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Belantamab mafodotin (BM) is an anti-BCMA antibody-drug conjugate (GSK2857916) that represents an alternative option in multiple myeloma. We sought to assess the efficacy and safety in real-world of BM in patients who benefited from an early access program. We conducted an observational, retrospective, multicenter study. Eligibility criteria were treatment of relapsed or refractory multiple myeloma (RRMM) in monotherapy in adult patients who have received at least 3 lines of therapy previously, including at least one immunomodulatory agent (IMiD), a proteasome inhibitor (PI) and an anti-CD38 monoclonal antibody, and whose disease progressed during the last treatment period. The primary endpoint of the study is to assess the overall survival (OS). The trial was sponsored by the French group IFM and supported by GSK. Between November 2019 and December 2020, 106 patients were treated with BM; 97 were eligible for the efficacy evaluation and 104 for safety. The median age was 66 (range: 37–82) years. High risk cytogenetics were identified in 40.9% of patients. Fifty-five (56.7%) patients were triple-class refractory and 11 (11.3%) were penta-class refractory. The median number of prior lines of treatment was 5 (range: 3–12). The median number of BM cycles administered was 3 (range: 1–22). The overall response rate at best response was 38.1% (37/97). The median OS was 9.3 months (95%CI: 5.9; 15.3), and median progression-free survival was 3.5 months (95%CI: 1.9; 4.7). The median duration of response was 9 months (range 4.65-10.4). Treatment was delayed for 55 (52.9%) patients including 36.5% for treatment-related toxicity. Ophthalmic adverse events, mainly grade ≤2, were the most common toxicity (48%). The occurrence of keratopathy was 37.5%. Overall, our data are concordant with the results from DREAMM-2 in terms of efficacy and safety on a non-biased population.

International audience; Different regimes are usually observed for fluid migration through an immersed granular layer. In this work, we report a puzzling behavior when injecting water at a constant flow rate through a nozzle at the bottom of an immersed granular layer in a Hele-Shaw cell. In a given range of parameters (granular layer height and fluid flow-rate) the granular bed is not only fuidized, but the particle-laden jet also exhibits periodic oscillations. The frequency and amplitude of the oscillations are quantified. The Strouhal number displays a power-law behavior as a function of a non-dimensional parameter, J, defined as the ratio between the jet velocity at the initial granular bed height and the inertial particle velocity. Fluid-particle coupling is responsible for the jet oscillations. This mechanism could be at the origin of the cyclic behavior of pockmarks and mud volcanoes in sedimentary basins.

International audience; This paper is devoted to an unresolved model for the simulation of air invasion in immersed granular flows without interface reconstruction between the liquid and the gas. Experiments of air invading a granular bed immersed in ethanol were achieved in a Hele-Shaw cell to observe the gas invasion paths and to calibrate the numerical multiscale model. The grains movements are computed at a fine scale using the non-smooth contact dynamics method, a time-stepping method considering impenetrable grains. The fluid flow is modelled by equations averaged using the volume fraction of fluid and computed at a coarse scale with the finite element method. A phase indicator function is used to dissociate the gas and the liquid constituting the fluid and to compute the density and viscosity of the fluid at each position. It is moved using a convection equation at each time step. The fluid, solid and phase indicator function computations are validated on simple cases before being used to reproduce experiments of air invasion in immersed granular flows. The experiments are supported by simulations in two dimensions to refine the study and the understanding of the invasion dynamics at short times.

The rise of a single bubble confined between two vertical plates is investigated over a wide range of Reynolds numbers. In particular, we focus on the evolution of the bubble speed, aspect ratio and drag coefficient during the transition from the viscous to the inertial regime. For sufficiently large bubbles, a simple model based on power balance captures the transition for the bubble velocity and matches all the experimental data despite strong time variations of bubble aspect ratio at large Reynolds numbers. Surprisingly, bubbles in the viscous regime systematically exhibit an ellipse elongated along its direction of motion while bubbles in the inertia-dominated regime are always flattened perpendicularly to it., accepted for publication in JFM Rapids as of April 2022; 10 pages; 5 figures

International audience; The destabilization of oceanic lithosphere by small scale convection at its base is important for providing a holistic picture of mantle/lithosphere coupling. We use three highly resolved tomography models to characterize the base of the oceanic lithosphere in the Pacific Ocean. Regions associated with abnormally thick lithosphere are associated with seafloor older than 100 Ma and are elongated parallel to the direction of present-day Pacific plate motion. They are correlated with bathymetric lows and negative geoid anomalies (for l=10-39 and l=14-39), which can be accounted for by dynamic topography. They do not correlate with volcanic features. We interpret these regions of thickened lithosphere as evidence for sites of lithospheric instabilities where denser lithosphere detaches and sinks into underlying mantle. To understand the phenomena at the origin of these lithospheric 'drips', we performed laboratory experiments. Fluids with different properties are heated from one side to generate a large-scale convection and cooled from the top. This configuration results in the generation of small-scale convection at the base of the upper cold thermal boundary layer. The experimental results show the existence of two possible structures: instabilities organized into longitudinal rolls, aligned in the direction of the large-scale motion and 3D, time-dependent cold plumes that drip from the base of the lithosphere and are sheared away by the large-scale flow. The 3D plume morphology is similar to what we observe in tomography models. This provides insights into the phenomenology at the origin of the lithospheric drips observed in the geophysical data.

