Positive definiteness of fourth-order partially symmetric tensors

In this paper,we consider the positive definiteness of fourth-order partially symmetric tensors.First,two analytically sufficient and necessary conditions of positive definiteness are provided for fourth-order two dimensional partially symmetric tensors.Then,we obtain several sufficient conditions for rank-one positive definiteness of fourth-order three dimensional partially symmetric tensors.

Local pointwise convergence of the 3D finite element

For an elliptic problem with variable coefficients in three dimensions,this article discusses local pointwise convergence of the three-dimensional(3D)finite element.First,the Green's function and the derivative Green's function are introduced.Secondly,some relationship of norms such as L^(2)-norms,W^(1,∞)-norms,and negative-norms in locally smooth subsets of the domainΩis derived.Finally,local pointwise convergence properties of the finite element approximation are obtained.

基于NITE平台的卓越工程师培养模式探索

NITE定位于国家重点领域信息技术紧缺人才培养,担负为国家培育人才,为产业储备人才,为企业提供人才的职责。从行业工程师认证、建立联合培养学院、多渠道师资来源等方面探索了基于NITE平台的卓越工程师培养模式。

NiTe/TiO2复合材料的制备与多模式光催化降解染料

以硝酸镍、碲粉和异丙氧基钛(TTIP)为原料,采用程序升温水热法结合高温煅烧,通过控制Ni∶Ti摩尔比制备一系列NiTe/TiO2复合材料.结果表明,所制备的NiTe/TiO2复合材料为六方相NiTe和锐钛矿相TiO2的混合晶相,且在可见光区具有较强的光吸收能力.通过紫外光、可见光和模拟日光等多模式光催化降解孔雀石绿(MG)考察NiTe/TiO2复合材料的光催化性能.结果表明,当摩尔比为1∶7时,复合材料的光催化活性最佳.该复合材料对不同结构的有机污染物降解具有一定的广泛性.

NITE工艺制备SiC_f/SiC复合材料的研究进展

NITE(nano-infiltration and transient eutectic)工艺作为一种制备碳化硅纤维增强碳化硅基(SiCf/SiC)复合材料的新方法,具备周期短、工艺简单、生产成本低等优点,制备出的复合材料基体致密、孔隙率低、不含残余硅,适用于1400℃及以上高温长时服役环境应用。目前,日本、美国等国家基于其成熟的第三代碳化硅纤维,对该技术开展了较为深入的研究,并在核能工业热交换器、航空发动机燃烧室衬套等领域进行了应用验证。本文针对NITE工艺从基本概念、工艺流程、制备的SiCf/SiC复合材料和构件考核验证及前景展望四方面进行综合阐述,以期为国内该工艺的发展及应用提供一定程度的参考。

The closed finite-to-one mappings and their applications

In this paper, we discuss the closed finite-to-one mapping theorems on generalized metric spaces and their applications. It is proved that point-Gδ properties,?0-snf-countability and csf-countability are invariants and inverse invariants under closed finite-to-one mappings. By the relationships between the weak first-countabilities, we obtain the closed finite-to-one mapping theorems of weak quasi-first-countability, quasi-first-countability, snf-countability, gfcountability and sof-countability. Furthermore, these results are applied to the study of symmetric products of topological spaces.

Quantile inference for nonstationary processes with in nite variance innovations

Based on the quantile regression,we extend Koenker and Xiao(2004)and Ling and McAleer(2004)'s works from nite-variance innovations to in nite-variance innovations.A robust t-ratio statistic to test for unit-root and a re-sampling method to approximate the critical values of the t-ratio statistic are proposed in this paper.It is shown that the limit distribution of the statistic is a functional of stable processes and a Brownian bridge.The nite sample studies show that the proposed t-ratio test always performs signi cantly better than the conventional unit-root tests based on least squares procedure,such as the Augmented Dick Fuller(ADF)and Philliphs-Perron(PP)test,in the sense of power and size when in nitevariance disturbances exist.Also,quantile Kolmogorov-Smirnov(QKS)statistic and quantile Cramer-von Mises(QCM)statistic are considered,but the nite sample studies show that they perform poor in power and size,respectively.An application to the Consumer Price Index for nine countries is also presented.

