单面柱局域共振声子晶体低频带隙特性分析及结构改进研究

基于有限元法对单面柱局域共振声子晶体进行带隙特性分析,研究了结构参数对该类型声子晶体的影响。结果表明:随着散射体高度的增加,单面柱声子晶体的第一完全带隙的起始频率逐渐降低,带宽逐渐增大;随着基板厚度的增大,单面柱声子晶体的起始频率逐渐升高,截止频率先增大后减小。并且在经典单面柱声子晶体的基础上,组合了两种新型的三组元单面柱声子晶体结构:嵌入式单面柱声子晶体(以下简称结构Ⅰ)和粘接式单面柱声子晶体(以下简称结构Ⅱ)。通过对其带隙特性的分析得出:这两种新结构与经典的单面柱声子晶体相比,都具有更低频的带隙,这对于低频减振降噪是非常有利的。本文的结果将对实际的工程应用提供一定的理论指导。     

On the Brauer p-dimension of Henselian discrete valued fields of residual characteristic p > 0

Let $(K,v)$ be a Henselian discrete valued field with residue field $\stackrel{?}{K}$ of characteristic $p>0$, and ${\text{Brd}}_p(K)$ be the Brauer p-dimension of K. This paper shows that ${\text{Brd}}_p(K)\ge n$ if $[\stackrel{?}{K}:{\stackrel{?}{K}}^p]=p^n$, for some $n\in \mathbb{N}$. It proves that ${\text{Brd}}_p(K)=\infty$ if and only if $[\stackrel{?}{K}:{\stackrel{?}{K}}^p]=\infty$.     

(Sm0.5Gd0.2Nd0.3)2(Hf0.3Ce0.7)2O7复合氧化物的热物理性能

为寻求新型热障涂层用陶瓷材料,本文采用高温固相烧结法制备了(Sm_0.5Gd_0.2Nd_0.3)₂(Hf_0.3Ce_0.7)₂O₇复合氧化物。利用XRD分析了其晶体结构,SEM分析其显微组织,膨胀仪测试其热膨胀性能,激光热导仪测试其热扩散系数。结果表明,成功制备了具有单一萤石晶体结构的(Sm_0.5Gd_0.2Nd_0.3)₂(Hf_0.3Ce_0.7)₂O₇复合氧化物。其显微组织结构致密,晶界清晰无其他相存在。由于复杂的元素组成和较大的原子量,其热导率明显低于7YSZ和Sm₂Ce₂O₇。其较低的热膨胀系数则归因于B位离子较小的离子半径,但其热膨胀系数依然满足热障涂层的要求。     

基于内聚力模型的快速荷载下CFRP-混凝土界面剪切剥离模拟

鉴于纤维增强复合材料(Fiber Reinforced Polymer, FRP)已在混凝土结构加固中普遍应用, 能有效提高结构的承载和变形能力. 为揭示动载作用下FRP-混凝土界面的剥离机理, 本文基于ABAQUS平台, 采用内聚力模型模拟CFRP-混凝土界面层, 实现了快速荷载下CFRP-混凝土界面剥离的高效模拟. 结果表明: CFRP表面应变在加载过程中由加载端向自由端方向传递, 随着加载速率的提高, 界面承载能力也随之提高; 界面峰值剪应力也存在显著的应变率效应; 模拟结果与试验结果基本吻合, 说明了新方法的有效性.     