International audience; An experimental study of the hydrodynamics of a gas-liquid co-current flow inside a thin sheet of Open Cell Solid Foam (OCSF) confined in a plate reactor is proposed. Image processing is used to quantify the flow patterns when varying the gas and liquid flow rates and buoyancy (horizontal and vertical upflow). The fraction of {\it joint flow} and {\it interface motion} areas, respectively $\varepsilon_m$ and $\varepsilon_i$, are defined as relevant quantities to characterize the different flow regimes and phases interaction. Two distinct regimes are observed for the vertical flow: the low (LA) and high (HA) activity regimes characterized by a low or high phases interaction. In the horizontal configuration, an additional regime is observed and is called pseudo-trickling (PT) regime due to its similarity with the trickling regime observed in vertical downflow packed beds. The transition between LA and HA regimes is compared to the regime transition in trickle beds.

International audience; Nine new human invasive infections caused by the keratinophilic fungi Nannizziopsis obscura have been reported in France since 2004. The patients had variable clinical manifestations, had frequent dissemination, were mainly T-cell immunocompromised, and all originated from sub-Saharan West Africa. Before collection of the isolates, the etiologies of these infections were often misidentified, underscoring the extent of microscopic and cultural polymorphisms. All isolates but 1 had low MICs for the 8 antifungal drugs tested. When treated, patients received mainly azole therapy. Two of 7 patients with a known outcome died. We performed multilocus sequence analysis of N. obscura clinical strains and several strains of Nannizziopsis spp. isolated from reptiles. The human strains were clearly differentiated from the animal strains. N. obscura might be endemic to West Africa and responsible for undetected infections, which might become reactivated when immunosuppression occurs. N. obscura infection is probably underestimated because only sequencing enables proper identification.

International audience; This work focuses on the dynamics of a liquid jet impacting the surface of a confined, immersed granular bed. Although previous works have considered the erosion process and surface morphology, less attention has been given to the jet hydrodynamics. Based on laboratory experiments, we show that when the liquid jet forms a crater, two situations arise. In the case of weak/no erosion or open craters, the jet is stationary. For vertical or overhanging crater walls, the jet displays a wide range of behaviors, from quasi-periodic oscillations to symmetry breaking and exploration of different states in time. An analysis of the different system states leads to the emergence of a bifurcation diagram depending on a dimensionless parameter, J, comparing the jet impact force to the force necessary to eject a grain. The frequency of the jet oscillations depends on the inertial velocity, the jet dispersion and the ratio between the injector cross-section and the confinement length.

International audience; Numerous fields of nonlinear physics, very different in nature, produce signals and images, that share the common feature of being essentially constituted of piecewise homogeneous phases. Analyzing signals and images from corresponding experiments to construct relevant physical interpretations thus often requires detecting such phases and estimating accurately their characteristics (borders, feature differences, ...). However, situations of physical relevance often comes with low to very low signal to noise ratio precluding the standard use of classical linear filtering for analysis and denoising and thus calling for the design of advanced nonlinear signal/image filtering techniques. Additionally, when dealing with experimental physics signals/images, a second limitation is the large amount of data that need to be analyzed to yield accurate and relevant conclusions requiring the design of fast algorithms. The present work proposes a unified signal/image nonlinear filtering procedure, with fast algorithms and a data-driven automated hyperparameter tuning, based on proximal algorithms and Stein unbiased estimator principles. The interest and potential of these tools are illustrated at work on low-confinement solid friction signals and porous media multiphase flows.

International audience; We have studied experimentally particle suspension when injecting a gas at the bottom of an immersed granular layer confined in a Hele-Shaw cell. This work focuses on the dynamics of particles slightly denser than the surrounding fluid. The gas, injected at constant flow-rate, rises through the granular bed then forms bubbles which entrain particles in the above liquid layer. The particles settle down on the edges of the cell, avalanche on the crater formed at the granular bed free surface, and are further entrained by the continuous bubbling at the center. We report the existence of a stationary state, resulting from the competition between particle entrainment and sedimentation. The average solid fraction in the suspension is derived from a simple measurement of the granular bed apparent area. A phenomenological model based on the balance between particle lift by bubbles at the center of the cell and their settling on its sides demonstrates that most of the particles entrained by bubbles come from a global recirculation of the suspension.

