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This review summarizes what the volcanology community has learned thus far from studying the deposits of pyroclastic currents (PCs) from the 1980 eruption sequence at Mount St. Helens. The review includes mass flow events during the May 18 eruption, including the lateral blast, the afternoon column collapse and boil-over PC activity, and some aspects of the debris avalanche. We also include a summary of PCs generated in the smaller eruptions following the climactic May 18 event. Our objective is to summarize the state of our understanding of PC transport and emplacement mechanisms from the combination of field and laboratory observations, granular flow experiments, and numerical modeling techniques. Specifically, we couple deposit characteristics, experiments, and numerical modeling techniques to critically address the problems of (1) constraining conditions in the flow boundary zone at the time of deposition; (2) the influence of substrate roughness and topography on PC behavior; (3) the prevalence, causes, and consequences of substrate erosion by PCs; and (4) the reconstruction of PC transportation and sedimentation processes from a combination of geophysical and sedimentological observations. We conclude by providing opportunities for future research as our field, experimental, and numerical research techniques advance.

Files are Exp_'particle size'_* :acoustic signals obtained in 1vol.% suspension of particles of sizes (49, 78, 206, 315 and 467 µm) Exp_'particle size'_Pressure_* :corresponding pressure signals obtained in 1vol.% suspension of particles of sizes (49, 78, 206, 315 and 467 µm). These data are used for figure 2. U_up_particle size'_*: acoustic signals obtained in suspension of particles of sizes (78 and 467 µm) for increasing air velocities U. U_up_particle size'_Pressure*: corresponding pressure signals obtained in the suspension for increasing air velocities U. These data were used for figure 3. All_Pressure_Data: differential pressure signals for different particle sizes (78 and 467 µm) and different input particle concentrations. These data were used for figure 4., This is Laboratory of Excellence ClerVolc contribu538 tion . M.M. is supported CIFAR Earth 4D and NSF 2042173.

Pyroclastic density currents are hazardous, ground-hugging, hot mixtures of gas and solid particles produced by volcanoes. Currents generated by the largest explosive eruptions have traveled distances on the order of 100 km, and their devastating impact has repeatedly marked Earth's geologic history. We show that pyroclastic density currents from super-eruptions during the Oligocene in the Great Basin of the United States had exceptional runout distances that may have exceeded 300 km. We present a quantitative analysis of the data from these currents and consider, in particular, the areal extent of their deposits (ignimbrites) as well as the relationship between their runout and the eruption mass discharge rate. The ignimbrites have elliptical distributions characterized by axis length ratios of ~2–6, in contrast to common subcircular ignimbrites, while the maximum runouts versus the discharge rates are clearly outside of the prediction intervals defined by other eruption data. We argue that the long runouts resulted from the channeling of concentrated currents in regional paleovalleys whose gentle slope worked to lengthen the travel distance. Our study demonstrates that these additional factors should be considered in assessing hazards posed by future super-eruptions.

Supplemental figures, detailed information on the Great Basin ignimbrites and the paleovalleys, a summary of the database and the characteristics of the pyroclastic density currents, and the statistical model used.

International audience; We applied systematically the branching energy cone model to a large (N =50 ) set of stratovolcanoes around the world in order to evaluate the main topographic characteristics that may control the propagation of dense pyroclastic density currents (PDCs). Results indicate that the channelization efficiency of a PDC is strongly controlled by the relative scale between flow size and volcano topographic features. Most of the studied stratovolcanoes topographies are able to induce significant PDC channelization in proximal domains, while strong channelization in distal zones is mainly observed for volcanoes with steep flanks, with long, uninterrupted valleys, and with catchments zones of pyroclastic material (i.e. the valleys heads) located near the source. From the statistical analysis of numerical results, we recognise five groups of stratovolcanoes in terms of the mode of interaction between their topographies and dense PDCs: (1) intense channelization through different valleys up to distal domains (e.g. Colima and Peteroa); (2) intense channelization through a single, dominant valley up to distal domains (e.g. Reventador and Mt. St. Helens); (3) intense channelization near the source and moderate distal channelization, frequently involving intertwined drainage networks (e.g. Tungurahua and El Misti); (4) potentially intense channelization only near the source, typically involving flat distal topographies (e.g. Sinabung and Mayon); and (5) weak channelization in proximal domains, resulting in efficient early energy dissipation and thus reduced PDC run-out distance (e.g. Kelut and Akagi). The relevance of this classification lies in the possibility of defining volcanic analogues (defined here as volcanoes that share a suite of topographic characteristics and may be considered comparable to a certain extent) and identifying the main processes that may affect PDC propagation in specific topographic contexts. These aspects are useful for studying poorly documented volcanic edifices and for volcanic hazard assessment. Additionally, we compare this classification with published morphometric characteristics of volcanoes, showing morphometric parameters such as the mean slope of the low flank, irregularity index, ratio of volcano height and basal width and ratio of crater width and basal width are useful variables for recognising the groups we defined. These parameters can be used as rough indicators of the expected interaction patterns between the topography of a given volcano and dense PDCs.

Several competing concepts of anteroposterior stabilization have been developed for total knee arthroplasty (TKA), with an overall great success despite some differences in terms of clinical or radiological outcomes. The CORIN KneeTec DeepDish TM is a novel mobile-bearing implant, stabilized with an ultra-congruent deep-dish poly- ethylene insert. The aim of the present study was to report clinical and radiological outcomes of a series of patients who received the KneeTec DeepDish TM after a follow-up of 12 months, and to compare them to those of a comparable series of patients who received the STRYKER Triathlon ® posterior- stabilized. This was a retrospective comparative cohort study (level of evidence III). Demographic data, radiographic data and range of motion (ROM), as well the International Knee Society score and Oxford Knee Score were collected pre-operatively, and after a follow-up of 12 months. 106 KneeTec DeepDish TM and 80 Triathlon ® PS were evaluated at follow-up. Patients who received the KneeTec DeepDish TM had significant improvement in ROM, radiographic and clinical outcomes. There were no significant differences between the cohorts in terms of ROM, radiographic and clinical outcomes, as well as antero-posterior stability. This study is the first to report the 12-month outcomes of the CORIN KneeTec DeepDish TM. The novel KneeTec DeepDish TM achieved comparable ROM, radiographic and clinical outcomes to the Triathlon ® PS after 12 months. Further studies will be necessary to evaluate the mid- to long-term outcomes of the KneeTec DeepDish TM.

