A neutron activation technique for the analysis for fluorine in fluorspar samples

This article explains the results of the feasibility study about using neutron activation technique via Deferred gamma rays, to analyze the fluorine content in a sample from a fluorspar concentration plant. The theoretical responses of 12 items, constituting the samples have been analyzed. 468 reactions have been obtained from the study with the database EXFOR of these elements with neutrons from an Americium Beryllium source of 1 Ci activity.The radioactive decay of 29 products, anticipated from such an activation, has also been analyzed. From these results, a prototype for neutron activation has been designed. The different criteria of the measurement procedure to enable the activation of the fluorspar samples and to record their spectra with minimal interference from the source have been adjusted. A mathematical model of the activation response has been created and validated. The activation method to determine the fluorine content in fluorspar samples proved to be scientifically and technically feasible and verified by the results obtained.     

Fundamental Problems in Astrophysics

Progress of modern astrophysics requires the access to the electromagnetic spectrum in the broadest energy range. The Ultraviolet is a fundamental energy domain since it is one of the most powerful tool to study plasmas at temperatures in the 3,000–300,000 K range as well as electronic transitions of the most abundant molecules in the Universe. Moreover, the UV radiation field is a powerful astrochemical and photoionizing agent.The objective of this review is to describe the crucial issues that require access to the UV range. A summary has been added to the end with a more classic view of UV needs by astronomical object type; this approach is followed at length in the rest of the contributions of this issue.     

Deep colour–magnitude diagrams of LMC field stars imaged with HST

We present deep photometry ( V ≲26) in V and I bands obtained with the Wide Field and Planetary Camera 2 on board the Hubble Space Telescope for 7 fields ∼5° away from the Large Magellanic Cloud centre. The fields contain, typically, 2000 stars each. Isochrones were fitted to the colour–magnitude diagrams in order to identify different star populations in these fields. An old population ( τ >10 Gyr) has been found in all fields. Some events of enhanced star formation, with ages between 2 and 4 Gyr, were identified in the fields localized in the north to north-west regions. Luminosity functions of low-mass stars were also obtained for all fields. Kolmogorov Smirnov test results suggest differences smaller than 30 per cent in the mixture of stellar populations contributing to the fields. Finally, density profiles were derived for old and intermediate-age stars. The former shows a slightly steeper decline than the latter.     

Interactions of river discharge and tidal modulation in a tropical estuary, NE Brazil

Observations of thermohaline properties and currents were undertaken in the Curimataú River estuary (6°18′S), Rio Grande do Norte state (RN), Brazil, during consecutive neap–spring tidal cycles in the austral autumn rainy season. Highly asymmetric neap tide along channel velocities (−0.4 to 0.9 m s⁻¹) and highly stratified conditions were generated by an increase of the buoyancy energy from the freshwater input (R _iE≈5.6). During the spring-tidal cycle the river discharge decreased and the longitudinal velocity components were higher, less asymmetrical (−0.8 to 1.1 m s⁻¹) and semidiurnal, associated with moderately stratified conditions (R _iE≈0.1) due to the increase of the kinetic tidal energy forcing mechanism. The overall salinity variation from surface to bottom during two tidal cycles was from 20.5 to 36.3 and 29 to 36.7 in the neap and spring tide experiments, respectively; in the last experiment, the tropical water (TW) mass intrusion was enhanced. The net salt transport reversed from down to up estuary during the neap and spring tide experiments, respectively, varied from 6.0 to –2.0 kg m⁻¹ s⁻¹, an indication of changes in the main forcing of the estuary dynamics. Evaluation of a classical steady analytical model, in comparison with nearly steady experimental vertical profiles of velocity, shows an agreement classifiable as reasonably fair.     

Predicting the future climatic suitability for cocoa farming of the world’s leading producer countries, Ghana and Côte d’Ivoire

