Influence de l'épaisseur en fatigue oligocyclique d'assemblages soudés : une méthode rapide

Les assemblages soudés demeurent largement utilisés dans le domaine de la construction navale. Même si, en raison des concentrations de contraintes et du chargement cyclique rencontré, les joints soudés sont des sites d'amorçage privilégiés de fissures de fatigue. Aussi, connaitre l'historique des contraintes et des déformations aux points critiques de la structure est indispensable, en particulier dans les zones de plasticité confinée. Afin d'éviter de longs calculs non linéaires par éléments finis, des méthodes de calcul simplifié du champ élasto-plastique de contrainte/déformation peuvent être utilisées. Lors de précédents travaux, une approche pour estimer l'état de contraintes aux points critiques a été développée et appliquée aux cas d'éprouvettes entaillées. Le travail porte cette fois sur son application à des joints soudés en T dans le but de calculer leur durée de vie à l'amorçage d'une fissure de fatigue. Enfin, une approche paramétrique, destinée à s'affranchir de tout calcul par éléments finis, a été adoptée afin de prendre en compte les géométries locales du cordon soudé. Les prévisions issues de cette approche ont alors été comparées à des résultats expérimentaux et ont permis d'évaluer l'effet de l'épaisseur sur la tenue en fatigue oligocyclique de ces structures soudées

Regulation of LRRK2 Expression Points to a Functional Role in Human Monocyte Maturation

Genetic variants of Leucine-Rich Repeat Kinase 2 (LRRK2) are associated with a significantly enhanced risk for Parkinson disease, the second most common human neurodegenerative disorder. Despite major efforts, our understanding of LRRK2 biological function and regulation remains rudimentary. In the present study we analyze LRRK2 mRNA and protein expression in sub-populations of human peripheral blood mononuclear cells (PBMCs). LRRK2 mRNA and protein was found in circulating CD19+ B cells and in CD14+ monocytes, whereas CD4+ and CD8+ T cells were devoid of LRRK2 mRNA. Within CD14+ cells the CD14+CD16+ sub-population of monocytes exhibited high levels of LRRK2 protein, in contrast to CD14+CD16- cells. However both populations expressed LRRK2 mRNA. As CD14+CD16+ cells represent a more mature subset of monocytes, we monitored LRRK2 expression after in vitro treatment with various stress factors known to induce monocyte activation. We found that IFN-γ in particular robustly increased LRRK2 mRNA and protein levels in monocytes concomitant with a shift of CD14+CD16− cells towards CD14+CD16+cells. Interestingly, the recently described LRRK2 inhibitor IN-1 attenuated this shift towards CD14+CD16+ after IFN-γ stimulation. Based on these findings we speculate that LRRK2 might have a role in monocyte maturation. Our results provide further evidence for the emerging role of LRRK2 in immune cells and regulation at the transcriptional and translational level. Our data might also reflect an involvement of peripheral and brain immune cells in the disease course of PD, in line with increasing awareness of the role of the immune system in PD

Large Energy Depletion of a Beam Driver in a Plasma-Wakefield Accelerator

Beam-driven plasma-wakefield acceleration has the potential to reduce the size and construction cost of large-scale accelerator facilities, by providing accelerating fields orders of magnitude greater than that of conventional accelerating structures. To keep the running costs affordable, high energy-transfer efficiency from the wall-plug to the accelerated bunch has to be demonstrated. For this, drive bunches must be efficiently produced, strong decelerating fields must be sustained for the drive bunches until their energy is depleted, and the resulting accelerating fields must be strongly beam loaded by the trailing bunches. Here we address the second of these points, showing measurements performed at FLASHForward using a 500 MeV drive bunch where approximately half of its total energy is deposited into a 20 cm long plasma. This level of energy-transfer efficiency demonstrates that plasma accelerators hold the potential to become competitive with conventional accelerators

Large Energy Depletion of a Beam Driver in a Plasma-Wakefield Accelerator

Beam-driven plasma-wakefield acceleration has the potential to reduce the building cost of accelerator facilities, with large accelerating fields that are orders of magnitude greater than those of radio-frequency cavities. Sustaining strong decelerating fields for the driver and strong accelerating fields for the trailing bunch across long plasma stages will be key to demonstrating high energy efficiency in this scheme, which is necessary to keep the running costs low for such a facility. We show first measurements at FLASHForward with a 500 MeV drive bunch depositing approximately half of its energy into a 20 cm long plasma