Defects in optic fissure closure can lead to congenital ocular coloboma. This ocular malformation, often associated with microphthalmia, is described in various clinical forms with different inheritance patterns and genetic heterogeneity. In recent times, the identification of an increased number of genes involved in numerous cellular functions has led to a better understanding in optic fissure closure mechanisms. Nevertheless, most of these genes are also involved in wider eye growth defects such as micro-anophthalmia, questioning the mechanisms controlling both extension and severity of optic fissure closure defects. However, some genes, such as FZD5, have only been so far identified in isolated coloboma. Thus, to estimate the frequency of implication of different ocular genes, we screened a cohort of 50 patients affected by ocular coloboma by using targeted sequencing of 119 genes involved in ocular development. This analysis revealed seven heterozygous (likely) pathogenic variants in RARB, MAB21L2, RBP4, TFAP2A, and FZD5. Surprisingly, three out of the seven variants detected herein were novel disease-causing variants in FZD5 identified in three unrelated families with dominant inheritance. Although molecular diagnosis rate remains relatively low in patients with ocular coloboma (14% (7/50) in this work), these results, however, highlight the importance of genetic screening, especially of FZD5, in such patients. Indeed, in our series, FZD5 variants represent half of the genetic causes, constituting 6% (3/50) of the patients who benefited from a molecular diagnosis. Our findings support the involvement of FZD5 in ocular coloboma and provide clues for screening this gene during current diagnostic procedures.

Aims The diversity of femoral morphology renders femoral component sizing in total hip arthroplasty (THA) challenging. We aimed to determine whether femoral morphology and femoral component filling influence early clinical and radiological outcomes following THA using fully hydroxyapatite (HA)-coated femoral components. Methods We retrospectively reviewed records of 183 primary uncemented THAs. Femoral morphology, including Dorr classification, canal bone ratio (CBR), canal flare index (CFI), and canal-calcar ratio (CCR), were calculated on preoperative radiographs. The canal fill ratio (CFR) was calculated at different levels relative to the lesser trochanter (LT) using immediate postoperative radiographs: P1, 2 cm above LT; P2, at LT; P3, 2 cm below LT; and D1, 7 cm below LT. At two years, radiological femoral component osseointegration was evaluated using the Engh score, and hip function using the Postel Merle d’Aubigné (PMA) and Oxford Hip Score (OHS). Results CFR was moderately correlated with CCR at P1 (r = 0.44; p < 0.001), P2 (r = 0.53; p < 0.001), and CFI at P1 (r = − 0.56; p < 0.001). Absence of spot welds (n = 3, 2%) was associated with lower CCR (p = 0.049), greater CFI (p = 0.017), and lower CFR at P3 (p = 0.015). Migration (n = 9, 7%) was associated with lower CFR at P2 (p = 0.028) and P3 (p = 0.007). Varus malalignment (n = 7, 5%), predominantly in Dorr A femurs (p = 0.028), was associated with lower CFR at all levels (p < 0.05). Absence of spot welds was associated with lower PMA gait (p = 0.012) and migration with worse OHS (p = 0.032). Conclusion This study revealed that femurs with insufficient proximal filling tend to have less favourable radiological outcomes following uncemented THA using a fully HA-coated double-tapered femoral component. Cite this article: Bone Joint Res. 2020;9(4):182–191.

Contains fulltext : 220455.pdf (Publisher’s version ) (Closed access) Microphthalmia, anophthalmia, and anterior segment dysgenesis are severe ocular developmental defects. There is a wide genetic heterogeneity leading to these ocular malformations. By using whole genome, exome and targeted sequencing in patients with ocular developmental anomalies, six biallelic pathogenic variants (including five novel variants) were identified in the PXDN gene in four families with microphthalmia and anterior segment dysgenesis. Only 11 different mutations (11 families) have been described in this gene to date. The phenotype of these patients is variable in severity, ranging from cataract and developmental glaucoma to complex microphthalmia. Interestingly, two unrelated patients of our series presented with an ocular phenotype including aniridia and microspherophakia. However, despite various phenotypic presentations and types of mutations, no genotype-phenotype correlation could be made. Thus, this work improves our knowledge of the recessive phenotype associated with biallelic variants in this gene and highlights the importance of screening PXDN in patients with anterior segment dysgenesis with or without microphthalmia.

co-auteur étranger; International audience; Tephra fallout hazard assessment is undertaken with probabilistic maps that rely on numerical models. Regarding maps production, the input parameters of the model (including atmospheric conditions), the physical approximations of the numerical simulations, and the probabilities of occurrence of different eruption types in specific time frames are among the most critical sources of uncertainty. We therefore present a tephra fallout hazard assessment study for two active volcanoes (Cotopaxi and Guagua Pichincha) in Ecuador. We utilize PLUME-MoM/HYSPLIT models, and a procedure for uncertainty quantification where: i) the uncertainty on eruptive source parameters and eruption type occurrence is quantified through expert elicitation; ii) we implement a new procedure for correlations between the different parameters, and iii) we use correction coeffients to take into account the uncertainty of the numerical model. Maps of exceedance probability given a deposit thickness threshold, and thickness maps given a robability of exceedence, are produced 1) for two eruptive scenarios (sub-plinian and Plinian) and 2) as a combination of these scenarios in case the next eruption will be sub-Plinian or Plinian. These maps are described according to the uncertainty distribution of eruption type occurrence probabilities, considering their 5th percentile, mean, and 95th percentile values. We finally present hazard curves describing exceeding probabilities in 10 sensitive sites within the city of Quito. Additional information includes the areal extent and the population potentially affected by different isolines of tephra accumulation. This work indicates that full uncertainty quantification helps in providing more robust scientific information, improving the hazard assessment reliability.

