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We formulate a security game in a context of mixed armament acquisition, involving a finite set of Nations in strategic relationship, with utility functions which are nonlinear and non-differentiable on the boundary of their sets of definition. Since we want to study the long-term effect of the Nations' investment in nuclear weapons, we focus on the steady-state analysis of the game. This requires us to extend the classical results from Rosen on compact-convex games, to unbounded convex games, relying on the coercivity property of the Nations' utility functions. In addition, we prove the existence and uniqueness, under mild assumptions, of an interior point Nash Equilibrium solution of the game. Simulations are performed in case of a duopoly, highlighting the efficiency loss reduction and stabilizing effect of nuclear armaments by comparison with the conventional-only setting.

International audience; This work experimentally addresses aluminum combustion in steam, pure or mixed with diluents, for aluminum particles in size range 40 ∼80 μm, using an electrodynamic levitator. High-speed videos unveil an unreported and complex mechanism in steam, not observed in other oxidizers. The detached flame is quite faint and very close to the surface. Alumina smoke around the droplet rapidly condenses and coalesces into a large, single orbiting alumina satellite. It eventually collides the main aluminum droplet while generating secondary alumina droplets. A unique feature is the presence of several distinct oxide lobes on the droplet, which merge only at the end of burning and encapsulate the remaining aluminum, possibly promoting an incomplete combustion. The measured burning times in pure water vapor are longer than expected and the efficiency of steam is found to be 30% that of oxygen, lower than the usually accepted value of 60%. A general correlation on burning time, including the major oxidizers, is proposed. Direct numerical simulations are conducted and are in line with experiments, in terms of burning rate or flame stand off ratio. Combustion in steam seems mostly supported by surface reactions, giving a faint flame with low gas temperatures and high hydrogen content. It is speculated that those two specific features could help explain the peculiarity of steam.

International audience; Aluminum particles are widely used as an additive to increase energetic performances. Recently, Aluminum has also received a growing interest as a source of hydrogen for fuel cell applications, or in novel power generation concepts as it provides a carbon-free energy that meets current policies for reducing emissions of greenhouse gases. Our recent studies focused on the description of the combustion process varying ambient conditions (pressure and oxidizer). Only the second stage of the combustion process, after the establishment of a steady state, was scrutinized. The proposed work sheds light more specifically to the initial stages where the particle is warmed up from the initial state to a thermal runaway condition. Indeed, the question arises at what temperature do these condensed fuels burst into flames, knowing that the presence of a passive coat greatly influences the process.For this study, a dedicated set-up has been improved. It consists of an electrodynamic levitator in which a single particle, trapped by electrostatic forces, burns in a controlled atmosphere. A two-color ratio pyrometer has been specifically assembled with photomultipliers (PM) to obtain the time evolution of mean surface temperature. The PM signals are synchronised witha particle visualization device that is composed of a high-speed camera combined with a long-distance microscope. Subsequently, the temperature measurement of high temporal resolution can then be associated for the first time at a rate of 250 000 fps with the fast-apparent phenomenology of the pre-ignition processes. In addition, the spatial resolution of the visualization (1.92 μm/pix) allows the interpretation of the PM signals to be commented.

Karst aquifers are known for their wide distribution of water transfer velocities. From this observation, a multiple geochemical tracer approach seems to be particularly well suited to provide a significant assessment of groundwater flows, but the choice of adapted tracers is essential. In this study, several common tracers in karst aquifers such as physicochemical parameters, major ions, stable isotopes, and δ13C to more specific tracers such as dating tracers – 14C, 3H, 3H–3He, CFC-12, SF6 and 85Kr, and 39Ar – were used, in a fractured karstic carbonated aquifer located in Burgundy (France). The information carried by each tracer and the best sampling strategy are compared on the basis of geochemical monitoring done during several recharge events and over longer time periods (months to years). This study’s results demonstrate that at the seasonal and recharge event time scale, the variability of concentrations is low for most tracers due to the broad spectrum of groundwater mixings. The tracers used traditionally for the study of karst aquifers, i.e., physicochemical parameters and major ions, efficiently describe hydrological processes such as the direct and differed recharge, but require being monitored at short time steps during recharge events to be maximized. From stable isotopes, tritium, and Cl− contents, the proportion of the fast direct recharge by the largest porosity was estimated using a binary mixing model. The use of tracers such as CFC-12, SF6, and 85Kr in karst aquifers provides additional information, notably an estimation of apparent age, but they require good preliminary knowledge of the karst system to interpret the results suitably. The CFC-12 and SF6 methods efficiently determine the apparent age of baseflow, but it is preferable to sample the groundwater during the recharge event. Furthermore, these methods are based on different assumptions such as regional enrichment in atmospheric SF6, excess air, and flow models among others. 85Kr and 39Ar concentrations can potentially provide a more direct estimation of groundwater residence time. Conversely, the 3H–3He method is inefficient in the karst aquifer for dating due to 3He degassing.

