the engravings. Second, high temperatures associated with wildfires cause mineral transformations that increase the susceptibility of the rock to weathering. Identifying deterioration factors is a first step in developing appropriate preventive conservation measures, which should aim to reduce rock contact time with water (technically affordable in the short term) and to reduce the probability of wildfire occurrence (technically more complex and possibly with longer‐term results). Copyright © 2018 John Wiley & Sons, Ltd.     

Response of antioxidant systems to copper in the gills of the clam Ruditapes decussatus

Copper (Cu) is an essential element for biological systems, however, when present in excess, is toxic. Metallothioneins can play an important role in Cu homeostasis and detoxification. Moreover, Cu can catalyse the production of toxic hydroxyl radicals that cause lipid peroxidation but defence systems in the cells can limit the oxidative damage. The present study was performed to investigate the effect of three Cu concentrations (0.5, 2.5 and 25 μg l⁻¹) on the response of antioxidant enzyme activities (superoxide dismutase (SOD), catalase (CAT), selenium-dependent glutathion peroxidase and total glutathion peroxidase), total proteins, metallothioneins (MT), malondialdehyde (MDA) concentrations in the gills of the clam, Ruditapes decussatus. The activity of antioxidant enzymes and total proteins, MT and MDA concentrations were measured in the gills of the clams after 1, 3, 7, 14, 21 and 28 days of Cu exposure. Results indicate that Cu only induces an imbalance in the oxygen metabolism during the first week of Cu exposure due to a decrease in mitochondrial SOD and CAT, selenium-dependent and total glutathion peroxidase activities. Cu also causes lipid peroxidation, measured by the MDA formation, that was Cu dependent. In the gills of clams exposed to 25 μg Cu/l, the excess of Cu triggers the induction of MT synthesis after 3 days of exposure.     

Precision A.C. bridge set for measuring magnetic susceptibility of rocks and its anisotropy

Summary A bridge set for measuring the magnetic susceptibility of rocks and its anisotropy is described. The classical transformer bridge has been supplemented with an auxiliary compensating arm for balancing the bridge without any mechanical infringement of the measuring coils. By employing this principle and the appropriate methods a sensitivityof 4 × 10 ^–8 SI units (3 × 10 ^–9 e.m.u./cm³) has been achieved for a sample of 8 cm³ in volume. In addition to its high sensitivity the device has a considerable accuracy, which makes it suitable for susceptibility anisotropy measurements even of samples with a very low susceptibility and only slight anisotropy. Well-reproducible results have been achieved for samples with a mean susceptibility of the order of10 ^–5 SI units with an anisotropy degree of only about 1.05.Institute of Applied Geophysics.     

Three-dimensional tomographic inversion of the seismic velocity structure of the crust and upper mantle of northwestern Nicaragua

Journal of Seismology - A three-dimensional tomographic image of the seismic velocity structure in the crust and upper mantle of northwestern Nicaragua was performed using the back-projection...     

Entropy‐based equation to assess hillslope sediment production

A new equation to assess hillslope sediment production, based on physical and probabilistic approaches, is presented. The equation, which allows the computation of the delivery ratio for every event, considers the physical variables of travel distance, stream power, settling velocity and gross erosion. The probability density function that arises from the new formulation is solved using the principle of maximum entropy. Based on data from five watersheds in both tropical and temperate zones, the new delivery parameter K_v is calibrated and associated with vegetation cover and conservation practice. The proposed equation is rationally based in relation to parameter K_v. The entropy‐based equation was applied to assess sediment yield in two other experimental watersheds, showing good predictability for the set (mean absolute error of 20·8%). No systematic error was found in the analysed data. The entropy‐based equation showed good predictability for long‐term sets of data and for high‐erosivity events, but did not perform well for the low‐erosivity ones. Copyright © 2007 John Wiley & Sons, Ltd.