New ideas on the Proterozoic-Early Palaeozoic evolution of NW Iberia: insights from U–Pb detrital zircon ages

U–Pb ages were obtained on single detrital zircon grains separated from six samples of Neoproterozoic and Lower Palaeozoic sedimentary and volcanosedimentary rocks from NW Iberia using the laser ablation microprobe-inductively coupled plasma mass spectrometry (LAM-ICP-MS) method. Precambrian greywackes yielded abundant zircons with Neoproterozoic (800–640 Ma) and Mesoproterozoic (0.9–1.2 Ga) ages, and a smaller proportion of Palaeoproterozoic (1.8–2 Ga) and Archaean zircons. Palaeozoic samples (Lower Cambrian and Ordovician) yielded abundant zircons with younger Neoproterozoic (ca. 550 and 620 Ma) and Mesoproterozoic (0.9–1.2 Ga) ages. Palaeoproterozoic (1.8–2 Ga) and Archaean zircons were also found. This data set, used in conjuction with previous paleogeographic and isotopic studies sheds new light on the Precambrian-early Palaeozoic evolution of NW Iberia and is consistent with the following sequence of events: (1) Early Cadomian-Avalonian subduction and arc construction (ca. 800–640 Ma). This magmatic episode created the main arc edifice (Avalonia); (2) full development of a back arc basin upon which the Neoproterozoic sediments were deposited (ca. 640–640 Ma). The combined U–Pb ages of detrital zircons and Nd isotopic features of these sedimenary rocks suggest that they were mostly shed from the main magmatic arc. On the basis of the presence of Grenvillian age detrital zircons with short waterborne transport before incorporation in the sediment, we propose that the basin was possibly located in a peri-Amazonian realm close to West Avalonian terranes. These basins were developed upon a cratonic basement that possibly involved both Grenvillian (ca. 0.9–1.2 Ga) and Transamazonian (ca. 1.9–2.1) igneous rocks. The reported zircon ages suggest a long-lived subduction, starting at ca. 800 Ma and terminated by ca. 580–570 Ma with no geological record of a final collision event; (3) the continuation of extension gave rise to the undocking of Avalonia from the back-arc. Detrital zircon ages in Lowermost Cambrian strata suggest that the main arc edifice had drifted away by ca. 550–540 Ma and was no longer shedding detritus into the back-arc basin. (4) During the Lower Ordovician, further extension of an already thinned crust gave rise to the Lower Ordovician ‘Ollo de Sapo’ magmatic event (ca. 480 Ma). Coeval volcanism in neighbouring areas displaying within-plate geochemical signatures is consistent with an extensional setting for the generation of the Lower Ordovician igneous and sedimentary rocks. Detrital zircon ages and Nd isotopic features of the Ordovician greywackes reflect both an increase in the contribution from older crustal components and the addition of newly accreted crust. A progressively thinning crust is a likely scenario that would explain the simultaneous exhumation of lower crustal (Grenvillian+Transamazonian/Icartian) material and the generation of coeval magmatism. This latter scenario is consistent with models proposed for other circum-North Atlantic Avalonian-Cadomian terranes where repeated episodes of melting occurred in response to subduction and subsequent rifting events

Terrane accretion and dispersal in the northern Gondwana margin. An Early Paleozoic analogue of a long-lived active margin

If reconstruction of major events in ancient orogenic belts is achieved in sufficient detail, the tectonic evolution of these belts can offer valuable information to widen our perspective of processes currently at work in modern orogens. Here, we illustrate this possibility taking the western European Cadomian–Avalonian belt as an example. This research is based mainly on the study and interpretation of U–Pb ages of more than 300 detrital zircons from Neoproterozoic and Early Paleozoic sedimentary rocks from Iberia and Brittany. Analyses have been performed using the laser ablation–ICP–MS technique. The U–Pb data record contrasting detrital zircon age spectra for various terranes of western Europe. The differences provide information on the processes involved in the genesis of the western European Precambrian terranes along the northern margin of Neoproterozoic Gondwana during arc construction and subduction, and their dispersal and re-amalgamation along the margin to form the Avalonia and Armorica microcontinents. The U–Pb ages reported here also support the alleged change from subduction to transform activity that led to the final break-up of the margin, the birth of the Rheic Ocean and the drift of Avalonia. We contend that the active northern margin of Gondwana evolved through several stages that match the different types of active margins recognised in modern settings