The realization of positive definite matrices via planar networks and mixing-type sub-cluster algebras

As an improvement of the combinatorial realization of totally positive matrices via the essential positive weightings of certain planar network by S.Fomin and A.Zelevinsky[7],in this paper,we give a test method of positive definite matrices via the planar networks and the so-called mixing-type sub-cluster algebras respectively,introduced here originally.This work firstly gives a combinatorial realization of all matrices through planar network,and then sets up a test method for positive definite matrices by LDU-decompositions and the horizontal weightings of all lines in their planar networks.On the other hand,mainly the relationship is built between positive definite matrices and mixing-type sub-cluster algebras.

NiTe电极材料的制备及其在超级电容器中的应用

采用二氧化碲(TeO_2)为碲源,泡沫镍作为镍源及基底,水合肼(N_2H_4·H_2O)为还原剂,利用一步水热法原位生长片状Ni Te材料。将制得的Ni Te作为超级电容器的电极材料,研究了水热温度对产物的微观形貌及电化学性能的影响规律,结果表明:当水热温度为180℃时,所制得的Ni Te为均匀的片状结构,在三电极体系下获得的Ni Te电极最大的质量比电容为603.6 F·g^(-1)。利用Ni Te和AC分别作为正极和负极,制备了非对称超级电容器(ASC)。NiTe//AC ASC可以将电位窗口扩展到1.6 V,最大的能量密度和功率密度分别为25.8 Wh·kg^(-1)和3994W·kg^(-1)。ASC显示出良好的循环稳定性,5000次循环之后保持了初始电容的83.3%。

Lumped Mass Finite Element Method of the Nonlinear BBM Equation

In this paper, the full-discrete approximation scheme of the lumped mass nonconforming finite element method for BBM equation is discussed. Without the Riesz projection used in the traditional finite element analysis, the optimal error estimations are derived based on interpolation technique and special properties of element.

Infinite Sequence Soliton-Like Exact Solutions of (2 + 1)-Dimensional Breaking Soliton Equation

寻求新无限的顺序象 soliton 一样非线性的进化方程的准确答案(旧姓) 由在辅助方程方法上开发建设和机械化的二个特征，秒种椭圆形的方程高度被学习并且新类型答案和 B ? cklund 转变被获得。( 2+1 )然后，维的碎 soliton 方程作为一个例子和它的无限的顺序被选象soliton一样准确解决方案在符号的计算系统 Mathematica 的帮助下被构造，它包括无限的顺序 Jacobi 椭圆形的类型的光滑的象soliton一样解决方案， Jacobi 椭圆形的类型的无限的顺序协议 soliton 解决方案和指数的函数类型和三角形的功能的无限的顺序山峰 soliton 解决方案打字。

A Quadratic Finite Volume Method for Parabolic Problems

.In this paper,a quadratic finite volume method(FVM)for parabolic problems is studied.We first discretize the spatial variables using a quadratic FVM to obtain a semi-discrete scheme.We then employ the backward Euler method and the Crank-Nicolson method respectively to further disctetize the time vatiable so as to derive two full-discrete schemes.The existence and uniqueness of the semi-discrete and full-discrete FVM solutions are established and their optimal error estimates are derived.Finally,we give numerical examples to illustrate the theoretical results.

A Coercivity Result of Quadratic Finite Volume Element Schemes over Triangular Meshes

In this work,we study the coercivity of a family of quadratic finite volume element(FVE)schemes over triangular meshes for solving elliptic boundary value problems.The analysis is based on the standard mapping from the trial function space to the test function space so that the coercivity result can be naturally incorporated with most existing theoretical results such as H^(1) and L^(2) error estimates.The novelty of this paper is that,each element stiffness matrix of the quadratic FVE schemes can be decomposed into three parts:the first part is the element stiffness matrix of the standard quadratic finite element method(FEM),the second part is the difference between the FVE and FEM on the element boundary,while the third part can be expressed as the tensor product of two vectors.As a result,we reach a sufficient condition to guarantee the existence,uniqueness and coercivity result of the FVE solution on general triangular meshes.Moreover,based on this sufficient condition,some minimum angle conditions with simple,analytic and computable expressions are obtained.By comparison,the existing minimum angle conditions were obtained numerically from a computer program.Theoretical findings are conformed with the numerical results.

