Search

Quantitative understanding of the load–deflection mechanisms of a flexible barrier in intercepting debris flows is critical for barrier design, but remains practically challenging due to the difficulties involved in capturing multi-phase, multi-way interactions. This study employs a physics-based coupled computational fluid dynamics and discrete-element method (CFD–DEM) to simulate a flexible ring-net barrier as a permeable, deformable multi-component system by DEM and model a debris flow as a mixture of discrete particles and a continuous slurry by DEM and CFD, respectively. The CFD–DEM coupling framework offers a unified treatment of in-flow solid–fluid interaction, flow–barrier interaction and interactions among barrier components. Numerical predictions of key flow–barrier interactions and cable forces show reasonable consistency with large-scale experiments. Systematic simulations with varying flow–barrier height ratios ε and flow dynamics are performed to examine the evolving mechanisms of load sharing and transmission and quantify the ε-dependent load–deflection modes. The ratio ε is found to bear a strong, positive correlation with the key barrier response in three typical modes. The post-peak barrier deformations experience shrinkages with ε ≤ 0·6 and expansions when ε > 0·6. This study helps to improve understanding of the load–deflection mechanisms for practical design of flexible barriers in mitigating debris flows.

Grain crushing underpins key mechanical behaviours of granular materials. A variety of factors, including grading, particle shapes and loading conditions, have been recognised to affect the crushability of grains and the overall behaviour of a granular material. Among them, the role of intermediate principal stress in a general stress condition on the shear behaviour of crushable granular sand remains less understood, owing to the scarcity of experimental data and analytical tools available. In this paper, a multi-scale computational approach is employed to investigate the shear behaviour of crushable granular sand under general stress conditions with varying intermediate principal stresses and confining pressures. The computational approach features multi-scale coupling between non-smooth contact dynamics and peridynamics, and offers a rigorous way to consider the intertwined evolution of particle size and shape during the process of grain crushing. The numerical study helps to quantify comprehensively and analyse the grain crushing-induced changes of macro- and micro-scale material behaviours including strength, deformability, particle size and shape evolution, particle-scale forces and contact conditions, and the development of anisotropy. The competition between a void-filling mechanism due to grain size change and enhanced friction and interlocking due to grain shape change in dictating the deformation of crushable sand is further discussed. The findings offer insights into the complex behaviours of crushable granular materials under general stress conditions and facilitate future development of physics-based constitutive theories on crushable sand.

Objective. To comprehensively explore the survival characteristics of primary esophageal small-cell carcinoma (PSCCE) and identify the main factors affecting the prognosis. Methods. The clinical and follow-up data of PSCCE patients admitted to the Fourth Hospital of Hebei Medical University from 2006 to 2010 were retrospectively analyzed. The primary endpoint was five-year survival. Survival curves were drawn using the Kaplan-Meier method, and log-rank test was used to compare the differences in survival rates among the groups. Cox regression models were used to analyze prognostic factors. Results. A total of 119 eligible patients were retrieved. Median survival was 27 months (3-100 months). Changes in overall survival (OS) in PSCCE patients were associated with TNM stage ( P = 0.007 ), T stage ( P = 0.049 ), and lymph node metastasis ( P = 0.004 ). When TNM was in stage I-IIb, lymph node metastasis ( P = 0.003 ) or combined adjuvant therapy ( P = 0.004 ) was an independent factor affecting OS. Survival analysis showed that TNM staging had no predictive value for 5-year survival time or disease-free survival (DFS) of PSCCE ( P > 0.05 ). Conclusion. TNM stage, T stage, and lymph node metastasis were related to the survival of patients. Negative lymph node metastasis and treatment are independent prognostic factors in PSCCE TNM stage I-IIb patients.