Ghana and Côte d’Ivoire are the world’s leading cocoa (Thebroma cacao) producing countries; together they produce 53 % of the world’s cocoa. Cocoa contributes 7.5 % of the Gross Domestic Product (GDP) of Côte d’Ivoire and 3.4 % of that of Ghana and is an important cash crop for the rural population in the forest zones of these countries. If progressive climate change affected the climatic suitability for cocoa in West Africa, this would have implications for global cocoa output as well as the national economies and farmer livelihoods, with potential repercussions for forests and natural habitat as cocoa growing regions expand, shrink or shift. The objective of this paper is to present future climate scenarios for the main cocoa growing regions of Ghana and Côte d’Ivoire and to predict their impact on the relative suitability of these regions for growing cocoa. These analyses are intended to support the respective countries and supply chain actors in developing strategies for reducing the vulnerability of the cocoa sector to climate change. Based on the current distribution of cocoa growing areas and climate change predictions from 19 Global Circulation Models, we predict changes in relative climatic suitability for cocoa for 2050 using an adapted MAXENT model. According to the model, some current cocoa producing areas will become unsuitable (Lagunes and Sud-Comoe in Côte d’Ivoire) requiring crop change, while other areas will require adaptations in agronomic management, and in yet others the climatic suitability for growing cocoa will increase (Kwahu Plateu in Ghana and southwestern Côte d’Ivoire). We recommend the development of site-specific strategies to reduce the vulnerability of cocoa farmers and the sector to future climate change.     

Regional oxygen isotope systematics of felsic volcanics; a potential exploration tool for volcanogenic massive sulphide deposits in the Iberian Pyrite Belt

Regional oxygen isotopic sytematics have been performed mainly on the felsic volcanic footwall rocks of the orebodies but also on purple schist characteristic of the hanging wall series, around two giant VMS deposits in the Spanish Iberian Pyrite Belt, Riotinto and La Zarza. As the terranes of the Iberian Pyrite Belt, these two giant deposits have been affected by the Hercynian tectono-metamorphic events, strongly modifying their geometry. About 60 and 40 samples were collected over a 10×4 km² area at Riotinto and a 3×2 km² area at La Zarza, respectively. Whole-rock powders were analysed for oxygen by CO₂-laser fluorination. At both sites, a same type of low-δ¹⁸O anomaly down to +3.6‰, well differentiated from the regional background (up to 20‰), was identified near the orebodies. The lowest δ¹⁸O values (+4 to +11‰) correspond to the chlorite hydrothermal halo, essentially restricted to the feeder zones of the orebody. Intermediate δ¹⁸O values (+9 to +15‰) correspond to the sericite hydrothermal halo, mostly developed laterally to the orebody until 0.5–1 km. The regional background (+16 to +20‰) is represented by spilitised volcanic rocks. A same kind of low anomaly, but with less contrast, was defined in purple schist in the immediate hanging wall of the orebodies. All these results demonstrate that, despite high geometrical modifications of the orebodies related to the Hercynian tectonics, oxygen isotopic anomalies recorded by volcanic host rocks during the emplacement of the mineralising hydrothermal systems are still identified. This strongly suggests that oxygen isotopic systematics could be useful to identify target areas in the Iberian Pyrite Belt, as already demonstrated on other VMS targets in the world.     

Proto-Adamastor ocean crust (920 Ma) described in Brasiliano Orogen from coetaneous zircon and tourmaline

Proto-Adamastor ocean bathed Rodinia and successor continental fragments from 1.0–0.9 Ga up to 0.75 Ga, and evolved into world Adamastor Ocean at 0.75–0.60 Ga. Mesoproterozoic oceanic crust is poorly preserved on continents, only indirect evidence registered in Brasiliano Orogen. We report first evidence of ophiolite originated in proto-Adamastor. We use multi-technique U-Pb-Hf zircon and δ¹¹B tourmaline isotopic and elemental compositions. The host tourmalinite is enclosed in metaserpentinite, both belonging to the Bossoroca ophiolite. Zircon is 920 Ma-old, ?_{Hf(920 Ma)} = +12, Hf_TDM = 1.0 Ga and has ‘oceanic’ composition (e.g., U/Yb < 0.1). Tourmaline is dravite with δ¹¹B = +1.8‰ (Tur 1), 0‰ (Tur 2), ?8.5‰ (Tur 3). These characteristics are a novel contribution to Rodinia and associated world ocean, because a fragment of proto-Adamastor oceanic crust and mantle evolved at the beginning of the Brasiliano Orogen.     

