MODAL DISCONTINUOUS GALERKIN METHOD FOR SHOCK WAVE STRUCTURES

The discontinuous Galerkin(DG)finite element method has been popular as a numerical technique for solving the conservation laws.In the present study,in order to investigate the shock wave structures in highly thermal nonequilibrium,an explicit modal cell-based DG scheme is developed for solving the conservation laws in conjunction with nonlinear coupled constitutive relations(NCCR).Convergent iterative methods for solving algebraic constitutive relations are also implemented in the DG scheme.It is shown that the new scheme works well for all Mach numbers,for example,Ma=15.

Biomimicking synovial joints trans-scale structured AgQDs/MXene/SiOC achieving macroscale high lubrication and superior wear resistance

Naturally optimized successful synovial joints with lightweight,high load-carrying,ultra-low friction and wear have attracted tribological communities to constantly imitate and replicate.Despite impressive advances in cartilage lubrication,extending such extraordinary performance advantages to macroscale solid lubrication remains a challenge.Herein,inspired by the fascinating interplay of synovial joints,a novel kind of trans-scale hierarchical structured ceramic-based composite was developed.Intro-ducing microscale Ag microspheres(AgMs)“cartilage”layer and nanoscale Ag quantum dots/MXene(AgQDs/MXene)“synovial fluid”into the interior and exterior of printed macroscale SiOC“hard bone”realistically restores the gradient structure of synovial joint prototype.The resulted composite with ideal compressive strength(70.44 MPa)can achieve a 60.53%friction reduction and a low wear rate(2.05×10^(−6)mm 3 N^(−1)m^(−1))in dry tribo-contact for 3600 sliding cycles,while also maintaining considerable low friction(∼0.11)over 10,000 sliding cycles and long-term stable lubrication(∼0.13)for up to 50,000 re-ciprocating cycles.Such extraordinary performance can be explained by the division of macro contacts,full loading of AgMs and AgQDs/MXene,abrasive debris capture and removal,as well as the shear rolling effect induced by friction process.This work opens a new avenue to develop structural lubricating mate-rials for complex engineering applications.

MODE THEORY OF MULTILAYER WAVEGUIDE STRUCTURE WITH DISCONTINUITIES

TEn mode (whose electric field is zero in the normal direction of the boundaries between layers) and TMn mode (whose magnetic field is zero in the normal direction of the boundaries between layers) are defined. Then conditions under which pure TEn (TMn) modes may exist in multilayer waveguide structure with discontinuities are presented. E (H) step wavguides, ridged wavguides, microstrip lines and fin lines all satisfy the conditions, and hold for TEn (TMn) mode. The conventional conclusion that ridged waveguides with inhomogeneous dielectric-slab loading, microstrip lines and fin lines only hold for hybrid modes is revised. Compared with hybrid modes, the number of unknown variations and matching equations is reduced by half for pure TEn (TMn) modes, and the computation cost is decreased dramatically.

A study on 3-D velocity structure of crust and upper mantle in Sichuan -Yunnan region, China

Based on the first arrival P and S data of 4 625 regional earthquakes recorded at 174 stations dispersed in the Yunnan and Sichuan Provinces, the 3-D velocity structure of crust and upper mantle in the region is determined, incorporating with previous deep geophysical data. In the upper crust, a positive anomaly velocity zone exists in the Sichuan basin, whereas a negative anomaly velocity zone exists in the western Sichuan plateau. The boundary between the positive and negative anomaly zones is the Longmenshan fault zone. The images of lower crust and upper mantle in the Longmenshan fault, Xianshuihe fault, Honghe fault and others show the characteristic of tectonic boundary, indicating that the faults likely penetrate the Moho discontinuity. The negative velocity anomalies at the depth of 50 km in the Tengchong volcanic area and the Panxi tectonic zone appear to be associated with the temperature and composition variations in the upper mantle. The overall features of the crustal and the upper mantle structures in the SichuanYunnan region are the lower average velocity in both crust and uppermost mantle, the large crustal thickness variations, and the existence of high conductivity layer in the crust or/and upper mantle, and higher geothermal value. All these features are closely related to the collision between the India and the Asia plates. The crustal velocity in the SichuanYunnan rhombic block generally shows normal value or positive anomaly, while the negative anomaly exists in the area along the large strike-slip faults as the block boundary. It is conducive to the crustal block side-pressing out along the faults. In the major seismic zones, the seismicity is relative to the negative anomaly velocity. Most strong earthquakes occurred in the upper-mid crust with positive anomaly or normal velocity, where the negative anomaly zone generally exists below.

