Quantification and localization of the liquid zone of partially remelted M2 tool steel using X-ray microtomography and scanning electron microscopy

The authors warmly thank Luc Morhain and Marc Wary (Arts et Métiers ParisTech CER Metz) for their technical support.Thixoforming of steels poses challenges due to the high temperatures involved and the lack of understanding of thermomechanical behavior. The volume fractions of the liquid and solid phases in the semi-solid state are the most important parameters for such a form-ing process, as they affect the viscosity and hence the flow behavior of the material. Two-dimensional observations might not always be sufficient, as the size distribution and the connectivity of phases cannot be obtained from associated measurements, which can only be determined by three-dimensional (3-D) investigation. This paper presents the first application of high-energy X-ray microtomography to the microstructure of steel in the semi-solid state. The microstructure of M2 high-speed tool steel was studied in both as-received and heated-and-quenched states. From the reconstructed images, 3-D information could be obtained and was compared with scanning elec-tron microscopy and energy dispersive spectrometry observations. The volume fraction and the location of liquid phase in the semi-solid state were determined in particular, and the continuous solid skeleton was investigated

Evaluating kernels on Xeon Phi to accelerate Gysela application

This work describes the challenges presented by porting parts ofthe Gysela code to the Intel Xeon Phi coprocessor, as well as techniques used for optimization, vectorization and tuning that can be applied to other applications. We evaluate the performance of somegeneric micro-benchmark on Phi versus Intel Sandy Bridge. Several interpolation kernels useful for the Gysela application are analyzed and the performance are shown. Some memory-bound and compute-bound kernels are accelerated by a factor 2 on the Phi device compared to Sandy architecture. Nevertheless, it is hard, if not impossible, to reach a large fraction of the peek performance on the Phi device,especially for real-life applications as Gysela. A collateral benefit of this optimization and tuning work is that the execution time of Gysela (using 4D advections) has decreased on a standard architecture such as Intel Sandy Bridge.Comment: submitted to ESAIM proceedings for CEMRACS 2014 summer school version reviewe

Adaptive Covariance Estimation with model selection

We provide in this paper a fully adaptive penalized procedure to select a covariance among a collection of models observing i.i.d replications of the process at fixed observation points. For this we generalize previous results of Bigot and al. and propose to use a data driven penalty to obtain an oracle inequality for the estimator. We prove that this method is an extension to the matricial regression model of the work by Baraud

Ultrafast Magneto-Acoustics in Nickel Films

We report about the existence of magneto-acoustic pulses propagating in a 200-nm-thick ferromagnetic nickel film excited with 120 fs laser pulses. They result from the coupling between the magnetization of the ferromagnetic film and the longitudinal acoustic waves associated to the propagation of the lattice deformation induced by the femtosecond laser pulses. The magneto-acoustic pulses are detected from both the front and back sides of the film, using the time-resolved magneto-optical Kerr technique, measuring both the time dependent rotation and ellipticity. We show that the propagating acoustic pulse couples efficiently to the magnetization and is strong enough to induce a precession of the magnetization. It is due to a transient change of the crystalline anisotropy associated to the lattice deformation. It is shown that the results can be interpreted by combining the concepts of acoustic pulse propagation and ultrafast magnetization dynamics.Comment: 4 pages, 3 figures, Submitted to Physical Review Letters on November 30th 201

Toward high-precision values of the self energy of non-S states in hydrogen and hydrogen-like ions

The method and status of a study to provide numerical, high-precision values of the self-energy level shift in hydrogen and hydrogen-like ions is described. Graphs of the self energy in hydrogen-like ions with nuclear charge number between 20 and 110 are given for a large number of states. The self-energy is the largest contribution of Quantum Electrodynamics (QED) to the energy levels of these atomic systems. These results greatly expand the number of levels for which the self energy is known with a controlled and high precision. Applications include the adjustment of the Rydberg constant and atomic calculations that take into account QED effects.Comment: Minor changes since previous versio

Switching dynamics of spatial solitary wave pixels

Separatrices and scaling laws in the switching dynamics of spatial solitary wave pixels are investigated. We show that the dynamics in the full model are similar to those in the plane-wave limit. Switching features may be indicated and explained by the motion of the (complex) solitary wave amplitude in the phase plane. We report generalization, into the domain of transverse effects, of the pulse area theorem for the switching process and a logarithmic law for the transient dynamics. We also consider, for what is the first time to our knowledge, phase-encoded address of solitary pixels and find that a near-square-wave temporal switching pattern is permitted without (transverse) cross switching

Residual activity of insecticides applied against Lobesia botrana and its influence on resistance management strategies.

Some insect growth disruptors, in particular chitin synthesis inhibitors (benzoylphenyl ureas) and ecdysone agonists (bisacylhydrazines), show high efficacy against Lobesia botrana (Denis et Schiffermuller) (Lepidoptera Tortricidae) and are characterized by a longer residual activity than the traditional organophosphate active ingredients. Previous research had shown that the persistence of some active ingredients applied against the first generation of L. botrana also ensured control of the second generation. In this study, the residual activity of insecticides applied against the second generation was evaluated on the third generation in field trials and laboratory bioassays. Methoxyfenozide controlled the third generation at the same efficacy level (more than 90%) when applied against the second or the third generations. Some residual activity was observed in the field also for indoxacarb (efficacy 75%). In contrast, a very low residual activity (efficacy lower than 30%) was recorded for chlorpyrifos. Because a longer residual activity is associated with a higher risk of selecting insecticide resistant populations, operational resistance management strategies are discussed to ensure a longer usable life span of these insecticides