International audience; We investigate the influence of gas pore pressure in granular flows through numerical simulations on horizontal and low-angle inclined surfaces. We present a two-phase formulation that allows a description of dam-break experiments considering high-aspect-ratio collapsing columns and depth-dependent variations of flow properties. The model is confirmed by comparing its results with data from analogue experiments. The results suggest that a constant, effective pore pressure diffusion coefficient can be determined in order to reproduce reasonably well the dynamics of the studied dam-break experiments, with values of the diffusion coefficient consistent with experimental estimates from defluidizing static columns. The discrepancies between simulations performed using different effective pore pressure diffusion coefficients are mainly observed during the early acceleration stage, while the final deceleration rate, once pore pressure has been dissipated, is similar in all the studied numerical experiments. However, these short-lasting discrepancies in the acceleration stage can be manifested in large differences in the resulting run-out distance. We also analyze the pore pressure at different distances along the channel. Although our model is not able to simulate the under-pressure phase generated by the sliding head of the flows in experiments and measured beneath the flow-substrate interface, the spatio-temporal characteristics of the subsequent over-pressure phase are compatible with experimental data. Additionally, we studied the deposition dynamics of the granular material, showing that the timescale of deposition is much smaller than that of the granular flow, while the time of the deposition onset varies as a function of the distance from the reservoir, being strongly controlled by the surface slope angle. The simulations reveal that an increment of the surface slope angle from 0° to 10° is able to increase significantly the flow run-out distance (by a factor between 2.05 and 2.25, depending on the fluidization conditions). This has major implications for pyroclastic density currents, which typically propagate at such gentle slope angles.

Infection is a serious complication of 0.2-0.7% of primary total hip arthroplasties (THA) and 1-22% of prosthetic revisions. The objective of our study was to compare two types of spacers (unipolar versus bipolar) for two-stage revisions of periprosthetic hip infections. The primary hypothesis was that bipolar spacers have fewer mechanical complications than unipolar spacers. The secondary hypothesis was that bipolar spacers decrease the rate of septic revisions and promote primary prosthesis reimplantation.This retrospective, monocentric, multi-operator study was carried out between January 2012 and July 2018, including patients operated on for septic arthritis of the native or prosthetic hip (two-stage procedure). The patients were divided into two groups: group A, including the articulated spacers and group B, including the unipolar spacers. We studied the complications of the spacers and the course of the infection over a minimum of two years. Functional status was assessed by the Postel Merle d'Aubigné (PMA) score, the Harris Hip Score (HHS) and pre- and postoperative patient satisfaction scores.We collected data for 39 hips from 37 patients (mean age 63, 22 men and 14 women: 16 patients in group A, 21 in group B). We found no mechanical complications in group A versus 12 (52%) in group B. At 2 years, 93.8% of patients in group A no longer had any signs indicative of an active infection, compared with 71.4% in group B. In group A, the median PMA score increased from 5.5 (4-10.5) to 13.5 (12.5-15.5) and the HHS score from 27.5 (17-41.5) to 79 (64.5-89.5), postoperatively. In the final group B, the PMA score increased from 7 (6-9) to 14 (12-16) and the HHS score from 24 (11-41) to 72 (48-82) postoperatively.The use of articulated spacers in THA or septic THA two-stage revision significantly reduces the occurrence of mechanical complications in the short term, as well as the pain between the two procedures.IV.

International audience; Several processes have been proposed as triggering mechanisms for the large sector collapses that affect most volcanoes, and which may occur several times in the volcano’s lifetime. Here we present and discuss the case of Tutupaca volcano, located in southern Peru and part of the Central Volcanic Zone of the Andes. Tutupaca is composed of an old, hydrothermally altered and highly eroded Basal edifice, as well as younger twin peakslocated in the northern part of the complex (the Western and Eastern Tutupaca). The youngest Eastern edifice of Tutupaca is composed of at least seven coalescing lava domes and associated deposits, including block-and-ash flow and debris avalanche deposits. We identified two debris avalanche deposits. An older unit (Azufre debris avalanche deposit) was channeled in the valleys located to the E and SE of the basal volcano, reaching up to 3.5 km from its source region. Four cosmogenic nuclide exposure dates (10Be/feldspar) were obtained from boulders of this debris avalanche deposit and ranged between 6.0 ± 0.7 and 7.8 ± 1.5 ka. The younger unit (Paipatja deposit) was associated with the sector collapse of the edifice reconstructed just after the first debris avalanche (domes IV to VIII). The sector collapse produced a debris avalanche deposit that outcrops immediately to the NE of the amphitheater and was associated with a large pyroclastic density current deposit that was previously dated by radiocarbon at 218 ± 14 a BP (Samaniego et al., 2015). Both debris avalanche deposits have two contrasting sub-units: (1) the main subunit, hereafter called hydrothermal-altered debris avalanche deposit, is a whitishyellow volcanic breccia with heterolithic and heterometric blocks, which originated from the Basal edifice, and (2) a dome-rich debris avalanche deposit, composed by non-altered dome blocks from Eastern Tutupaca. Inproximal areas, the dome-rich unit overlaps the hydrothermally-altered unit while in distal areas, these two units are mixed forming a hummocky and/or ridged topography. In addition to the similarity of both debris avalanches, we propose that the triggering mechanism for these debris avalanches was similar. The dacitic dome growth, coupled with a substrate of older, hydrothermally-altered rock, induced the destabilization of the edifice, producing the debris avalanches and the related pyroclastic density currents.