梁柱简化模型在自立塔塔线体系动态响应中的适用性研究

对输电塔进行合理简化可以提高塔线体系动力学仿真的效率。本文给出自立塔梁柱简化模型的计算方法，并提出利用梁柱简化模型计算方法建立自立塔塔线体系整体模型，同时采用桁梁混合模型建立精细化塔线体系整体模型，对两种模型塔线体系静力特性及振型和固有频率等动力特性进行对比分析。以脱冰工况为例，采用生死单元技术将施加在输电线节点上的集中质量单元杀死来模拟脱冰，实现对塔线体系动力学响应的有限元模拟，研究塔线体系简化模型在动态响应中的适用性。结果表明，两种模型弯曲变形误差小，低阶的振型相同，固有频率值误差小，动力特性基本相同；脱冰工况下，自立塔节点位移和塔材内力时程曲线一致，在提高计算效率的情况下，能有效保证计算精度。     

以含碘氨基酸类激素为例刍议微量非金属元素在生物体内的作用机制

选取第五周期元素碘,结合多学科的研究方法论对含碘氨基酸类激素在生物体内的合成和分解代谢进行系统性分析。通过解析碘元素本身性质及其各个氧化态之间的转化,探讨碘元素在生物体内的作用机制,揭示自然界对物质代谢的精细调控。这一教学模式探索性地融入无机化学、元素有机化学、分子生物学、生物化学、生物物理学、化学生物学等一系列学科内容,旨在让学生在领悟生命科学内在规律,从而激发其科研及学习热情,并训练学生的类比思维和思辨能力。期对培养21世纪跨学科综合型人才的培养有所助益。     

“多才多艺”的铁元素*

铁在自然界中含量丰富,化学性质活泼,能够形成多种应用广泛的物质及材料,富有发展潜力。简述了铁元素的发现与性质,并重点介绍了铁的功能与应用。其中铁的应用主要围绕铁及其化合物在医学治疗、能源材料和环境保护领域所发挥的重要作用进行了阐述。     

A control volume finite element method for three-dimensional three-phase flows

A novel control volume finite element method with adaptive anisotropic unstructured meshes is presented for three-dimensional three-phase flows with interfacial tension. The numerical framework consists of a mixed control volume and finite element formulation with a new P₁DG-P₂ elements (linear discontinuous velocity between elements and quadratic continuous pressure between elements). A “volume of fluid” type method is used for the interface capturing, which is based on compressive control volume advection and second-order finite element methods. A force-balanced continuum surface force model is employed for the interfacial tension on unstructured meshes. The interfacial tension coefficient decomposition method is also used to deal with interfacial tension pairings between different phases. Numerical examples of benchmark tests and the dynamics of three-dimensional three-phase rising bubble, and droplet impact are presented. The results are compared with the analytical solutions and previously published experimental data, demonstrating the capability of the present method.     

Shape optimisation problem for stability of Navier–Stokes flow field

ABSTRACT

This paper presents the numerical results of a shape optimisation problem with regard to delaying the transition of a Navier–Stokes flow field from laminar to turbulent by using the theory developed by Nakazawa and Azegami. The theory was reviewed within the framework of functional analysis and updated with another expression of the shape derivative with respect to the objective function. A computer program was developed with the FreeFEM++. Numerical analyses were performed for two types of problems: a two-dimensional Poiseuille flow field with a sudden expansion and a two-dimensional uniform flow field around an isolated body. From the first example, two local minimum points of symmetric and asymmetric flow fields were determined, and the asymmetric flow field was found to be more stable. With regard to the second example, we reached the local minimum point of an elliptical shape, and infrequently determined a solution converging to an elliptical shape with the bluff in the leeward direction. By comparison, the superiority of the elliptical shape was obvious.     

A Highly Lewis Acidic Strontium ansa-Arene Complex for Lewis Acid Catalysis and Isobutylene Polymerization

The potential of a dicationic strontium ansa-arene complex for Lewis acid catalysis has been explored. The key to its synthesis was a simple salt metathesis from SrI₂ and 2 Ag[Al(OR^F)₄], giving the base-free strontium-perfluoroalkoxyaluminate Sr[Al(OR^F)₄]₂ (OR^F=OC(CF₃)₃). Addition of an ansa-arene yielded the highly Lewis acidic, dicationic strontium ansa-arene complex. In preliminary experiments, the complex was successfully applied as a catalyst in CO₂-reduction to CH₄ and a surprisingly controlled isobutylene polymerization reaction.