International audience; The resolution of data acquired over modern seafloors does not allow imaging of the inner features of a fluid seep structure, particularly in the shallow subsurface. In the SE Basin of France (Drôme), fossil cold seep structures comprising fossil-rich carbonate lenses were identified about 30 years ago within the Oxfordian (Late Jurassic) Terres Noires Formation. These structures were first interpreted as pseudo-bioherms related to hydrothermal activity, but comparison with active seep sites on modern margins, together with isotopic analyses, led to a reinterpretation involving cold fluids instead. To date, all seep sites have generally been studied individually without considering any link to neighbouring or more distant sites. Based on 23 high-resolution stratigraphic logs within the structure coupled to mosaicked aerial photographs from a drone survey, 19 fluid seep events were correlated in the area, including two new sites exposed as a result of weathering. We have shown that each identified sub-site is composed of subvertically stacked fossil-rich carbonate lenses interbedded with marls, which developed in smooth, 4-6 m deep depressions beneath the local seabed. The nodules present within the depressions are of primary importance as they mark the area of active seeping. This general organization is very similar to the modern Regab giant pockmark in the Lower Congo Basin where only a few sub-sites are active at the same time. A spatio-temporal 3D reconstruction of the position of these sub-sites shows that the carbonate lenses are organized into clusters comprising up to seven sub-sites grouped together in the same stratigraphic interval and the same geographical zone. A sandbox experiment where gas is injected at constant flow rate at the base of a box filled with a matrix of water-saturated grains displays a pattern consisting of disturbed sediments inside a parabolic-shaped area. This parabolic shape was also identified on a seismic profile across the Regab giant pockmark, suggesting that the processes are similar for the Beauvoisin and Regab seep areas. The laboratory experiments also show that the seeping conduit is stable during a given period of time and suddenly shifts laterally. This is mainly as a result of the collapse of the conduit, the lateral migration and the reopening at a new position. The general log obtained in the Beauvoisin seep area suggests a similar pattern with periods of seeping alternating with periods of quiescence, each of which is c. 200 kyr. Even if a pockmark seems to have been inactive for a long period of time, this could be due to the lateral shift of the feeder conduit, meaning that the sub-seafloor is still charged with gas. This is of primary importance for risk assessment, hydrocarbon exploration and general understanding of geobiology at seafloor seeps.

A robust approach to access liquid residence time distribution (RTD) adapted to multiphase flow in porous media is presented. It is tailored to meet specific requirements of small scale systems (centimeter, millimeter or less) with Taylor segmented flow feed. The method involves direct visualization using fluorescence microscopy close to both extremities of a porous packing. Critical image treatment steps and optimization of a versatile discrete model with 4 parameters are detailed and discussed. They allow the precise and rapid determination of RTD curves and their 1st- and 2nd-order moments. The application of the method is successfully illustrated with dense micro-packed beds of sub-millimeter particles and highly porous media like open cell solid foams undergoing a preformed G-L segmented (Taylor) flow. Original results regarding the effect of fluid flowrates and different confined porous media are discussed and lead to a single two-parameter liquid hold up correlation, which is valid for both packings. As usual, RTD broadening is treated as a combination of convective dispersion and mass transfer to a fraction of immobile liquid. The predominant role of mass transfer is underlined with an analysis of characteristic times.

In a recent work, Serres et al. (2016) considered the stability of Taylor bubbles entering a confined highly porous medium (open cell solid foam of 96% porosity). This experimental work pointed out that a periodic alternation of gas bubbles and liquid slugs in a millichannel can either keep its regularity, or be destructured at the porous medium entrance. A critical bubble length was proposed as a transition parameter between the two observed regimes. This study presents two key results which complement the previous work and explain the regime transition. (1) The comparison of the Taylor flow upstream the porous medium with the Taylor flow in an empty millichannel demonstrates that the regime transtion is not due to the possible feedback of the foam on the upstream flow. (2) A phenomenological model is proposed, which accounts for the observed bubble coalescence and gas channelling in the porous medium in the range of parameters explored in the experiments.

This work investigates the dynamics of a single bubble rising in a polymer solution confined in a vertical Hele-Shaw cell. Different mixtures of PEO (polyethylene oxide) in water have been used, which exhibit a Newtonian viscosity plateau, followed by a shear-thinning behavior above a shear rate of 0.1 to 1, typically. Depending on the bubble volume, different regimes are reported. When increasing the bubble volume, a transition is observed from a small, round bubble to a cusped bubble, which exhibits a singularity at the rear. Below a critical volume, the bubble rises vertically and does not exhibit any apparent shape deformation. However, above a critical volume, the cusped bubble develops a peculiar instability. Its front flattens at a given angle respect to the horizontal, leading to either a deflection in its trajectory, or its fragmentation. We characterize these two dynamics and interpret the fragmentation process in terms of a viscous fingering recalling the Saffman–Taylor instability. Interestingly, the finger growth is directly controlled by the bubble size.

