Inferring the photometric and size evolution of galaxies from image simulations

Current constraints on models of galaxy evolution rely on morphometric catalogs extracted from multi-band photometric surveys. However, these catalogs are altered by selection effects that are difficult to model, that correlate in non trivial ways, and that can lead to contradictory predictions if not taken into account carefully. To address this issue, we have developed a new approach combining parametric Bayesian indirect likelihood (pBIL) techniques and empirical modeling with realistic image simulations that reproduce a large fraction of these selection effects. This allows us to perform a direct comparison between observed and simulated images and to infer robust constraints on model parameters. We use a semi-empirical forward model to generate a distribution of mock galaxies from a set of physical parameters. These galaxies are passed through an image simulator reproducing the instrumental characteristics of any survey and are then extracted in the same way as the observed data. The discrepancy between the simulated and observed data is quantified, and minimized with a custom sampling process based on adaptive Monte Carlo Markov Chain methods. Using synthetic data matching most of the properties of a CFHTLS Deep field, we demonstrate the robustness and internal consistency of our approach by inferring the parameters governing the size and luminosity functions and their evolutions for different realistic populations of galaxies. We also compare the results of our approach with those obtained from the classical spectral energy distribution fitting and photometric redshift approach.Our pipeline infers efficiently the luminosity and size distribution and evolution parameters with a very limited number of observables (3 photometric bands). When compared to SED fitting based on the same set of observables, our method yields results that are more accurate and free from systematic biases.Comment: 24 pages, 12 figures, accepted for publication in A&

A model to describe the mechanical behavior and the ductile failure of hydrided Zircaloy-4 fuel claddings between 25 °C and 480 °C

International audienceA model is proposed to describe the mechanical behavior and the ductile failure at 25, 350 and 480 °C of Zircaloy-4 cladding tubes, as-received and hydrided up to 1200 wt. ppm (circumferential hydrides). The model is based on the Gurson–Tvergaard–Needleman model extended to account for plastic anisotropy and viscoplasticity. The model considers damage nucleation by both hydride cracking and debonding of the interface between the Laves phase precipitates and the matrix. The damage nucleation rate due to hydride cracking is directly deduced from quantitative microstructural observations. The other model parameters are identified from several experimental tests. Finite element simulations of axial tension, hoop tension, expansion due to compression and hoop plane strain tension experiments are performed to assess the model prediction capability. The calibrated model satisfactorily reproduces the effects of hydrogen and temperature on both the viscoplastic and the failure properties of the material. The results suggest that damage is anisotropic and influenced by the stress state for the non-hydrided or moderately hydrided material and becomes more isotropic for high hydrogen contents

PHEW: a parallel segmentation algorithm for three-dimensional AMR datasets

We introduce phew ( Parallel Hi Erarchical Watershed), a new segmentation algorithm to detect structures in astrophysical fluid simulations, and its implementation into the adaptive mesh refinement (AMR) code ramses. phew works on the density field defined on the adaptive mesh, and can thus be used on the gas density or the dark matter density after a projection of the particles onto the grid. The algorithm is based on a `watershed' segmentation of the computational volume into dense regions, followed by a merging of the segmented patches based on the saddle point topology of the density field. phew is capable of automatically detecting connected regions above the adopted density threshold, as well as the entire set of substructures within. Our algorithm is fully parallel and uses the MPI library. We describe in great detail the parallel algorithm and perform a scaling experiment which proves the capability of phew to run efficiently on massively parallel systems. Future work will add a particle unbinding procedure and the calculation of halo properties onto our segmentation algorithm, thus expanding the scope of phew to genuine halo finding

Failure of hydrided zircaloy-4 fuel cladding tubes under RIA loading conditions

2-5 septembre 2008International audienceThe anisotropic viscoplastic behavior and the fracture of cold worked ...

Plastic deformation process and fracture of Zircaloy-4 PWR cladding samples tested under RIA loading conditions monitored with high speed optical and infrared cameras

The hypothetical scenario of a control rod ejection in a Pressurised Water Reactor leads to a Reactivity Initiated Accident (RIA [1]) triggering rapid thermal expansion of the pellet. Theses conditions result in a strain-controlled loading on the cladding with large strain rate (about 1s-1). Because the cladding does not have time to increase in temperature, its ductility is limited. Such strain rates are high enough to enhance adiabatic conditions, in which localized heating due to rapid plastic deformation could be significant enough to lead to material softening. Tensile tests at strain rates ranging from 0.1s-1 to 10s-1 and temperatures ranging from 25°C to 480°C were performed on cold-worked Zircaloy-4 samples. All tests were monitored by either a high-speed infrared camera at frame rates up to 3600Hz or optical high speed camera at frames rates up to 12500hz. Some tests were performed monitored simultaneously by theses two cameras. Three different tubular sample geometries were tested, allowing the study of cladding behaviour and failure in the axial and circumferential directions. An increase in temperature of up to 80°C was measured for strain rates of 5s-1 and 10s-1 , and its effects on mechanical response is under analysis by thermo-mechanical FEM calculations, where Taylor- Quinney coefficient would be taken into account