The compression of argon is measured between 10 K and 296 K up to 20 GPa and and up to 114 GPa at 296 K in diamond anvil cells. Three samples conditioning are used: (1) single crystal sample directly compressed between the anvils, (2) powder sample directly compressed between the anvils, (3) single crystal sample compressed in a pressure medium. A partial transformation of the face-centered cubic (fcc) phase to a hexagonal close-packed (hcp) structure is observed above 4.2–13 GPa. Hcp phase forms through stacking faults in fcc-Ar and its amount depends on pressurizing conditions and starting fcc-Ar microstructure. The quasi-hydrostatic equation of state of the fcc phase is well described by a quasi-harmonic Mie–Grüneisen–Debye formalism, with the following 0 K parameters for Rydberg-Vinet equation: $$V_0$$ V 0 = 38.0 Å$$^3$$ 3 /at, $$K_0$$ K 0 = 2.65 GPa, $$K'_0$$ K 0 ′ = 7.423. Under the current experimental conditions, non-hydrostaticity affects measured P–V points mostly at moderate pressure ($$\le$$ ≤ 20 GPa).

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Plastic deformation, static recovery and recrystallization in pure tantalum are analyzed in the present paper. Quantitative analysis of dislocation sub-structures were done. Sub-structures development is completely dependent on crystallographic orientation. No clear effect of recovery was observed when direct analysis was made. Hence, recovery was studied through its effect on recrystallization. Recovery heat treatments followed by a recrystallization heat treatment were applied to compare the recrystallized state of samples which were subject to prior recovery with those which were not. Results show that recrystallization is accelerated in the early stages of recovery (low temperature or low annealing time or low plastic strain). On the opposite, in the advanced stages of recovery, it slows down recrystallization. Results show again an influence of crystallographic orientation. Static recrystallization was also investigated and the influence of crystallographic orientation, most probably inherited from the deformed state through dislocation sub-structures, was observed. Based on experimental results, a discussion on the mechanisms of nucleation in the different orientation grains is presented. Finally, a discussion is made on the quantification of stored energy. The effect of the observation scale and the choices of considering dislocation density or dislocation sub-boundaries energies from EBSD data is discussed.

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International audience; We investigated in this work the radioluminescence properties of a Ce-doped multimode silica-based optical fiber (core diameter of 50 µm) manufactured by the sol–gel technique when exposed to the high-energy X-rays (~600 keV) of the ORIATRON facility of CEA. We demonstrated its potential to monitor in real-time the beam characteristics of this facility that can either operate in a pulsed regime (pulse duration of 4.8 µs, maximum repetition rate of 250 Hz) or in a quasi-continuous mode. The radiation-induced emission (radioluminescence and a minor Cerenkov contribution) linearly grew with the dose rate in the 15–130 mGy(SiO$_2$)/s range, and the afterglow measured after each pulse was sufficiently limited to allow a clear measurement of pulse trains. A sensor with ~11 cm of sensitive Ce-doped fiber spliced to rad-hard fluorine-doped optical fiber, for the emitted light transport to the photomultiplier tube, exhibited interesting beam monitoring performance, even if the Cerenkov emission in the transport fiber was also considered (~5% of the signal). The beam monitoring potential of this class of optical fiber was demonstrated for such facilities and the possibilities of extending the dose rate range are discussed based on possible architecture choices such as fiber type, length or size.