Geophysical granular flows occur at the surface of the Earth and other planets with reduced atmospheric pressure. In this paper, we investigate the run-out of dam-break flows of particle-air mixtures with fine ( $$d=75\,\upmu {\hbox {m}}$$ ) or coarse ( $$d=150\,\upmu {\hbox {m}}$$ ) grains in a flume with different bottom roughness ( $$\delta$$ ) and vacuum degrees ( $$P^*$$ ). Our results reveal an increase of the flow run-out as $$d/\delta$$ decreases for fine $$d=75 \,\upmu {\hbox {m}}$$ -particles, and run-out decreases with the dimensionless ambient pressure ( $$P^*$$ ) for a given $$d/\delta$$ . In contrast, the run-out for coarser $$d=150\,\upmu {\hbox {m}}$$ -particles, is almost invariant respect to $$P^*$$ and $$d/\delta$$ . These results show that autofluidization of fine-grained flows demonstrated by earlier works at ambient pressure also occurs at reduced pressure though being less efficient. Hence, autofluidization is a mechanism, among others, to explain long run-out of geophysical flows in different environments.

International audience; BackgroundLe comblement des pertes de substance osseuses (PSO) peut être réalisé par des greffes osseuses type allogreffe traitée ou non. Les données de la littérature sont souvent contradictoires et peu de données sont accessibles sur la comparaison entre allogreffes traitées versus cryoconservées. Aussi nous avons mené une large étude afin de mesurer les facteurs qui avaient une influence sur la survie : (1) le type d’allogreffe et de cupule, (2) les facteurs techniques ou liés au patient.HypothèseLa reconstruction des PSO pouvait être effectuée indifféremment par des allogreffes morcelées cryoconservées ou traitées.Matériel et méthodesCette étude sur les PSO acétabulaires rétrospective et multicentrique incluait 508 dossiers de reconstruction ont pu être exploités au recul minimal de 5 ans. Le recul des greffes cryoconservées était plus faible (7,86 ans ± 1,89 [5–12,32]) que celui des traitées (8,22 ans ± 1,77 [5,05–15,48]) (p = 0,029). Mais les patients étaient plus jeunes au moment de leur première intervention pour les greffes cryoconservées (51,5 ans ± 14,2 [17–80]) contre traitées (57,5 ans ± 13,0 [12–94]) (p < 0,001), de même pour l’âge lors de la reprise acétabulaire (67,8 ans ± 12,2 [36,9–89,3] versus 70 ans ± 11,7 [25–94,5]) (p = 0,041).RésultatsIl y a eu globalement plus de complication dans le groupe cryoconservé (46/242 = 19,0 %) par rapport au groupe traité (35/256 = 13,2 %) (p = 0,044) avec plus de descellement dans le groupe cryoconservé (20/242 [8,2 %]) que dans le groupe os traité (6/266 [3,3 %]) (p = 0,001). En revanche, le nombre de luxation (16/242 = 6,6 % vs 17/266 = 6,4 %) (p = 0,844) ou d’infection (18/242 = 7,4 % vs 15/266 = 5,7 %) (p = 0,264), n’étaient pas différents. L’analyse en sous-groupe révélait qu’il y avait une corrélation entre la survenue de complication et la valeur croissante de l’IMC (p = 0,037) avec un risque global de complication supérieur chez les patients ayant un IMC supérieur à 30 ou inférieur à 20 (p = 0,006) avec un risque relatif de 1,95 (IC95 % : 1,26–2,93). Le surpoids était associé à un risque plus élevé de luxation avec un risque relatif de 2,46 (IC95 % : 1,23–4,70) (p = 0,007). Les descellements étaient plus fréquents chez les patients plus jeunes lors de l’intervention avec un risque relatif de 2,77 (IC95 % : 1,52–6,51) (p = 0,040) avant 60 ans lors de la reprise. Enfin les patients faiblement actifs selon Devane en préopératoire avaient un risque majoré de luxation avec un risque relatif de 2,51 (IC95 % : 1,26–8,26) (p = 0,022).DiscussionNotre hypothèse n’est pas confirmée par cette étude. Nos groupes n’étaient pas comparables initialement et ceci peut expliquer les différences retrouvées car le nombre plus important de descellement dans le groupe cryoconservé peut s’expliquer par l’hétérogénéité des groupes. Les allogreffes morcelées paraissent néanmoins adaptées à la reconstruction des PSO acétabulaires. La comparaison des formes cryoconservées ou traitées nécessite une étude randomisée pour déterminer laquelle est supérieure.

International audience; We present the results of analogue laboratory experiments on pyroclastic fountain collapse. Mixtures of air and glass beads ranging in size around 75 ± 15 μm, with Stokes number of ~10−3−101 and representative of 0.1–1 mm sized particles in nature, were released from a hopper at heights of 0.45–2.95 m above the base of a horizontal channel. Free fall caused continuous dilation of the granular material and led to mean particle concentrations of ~9–36 vol%, with concentration inversely proportional to drop height, before the particles impacted the channel base. Decoupling between the particles and the ambient air upon impact caused deflation of the mixture, which then propagated laterally as a dense granular flowoverridden by a dilute suspension. Measurements at the impingement surface revealed that pore fluid pressure, generated through high air-particle relative velocity during deflation, counterbalanced up to ~50% of theweight of theemerging granular flow. The runout distance of the dense flow increased linearly with the fall height, similar to published results on unidirectional flows generated from collapse of packed granular columns. This suggests that the runout of flows resulting from release of granular material is controlled essentially by conversion of potential to kinetic energy and that the initial particle concentration is a second order parameter.We conclude that fountaining of pyroclastic material containing largeamounts of particles with Stokes numbers of the order 10−3−101 can generate dense pyroclastic flows with some degree of pore fluid pressure.

