Simultaneous laser-driven x-ray and two-photon fluorescence imaging of atomizing sprays

In this Letter, we report for the first time, to the best of our knowledge, the possibility of visualizing an atomizing spray by simultaneously recording x-ray absorption and two-photon laser-induced fluorescence imaging. This unique illumination/detection scheme is made possible due to the use of soft x rays emitted from a laser-driven x-ray source. An 800 mJ laser pulse of 38 fs duration is used to generate an x-ray beam with up to 4 × 108 photons ranging from 1 to 10 keV, allowing projection radiography of water jets generated by an automotive port fuel injector. In addition, a fraction of the laser pulse (∼10mJ) is employed to form a light sheet and to induce two-photon fluorescence in a dye added to the water. The resulting high-contrast fluorescence images provide fine details of the spray structure, with reduced blur from multiple light scattering, while the integrated liquid mass is extracted from the x-ray radiography. In this proof of principle, we show that the combination of these two highly complementary techniques, in both the visible and soft x-ray regimes, is very promising for future characterization of challenging spray, as well as for further understanding of the physics of liquid atomization

De Pierre Corneille à Paul Valéry

Guénot H. De Pierre Corneille à Paul Valéry. In: La revue pédagogique, tome 88, Janvier-Juin 1926. pp. 265-278

De Pierre Corneille à Paul Valéry

Guénot H. De Pierre Corneille à Paul Valéry. In: La revue pédagogique, tome 88, Janvier-Juin 1926. pp. 265-278

Multidisciplinary approach for assessing the atmospheric impact of launchers

Exhausts from rockets influence the atmospheric chemistry and the atmospheric radiative transfer. Assessing these effects requires a multidisciplinary approach. It ranges from combustion calculations in the rocket engines to plume simulations on different scales. The plume is first analysed with computational fluid dynamic models and engineering methods. Then a diffusion model is applied and lastly a chemical transport model is used for simulations on a global scale. This approach is currently being implemented in the Atmospheric Impact of Launchers project, which is funded by ESA as part of its CleanSpace Initiative. Therefore, the focus of this study lies on rockets launching from Kourou, which are Ariane 5, Vega and Soyuz

Interaction of ultraintense radially-polarized laser pulses with plasma mirrors

International audienceWe present experimental results of vacuum laser acceleration (VLA) of electrons using radially polarized laser pulses interacting with a plasma mirror. Tightly focused, radially polarized laser pulses have been proposed for electron acceleration because of their strong longitudinal electric field, making them ideal for VLA. However, experimental results have been limited until now because injecting electrons into the laser field has remained a considerable challenge. Here, we demonstrate experimentally that using a plasma mirror as an injector solves this problem and permits us to inject electrons at the ideal phase of the laser, resulting in the acceleration of electrons along the laser propagation direction while reducing the electron beam divergence compared to the linear polarization case. We obtain electron bunches with few-MeV energies and a 200-pC charge, thus demonstrating, for the first time, electron acceleration to relativistic energies using a radially polarized laser. High-harmonic generation from the plasma surface is also measured, and it provides additional insight into the injection of electrons into the laser field upon its reflection on the plasma mirror. Detailed comparisons between experimental results and full 3D simulations unravel the complex physics of electron injection and acceleration in this new regime: We find that electrons are injected into the radially polarized pulse in the form of two spatially separated bunches emitted from the p-polarized regions of the focus. Finally, we leverage on the insight brought by this study to propose and validate a more optimal experimental configuration that can lead to extremely peaked electron angular distributions and higher energy beams

