A High-Order Cell-Centered Discontinuous Galerkin Multi-Material Arbitrary Lagrangian-Eulerian Method

In this paper, a high-order cell-centered discontinuous Galerkin (DG) multi-material arbitrary Lagrangian-Eulerian (MMALE) method is developed for compressible fluid dynamics. The MMALE method utilizes moment-of-fluid (MOF) interface reconstruction technology to simulate multi-materials of immiscible fluids. It is an explicit time-marching Lagrangian plus remap type. In the Lagrangian phase, an updated high-order discontinuous Galerkin Lagrangian method is applied for the discretization of hydrodynamic equations, and Tipton's pressure relaxation closure model is used in the mixed cells. A robust moment-of-fluid interface reconstruction algorithm is used to provide the information of the material interfaces for remapping. In the rezoning phase, Knupp's algorithm is used for mesh smoothing. For the remapping phase, a high-order accurate remapping method of the cell-intersection-based type is proposed. It can be divided into four stages: polynomial reconstruction, polygon intersection, integration, and detection of problematic cells and limiting. Polygon intersection is based on the "clipping and projecting" algorithm, and detection of problematic cells depends on a troubled cell marker, and a posteriori multi-dimensional optimal order detection (MOOD) limiting strategy is used for limiting. Numerical tests are given to demonstrate the robustness and accuracy of our method.     

A GPU-Accelerated Hybridizable Discontinuous Galerkin Method for Linear Elasticity

We design and analyze an efficient GPU-accelerated hybridizable discontinuous Galerkin method for linear elasticity. Performance analysis of the method is done using the state-of-the-art Time-Accuracy-Size (TAS) spectrum. TAS is a new performance measure which takes into account the accuracy of the solution. Standard performance measures, like floating point operations or run-time, are not completely appropriate for gauging the performance of approximations of continuum mechanics problems, as they neglect the solutions accuracy. A standard roofline model demonstrates that our method is utilizing computational resources efficiently, and as such, significant speed ups over a serial implementation are obtained. By combining traditional performance measures and the novel time-accuracy measures [7] into our performance model, we are able to draw more complete conclusions about which discretizations are best suited for an application. Several numerical experiments validate and verify our numerical scheme.     

Extrapolation Cascadic Multigrid Method for Cell-Centered FV Discretization of Diffusion Equations with Strongly Discontinuous and Anisotropic Coefficients

Extrapolation cascadic multigrid (EXCMG) method with conjugate gradient smoother is very efficient for solving the elliptic boundary value problems with linear finite element discretization. However, it is not trivial to generalize the vertex-centred EXCMG method to cell-centered finite volume (FV) methods for diffusion equations with strongly discontinuous and anisotropic coefficients, since a non-nested hierarchy of grid nodes are used in the cell-centered discretization. For cell-centered FV schemes, the vertex values (auxiliary unknowns) need to be approximated by cell-centered ones (primary unknowns). One of the novelties is to propose a new gradient transfer (GT) method of interpolating vertex unknowns with cell-centered ones, which is easy to implement and applicable to general diffusion tensors. The main novelty of this paper is to design a multigrid prolongation operator based on the GT method and splitting extrapolation method, and then propose a cell-centered EXCMG method with BiCGStab smoother for solving the large linear system resulting from linear FV discretization of diffusion equations with strongly discontinuous and anisotropic coefficients. Numerical experiments are presented to demonstrate the high efficiency of the proposed method.     

Prognostic value of various morphometric measurements of tumour extent in prostate needle core tissue

Aims:  Predicting prostatic cancer patients' outcome is a major objective for clinicians and patients. Several nomograms are currently implemented prior to treatment to help predict clinical and pathological outcome. The aim of this study was to investigate the prognostic significance of morphometric measurements of cancer on the needle biopsy specimen in relation to the final pathological stage or the biochemical failure status following radical prostatectomy, and to determine which measurement of tumour length in cases with discontinuous foci of cancer (DFC) is most reliably reflective of the pathological stage.
Methods and results:  Of the 100 patients included in this study, 34% had high-stage disease (pT ≥ 3 and/or pN1) and 16% experienced biochemical recurrence. The analysis showed that fraction of positive cores, total percentage of cancer and both total and greatest millimetric cancer lengths were the variables most closely associated with pathological stage and biochemical failure status.
Conclusions:  This study confirms the prognostic value of recording tumour extent in prostatic needle biopsy reporting. However, the results are inconclusive in determining the best method to record tumour length in cores with DFC and larger studies are needed to answer this question fully.     

