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Potential dust avalanches as aftermaths of the seismic event of S1222a detected by the SEIS/InSight seismometer are investigated. Orbital observations emphasize that the area around the estimated location shows rather flat topography with North-South ridge structures. Thermal inertia data attests that the surface is essentially composed of granular materials, including dust. Thus, only a few locations show steep slopes with fragile soil. We investigated the orbital archive and requested targeted locations to assess the avalanche rate in the area and the influence of the M$_{W}^{Ma}$ 4.7, S1222a event. We find an increase in the avalanche rates when thermal inertia is low. We investigate the best location that could explain these avalanche rates from the aftermath ground deformation and discuss the implications in regards to the regional geology.

International audience; PURPOSE: Segmentation of vascular structures in preoperative computed tomography (CT) is a preliminary step for computer-assisted endovascular navigation. It is a challenging issue when contrast medium enhancement is reduced or impossible, as in the case of endovascular abdominal aneurysm repair for patients with severe renal impairment. In non-contrast-enhanced CTs, the segmentation tasks are currently hampered by the problems of low contrast, similar topological form, and size imbalance. To tackle these problems, we propose a novel fully automatic approach based on convolutional neural network. APPROACH: The proposed method is implemented by fusing the features from different dimensions by three kinds of mechanisms, i.e., channel concatenation, dense connection, and spatial interpolation. The fusion mechanisms are regarded as the enhancement of features in non-contrast CTs where the boundary of aorta is ambiguous. RESULTS: All of the networks are validated by three-fold cross-validation on our dataset of non-contrast CTs, which contains 5749 slices in total from 30 individual patients. Our methods achieve a Dice score of 88.7% as the overall performance, which is better than the results reported in the related works. CONCLUSIONS: The analysis indicates that our methods yield a competitive performance by overcoming the above-mentioned problems in most general cases. Further, experiments on our non-contrast CTs demonstrate the superiority of the proposed methods, especially in low-contrast, similar-shaped, and extreme-sized cases.

International audience; The purpose of this work is to present a patient-specific (PS) modeling approach for simulating percutaneous transluminal angioplasty (PTA) endovascular treatment and assessing the balloon sizing influence on short-term outcomes in peripheral arteries, i.e. without stent implantation. Two 3D PS stenosed femoral artery models, one with a dominant calcified atherosclerosis while the other with a lipidic plaque, were generated from pre-operative computed tomography angiography images. Elastoplastic constitutive laws were implemented within the plaque and artery models. Implicit finite element method (FEM) was used to simulate the balloon inflation and deflation for different sizings. Besides vessel strains, results were mainly evaluated in terms of the elastic recoil ratio (ERR) and lumen gain ratio (LGR) attained immediately after PTA. Higher LGR values were shown within the stenosed region of the lipidic patient. Simulated results also showed a direct and quantified correlation between balloon sizing and LGR and ERR for both patients after PTA, with a more significant influence on the lumen gain. The max principal strain values in the outer arterial wall increased at higher balloon sizes during inflation as well, with higher rates of increase when the plaque was calcified. Results show that our model could serve in finding a compromise for each stenosis type: maximizing the achieved lumen gain after PTA, but at the same time without damaging the arterial tissue. The proposed methodology can serve as a step toward a clinical decision support system to improve angioplasty balloon sizing selection prior to the surgery.

We develop a phenomenological model of suspended sediment transport on the basis of data acquired in the Capesterre river, which drains a small tropical catchment in Guadeloupe. The model correctly represents the concentration of suspended sediment during floods, provided that the relation between concentration and water level forms a counterclockwise loop. In the model, the properties of the sediment and of the river are all lumped into four parameters: a settling velocity related to the size of the suspended sediment, a threshold water level which acts as a proxy for the threshold shear stress, a characteristic entrainment rate, and a dimensionless exponent. The value of the parameters changes from one flood to the next, probably reflecting changes in the characteristics of the river and the fine sediment. Finally, a test of the model against data acquired in a small catchment in the French Alps suggests that the model is versatile enough to be used in diverse hydrological settings.

In recent decades, with the placement of LiDAR remote sensing instruments in orbit, we now have global coverage of the bare ground elevation on the Earth, Mars and beyond. Encoded in such planetary LiDAR data are interesting landscape features that promise to further our knowledge of planetary topography. However, discovery of such features comes with 3 major challenges: First, the volume of planetary LiDAR data can be massive, often comprising of hundreds of millions to billions of data points. This calling for analytical algorithms with great efficiency. Second, interesting features can often repeat themselves in multiple scales in local regions, thus it is vital to enable multi-scale feature discovery. Third, planetary LiDAR data can be heterogeneous, and evaluation of the quality of the extracted features can often be hampered by a variety of interfering factors. In response to these challenges, we propose FARMYARD, a generic pipeline for Feature Discovery From Planetary LiDAR Data. To the best of our knowledge, this is the first time such a pipeline has been proposed, which provides a brand new methodology for comparative studies of planetary topography. Specifically, drawing on the parallel computing power of the Graphics Processing Unit (GPU), we propose a novel pseudo-on-pass sweep (POPS) framework for fast and memory-efficient feature extraction for massive planetary LiDAR data, a two-level division scheme for local regions with support for multi-scale features, and a Domain-Shifted Partition (DSP) scheme for feature evaluation that is robust against interfering factors. To showcase the utility of our FARMYARD pipeline, we deploy it to an ongoing real-world research project called PARKER, which seeks to find topographical signatures of life by discovering features that can potentially distinguish between the Earth and alien worlds with no known life activity. We also highlight the efficiency of our POPS framework with experiments on both synthetic and real data, which can be hundreds or even thousands of times faster than its CPU-based counterpart, including an MPI-based multi-core parallel solution.