Numerical simulations of compressible mixing layers with a discontinuous Galerkin method

Discontinuous Galerkin（DG） method is known to have several advantages for flow simulations,in particular,in fiexible accuracy management and adaptability to mesh refinement. In the present work,the DG method is developed for numerical simulations of both temporally and spatially developing mixing layers. For the temporally developing mixing layer,both the instantaneous fiow field and time evolution of momentum thickness agree very well with the previous results. Shocklets are observed at higher convective Mach numbers and the vortex paring manner is changed for high compressibility. For the spatially developing mixing layer,large-scale coherent structures and self-similar behavior for mean profiles are investigated. The instantaneous fiow field for a three-dimensional compressible mixing layer is also reported,which shows the development of largescale coherent structures in the streamwise direction. All numerical results suggest that the DG method is effective in performing accurate numerical simulations for compressible shear fiows.

High-order discontinuous Galerkin solver on hybrid anisotropic meshes for laminar and turbulent simulations

Efficient and robust solution strategies are developed for discontinuous Galerkin （DG） discretization of the Navier-Stokes （NS） and Reynolds-averaged NS （RANS） equations on structured/unstructured hybrid meshes. A novel line-implicit scheme is devised and implemented to reduce the memory gain and improve the computational eificiency for highly anisotropic meshes. A simple and effective technique to use the mod- ified Baldwin-Lomax （BL） model on the unstructured meshes for the DC methods is proposed. The compact Hermite weighted essentially non-oscillatory （HWENO） limiters are also investigated for the hybrid meshes to treat solution discontinuities. A variety of compressible viscous flows are performed to examine the capability of the present high- order DG solver. Numerical results indicate that the designed line-implicit algorithms exhibit weak dependence on the cell aspect-ratio as well as the discretization order. The accuracy and robustness of the proposed approaches are demonstrated by capturing com- plex flow structures and giving reliable predictions of benchmark turbulent problems.

Peculiarity of magnetoresistance of discontinuous ferromagnetic thin films

The magnetoresistive properties of discontinuous ferromagnetic Fe and Co thin films deposited by electron-beam sputtering onto glass substrates at room temperature were investigated. Tunnel magnetoresistance(MR) was observed for all of the as-deposited samples. The maximum MR was observed for Fe thin films with an effective thickness of 17 nm. In the case of the Co thin films, the annealing process led to a change of the type of MR to anisotropic at Co film thicknesses(dCo) of 15 ≤ d_(Co) ≤ 25 nm and to positive isotropic at thicknesses of d_(Co) < 15 nm. By contrast, the MR type of Fe thin films did not change.

Structure and physical properties of the Earth's interior

The studies on the structure and physical properties of the Earths interior done by Chinese geophysicists from 1999 to 2002 were reviewed in this paper. It includes several research areas: the structure of the Earths interiors using seismic tomography, anisotropy of the upper mantle in China and its adjacent areas, quality factor Qb for S waves, subduction zone, mantle discontinuities, physical properties of Earths materials and others. The review concerns mainly the contents, the methods and the results of the studies. It can be seen that new progress in the study on the structure and physical properties of the Earths interior has been made in the last 4 years in China. It is shown on three aspects: advancement made on some preexistent areas; pioneering on some new fields and new methods adopted.

Microstructure and properties of Cu-15Ni-8Sn-0.4Si alloy

By metallographic test, SEM, TEM and energy spectrum, the microstructure and properties of Cu 15Ni 8Sn 0.4Si alloy were studied. The results show that the added Si combines with Ni and forms Ni 3Si and Ni 2Si phases. During ageing at 380 ℃, the precipitation of Ni 2Si phase suppresses discontinuous precipitation to some degree. After adding Si, the conductivity and hardness of Cu 15Ni 8Sn alloy are increased to some degree.

