A resistance formula for coherent multi-barrier structures

Using the Landauer formula and the quantum S-matrix scattering theory, we derive a resistance formula for multi-barrier structure under phase coherent transmission condition. This formula shows that when the transport is coherent, the potential wells of the structure are just like conductors contributing to the overall resistance. And because the resistance formula is derived based on the scattering theory, the barrier resistance will change with the number of scattering centres （i.e. the number of barriers） in the structure.

A 3-Node Co-Rotational Triangular Finite Element for Non-Smooth,Folded and Multi-Shell Laminated Composite Structures

Based on the first-order shear deformation theory,a 3-node co-rotational triangular finite element formulation is developed for large deformation modeling of non-smooth,folded and multi-shell laminated composite structures.The two smaller components of the mid-surface normal vector of shell at a node are defined as nodal rotational variables in the co-rotational local coordinate system.In the global coordinate system,two smaller components of one vector,together with the smallest or second smallest component of another vector,of an orthogonal triad at a node on a non-smooth intersection of plates and/or shells are defined as rotational variables,whereas the two smaller components of the mid-surface normal vector at a node on the smooth part of the plate or shell(away from non-smooth intersections)are defined as rotational variables.All these vectorial rotational variables can be updated in an additive manner during an incremental solution procedure,and thus improve the computational efficiency in the nonlinear solution of these composite shell structures.Due to the commutativity of all nodal variables in calculating of the second derivatives of the local nodal variables with respect to global nodal variables,and the second derivatives of the strain energy functional with respect to local nodal variables,symmetric tangent stiffness matrices in local and global coordinate systems are obtained.To overcome shear locking,the assumed transverse shear strains obtained from the line-integration approach are employed.The reliability and computational accuracy of the present 3-node triangular shell finite element are verified through modeling two patch tests,several smooth and non-smooth laminated composite shells undergoing large displacements and large rotations.

Phonon Focusing Effect in an Atomic Level Triangular Structure

The rise of artificial microstructures has made it possible to modulate propagation of various kinds of waves,such as light,sound and heat.Among them,the focusing effect is a modulation function of particular interest.We propose an atomic level triangular structure to realize the phonon focusing effect in single-layer graphene.In the positive incident direction,our phonon wave packet simulation results confirm that multiple features related to the phonon focusing effect can be controlled by adjusting the height of the triangular structure.More interestingly,a completed different focusing pattern and an enhanced energy transmission coefficient are found in the reverse incident direction.The detailed mode conversion physics is discussed based on the Fourier transform analysis on the spatial distribution of the phonon wave packet.Our study provides physical insights to achieving phonon focusing effect by designing atomic level microstructures.

Adaptive Neural Control for a Class of Low-triangular-structured Nonlinear Systems with H-∞ Performance Analysis

In this paper, a neural-network-based variable structure control scheme is presented for a class of nonlinear systems with a general low triangular structure. The proposed variable structure controller is proved to be Cl, thus can be applied for backstepping design, which has extended the scope of previous nonlinear systems in the form of strict-feedback and pure-feedback. With the help of neural network approximator, H-∞ performance analysis of stability is given. The effectiveness of proposed control law is verified via simulation.

THE STRUCTURE SENSITIVITY ANALYSIS FOR TRIANGULAR SYSTEMS

Triangular systems play a fundamental role in matrix computations. It has become commonplace that triangular systems are solved to be more accurate even if they are ill-conditioned. In this paper, we define structured condition number and give structured (forward) perturbation bound. In addition, we derive the representation of optimal structured backward perturbation bound.

Reaction of Mo(CO)_6 with Alkoxide: Synthesis and Structure of the Mo(0)-OR Complex [Et_4N]_3[Mo_2(CO)_6(μ-OC_6H_4OCH_2C_6H_5)_3]