Anomalous arc volcanoes tend to exist where a linear topographic feature （fracture zone, line of seamounts, or ridge） on the oceanic plate is subducting. “Dots-and-lines tectonics” are proposed for clarifying this tendency and understanding the mechanisms that generate it. Stateof-the-art studies on along-arc variations of volcanism around the Pacific ring of fire and possible effects of inhomogeneities on the subducting oceanic plate are reviewed. Mechanisms generating the clustered distribution of active volcanoes in North-eastern Japan and the extraordinary volcanism at Mount Fuji are reconsidered from a “dots-and-lines” tectonics point of view. Although there still remain many unsolved problems, “dots-and-lines” tectonics could offer a unified explanation of along-arc variations in volcanism, combining processes in mid-ocean ridges, hot spots, and subduction zones. Fil: Ichihara, Mie. The University Of Tokyo; Japón Fil: Adam, Claudia. Kansas State University; Estados Unidos Fil: Vidal, Valérie. Université Claude Bernard Lyon 1; Francia Fil: Grosse, Pablo. Fundación Miguel Lillo; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico - Tucumán. Unidad Ejecutora Lillo; Argentina Fil: Mibe, Kenji. The University Of Tokyo; Japón Fil: Orihashi, Yuji. The University Of Tokyo; Japón

International audience; Frictional weakening by vibrations was first invoked in the 70's to explain unusual fault slips and earthquakes, low viscosity during the collapse of impact craters or the extraordinary mobility of sturzstroms, peculiar rock avalanches which travels large horizontal distances. This mechanism was further invoked to explain the remote triggering of earthquakes or the abnormally large runout of landslides or pyroclastic flows. Recent experimental and theoretical works pointed out that the key parameter which governs frictional weakening in sheared granular media is the characteristic velocity of the vibrations. Here we show that the mobility of the grains is not mandatory and that the vibration velocity governs the weakening of both granular and solid friction. The critical velocity leading to the transition from stick-slip motion to continuous sliding is in both cases of the same order of magnitude, namely a hundred microns per second. It is linked to the roughness of the surfaces in contact.

International audience; A joint gas-liquid flow through a quasi-2D porous medium leads to three hydrodynamic regimes depending on the imposed gas and liquid flow rates. The image analysis highlights the difficulty of a classical morphological algorithm in accurately detecting the bubbles contour and structure. We introduce two more sophisticated methods leading to more realistic contours, and compare quantitatively these three methods. The statistical properties of the bubbles make it possible to determine the typical bubble sizes in the different flow regimes and the global perimeter, characteristic of the interfaces. This latter seems to exhibit a minimum for the transition regime, due to bubble coalescence in the system.; Un écoulement conjoint gaz-liquide dans un milieu poreux quasi-2D conduit à trois régimes hydrodynamiques suivant la valeur des débits imposés. L'analyse des images met en évidence la difficulté d'un algorithme morphologique classique à détecter précisément le contour et la structure des bulles. Nous introduisons deux méthodes plus sophistiquées permettant d'obtenir des contours plus réalistes, et comparons quantitativement ces trois méthodes. L'étude statistique des propriétés des bulles permet de déterminer les tailles typiques des bulles dans les différents régimes d'écoulement, ainsi que le périmètre global, caractéristique des interfaces. Ce dernier semble atteindre un minimum pour le régime de transition, dûà la coalescence de bulles dans le système.

International audience; The present work investigates paper-paper friction dynamics by pulling a slider over a substrate. It focuses on the transition between stick-slip and inertial regimes. Although the device is classical, probing solid friction with the fewest contact damage requires that the applied load should be small. This induces noise, mostly impulsive in nature, on the recorded slider motion and force signals. To address the challenging issue of describing the physics of such systems, we promote here the use of nonlinear filtering techniques relying on recent nonsmooth optimization schemes. In contrast to linear filtering, nonlinear filtering captures the slider velocity asymmetry and, thus, the creep motion before sliding. Precise estimates of the stick and slip phase durations can thus be obtained. The transition between the stick-slip and inertial regimes is continuous. Here we propose a criterion based on the probability of the system to be in the stick-slip regime to quantify this transition. A phase diagram is obtained that characterizes the dynamics of this frictional system under low confinement pressure.

This work focuses on the local hydrodynamics of a multiphase gas–liquid flow forced into an innovative medium of high porosity (96%): an open cell solid foam. The gas (nitrogen) and liquid (ethanol) phases are injected at constant flow-rates in a millichannel to form a well-controlled Taylor flow which enters the porous medium. Based on a fluorescence technique, the apparent liquid holdup in the porous medium is quantified, and its evolution in time and along the porous medium extracted from spatiotemporal diagrams. The analysis of the main frequency, when varying the gas–liquid flow-rate ratio, leads to the identification of two hydrodynamic regimes. A model based on a scaling analysis is proposed to quantify the dimensionless numbers describing the transition between both regimes. It points out that the bubble length fixed by the Taylor flow is the control parameter. The model prediction of the critical bubble length at which the transition occurs is in good agreement with the experimental observations.