Co-auteur étranger; International audience; Future occurrence of explosive eruptive activity at Cotopaxi and Guagua Pichincha volcanoes, Ecuador, is assessed probabilistically, utilizing expert elicitation. Eight eruption types were considered for each volcano. Type event probabilities were evaluated for the next eruption at each volcano and for at least one of each type within the next 100 years. For each type, we elicited relevant eruption source parameters (duration, average plume height, and total tephra mass). We investigated the robustness of these elicited evaluations by deriving probability uncertainties using three expert scoring methods. For Cotopaxi, we considered both rhyolitic and andesitic magmas. Elicitation findings indicate that the most probable next eruption type is an andesitic hydrovolcanic/ash-emission (~ 26–44% median probability), which has also the highest median probability of recurring over the next 100 years. However, for the next eruption at Cotopaxi, the average joint probabilities for sub-Plinian or Plinian type eruption is of order 30–40%—a significant chance of a violent explosive event. It is inferred that any Cotopaxi rhyolitic eruption could involve a longer duration and greater erupted mass than an andesitic event, likely producing a prolonged emergency. For Guagua Pichincha, future eruption types are expected to be andesitic/dacitic, and a vulcanian event is judged most probable for the next eruption (median probability ~40–55%); this type is expected to be most frequent over the next 100 years, too. However, there is a substantial probability (possibly >40% in average) that the next eruption could be sub-Plinian or Plinian, with all that implies for hazard levels.

We report on direct measurements of the basal force components for granular material flowing down a smooth incline. We investigate granular flows for a large range of inclination angles from teta=13.4{\deg} to 83.6{\deg} and various gate opening of the chute. We find that the effective basal friction coefficient, muB, obtained from the ratio of the longitudinal force to the normal one exhibits a systematic increase with increasing slope angle and a significant weakening with increasing particle hold-up H (the depth-integrated particle volume fraction). At low angles, the basal friction is slightly less than or equal to tan(teta). The deviation from tan(teta) can be interpreted as a contribution from the side-wall to the overall friction. At larger angles, the basal friction muB saturates at an asymptotic value that is dependent on the gate opening of the chute. Importantly, our data confirm the outcomes of recent discrete numerical simulations. First, for steady and fully developed flows as well as for moderately accelerated ones, the variation of the basal friction can be captured through a unique dimensionless number, the Froude number Fr, defined as Fr=U/(gHcos(teta))^1/2, where U is the mean flow velocity. Second, the mean velocity scales with the particle hold-up H with a power exponent close to 1/4, contrasting with the Bagnold scaling (U~H^3/2)., Comment: 18 pages, 12 figures

Co-auteur étranger; International audience; Granular flows that propagate down a mountainside, then reach the sea, a lake or a river and finally, travel underwater, is a common event on the Earth’s surface. To help the description of such events, laboratory experiments on gas-fluidized granular flows entering water are performed, analyzed, and compared to those propagating in air. The originality of this study lies in the fluidization process, which improves the laboratory modelling of geophysical flows by taking their high mobility into account. Qualitatively, the presence of the water body promotes the generation of a granular jet over the water surface, a leading and largest wave, and a particle-driven gravity current underwater. Hydrodynamic forces mainly play a dissipative role by slowing and reducing the spreading of the granular mass underwater, but a low amount of grains are still transported by the turbulent fluid as a gravity current far away. The temporal evolution of the granular jet and the particle-driven gravity current are well described by ballistic motion theory and scaling laws of homogeneous gravity currents, respectively. Most currents propagate with a constant flow-front velocity along the horizontal bottom, which is controlled by the flow height depending on the water depth. In constrast, the bulk volume concentration of particles in the current is estimated to be nearly constant, interpreted as a critical concentration above which the excess of particles cannot be maintained by the turbulent fluid. This experimental study highlights the complexity of the dynamics and deposits of granular masses when they encounter a water body.

Numerical simulations, performed with a new two-phase bi-projection scheme, of the collapse of columns of glass beads with aspect ratios equal to 0.7 and 2 over a horizontal plane are reported and comparison with experiments are presented. A level-set formulation for the Navier–Stokes equations is used, so that the interface between the granular material and the ambient air is tracked. The granular flow is modeled with a viscoplastic rheology, derived from the μ ( I ) –rheology, resulting in a Drucker–Prager plasticity criterion combined with a spatio-temporal variable viscosity depending on the pressure and on the shear rate. The computational effort is reduced by using instead a constant viscosity. The dependence of the results upon the value of the constant viscosity, which has been reduced by two orders of magnitude, is very weak suggesting that these granular flows are mainly governed by the Drucker–Prager plasticity criterion. The rheology is formulated as a projection, allowing for an efficient computation of the plastic part of the stress tensor. Coulomb friction conditions are applied on the walls. The dynamics of the collapse and the morphology of the final deposit are accurately reproduced. Sensitivity of the results, with respect to the resolution and the basal friction coefficient, is also studied. During the collapse, the granular material consists of a basal deposit overlain by a flowing layer, which are separated by an interface that migrates upwards until the flowing layer is consumed. The time evolution of this static-mobile interface is quantified and a good agreement is found with experiments. To the best of our knowledge this is the first simulation of internal flow dynamics validated by experiments. We also report results obtained with a viscoplastic model where the dynamic pressure in the yield is replaced by the hydrostatic pressure, depending on the granular flow height. This model produces non-physically relevant solutions. Nevertheless, from a numerical point of view, it provides interesting and challenging test cases for two-phases viscoplastic simulations as the interface rolls up before the head of the granular mass falls on the bottom wall.