Driver energy depletion - Large energy depletion of a beam driver in a plasma-wakefield accelerator

Beam-driven plasma-wakefield acceleration has the potential to reduce the building cost of accelerator facilities, with large accelerating fields that are orders of magnitude greater than those of radio-frequency cavities. Sustaining strong decelerating fields for the driver and strong accelerating fields for the trailing bunch across long plasma stages will be key to demonstrating high energy efficiency in this scheme, which is necessary to keep the running costs low for such a facility. We show first measurements at FLASHForward with a 500 MeV drive bunch depositing approximately half of its energy into a 20 cm long plasma

Progress Towards High Overall Energy Efficiency in a Beam-Driven Plasma-Wakefield Accelerator Stage

Beam-driven plasma-wakefield acceleration has the potential to reduce the building cost of accelerator facilities, with large accelerating fields that are orders of magnitude greater than radio-frequency cavities. Sustaining strong decelerating fields for the driver and strong accelerating fields for the trailing bunch across long plasma stages will be key to demonstrating high energy efficiency in this scheme. We present preliminary experimental results of driver electrons decelerated to zero energy at the FLASHForward plasma-accelerator facility at DESY

Driver energy depletion - Energy Depletion and Re-Acceleration of Driver Electrons

For plasma-wakefield accelerators to fulfil their potential for cost effectiveness and reduced envi-ronmental footprint, it is essential that their energy-transfer efficiency be maximized. A key aspectof this efficiency is the near-complete transfer of energy, or depletion, from the driver electrons tothe plasma wake. Achieving full depletion is limited by the process of re-acceleration, which oc-curs when the driver electrons decelerate to non-relativistic energies, slipping backwards into theaccelerating phase of the wakefield and being subsequently re-accelerated. Such re-accelerationis observed here for the first time. At this re-acceleration limit, we measure a beam driver de-positing (56 ± 5)% of its energy into a 195-mm-long plasma. Combining this driver-to-plasmaefficiency with previously measured plasma-to-beam and expected wall-plug-to-driver efficien-cies, our result shows that plasma-wakefield accelerators can in principle reach or even exceed theenergy-transfer efficiency of conventional accelerators

Energy depletion in Plasma-Wakefield Acceleration - Progress toward high overall energy efficiency in a beam-driven plasma-wakefield accelerator stage

Beam-driven plasma-wakefield acceleration has the potential to reducethe building cost of accelerator facilities, with large accelerating fieldsthat are orders of magnitude greater than radio-frequency cavities.Sustaining strong decelerating fields for the driver and strong acceler-ating fields for the trailing bunch across long plasma stages will be keyto demonstrating high energy efficiency in this scheme. We presentpreliminary experimental results towards high overall energy efficiencyperformed at the FLASHForward plasma-accelerator facility at DESY

Large Energy Depletion of a Beam Driver in a Plasma-Wakefield Accelerator

Beam-driven plasma-wakefield acceleration has the potential to reduce the size and construction cost of large-scale accelerator facilities, by providing accelerating fields orders of magnitude greater than that of conventional accelerating structures. To keep the running costs affordable, high energy-transfer efficiency from the wall-plug to the accelerated bunch has to be demonstrated. For this, drive bunches must be efficiently produced, strong decelerating fields must be sustained for the drive bunches until their energy is depleted, and the resulting accelerating fields must be strongly beam loaded by the trailing bunches. Here we address the second of these points, showing measurements performed at FLASHForward using a 500 MeV drive bunch where approximately half of its total energy is deposited into a 20 cm long plasma. This level of energy-transfer efficiency demonstrates that plasma accelerators hold the potential to become competitive with conventional accelerators. An experimental outlook of how to achieve this goal will conclude the talk

Large Energy Depletion of a Beam Driver in a Plasma-Wakefield Accelerator

Beam-driven plasma-wakefield acceleration has the potential to reduce the building cost of accelerator facilities, with large accelerating fields that are orders of magnitude greater than radio-frequency cavities. Sustaining strong decelerating fields for the driver and strong accelerating fields for the trailing bunch across long plasma stages will be key to demonstrating high energy efficiency in this scheme. We present preliminary experimental results of driver electrons decelerated to zero energy at the FLASHForward plasma-accelerator facility at DESY