POLYCRYSTALLINE MODELLING OF UDIMET 720 FORGING

International audienceA crystalline modelling of deformation implemented in a finite element code coupled to a recrystallization Cellular Automaton code is proposed and applied to forging processes of superalloys. The coupled modelling is used in order to obtain a better understanding of the microstructural evolution of superalloys during high temperature forging at different strain rates and temperatures. The framework of the modelling is large plastic deformation and large lattice rotation. The used internal variables are dislocations densities on slip systems of the different phases. Modelling is based on viscoplatic constitutive and hardening laws at the scale of the slip systems and describes local strain and stress fields as well as the stored energy and the rotation of the lattice in the grains of the microstructure. At different steps of deformation, formation of subgrains, annihilation of dislocations, nucleation, growth and new orientation of grains are computed. The 3D aggregates representing the superalloy, are built up from Electron Back Scattered Diffraction method (EBSD) by means of a high resolution Scanning Electron Microscope. The phases are identified by means of EBSD, chemical analysis (EDS) and observations with a Scanning Electron Microscope. In this paper the studied aggregate is realised from a semi product of Udimet 720. Such technique is able to give us, a realistic description of the crystalline orientation, morphology and position of grains in the aggregate. The Finite Element meshing is deduced from the EBSD analysis. At high temperature, the Udimet 720 is constituted by a γ matrix with a Face Centred Cubic structure (FCC) and γ' precipitates (Ni3(Ti,Al)) with a Simple Cubic structure (SC). The various material parameters used for the coupled modelling are previously determined from compression tests performed at several strain rate and temperature; The dislocation densities are measured from Transmission Electronic Microscope

Reconstruction of seasonal temperature variability in the tropical Pacific Ocean from the shell of the scallop, <i>Comptopallium radula</i>

International audienceWe investigated the oxygen isotope composition (d18O) of shell striae from juvenile Comptopallium radula (Mollusca; Pectinidae) specimens collected live in New Caledonia. Bottom-water temperature and salinity were monitored in-situ throughout the study period. External shell striae form with a 2-day periodicity in this scallop, making it possible to estimate the date of precipitation for each calcite sample collected along a growth transect. The oxygen isotope composition of shell calcite (d18Oshell calcite) measured at almost weekly resolution on calcite accreted between August 2002 and July 2003 accurately tracks bottom-water temperatures. A new empirical paleotemperature equation for this scallop species relates temperature and d18Oshell calcite: t(°C)=20.00(+/-0.61)-3.66(+/-0.39)x(d18Oshell calcite VPDB -d18Owater VSMOW) The mean absolute accuracy of temperature estimated using this equation is 1.0 °C at temperatures between 20 and 30 °C. Uncertainties regarding the precise timing of CaCO3 deposition and the actual variations in d18Owater at our study sites probably contribute to this error. Comparison with a previously published empirical paleotemperature equation indicates that C. radula calcite is enriched in 18O by ~0.7‰ relative to equilibrium. Given the direction of this offset and the lack of correlation between shell growth rate and d18Oshell calcite, this disequilibrium is unlikely to be related to kinetic isotope effects. We suggest that this enrichment reflects (1) a relatively low pH in the scallop's marginal extrapallial fluid (EPF), (2) an isotopic signature of the EPF different from that of seawater, or (3) Rayleigh fractionation during the biocalcification process. Relative changes in d18Oshell calcite reflect seawater temperature variability at this location and we suggest that the shell of C. radula may be useful as an archive of past seawater temperatures

Apocenter pile-up and arcs: a narrow dust ring around HD 129590

Observations of debris disks have significantly improved over the past decades, both in terms of sensitivity and spatial resolution. At near-infrared wavelengths, new observing strategies and post-processing algorithms allow us to drastically improve the final images, revealing faint structures in the disks. These structures inform us about the properties and spatial distribution of the small dust particles. We present new $H$-band observations of the disk around HD 129590, which display an intriguing arc-like structure in total intensity but not in polarimetry, and propose an explanation for the origin of this arc. Assuming geometric parameters for the birth ring of planetesimals, our model provides the positions of millions of particles of different sizes to compute scattered light images. We demonstrate that if the grain size distribution is truncated or strongly peaks at a size larger than the radiation pressure blow-out size we are able to produce an arc quite similar to the observed one. If the birth ring is radially narrow, given that particles of a given size have similar eccentricities, they will have their apocenters at the same distance from the star. Since this is where the particles will spend most of their time, this results in a "apocenter pile-up" that can look like a ring. Due to more efficient forward scattering this arc only appears in total intensity observations and remains undetected in polarimetric data. This scenario requires sharp variations either in the grain size distribution or for the scattering efficiencies $Q_\mathrm{sca}$. Alternative possibilities such as a wavy size distribution and a size-dependent phase function are interesting candidates to strengthen the apocenter pile-up. We also discuss why such arcs are not commonly detected in other systems, which can mainly be explained by the fact that most parent belts are usually broad.Comment: Accepted for publication in A&A, abstract shortene