Dilute gas–particle suspensions in which the particles are carried by the fluid are found in various industrial and geophysical contexts. One fundamental issue that limits our understanding of such systems is the difficulty to obtain information on the particle concentration inside these often optically opaque suspensions. To overcome this difficulty, we develop ultrasonic spectroscopy to monitor the local particle concentration \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\phi$$\end{document}ϕ of glass particles (with diameters \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$d\sim$$\end{document}d∼ 77 \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\upmu$$\end{document}μm or 155 \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\upmu$$\end{document}μm) suspended in air. First, we determine the minimal air velocity, \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$U^*$$\end{document}U∗, necessary to suspend the particles from the maximum decrease in the transmitted wave amplitude and velocity of ultrasound propagating through the suspension. Next, setting the air velocity at \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$U^*$$\end{document}U∗, we increase the mass of particles and monitor acoustically the local solid volume fraction, \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\phi$$\end{document}ϕ, by measuring the ultrasound wave attenuation coefficient and phase velocity as a function of frequency on the basis of classical scattering and hydrodynamic models. For the frequency ranges and suspensions considered here, the viscous dissipation dominates over scattering and thermal conduction losses. We show that, for a characteristic air velocity \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$U^*$$\end{document}U∗, the locally measured \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\phi$$\end{document}ϕ reaches a critical value, in agreement with a recent study on turbulent gas–particle mixtures. Moreover, we find that this critical \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\phi$$\end{document}ϕ increases with the size of the particles. Finally, analysis of the temporal fluctuations of the locally measured solid volume fraction, suggests that high density regions (clusters) are present even in suspensions with concentrations below the critical concentration. This differs from the current hypothesis according to which the critical concentration coincides with the onset of cluster formation.

International audience

International audience; Novel laboratory experiments of fluidized granular flows entering water are reported, for the purpose of investigating tsunamis generated by pyroclastic flows. Qualitatively, the impact of a fluidized granular flow into water leads to (i) an initial vertical granular jet over water, (ii) a leading and largest wave, and (iii) a turbulent mixing zone forming a turbidity current. The present study focuses on the leading wave features in the near‐field region, as a function of the mass flux per width qm and the volume per width υ of the flow, the maximum water depth Ho, and the slope angle θ of the inclined plane. The obtained waves are of Stokes and cnoidal types, for which the generation is mostly controlled by qm and υ. By contrast, Ho plays no role on the wave generation that occurs in the shallowest region. Moreover, a comparison between fluidized granular, dry (nonfluidized) granular, and water flows entering water is addressed under similar flow conditions. The dimensionless amplitude scales as A/Ho=f(ζ), where urn:x-wiley:jgrb:media:jgrb54190:jgrb54190-math-0001 is a dimensionless parameter depending on the Froude number Fr, the relative slide thickness S, the relative mass M, and the slope angle θ. Data of fine fluidized granular, fine dry granular, and water flows collapse on a master curve, which implies that the nature of the flowing material is of lesser importance in the current setup. By contrast, coarse granular flows generate lower amplitude waves, which is attributed to the penetration of water into the porous granular medium.

Co-auteur étranger; International audience; Numerical modelling of tephradispersaland depositionis essential forevaluation of volcanichazards. Manymodels consider reasonable physical approximations in order toreducecomputational times, but this may introduce a certain degree of uncertainty in the simulation outputs.The important step of uncertainty quantification is dealt in this paper with respect to a coupled version of a plume model (PLUME-MoM) and a tephra dispersal model (HYSPLIT). The performances of this model are evaluated through simulationsoffourpasteruptions of different magnitudesand styles from three Andean volcanoes, and the uncertainty is quantified by evaluating the differences between modeled and observed data of plume height (at different time steps above the vent)as well asmass loading and grain sizeat givenstratigraphic sections.Different meteorological datasets were alsotestedand hada sensible influence on the model outputs. Other results highlight that the modeltendsto underestimate plume heights whileoverestimatingmass loading values, especially for higher magnitude eruptions.Moreover, the advective part of HYSPLIT seems to work more efficiently than the diffusive part.Finally, though the coupledPLUME-MoM/HYSPLIT model generally is less efficient inreproducing deposit grain sizes, we propose itmay be used for hazard maps production for higher magnitude eruptions (sub-Plinian or Plinian)for what concern mass loading.

Background Short uncemented stems have recently been proposed as an alternative to classic long stems for shoulder arthroplasty. The early results are promising, but bony adaptations of the proximal humerus have been reported. The aim of this study was to quantify these phenomena using the Ascend Flex stem and to determine the risk factors. Materials and methods In a retrospective, single-center study, 183 shoulder arthroplasties were evaluated at 2-year follow-up. All patients underwent clinical evaluations preoperatively and at last follow-up. Radiographs were obtained preoperatively, postoperatively, and at last follow-up. Four types of bony adaptations were analyzed: medial cortical narrowing (MCN), medial metaphysis thinning (MMT), lateral metaphysis thinning (LMT), and under-the-baseplate osteolysis. The risk factors were analyzed in a multivariate model. Results MCN was found in 72.6% of cases and was severe (>50%) in 4.4%. MMT was found in 46.4% of cases and was severe in 3.3%. LMT was found in 9.8% of cases and was severe in 2.8%. The risk factors for MCN were the distal filling ratio, osteoporosis, and female sex, whereas MMT and LMT were only influenced by stem axis deviation. Under-the-baseplate osteolysis was found in 34.4% of cases. No influence of bony adaptations on the clinical outcomes was observed. We found no complications related to the stem or to stem loosening. Conclusion The radiographic evolution was satisfactory at mid-term follow-up. Bony adaptations seemed to be limited phenomena, without any observed consequence. Avoiding excessive filling and axis deviation may limit these phenomena.