Raman phonons as a probe of disorder, fluctuations and local structure in doped and undoped orthorhombic and rhombohedral manganites

We present a rationalization of the Raman spectra of orthorhombic and rhombohedral, stoichiometric and doped, manganese perovskites. In particular we study RMnO3 (R= La, Pr, Nd, Tb, Ho, Er, Y and Ca) and the different phases of Ca or Sr doped RMnO3 compounds as well as cation deficient RMnO3. The spectra of manganites can be understood as combinations of two kinds of spectra corresponding to two structural configurations of MnO6 octahedra and independently of the average structure obtained by diffraction techniques. The main peaks of compounds with regular MnO6 octahedra, as CaMnO3, highly Ca doped LaMnO3 or the metallic phases of Ca or Sr doped LaMnO3, are bending and tilt MnO6 octahedra modes which correlate to R-O(1) bonds and Mn-O-Mn angles respectively. In low and optimally doped manganites, the intensity and width of the broad bands are related to the amplitude of the dynamic fluctuations produced by polaron hopping in the paramagnetic insulating regime. The activation energy, which is proportional to the polaron binding energy, is the measure of this amplitude. This study permits to detect and confirm the coexistence, in several compounds, of a paramagnetic matrix with lattice polaron together with regions without dynamic or static octahedron distortions, identical to the ferromagnetic metallic phase. We show that Raman spectroscopy is an excellent tool to obtain information on the local structure of the different micro or macro-phases present simultaneously in many manganites.Comment: Submitted to PR

Photon-assisted tunneling in a Fe8 Single-Molecule Magnet

The low temperature spin dynamics of a Fe8 Single-Molecule Magnet was studied under circularly polarized electromagnetic radiation allowing us to establish clearly photon-assisted tunneling. This effect, while linear at low power, becomes highly non-linear above a relatively low power threshold. This non-linearity is attributed to the nature of the coupling of the sample to the thermostat.These results are of great importance if such systems are to be used as quantum computers.Comment: 4 pages, 4 figure

As lideranças e a diferenciação curricular inclusiva: que caminhos para a escola do século XXI?

Com este artigo pretende-se analisar num primeiro momento, o conceito de diferenciação curricular no plano conceptual e dentro de um quadro de análise que permita aprofundar e clarificar o seu sentido no contexto da escola para todos e no enquadramento da massificação da escolarização, fazendo referência à globalização a qual traz novos aspectos para o debate em torno da finalidade da escola. Analisa-se num segundo momento, o papel da liderança democrática e participativa no desempenho do binómio curricular (currículo nacional e projectos curriculares) na medida em que a articulação entre níveis centrais e de escola para o desenvolvimento da diferenciação curricular inclusiva se constitui como meta indispensável para algo assim. Considera-se nesta perspectiva a liderança propulsora da diferenciação curricular inclusiva na dimensão da praxis curricular das escolas e dos professores. Por último relaciona-se esta problemática com a perspectiva da teoria crítica no quadro de escolas entendidas como boas escolas

Enhanced skin delivery of vismodegib-loaded rigid liposomes combined with ethosomes

Vismodegib, first approved in 2012 for the treatment of basal cell carcinoma, is an inhibitor of the Hedgehog signaling pathway that becomes active in certain tumors. However, its secondary effects after oral administration and systemic distribution are severe. In this study, we loaded vismodegib into conventional liposomes, which are typically unable to penetrate the stratum corneum barrier effectively after topical application. We studied its skin penetration when coadministered with empty ethosomes, aimed at transiently disrupting the skin impermeability. The drug was successfully recovered from the deeper viable epidermal layers in an in vitro model. The preparation method for the liposomal formulation is reproducible and relatively straightforward to scale up. Furthermore, it involves the use of biocompatible lipids, thus avoiding the utilization of potentially risky compounds.Instituto Multidisciplinario de Biología CelularInstituto de Investigaciones Fisicoquímicas Teóricas y AplicadasComisión de Investigaciones Científicas de la provincia de Buenos Aire

Soil-landscape and climatic relationships in the middle Miocene of the Madrid Basin