International audience; An analytical formula for the ionizing dose of low energy electrons is proposed. The expressions have been validated for 11 monatomic elements (C, Be, Al, Si, Ti, Ni, Cu, Ge, Ag, Fe and W) and for energies ranging from ∼ 10 eV up to 14.5 keV by the use of low energy Monte Carlo simulations. These expressions can be used to evaluate the energy loss of low energy electrons as an input for other simulation codes.; Une formule analytique pour la dose ionisante des électrons de basse énergie est proposée. Les expressions ont été validées pour 11 éléments monatomiques (C, Be, Al, Si, Ti, Ni, Cu, Ge, Ag, Fe et W) et pour des énergies allant de ∼ 10 eV jusqu'à 14,5 keV par l'utilisation de simulations Monte Carlo de basse énergie. Ces expressions peuvent être utilisées pour évaluer la perte d'énergie des électrons de basse énergie comme entrée pour d'autres codes de simulation.

International audience; In order to ensure reliability of systems early in the design phase, it is becoming crucial to have models able to predict the behavior of systems exposed to ElectroStatic Discharge (ESD). This is an increasing necessity since the number of embedded electronic products is growing and since they are employed in applications where people's safety is a requirement, such as automotive and aeronautic applications. Until now, quasi-static models of protection devices have succeeded in providing fairly good results in failure predictions (mainly hard failures). Today, the increased frequency range of such devices requires dynamic models able to reproduce their transient behavior. In this paper, we investigate if conventional methods for modeling linear devices, generally used in the frequency domain, could be used to obtain an equivalent frequency model for ESD protection devices, which exhibit non-linear behavior. A methodology to extract an ESD protection SPICE model from Transmission Line Pulse (TLP) measurements to address transient and frequency simulation is proposed and detailed. We demonstrate that, in well-defined conditions, such frequency models can give accurate results to predict overshoots related to protection device triggering delays. Validation of the models is performed under TLP and Human Metal Model (HMM) conditions on three off-the-shelf devices.

International audience; Some recent space experiments, e.g. OTD, LIS, show the large interest of lightning monitoring from space and the efficiency of optical measurement. Future instrumentations are now defined for the next generation of geostationary meteorology satellites. Calibration of these instruments requires ground truth events provided by lightning location networks, as NLDN in US, and EUCLID or LINET in Europe, using electromagnetic observations at a regional scale. One of the most challenging objectives is the continuous monitoring of the lightning activity over the tropical zone (Africa, America, and Indonesia). However, one difficulty is the lack of lightning location networks at regional scale in these areas to validate the data quality. TARANIS (Tool for the Analysis of Radiations from lightNings and Sprites) is a CNES micro satellite project. It is dedicated to the study of impulsive transfers of energy, between the Earth atmosphere and the space environment, from nadir observations of Transient Luminous Events (TLEs), Terrestrial Gamma ray Flashes (TGFs) and other possible associated emissions. Its orbit will be sun-synchronous at 10:30 local time; its altitude will be 700 km. Its lifetime will be nominally 2 years. Its payload is composed of several electromagnetic instruments in different wavelengths: X and gamma-ray detectors, optical cameras and photometers, electromagnetic wave sensors from DC to 30 MHz completed by high energy electron detectors. The optical instrument includes 2 cameras and 4 photometers. All sensors are equipped with filters for sprite and lightning differentiation. The filters of cameras are designed for sprite and lightning observations at 762 nm and 777 nm respectively. However, differently from OTD or LIS instruments, the filter bandwidth and the exposure time (respectively 10 nm and 91 ms) prevent lightning optical observations during daytime. The camera field of view is a square of 500 km at ground level with a spatial sampling frequency of about 1 km. One of the photometers will measure precisely the lightning radiance in a wide spectral range from 600 to 900 nm with a sampling frequency of 20 kHz. We suggest using the Event and mainly Survey mode of MCP instrument to monitor lightning activity and compare it to the geostationary satellite lightning mapper data. In the Event mode, data are recorded with their highest resolution. In the camera survey mode, every image is archived using a specific compression algorithm. The photometer Survey mode consists in decimating the data by a factor of 10 and to reduce the data dynamic. However, it remains well adapted to provide a good continuous characterization of lightning activity. The use of other instruments for example 0+ whistler detector will complete the lightning characterization.

