GaAs(111)A and B in hydrazine sulfide solutions : extreme polarity dependence of surface adsorption processes

Chemical bonds formed by hydrazine-sulfide treatment of GaAs(111) were studied by synchrotron photoemission spectroscopy. At the B surface, the top arsenic atoms are replaced by nitrogen atoms, while GaAs(111)A is covered by sulfur, also bonded to underlying gallium, despite the sulfide molar concentration being 103 times smaller than that of the hydrazine. This extreme dependence on surface polarity is explained by competitive adsorption processes of HS- and OH- anions and of hydrazine molecules, on Ga- adsorption sites, which have distinct configurations on the A and B surfaces

A Detailed Geochemical Study of a Shallow Arc-related Laccolith; the Torres del Paine Mafic Complex (Patagonia)

The shallow crustal Torres del Paine Intrusive Complex in southern Patagonia offers an opportunity to understand the chemical evolution and timing of crystallization processes in shallow plutonic rocks. It is characterized by hornblende-gabbros, gabbronorites, monzodiorites and granitic plutonic rocks. The exceptional exposure of the intrusion permits the identification of two structurally and petrographically different zones. Layered gabbronorite, olivine-bearing pyroxene-hornblende gabbronorite and monzodiorite forming vertical sheets and stocks in the west are referred to here as the feeder zone. These mafic rocks are in vertical contact with younger granitic rocks on their eastern border. The eastern part is a laccolith complex. It is characterized by three major units (I, II, III) of granitic rocks of over 1000 m vertical thickness; these are underlain in places by a sequence of hornblende-gabbro sills intermingled with evolved monzodiorite granite. Chilled, crenulated margins as well as flame structures between gabbroic rocks and monzodiorites suggest that the mafic sill complex remained partially molten during most of its construction. Bulk-rock major and trace element data indicate that the Paine mafic rocks follow a high-K calc-alkaline to shoshonitic differentiation trend. The parental magmas were basaltic trachyandesite liquids, with variable H2O and alkali contents. The majority of the feeder zone gabbronorites have high Al2O3 contents and positive Eu and Sr anomalies, consistent with accumulation of plagioclase and efficient extraction of intercumulus melt. The mafic sill complex largely lacks these cumulate signatures. Comparisons of the intercumulus groundmass in the hornblende-gabbros with intra-sill dioritic stocks and pods reveal similar rare earth element patterns and trace element ratios indicating incomplete extraction of evolved interstitial liquids. The Sr, Nd and Pb isotopic compositions of the mafic and granitic rocks exhibit ranges of 87Sr/86Sr of 0·704-0·708, εNd +3·8 to −1·2, 206Pb/204Pb 18·61-18·77, 207Pb/204Pb 15·67-15·67 and 208Pb/204Pb 38·56-38·77. Crystal fractionation and assimilation-fractional crystallization modelling, combined with high-precision U-Pb dating of zircons, indicates that the western feeder zone gabbronorites are linked to the uppermost Paine granite (granite I), whereas the mafic sill complex is younger and not directly related to the voluminous granite units II and III. These results are interpreted to indicate that crystal-liquid separation is facilitated in subvertical, dynamic feeder systems whereas subhorizontal sill complexes are inefficient in separating large volumes of mafic cumulates and complementary felsic rock

Cs-induced charge transfer on (2x4)-GaAs(001) studied by photoemission

Cesium adsorption on 2x4 GaAs (001) was studied by photoemission and low energy electron diffraction. The different Cs induced changes of the As 3d and Ga 3d core level spectra show that charge transfer is almost complete for Ga surface sites, but is negligible to surface As at a coverage smaller than 0.3 ML. The situation is opposite for a coverage larger than 0.3ML, at which transfer occurs to As but no longer to Ga. Charge transfer to As atoms leads to disordering and destabilization and induces surface conversion from the As-rich surface to the Ga-rich 4x2 one after annealing at a reduced temperature of 450 C

Root reinforcement dynamics in subalpine spruce forests following timber harvest: A case study in Canton Schwyz, Switzerland

Root reinforcement is a key factor when dealing with slope stability problems and is an important quantitative criterion for the evaluation of the protective function of forests against shallow landslides, as well as for the adoption of appropriate practices in protection forest management. Although many models have been developed to estimate root reinforcement, a reliable quantification that considers both its spatial and temporal variability still remains a challenge. This work aims to extend the understanding of the long term spatial and temporal dynamics of root reinforcement after forest harvest in subalpine spruce forests by supplying new experimental data and applying a state-of-the-art model.We estimated root reinforcement decay 5, 10 and 15 years after timber had been harvested in spruce stands in a small catchment in the Swiss Alps. We collected root distribution data at different distances from the trees and calibrated and validated a root distribution model (RootDis). To estimate root mechanical properties, we tested roots up to 12 mm diameter in the field, and computed root reinforcement for each case study with the Root Bundle Model. Finally, we developed a new model for the estimation of root reinforcement decay, based on the observed change in root distribution after felling and on the decay of the root pullout force. The final result is a model for the spatial-temporal prediction of root reinforcement heterogeneity and dynamics in subalpine spruce forest stands. Five year old harvested spruce forest in the climatic conditions of the study area provides 40% of the root reinforcement of live forest, while 15 years old harvested forest provides no reinforcement at all. Shrub species and natural regeneration could guarantee almost the 30% of the root reinforcement of a live forest after 15 years from cutting. Additional work is now required to further validate the model and implement these results in a slope stability analysis