SIMULATION OF RIA TRANSIENTS ON MOX FUEL RODS WITH ALCYONE FUEL PERFORMANCE CODE

International audienceAs regards Reactivity-Initiated Accidents (RIAs), the ALCYONE multidimensional fuel performance code co-developed by CEA, EDF and Framatome within the PLEIADES software environment is intended to predictively simulate the response of a fuel rod by taking account of mechanisms in a way that models the physics as closely as possible, encompassing all possible stages of the transient (PCMI and post-DNB phases) as well as various fuel/cladding material types and irradiation conditions of interest. Validated for PWR-UO2 fuels, it is now being adapted to simulate the behaviour of Zircaloy-4-based claddings shrouding MOX fuel pellets. ALCYONE V1.4 RIA-related features and modelling are first presented. The constitutive model for the oxide fuel includes cracking in tension, thermal creep and grain-boundary cracking. The modelling of grain-boundary cracking-induced fission gas release (the dominant release mechanism in RIAs) and swelling are discussed in this paper. Simulations of RIA transients performed on MOX fuel rods from the French CABRI REP-Na programme in flowing sodium coolant conditions are then compared to relevant experimental results. This paper shows to what extent ALCYONE-starting from base irradiation conditions it itself computes-is currently ready to simulate and analyse further tests on MOX fuel to be performed under prototypical PWR conditions within the CABRI International Programme. The homogeneous modelling gives satisfactory results. An alternative and heterogeneous approach may be a complementary path towards a more local description of the MOX fuel behaviour under RIA conditions: if both heterogeneous and homogeneous approaches will give the same information and results at the macroscopic level, the heterogeneous one will enable to understand, via numerical simulations, what happens at lower (meso-and microscopic) scales

Stereotactic Electroencephalography Is a Safe Procedure, Including for Insular Implantations.

In some cases of drug-resistant focal epilepsy, noninvasive presurgical investigation may be insufficient to identify the ictal onset zone and the eloquent cortical areas. In such situations, invasive investigations are proposed using either stereotactic electroencephalography (SEEG) or subdural grid electrodes. Meta-analysis suggests that SEEG is safer than subdural grid electrodes, but insular implantation of SEEG electrodes has been thought to carry an additional risk of intraparenchymal hemorrhagic complications. Our objectives were to determine whether an insular SEEG trajectory is a risk factor for intracranial hematoma and to report the global safety of the procedure and provide some guidelines to prevent and detect complications. In a retrospective analysis of a surgical series of 525 consecutive procedures between 1995 and 2015, all electrodes were classified according to their insular or extrainsular trajectory. All complications were classified as major or minor according to their potential consequences regarding patient neurologic status. Four intraparenchymal hematomas, all related to extrainsular electrodes (4/4974; 0.08%) were reported; no hematoma was found along insular electrodes (0/1042; 0%). There were 8 major complications (1.52%): 7 intracranial hematomas (1.33%) and 1 case of meningitis. Two patients had long-term neurologic impairment (0.38%), and 1 death (not directly related to the procedure) occurred (0.19%). Eleven minor complications (2.09%) were encountered, including broken electrode (1.52%), acute pneumocephalus (0.38%), and local cutaneous infection (0.19%). SEEG is a safe procedure. Insular trajectories cannot be considered an additional risk of intracranial bleeding

SEEG-guided radiofrequency thermocoagulation (SEEG RF-TC): from in vitro and in vivo data to technical guidelines

International audienceBackgroundDeep brain electrodes have been used for the last ten years to produce bipolar SEEG-guided radiofrequency thermo-coagulation (SEEG RF-TC). However, this technique is based on empirical knowledge. The aim of this study is threefold: 1) provide in vivo animal data concerning the effect of bipolar RF-TC on brain and its safety 2) assess the parameters of this procedure (current delivery and dipole selection) which produce the most efficient lesion and 3) provide technical guidelines.MethodsFirst we achieved in vivo RF-TC on rabbit brain with several conditions (power delivered and lesioning duration) and analyzed their influence on the lesion produced. Only a difference in terms of volume was found and type of histological lesions was similar whatever the settings were. We then performed multiple RF-TC in vitro on egg albumen first with several parameters of radiofrequency then with different dipole spatial selections. The endpoint was the size of the radiofrequency thermo-lesion produced.ResultsUsing unfixed parameters of radiofrequency current delivery and increasing it until the power delivered by the generator collapsed produced significantly larger lesions (p = 0.008) than other conditions. Concerning the dipole selection, the use of contiguous contacts on electrodes lead to lesions with a higher volume (p = 7.7 x 10-13) than those produced with noncontiguous ones.ConclusionBeside the target selection in SEEG RF-TC, which are summarized based on a literature review, we report the optimal parameters: radiofrequency-current must be increased until the power delivered collapses and dipoles should be constituted by contiguous electrode contacts