The reaction of molybdenum hexacarbonyl with C6H5CH2OC6H4ONa and Et4NBr in CH3CN at 60 ℃ afforded the di-nuclear Mo（0） compound [Et4N]3[Mo2（CO）6（μ-OC6H4OCH2C6H5）3] 1. 1 crystallizes in monoclinic, space group P21/c with a = 15.359（2）, b = 18.378（3）, c = 24.952（2） A, β = 102.268（4）°, V = 6882.3（1 6） A^3, Mr = 1348.34, Z = 4, Dc = 1.301 g/cm^3, F（000） = 2832 and μ= 0.424 mm^-1 The final R = 0.0606 and wR = 0.1552 for 9396 observed reflections （I 〉 2σ（I））. I contains a [Mo2O3]^3 core in triangular bi-pyralnidal configuration and each Mo atom adopts a distorted octahedral geometry with three carbon atoms from carbonyls and three ,μ-O atoms from C6H5CH2OC6H4O^- bridging ligands. The Mo…Mo distance is 3.30（8） A, indicating no metalmetal bonding. A formation pathway via forming a di-molybdenum（0） di-bridging OR compound [Mo2（μ-OR）2（CO）8]2 has been figured out and the reaction of Mo（CO）6 with alkoxide has also been discussed.

Smooth cutting pattern generation technique for membrane structures using geodesic line on subplane and spline interpolation

Practical techniques for smooth geodesic patterning of membrane structures were investigated.For the geodesic search,adjustment of the subplane of the extracted elements series was proposed,and various spline approximation methods were used to flatten the strip for the generation of a smooth pattern.This search approach is very simple,and the geodesic line could be easily attained by the proposed method without the need for a difficult computation method.Smooth cutting patterning can also be generated by spline approximation without the noise in discrete nodal information.Additionally,the geodesic cutting pattern saved about 21%of the required area for the catenary model due to the reduction of the curvature of the planar pattern seam line.

On Quasi-Jacobi Bialgebroid and Its Dirac-Jacobi Structure

Notions of quasi-Jacobi bialgebroid and its Dirac-Jacobi structure are introduced.The necessary and sufficient conditions for a maximal isotropic subbundle L to be a DiracJacobi structure are proved.Meanwhile several special examples are presented.

Post-stack reverse-time migration using a finite difference method based on triangular grids

Compared with other migration methods, reverse-time migration is based on a precise wave equation, not an approximation, and performs extrapolation in the depth domain rather than the time domain. It is highly accurate and not affected by strong subsurface structure complexity and horizontal velocity variations. The difference method based on triangular grids maintains the simplicity of the difference method and the precision of the finite element method. It can be used directly for forward modeling on models with complex top surfaces and migration without statics preprocessing. We apply a finite difference method based on triangular grids for post-stack reverse-time migration for the first time. Tests on model data verify that the combination of the two methods can achieve near-perfect results in application.

A Comparative Investigation on the JT Effect in Triangular Compounds of NaMnO_(2), NaNiO_(2) and NaTiO_(2)

We present a study on the Jahn–Teller(JT)distortions of the TiO_(6),NiO_(6)and MnO_(6)complexes in NaTiO_(2),NaNiO_(2)and NaMnO_(2)triangular compounds with a C_(2)/m structure.The JT vibronic normal modes are found to be Q3,Q'4 and Q6 by the group symmetry on the C2/m structure.The magnitude of the normal coordinates(Q3,Q'4,Q6)and the structural parameters of distorted octahedra MO_(6)(M=Ti,Ni,Mn)are obtained and in good agreement with experimental data.The energy level splitting of 3d orbitals and the highest occupied molecular orbital(HOMO)character in the MO_(6)complex are also calculated in accordance with the JT distortions.These results provide a first insight into the groundstate and magnetic properties of distorted triangular compounds AMO_(2).

Surface-regulated triangular borophene as Dirac-like materials from density functional calculation investigation

By applying the first principles calculations combined with density functional theory (DFT), this study explored the optical properties, electronic structure, and structure stability of triangular borophene decorated chemically, B3X (X=F, Cl) in a systematical manner. As revealed from the results of formation energy, phonon dispersion, and molecular dynamics simulation study, all the borophene decorated chemically were superior and able to be fabricated. In the present study, triangular borophene was reported to be converted into Dirac-like materials when functionalized by F and Cl exhibiting narrow direct band gaps as 0.19 eV and 0.17 eV, separately. Significant light absorption was assessed in the visible light and ultraviolet region. According the mentioned findings, these two-dimensional (2D) materials show large and wide promising applications for future nanoelectronics and optoelectronics.