Introduction The PFMR® proximal femoral modular reconstruction implant (Protek, Sulzer Orthopedics, Switzerland) is a straight modular stem in sanded titanium with press-fit anchorage, intended to achieve spontaneous bone reconstruction following Wagner's principle. The aim of the present study was to analyze long-term clinical and radiological outcome. Material and method A single-center retrospective study included 48 PFMR stems implanted in 47 patients between 1998 and 2002. Results in this series were previously reported at 7 years’ follow-up. Clinical assessment used PMA and Harris scores. Radiologic assessment focused on stem stability and osseointegration, and bone stock following Le Beguec. Results Twenty-three patients were seen at a mean 14.5 years’ follow-up (13 deceased, 11 lost to follow-up), including 1 with bilateral implants, i.e., 24 stems. PMA and Harris scores, stem stability and osseointegration and bone stock were stable with respect to the 7-year findings. Radiology found 7 stem fractures in the Morse taper, i.e., in 29% of implants. Two of these cases required femoral implant replacement; 5 were asymptomatic. Discussion and conclusion Long-term outcome for PFMR stems was clinically and radiologically satisfactory for the 16 patients free of mechanical complications. The Morse taper fracture rate was high, and higher than reported elsewhere. The usual risk factors for implant fracture were not found in the present series. The modular design of the press-fit revision implant is its weak point; monoblock implants should be used in patients with good life-expectancy. Level of evidence IV (retrospective study).

Resume Introduction La prothese femorale modulaire de revision (PFM-R®, Protek, Sulzer Orthopedics, Suisse) est une tige modulaire, droite, en titane sable, a ancrage press-fit, visant a obtenir une reconstruction osseuse spontanee selon le principe de Wagner. L’objectif de ce travail etait d’analyser les resultats cliniques et radiographiques a long terme de cet implant. Materiels et methodes Il s’agit d’une etude retrospective, monocentrique, portant sur 48 tiges PFM-R® implantees chez 47 patients entre 1998 et 2002. Les resultats de cette serie avaient deja ete rapportes a 7 ans de recul. L’analyse clinique a comporte une evaluation du score PMA et du score de Harris. L’analyse radiographique a evalue la stabilite et l’osteointegration de la tige ainsi que le capital osseux femoral selon la methode de Le Beguec. Resultats Au recul moyen de 14,5 ans, 23 patients ont ete revus (13 decedes, 11 perdus de vue) dont une implantation bilaterale (24 tiges). Le score PMA et le score de Harris, la stabilite et l’osteointegration du pivot femoral ainsi que le capital osseux apparaissent stables en comparaison avec les resultats a 7 ans. L’analyse radiographique mettait en evidence 7 cas de rupture d’implant au niveau du cone morse, 29 % des cas revus. Deux cas ont necessite un changement de l’implant femoral, 5 cas restent asymptomatiques. Discussion et conclusion Les resultats a long terme de la tige PFM-R® apparaissent satisfaisants sur le plan clinique et radiographique pour les 16 patients indemnes de complication mecanique. Le taux de rupture du cone morse est important, superieur aux donnees de la litterature. Les facteurs habituellement incrimines dans les ruptures prothetiques n’ont pas ete retrouves dans cette serie. La modularite des protheses de revision a ancrage press-fit reste le point faible de ce type d’implant et doit pousser a l’utilisation d’implants de type monobloc pour les patients a esperance de vie elevee. Niveau de preuve IV : etude retrospective.

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International audience; Pyroclastic flows are mixtures of volcanic gases and particles that can be very hazardous owing to their fluid-like behavior. One possible mechanism to explain this behavior is the reduction of particles friction due to the internal gas pore pressure. To verify this hypothesis, we present a numerical model of a granular flow with high initial pore pressure that decreases with time as the gas-particle mixture propagates. First, we validate the model by reproducing laboratory experiments. Then, the numerical code is applied to pyroclastic flows of Lascar volcano (1993 eruption, Chile). The simulation reproduces the runout and the morphological features of the deposits, with lateral levées, a central channel, and a lobate front. Our results support the hypothesis of the role of gas pore pressure in pyroclastic flows and explain both the fluid-like behavior of the flows and the formation of lateral levees.

International audience; The experimental approach has become a major tool increasingly used by volcanologists in recent decades to investigate the physics of eruptive processes in complement to field and theoretical works. Researchers have developed various methodologies to study volcanic phenomena at reduced length scale. The works involve natural or analogue materials and their types range from first-order tests, to identify fundamental processes and make qualitative comparison with field observations, to more sophisticated experiments in which precise data obtained in a controlled environment can be used to validate outputs of theoretical models. Scaling is a central issue to ensure dynamic similarity between the small-scale experiments and the large-scale volcanic phenomena when natural conditions cannot be simulated due to inherent length scale difference and/or technical limitations. In this respect, dimensionless numbers are used to map physical regimes and to define scaling laws, which allow experimental results to be extrapolated to natural scale. This review presents the variety of experimental studies conducted to investigate subterraneous and aerial volcanic phenomena involving in particular fluid-particle mixtures. We focus on the major scaling issues and the physical regimes investigated, and we also highlight in a historical perspective some of the major advances achieved through experimental studies. Finally we conclude on some perspectives for future works.