Structural plane recognition from three-dimensional laser scanning points using an improved region-growing algorithm based on the robust randomized Hough transform

The staggered distribution of joints and fissures in space constitutes the weak part of any rock mass.The identification of rock mass structural planes and the extraction of characteristic parameters are the basis of rock-mass integrity evaluation,which is very important for analysis of slope stability.The laser scanning technique can be used to acquire the coordinate information pertaining to each point of the structural plane,but large amount of point cloud data,uneven density distribution,and noise point interference make the identification efficiency and accuracy of different types of structural planes limited by point cloud data analysis technology.A new point cloud identification and segmentation algorithm for rock mass structural surfaces is proposed.Based on the distribution states of the original point cloud in different neighborhoods in space,the point clouds are characterized by multi-dimensional eigenvalues and calculated by the robust randomized Hough transform(RRHT).The normal vector difference and the final eigenvalue are proposed for characteristic distinction,and the identification of rock mass structural surfaces is completed through regional growth,which strengthens the difference expression of point clouds.In addition,nearest Voxel downsampling is also introduced in the RRHT calculation,which further reduces the number of sources of neighborhood noises,thereby improving the accuracy and stability of the calculation.The advantages of the method have been verified by laboratory models.The results showed that the proposed method can better achieve the segmentation and statistics of structural planes with interfaces and sharp boundaries.The method works well in the identification of joints,fissures,and other structural planes on Mangshezhai slope in the Three Gorges Reservoir area,China.It can provide a stable and effective technique for the identification and segmentation of rock mass structural planes,which is beneficial in engineering practice.

Global Solution of a Nonlinear Conservation Law with Weak Discontinuous Flux in the Half Space

This paper is concerned with the initial-boundary value problem of a nonlinear conservation law in the half space R+= {x |x > 0} where a>0 , u(x,t) is an unknown function of x ∈ R+ and t>0 , u ± , um are three given constants satisfying um=u+≠u- or um=u-≠u+ , and the flux function f is a given continuous function with a weak discontinuous point ud. The main purpose of our present manuscript is devoted to studying the structure of the global weak entropy solution for the above initial-boundary value problem under the condition of f '-(ud) > f '+(ud). By the characteristic method and the truncation method, we construct the global weak entropy solution of this initial-boundary value problem, and investigate the interaction of elementary waves with the boundary and the boundary behavior of the weak entropy solution.

DIAMOND CONTENT OF PRIMORSKIJ KRAJ ACCORDING TO DATA OF ANALYSIS OF FOCUS STRUCTURES─CENTERS OF ENDOGENIC ACTIVITY

The autbors consider focus structures or structures of central type to be a variety of geodepression (diwa) structures.They are related to the matter-energy evolution of geosphers and control the distribution of useful minerals,including diamond.The authors also have separated out 39 spherical guophysical discontinuities from the bottom of the crust (40km) to the inner core. In the paper diamond deposits have been discussed for Russia,China and Korean Peninsula, and evalution of diamond content has been made for the south of the Far East.

Construction of Global Weak Entropy Solution of Initial-Boundary Value Problem for Scalar Conservation Laws with Weak Discontinuous Flux

This paper is concerned with the initial-boundary value problem of scalar conservation laws with weak discontinuous flux, whose initial data are a function with two pieces of constant and whose boundary data are a constant function. Under the condition that the flux function has a finite number of weak discontinuous points, by using the structure of weak entropy solution of the corresponding initial value problem and the boundary entropy condition developed by Bardos-Leroux-Nedelec, we give a construction method to the global weak entropy solution for this initial-boundary value problem, and by investigating the interaction of elementary waves and the boundary, we clarify the geometric structure and the behavior of boundary for the weak entropy solution.