砖木结构古建筑火灾风险影响因子评估研究

提出模糊DEMATEL-ISM的方法,在建立古建筑火灾评价指标体系的基础上,对归属于4大类风险因素的25个潜在风险因子进行关联性分析,得出因子的因果属性及因子间的逻辑层次结构关系,从而对古建筑火灾风险进行评估。利用模糊DEMATEL-ISM法对华阴市西岳庙灏灵殿进行实例分析,结果表明:疏散与扑救条件、电器设备隐患的原因度较大,需要对其予以控制;耐火等级、火灾荷载的结果度大,为事故发生的主要原因;疏散与扑救条件、易燃易爆危险品、电器设备隐患、安全责任制、灭火应急预案和演练为古建筑火灾事故的关键风险因子,可为古建筑火灾风险管控工作提供相应参考。

三角形排列波浪锥柱绕流流动特性数值分析

采用大涡模拟方法,分析了亚临界雷诺数为3 900时三角形排列波浪锥柱的横流向间距比和顺流向间距比对其升阻力特性、尾流干涉效应及三维流动结构等的影响.结果表明,上游2个波浪锥柱的升阻力特性受下游波浪锥柱影响较小,下游波浪锥柱处于上游双波浪锥柱尾流中,其升阻力特性受横流向间距比和顺流向间距比影响更为显著.3个波浪锥柱间的流动状态可分为邻近干扰、漩涡撞击和涡相互作用状态.在漩涡撞击状态下,上游波浪锥柱尾涡得以发展充分,周期性撞击在下游波浪锥柱表面,从而产生较大的脉动升力.横流向间距比、顺流向间距比分别为3和6时,下游波浪锥柱脉动升力系数较单直圆柱提升了20.93倍.

三维激光扫描点云的岩体产状智能识别研究

目的为了降低传统的人工测量方式带来的工作量大、效率低、工作环境恶劣等影响。方法提出在深部工程或高陡边坡的地质工程测量中,采用三维激光扫描技术获取岩体结构面点云数据,结合一个特制三角形标靶将三维激光点云的局部坐标系下的法向量转化为大地坐标系下的法向量,再利用区域生长算法对结构面产状进行智能识别和输出。结果试验结果表明,利用Delaunay三角剖分三维点云表面的重建,在改进区域生长算法对点云数据的处理下,能够对大批量数据快速处理并获得结果,其独特的空圆特性、剖分中产生较少的畸形三角形和耗时极少的运行时间非常适合海量的点云数据的计算。结论和传统方法相比,该方法具有快速、自动、高精度和远距离测量的优点,对无GPS信号或者GPS信号弱的岩爆频发地区的地质测量具有重要意义。

基于改进DEMATEL-ISM的钢桁梁桥施工风险影响因素研究

为提高钢桁梁桥施工过程中的安全管理,对钢桁梁桥施工中的风险因素进行分析,提出了一种基于改进DEMATEL-ISM的评价方法,首先引入三角模糊数对DEMATEL法中的直接影响矩阵进行改进,从而去模糊化以减少专家评价的主观性,再通过DEMATEL法分析各影响因素的影响度、被影响度、中心度与原因度并加以排序,对得到的主要影响因素进行初步分析,利用ISM法对筛选出的影响因素进行层次划分,得到直接层影响因素、过渡层影响因素与本质影响因素,并针对分析得到的5个本质影响因素提出深入的预防预警措施,可为钢桁梁桥施工方向的安全管理提供针对性措施,为事故预防提供一定的参考依据。

预应力倒三角管桁架钢屋盖滑移施工技术

广交会展馆四期展馆扩建工程地处城市核心区,环境复杂,铁、隧、馆多重结构交互。工程体量大,结构复杂,施工难度大,总工期仅644d,在同类工程中工期最短,工期履约压力大。其中展厅屋盖钢结构为预应力倒三角管桁架结构,钢构体量大。针对此屋盖钢结构特点、难点,从缩短工期、高效建造方面开展研究,创新提出超长大跨度钢桁架分段等节奏滑移施工技术,即展馆两侧附属混凝土结构先行施工,提供滑移支撑体系,屋盖钢结构滑移与展厅下部2层主体混凝土结构同步施工,实现了展厅屋盖钢结构提前插入安装,各专业平面、立面穿插施工,缩短了关键线路工期;研发了基于装配式、自稳定高空平台的大跨度钢桁架拼装技术,实现超长大跨度重型钢桁架分单元快速拼装;针对主体结构作为滑移支撑体系两侧异标高的特点,设计双向滑移轨道,并研制滚针式滑靴及动力系统,确保滑移安全稳定;应用倒三角预应力钢绞线快速穿束和张拉技术,解决了超长预应力筋穿束张拉与高空滑移技术难题;液压同步控制系统与智能施工监测确保了大跨超重钢桁架屋盖滑移的应力、应变可控,按方案模拟过程平稳进行。