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International audience; L’accident de la centrale de Fukushima en mars 2011 a engendré un marquage, très faible mais néanmoins mesurable avec les techniques d’analyse les plus performantes, de l’environnement proche du site en isotopes à vie longue de l’uranium (U) et du plutonium (Pu). Ces actinides constituent des traceurs très intéressants pour évaluer les dynamiques de transport des particules de sédiments jusqu’à l’Océan. Ainsi, des analyses d’ultra-traces d’U et de Pu dans des sédiments de la région de Fukushima ont été effectuées, essentiellement dans le cadre de la thèse d’Hugo Jaegler, afin d’établir les variations spatio-temporelles de leurs concentrations.Les analyses ont nécessité un traitement chimique long et complexe pour extraire, concentrer et purifier l’U et le Pu à partir de 5 g d’échantillon. Les mesures isotopiques se sont également révélées délicates, tout d’abord en raison de la faiblesse des teneurs en actinides, mais surtout en raison de la préexistence dans les sédiments d’U naturel, mais aussi d’U et de Pu issus des retombées des essais nucléaires atmosphériques. Cependant, la mesure des abondances isotopiques des deux éléments, en particulier celles des isotopes 241Pu et 236U, permet de déterminer leur origine. Les rapports isotopiques du Pu (240Pu/239Pu, 241Pu/239Pu et 242Pu/239Pu) ont été mesurés au CEA (Direction des Applications Militaires, Arpajon) par ICPMS haute résolution (Thermo "Element XR") et ICPMS multi-collection (Thermo "Neptune Plus"). Un soin tout particulier a été apporté à l’optimisation de la sensibilité des instruments afin d’obtenir des limites de détection inférieures au fg. Les rapports isotopiques de l’U ont été mesurés par ICPMS/MS (Agilent 8800) à l’IRSN (Fontenay-aux-Roses) et au CEA (Direction des Energies, Gif-sur-Yvette). Ces deux laboratoires ont mis en œuvre de nouvelles méthodes d’analyse qui permettent de déterminer des rapports 236U/238U extrêmement faibles, de l’ordre de 10-9.Cette présentation décrit les méthodes et techniques d’analyse utilisées, en particulier pour les mesures isotopiques par ICPMS. Quelques exemples de résultats sont donnés pour illustrer les performances analytiques obtenues.

Novel properties associated with nanothermites have attracted great interest for several applications, including lead-free primers and igniters. However, the prediction of quantitative structure-energetic performance relationships is still challenging. This study investigates machine learning methods as tools to surrogate complex physical models to design novel nanothermites with optimized burning rates chosen for energetic performance. The study focuses on Al/CuO nanolaminates, for which nine supervised regressors commonly used in ML applied to materials science are investigated. For each, an ML model is built using a database containing a set of 2700 Al/CuO nanolaminate systems, specifically generated for this study. We demonstrate the superiority of the multilayer perceptron algorithm to surrogate conventional physical-based models and predict the Al/CuO nanolaminate microstructure-burn rate relationship with good efficiency: the burn rate is estimated with less than 1% error (0.07 m·s

International audience; We combine electromagnetic measurements with meteorological and lightning detection data to explain an observation of unusually strong preliminary breakdown (PB) produced by a thunderstorm system that developed along the Mediterranean Coast of Southern France in the early hours of 19 June 2013. This multi-cellular storm was composed of several parallel convective lines in the NW-SE direction. Our analysis focuses on 10 sequences of energetic electromagnetic PB pulses recorded by two receivers located at different distances from this thunderstorm. The peak currents, which generated these strong PB pulses, reached −36 kA. The initial polarity of all observed energetic PB pulses confirmed the movement of the negative charge downward, as in case of PB pulses preceding negative cloud-to-ground discharges. The locations of PB pulses appeared in areas with none or very weak lightning activity. Most PB pulses were initiated in small, short-living, rapidly moving convective storm cells characterized by low reflectivity values (generally