Background. Folic acid receptor 4 (FR4) significantly downregulates the expression of regular T cells (Treg) and improves the effect of chemotherapy and PD-1/PD-L1 inhibitors. However, the FR4 expression in squamous cell carcinoma (ESCC) remains unclear. Methods. Patients with primary ESCC who visited our hospital between 1st February 2012 and 30th September 2016 were enrolled in this study. FR4 expressions in ESCC patients were detected by immunohistochemistry staining, and the association with clinical characteristics and the overall survival (OS) or disease-free survival (DFS) was analyzed. Results. One hundred and forty-eight qualified cases of ESCC patients were retrieved, including 34 females. Ninety-four cases had lymph node metastasis (63.51%), 104 patients received adjuvant therapy (70.27%), and the rate of FR4 positive was 67.57% (100/148). Among FR4 positive patients, 75 cases received adjuvant therapy, and patients who received chemotherapy were significantly better than that of patients who did not receive chemotherapy. In patients with FR4 negative expression, 48 cases received adjuvant therapy, which was significantly worse than that of patients who did not receive chemotherapy. Conclusions. Postoperative adjuvant chemotherapy prolonged the survival in FR4 positive ESCC patients, whereas adjuvant therapy in patients with FR4 negative needs to be further improved.

A new molecular rearrangement, the aza-Quasi-Favorskii rearrangement, has been developed for the construction of highly-substituted aziridines. Electron deficient O-sulfonyl oximes react readily with α,α-disubstituted acetophenone-derived enolates to furnish highly substituted aziridines via this unprecedented domino process. In-depth computational studies reveal an asynchronous yet concerted nitrenoid-type rearrangement pathway.

Background: We conducted a trial to evaluate the efficacy and safety of apatinib, a tyrosine inhibitor against vascular endothelial growth factor receptor 2, combined with neoadjuvant chemotherapy ...

Both the solid and fluid phases in a debris flow vitally influence the impact dynamics against a rigid barrier. However, previous numerical and analytical models commonly adopt an equivalent fluid approach, which does not explicitly consider solid–fluid interaction when impacting a barrier. This study investigates the role of solid–fluid interaction on the impact mechanism and load exerted on a rigid barrier. A coupled computational fluid dynamics and discrete-element method (CFD–DEM) is used to study the effect of solid–fluid interaction on impact by varying the solid fraction from 0 to 0·5. The mesoscopic insight from CFD–DEM modelling reveals that the particle–fluid interaction plays two roles in increasing the kinematic energy of particles: (a) imposing driving force to the particles; (b) reducing inter-particle contact forces and therefore energy dissipation from shearing among grains by applying buoyancy to the particles. Consequently, the run-up height and impact pressure of the water–particle mixture flows at the barrier are higher than those of dry granular flows with the same Froude number (Fr). While impacting the rigid barrier, most of the energy of water–particle mixtures (exhibiting a run-up mechanism) is dissipated as the fluid phase segregates from the mixture and rolls back towards subsequent flow. This differs from the conventional impact mechanism observed for dry granular flows, where the energy is mainly dissipated by way of shearing between layers of sand piling up behind a barrier.

This work revisits the Gilbert–Johnson–Keerthi (GJK) and the radial direction-based shape erosion method for the contact resolution of non-spherical particles in discrete element method (DEM). Tests on single contact indicate that the shape erosion would frequently lead to an overestimation on contact overlap, but has a minor effect on contact normal and contact point. The undesired effect of shape erosion on contact overlap is more pronounced for small overlaps and elongated particles. Further study based on random packing and triaxial compression tests suggests that the shape erosion has a dominant effect on the weak contacts within the packing. The overestimation of contact overlaps due to shape erosion may tend to push particles away, thereby dismiss the weak contacts and result in an overall smaller coordination number. Nonetheless, as the contribution of weak contacts to particle shear resistance is relatively small, the shape erosion exhibits negligible effects on the packing fabric and the stress–strain behaviors. In practice, it is suggested that the erosion ratio should be carefully set such that it is compatible (e.g., in a similar order of magnitude) to the overlaps of strong contacts.

The shear strength of granular materials has been found to increase nonlinearly with particle asphericity before reaching a steady value independent of particle asphericity. Although the origin of shear strength has been extensively studied, the underlying mechanism of its nonlinear dependency on particle shape remains unclear. In this study, we present a microscopic investigation of shape-dependent shear strength from the perspective of particle dynamics. A series of numerical simple shear tests on assemblies of ellipsoids with different aspect ratios are performed using the discrete element method. It is confirmed that the power-law scaling in nonlocal granular rheology is still valid for granular materials composed of non-spherical particles, such that the macroscopic shear strength and microscopic dynamics can be bridged using granular temperature. Analogous to other amorphous solids, granular materials with higher granular temperature are much softer and exhibiting less resistance to shear. The statistics of the clusters of the particles with higher granular temperature indicate that granular systems with different particle shapes showing different collective motion patterns. We further explore the coupling between rotational and translational particle dynamics and their long-range correlations. The macroscopic shear strength shows a clear monotonic relation with the intrinsic length scale reflecting long-range dynamic correlations. Finally, we propose a picture illustrating the negative feedback mechanism between particle rolling and sliding, which leads to the nonlinear increase and steady value of shear strength with particle asphericity. Our finding may shed light not only on the particle shape effects, but also on the fundamental understanding of the microscopic origin of shear strength of granular materials.

