The central Alentejo plateaus: a review of the regional relief units

Since the 1990s, detailed studies on the relief units of the central and upper Alentejo region have been lacking. Previously, tectonics were used to explain most of the relief units, even those in which lithological differentiation is remarkable, such as the dolomitic plateaus of Elvas and Estremoz. The morphotectonic reliefs like Serra d’Ossa and Serra de S. Mamede were previously explained by vertical tectonics, in a horst-graben system, difficult to understand under the Cenozoic compressive tectonic regime affecting the Western Iberian margin. The superposition of geological maps with digital terrain models suggests a more complex genesis in the formation of the morphotectonic regional reliefs. The Serra d’Ossa (652 m) develops in a WNW-ESE general trend (N80ºW), slightly asymmetrical with a 200 m high north-facing escarpment, much steeper than the south-facing slope. The north-facing escarpment (Ossa Fault – OF) is transversal to the NW-SE variscan structures (N40ºW). Thus, this escarpment cannot be explained by differential erosion. Indeed, Feio (1983) already hypothesized a tectonic origin to the Serra d'Ossa, although without presenting a tectonic model. The western termination of the Serra d‘Ossa small scarps, with NE-SW orientation, coincide with the horse tail terminations of the NNE-SSW left strike-slip Graça do Divor fault (GDF). If both GDF and OF are connected, the Serra d’Ossa can be interpreted as a push up deformation of the South Portuguese Planation Surface (SPPS). In this work, a greater relevance of differential erosion is highlighted in the individualisation of Elvas and Estremoz plateaus, as well as the Serra de Monfurado. Towards the north of the town of Évora, the landscape is formed by broad-bottomed valleys at 240 m, with gentle slope and flat uplands at ca. 320-340 m. Looked in Davisian terms, the valleys looks like a mid-cycle maturity landscape. The flat upland level corresponds to the SPPS, well developed in the upper Alentejo (Nisa and Alpalhão), while the bottom of the valleys correspond to a younger level, embedded ca. 80–100 m in the SPPS. The valley bottoms widens to downstream forming a flattening surface (named N1 fluvial surface) related with the beginning of the incision of the drainage network in the SPPS and with the first (older) terraces of the Tejo and Guadiana rivers. The prominence in the landscape of the Serra de Monfurado should be understood as a resistant ridge, whose summits were not completely flattened due to the lithological diversity and to the geographic location in the watershed limit of the Tejo, Guadiana and Sado rivers, where the flattening of the SPPS was difficult to achieve. Differential erosion during the formation of the N1 fluvial surface is thought to be the main responsible for the prominence of this ridge in the central Alentejo landscape, as well as other resistant reliefs as the Monsaraz inselberg

Young LMC clusters: the role of red supergiants and multiple stellar populations in their integrated light and CMDs

The optical integrated spectra of three LMC young stellar clusters (NGC 1984, NGC 1994 and NGC 2011) exhibit concave continua and prominent molecular bands which deviate significantly from the predictions of single stellar population (SSP) models. In order to understand the appearance of these spectra, we create a set of young stellar population (MILES) models, which we make available to the community. We use archival International Ultraviolet Explorer integrated UV spectra to independently constrain the cluster masses and extinction, and rule out strong stochastic effects in the optical spectra. In addition, we also analyze deep colour-magnitude diagrams of the clusters to provide independent age determinations based on isochrone fitting. We explore hypotheses including age-spreads in the clusters, a top-heavy initial mass function, different SSP models and the role of red supergiant stars (RSG). We find that the strong molecular features in the optical spectra can only be reproduced by modeling an increased fraction of about 20 per cent by luminosity of RSG above what is predicted by canonical stellar evolution models. Given the uncertainties in stellar evolution at Myr ages, we cannot presently rule-out the presence of Myr age-spreads in these clusters. Our work combines different wavelengths as well as different approaches (resolved data as well as integrated spectra for the same sample) in order to reveal the complete picture. We show that each approach provides important information but in combination can we better understand the cluster stellar populations.Comment: Accepted for publication in MNRA

Geodynamic evolution of Ossa-Morena Zone in a SW Iberian context during the Variscan cycle

Ossa-Morena Zone (OMZ) is crucial to understanding the geodynamic evolution of the Variscan cycle in SW Iberia. We review previous data, from Early to Late Paleozoic. The early Cambrian (conglomeratic and felsic metavolcanic units) lies unconformably upon Neoproterozoic formations and shows a carbonate sequence with bimodal volcanic rocks, accompanied by intrusion of plutonic bodies (535–520 Ma). This could be interpreted as result of rifting process (Sánchez-García et al., 2010). The middle Cambrian is marked by a significant crustal stretching episode: siliciclastic sedimentation is accompanied by bimodal volcanism, with transitional alkaline geochemical features, symptomatic of an intra-plate environment. The Cambrian–Ordovician transition is marked by the absence of sedimentation and/or an erosional episode. This period is concomitant with large plutonic intrusions (~ 510–485 Ma). This is related to opening of the Rheic Ocean: geochemical (N- and T-MORB signatures) and geochronological data support the existence of anorogenic oceanic magmatic activity during this period (~ 485–480 Ma). From the Mid Ordovician until the end of Silurian, magmatic features are related to passive margin evolution and tectonic stability

Development of a topology optimization method for the design of ground heat exchangers