On December 15th 1952, at approximately 14:00 local time a mass of 5.9 × 106 m3 of permafrozen talus deposits failed in a landslide close to the Niiortuut mountain on the south coast of the Nuussuaq peninsula, central West Greenland. Between 1.8 and 4.5 × 106 m3 of the material entered the sea and generated a tsunami that propagated through the Vaigat strait (Sullorsuaq). Here we describe this catastrophic event for the first time by analysis of historical material supplemented by recent fieldwork and discuss the implications for the state of contemporary permafrozen slopes. The tsunami killed a fisherman working on the shore of southern Nuussuaq, 10 km south-east of the landslide. In the mining town of Qullissat, 30 km south of the landslide, it had a runup height of 2.2–2.7 m and caused minor material damage. Morphological evidence show that the basal surface of rupture was 80 m inside the permafrost cemented talus slope, whose degradation was a dynamic conditioning factor for the landslide. The 1952 Niiortuut landslide is the first historically recorded event of permafrost degradation induced landslide-tsunamis in the Arctic. We infer that the landslide and its cascading consequences occurred due to the early-twentieth century warming that started in the late 1910's in the Arctic. Warming is now increasingly affecting this region, as shown by an enhanced recent landslide activity. Part 1.

Motivation Granular avalanches such as slope streaks, have been observed on Mars since the beginning of the high resolution era with MOC on MGS. Such mass wasting processes are active and their dynamics has a few implications in terms of climatic conditions. However, understanding the slope streaks dynamics is still undergoing. Many authors have proposed dry spreading of fine dust or wet processes (e.g., Schorghofer et al., 2002; 2007). For instance, Head et al., (2007) have proposed spring discharge involving salty ground-water. Many of those studies have been performed from interpretations of geomorphic features by comparing knowing processes occurring on Earth and/or a few comparisons with experimental works. Consequently, a key parameter is the triggering conditions, along with the dynamical behavior of these avalanches. We hence propose a combined approach involving numerical simulations, seismology and orbital imagery in order to provide new insights. Orbital image constraints We investigate the orbital images from CTX and HiRISE cameras, both onboard MRO spacecraft. They provide a complete coverage of the two regions of interest being the InSight landing site (135.61ºE 4.49ºN) and the vicinity of the large quake (170.85ºE, 7.05ºS, being at 37º from the SEIS instrument) named 1222 which occurred on 5 May 2020. In both areas, we identified many past avalanche events (Figure 1-A). More specifically, we investigate the complete set of orbital data (imagery, topography, and thermo-physical properties) to estimate in particular the rate of formation of these avalanches in the vicinity of the 1222 event location (Fig. 1-B,C). This has led to request new orbital observations targeted to the most favorable areas for avalanches and hence try to link the ground acceleration resulting from the 1222 event with the triggering of new avalanches by using detection techniques (Fig. 1-D). This work, essentially observational, is combined with the following part on the detectability of this type of source by the SEIS sensor. Figure 1 - (A) Location of identifiable landslides and avalanches (rockfall sign) around the InSight landing site (symbolized with the SEIS/WTS sign). The circles show epicentral distance from the receiver at 5º (red), 10º (orange), 15º (yellow) and 20º (light gray), which correspond to ∼300, ∼600, ∼900 and ∼1200 km respectively. Active avalanches (slope streaks) are detected at 150°E. (B) Location of active avalanches (rockfall sign) around the 1222 event location (green flag). (C) Examples of avalanches in the vicinity of the 1222 event location as seen by the CTX camera. This image was taken in May 2011 and reflects the high occurrence of such processes in the area. (D) Detection of slope streaks (and old craters) from neural networks (i.e., using darknet algorithm). Dynamics and source function of avalanches from numerical simulations In order to generate synthetic seismic sources due to gravity-driven sediment transport we based our simulations on a depth-averaged Saint-Venant equations model, named SHATLOP, which accounts for the curvature of the topography and on various frictional behavior for the source term following (Lucas & Mangeney, 2007; Lucas et al., 2011;2014). Volumes involved are around 8,000-40,000 m3 with a total drop height up to 1 km. The typical duration of the event is of a few minutes up to 20 minutes for a +2 km runout slope streaks, depending on the frictional law considered and small fluctuation on the bottom topography, which generates surges as shown on Fig. 2-A. ​​The source is considered as a point force applied at the surface from the spatial integration of the avalanche resultant force, where the velocity, the resistance force, the density of the flow and the acceleration due to gravity accounting for the bottom topography curvature are all taken into account (Fig. 2-B). The velocity models are obtained after geological considerations after Pan et al., (2019), where active mass wasting processes have been identified (Fig. 2-C). Examples of resulting seismograms are shown in Fig. 2-D. The velocity model, still under investigation for Mars, is also an important open issue that has a strong impact on the resulting seismic signal. Finally, depending on source functions, velocity models, such an event may be detectable, in particular when occurring during the night at local time of the sensors, when the noise level is low and when spectral content is above SEIS sensitivity (Fig. 2-E). Figure 2 - (A) Example numerical simulation of a martian dust avalanche over a DTM generated from HiRISE stereo pair (Color scales with the velocity). (B) Resulting source force history. (C) Example of a velocity and attenuation model for Mars. (D) Synthetic seismograms accounting source distance for various velocity models and epicentral distances. (E) ADS example for a small event at 140 km. References Head, J., Marchant, D., Dickson, J.,Levy, J., Morgan, G. Slope streaks in the Antarctic Dry Valleys: Characteristics, candidate formation mechanisms, and implications for slope streak formation in the Martian environment. 7 th International Conf. (2007) Lucas A., and A. Mangeney. “Mobility and topographic effects for large Valles Marineris landslides on Mars”. In: Geophys. Res. Lett., 34, L10201 (2007) Lucas A., et al. “Influence of the scar geometry on landslide dy-namics and deposits: Application to Martian landslides”. In: J. Geophys. Res. - Planets, 116, E10001 (2011) Lucas, A., A. Mangeney, and J-P. Ampuero. “Frictional velocity-weakening in landslides on Earth and on other planetary bodies”. In: Nature Comm.,5:3417 (2014) Pan L., et al. “Crust stratigraphy and heterogeneities of the first kilometers at the dichotomy boundary in western Elysium Planitia and implications for InSight lander”. In: Icarus (2019) Schorghofer N., Aharonson O., and Khatiwala S. “Slope streaks on Mars: Correlations with surface properties and the potential role of water”. In: Geophys. Res. Lett.,29(23) (2002) Schorghofer, N., Aharonson, O., Gerstell, M. & Tatsumi, L. Three decades of slope streak activity on Mars. Icarus. 191. 132-140 (2007)