The multi-scale characteristics of particle morphology, including the overall form, local roundness and surface roughness, affect the critical state behavior of sands and should be considered in modern critical state-based continuum constitutive modeling. Despite extensive experimental and numerical studies, no consensus has been reached as to how particle morphology may quantitatively dictate the critical state response of sands. This study presents a numerical investigation based on discrete element method (DEM) in an attempt to address this outstanding issue. Five DEM samples of uniformly graded sands consisting of realistic shape clumps and ideal spheres of different mass proportions are prepared and subjected to conventional drained and undrained triaxial compression under different initial void ratios and stress states. A 3D overall regularity (OR) index is adopted to quantify both the overall form and local roundness characteristics of these assemblies. It is shown that this shape parameter OR may effectively help to elucidate the correlation between mechanical properties, especially the critical state behavior of sand and particle shape, and has a great potential for incorporation into the framework of anisotropic critical state theory for constitutive modeling of sand behavior. The study helps to advance our cross-scale understanding of microscopic grain-scale morphology information in relation to macroscopic soil behavior.

A new analytical model is proposed to estimate the peak impact pressure of debris flow exerted on a rigid barrier. The new model consists of two terms, p = α1ρ0gh0 + 0·5ρ0u02, accounting for static and dynamic impacting effects, respectively. The static coefficient α1 is determined according to equations governing the mass and momentum conservation and energy conservation, and the dynamic coefficient 0·5 is adopted on the basis of the Bernoulli equation. The new analytical model is validated for a wide range of Froude number (Fr) with data collected from past studies on small-scale experiments and field observations and numerical simulations of debris flow as a particle–fluid mixture performed by coupled computational fluid dynamics–discrete-element method (CFD–DEM, for wide-range coverage of Fr). Based on equivalence with the new model, the empirical coefficients involved in conventional pure hydrostatic (k) and pure hydrodynamic (α) impact models are found positively and negatively correlated to Fr, respectively. A unique relationship between k and α is further derived: (cos θ/k) + (1/α) = 1, where θ denotes slope angle. The underlying physics of this relationship is interpreted. According to the proposed model, a design chart in terms of Fr is further recommended for practical design of debris-resisting barriers. The new analytical model offers a possible improvement on robust and reliable estimation of debris flow impact on a rigid barrier.

When a gravity-driven solid-fluid mixture, such as those in geophysical flows, hits a wall-like rigid obstacle, a metastable jammed zone called hydrodynamic dead zone (HDZ) may emerge. The unjammed-jammed transition of HDZ, controlled by the intricate interactions among the obstacle, the fluid and the solid of the flow, remains an open issue to be quantified for thorough understanding its underlying physics and mechanics. This study employs a coupled Computational Fluid Dynamics and Discrete Element Method (CFD-DEM) to examine the characteristics of HDZ formed when a geophysical flow comprised of gap-graded particles and a viscous liquid impacts an obstacle. To identify key features in the zonation of HDZ, a modified granular temperature is proposed considering the influences of inherent polydispersity and both translational and rotational motions of the particles in the impacting mixture. A source-sink model is further established to offer an interpretation of the nonlinear energy dissipation process during the unjammed-jammed transition of HDZ, where the modified granular temperature serves as a function of either time or distance. The structural anisotropy is found to serve as a good indicator for illuminating the flow-structure interaction transitions. Three regimes, namely, impact-up, roll-up and heap-up regimes, have been identified according to the statistical energy conversion and dissipation in the flowing layer upon the HDZ. The influence of particle rotation is found to be more significant in the dynamical exchange of HDZ when the impacting flow contains a wider polydispersity. (c) 2021 Elsevier B.V. All rights reserved.