The subsidence of young seafloor is generally considered to be a passive phenomenon related to the conductive cooling of the lithosphere after its creation at mid-oceanic ridges. Recent alternative theories suggest that the mantle dynamics plays an important role in the structure and depth of the oceanic lithosphere. However, the link between mantle dynamics and seafloor subsidence has still to be quantitatively assessed. Here we provide a statistical study of the subsidence parameters (subsidence rate and ridge depth) for all the oceans. These parameters are retrieved through two independent methods, the positive outliers method, a classical method used in signal processing, and through the MiFil method. From the subsidence rate, we compute the effective thermal conductivity, k eff , which ranges between 1 and 7 W m−1 K−1. We also model the mantle flow pattern from the S40RTS tomography model. The density anomalies derived from S40RTS are used to compute the instantaneous flow in a global 3D spherical geometry. We show that departures from the k eff = 3 W m − 1 K − 1 standard value are systematically related to mantle processes and not to lithospheric structure. Regions characterized by k eff > 3 W m − 1 K − 1 are associated with mantle uplifts (mantle plumes or other local anomalies). Regions characterized by k eff 3 W m − 1 K − 1 are related to large-scale mantle downwellings such as the Australia–Antarctic Discordance (AAD) or the return flow from the South Pacific Superswell to the East Pacific Rise. This demonstrates that mantle dynamics plays a major role in the shaping of the oceanic seafloor. In particular, the parameters generally considered to quantify the lithosphere structure, such as the thermal conductivity, are not only representative of this structure but also incorporate signals from the mantle convection occurring beneath the lithosphere. The dynamic topography computed from the S40RTS tomography model reproduces the subsidence pattern observed in the bathymetry. Overall we find a good correlation between the subsidence parameters derived from the bathymetry and the dynamic topography. This demonstrates that these parameters are strongly dependent on mantle dynamics.

This work investigates the dynamics of air rising through a water-saturated sand confined in a Hele- Shaw cell in which a circular obstacle is trapped. The air is injected at constant flow rate through a single nozzle at the bottom center of the cell. Without obstacle, in a similar configuration, previous studies pointed out the existence of a fluidized zone generated by the central upward gas motion which entrains two granular convection rolls on its sides. Here, a circular obstacle which diameter is of the order of the central air channel width is trapped at the vertical of the injection nozzle. We analyze the influence of the obstacle location on the size of the fluidized zone and its impact on the morphology of the central air channel. Finally, we quantify the variations of the granular free surface. Two configurations with multiple obstacles are also considered.

The acoustic signal produced by gas slugs bursting at volcano vents is investigated by means of laboratory experiments. In order to explore the transition between linear and nonlinear acoustics, we model the bubble by an overpressurized cylindrical cavity closed by a membrane. We find that the acoustic waveform inside and outside the cavity, produced by the membrane bursting, is well described by the linear acoustics equations and a monopole source model up to an initial overpressure inside the cavity of about 24 kPa. For higher overpressure, the amplitude inside the conduit is smaller than the linear prediction, whereas the amplitude measured outside is larger. The frequency content remains harmonic, even at high initial overpressure. Changing the bursting depth in the conduit does not change the scaling of the amplitudes but affects the waveform and energy partitioning. We show that the energy of the first signal period is about 30% of the total acoustic energy and can be used as a good estimate, with a geometrical correction to account for the bursting depth.

International audience; Multi-scale analysis of gas-liquid flow in confined porous media

This work investigates the dynamics of bubbles in a confined, immersed granular layer submitted to an ascending gas flow. In the stationary regime, a central fluidized zone of parabolic shape is observed, and the bubbles follow different dynamics: either the bubbles are initially formed outside the fluidized zone and do not exhibit any significant motion over the experimental time or they are located inside the fluidized bed, where they are entrained downwards and are, finally, captured by the central air channel. The dependence of the air volume trapped inside the fluidized zone, the bubble size, and the three-phase contact area on the gas injection flow rate and grain diameter are quantified. We find that the volume fraction of air trapped inside the fluidized region is roughly constant and of the order of 2%-3% when the gas flow rate and the grain size are varied. Contrary to intuition, the gas-liquid-solid contact area, normalized by the air injected into the system, decreases when the flow rate is increased, which may have significant importance in industrial applications.

SUMMARY Different types of 4-component ocean bottom seismometers (OBS) were deployed for variable durations ranging from 1 week to about 4 months in 2007, over soft sediments covering the seafloor of the Tekirdag Basin (western part of the Sea of Marmara, Turkey). Non-seismic microevents were recorded by the geophones, but generally not by the hydrophones, except when the hydrophone is located less than a few tens of centimetres above the seafloor. The microevents are characterized by short durations of less than 0.8 s, by frequencies ranging between 4 and 30 Hz, and by highly variable amplitudes. In addition, no correlation between OBSs was observed, except for two OBSs, located 10 m apart. Interestingly, a swarm of ∼400 very similar microevents (based on principal component analysis) was recorded in less than one day by an OBS located in the close vicinity of an active, gas-prone fault cutting through the upper sedimentary layers. The presence of gas in superficial sediments, together with analogies with laboratory experiments, suggest that gas migration followed by the collapse of fluid-filled cavities or conduits could be the source of the observed microevents. This work shows that OBSs may provide valuable information to improve our understanding of natural degassing processes from the seafloor.