We develop a phenomenological model of suspended-sediment transport on the basis of data acquired in the Capesterre river, which drains a small tropical catchment in Guadeloupe. The model correctly represents the transport of suspended sediment during floods, provided that the relation between concentration and water-level forms a counterclockwise loop. In the model, the properties of the sediment and of the river are all lumped into four parameters: a settling velocity related to the size of the suspended sediment, a threshold water-level which acts as a proxy for the threshold shear stress, a characteristic erosion rate and a dimensionless exponent, both of which are related to the availability of fine sediment. The assimilation of field data to our model shows that the value of the parameters change from one flood to the next, probably reflecting changes in the characteristics of the river and the sediment. Finally, a test of the model against data acquired in a small catchment in the french Alps, suggests that the model is versatile enough to be used in diverse hydrological settings.

Hematophagous flies are a pest for livestock; their direct impact reduces productivity, and they are vectors of parasites, bacteria and viruses. Their control using insecticides is inefficient and highly polluting. The validation of new control tools requires efficacy and cost-effectiveness evaluation. The quantification of hematophagous insects’ impact in livestock is a challenging prerequisite. Tail flicks counts can reliably evaluate fly-burden; however, visual records are tedious and time-consuming. In the present study, automation of tail flick counts was made through the use of pedometers attached to the tail, in two groups of feeder cattle. Group A was kept in a pen under the protection of a mosquito net, and Group B was kept in an open-air pen. The fly density of Group B was evaluated using fly traps. The apparent density per trap ranged from 130 to 1700 in the study. The mean pedometer records per 24 h ranged from 957+/−58 bits in Group A to 11,138+/−705 bits in Group B. The night/day records observed in Group A (200/800 bits) were drastically increased in Group B (1000–4000/4000–14,000 bits) and variable along seasons. A very high correlation was observed between fly density and visual records or pedometer records (PR). Two-hour PRs proved to be a reliable predictive tool for fly density. Moreover, the pedometers revealed an unsuspected but significant nuisance of mosquitoes, which should be thoroughly investigated.

Our study looks at how to use the landform called “molard” as a marker of permafrost degradation in arctic, sub-arctic and mountain environments. Molards in permafrost terrains are mound of loose debris that derive from the degradation of blocks of ice-rich sediments mobilised by a landslide. Such molards cannot form without ground ice, which cements the source material, allowing it to behave like solid during transport. Once the ground ice has thawed, its cementing action is lost, inducing collapse of the material into molards. We reconstruct the permafrost, geological, geographical settings of more than 50 landslides characterised by molards, compiling data available in the literature. We apply quantitative terrain analysis using high-resolution DEMs to describe, quantify and compare their topographic characteristics, morphometry, dynamics, and molards distribution and density. Our results show that landslides with molards can occur in terrains characterised by various permafrost distribution, from continuous to isolated. These landslides show a variety of morphological and morphometric characteristics, source materials often composed of loose debris or rheologically weak bedrock, and their molard distribution reflects the dynamics of the landslide. In this study, we show that molards are an indicator landform of permafrost degradation under different permafrost, geomorphological and geological conditions, and that they can be used to decipher landslide dynamics in cold environments.Acknowledgements: This study is funded by the Agence Nationale de la Recherche in the framework of the project ANR-19-CE01-0010 PERMOLARDS

International audience; Background - Fusion imaging makes it possible to improve endovascular procedures and is mainly used in hybrid rooms for aortic procedures. The objective of this study was to evaluate the feasibility of fusion imaging for femoropopliteal endovascular procedures with a mobile flat plane sensor and dedicated software to assist endovascular navigation. Materials and methods - Between May and December 2017, 41 patients requiring femoropopliteal endovascular revascularization were included. Interventions were carried out in a conventional surgical room equipped with a mobile plane sensor (Cios Alpha, Siemens). The numerical video stream was transmitted to an angionavigation station (EndoNaut (EN), Therenva). The software created an osseous and arterial panorama of the treated limb from the angiographies carried out at the beginning of procedure. After each displacement of the table, the software relocated the current image on the osseous panorama, with 2D-2D resetting, and amalgamated the mask of the arterial panorama. The success rates of creation of osseous and arterial panorama and the success of relocation were evaluated. The data concerning irradiation, the volume of contrast (VC) injected, and operative times were recorded. Results - Osseous panoramas could be automatically generated for the 41 procedures, without manual adjustment in 33 cases (80.5%). About 35 relocations based on a 2D-2D resetting could be obtained in the 41 procedures, with a success rate of 85%. The causes of failure were a change in table height or arch angulation. The average duration of intervention was 74.5 min. The irradiation parameters were duration of fluoroscopy 17.8 ± 13.1 min, air kerma 80.5 ± 68.4 mGy, and dose area product 2140 ± 1599 μGy m. The average VC was 24.5 ± 14 mL. Conclusions - This preliminary study showed that fusion imaging is possible in a nonhybrid room for peripheral procedures. Imagery of mobile C-arms can be improved for femoropopliteal endovascular procedures without heavy equipment. These imagery tools bring an operative comfort and could probably reduce irradiation and the injected VC. The clinical benefit must be evaluated in more patients in a randomized comparative study with a rigorous methodology.

Titan's rich and dense atmosphere, composed mainly of methane and nitrogen, maintains a methane cycle that shapes its surface, like the water cycle on Earth. Methane precipitations erodes Titan's surface and forms complex river networks observed at all latitudes by the Cassini-Huygens mission. However, precipitation rates are poorly constrained and, in the absence of in situ measurements, understanding Titan’s global climate and meteorology is done primarily through climate models. Here, we apply a physics-based theory of river morphogenesis to provide new constraints on methane precipitation rates. In particular, we estimate the river discharges and precipitation rates required to shape two methane rivers located at the equator and south pole, which incise the surface of Titan. Our results show that the use of river morphology is relevant for inferring methane precipitation rates at various latitudes. Our estimates reduce the uncertainties from the climate models. In addition, our results reflect the climate variability between the equator and the south pole. Finally, this work sheds the light to unknown river on Earth: the giant gravel-bed rivers.