A new method for sizing vertical ground heat exchangers is proposed using topology optimization to reduce the number of boreholes required to fulfill the cooling and heating demand. The ASHRAE sizing equation is adapted to formulate a topology optimization problem to minimize the number of boreholes required in a bore field. The results show that topology optimization can help reduce the number of boreholes required when compared to a sizing performed on a regular grid using conventional sizing methods. These optimized configurations show smaller spacings between the boreholes located on the perimeter and larger spacings between the boreholes located in the center of the bore field

The Neoproterozoic-Cambrian transition in Abrantes Region (Central Portugal); Litostratigraphic correlation with the Cambrian Series of Ossa-Morena Zone

Abrantes region presents a litostratigraphic succession with clear similarities with typical sequences of Neoproterozoic-Cambrian transition in Ossa-Morena Zone (OMZ). Classical works have attributed Abrantes entire sequence to Neoproterozoic (e.g. Gonçalves et al., 1979). Detailed characterization, based on fieldwork, of the stratigraphic succession allows to discriminate the presence of litostratigraphic units, attributed to lower Cambrian by correlation with other localities of the OMZ; these units overly Neoproterozoic series. The Cambrian sequence begins with a volcano-sedimentary unit composed by detrital rocks, which includes meta-arkoses, meta-pelites and meta-psamites; some rocks show immature content. The volcanic component is mostly composed by abundant felsic rocks, generally with rhyodacitic composition (Abrantes Felsic Unit). The previous characteristics are common in OMZ, where a clastic unit (often missing), sometimes with felsic volcanics and conglomerates, overlies the Serie Negra succession, previously deformed during the Cadomian orogeny at N1; Nance et al., 2012). Abrantes felsic unit gradually change to a carbonate unit (S. Miguel do Rio Torto Carbonates), with calcitic and dolomitic marbles and interbeded mafic volcanics. This unit can be correlated with a range of carbonated units present in all OMZ (Fig. 1C). These units represent a carbonate platform during lower Cambrian showing the beginning of an oceanization process that culminates with the opening of Rheic in lower Ordovician times (Pedro et al., 2010). The lower Cambrian succession culminates with another volcano-sedimentary complex, poorly outcropping; the clastic succession of this complex is dominated by pelitic rocks, interbedded with bimodal volcanics. The transition between the carbonated sedimentation and the overlying volcano-sedimentary one is gradual. All the previous units have not fossiliferous content, mainly due to the action of metamorphic process, which reaches the amphibolitic facies

Lithogeochemistry of metabasites from the Moura Phyllonitic Complex (Ossa Morena Zone, SW Portugal)

The Moura Phyllonitic Complex (MPC) is interpreted as a tectonic mélange that extends along the Montemor - Ficalho sector, overlaying the Relative Autochthone of the Ossa Morena Zone (Iberian Variscides, SW Portugal). Its northern boundary with the Estremoz-Barrancos sector is demarked by the Sto. Aleixo da Restauração Thrust. Generally, the MPC comprises several sericitic-chloritic and siliceous metasedimentary and metavolcanic rocks in a sheared matrix with unknown age, possible ranging from Cambrian to lower Devonian. Frequent imbrications of mafic suites with tholeiitic affinities are known within the MPC: obduction-related sequences, HP metamorphic rocks and dismembered volcanics interpreted as parautochthonous imbrications variably metamorphosed from lower-medium grade greenschist to amphibolite facies. Several of these metabasites were sampled for major and trace element ICP-OES analysis (prepared with alkaline fusion, acid digestion and cation-exchange chromatography), in order to characterize their geochemical variability and attempt to correlate with other autochthonous volcanic rocks, thus inferring their geodynamic setting

Tuning the optical properties of luminescent down shifting layers based on organic dyes to increase the efficiency and lifetime of P3HT: PCBM photovoltaic devices

Mixtures of luminescence downshifting (LDS) materials has been used to increase the efficiency of poly(3-hexylthiophene-2,5-diyl):phenyl-C61-butyric acid methyl ester (P3HT:PC61BM) bulk heterojunction solar cell. This layers convert more energetic photons to lower energies that are better matched with wavelength peak of the external quantum efficiency (EQE) of a P3HT:PC61BM solar cell. Experimental studies were used to optimise the optical properties of LDS layers including the maximum of absorbance and the photoluminescence quantum yield (PLQY). To provide the significant improvements, combinations of LDS mixtures were prepared to provide the greatest absorption and PLQY. The approach is shown to simultaneously improve the photocurrent and increase the lifetime of the device by absorbing UV light. By optimising the optical properties of the LDS mixture, a relative increase of about 20% in the photocurrent density produced by the P3HT:PCBM cell could be achieved, which to our knowledge is one of the most significant reported for OPVs

A reciprocal effects model of children's body fat self-concept : Relations with physical self-concept and physical activity

This study investigated a reciprocal effects model (REM) of children’s body fat self-concept and physical self-concept, and objectively measured school physical activity at different intensities. Grade four students (N = 376; M age = 9.07, SD = .61; 55% boys) from the midwest region of the United States completed measures of physical self-concept and body fat self-concept, and wore accelerometers for three consecutive school days at the beginning and end of one school year. Findings from structural equation modeling analyses did not support reciprocal effects. However, children’s body fat self-concept predicted future physical self-concept and moderate-to-vigorous physical activity (MVPA). Multigroup analyses explored the moderating role of weight status, sex, ethnicity, and sex*ethnicity within the REM. Findings supported invariance, suggesting that the observed relations were generalizable for these children across demographic groups. Links between body fat self-concept and future physical self-concept and MVPA highlight self-enhancing effects that can promote children’s health and well-being