We report on the fluidization dynamics of an attractive gel composed of non-Brownian particles made of fused silica colloids. Extensive rheology coupled to ultrasonic velocimetry allows us to characterize the global stress response together with the local dynamics of the gel during shear startup experiments. In practice, after being rejuvenated by a preshear, the gel is left to age during a time $t_w$ before being submitted to a constant shear rate $\dot \gamma$. We investigate in detail the effects of both $t_w$ and $\dot \gamma$ on the fluidization dynamics and build a detailed state diagram of the gel response to shear startup flows. The gel may either display transient shear banding towards complete fluidization, or steady-state shear banding. In the former case, we unravel that the progressive fluidization occurs by successive steps that appear as peaks on the global stress relaxation signal. Flow imaging reveals that the shear band grows up to complete fluidization of the material by sudden avalanche-like events which are distributed heterogeneously along the vorticity direction and correlated to large peaks in the slip velocity at the moving wall. These features are robust over a wide range of values of $t_w$ and $\dot \gamma$, although the very details of the fluidization scenario vary with $\dot \gamma$. Finally, the critical shear rate $\dot \gamma^*$ that separates steady-state shear-banding from steady-state homogeneous flow depends on the width on the shear cell and exhibits a nonlinear dependence with $t_w$. Our work brings about valuable experimental data on transient flows of attractive dispersions, highlighting the subtle interplay between shear, wall slip and aging which modeling constitutes a major challenge that has not been met yet., Comment: main: 12 pages, 10 figures; supplemental: 3 pages, 5 movies and 6 figures

International audience; Triggering large-scale motion by imposing vibrations to a system can be encountered in many situations, from daily-life shaking of saltcellar to silo unclogging or dynamic earthquakes triggering. In the well-known situation of solid or granular friction, the acceleration of imposed vibrations has often been proposed as the governing parameter for the transition between stick-slip motion and continuous sliding. The threshold acceleration for the onset of continuous slip motion or system unjamming is usually found of the order of the gravitational acceleration. These conclusions are mostly drawn from numerical studies. Here, we investigate, in the laboratory, granular friction by shearing a layer of grains subjected to horizontal vibrations. We show that, in contrast with previous results, the quantity that controls the frictional properties is the characteristic velocity, and not the acceleration, of the imposed mechanical vibrations. Thus, when the system is statically loaded, the typical acceleration of the vibrations which trigger large slip events is much smaller than the gravitational acceleration. These results may be relevant to understand dynamic earthquake triggering by small ground perturbations. Granular assemblies are athermal systems, often used as paradigms to study the dynamics of industrial or natural processes, such as fault gouge and earthquake nucleation 1–6. When submitted to mechanical vibrations, granular media can behave as thermalized fluids when the vibrations are large enough, or remain in a solid-like state for small enough vibrations. Such a transition between jammed and unjammed states has been reported to occur when the peak-acceleration characterizing the vibration is of the order of the gravitational acceleration 7,8

Colloque avec actes et comité de lecture. Internationale.; International audience; Ce travail présente l'étude expérimentale du phénomène de stick-slip pour un milieu granulaire sec auquel on impose des vibrations mécaniques horizontales (amplitude A, pulsation ω). Nous avons mis en évidence une diminution de la friction moyenne lorsque l'amplitude des vibrations augmente. Pour des amplitudes de vibrations étonnamment faibles (correspondant à des accélérations de l'ordre de 1% de l'accélération gravitationnelle), on observe une disparition complète du stick-slip. Le système masse-ressort glisse alors continûment sur le lit de grains. Une étude de ce comportement à diverses fréquences de vibration fait apparaître que le paramètre pertinent décrivant la transition stick-slip / glissement continu est la vitesse des vibrations mécaniques, Aω. Pour Aω ≥ 100 microns/s, le stick-slip disparaît, indépendamment de tous les paramètres expérimentaux explorés (vitesse de traction, fréquence de vibration, taille et nature des grains, etc.). Nous interprétons cette très faible valeur du seuil comme la vitesse nécessaire pour franchir la barrière d'énergie qu'un grain doit vaincre pour passer sur les rugosités des grains voisins.

We report an experimental study of the acoustic signal produced by the rupture of an elastic membrane that initially closes a cylindrical overpressurized cavity. This configuration has been recently used as an experimental model system for the investigation of the acoustic emission from the bursting of elongated gas bubbles rising in a conduit. Here, we investigate the effect of the membrane rupture dynamics on the acoustic signal produced by the pressure release by changing the initial tension of the membrane. The initial overpressure in the cavity is fixed at a value such that the system remains in the linear acoustic regime. For large initial membrane deformation, the rupture time τ rup is small compared to the wave propagation time in the cavity and the pressure wave inside the conduit can be fully captured by the linear theory. For low membrane tension, a hole is pierced in the membrane but its rupture does not occur. For intermediate deformation, finally, the rupture progresses in two steps: first the membrane opens slowly; then, after reaching a critical size, the rupture accelerates. A transversal wave is excited along the membrane surface. The characteristic signature of each opening dynamics on the acoustic emission is described.