This paper presents a novel computational-geometry-based approach to generating random packing of complex-shaped 3D particles with quantitatively controlled sizes and shapes for discrete modeling of granular materials. The proposed method consists of the following five essential steps: (1) partitioning of the packing domain into a prescribed number of random polyhedrons with desired sizes and form-scale shapes using the constrained Voronoi tessellation; (2) extraction of key points from the edges and facets of each polyhedron; (3) construction of a freeform curve network in each polyhedron based on Bezier curve fitting; (4) generation of solid particles with smooth, convex surfaces using the biharmonic-based surface interpolation of the constructed network; and (5) creation of concavity by superimposing spherical harmonic-based random noise. To ensure that the obtained shape descriptors (e.g., the elongation, flatness, roundness and convexity ratio) match the hypothesized values, an inverse Monte Carlo algorithm is employed to iteratively fine-tune the control parameters during particle generation. The ability of the proposed approach to generate granular particles with the desired geometric properties and packing is demonstrated through several examples. This study paves a viable pathway for realistic modeling of granular media pertaining to various engineering and industrial processes.

Footing foundations are sometimes built on sloping grounds of natural sand which is highly anisotropic. The anisotropic mechanical behaviour of sand can significantly influence the bearing capacity of a foundation and the failure mechanism of its supporting slope. Neglecting sand anisotropy may lead to overestimated bearing capacity and under‐design of foundations. A numerical investigation on the response of a supporting slope under a strip footing is presented, placing a special focus on the effect of sand anisotropy. A critical state sand model accounting for fabric evolution is used. The nonlocal method has been used to regularize the mesh‐dependency of the numerical solutions. Predictions of the anisotropic model on the bearing capacity of strip footings on slopes are validated by centrifuge test data on Toyoura sand. Compared to the centrifuge test data, an isotropic model may overpredict the bearing capacity of the footing by up to 100% when the model parameters are determined based on test data on a horizontal bedding plane case. When the isotropic model parameters are determined based on test data where the bedding plane is vertical, the predictions of bearing capacity can be improved for some cases but the settlement at failure may be significantly overestimated. The soil body tends to move along the bedding plane upon the footing loading due to the non‐coaxial strain increment caused by fabric anisotropy. The slip surface appears to be deeper with lower bearing capacity when the preferred soil movement direction caused by bedding plane is towards the slope.

Interleukin-22 (IL-22), secreted by tumor infiltrated lymphocytes, is identified as a tumor-promoting factor in certain cancers, which was secreted by tumor infiltrated lymphocytes. However, the role of IL-22 in breast cancer remains conflicting. In this study, we assessed the expression of IL-22, IL-22 receptor 1 (IL-22R1), CD4, CD8, FOXP3, and CD68 in breast cancer by immunohistochemistry. IL-22 expression was exhibited in 105 (69.1%) cases in tumor cells (tIL-22), whereas only 24 (15.8%) samples displayed IL-22 expression in stromal cells. Multivariate analysis showed that tIL-22 expression was a poor prognostic factor for overall survival (OS) (

The at-rest coefficient of lateral pressure, $$K_0$$ , is a critical macroscopic parameter for evaluating stress transmission in granular media for engineering practice. This paper revisits the microscopic origin of $$K_0$$ and its corresponding underlying physics based on micromechanics-based theories and numerical simulations, with a focus placed on the effect of particle shape. Two typical kinds of distortion (elongation and blockiness) in particle shape are considered, modeled by ellipsoids and superballs in the discrete element method. One-dimensional compression tests are performed on numerical specimens with dense and loose initial states for different particle shapes. An analytical relationship between $$K_0$$ and anisotropy of fabric measures (i.e., contact normal, contact force, and shape-related anisotropy) is established within the stress-force-fabric framework. It is found that the analytical $$K_0$$ is consistent with the measured one directly from the simulation regardless of particle shape, verifying a well-established relationship between $$K_0$$ and fabric. It is further found that contact force partition of $$K_0$$ plays the most prominent role in $$K_0$$ compared to contact normal and shape-related partitions. Results also reveal the different influence of shape distortion on $$K_0$$ and the corresponding mechanical properties related to $$K_0$$ , such as void ratio, mobilized friction angle, and coordination number. More specifically, $$K_0$$ has a ‘W’-shape relationship with elongation for dense ellipsoids and an ‘M’-shape relationship with blockiness for superballs.