Retention of nutrients, suspended particulate matter and phytoplankton in a pondage associated with a run-of-the-river type hydroelectric power plant

Reservoirs associated with run-of-the-river type hydroelectrical power plants (i.e. pondages) have short water residence times. For this reason, pondages are thought to have a limited impact on the fluxes of particles and solutes transported by rivers. The Malause reservoir (South West France) is such a pondage. Fed by both the Garonne and Tarn rivers, it has a water residence time of only a few days. Incoming and outgoing fluxes of nutrients, suspended particulate matter (SPM) and phytoplankton were measured weekly over the course of 1 year. Mass balance calculations showed that Malause pondage retained 24% of soluble reactive phosphorus (SRP) supplied by both rivers on an annual basis. SRP retention occurred mostly in spring–summer,pointing to biological uptake. In addition, the pondage was a sink for SPM and phytoplankton, retaining 39% of SPM and 14% of chlorophyll a supplied by both rivers on an annual basis. The retention efficiency appeared to be constrained by water temperature and residence time. The pondage was a source of phytoplankton during summer, when temperature and water residence time was high. The pondage was a sink for SPM when water residence time was low (<1 day). Our observations highlight the need to reconsider the impact of minor hydrological discontinuities on the functioning of the river continuum. The shallow depth of the pondage and the presence of dense stands of submerged macrophytes have probably favoured the retention of nutrients and the sedimentation of particles within the pondage

Viral infection prevents diabetes by inducing regulatory T cells through NKT cell–plasmacytoid dendritic cell interplay

iNKT cell and pDC cross talk prevents type 1 diabetes by inducing T reg cells in the pancreatic lymph node during viral infection

International Geomagnetic Reference Field: the 12th generation

The 12th generation of the International Geomagnetic Reference Field (IGRF) was adopted in December 2014 by the Working Group V-MOD appointed by the International Association of Geomagnetism and Aeronomy (IAGA). It updates the previous IGRF generation with a definitive main field model for epoch 2010.0, a main field model for epoch 2015.0, and a linear annual predictive secular variation model for 2015.0-2020.0. Here, we present the equations defining the IGRF model, provide the spherical harmonic coefficients, and provide maps of the magnetic declination, inclination, and total intensity for epoch 2015.0 and their predicted rates of change for 2015.0-2020.0. We also update the magnetic pole positions and discuss briefly the latest changes and possible future trends of the Earth’s magnetic fiel

Variation in Size and Growth of the Great Scallop Pecten maximus along a Latitudinal Gradient

Understanding the relationship between growth and temperature will aid in the evaluation of thermal stress and threats to ectotherms in the context of anticipated climate changes. Most Pecten maximus scallops living at high latitudes in the northern hemisphere have a larger maximum body size than individuals further south, a common pattern among many ectotherms. We investigated differences in daily shell growth among scallop populations along the Northeast Atlantic coast from Spain to Norway. This study design allowed us to address precisely whether the asymptotic size observed along a latitudinal gradient, mainly defined by a temperature gradient, results from differences in annual or daily growth rates, or a difference in the length of the growing season. We found that low annual growth rates in northern populations are not due to low daily growth values, but to the smaller number of days available each year to achieve growth compared to the south. We documented a decrease in the annual number of growth days with age regardless of latitude. However, despite initially lower annual growth performances in terms of growing season length and growth rate, differences in asymptotic size as a function of latitude resulted from persistent annual growth performances in the north and sharp declines in the south. Our measurements of daily growth rates throughout life in a long-lived ectothermic species provide new insight into spatio-temporal variations in growth dynamics and growing season length that cannot be accounted for by classical growth models that only address asymptotic size and annual growth rate

Fundamental questions and applications of sclerochronology: Community-defined research priorities.

Horizon scanning is an increasingly common strategy to identify key research needs and frame future agendas in science. Here, we present the results of the first such exercise for the field of sclerochronology, thereby providing an overview of persistent and emergent research questions that should be addressed by future studies. Through online correspondence following the 5th International Sclerochronology Conference in 2019, participants submitted and rated questions that addressed either knowledge gaps or promising applications of sclerochronology. An initial list of 130 questions was compiled based on contributions of conference attendees and reviewed by expert panels formed during the conference. Herein, we present and discuss the 50 questions rated to be of the highest priority, determined through an online survey distributed to sclerochronology community members post the conference. The final list (1) includes important questions related to mechanisms of biological control over biomineralization, (2) highlights state of the art applications of sclerochronological methods and data for solving long-standing questions in other fields such as climate science and ecology, and (3) emphasizesthe need for common standards for data management and analysis. Although research priorities are continually reassessed, our list provides a roadmap that can be used to motivate research efforts and advance sclerochronology towardnew, and more powerful, applications.N/