International audience; PURPOSE: Endovascular revascularization is becoming the established first-line treatment of peripheral artery disease (PAD). Ultrasound (US) imaging is used pre-operatively to make the first diagnosis and is often followed by a CT angiography (CTA). US provides a non-invasive and non-ionizing method for the visualization of arteries and lesion(s). This paper proposes to generate a 3D stretched reconstruction of the femoral artery from a sequence of 2D US B-mode frames. METHODS: The proposed method is solely image-based. A Mask-RCNN is used to segment the femoral artery on the 2D US frames. In-plane registration is achieved by aligning the artery segmentation masks. Subsequently, a convolutional neural network (CNN) predicts the out-of-plane translation. After processing all input frames and re-sampling the volume according to the vessel’s centerline, the whole femoral artery can be visualized on a single slice of the resulting stretched view. RESULTS: 111 tracked US sequences of the left or right femoral arteries have been acquired on 18 healthy volunteers. fivefold cross-validation was used to validate our method and achieve an absolute mean error of 0.28 ± 0.28 mm and a median drift error of 8.98%. CONCLUSION: This study demonstrates the feasibility of freehand US stretched reconstruction following a deep learning strategy for imaging the femoral artery. Stretched views are generated and can give rich diagnosis information in the pre-operative planning of PAD procedures. This visualization could replace traditional 3D imaging in the pre-operative planning process, and during the pre-operative diagnosis phase, to identify, locate, and size stenosis/thrombosis lesions.

The objective of this work was to study the elastic recovery of EPDM samples crosslinked either by a phenolic resin (resol) or by a radical peroxide (dicumyl peroxide, DCP). From compression set experiments, it was observed that radically crosslinked EPDMs have better elastic recovery properties. On the other hand, for the same crosslinking density, radically crosslinked EPDM shows better compression set than EPDM crosslinked with phenolic resins. The Chasset-Thirion equation was then used to successfully fit the experimental relaxation curves. As a notable result, the preferential statistics of a peroxide-crosslinked network over a phenolic resin (resol) showed that better elastic recovery properties were obtained. Finally, the influence of fillers (carbon black and silica) was also studied. Carbon black with DCP crosslinking was shown to improve elasticity recovery whereas silica fillers lead to worse properties. It was then assumed that the interaction between particle surface and a voir comme dans autre publi a modifier ce crosslinking agent induced crosslinking gradients in the inter-particle volume.

International audience; Blends of a copolyether−ester thermoplastic with different multifunctional (mono, di, and tri) amine-terminated polyethers have been carried out by reactive extrusion. The reaction with polyetheramine Jeffamine T-403 allows one to reduce drastically the viscosity of the blends while at the same time improving the Young's modulus of the matrix up to 30% and keeping elongation at break around 700% and stress at break around 20 MPa. The mechanism and the structures deeply scrutinized by NMR (in particular 2D DOSY), chromatography, and mass spectrometry evidenced the in situ formation of star-shaped-based structures. These complex structures are responsible of these changes in rheological and mechanical behaviors. This one-step approach represents an efficient and relevant way to enhance some mechanical properties while favoring the flow behavior of these copolyether−esters.

On the seasonal time scale, for accessible locations and when manpower is available, direct observations and field survey are the most useful and standard approaches. However very limited studies have been conducted on direct observation at the decennial to century time-scale due to observational constrains. Here, we present an open and reproducible pipeline based on historical aerial images (up to 70 yrs time span) that includes sensor calibration, dense matching and elevation reconstruction over two areas of interest that represent pristine examples for tropical and alpine environments. The Remparts Canyon and Langevin River in Reunion Island, and the Bossons glacier in the French Alps share a limited accessibility (in time and space) that can be overcome only from remote-sensing. We reach a metric to sub-metric resolution close to the nominal images spatial sampling. This provides elevation time series with a better resolution to most recent satellite images such as Pleiades over decennial time period.

Beside blood pathogens transmission, insects of the order Diptera affect livestock by visual and contact harassment; blood-feeders are responsible of painful bites and blood despoliation, generating behavioural modifications, anaemia and production losses. Knowledge of their economic impact is a basis for cost-effective control. Here, we measured the global impact of Diptera by comparing two batches of six feeder cattle, one in open air, the other protected by a mosquito net. Analytical data were: insect density in open air, and, for feeder cattle: tail-flick counts, hematocrit values (Ht), feed intake, feed conversion ratio (FCR) and live body weight gains (LBWG). Over a period of five months, results showed significant losses of LBWG of cattle exposed to insects, estimated at 8.0±1.5 Kg/month [2.7;13.3], with a total loss reaching 40.0±5.5 Kg/head. Main diurnal insects were Stomoxys spp. and M. crassirostris. There was a strong correlation between fly density and diurnal tail-flicks. Night trapping and tail-flicks showed a potentially important role of mosquitoes to be further explored. Ht of exposed animals was 3-4% lower than controls. FCRs indicated that exposed animals needed 33% more dry matter intake/Kg of LBWG. Economic assessment showed that dipterans were responsible of 10-11% loss of LBWG during the main growing period of feeder-cattle (10-15 months). A feedlot of 100 calves would register a total loss of 16,000$ within 5 months, which appears to be an unexpectedly huge loss caused by dipterans. Investing part of this money in fly control would probably be beneficial.