Comparative performance of convolutional neural network,weighted and conventional support vector machine and random forest for classifying tree species using hyperspectral and photogrammetric data

ABSTRACT

The classification of tree species can significantly benefit from high spatial and spectral information acquired by unmanned aerial vehicles (UAVs) associated with advanced classification methods. This study investigated the following topics concerning the classification of 16 tree species in two subtropical forest fragments of Southern Brazil: i) the potential integration of UAV-borne hyperspectral images with 3D information derived from their photogrammetric point cloud (PPC); ii) the performance of two machine learning methods (support vector machine – SVM and random forest – RF) when employing different datasets at a pixel and individual tree crown (ITC) levels; iii) the potential of two methods for dealing with the imbalanced sample set problem: a new weighted SVM (wSVM) approach, which attributes different weights to each sample and class, and a deep learning classifier (convolutional neural network – CNN), associated with a previous step to balance the sample set; and finally, iv) the potential of this last classifier for tree species classification as compared to the above mentioned machine learning methods. Results showed that the inclusion of the PPC features to the hyperspectral data provided a great accuracy increase in tree species classification results when conventional machine learning methods were applied, between 13 and 17% depending on the classifier and the study area characteristics. When using the PPC features and the canopy height model (CHM), associated with the majority vote (MV) rule, the SVM, wSVM and RF classifiers reached accuracies similar to the CNN, which outperformed these classifiers for both areas when considering the pixel-based classifications (overall accuracy of 84.4% in Area 1, and 74.95% in Area 2). The CNN was between 22% and 26% more accurate than the SVM and RF when only the hyperspectral bands were employed. The wSVM provided a slight increase in accuracy not only for some lesser represented classes, but also some major classes in Area 2. While conventional machine learning methods are faster, they demonstrated to be less stable to changes in datasets, depending on prior segmentation and hand-engineered features to reach similar accuracies to those attained by the CNN. To date, CNNs have been barely explored for the classification of tree species, and CNN-based classifications in the literature have not dealt with hyperspectral data specifically focusing on tropical environments. This paper thus presents innovative strategies for classifying tree species in subtropical forest areas at a refined legend level, integrating UAV-borne 2D hyperspectral and 3D photogrammetric data and relying on both deep and conventional machine learning approaches.     

Age constraints to the relationships between magmatism, metamorphism and tectonism in the Aracena metamorphic belt, southern Spain

 The Aracena metamorphic belt (AMB), southwest Iberian peninsula, is characterized by the following geological elements: (a) a high-temperature/low-pressure (HT/LP) metamorphic belt a few kilometres wide and more than 200 km long; (b) a linear belt of oceanic amphibolites with a low-pressure inverted metamorphic gradient; (c) crustal-scale ductile shear zones; and (d) mafic, noritic intrusions of high-Mg andesite (boninite) composition. The relationships between these elements led to the proposal of a model of ridge subduction for this sector of the Hercynian belt of Europe. This interpretation is supported by the age relationships displayed between the main rock units considered representative of the main tectonic and petrological processes responsible for the geological elements mentioned previously. The results of a geochronological study (Ar–Ar, Rb–Sr and Sm–Nd) clearly support a Late Paleozoic tectonic evolution at an active continental margin. The time evolution of the metamorphism in the oceanic domain, ranging from 342.6±0.6 Ma in the west to 328.4±1.2 Ma in the east, over a distance of 70 km along the metamorphic belt, support a tectonic model of triple-junction migration responsible for the creation at depth of a slab-free window with decisive consequences for the thermal evolution of the region. The origin of the linear metamorphic belt of HT/LP regime may be explained by the migration along a continental margin of a punctual thermal anomaly induced by the creation of a triple-junction at the continental margin. Received: 9 March 1998 / Accepted: 9 December 1998     

Continuous metal biosorption applied to industrial effluents: a comparative study using an agricultural by-product and a marine alga

Fixed-bed column experiments have been conducted to evaluate the removal of metals from real industrial wastewaters. The effluents tested were provided by two different metallurgical companies: Industrial Goñabe, a galvanizing plant, and Sao Domingos mine, an abandoned sulfide mine. Sugar-beet pulp, a by-product of the sugar industry, and brown alga Fucus vesiculosus were used as biosorbents. The influence of pH on the sorption process was insignificant for the tests using Industrial Goñabe wastewater. On the contrary, an increase of pH improved metal sorption uptake and yield and saturation rate in the case of the Sao Domingos wastewater. A lower metal concentration in Sao Domingos wastewater resulted in a higher availability of metal-binding sites on the biomass. Better sorption parameters for both real wastewaters were obtained using brown alga Fucus vesiculosus. At pH 5, Zn sorption in continuous mode increased from 36 to 48% for Industrial Goñabe wastewater and from 34 to 37% for Sao Domingos wastewater. In the latter case, copper sorption increased from 73 to 88%. Breakthrough points that determine the service time of columns were reached later using alga as biosorbent. For Zn, column adsorption performance improved substantially with alga and its service time by 5 times. In the case of Cu, the breakthrough point of the second column was not reached during 1750 min of experimentation. The results obtained reaffirm the industrial applicability of these techniques.