An approach for valid covariance estimation via the Fourier series

The use of kriging for construction of prediction or risk maps requires estimating the dependence structure of the random process, which can be addressed through the approximation of the covariance function. The nonparametric estimators used for the latter aim are not necessarily valid to solve the kriging system, since the positive-definiteness condition of the covariance estimator typically fails. The usage of a parametric covariance instead may be attractive at first because of its simplicity, although it may be affected by misspecification. An alternative is suggested in this paper to obtain a valid covariance from a nonparametric estimator through the Fourier series tool, which involves two issues: estimation of the Fourier coefficients and selection of the truncation point to determine the number of terms in the Fourier expansion. Numerical studies for simulated data have been conducted to illustrate the performance of this approach. In addition, an application to a real environmental data set is included, related to the presence of nitrate in groundwater in Beja District (Portugal), so that pollution maps of the region are generated by solving the kriging equations with the use of the Fourier series estimates of the covariance.     

Partition of arsenic in soils sediments and the origin of naturally elevated concentrations in groundwater of the southern pampa region (Argentina)

Excessive arsenic concentrations above the Argentinean and WHO guidelines for drinking water (10 μg L⁻¹) affects shallow aquifers of the southern Pampean Plain (Argentina) hosted in the Pampean and the Post Pampean formations (loess and reworked loess; Plio-Pleistocene–Holocene). Health problems related to high As concentrations in drinking waters are known as Endemic Regional Chronic Hydroarsenicism. Hydrochemistry of shallow groundwaters and soil geochemistry were investigated aiming to (1) understand the partition of As in the solid phase and its relationship with unacceptable As concentrations in waters, (2) identify the provision source of As to groundwaters. Only 5% of the samples had As concentrations <10 μg L⁻¹; in 27% As concentrations ranged from 10 to 50 μg L⁻¹ and in 58% it reached 60–500 μg L⁻¹. The coarse fraction (50–2,000 μm) hosts about 27% of the total As in the solid phase, being positively correlated to Ba (p < 0.01; r ² = 0.93). About 70% is included in the <2 μm fraction and had positive correlations of As–Fe (p < 0.05; r ² = 0.85) and As–Cr (p < 0.05; r ² = 0.68). Soils and sediment sand fractions of vadose zones are the primary sources of As in shallow groundwater while adsorption–desorption processes, codisolution–coprecipitation, and evaporation during the dry seasons raise As concentrations in waters exceeding the guideline value for drinking water.     

Geochemistry of the Neoproterozoic (800–767 Ma) Cerro Bori orthogneisses, Dom Feliciano Belt in Uruguay: tectonic evolution of an ancient continental arc

The Cerro Bori orthogneisses, crystallized between ca. 800 and 767 Ma, are composed of a sequence of mafic gneisses, with dioritic-gabbroic and dioritic composition tectonically interleaved with a sequence of tonalitic and granodioritic gneisses. These rocks intruded the Chafalote paragneisses (metapelites, semipelites, carbonate and mafic rocks) and they were metamorphosed of high P-T conditions at ca. 676–654 Ma. This paper presents the first major and trace geochemical signatures, as well as Sm and Pb isotopic composition for the Cerro Bori orthogneisses, which allow distinguishing three different groups of rocks. Type I rocks are mafic gneisses with tholeiitic affinity, whereas the Type II rocks are tonalitic and granodioritic gneisses with calc-alkaline affinity. The third type is composed of biotite-rich mafic gneisses with potassic and ultrapotassic affinities. All the three types of rocks have negative ?_ND values (between ?2.12 and ?6.67) and old T_DM ages (between 1.2 and 2.0 Ga), indicating that the process of crustal assimilation/contamination was an important process, together with fractional crystallization. An continental arc tectonic setting is suggested to this association of rocks between 800 and 767 Ma. This subduction suggests the existence of an ocean between Rio de La Plata and adjacent cratons during the break up of the Rodinia supercontinent.     