International audience; We report the aeolian changes observed in situ by NASA's InSight lander during the first 400 sols of operations: Granule creep, saltation, dust removal, and the formation of dark surface tracks. Aeolian changes are infrequent and sporadic. However, on sols, when they do occur, they consistently appear between noon to 3 p.m., and are associated with the passage of convective vortices during periods of high vortex activity. Aeolian changes are more frequent at elevated locations, such as the top surfaces of rocks and lander footpads. InSight observed these changes using, for the first time, simultaneous insitu and orbital imaging and high-frequency meteorological, seismological, and magnetic measurements. Seismometer measurements of ground acceleration constrain the timing and trajectory of convective vortex encounters, linking surface changes to source vortices. Magnetometer measurements show perturbations in magnetic field strength during the passage of convective vortices consistent with chargedparticle motion. Detachment of sand-scale particles occurs when high background winds and vortexinduced turbulence provide a peak surface friction wind speed above the classic saltation fluid threshold. However, detachment of dust-and granule-scale particles also occurred when the surface friction wind speed remained below this threshold. This may be explained by local enhancement of the surface roughness and other effects described here and further studied in Part 2 (Baker et al., 2021). The lack of saltation and bright dust-coated surfaces at the InSight landing site implies surface stability and the onset of particle motion may be suppressed by dust "cushioning." This differentiates the InSight landing site from other areas on Mars that exhibit more aeolian activity. Plain Language Summary Aeolian activity, the movement of dust and sand by the wind, is common on Earth and has been observed on other planets, including Mars. A new Mars lander, InSight, has for the first time monitored aeolian changes by combining imaging with weather, seismic and CHARALAMBOUS ET AL.

Some of the most spectacular instances of deep-seated gravitational slope deformation (DSGSD) are found on Mars in the Valles Marineris region. They provide an excellent opportunity to study DSGSD phenomenology using a scaling approach. The topography of selected DSGSD scarps in Valles Marineris and in the Tatra Mountains is investigated after their likely similar postglacial origin is established. The deformed Martian ridges are larger than the deformed terrestrial ridges by one to two orders, with however a similar height-to-width ratio, ~ 0.24. The measured finite strain of the Valles Marineris ridges is 3 times larger than in the Tatra Mountains, suggesting that starting from two different initial conditions, with steeper slopes in Valles Marineris, the final ridge geometry is now similar. Because DSGSD is expected to be now inactive in both regions, their comparison suggests that whatever the initial ridge morphology, DSGSD proceeds until a mature profile is attained. On both planets, strain is distributed over the same number (~ 5) of major scarps; fault displacements are therefore much larger on Mars. The large offsets make necessary reactivation of the DSGSD fault scarps in Valles Marineris, whereas single seismic events would be enough to generate DSGSD fault scarps in the Tatra Mountains. The required longer activity of the Martian faults may be correlated with a long succession of climate cycles generated by the unstable Mars obliquity. In spite of similar global geometry today, the studied ridges on Mars and Earth affected by DSGSD did not start from similar initial conditions and did not follow the same structural evolution.

The Selk crater region is the future landing site of NASA’s Dragonfly mission to Titan. The region was imaged by the Cassini RADAR at incidence angles from 5° to 72° and at various polarization angles. Using this data set, we mapped six terrain units and assembled a backscatter curve for each, providing normalized backscatter cross section (σ 0) as a function of incidence angle. By fitting these backscatter curves with a sum of a quasi-specular and diffuse terms and evaluating three alternative formulations of the first and two for the second, we extracted the best-fit surface effective dielectric constant, rms slope, and scattering albedo. Although the parameters’ absolute values are model dependent, relative values between terrains indicate real variations in surface properties. The results are consistent with the impact exposing and fracturing a low-loss tangent material such as the water-ice bedrock, which is likely also present in the hummocky terrains and to a lesser degree in the plains and interdune regions. The dunes and dark terrains are composed of smooth, uniform material with low dielectric constant (1.5–2.3 median values for all models) compatible with organic sand. A diffuse single-scattering model enabled independent derivation of the dielectric constant from high-incidence observations, leading to low values (

The 125-km-diameter Hale impact crater is located in the southern hemisphere of Mars and has been dated to 1 Ga (Early to Middle Amazonian; Jones et al., 2011). It is thought to have penetrated the martian cryosphere, because it hosts landforms indicating volatile mobilisation post-impact: its ejecta are lobate and bear channels, and the interior is pervasively pitted and hosts alluvial fans (Collins-May et al. 2020; El-Maarry et al., 2013; Jones et al., 2011; Tornabene et al., 2012). Here, we test the hypothesis that conical mounds found within the ejecta are “molards” by comparing them to terrestrial analogues. Molards are conical mounds of debris resulting from the degradation of blocks of ice-rich material which have been mobilised by a landslide and are found in periglacial environments (Morino et al., 2019).Our study area (240x180 km) is in the South-East part of the Hale impact crater ejecta (36°–39°S, 36°–31°W). We analyse the spatial and topographic distribution of the conical mounds using orbital images from 25 cm/pixel to 15 m/pixel and measure their height, width and slope using 1 m/pixel elevation data. We then compare them to conical mounds on the deposits of the 2010 Mount Meager debris avalanche, Canada (Roberti et al. 2017) and of the 2000 Paatuut landslide in western Greenland (Dahl-Jensen et al. 2004).The conical mounds of the Hale impact crater are located at the distal boundary of the thickest part of the ejecta blanket, which reflects the spatial distribution of mounds along the distal parts of the terminal lobe of the Mount Meager debris avalanche. Furthermore, mounds in the Hale impact crater have comparable shapes and flank slopes to molards in the Mount Meager and Paatuut case studies, but are one order of magnitude bigger. This size difference is consistent with the flow-depth that transported the blocks also being one order of magnitude bigger than on Earth.We infer that conical mounds near the Hale impact crater are a result of fragmented blocks of ice-cemented regolith produced by the impact and transported by the ejecta flows, and finally degraded into cones of debris (molards) by the loss of interstitial ice. Our interpretation supports the prevailing hypothesis that the Hale impact event penetrated the martian cryosphere and further provides important constraints on the rheology of martian ejecta deposits that can be tested by future studies and in other locations on Mars.We acknowledge financial support for the PERMOLARDS project from French National Research Agency (ANR-19-CE01-0010).

