Observations from Preliminary Experiments on Spatial and Temporal Pressure Measurements from Near-Field Free Air Explosions

It is self-evident that a crucial step in analysing the performance of protective structures is to be able to accurately quantify the blast load arising from a high explosive detonation. For structures located near to the source of a high explosive detonation, the resulting pressure is extremely high in magnitude and highly non-uniform over the face of the target. There exists very little direct measurement of blast parameters in the nearfield, mainly attributed to the lack of instrumentation sufficiently robust to survive extreme loading events yet sensitive enough to capture salient features of the blast. Instead literature guidance is informed largely by early numerical analyses and parametric studies. Furthermore, the lack of an accurate, reliable data set has prevented subsequent numerical analyses from being validated against experimental trials. This paper presents an experimental methodology that has been developed in part to enable such experimental data to be gathered. The experimental apparatus comprises an array of Hopkinson pressure bars, fitted through holes in a target, with the loaded faces of the bars flush with the target face. Thus, the bars are exposed to the normally or obliquely reflected shocks from the impingement of the blast wave with the target. Pressure-time recordings are presented along with associated Arbitary-Langrangian-Eulerian modelling using the LS-DYNA explicit numerical code. Experimental results are corrected for the effects of dispersion of the propagating waves in the pressure bars, enabling accurate characterisation of the peak pressures and impulses from these loadings. The combined results are used to make comments on the mechanism of the pressure load for very near-field blast events

Impact of the hypoxic microenvironment on spermatogonial stem cells in culture

The stem cell niche plays a crucial role in the decision to either self-renew or differentiate. Recent observations lead to the hypothesis that O2 supply by blood and local O2 tension could be key components of the testicular niche of spermatogonial stem cells (SSCs). In this study, we investigated the impact of different hypoxic conditions (3.5%, 1%, and 0.1% O2 tension) on murine and human SSCs in culture. We observed a deleterious effect of severe hypoxia (1% O2 and 0.1% O2) on the capacity of murine SSCs to form germ cell clusters when plated at low density. Severe effects on SSCs proliferation occur at an O2 tension ≤1% and hypoxia was shown to induce a slight differentiation bias under 1% and 0.1% O2 conditions. Exposure to hypoxia did not appear to change the mitochondrial mass and the potential of membrane of mitochondria in SSCs, but induced the generation of mitochondrial ROS at 3.5% and 1% O2. In 3.5% O2 conditions, the capacity of SSCs to form colonies was maintained at the level of 21% O2 at low cell density, but it was impossible to amplify and maintain stem cell number in high cell density culture. In addition, we observed that 3.5% hypoxia did not improve the maintenance and propagation of human SSCs. Finally, our data tend to show that the transcription factors HIF-1α and HIF-2α are not involved in the SSCs cell autonomous response to hypoxia

Guidelines of a metamaterial for launcher tank dynamic experiment

International audienceLiquid hydrogen is at the center of space propulsion and new launcher generation issues. Nowadays, experiments and modelling of liquid hydrogen (LH2) dynamic vibratory behaviour in deformable launcher tanks cause some scientific and technical problems. Indeed, the conditioning, transport and security problematics still remain critical. The TANKYOU project aim is to provide to the French space domain a substitute metamaterial replacing LH2 during dynamic experiment tests. This specified metamaterial will represent the LH2 dynamic behaviour within a tank, without presenting the same flammability, explosiveness and fugacity risks. This new material developed by combining a numerical and an experimental methodologies should permit to simplify and secure cryotechnical launcher tanks qualification

Application of the Discrete Elements Method to frequency analysis and use of the “bond” method for fracture modeling

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Discrete Element Modelling of a metamaterial for launcher tanks dynamic experiments

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The Body We Care for: Figures of Anthropo-zoo- genesis

M. Akrich et M. Berg, (éds.) Body and Society. Special Issue on « Bodies on Trial ». Sage Publications (London, Thousand Oaks and New Delhi)SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Modeling of multi-edge effects in the case of laser shock loadings applied on thin foils: Application for material characterization of aluminum alloys

This article presents the study of the shock wave propagation through aluminum alloys (pure aluminum and aluminum 2024-T3) produced by laser plasma using experimental and numerical tests. Water confinement regime interaction, pulse duration (7.2 ns), and power density (1-5 GW / cm 2) range correspond to laser shock peening process configuration and parameters. To that scope, we simulate the shock wave propagation using non-linear explicit code LS-DYNA, which we validate with experimental results. Thereupon, we present a descriptive analysis that links separately the material model and loading conditions to the dynamic response of aluminum alloys under high strain rate laser shock by coupling the Johnson-Cook (J-C) material model with the Grüneisen equation of state (MAT_015 and EOS_GRUNEISEN accordingly). In addition, we make use of stress propagation into target thickness to analyze the origin of different points on the Back Face Velocity (BFV) profile during shock propagation. Finally, we provide evidence that 2D compressive effects do not depend only on the focal spot size or target thickness such as the edge effects but also on power density and material initial yield strength

Impact of the hypoxic microenvironment on spermatogonial stem cells in culture

International audienceThe stem cell niche plays a crucial role in the decision to either self-renew or differentiate. Recent observations lead to the hypothesis that O 2 supply by blood and local O 2 tension could be key components of the testicular niche of spermatogonial stem cells (SSCs). In this study, we investigated the impact of different hypoxic conditions (3.5%, 1%, and 0.1% O 2 tension) on murine and human SSCs in culture. We observed a deleterious effect of severe hypoxia (1% O 2 and 0.1% O 2 ) on the capacity of murine SSCs to form germ cell clusters when plated at low density. Severe effects on SSCs proliferation occur at an O 2 tension ≤1% and hypoxia was shown to induce a slight differentiation bias under 1% and 0.1% O 2 conditions. Exposure to hypoxia did not appear to change the mitochondrial mass and the potential of membrane of mitochondria in SSCs, but induced the generation of mitochondrial ROS at 3.5% and 1% O 2 . In 3.5% O 2 conditions, the capacity of SSCs to form colonies was maintained at the level of 21% O 2 at low cell density, but it was impossible to amplify and maintain stem cell number in high cell density culture. In addition, we observed that 3.5% hypoxia did not improve the maintenance and propagation of human SSCs. Finally, our data tend to show that the transcription factors HIF-1α and HIF-2α are not involved in the SSCs cell autonomous response to hypoxia