Geophysical Significance of the Senegalo-Mali Discontinuity: Evidence from Secondary Structures, Kédougou-Kéniéba Inlier, Western Mali

The present study focuses on the analysis and description of lineaments interpreted as secondary structures to describe the nature of Senegalo Malian Discontinuity. These lineaments cross-cut the large north-south oriented transcurrent lithospheric structure known as the Senegalo Malian Discontinuity (SMD). Two lineaments were selected oriented NNE (N15˚ to N25˚), one at Dialafara and one at Sadiola. Four profiles on each lineament of these 2 zones, so that there were 2 on each side of the SMD. The ground data collected were processed using proper parameter and software. Some filters were applied to enhance the signal level. These ground data were later compared to the existing airborne magnetic data for consistency and accuracy using the upward continuation filter. The results show that the quality of ground data is good. In addition, the ground magnetic data show the presence of certain local anomalies that are not visible in the regional data. The analytical signal was also used to determine domain boundaries or possible contact zones. The contact zone can be highlighted on certain profiles such as L300 and L600. The study showed that the west and east sides of the SMD are not the same. Secondary structures become wide when approaching the SMD on both sides. They are also duplicated to the east of the SMD when we move progressively away. In the Dialafara area, the ground magnetic data intersect an interpreted fold. The results of this work confirm the presence of the secondary structures and their evolution in relation to the SMD. The relationships between the secondary structures in the Dailafara and Sadiola zones and their relations with the SMD are highlighted. The technique used in this study, is an important approach to better description and interpreting of regional structures using the secondary structures and proposing a structural model.

天津中医药大学体育馆不连续支承弦支穹顶结构抗火分析

以天津中医药大学体育馆为背景,对大跨度不连续支承弦支穹顶结构进行抗火性能分析。利用高大空间火灾升温公式对结构进行火灾温度场模拟。采用ANSYS软件对不连续支承弦支穹顶结构进行火灾响应分析,得到火灾下该结构变形规律、节点位移及构件预应力损失规律;改变火源位置和火源释热功率,探究火源参数变化对结构抗火性能的影响。结果表明:中心火源工况下,不连续支承弦支穹顶结构变形呈“部分微上凸,局部桁架处下陷明显”;该结构对偏心火灾敏感,偏心火灾下结构最大正、负向位移及环索预应力损失较中心火灾显著增大,且第1、2圈部分环索预应力降为0;局部桁架处压杆及第1、2圈环索为抗火设计重点。火源释热功率越大对不连续支承弦支穹顶结构抗火越不利,但火源释热功率改变对结构火灾响应的影响较小。

强扰煤岩体蠕变过程中跨尺度非连续结构演化研究进展

【目的和方法】巷道围岩时效变形破坏、蠕变型冲击地压等灾害是深井面临的重大威胁,加之深部采动与结构变化的影响,亟需研究强扰煤岩体蠕变过程中跨尺度非连续结构演化规律,系统回顾煤岩体力学性质的尺度效应、非连续结构与多物理场效应,以及煤岩体长时稳定性、蠕变演化规律与力学模型。【结果和结论】强调不同尺度(细观-宏观-工程尺度)、不同尺寸(REV范围内)煤岩变形破裂过程中非连续结构(包括裂隙和矿物)与物理力学性质存在密切的关联特征。指出煤岩体跨尺度非连续结构导致应力场非均匀分布,造成力学各向异性、尺度效应及尺寸效应,进而出现非协调宏观破裂现象。透明解析与推演煤岩变形破裂过程中跨尺度非连续结构与多物理场演化规律,是认识煤岩灾变内禀机制的关键。明确指出现有蠕变实验与蠕变模型在煤岩表面变形及破裂方面具有优势,但无法预测煤岩内部变形与非连续结构;为此提出了全尺寸CT扫描重构、数字体图像相关(DVC)、跨尺度等效岩体-等效晶质建模(SRM-GBM)相结合的破解方法。对扰动煤岩体蠕变前沿问题进行了讨论,阐明了非连续结构与应力引起内部变形损伤诱发蠕变这一新观点,指出非连续结构和应力是煤岩非协调蠕变的主控因素,最后建立了强扰煤岩体蠕变过程中跨尺度非连续结构与多物理场演化的精细化建模及透明解析新方法。研究成果为相关矿山灾害的发生机理、预警与防控提供理论基础。