Depth-averaged thin-layer models are commonly used to model rapid gravity-driven flows such as debris flows or debris avalanches. However, the formal derivation of thin-layer equations for general topographies is not straightforward. The curvature of the topography results in a force that keeps the velocity tangent to the topography. Another curvature term appears in the bottom friction force when frictional rheologies are used. In this work, we present the main lines of the mathematical derivation for these curvature terms that are proportional to the square velocity. Then, with the SHALTOP numerical model, we quan- tify their influence on flow dynamics and deposits over synthetic and real topographies. This is done by comparing simulations in which curvature terms are exact, disregarded or approximated. With the Coulomb rheology, for slopes θ = 10° and for friction coefficients below μ = tan(5°), neglecting the curvature force increases travel times by up to 10% and 30%, for synthetic and real topographies respectively. When the curvature in the friction force is neglected, the travel distance may be increased by several hundred meters on real topographies, whatever the topography slopes and friction coefficients. We observe similar effects on a synthetic channel with slope θ = 25° and μ = tan(15°), with a 50% increase of the kinetic energy. Finally, approximations of curvature in the friction force can break the non-invariance of the equations and decelerate the flow. With the Voellmy rheology, these discrepancies are less significant. Curvature effects can thus have significant impact for model calibration and for overflows prediction, both being critical for hazard assessment.

International audience

In response to ESA Voyage 2050 announcement of opportunity, we propose an ambitious L-class mission to explore one of the most exciting bodies in the Solar System, Saturn largest moon Titan. Titan, a "world with two oceans", is an organic-rich body with interior-surface-atmosphere interactions that are comparable in complexity to the Earth. Titan is also one of the few places in the Solar System with habitability potential. Titan remarkable nature was only partly revealed by the Cassini-Huygens mission and still holds mysteries requiring a complete exploration using a variety of vehicles and instruments. The proposed mission concept POSEIDON (Titan POlar Scout/orbitEr and In situ lake lander DrONe explorer) would perform joint orbital and in situ investigations of Titan. It is designed to build on and exceed the scope and scientific/technological accomplishments of Cassini-Huygens, exploring Titan in ways that were not previously possible, in particular through full close-up and in situ coverage over long periods of time. In the proposed mission architecture, POSEIDON consists of two major elements: a spacecraft with a large set of instruments that would orbit Titan, preferably in a low-eccentricity polar orbit, and a suite of in situ investigation components, i.e. a lake lander, a "heavy" drone (possibly amphibious) and/or a fleet of mini-drones, dedicated to the exploration of the polar regions. The ideal arrival time at Titan would be slightly before the next northern Spring equinox (2039), as equinoxes are the most active periods to monitor still largely unknown atmospheric and surface seasonal changes. The exploration of Titan northern latitudes with an orbiter and in situ element(s) would be highly complementary with the upcoming NASA New Frontiers Dragonfly mission that will provide in situ exploration of Titan equatorial regions in the mid-2030s., Comment: arXiv admin note: substantial text overlap with arXiv:1908.01374

International audience; Fenestrated endovascular aneurism repair (FEVAR) is a minimally invasive technique, and its success depends on the adequacy of the correspondence between the visceral arteries ostia and position of the fenestrations of the stent graft (SG) during its deployment in juxtarenal aneurisms. However, the fenestration position is generally determined from a preoperative computerised tomography (CT) scan, without considering the vascular deformation induced by the insertion of the endovascular tools. Catheterisation difficulties may occur during clinical procedures. Accordingly, the objective of this work is to present an initial proof of concept aimed at anticipating and optimising the position of the fenestrations, while considering the vascular deformation induced by the insertion of the endovascular tools. The proposed method relies on the finite element method to simulate the SG deployment in a vascular structure (VS), and considers the vascular deformation induced by the tools. After determining the optimal simulation parameters for a patient-specific case, the robustness of the method is demonstrated on six other representative anatomies. The simulated SG is also compared with post-deployment CT observations, and demonstrates good adequacy. The results show that the numerically corrected fenestration positions, as determined from the simulated results following the insertion of the endovascular tools, deviate from those of the standard plan (as determined from the preoperative CT scan). This indicates that the SG-VS adequacy could be improved via simulation-based planning, to anticipate potential catheterisation difficulties.

International audience; In this work we propose a generic modeling approach for simulating percutaneous transluminal angioplasty (PTA) endovascular treatment, and evaluating the influence of balloon design, plaque composition, and balloon sizing on acute post-procedural outcomes right after PTA, without stent implantation. Clinically-used PTA balloons were classified into two categories according to their compliance characteristics, and were modeled correspondingly. Self-defined elastoplastic constitutive laws were implemented within the plaque and artery models, after calibration based on experimental and clinical data. Finite element method (FEM) implicit solver was used to simulate balloon inflation and deflation. Besides balloon profile at max inflation, results are mainly assessed in terms of the elastic recoil ratio (ERR) and lumen gain ratio (LGR) obtained immediately after PTA. No variations in ERR nor LGR values were detected when the balloon design changed, despite the differences observed in their profile at max inflation. Moreover, LGR and ERR inversely varied with the augmentation of calcification level within the plaque (-11% vs. +4% respectively, from fully lipidic to fully calcified plaque). Furthermore, results showed a direct correlation between balloon sizing and LGR and ERR, with noticeably higher rates of change for LGR (+18% and +2% for LGR and ERR respectively for a calcified plaque and a balloon pressure increasing from 10 to 14 atm). However a larger LGR comes with a higher risk of arterial rupture. This proposed methodology opens the way for evaluation of angioplasty balloon selections towards clinical procedure optimization.

Fine particles represent an important fraction of the mass of sediment transported by rivers (Syvitski et Saito, 2007). Suspended load is therefore a significant contributor to the erosion of landscapes. Fine particles are often considered to travel through streams and rivers with minimal interaction. Yet, recent field campaigns demonstrate that fine particles interact with the bed through erosion and deposition (Misset et al., 2019). Based on this observation, we develop a simplified model of suspended transport that accounts explicitly for the exchange of small particles between the river bed and the water column. This model involves three parameters: (1) a threshold water level above which the flow starts eroding fine particles from the bed, (2) an erosion rate that characterizes the intensity of sediment entrainment, and (3) a characteristic settling time accounting for sediment deposition.We then test the validity of the model against data collected in the Capesterre catchment, a small catchment (16.6 km2) monitored by the Observatory of Water and Erosion in the Antilles (ObsErA). Located in Basse-Terre Island (Guadeloupe archipelago, lesser Antilles arc), this catchment is regularly exposed to floods induced by hurricanes and tropical storms (Allemand et al., 2014; Gaillardet et al., 2011). The discharge and the turbidity of the river are measured with a time step of 5 minutes. Using in-situ calibrations, we convert the turbidity signal into a suspended load concentration. The resulting data reveal that the transport of fine sediment is highly intermittent: the concentration of suspended particles rises abruptly when the river height exceeds a threshold of the order of 25cm, corresponding to a discharge of 5 m3/s. The concentration decrease following the flood peak is more gentle. The resulting concentration-discharge curve takes the form of a counter-clockwise hysteretic loop, as commonly observed in many streams (Williams, 1989).