Cardiac structure and electrical activation: models and measurement

1. Our group has developed finite element models of ventricular anatomy that incorporate detailed structural information. These have been used to study normal electrical activation and re-entrant arrhythmia. 2. A model based on the actual three-dimensional microstructure of a transmural left ventricular (LV) segment predicts that cleavage planes between muscle layers may give rise to non-uniform, anisotropic electrical propagation and also provide a substrate for bulk resetting of the myocardium during defibrillation. 3. The model predictions are consistent with the results of preliminary experiments in which a novel fibre-optic probe is used to record transmembrane potentials at multiple intramural sites in the intact heart. Extracellular potentials are recorded at adjacent LV sites in these studies. 4. We conclude that structural discontinuities in ventricular myocardium may play a role in the initiation of re-entrant arrhythmia and discuss future studies that address this hypothesis.     

非连续分子动力学模拟方法及其在大分子研究中的应用

计算机模拟技术已成为大分子构象等基础研究的一种重要手段。非连续分子动力学模拟(DMD)与传统的分子动力学模拟(MD)方法有所不同,基于不连续势能和相关的模拟编程方法,运行速度大大提高。本文讨论了DMD方法的特点,总结了DMD方法的应用,重点以蛋白质折叠为例介绍了如何使用DMD方法,最后对DMD方法的发展前景进行了展望。     

胰管-空肠黏膜对黏膜间断式吻合在腹腔镜胰十二指肠切除术中的应用

目的 探讨腹腔镜胰十二指肠切除术中应用胰管-空肠黏膜对黏膜间断式吻合预防和减少胰瘘的临床效果。方法 回顾性分析2016年3月至2019年6月西安交通大学附属咸阳市中心医院收治的86例行胰十二指肠切除术患者的临床资料,根据不同胰肠吻合方式分为传统吻合组（传统组,45例）和改良胰管-空肠黏膜对黏膜间断式吻合组（改良组,41例）。观察比较两组手术时间、胰肠吻合时间、术中出血量、术后胰瘘发生率和其他并发症、术后住院时间等围手术期指标的差异。结果 两组患者无围手术期死亡,均成功完成预定Whipple手术,全部采用Child消化道重建。术中情况：传统组与改良组术中出血量分别为（410±220）mL、（365±150）mL（t=0.321,P=0.060）,胆肠吻合时间分别为（22±9）min、（23±11）min（t=0.838,P=0.563）,胃肠吻合时间分别为（23±8）min、（22±9）min（t=0.726,P=0.212）,上述指标两组比较无统计学差异;术中胰肠吻合时间分别为（25±10）min、（41±12）min（t=2.512,P=0.032）;总手术时间分别为（240±20）min、（315±25）min（t=5.362,P=0.048）,两组比较有统计学差异,改良组多于传统组。术后情况：传统组A级胰瘘5例、B级胰瘘8例,改良组A级胰瘘1例、B级胰瘘2例（χ2 =3.216,P=0.019）;术后住院时间分别为（15.2±3.2）d、（10.3±1.1）d（t=-1.526,P=0.016）,两组比较有统计学差异,改良组优于传统组。结论 应用改良胰管-空肠黏膜对黏膜间断式吻合,相较于传统的胰肠套入式吻合可以降低胰十二指肠切除术后胰瘘发生率,缩短住院时间,从而改善临床疗效。     

Toward Eliminating Discontinuous Yielding Behavior of the EA4T Steel

Cold-rolled EA4T steel was heat-treated by inter-critical holding at 755 °C for 90, 120, 180, and 240 s, respectively, and then quenching in water. The tensile testing results of the EA4T specimens show an evident transition from the discontinuous yielding to the continuous yielding of the steel specimens by prolonging the holding time. A novel relationship between the discontinuous yielding behavior of tensile-deformed steel specimens and the carbide size was proposed based on experimental results and Cottrell’s theory. The model may provide a new clue for avoiding discontinuous yielding and improving mechanical properties of metals with static strain aging behaviors.     

Jerky Motion of the Reaction Front during Discontinuous Dissolution in a Fe-13.5 at.% Zn Alloy

This paper studies the go- and -stop movement of a receding reaction front (RF) during a discontinuous dissolution (DD) process. A special simulation procedure was applied for the DD reaction to predict a jerky motion of the RF. The Fe-13.5 at.% Zn alloy was selected in which go- and -stop behaviour was revealed in the form of characteristic lines (called “ghost lines”) showing successive positions of receding RF. The results presented for the DD process are quite different from those relevant for the DP reaction at the same Fe-13.5 at.% Zn alloy in terms of go- and -stop motion and movement distance. For the presented case, the go- and -stop periods are relatively long and obtain an order of several dozen seconds, while for the DP reaction, it was only a few seconds. A similar conclusion was formulated after a comparison of the movement distance which, for the DD reaction, is usually longer by 1–2 orders of magnitude. The simulation results of the DD reaction indicate a good agreement with the experimental data presented in the literature for the same dissolution rate. It is necessary to emphasize that the simulation is the only source of data for z parameter changes during the -stop period of the DD reaction.