International audience; We design an unfitted hybrid high-order (HHO) method for the wave equation. The wave propagates in a domain where a curved interface separates subdomains with different material properties. The key feature of the discretization method is that the interface can cut more or less arbitrarily through the mesh cells. We address both the second-order formulation in time of the wave equation and its reformulation as a first-order system. We prove H 1-error estimates for a space semi-discretization in space of the second-order formulation, leading to optimal convergence rates for smooth solutions. Numerical experiments illustrate the theoretical findings and show that the proposed numerical schemes can be used to simulate accurately the propagation of acoustic waves in heterogeneous media, with meshes that are not fitted to the geometry. For the second-order formulation, the implicit, second-order accurate Newmark scheme is used for the time discretization, whereas (diagonally-implicit or explicit) Runge-Kutta schemes up to fourth-order accuracy are used for the first-order formulation. In the explicit case, we study the CFL condition on the time step and observe that the unfitted approach combined with local cell agglomeration leads to a comparable condition as when using fitted meshes.

International audience; The inclusion of sophisticated density-dependent electronic stopping and electron-phonon coupling calculated with first-principles methods into molecular dynamics simulations of collision cascades has recently become possible thanks to the development of the so-called EPH (for Electron-PHonon) model. This work aims at employing the EPH model in molecular dynamics simulations of collision cascades in Si. In this context, the electronic stopping power is investigated in Si at low energies with Ehrenfest Dynamics calculations. Also, the parametrization of the EPH model for Si, from firstprinciples Ehrenfest Dynamics simulations to actual molecular dynamics simulations of collision cascades, is performed and detailed. We demonstrate that the EPH model is able to reproduce very closely the density-dependent features of the energy lost to electrons obtained with ab initio calculations. Molecular dynamics collision cascade simulations results obtained in Si using the EPH model and the simpler but widely employed Two Temperature Model (TTM) are compared, showing important discrepancies in the collision cascades results obtained depending on the model employed.

The work deals with a macroscopically isotropic energetic material based on triamino-trinitrobenzene (TATB) crystals bonded with a small volume fraction of a thermoplastic polymer. This material is shown experimentally to display an irreversible thermal expansion behavior characterized by dilatancy and variations of its thermal expansion coefficient when heated or cooled outside a narrow reversibility temperature range. The analysis of cooling results suggests the existence of residual stresses in the initial state, attributed to the manufacturing process. Microstructure-level FFT computations including the very strong anisotropic thermoelastic TATB crystal response and temperature-dependent binder plasticity, show that strong internal stresses develop in the disoriented crystals under thermal load, either heating or cooling. Upon cooling, binder plastic yielding in hindered, thus promoting essentially brittle microcracking, while it is favored upon heating. Despite its low volume fraction, the role of the binder is essential, its plastic yielding causing stress redistribution and residual stresses upon cooling back to ambient.

International audience; Construire des catalogues d'informations sismologiques des plus complets représente un enjeu majeur en sismologie. L'implémentation régulière d'instruments sur le territoire national et l'accroissement massif de la quantité de données qui y est associée rend cependant difficile le traitement et l'analyse exhaustif des données obtenues. Depuis peu des techniques d'apprentissage machine sont développées par la communauté scientifique pour aider à l'automatisation du traitement de la donnée et palier à ce problème. Parmi ces méthodes, PhaseNet, un algorithme de détection et pointé des phases sismiques régionales basé sur les réseaux de neurones convolutifs, semble particulièrement efficace. Nous présentons ici une analyse des performances et de l'apport potentiel de cet algorithme dans différents cas de figures, de l'utilisation dans le cas d'une antenne sismique temporaire à faible ouverture géométrique (10km2) à celle d'un réseau permanent régional (105 km2), en passant par des installations temporaires en réseaux denses (103 km2), et en intégrants plusieurs types de capteurs.