International audience; BackgroundIn the context of acetabular reconstruction, bone defects can be filled with processed or unprocessed bone allografts. Published data are often contradictory on this topic and few studies have been done comparing processed allografts to fresh-frozen ones. This led us to conduct a large study to measure the factors impacting the survival of THA revision: (1) type of allograft and cup, (2) technical factors or patient-related factors.HypothesisAcetabular reconstruction can be performed equally well with frozen or processed morselized allografts.Materials and methodsThis retrospective, multicenter study of acetabular reconstruction included 508 cases with a minimum follow-up of 5 years. The follow-up for the frozen grafts was shorter (7.86 years ± 1.89 [5–12.32]) than that of the processed grafts (8.22 years ± 1.77 [5.05–15.48]) (p = 0.029). However, the patients were younger at the time of the primary THA procedure in the frozen allograft group (51.5 years ± 14.2 [17–80]) than in the processed group (57.5 years ± 13.0 [12–94]) (p < 0.001) and were also younger at the time of THA revision (67.8 years ± 12.2 [36.9–89.3] versus 70 years ± 11.7 [25–94.5]) (p = 0.041).ResultsThere were more complications overall in the frozen allograft group (46/242 = 19.0%) than the processed allograft group (35/256 = 13.2%) (p = 0.044) with more instances of loosening in the frozen group (20/242 [8.2%]) than in the processed group (6/266 [3.3%])(p = 0.001). Conversely, the dislocation rate (16/242 = 6.6% vs. 17/266 = 6.4%) (p = 0.844) and infection rate (18/242 = 7.4% vs. 15/266 = 5.7%) (p = 0.264) did not differ between groups. The subgroup analysis reveal a correlation between the occurrence of a complication and higher body mass index (BMI) (p = 0.037) with a higher overall risk of complications in patients with a BMI above 30 or under 20 (p = 0.006) and a relative risk of 1.95 (95% CI: 1.26–2.93). Being overweight was associated with a higher risk of dislocation (relative risk of 2.46; 95% CI: 1.23–4.70) (p = 0.007). Loosening was more likely to occur in younger patients at the time of the procedure (relative risk of 2.77; 95% CI: 1.52–6.51) (p = 0.040) before 60 years during the revision. Lastly, patients who were less active preoperatively based on the Devane scale had an increased risk of dislocation (relative risk of 2.51; 95% CI: 1.26–8.26) (p = 0.022).DiscussionOur hypothesis was not confirmed. The groups were not comparable initially, which may explain the differences found since the larger number of loosening cases in the frozen allograft group can be attributed to group heterogeneity. Nevertheless, morselized allografts appear to be suitable for acetabular bone defect reconstruction. A randomized study would be needed to determine whether frozen or processed allografts are superior.Level of evidenceIII, comparative retrospective study.

Tsunamis generated by the collapse of a granular mass into water represent a low amount of documented tsunamis in the world. However, they can locally cause severe human and material damages as they occur near coastlines. In order to identify physical mecanisms controlling the features of induced waves, the simple configuration of a granular material entering into water has been widely investigated. This study extends the configuration to the case of a fluidized granular flow, representative of tsunamis generated by pyroclastic flows during volcanic eruptions. We show that, in dam-break configuration, the fluidization process enhances the mobility of the granular flow with larger front velocities and larger propagation distances of the mass. The consequence is a significant increase of the maximum wave amplitude in comparison to an analogous situation without fluidization. The influence of the impact velocity and of the mass on the amplitude of the wave is also supported by varying the initial height of the granular column released. Finally, we show that the level of water does not affect the characteristics of the wave, in the range of parameters considered here., Les tsunamis générés par l'entrée d'une masse granulaire dans l'eau ne représentent qu'une faible proportion des tsunamis répertoriés dans le monde. Toutefois, ils peuvent localement causer d'importants dégâts humains et matériels car ils sont généralement créés proche des côtes. Afin d'identifier les méca-nismes physiques contrôlant les propriétés des vagues induites, la configuration simplifiée d'un matériau granulaire impactant l'eau a été largement étudiée en laboratoire. Cette étude étend la configuration au cas d'un écoulement granulaire fluidisé, représentatif des tsunamis générés par des écoulements py-roclastiques lors d'éruptions volcaniques. Nous montrons qu'en configuration de rupture de barrage (dam-break), le processus de fluidisation améliore la mobilité de l'écoulement granulaire, caractérisée par une augmentation de la vitesse du front et de la distance de propagation de la masse. La consé-quence est une amplitude de vague plus grande par rapport à une situation analogue sans fluidisation. L'influence de la vitesse d'impact et de la masse sur l'amplitude de la vague est également confirmée en variant la hauteur initiale de la colonne granulaire relâchée. Finalement, nous montrons que la hauteur d'eau n'affecte pas les caractéristiques de la vague, dans la gamme des paramètres considérées ici.

Microphthalmia, anophthalmia, and anterior segment dysgenesis are severe ocular developmental defects. There is a wide genetic heterogeneity leading to these ocular malformations. By using whole genome, exome and targeted sequencing in patients with ocular developmental anomalies, six biallelic pathogenic variants (including five novel variants) were identified in the PXDN gene in four families with microphthalmia and anterior segment dysgenesis. Only 11 different mutations (11 families) have been described in this gene to date. The phenotype of these patients is variable in severity, ranging from cataract and developmental glaucoma to complex microphthalmia. Interestingly, two unrelated patients of our series presented with an ocular phenotype including aniridia and microspherophakia. However, despite various phenotypic presentations and types of mutations, no genotype-phenotype correlation could be made. Thus, this work improves our knowledge of the recessive phenotype associated with biallelic variants in this gene and highlights the importance of screening PXDN in patients with anterior segment dysgenesis with or without microphthalmia.

The adolescent's painful functional disorders deserve management by a specialized interdisciplinary team. In recent years, intensive interdisciplinary physical therapy (IIPT) programs have developed in a hospital environment in Europe and around the world. While the short-term objective is often to restore trust between the patient and the therapists by relieving parents of the need to coordinate a network of multidisciplinary practitioners. These programs have proven to be effective in the medium and long term in improving the patient's clinical performance and for the benefits associated with restoring normal life for the family. Finally, these programs can have a positive impact in a cost-benefit approach when considering these often long and complex care arrangements.Les troubles fonctionnels douloureux chroniques de l’adolescent méritent une prise en charge interdisciplinaire spécialisée. Depuis quelques années, des programmes de thérapie physique intensive interdisciplinaire (intensive interdisciplinary physical therapy, IIPT) se sont développés dans un environnement hospitalier en Europe et dans le monde. Si l’objectif à court terme est souvent de remettre les patients en mouvement, un autre objectif est de restaurer une confiance entre le patient et les professionnels de la santé en soulageant notamment les parents de la coordination d’un réseau de praticiens multidisciplinaires. Ces programmes ont montré leur efficacité à moyen et long termes sur l’amélioration clinique du patient et sur les bénéfices associés à la reprise d’une vie normale pour la famille. Enfin, ces programmes peuvent avoir un impact positif en termes de coût/bénéfice dans ces prises en charge souvent longues et complexes.