Amongst the numerous achievements of the Cassini-Huygens mission, the exploration of the Titan environment has had an unprecedented impact on the knowledge of this planet-like satellite of Saturn. The next milestone is the Dragonfly mission selected for a launch in 2026 and an arrival on Titan in 2034 (Turtle et al. LPSC abstract 2019). Now is the moment to bridge the gap between the end of the Cassini-Huygens measurements and the preparation of Dragonfly operations by prospecting on the work needed to take Titan’s science to the next level prior to DragonFly’s future discoveries. Those first remarks are generic for all possible Titan science; yet those apply particularly to Titan’s atmosphere (Hörst et al. JGR planets 2017). In this piece we address the need for innovative atmospheric modeling for Titan. The present state of the art on Titan’s atmospheric modeling could be summarized as follows. On the one hand, global climate modeling for Titan helped to make sense of Titan’s atmospheric circulation on a planetary scale (Lebonnois et al. Icarus 2012, Lora et al. Icarus 2015). On the other hand, regional climate (“mesoscale”) modeling was employed to understand the dynamics of convective storms made of methane and hydrocarbons (Barth and Rafkin Icarus 2010) and atmospheric dynamics in the vicinity of lakes and seas (Rafkin and Soto, submitted arxiv 1904.00120). The two approaches are complementary. Maybe the best example of this is the demonstration that the direction of equatorial dunes can only be explained when the large-scale winds are combined with convective methane storms able to cause wind maxima close to the surface opposite to the GCM predictions and compliant with observed dune propagation (Charnay et al. Nature Geoscience 2015). At the time of writing, no three-dimensional atmospheric model, suitable for the small scales and including complete physical packages (radiative transfer, cloud microphysics, etc), is available to resolve turbulence, convection and regional winds on Titan. Furthermore, assuming the Rafkin and collaborators’ model will soon be upgraded to those capabilities, having a diverse set of mesoscale models for Titan available is an asset for the community. Why would a regional-scale and turbulence-resolving model for Titan be needed? 1/ To characterize turbulent motions and help to constrain the flight conditions for the Dragonfly mission and, more generally, to understand turbulent motions on Titan. 2/ To resolve the three-dimensional convective dynamics in Titan’s methane and hydrocarbon storms and elucidate how they form, develop and dissipate; to assess the role of those storms in the near-surface exchanges and the organic cycle. 3/ To characterize surface-atmosphere exchange of particles and organic matter, in particular aeolian processes and sediment transport shaping Titan’s surface and dunes as major organic reservoirs; to understand the dynamics and aeolian potential of dust storms and dust devils on Titan. 4/ To elucidate the possibility of mesoscale dynamical features on Titan: slope winds, sea breezes, gravity waves, etc… and how those mesoscale phenomena impact the global dynamics. 5/ To make available a modeling platform used in specific, targeted regions, in which to couple photochemical models of interest for organic matter studies. Our team started to develop such a new atmospheric model for Titan and to propose it as a tool to the Titan community. We base our efforts on similar modeling tools developed for Mars (Spiga and Forget JGR planets 2009 ; Spiga et al. Nature Geoscience 2017) and Venus (Lefèvre et al. JGR planets 2017 & Icarus 2020). Our initial idea for developing mesoscale models is simple: an atmospheric model comprises a dynamical core (hydrodynamical solver for the Navier Stokes equations) coupled with physical packages for sub-grid scale unresolved processes (radiative transfer, cloud microphysics); we take the latter out of a Titan GCM (here, the IPSL Titan GCM) and we borrow the former from the terrestrial mesoscale model Weather Research and Forecast (WRF, Skamarock et al. Journal of Computational Physics 2008). That way, both the Titan GCM providing initial and boundary conditions for wind, temperature, and chemical species and our newly-built Titan mesoscale model share similar physical packages, ensuring optimal consistency in the downscaling approach. With such an admittedly ambitious program, which starting point could we adopt? Our experience with other planets is that the first applications shall be three-dimensional idealized simulations before the complete workflow for fully realistic simulations can be developed. Modeling instabilities caused by wind shear in Titan’s lower stratosphere, to explain the unexpected wind minima experienced by the Huygens probe is a first example (Lefèvre et al. EPSC-DPS abstract 2019). Another possibility explored here is to carry out large-eddy simulations for Titan’s near-surface turbulence. Those simulations are named as such because only the largest turbulent eddies are resolved / predicted by the model’s dynamics. Our prospect is, for instance, to evaluate the ability of dust devils to redistribute organic dust at the surface and in the atmosphere. Preliminary results show horizontally-organized turbulent structures (Figure 1), yet organized swirling motions are not yet reproduced at the time of writing. Figure 1 : Near-surface turbulent wind fields simulated by a prototype large-eddy simulation for Titan, using coupling of the adapted WRF dynamical core with the Titan physics from the IPSL Titan GCM. The development of the model is currently ongoing ; the first test for mesoscale simulations with existing topography (Corlies et al. GRL 2017) will be in the region enclosing the Shangri-La dune field, the Dragonfly provisional landing site (Figure 2). The development of our modeling system makes it easy to update the surface thermophysical properties with new datasets arising for topography, albedo, thermal inertia. Ideas for collaboration are very welcome following the presentation of this abstract. Figure 2 : An example of horizontal domain for mesoscale applications with our model, considered in the region of the Dragonfly landing site.