Calibration and application of a continuum damage model on the simulation of stone masonry structures: Gondar church as a case study

The conservation and rehabilitation of monuments is a matter of important investigation, and the need for accurate structural analysis, capable of effectively predicting the structural behaviour of this type of constructions, under static and dynamic loads, is increasing. Currently there are numerous computational methods and tools, supported by different theories and strategies with different levels of complexity, computation time and cost which are available to perform such analyses. A complex analysis is not always synonym of a better result and the choice of a method over another depends mostly on the purpose of the analysis. This work aims at evaluating the capacity of a non linear continuum damage model (Faria et al. in Int J Solids Struct 35(14):1533–1558, 1998), originally developed for concrete structures, to simulate the behaviour of stone masonry structures. In particular, the seismic response of an old stone masonry construction, the Gondar church, is analysed considering different levels of geometrical and material complexity. The verification and calibration procedures use the experimental results from tests performed on stone masonry walls at the Laboratory for Earthquake and Structural Engineering of the Faculty of Engineering of Porto University and from other tests found in the bibliography (Vasconcelos in Experimental investigations on the mechanics of stone masonry: Characterization of granites and behaviour of ancient masonry shear walls. PhD Thesis, Universidade do Minho, Guimar?es, Portugal, 2005). The results are compared, assessing the differences and the importance of using complex tools, such as the continuum damage model, to better simulate and understand the global behaviour of such constructions.     

Establishing the wave climate influence on the morphodynamics of a coastal lagoon inlet

The morphologic changes in estuaries and coastal lagoons are very complex and constitute a challenging task in coastal research. The bathymetric changes result from the combined action of tides, waves, rivers discharge and wind stress in the area of interest. Additionally, an accurate knowledge of the sediment transport is essential to achieve a good morphological characterization. This work establishes the influence of the wave climate on the morphodynamics of the Ria de Aveiro lagoon inlet by analysing the numerical results of the morphodynamic modelling system MORSYS2D. The numerical simulations considered a realistic coupled forcing of tidal currents and waves. The computed sediment fluxes and bathymetric changes are analysed and compared with the erosion and accretion trends obtained from the numerical simulations forced only by tidal currents, in order to establish the wave climate influence. The final bathymetry and the corresponding changes are compared with bathymetric data collected through surveys. It is concluded that: (a) the morphodynamics of the study area is dominated by the wave regime in the lagoon inlet and nearshore areas, while in the inner areas is tidally dominated; and (b) the inclusion of the wave regime forcing constitutes an improvement in order to accurately reproduce the local morphodynamics.     

Stochastic tracking of mesoscale convective systems: evaluation in the West African Sahel

In this work we apply a recently proposed Bayesian multiple target tracking model to mesoscale convective systems tracking. This stochastic model follows the multiple hypothesis tracking paradigm and can handle a varying number of targets while detecting the target birth, death, split, and merge events. The model is tested experimentally with real MCS targets detected from meteosat IR data over the Sahelian region. The performance of the stochastic tracking is evaluated by comparing it qualitatively and quantitatively with well established deterministic methods.     

Empirical seismic vulnerability analysis for masonry buildings based on school buildings survey in Iran

School facilities in Iran, in particular masonry schools, have shown poor performance during past earthquakes and can be identified as one of the parts of the country’s infrastructure that is most vulnerable to earthquakes. Hence, in this paper a method to perform index-based damage assessment for brick masonry schools located in the province of Yazd, the central region of Iran, using a comprehensive database of school buildings, is proposed. The database was obtained from the field survey forms applied for each observed school to collect the features of and damage to the structure. The results of a vulnerability index method developed in Iran are employed as input data to obtain empirical fragility curves for the school inventory. The Macroseismic model and GNDT II level method are two empirical methods combined in this procedure. Finally, the procedure is verified using damage survey data obtained after recent earthquakes (1990 Manjil–Rudbar earthquake and 2003 Bam earthquake) that occurred in Iran.