Search

The focus of this study is the experimental characterization of cemented granular materials, with the aim of identifying the microscopic properties of the solid bonds and describing the extension to macroscopic mechanical strength of cemented samples. We chose to use artificially bonded granular materials, made of glass beads connected by solid paraffin bridges. The results of several sets of laboratory tests at different scales are presented and discussed. Micromechanical tests investigate the yield strength of single solid bonds between particles under traction, shearing, bending and torsion loading, as a function of variations in particle size, surface texture and binder content. Macro-scale tensile tests on cemented samples explore then the scale transition, including influence of confining walls through homothetic variations of the sample size. Despite the large statistical dispersion of the results, it was possible to derive and validate experimentally an analytical expression for micro tensile yield force as a function of the binder content, coordination number and grain diameter. In view of the data, an adhesive bond strength at the contact between bead and solid bond is deduced with very good accuracy and it is even reasonable to assume that the other threshold values (shear force, bending and torsion moments) are simply proportional to the tensile yield, thus providing a comprehensive 3D model of cemented bond. However, the considerable dispersion of the data at the sample scale prevents validation of the extended model for macroscopic yield stress. A final discussion examines the various factors that may explain intrinsic variability. By comparison with other more realistic systems studied in the literature in the context of bio-cementation, our artificial material nevertheless appears suitable for representing a cemented granular material. Being easy to implement, it could thus enable the calibration of discrete cohesion models for simulation of practical applications. [ABSTRACT FROM AUTHOR]

The repose of granular materials is investigated via two different Discrete Element Method (DEM) implementations in comparison with an experimental reference from a recently proposed benchmark setup. On a methodological standpoint, a rigorous measurement method of the angle of repose (AOR) is first proposed for plane-strain and axisymmetric conditions as encountered in the reference experiments.Additionally, two systematic procedures are designed in order to also determine the void ratio of the heap, as a fundamental property of granular matter possibly influencing the AOR. A physical discussion is then developed on the role of particle shape, considering the non-spherical nature of reference particles with a convexity value of C = 0.954 . Adoping non-convex multi-spheres aggregates (i.e. clumps), the first DEM modelling approach successfully predicts the AOR within a 8% tolerance. After a convex simplification that neglects local concavities, another approach based on potential particles underestimates to a greater extent the AOR, bringing it down from 35.95 ± 0. 88 ∘ to 31.26 ± 0. 95 ∘ . For the loading setup(s) at hand, the AOR is eventually shown to bear no constitutive nature. It is for instance independent of initial void ratio but is still different than the critical friction angle. The latter may actually serve as a lower bound for the process-dependent AOR. These conclusions are drawn from a statistical analysis of a large set of results, accounting for the random nature of the microscopic arrangement in the studied process. [ABSTRACT FROM AUTHOR]

Background: The protein phosphatase 2 (PP2A) is one of the major serine/threonine phosphatases in humans. The most frequently reported pathogenic PP2A variants have been identified in PPP2R5D, encoding the regulatory subunit B' delta, and are known to cause intellectual developmental disorder autosomal dominant 35 (MRD35). Case presentation: Herein, we describe a unique case of a patient with a heterozygous pathogenic variant, c.592G>A/p.(Glu198Lys) in the PPP2R5D gene which was associated with hyperpigmented skin lesions arising from increased melanin production, known as Café-au-lait macules (CALMs). To our knowledge, this is the first reported case of a PPP2R5D-related neurodevelopmental disorder associated with CALMs. Conclusions: Our findings suggest that the documentation and reporting of CALMs when associated with one or more physical and/or neurodevelopmental findings are of utmost importance as they could be indicative of an underreported phenotype and may extend the phenotypic spectrum of MRD35. [ABSTRACT FROM AUTHOR]