International audience; Specialty section: This article was submitted to Interdisciplinary Physics, a section of the journal Frontiers in Physics The injection of gas in a liquid-saturated granular bed gives rise to a wide variety of invasion patterns. Many studies have focused on constrained porous media, in which the grains are fixed in the bed and only the interstitial fluid flows when the gas invades the system. With a free upper boundary, however, the grains can be entrained by the ascending gas or fluid motion, and the competition between the upward motion of grains and sedimentation leads to new patterns. We propose a brief review of the experimental investigation of the dynamics of air rising through a water-saturated, unconstrained granular bed, in both two and three dimensions. After describing the invasion pattern at short and long time, a tentative regime-diagram is proposed. We report original results showing a dependence of the fluidized zone shape, at long times, on the injection flow rate and grain size. A method based on image analysis makes it possible to detect not only the fluidized zone profile in the stationary regime, but also to follow the transient dynamics of its formation. Finally, we describe the degassing dynamics inside the fluidized zone, in the stationary regime. Depending on the experimental conditions, regular bubbling, continuous degassing, intermittent regime or even spontaneous flow-to-fracture transition are observed.

International audience; Gas invasion in liquid-saturated sands exhibits different morphologies and dynamics. For mobile beds, the repeated rise of gas through the layer leads to the growth of a fluidized zone, which reaches a stationary shape. Here, we present experimental results characterizing the evolution of the fluidized region as a function of the gas-flow rate and grain size. We introduce a new observable, the flow density, which quantifies the motion of the grains in the system. The growth of the fluidized zone is characterized by a spatiotemporal analysis, which provides the stabilization time, τ_s. In the stationary regime, we report two main contributions to motion in the fluidized region: the central gas rise and a convective granular motion. Interestingly, a static model with a fixed porous network accounts for the final shape of the invasion zone. We propose an explanation where the initial gas invasion weakens the system and fixes since the early stage the morphology of the fluidized zone.

We characterized the potent in vitro antimalarial activity and biologic assessment of 13 phospholipid polar head analogs on a comparative basis. There was a positive relationship between the abilities of the drugs to inhibit parasite growth in culture and their abilities to specifically inhibit phosphatidylcholine biosynthesis of Plasmodium falciparum -infected erythrocytes. Maximal activity of G25 was observed for the trophozoite stage of the 48-h erythrocytic cycle (50% inhibitory concentration, 0.75 nM), whereas the schizont and ring stages were 12- and 213-fold less susceptible. The compounds exerted a rapid nonreversible cytotoxic effect, with complete clearance of parasitemia after 5 h of contact with the mature stages. The compounds were highly specific against P. falciparum , with much lower toxicity against three other mammalian cell lines, and the in vitro therapeutic indices ranged from 300 to 2,500,000. Finally, the monoquaternary ammonium E10 and two bis-ammonium salts, G5 and G25, were similarly active against multiresistant strains and fresh isolates of P. falciparum . This impressive selective in vitro toxicity against P. falciparum strongly highlights the clinical potential of these quaternary ammonium salts for malarial chemotherapy.

We investigate the morphology and dynamics of the region invaded by air injected at the bottom of an immersed granular bed. Previous experimental results point out the formation of a fluidized zone with a parabolic shape which does not depend, in the stationary regime, on the injection flow-rate. By tilting the experiment, we can tune the effective gravity in the system. We show that it does not affect significantly the morphology either. A numerical study made it possible to access the typical height and width of the structure, which are governed by the relative effects of gravity and capillarity. After a brief review on this subject, we propose first, new experimental observations on the air invasion regimes and on the morphology of the fluidized zone, in particular its growth dynamics; then, we complement the previous numerical study by considering the influence of the bottom boundary condition. In particular, we quantify the morphology of the invaded region when the gas is injected in the bulk, thus when air is likely to propagate downwards. These results are of practical importance in the prediction of the morphology of gas invasion in soils, from $$\hbox {CO}_2$$ sequestration to pollutant propagation.

We report a study of the paths formed by a finite volume of air gently injected at the base of an immersed granular material. A two-dimensional model, based on experimental observations, shows that the typical height and width of the region explored by the branched path depends not only on the injected volume $V$, but also on a dimensionless parameter $\ensuremath{\chi}$ which accounts for the relative effects of the gravity and capillarity. For a given injected volume $V$, larger gravity effects lead to taller and narrower structures; for a given $\ensuremath{\chi}$, the typical height and width of the structure scale like ${V}^{1/2}$ and ${V}^{1/4}$, respectively, while the typical gaseous fraction in the corresponding region increases accordingly like ${V}^{1/4}$. Such results can be of practical importance: For instance, gas can be trapped on purpose in an underground natural container below a granular slurry. Our results can help in predicting if the gas is likely to reach the free surface and escape the system if the container presents a defect (hole or fracture).

