Seismic response of nonstructural components in case of nonlinear structures based on floor response spectra method

This paper investigates the response of nonstructural components in the presence of nonlinear behavior of the primary structure using floor response spectra method (FRS). The effect of several parameters such as initial natural frequency of the primary structure, natural frequency of the nonstructural components (subsystem), strength reduction factor and hysteretic model have been studied. A database of 164 registered ground acceleration time histories from the European Strong-Motion Database is used. Results are presented in terms of amplification factor and resonance factor. Amplification factor quantifies the effect of inelastic deformations of the primary structure on subsystem response. Resonance factor quantifies the variation of the subsystem response considering the primary structure acceleration. Obtained results differed from precedent studies, particularly for higher primary structure periods. Values of amplification factor are improved. Obtained results of resonance factor highlight an underestimation of peak values according to current design codes such as Eurocode 8. Therefore a new formulation is proposed.     

Shifts in an epibenthic trophic web across a marine frontal area in the Southwestern Atlantic (Argentina)

Marine benthic trophic relationships and food web structures may be influenced by benthic–pelagic coupling processes, which could also be intensified by the physical dynamics of marine fronts. In this work, we employed stable isotope (δ¹³C and δ¹⁵N) analysis to investigate the influence of the Southwest (SW) Atlantic shelf-break front (SBF; 38–39°S, 55–56°W; Argentina) on an epibenthic trophic web. Epibenthic organisms were sampled, at depths of ~ 100 m, with a non-selective dredge from a sandy bottom community located in frontal (F) and marginal (M) areas. The SBF position and the chlorophyll-a (chl-a) concentrations were inferred using satellite data of the sea surface temperature (SST) and satellite chl-a concentration, respectively. The most noticeable shifts in stable isotopes between the sampled areas were those of the Patagonian scallop, Zygochlamys patagonica (δ¹³C), and those of the sea urchin, Sterechinus agassizi (δ¹⁵N). Diet analyses inferred from stable isotopes and mixing models demonstrated that the dominant component of this community, Z. patagonica, had variable contributions to higher trophic levels between areas. More importantly, the epibenthic assemblage in F areas showed δ¹³C-enriched and δ¹⁵N-depleted isotopic signatures with respect to the M areas. Collectively, this evidence suggests that frontal dynamics promotes the accumulation of δ¹³C-enriched phytoplankton in the seabed in F areas, while in M areas the more degraded organic matter becomes more important in the trophic web, decreasing the δ¹⁵N isotopic signature of the assemblage. Therefore, the trophic web was sustained by fresher food in F areas than in M areas, demonstrating the role of frontal dynamics in the shaping of these communities.     

Application of Laser‐Induced Breakdown Spectroscopy and Hyperspectral Images for Direct Evaluation of Chemical Elemental Profiles of Coprolites

This study demonstrates the application of laser‐induced breakdown spectroscopy (LIBS) and hyperspectral imaging to the investigation of coprolite and fossil samples. Solid samples from the Permian (seven coprolites and one fossil), Cretaceous (one coprolite) and Oligo‐Miocene (two coprolites) periods were directly analysed, and emission spectra from 186 to 1042 nm were obtained in several areas covering coprolite/fossil and rock material. Initial exploratory analyses were performed using principal component analysis with the data set normalised by the norm (Euclidean norm = 1). After identification and selection of emission lines of eleven elements (Al, Ca, Cr, Fe, K, Mg, Mn, Na, Ni, P and Si), the signals were normalised again by the relative intensity of the selected element. Phosphorus was identified mainly in the coprolites, while K and Na were primarily found in the rock material. In several cases, there was a positive correlation between Ca and P. A sample from the Oligo‐Miocene series was also analysed using inductively coupled plasma‐optical emission spectrometry (ICP‐OES) (rock and coprolites were analysed separately). Based on the quantitative results from ICP‐OES, it was confirmed that the tendency was the same as that observed with the results obtained from LIBS directly in the solid sample.     

Temporal and spatial distribution of floating objects in coastal waters of central–southern Chile and Patagonian fjords

Floating objects are suggested to be the principal vector for the transport and dispersal of marine invertebrates with direct development as well as catalysts for carbon and nutrient recycling in accumulation areas. The first step in identifying the ecological relevance of floating objects in a specific area is to identify their spatio-temporal distribution. We evaluated the composition, abundance, distribution, and temporal variability of floating objects along the continental coast of central–southern Chile (33–42°S) and the Patagonian fjords (42–50°S) using ship surveys conducted in austral winter (July/August) and spring (November) of the years 2002–2005 and 2008. Potential sources of floating items were identified with the aid of publicly available databases and scientific reports. We found three main types of floating objects, namely floating marine debris (mainly plastic objects and Styrofoam), wood (trunks and branches), and floating kelps (Macrocystis pyrifera and Durvillaea antarctica). Floating marine debris were abundant along most of the examined transects, with markedly lower abundances toward the southern fjord areas. Floating marine debris abundances generally corresponded to the distribution of human activities, and were highest in the Interior Sea of Chiloé, where aquaculture activities are intense. Floating wood appeared sporadically in the study area, often close to the main rivers. In accordance with seasonal river run-off, wood was more abundant along the continental coast in winter (rainy season) and in the Patagonian fjords during the spring surveys (snow melt). Densities of the two floating kelp species were similar along the continental coast, without a clear seasonal pattern. M. pyrifera densities increased towards the south, peaking in the Patagonian fjords, where it was dominant over D. antarctica. Densities of M. pyrifera in the Patagonian fjords were highest in spring. Correlation analyses between the abundances of floating objects and the distance to the nearest sources were generally non-significant, suggesting that post-supply processes affect the distribution of the floating objects in the study region. The identification of several major retention zones supports this idea. Accumulation areas of floating objects appear to be more common in the fjord zones. In general, the results underscore the abundance of floating objects throughout the study region and the fact that floating marine debris sources are mostly local, whereas floating algae may be dispersed over greater distances. Future studies should focus on the ecological role of floating objects in biota dispersal and nutrient cycling.     