This paper presents an erosion interpretation of cohesive granular materials stressed by an impinging jet based on the results of a micromechanical simulation model. The numerical techniques are briefly described, relying on a two-dimensional Lattice Boltzmann Method coupled with a Discrete Element Methods including a simple model of solid intergranular cohesion. These are then used to perform a parametric study of a planar jet in the laminar regime impinging the surface of granular samples with different degrees of cohesive strength. The results show the pertinence of using a generalized form of the Shields criterion for the quantification of the erosion threshold, which is valid for cohesionless samples, through empirical calibration, and also for cohesive ones. Furthermore, the scouring kinetics are analysed here from the perspective of a self-similar expansion of the eroded crater leading to the identification of a characteristic erosion time and the quantification of the classical erosion coefficient. However, the presented results also challenge the postulate of a local erosion law including erodibility parameters as intrinsic material properties. The paper then reviews the main limitations of the simulation and current interpretation models, and discusses the potential causes for the observed discrepancies, questioning the pertinence of using time-averaged macroscopic relations to correctly describe soil erosion. The paper concludes addressing this question with a complementary study of the presented simulations re-assessed at the particle-scale. The resulting local critical shear stress of single grains reveals a very wide dispersion of the data but nevertheless appears to confirm the general macroscopic trend derived for the cohesionless samples, while the introduction of cohesion implies a significant but systematic quantitative deviation between the microscopic and macroscopic estimates. Nevertheless, the micro data still shows consistently that the critical shear stress does actually vary approximately in linear proportion of the adhesive force. [ABSTRACT FROM AUTHOR]

The behavior of a natural soil is known to change substantially in presence of water under unsaturated conditions, due to additional capillary forces. Water can be absorbed by hygroscopic soil particles (such as clay), or remains at the surface of solid grains (sand, silt) and forms either a discontinuous (pendular regime) or a continuous phase (funicular regime), depending on the water content of the soil. Capillary bridges exist solely between pairs of grains at small water contents, giving rise to simple capillary force expressions and straightforward subsequent modeling. For larger water contents, these generic capillary bridges progressively merge into more complex coalesced bridges involving several grains (i.e. at least three) and whose description remains little known. In the present study, a numerical approach based on surface energy minimization is proposed to compute capillary forces for assemblies of two or three grains. The methodology is first validated for a standard capillary bridge between two grains by comparison both with previous experiments and with other alternative theoretical and numerical approaches. The method is next extended to a triplet of grains within a wide range of water content (or equivalently reduced water volume) during imbibition, to switch from uncoalesced to coalesced bridges. Eventually, the influence of contact angle, surface tension and gravity on the capillary force, the volume of coalescence and the morphology of the bridge as well is investigated. The present study paves the way for the implementation of capillary effects in micromechanical models relying on mesostructures composed of a few grains. [ABSTRACT FROM AUTHOR]

Collapse of granular material is usually accompanied by long run-out granular flows in natural hazards, e.g. rock/debris flow and snow avalanches. This paper presents a novel multi-scale approach for modelling granular column collapse with large deformation. This approach employs the smoothed particle hydrodynamics (SPH) method to solve large deformation boundary value problems, while using a micromechanical model to derive the nonlinear material response required by the SPH method. After examining the effect of initial cell size, the proposed approach is subsequently applied to simulate the flow of granular column in a rectangular channel at a low water content by varying the initial aspect ratio. The numerical results show good agreement with various experimental observations on both collapse process and final deposit morphology. Furthermore, the meso-scale behaviour is also captured owing to the advantages of the micromechanical model. Finally, it was demonstrated that the novel multi-scale approach is helpful in improving the understanding of granular collapse and should be an effective computational tool for the analysis of real-scale granular flow. [ABSTRACT FROM AUTHOR]