A key point of landslide hazard assessment is the estimation of their runout. Empirical relations linking angle of reach to volume can be used relatively easily, but they are generally associated with large uncertainties as they do not consider the topographic specificity of a given study site. On the contrary, numerical simulations provide more detailed results on the deposits morphology, but their rheological parameters can be difficult to constrain. Simulating all possible values can be time consuming and incompatible with operational requirements of rapid estimations. We propose and compare three operational methods to derive scaling power laws relating the landslide travel distance to the destabilized volume. The first one relies only on empirical relations, the second one on numerical simulations with back-analysis, and the third one combines both approaches. Their efficiency is tested on three case studies: the Samperre cliff collapses in Martinique, Lesser Antilles (0.5 to 4&times, 106 m3), the Frank Slide rock avalanche (36&times, 106 m3) and the Samperre cliff collapses in Martinique, Lesser Antilles (0.5 to 4&times, 106 m3) the Fei Tsui debris slide in Hong Kong (0.014&times, 106 m3). Purely numerical estimations yield the smallest uncertainty, but the uncertainty on rheological parameters is difficult to quantify. Combining numerical and empirical approaches allows to reduce the uncertainty of estimation by up to 50%, in comparison to purely empirical estimations. However, it may also induces a bias in the estimation, though observations always lie in the 95% prediction intervals. We also show that empirical estimations fail to model properly the dependence between volume and travel distance, particularly for small landslides (&lt, 20,000 &lt, 0.02&times, 106 m3).

International audience; A new digital terrain model of the Huygens landing 1 site on Saturn's largest moon • We create a new digital terrain model (DTM) of the Huygens landing site that 14 offers the best available resolution of river valleys on Titan. 15 • The complexity of the data set requires a tailor-made reconstruction procedure 16 that is detailed. 17 • The workflow uses reprocessed Huygens/DISR images and an automated shape-18 from-motion algorithm to improve an earlier DTM. Abstract 20 River valleys have been observed on Titan at all latitudes by the Cassini-Huygens 21 mission. Just like water on Earth, liquid methane carves into the substrate to form a com-22 plex network of rivers, particularly stunning in the images acquired near the equator by 23 the Huygens probe. To better understand the processes at work that form these land-24 scapes, one needs an accurate digital terrain model (DTM) of this region. The first and 25 to date the only existing DTM of the Huygens landing site was produced by the United 26 States Geological Survey (USGS) from high-resolution images acquired by the DISR (De-27 scent Imager/Spectral Radiometer) cameras onboard the Huygens probe and using the 28 SOCET SET photogrammetric software. However, this DTM displays inconsistencies, 29 primarily due to non optimal viewing geometries and to the poor quality of the origi-30 nal data, unsuitable for photogrammetric reconstruction. We investigate a new approach, 31 benefiting from a recent reprocessing of the DISR images correcting both the radiomet-32 ric and geometric distortions. For the DTM reconstruction, we use MicMac, a photogram-33 metry software based on automatic open-source shape-from-motion algorithms. To over-34 come challenges such as data quality and image complexity (unusual geometric config-35 uration), we developed a specific pipeline that we detailed and documented in this ar-36 ticle. In particular, we take advantage of geomorphic considerations to assess ambigu-37 ity on the internal calibration and the global orientation of the stereo model. Besides the 38 novelty in this approach, the resulting DTM obtained offers the best spatial sampling 39 of Titan's surface available and a significant improvement over the previous results. 40

Atherosclerosis is one of the most common vascular pathologies in the world. Among the most commonly performed endovascular treatments, percutaneous transluminal angioplasty (PTA) has been showing significantly positive clinical outcomes. Due to the complex geometries, material properties and interactions that characterize PTA procedures, finite element analyses of acute angioplasty balloon deployment are limited. In this work, finite element method (FEM) was used to simulate the inflation and deflation of a semi-compliant balloon within the 3D model of a stenosed artery with two different plaque types (lipid and calcified). Self-defined constitutive models for the balloon and the plaque were developed based on experimental and literature data respectively. Balloon deployment was simulated at three different inflation pressures (10, 12 and 14 atm) within the two plaque types. Balloon sizing influence on the arterial elastic recoil obtained immediately after PTA was then investigated. The simulated results show that calcified plaques may lead to higher elastic recoil ratios compared to lipid stenosis, when the same balloon inflation pressures are applied. Also, elastic recoil increases for higher balloon inflation pressure independent of the plaque type. These findings open the way for a data-driven assessment of angioplasty balloon sizing selection and clinical procedures optimization.Clinical Relevance- The FE model developed in this work aims at providing quantitative evaluation of recoil after balloon angioplasty. It may be useful for both manufacturers and clinicians to improve efficiency of angioplasty balloon device design and sizing selection with respect to plaque geometry and constitution, consequently enhancing clinical outcomes.

Orbital and surface observations demonstrate that aeolian activity is occurring on Mars. Here we report the aeolian changes observed in situ by NASA's InSight lander during the first 400 sols of op...

The evolution of landscapes with steep slopes and subject to tropical or alpine climates is mainly controlled by several mechanisms of geomorphic transport such as soil formation, river dynamics, slope stability and mass wasting. The time scale over which the climate influence acts on these mechanisms ranges from seasonal to decennial time span.On the seasonal time scale, for accessible locations and when manpower is available, direct observations and field survey are the most useful and standard approaches. While very limited studies have been focused on the decennial and century scale due to observational constrains. Here, we present a reproducible workflow based on historical aerial images (up to ~70yrs time span) that includes sensor internal calibration and external orientation, dense matching and elevation reconstruction over two areas of interest that represent pristine examples for tropical and alpine environments: The Rempart Canyon in Reunion Island, and the Arveyron river in the French Alps share a limited accessibility (in time and space) that can be overcome only from archive remote-sensing observations. We reach unprecedented resolution: the aero-triangulation falls at sub-metric scale based on ground truth, which is comparable to the initial images spatial sampling. This provides elevation time series with a better resolution to most recent satellite images such as Pleiades. In the case of the Rempart Canyon, we identified and quantified the results of 2 landslides that occurred in 1965 and 2001, and characterized the landslides dynamics. As for the river sediment transdport we emphasize similar tracking for the alpine case, which is controlled by glacial dynamics. In both cases, we emphasize the strong effect of climatic forcing (precipitation and temperature) over multi-decennial to century time-scales.