Most real optimization problems are defined over a mixed search space where the variables are both discrete and continuous. In engineering applications, the objective function is typically calculated with a numerically costly black-box simulation.General mixed and costly optimization problems are therefore of a great practical interest, yet their resolution remains in a large part an open scientific question. In this article, costly mixed problems are approached through Gaussian processes where the discrete variables are relaxed into continuous latent variables. The continuous space is more easily harvested by classical Bayesian optimization techniques than a mixed space would. Discrete variables are recovered either subsequently to the continuous optimization, or simultaneously with an additional continuous-discrete compatibility constraint that is handled with augmented Lagrangians. Several possible implementations of such Bayesian mixed optimizers are compared. In particular, the reformulation of the problem with continuous latent variables is put in competition with searches working directly in the mixed space. Among the algorithms involving latent variables and an augmented Lagrangian, a particular attention is devoted to the Lagrange multipliers for which a local and a global estimation techniques are studied. The comparisons are based on the repeated optimization of three analytical functions and a beam design problem., Accepted for publication in Advanced Modeling and Simulation in Engineering Sciences, march 2022

The largest (M8+) known earthquakes in the Himalaya have ruptured the upper locked section of the Main Himalayan Thrust zone, offsetting the ground surface along the Main Frontal Thrust at the range front. However, out-of-sequence active structures have received less attention. One of the most impressive examples of such faults is the active fault that generally follows the surface trace of the Main Boundary Thrust (MBT). This fault has generated a clear geomorphological signature of recent deformation in eastern and western Nepal, as well as further west in India. We focus on western Nepal, between the municipalities of Surkhet and Gorahi where this fault is well expressed. Although the fault system as a whole is accommodating contraction, across most of its length, this particular fault appears geomorphologically as a normal fault, indicating crustal extension in the hanging wall of the MHT. We focus this study on the reactivation of the MBT along the Surkhet-Gorahi segment of the surface trace of the newly named Reactivated Boundary Fault, which is ~ 120 km long. We first generate a high-resolution Digital Elevation Model from triplets of high-resolution Pleiades images and use this to map the fault scarp and its geomorphological lateral variation. For most of its length, normal motion slip is observed with a dip varying between 20° and 60° and a maximum cumulative vertical offset of 27 m. We then present evidence for recent normal faulting in a trench located in the village of Sukhetal. Radiocarbon dating of detrital charcoals sampled in the hanging wall of the fault, including the main colluvial wedge and overlying sedimentary layers, suggest that the last event occurred in the early sixteenth century. This period saw the devastating 1505 earthquake, which produced ~ 23 m of slip on the Main Frontal Thrust. Linked or not, the ruptures on the MFT and MBT happened within a short time period compared to the centuries of quiescence of the faults that followed. We suggest that episodic normal-sense activity of the MBT could be related to large earthquakes rupturing the MFT, given its proximity, the sense of motion, and the large distance that separates the MBT from the downdip end of the locked fault zone of the MHT fault system. We discuss these results and their implications for the frontal Himalayan thrust system. Nanyang Technological University Published version Tis work was funded by the Nanyang Technological University (NTU, Singapore) and the Commissariat à l’énergie atomique et aux énergies alternatives (CEA, France) as well as the French embassy in Singapore through the PHC-Merlion program (2018–2019). All radiocarbon dating analysis were performed by Beta analytics (Miami, USA). We thank Paul Tapponnier for his contribution in selecting some of the feldwork excursion sites and the Department of Mines and Geology of Nepal for administrative work. Kyle Bradley is also thanked for discussions on Digital Elevation Model analysis. Mara Tiberti, Roger Bilham and two anonymous reviewers provided constructive comments that helped improve the original manuscript.

International audience; In order to demonstrate that digital material engineering methodology is able to address the design and optimisation of architectured ceramic materials, solar volumetric receivers employed in Solar Thermal Power Plants (STPP) have been studied. A digital design approach for obtaining new receivers, at the macroscopic structural scale, is proposed. This approach couples virtual structure generation, ray tracing and thermal simulations at the scale of the base structural components (microscopic scale). Then, a recently developed process for manufacturing silicon carbide (SiC) parts by binder jetting is used to elaborate three optimised structures which are tested on-sun at high temperature in a solar concentrator reproducing the STPP operation conditions. The results obtained with these structures, having original shapes, are promising: the average experimental outlet air temperature reaches a maximum of 1133 K, energy yields can reach 0.49 despite high experimental heat losses, and all the SiC structures, made with a new material based on 3D printing, withstood the high temperatures reached, up to 1500 K. Comparison between digital and experimental results shows that the approach presented in this paper paves the way to a new digital material engineering approach.