PAX5 and EBF1 work synergistically to regulate genes that are involved in B lymphocyte differentiation. We used the KIS-1 diffuse large B cell lymphoma cell line, which is reported to have elevated levels of PAX5 expression, to investigate the mechanism of EBF1- and PAX5-regulated gene expression. We demonstrate the lack of expression of hallmark B cell genes, including CD19, CD79b, and EBF1, in the KIS-1 cell line. Upon restoration of EBF1 expression we observed activation of CD19, CD79b and other genes with critical roles in B cell differentiation. Mass spectrometry analyses of proteins co-immunoprecipitated with PAX5 in KIS-1 identified components of the MLL H3K4 methylation complex, which drives histone modifications associated with transcription activation. Immunoblotting showed a stronger association of this complex with PAX5 in the presence of EBF1. Silencing of KMT2A, the catalytic component of MLL, repressed the ability of exogenous EBF1 to activate transcription of both CD19 and CD79b in KIS-1 cells. We also find association of PAX5 with the MLL complex and decreased CD19 expression following silencing of KMT2A in other human B cell lines. These data support an important role for the MLL complex in PAX5-mediated transcription regulation. [ABSTRACT FROM AUTHOR]

Empirical predictions of discharge rates for dry non-cohesive grains are commonly based on the Beverloo law (Chem Eng Sci 15:260–269, 1961). The present work extends this practical configuration to submerged and cohesive cases to investigate the flow behavior of granular media with applications in the geophysical process of sinkhole formation. The analysis of the hydrostatic collapse of soil in the presence of underground conduits is performed with a 2D GPU-parallelized simulation coupling the lattice Boltzmann method and the discrete element method to describe the fluid and the solid phases, respectively. The discharge rate of a large submerged granular sample is analyzed by varying orifice sizes and inter-particle cohesion strengths. For the submerged cohesionless case, we first study the revisited Beverloo relationship that includes the terminal velocity of a single falling particle in the fluid, proposed in the experimental work of Wilson et al. (Pap Phys 1307: 2812, 2014). We consistently take into account the interstitial fluid with an effective orifice size smaller than in the dry case. Then, the additional contribution of grain cohesion is examined. Our main finding is that the empirical prediction remains valid provided that the orifice cutoff increases with cohesion. Finally, the evolution of fluid pressure during the discharge, at the vicinity of the orifice, is studied and favorably compared with the recent experimental study of Guo et al. (Granul Matter 19(3): 1–8, 2017). By considering the pressure drop around the orifice as a driven-term, we succeed in predicting the solid flow rate with a similar Beverloo approach. [ABSTRACT FROM AUTHOR]

Internal erosion is a complex phenomenon which represents one of the main risks to the safety of earthen hydraulic structures such as embankment dams, dikes or levees. Its occurrence may cause instability and failure of these structures with consequences that can be dramatic. The specific mode of erosion by suffusion is the one characterized by seepage flow-induced erosion, and the subsequent migration of the finest soil particles through the surrounding soil matrix mostly constituted of large grains. Such a phenomenon can lead to a modification of the initial microstructure and, hence, to a change in the physical, hydraulic and mechanical properties of the soil. A direct comparison of the mechanical behaviour of soil before and after erosion is often used to investigate the impact of internal erosion on soil strength (shear strength at peak and critical state) using triaxial tests. However, the obtained results are somehow contradictory, as for instance in Chang's study (Chang and Zhang in Geotech Test J 34(6):579–589, 2011), where it is concluded that the drained strength of eroded soil decreases compared to non-eroded soil, while both Xiao and Shwiyhat (Geotech Test J 35(6):890–900, 2012) and Ke and Takahashi (Geotech Test J 37(2):347–364, 2014) have come to the opposite conclusion. A plausible explanation of these contradictions might be attributed to the rather heterogeneous nature of the suffusion process and to the way the coarse and fine grains are rearranged afterwards leading to a heterogeneous soil structure, a point that, for now, is not taken into account, nor even mentioned, in the existing analyses. In the present study, X-ray computed tomography (X-ray CT) is used to follow the microstructure evolution of a granular soil during a suffusion test, and, therefore, to capture the induced microstructural changes. The images obtained from X-ray CT reveal indeed that fine particles erosion is obviously not homogeneous, highlighting the existence of preferential flow paths that lead to a heterogeneous sample in terms of fine particles, void ratio and inter-granular void ratio distribution. [ABSTRACT FROM AUTHOR]