The Formulation of Finite Difference RBFWENO Schemes for Hyperbolic Conservation Laws:An Alternative Technique

To solve conservation laws,efficient schemes such as essentially nonoscillatory(ENO)and weighted ENO(WENO)have been introduced to control the Gibbs oscillations.Based on radial basis functions(RBFs)with the classical WENO-JS weights,a new type of WENO schemes has been proposed to solve conservation laws[J.Guo et al.,J.Sci.Comput.,70(2017),pp.551–575].The purpose of this paper is to introduce a new formulation of conservative finite difference RBFWENO schemes to solve conservation laws.Unlike the usual method for reconstructing the flux functions,the flux function is generated directly with the conservative variables.Comparing with Guo and Jung(2017),the main advantage of this framework is that arbitrary monotone fluxes can be employed,while in Guo and Jung(2017)only smooth flux splitting can be used to reconstruct flux functions.Several 1D and 2D benchmark problems are prepared to demonstrate the good performance of the new scheme.

耐事故SiCf/SiC复合材料包壳管CVI+无模具NITE制备技术研究

新型CVI+无模具NITE制备技术结合了化学气相渗透(CVI)技术和纳米渗透共晶转变(NITE)技术的优点,并且不受模具、压力限制,具有制备长尺寸的SiCf/SiC复合材料包壳管的潜力。研究表明,短时间的CVI沉积能够强化纤维预制体结构,并为纤维间的孔隙留出NITE浸渗孔隙;同时在NITE浆料中添加聚碳硅烷(PCS)能够有效降低NITE工艺的烧结难度,通过热等静压方法实现无压烧结,制备出具有较好致密度的SiCf/SiC复合材料短管;所制备的SiCf/SiC复合材料短管致密度最高达到了2.77 g/cm3,并且仍存在较大的提升空间。

Hypoplastic particle finite element model for cutting tool-soil interaction simulations:Numerical analysis and experimental validation

This study presents numerical and experimental models for the analysis of the excavation of soft soils by means of a cutting tool.The computational model is constructed using an Updated Lagrangean(UL)velocity-based Finite Element approach.A hypoplastic formu-lation is employed to describe the constitutive behavior of soft soils.Large displacements and deformations of the ground resulting from the cutting tool-soil interaction are handled by means of the Particle Finite Element method,characterized by a global re-meshing strat-egy and a boundary identification procedure called a-shape technique.The capabilities and performance of the proposed model are demonstrated through comparative analyses between experiments and simulations of cutting tool-soft soil interactions.The experiments are performed using an excavation device at Ruhr-Universita¨t Bochum(RUB),Germany.The main details concerning the setup and calibration and evolution of the measured draft forces are discussed.Selected computational results characterizing the cutting tool-soft soil interaction including the topology of the free surface,void ratio distribution ahead of the tool,spatio-temporal evolution of the reaction forces and abrasive wear behavior are evaluated.

利用CiteSpace分析有限元技术在法医学中的应用现状

本文利用CiteSpace可视化软件对CNKI和ISI Web of Science数据库所收录的有限元技术在法医学中应用的研究文献进行统计和可视化对比分析,得出国内外法医领域有限元应用研究文献的关键词、机构合作、作者合作的可视化知识图谱。在此基础上,作者对文献内容进行深入研究,发现有限元技术在法医学中的研究及应用主要集中在损伤机制分析方面,以车祸损伤、高坠损伤、钝器损伤、锐器损伤、枪弹损伤等为重点,研究方法主要是通过对人体、致伤物等建立高仿真模型,利用有限元技术,以数字化、可视化、可量化的方式研究各类损伤的生物力学机制。目前,国内外法医学者主要借助Mimics等软件将人体影像数据转换为分割化的三维模型,依托较为成熟的THUMS、ANSYS等有限元系统构建多种损伤模型,有效揭示了各类损伤的发生机制,在一定程度上推动了法医病理损伤专业的发展,为法医学者开展相关研究提供了参考和借鉴。同时,有限元技术在法医学中的应用属于学科交叉,但目前的研究人员多以法医为主,缺少相关学科专业技术人员的深度介入,在某种程度上限制了该技术在法医学中的应用发展,有必要加强与从事有限元等相关研究的专业技术人员之间的交流合作。