Mesures de champs de déformations et d'échauffements de gaines en Zircaloy-4 sollicitées en conditions représentatives d'un accident d'excursion de réactivité

The hypothetical scenario of a control rod ejection in a Pressurised Water Reactor leads to a Reactivity Initiated Accident (RIA) triggering rapid thermal expansion of the pellet. Theses conditions result in a strain-controlled loading on the cladding with large strain rate (about 1s- 1). Because the cladding does not have time to increase in temperature, its ductility is limited. Such strain rates are high enough to enhance adiabatic conditions, in which localized heating due to rapid plastic deformation could be significant enough to lead to material softening. Tensile tests at strain rates ranging from 0.1 s-1 to 10s-1 and temperatures ranging from 25°C to 480°C were performed on cold-worked Zircaloy-4 samples. All tests were monitored by either a high-speed infrared camera at frame rates up to 3600Hz or optical high speed camera at frames rates up to 12500hz. Some tests were performed monitored simultaneaously by theses two cameras. Three different tubular sample geometries were tested, allowing the study of cladding behaviour and failure in the axial and circumferential directions. An increase in temperature of up to 80°C was measured for strain rates of 5 /s and 10 /s , and its effects on mechanical response is under analysis by thermo-mechanical FEM calculations, where Taylor-Quinney coefficient would be taken into account

Behavior and failure of uniformly hydrided Zircaloy-4 fuel claddings between 25 °C and 480 °C under various stress states, including RIA loading conditions

International audienceThe anisotropic plastic behavior and the fracture of as-received and hydrided Cold-Worked Stress Relieved Zircaloy-4 cladding tubes are investigated under thermal-mechanical loading conditions representative of Pellet-Clad Mechanical Interaction during Reactivity Initiated Accidents in Pressurized Water Reactors. In order to study the combined effects of temperature, hydrogen content, loading direction and stress state, Axial Tensile, Hoop Tensile, Expansion Due to Compression and hoop Plane Strain Tensile tests are performed at room temperature, 350 °C and 480 °C on the material containing various hydrogen contents up to 1200 wt. ppm (hydrides are circumferential and homogeneously distributed). These tests are combined with digital image correlation and metallographic and fractographic observations at different scales. The flow stress of the material decreases with increasing temperature. The material is either strengthened or softened by hydrogen depending on temperature and hydrogen content. Plastic anisotropy depends on temperature but not on hydrogen content. The ductility of the material decreases with increasing hydrogen content at room temperature due to damage nucleation by hydride cracking. The plastic strain that leads to hydride fracture at room temperature decreases with increasing hydrogen content. The influence of stress triaxiality on hydride cracking is negligible in the studied range. The influence of hydrogen on material ductility is negligible at 350 °C and 480 °C since hydrides do not crack at these temperatures. The ductility of the material increases with increasing temperature. The evolution of material ductility is associated with a change in both the macroscopic fracture mode of the specimens and the microscopic failure mechanisms

Ductility and Failure Behaviour of both Unirradiated and Irradiated Zircaloy-4 Cladding Using Plane Strain Tensile Specimens

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Prognostic value of high-sensitivity measurable residual disease assessment after front-line chemoimmunotherapy in chronic lymphocytic leukemia

International audienceMeasurable residual disease (MRD) status is widely adopted in clinical trials in patients with chronic lymphocytic leukemia (CLL). Findings from FILO group trials (CLL2007FMP, CLL2007SA, CLL2010FMP) enabled investigation of the prognostic value of high-sensitivity (0.7 × 10-5) MRD assessment using flow cytometry, in blood (N = 401) and bone marrow (N = 339), after fludarabine, cyclophosphamide, and rituximab (FCR)-based chemoimmunotherapy in a homogeneous population with long follow-up (median 49.5 months). Addition of low-level positive MRD < 0.01% to MRD ≥ 0.01% increased the proportion of cases with positive MRD in blood by 39% and in bone marrow by 27%. Compared to low-level positive MRD < 0.01%, undetectable MRD was associated with significantly longer progression-free survival (PFS) when using blood (72.2 versus 42.7 months; hazard ratio 0.40, p = 0.0003), but not when using bone marrow. Upon further stratification, positive blood MRD at any level, compared to undetectable blood MRD, was associated with shorter PFS irrespective of clinical complete or partial remission, and a lower 5-year PFS rate irrespective of IGHV-mutated or -unmutated status (all p < 0.05). In conclusion, high-sensitivity (0.0007%) MRD assessment in blood yielded additional prognostic information beyond the current standard sensitivity (0.01%). Our approach provides a model for future determination of the optimal MRD investigative strategy for any regimen