Season‐based rainfall–runoff modelling using the probability‐distributed model (PDM) for large basins in southeastern Brazil

Southeastern Brazil is characterized by seasonal rainfall variability. This can have a great social, economic, and environmental impact due to both excessive and deficient water availability. During 2014 and 2015, the region experienced one of the most severe droughts since 1960. The resulting water crisis has seriously affected water supply to the metropolitan region of São Paulo and hydroelectric power generation throughout the entire country. This research considered the upstream basins of the southeastern Brazilian reservoirs Cantareira (2,279 km²; water supply) and Emborcação (29,076 km²), Três Marias (51,576 km²), Furnas (52,197 km²), and Mascarenhas (71,649 km²; hydropower) for hydrological modelling. It made the first attempt at configuring a season‐based probability‐distributed model (PDM‐CEMADEN) for simulating different hydrological processes during wet and dry seasons. The model successfully reproduced the intra‐annual and interannual variability of the upstream inflows during 1985–2015. The performance of the model was very satisfactory not only during the wet, dry, and transitional seasons separately but also during the whole period. The best performance was obtained for the upstream basin of Furnas, as it had the highest quality daily precipitation and potential evapotranspiration data. The Nash–Sutcliffe efficiency and logarithmic Nash–Sutcliffe efficiency were 0.92 and 0.93 for the calibration period 1984–2001, 0.87 and 0.88 for the validation period 2001–2010, and 0.93 and 0.90 for the validation period 2010–2015, respectively. Results indicated that during the wet season, the upstream basins have a larger capacity and variation of soil water storage, a larger soil water conductivity, and quicker surface water flow than during the dry season. The added complexity of configuring a season‐based PDM‐CEMADEN relative to the traditional model is well justified by its capacity to better reproduce initial conditions for hydrological forecasting and prediction. The PDM‐CEMADEN is a simple, efficient, and easy‐to‐use model, and it will facilitate early decision making and implement adaptation measures relating to disaster prevention for reservoirs with large‐sized upstream basins.     

Late Quaternary paleosols, stratigraphy and landscape evolution in the Northern Pampa, Argentina

The field properties, micromorphology, grain-size, geochemistry, and optically stimulated luminescence (OSL) ages of two late Quaternary sections have been used to reconstruct the sequence of pedosedimentary processes and to provide insights into landscape evolution in part of the Northern Pampa of Argentina. Paleosols developed in paludal sediments adjacent to the Paraná river at Baradero and in loess at Lozada can both be correlated and linked to other sites, thus enabling for the first time the tentative recognition and tracing of a diachronous soil stratigraphic unit that probably spans the equivalent of at least part of marine oxygen isotope stage (OIS) 5. The paleosol at Lozada was truncated and buried beneath fluvial sediments during the time span of OIS 4 and 3. Eolian gradually replaced paludal inputs at Baradero over this period, and there were also two clearly defined breaks in sedimentation and development of paleosols. The period corresponding to OIS 2 was marked by significant loess accumulation at both sites with accretion continuing into the mid-Holocene only at Lozada. The more developed nature of the surface soil at Baradero probably reflects a combination of a moister climate and a longer soil-forming interval.     

Effect of lateral variation and model parameterization on surface wave dispersion inversion to estimate the average shallow structure in the Paraná Basin

The average layered structure of the intracratonic Paraná Basin, SE Brazil, is investigated with surface-wave group velocities from a small regional earthquake recorded by two broadband stations. Rayleigh and Love waves in the period range 1–4.2 s are used to infer average properties down to about 4 km. Genetic algorithm techniques are used to find the best fitting 1-D S-wave model. The inverted 1-D models show fair correlation with the average properties of the propagation paths as expected from geology and borehole information. However, different S-wave velocity models are obtained for the different inversion parameterizations. Since lateral heterogeneities are expected along the paths, several synthetic tests are performed with heterogeneous propagation paths. For approximately homogenous path (i.e., little lateral variation), the main features of the average synthetic model can be retrieved for different model parameterizations. For strong lateral variations, however, the average dispersion curve can produce very different 1-D inverted models depending on the parameterization. Also, the 1-D inverted models may differ significantly from the average properties of the inhomogeneous path, and wrong depths to interfaces may be inferred. For real data inversions, it is then suggested that various different parameterizations should be tested. If the resulting models show consistent features, this probably indicates homogeneity in the propagation path. But, if very different and unstable features are obtained in the 1-D inversions, then strong lateral variation may be present in the propagation path, and the average 1-D model may not represent average properties along the path.     

Shear and vorticity in inflationary Brans–Dicke cosmology with lambda-term

We find a solution for exponential inflation in Brans–Dicke cosmology endowed with a cosmological term, which includes time-varying shear and vorticity. We find that the scalar field and the scale factor increase exponentialy while shear, vorticity, energy density, cosmic pressure and the cosmological term decay exponentialy for negative beta, where beta is defined in the text.