Many volcanoes exhibit temporal changes in their degassing process, from rapid gas puffing to lava fountaining and long-lasting quiescent passive degassing periods. This range of behaviors has been explained in terms of changes in gas flux and/or magma input rate. We report here a simple laboratory experiment which shows that the non- Newtonian rheology of magma can be responsible, alone, for such intriguing behavior, even in a stationary gas flux regime. We inject a constant gas flow-rate Q at the bottom of a non-Newtonian fluid column, and demonstrate the existence of a critical flow rate Q* above which the system spontaneously alternates between a bubbling and a channeling regime, where a gas channel crosses the entire fluid column. The threshold Q* depends on the fluid rheological properties which are controlled, in particular, by the gas volume fraction (or void fraction) {\phi}. When {\phi} increases, Q* decreases and the degassing regime changes. Non-Newtonian properties of magma might therefore play a crucial role in volcanic eruption dynamics.

6 pages; International audience; Air is injected locally at the base of an immersed granular bed. The gas, which is forced to flow gently through thematerial, creates several paths between the grains.We observe that the latter gas venting results in the emission of bubbles in a localized region at the free surface. Additional experiments, performed in two dimensions, permit a direct visualization of the paths, and a theoretical approach shows that the typical size of the region at the free surface can be accounted for by a diffusionlike process. The diffusion coefficient is expressed as a function of the system parameters.

Sinking Sea Floors The depths of ocean bottoms are constantly fluctuating at a very slow rate in response to the generation (at mid-ocean ridges) and consumption (at subduction zones) of sea-floor material. Because older sea floor is susceptible to sinking as it cools, it has been assumed that sea-floor depth varies directly with its age. However, Adam and Vidal (p. 83 ; see the Perspective by Tolstoy ) now show that the depth of the Pacific Ocean actually varies in response to the mantle underlying the oceanic crust. This effect is clear when sea-floor depth was measured along lithospheric flow lines—which represent the movement of oceanic crust triggered by mantle convection. Because the ocean bottom does not flatten as predicted by previous models, there is no need to invoke any additional heat supply to sustain old oceanic crust in thermal models of the mantle.

In order to assess the physical mechanisms at stake when giant gas bubbles burst at the top of a magma conduit, laboratory experiments have been performed. An overpressurized gas cavity is initially closed by a thin liquid film, which suddenly bursts. The acoustic signal produced by the bursting is investigated. The key result is that the amplitude and energy of the acoustic signal strongly depend on the film rupture time. As the rupture time is uncontrolled in the experiments and in the field, the measurement of the acoustic excess pressure in the atmosphere, alone, cannot provide any information on the overpressure inside the bubble before explosion. This could explain the low energy partitioning between infrasound, seismic and explosive dynamics often observed on volcanoes.

We study experimentally the acoustic signal associated with a continuous bubble bursting at the free surface of a non-Newtonian fluid. Due to the fluid rheological properties, the bubble shape is elongated, and, when bursting at the free surface, acts as a resonator. For a given fluid concentration, at constant flow rate, repetitive bubble bursting occurs at the surface. We report a modulation pattern of the acoustic waveform through time. Moreover, we point out the existence of a precursor acoustic signal, recorded on the microphone array, previous to each bursting. The time delay between this precursor and the bursting signal is well correlated with the bursting signal frequency content. Their joint modulation through time is driven by the fluid rheology, which strongly depends on the presence of small satellite bubbles trapped in the fluid due to the yield stress.

We report an experimental study of the intermittent dynamics of a gas flowing through a column of a non-Newtonian fluid. In a given range of the imposed constant flow rate, the system spontaneously alternates between two regimes: bubbles emitted at the bottom either rise independently one from the other or merge to create a winding flue which then connects the bottom air entrance to the free surface. The observations are reminiscent of the spontaneous changes in the degassing regime observed on volcanoes and suggest that, in the nature, such a phenomenon is likely to be governed by the non-Newtonian properties of the magma. We focus on the statistical distribution of the lifespans of the bubbling and flue regimes in the intermittent steady state. The bubbling regime exhibits a characteristic time whereas, interestingly, the flue lifespan displays a decaying power-law distribution. The associated exponent, which is significantly smaller than the value 1.5 often reported experimentally and predicted in some standard intermittency scenarios, depends on the fluid properties and can be interpreted as the ratio of two characteristic times of the system., 9 pages, 11 figures. Published in Phys. Rev. E

We report the formation of a crater at the free surface of an immersed granular bed,locally crossed by an ascending gas flow. In two dimensions, the crater consists of two piles which develop around the location of the gas emission. We observe that the typical size of the crater increases logarithmically with time, independently of the gas emission dynamics. We describe the related granular flows and give an account of the influence of the experimental parameters, especially of the grain size and of the gas flow., 7 pages, 7 figures