The Miocene alluvial-lacustrine sequences of the Madrid Basin, Spain, formed in highly varied landscapes. The presence of various types of palaeosols allows assessment of the effects of local and external factors onsedimentation, pedogenesis and geomorphological development. In the northern, more arid, tectonicallyactive arca, soils were weakly developed in aggrading alluvial fans, dominated by mass flows. reflecting high sedimentation rates. In more distal parts of the fans and in playa lakes calcretes and dolocretes developed: the former were associated with Mg-poor fan sediments whitc: the latter formed on Mg-rich lake clays exposed during minar lake lowstands. The nonh-east part of the basin had a less arid climate. Alluvial fans in this area were dominated by stream Aood deposits, sourced by carbonate terrains. Floodplain and freshwater lakc deposits formed in distal areas. The high local supply of calcium carbonate may have contributed to the preferential developmenl on calcretes on the fans. Both the fan and floodplain palaeosols exhibit pedofacies relationships and more mature soils developed in settings more distant from the sediment sources. Palaeosols also developed on pond and lake margin carbonates, and led to the formation of palustrine limestones. The spatial distributions and stratigraphies of palaeosols in the Madrid Basin alluvial fans suggest that soil formation was controlled by local factors. These palaeosols differ from those seen in Quatemary fans. Which are characterized by climatically induced periods of stability and instability

Theory and phenomenology of two-Higgs-doublet models

We discuss theoretical and phenomenological aspects of two-Higgs-doublet extensions of the Standard Model. In general, these extensions have scalar mediated flavour changing neutral currents which are strongly constrained by experiment. Various strategies are discussed to control these flavour changing scalar currents and their phenomenological consequences are analysed. In particular, scenarios with natural flavour conservation are investigated, including the so-called type I and type II models as well as lepton-specific and inert models. Type III models are then discussed, where scalar flavour changing neutral currents are present at tree level, but are suppressed by either specific ansatze for the Yukawa couplings or by the introduction of family symmetries. We also consider the phenomenology of charged scalars in these models. Next we turn to the role of symmetries in the scalar sector. We discuss the six symmetry-constrained scalar potentials and their extension into the fermion sector. The vacuum structure of the scalar potential is analysed, including a study of the vacuum stability conditions on the potential and its renormalization-group improvement. The stability of the tree level minimum of the scalar potential in connection with electric charge conservation and its behaviour under CP is analysed. The question of CP violation is addressed in detail, including the cases of explicit CP violation and spontaneous CP violation. We present a detailed study of weak basis invariants which are odd under CP. A careful study of spontaneous CP violation is presented, including an analysis of the conditions which have to be satisfied in order for a vacuum to violate CP. We present minimal models of CP violation where the vacuum phase is sufficient to generate a complex CKM matrix, which is at present a requirement for any realistic model of spontaneous CP violation.Comment: v3: 180 pages, 506 references, new chapter 7 with recent LHC results; referee comments taken into account; submitted to Physics Report

Association of lipid-related genetic variants with the incidence of atrial fibrillation: The AFGen consortium

Background: Several studies have shown associations between blood lipid levels and the risk of atrial fibrillation (AF). To test the potential effect of blood lipids with AF risk, we assessed whether previously developed lipid gene scores, used as instrumental variables, are associated with the incidence of AF in 7 large cohorts. Methods: We analyzed 64,901 individuals of European ancestry without previous AF at baseline and with lipid gene scores. Lipid-specific gene scores, based on loci significantly associated with lipid levels, were calculated. Additionally, non-pleiotropic gene scores for high-density lipoprotein cholesterol (HDLc) and low-density lipoprotein cholesterol (LDLc) were calculated using SNPs that were only associated with the specific lipid fraction. Cox models were used to estimate the hazard ratio (HR) and 95% confidence intervals (CI) of AF per 1-standard deviation (SD) increase of each lipid gene score. Results: During a mean follow-up of 12.0 years, 5434 (8.4%) incident AF cases were identified. After meta-analysis, the HDLc, LDLc, total cholesterol, and triglyceride gene scores were not associated with incidence of AF. Multivariable-adjusted HR (95% CI) were 1.01 (0.98-1.03); 0.98 (0.96-1.01); 0.98 (0.95-1.02); 0.99 (0.97-1.02), respectively. Similarly, non-pleiotropic HDLc and LDLc gene scores showed no association with incident AF: HR (95% CI) = 1.00 (0.97-1.03); 1.01 (0.99-1.04). Conclusions In this large cohort study of individuals of European ancestry, gene scores for lipid fractions were not associated with incident AF