双螺杆挤出机强化三角形转子作用下的腔内分布混合模拟

三角形转子作用下的腔内混合行为代表了典型的混合问题,具有广泛的工程应用潜力。为进一步改善分布混合,提出了增加转子边长、转子形状摄动变形以及改变转子拓扑结构等三种强化混合的方法。考虑转子运动的周期性,采用有限元叠加网格技术,建立了不同转子作用下的高黏度流体流动的数值模拟模型,求解得到瞬态速度场。采用自行开发的具有4阶精度的Runge-Kutta代码开展流体混合动力学研究。借助拉格朗日相干结构、示踪剂界面拉伸以及Poincaré截面等对搅拌腔内的分布混合行为进行表征。当转子边长为40 mm时,腔内出现围绕左右转子的两个独立的Komogorov-Arnold-Moser(KAM)岛;当边长增加到45 mm时,腔内的混合机理发生了改变,KAM岛演变为1个,并且沿着联通双环准周期轨道扫掠左右腔,提升分布混合的效果最好。相比改变转子形状,改变拓扑结构更有利于提升分布混合,而且功率消耗更低,但混合机理与转子边长40 mm时相同。

广交会展馆四期扩建工程展厅钢结构屋盖设计

广交会展馆四期扩建工程项目展厅的钢结构屋盖由珠江散步道、标准展厅和卡车通道组成。为了满足业主对标准展厅跨度及净高的功能要求,对5种钢结构屋盖的结构体系进行比选,最终采用了下弦设置穿心式预应力钢绞线的倒三角形立体桁架的结构体系。对所采用的结构体系的基本设计信息进行介绍,并对其进行了荷载分析、施工模拟分析及屋盖抗连续倒塌分析。结果表明所采用的结构方案在满足业主需求的情况下是安全可靠且经济合理的,各项指标均满足规范要求。

隐形三角引用:科学论文中的不规范引用行为

[目的/意义]在科学知识快速更迭的时代背景下,文献引用不规范行为逐渐演化为潜踪匿迹、形式多样的复杂现象,通过文献来源信息建立引用不规范行为的识别方法,并揭示其形成过程的影响因素与内在机理,对于科技期刊规范化、科学评价体系公平化、学术生态环境完善化具有重要意义。[方法/过程]首先,构建引文内容相似度、使用—引用转化率、耦合强度等多维度判定指标;其次,结合相关文献特征与引用内容特征,探究不规范引用行为背后的影响因素与引用情境。[结果/结论]本文在300万条文献耦合数据中发现了近4万组隐形三角引用关系,表征了隐形三角引用行为在科学界的普遍存在。在引用情境分析中,文献语言、文献类型、所属学科领域是文献C转引文献A的影响因素,文献A、B所在期刊影响力、自身被引影响力、发表时间差异是文献C选择匿引文献B的影响因素。科学界应意识到这种不规范引用行为的紧迫性和重要性,逐步建立识别与监督机制。

基于权值对三角关系中结构平衡的预测研究

[研究目的]随着信息化社会的不断发展变化,开源情报的重要性日益突出。通过社交网络中的公开信息对实体间的关系演化进行预测,为使用者提供决策支持。[研究方法]利用微博文本数据挖掘技术,对一年内的官博文本进行收集和清洗,再运用共现次数及链路赋予数值等方法,构建社会关系网络,以预测结构不平衡的社交网络。[研究结论]研究结果表明,该方法在一定参数约束下能够生成符合预期的社会关系网络,并有效预测在社会关系网络中结构不平衡状态下可能出现的变化。