Throughout this paper, the compressibility of granular soils is investigated by considering different loading modes. In particular, the difference in the response of the soil along an œdometric loading path, according to the nature of the axial loading, is explored. It is shown that the application of a boundary axial loading gives rise to a more pronounced nonlinear response with more important settlements than what is observed with a volume (downward hydraulic flow) loading. A theoretical approach is developed and the predicted results are confronted to experimental results obtained from an original apparatus allowing both volume and boundary loadings be applied. A satisfying agreement is obtained, validating the theoretical model proposed. [ABSTRACT FROM AUTHOR]

We report experimental results on incipient dynamics of gravitational destabilization in an immersed granular medium. Two protocols have been used to reach instability: a progressive loading and a dam-break situation. The instability triggering, analyzed by high-speed imaging and CIV post-processing, reveals distinct dynamical behaviours depending on the initial packing fraction of the medium. Two destabilisation modes have been observed: a surface avalanche and a deeper phenomenon that we called circular collapse. [ABSTRACT FROM AUTHOR]

Oral anticoagulants (OA) are commonly used, but they can lead to severe bleeding. We studied the indications and monitoring of OA in patients treated by general practitioners. Retrospective cross-sectional study. Primary care. Four hundred thirty-eight randomly selected patients of a population of 2,452 patients treated with OA were studied. We compared the indications for OA as reported by general practitioners with indications as defined according to recent guidelines. Twenty-five percent of patients should not have been treated with OA. Inappropriate indications (13% of patients) were atrial fibrillation without risk factor (3.9%), prior uncomplicated myocardial infarction (2.7%), peripheral arterial disease (2.7%), superficial thrombophlebitis (2.3%), and atherothrombotic ischemic stroke (1.6%). For 12% of patients, the duration of OA was too long (venous thromboembolism without permanent risk factor in 10%). Frequency of International Normalized Ratio (INR) measurement was insufficient for 14% of patients and target INR was not achieved in 31%. Our study demonstrated that clinicians’ adherence to recommendations regarding indications for OA and management of this treatment should be improved. Implementation of anticoagulation clinics is probably needed. J GEN INTERN MED 2003; 18:903–907. [ABSTRACT FROM AUTHOR]

The loss of fine particles can induce mechanical instabilities in granular soils subjected to internal fluid flow. An appealing countermeasure consists of the re-injection of fine grains with the objective of achieving retention in the soil matrix. In this study, both gravity- and fluid-driven infiltration of fine particles into coarse-grain columns with different solid fraction ϕ\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} and size ratios R have been studied using coupled pore-scale finite volume (PFV) and discrete element method (DEM) schemes. Three clogging regimes, surface clogging, deep infiltration, and percolation are detected, and the characteristic infiltration depths L0\documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{mathrsfs}\usepackage{upgreek}\setlength{\oddsidemargin}{-69pt}\begin{document}$$L_{0}$$\end{document} are found to grow exponentially with R under gravity- and fluid-driven cases. A probabilistic model derived from pore-constriction size statistics is then put forward, which could efficiently interpret the decaying distribution of fine retention for a given size ratio R and packing density. The mean transit velocity of fine grains follows an increasing trend with R under fixed ϕ\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} and can be collapsed over an almost constant value with the appropriate scaling of ϕ/R\documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{mathrsfs}\usepackage{upgreek}\setlength{\oddsidemargin}{-69pt}\begin{document}$$\phi /\sqrt{R}$$\end{document}. Compared to gravitational percolation, more lateral dispersion is found in fluid-driven conditions, and an estimation of the related lateral dispersion coefficient D is provided based on ϕ\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} and R. [ABSTRACT FROM AUTHOR]

A letter to the editor is presented discussing the treatment of a 62-year-old woman with postintubation tracheal membrane ruptures.