Numerical Simulation-Based Analysis of the Impact of Overloading on Segmentally Assembled Bridges

Segmentally assembled bridges are increasinglyfinding engineering applications in recent years due to their unique advantages,especially as urban viaducts.Vehicle loads are one of the most important variable loads acting on bridge structures.Accordingly,the influence of overloaded vehicles on existing assembled bridge structures is an urgent concern at present.This paper establishes thefinite element model of the segmentally assembled bridge based on ABAQUS software and analyzes the influence of vehicle overload on an assembled girder bridge struc-ture.First,afinite element model corresponding to the target bridge is established based on ABAQUS software,and the load is controlled to simulate vehicle movement in each area of the traveling zone at different times.Sec-ond,the key cross-sections of segmental girder bridges are monitored in real time based on the force character-istics of continuous girder bridges,and they are compared with the simulation results.Finally,a material damage ontology model is introduced,and the structural damage caused by different overloading rates is compared and analyzed.Results show that thefinite element modeling method is accurate by comparing with on-site measured data,and it is suitable for the numerical simulation of segmental girder bridges;Dynamic sensors installed at 1/4L,1/2L,and 3/4L of the segmental girder main beams could be used to identify the dynamic response of segmental girder bridges;The bottom plate of the segmental girder bridge is mostly damaged at the position where the length of the precast beam section changes and the midspan position.With the increase in load,damage in the direction of the bridge develops faster than that in the direction of the transverse bridge.Thefindings of this study can guide maintenance departments in the management and maintenance of bridges and vehicles.

Investigation of the Effect of the Force Arm on the Bending Capability of Prestressed Glulam Beam

Prestress enables the Glulam beam could make full use of the compression strength,and then increase the span,but it still could not reduce all drawbacks,such as cross-section weakening and small force arm.To avoid slotting and ensure suitable tension and compression couple,one kind of novel anchor has been proposed,which could meet the bearing capacity requirement.And then the bending test of prestressed Glulam beams with a geometric scale ratio of 1:2 was simulated,to investigate the effect of the force arm on bending capacities,failure modes,and deformation performance.Results show that increasing the force arm could improve the ultimate bending per-formance of the beam significantly,and the anchor arm length has a certain effect on the performance,but it is not obvious.Finally,based on Finite element method analysis,the practice design suggestions have been offered.

Impact Damage Testing Study of Shanxi-Beijing Natural Gas Pipeline Based on Decision Tree Rotary Tiller Operation

The North China Plain and the agricultural region are crossed by the Shanxi-Beijing natural gas pipeline.Resi-dents in the area use rototillers for planting and harvesting;however,the depth of the rototillers into the ground is greater than the depth of the pipeline,posing a significant threat to the safe operation of the pipeline.Therefore,it is of great significance to study the dynamic response of rotary tillers impacting pipelines to ensure the safe opera-tion of pipelines.This article focuses on the Shanxi-Beijing natural gas pipeline,utilizingfinite element simulation software to establish afinite element model for the interaction among the machinery,pipeline,and soil,and ana-lyzing the dynamic response of the pipeline.At the same time,a decision tree model is introduced to classify the damage of pipelines under different working conditions,and the boundary value and importance of each influen-cing factor on pipeline damage are derived.Considering the actual conditions in the hemp yam planting area,targeted management measures have been proposed to ensure the operational safety of the Shanxi-Beijing natural gas pipeline in this region.