Global approaches and local strategies for phase unwrapping

Phase unwrapping, i.e. the retrieval of absolute phases from wrapped, noisy measures, is a tough problem because of the presence of rotational inconsistencies (residues), randomly generated by noise and undersampling on the principal phase gradient field. These inconsistencies prevent the recovery of the absolute phase field by direct integration of the wrapped gradients. In this paper we examine the relative merit of known global approaches and then we present evidence that our approach based on “stochastic annealing” can recover the true phase field also in noisy areas with severe undersampling, where other methods fail. Then, some experiments with local approaches are presented. A fast neural filter has been trained to eliminate close residue couples by joining them in a way which takes into account the local phase information. Performances are about 60–70% of the residues. Finally, other experiments have been aimed at designing an automated method for the determination of weight matrices to use in conjunction with local phase unwrapping algorithms. The method, tested with the minimum cost flow algorithm, gives good performances over both simulated and real data

COVID-19 and Ophthalmology: A New Chapter in an Old Story

Editorial, No Abstrac

COVID-19 and Ophthalmology: A New Chapter in an Old Story

Editorial, No Abstrac

Petrological evolution of the magmatic suite associated with the Coroccohuayco Cu(-Au-Fe) porphyry-skarn deposit, Peru

The petrological evolution of magmatic rocks associated with porphyry-related Cu deposits is thought to exert a first-order control on ore genesis. It is therefore critical to understand and recognize petrological processes favourable to the genesis of porphyry systems. In this study we present new petrographic, geochemical (whole-rock and mineral), and isotopic (Pb, Sr, Nd) data for rocks from the magmatic suite associated with the Eocene Coroccohuayco porphyry–skarn deposit, southern Peru. Previously determined radiometric ages on these rocks provide the temporal framework for interpretation of the data. Arc-style magmatic activity started at Coroccohuayco with the emplacement of a composite precursor gabbrodiorite complex at c. 40·4 Ma. After a nearly 5 Myr lull, magmatic activity resumed at c. 35·6 Ma with the rapid emplacement of three dacitic porphyries associated with mineralization. However, zircon antecrysts in the porphyries show that intra-crustal magmatic activity started c. 2 Myr before porphyry emplacement and probably built a large intra-crustal magmatic body with an associated large thermal anomaly. Our data suggest that all magmas underwent a period of evolution in the deep crust before transfer and further evolution in the upper crust. The gabbrodiorite complex was sourced from a heterogeneous deep crustal reservoir and was emplaced at a pressure of 100–250 MPa where it underwent a limited amount of fractionation and formed a chemically zoned pluton. Its initial water content and oxygen fugacity were estimated to be around 3 wt % H2O and NNO ± 1 (where NNO is the nickel–nickel oxide buffer), respectively. The deep crustal source of the porphyries appears to have been more homogeneous. The porphyries are interpreted to be the product of advanced differentiation of a parental magma similar to the gabbrodiorite. Most of this evolution occurred at deep crustal levels (around 800 MPa) through fractionation of amphibole + pyroxene + plagioclase ± garnet, leading to the development of a high Sr/Y signature characteristic of porphyry-related magmatism worldwide. Subsequent upper crustal evolution (100–250 MPa) was dominated by crustal assimilation, cannibalism of previously emplaced magma batches (proto-plutons) and magma recharge. Water content and oxygen fugacity were estimated to be around 5 wt % H2O and NNO + 1 to NNO + 2, respectively, at the end of the period of upper crustal evolution. This high oxygen fugacity is inferred to have favoured sulphur and metal enrichment in the melt. The high thermal regime generated through 2 Myr of sustained magmatism in the upper crust favoured crustal assimilation, proto-pluton cannibalism, and efficient metal extraction upon fluid exsolution. The Coroccohuayco magmatic suite appears to have acquired its metallogenic potential (high fO2, high Sr/Y) through several million years of deep crustal evolution

Intra-articular administration of lidocaine plus adrenaline in dogs : pharmacokinetic profile and evaluation of toxicity in vivo and in vitro

The aim of this study was to evaluate the safety of intra-articular (IA) lidocaine plus adrenaline for improving peri-operative analgesia in anaesthetised dogs undergoing arthroscopy of the elbow. A solution of lidocaine (L) 1.98% plus adrenaline 1:100.000 was administered via the IA route and its safety evaluated in terms of cardio- neuro- and chondro-toxicity. No bradycardia or hypotension was recorded from induction to the last observational time point. Signs of toxicity of the nervous system could have been masked by the general anaesthesia but lidocaine concentrations detected in the blood were lower than those thought to be capable of producing toxicity. The assessment of in vitro chondrotoxicity showed a dose- and time-dependent effect of lidocaine on the viability of articular cells. Adrenaline appeared to reduce the chondrotoxicity of 1% lidocaine, following an exposure of up to 30 min

Happy Feet in a Hostile World? The Future of Penguins Depends on Proactive Management of Current and Expected Threats

Penguins face a wide range of threats. Most observed population changes have been negative and have happened over the last 60 years. Today, populations of 11 penguin species are decreasing. Here we present a review that synthesizes details of threats faced by the world’s 18 species of penguins. We discuss alterations to their environment at both breeding sites on land and at sea where they forage. The major drivers of change appear to be climate, and food web alterations by marine fisheries. In addition, we also consider other critical and/or emerging threats, namely human disturbance near nesting sites, pollution due to oil, plastics and chemicals such as mercury and persistent organic compounds. Finally, we assess the importance of emerging pathogens and diseases on the health of penguins. We suggest that in the context of climate change, habitat degradation, introduced exotic species and resource competition with fisheries, successful conservation outcomes will require new and unprecedented levels of science and advocacy. Successful conservation stories of penguin species across their geographical range have occurred where there has been concerted effort across local, national and international boundaries to implement effective conservation planning