社交媒体过载、疲惫对用户不持续使用意愿的作用机制——基于元分析结构方程模型的分析

文章在整合相关实证文献的基础上,构建了过载视角下社交媒体用户不持续使用意愿整合模型,并基于元分析结构方程模型方法,揭示了社交媒体过载对用户不持续使用意愿的影响效应。元分析方法结果显示:疲惫对社交媒体用户不持续使用意愿平均效应最大;过载因素中,交流过载对不持续使用意愿相关系数均值最大,其次为信息过载、技术过载。结构方程模型方法分析结果显示:疲惫、交流过载对不持续使用意愿具有显著的正向直接影响;技术过载对信息过载、交流过载、疲惫均有正向显著影响;信息过载通过疲惫的中介作用间接影响不持续使用意愿;文化背景、社交媒体类型对信息过载、疲惫与不持续使用意愿的影响具有调节作用。

基于非均质雷达图谱的沥青路面结构损伤识别技术

基于雷达图谱与深度神经网络的沥青路面结构损伤自动辨识方法存在数据量少且种类不均衡的问题,识别准确性与稳定性仍有待提高。提出基于非均质雷达图谱的路面结构损伤识别技术。采用探地雷达采集沥青路面结构裂缝与层间不连续病害,获取实测剖面图;基于时域有限差分法,模拟裂缝与层间不连续在匀质模型中的回波特征,与实测图谱组成数据集1#;基于芯样CT扫描图构建“沥青-集料”二相介质模型,模拟裂缝与层间不连续在二相介质模型中的回波特征,与实测图谱组成数据集2#;采用数据集1#和2#,分别训练YOLO v5深度神经网络。研究结果表明:数据集1#和2#在YOLO v5模型测试集上的m AP@0.5为93.79%与96.33%,证明非均质图谱特征可丰富网络训练样本,并提高深度学习模型识别的准确性。

考虑间断级配影响的土石混合体水力侵蚀分异机理

近年来,堆积体滑坡频发,已成为西南地区最典型的滑坡类型。研究表明,超过50%的库区堆积体滑坡诱因为水力侵蚀,因此降雨、岸坡侵蚀、波浪掏蚀成为库区滑坡灾害防治重点关注的问题。同时,土石混合体自身的间断级配会对其水力特性造成明显影响,进而导致水力侵蚀作用下堆积体内部的颗粒运移规律具有独特性。采用自主研发的土石混合体渗透侵蚀试验装置,模拟土石混合体内部细观侵蚀过程,阐明其侵蚀分异机理,揭示间断级配的影响。结果表明:土石混合体侵蚀过程主要分为快速侵蚀、侵蚀减缓、稳定渗流3个阶段,超过60%的侵蚀在快速侵蚀阶段完成;与良好级配试样相比,间断级配试样的侵蚀量更大,初始侵蚀更剧烈,快速侵蚀阶段更短暂;间断级配对土石混合体水力侵蚀分异的影响同样明显,细颗粒缺失结构的细颗粒尺寸单一,不易堵塞渗流通道,渗透系数高于良好级配试样,且最大渗透系数与最终渗透系数差异较小;中颗粒缺失结构因大量细颗粒下沉堵塞渗流通道导致渗透系数明显低于良好级配试样;粗颗粒缺失结构内部块石承载骨架结构差,孔隙大,易引发大块石局部破坏,渗透系数高于良好级配试样。

在役边坡耐久性弱化及整体稳定性影响分析

针对在役边坡长期耐久性能弱化及对整体稳定性影响问题,首先依据混凝土结构耐久性原理,建立边坡支护结构耐久性弱化分析模型,结合室内耐久性加速试验进行验证分析,接着基于混合型非连续变形分析法(HDDA)扩展了锚杆单元连接不同位移模式块体的算法,利用该扩展型混合DDA法结合有限元法以分析耐久性弱化边坡稳定性问题,建立了总体计算基本框架。最后以浙江省某沿海公路边坡为案例进行分析,结果表明:在特定环境条件下边坡多型支护结构物在30~60 a内有锈胀开裂及断裂失效的可能性;假定锚杆不失效时边坡安全系数随年限增加存在一定降幅,而在考虑锚杆陆续失效时边坡安全系数降幅明显,需要提前采取加固措施。此外还表明混合型DDA法建模灵活、模拟结果合理,具有较好的应用价值。