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关键词： Gradient nano-grained NiTi SMA   Multiscale continuum model   Analytical solution   Martensite transformation   Superelasticity  

摘要： A multiscale nonlocal continuum model is proposed to describe the superelastic deformation of gradient nano-grained NiTi shape memory alloys (SMAs). At the mesoscopic scale, the polycrystalline aggregate is regarded as a composite, i.e., the grain-interior (GI) phase is assumed to be a cuboidal inclusion embedded in a matrix of grain-boundary (GB) phase. An intrinsic energetic length and a gradient energy are introduced into the Helmholtz free energy of the GI phase. The criterion of martensite transformation (MT) is derived based on the principle of virtual power and second law of thermodynamics. The hindering effect of GB on MT in GI phase is addressed. By deriving the analytical solution of the proposed model and introducing a scale transition rule, the overall and local stress-strain responses of the specimen at the macroscopic scale are obtained. The prediction capability of the proposed model is verified by comparing the analytical solution with the experiment. The influences of the distribution form for the grain size (GS) on the superelastic deformation of gradient nano-grained NiTi SMAs are further predicted and discussed. The analytical form and low computational cost of the proposed model make it an appropriate theoretical tool to design the gradient nano-grained SMAs with desired mechanical property.

关键词： 饮食偏好   骨关节炎   欧洲人群   孟德尔随机化   全基因组关联研究   因果关系  

摘要： 背景:有研究表明饮食摄入与骨关节炎之间存在潜在的关联,但食物偏好与骨关节炎间是否存在因果关系仍未可知。国内目前尚未有大规模饮食偏好与骨关节炎全基因组关联研究。目的:探究欧洲人群饮食偏好与骨关节炎间的因果关联,以期为骨关节炎的预防提供理论依据,同时为国内髋膝关节骨关节炎高危人群识别提供参考数据。方法:选用人类全基因组关联研究数据中欧洲人群20种饮食偏好遗传统计数据集筛选暴露因素相关工具变量,结局选用骨关节炎遗传统计数据集,排除与混杂因素相关工具变量后,主要采用逆方差加权分析法进行两样本孟德尔随机化因果关联分析,其余4种统计方法作为补充,并对结果进行敏感性检验。结果与结论:①逆方差加权分析结果显示,喜好烤肉(OR=1.204,95%CI:1.058-1.370,P=0.005)、牛肉(OR=1.167,95%CI:1.034-1.317,P=0.012)、鸡肉(OR=1.399,95%CI:1.119-1.749,P=0.003)、猪排(OR=1.218,95%CI:1.039-1.427,P=0.015)及咖啡(OR=1.133,95%CI:1.037-1.238,P=0.006)是膝髋关节骨关节炎的风险因素;喜好蔬菜(OR=0.893,95%CI:0.827-0.964,P=0.004)和醋(OR=0.897,95%CI:0.812-0.991,P=0.032)是膝髋关节骨关节炎的保护因素;②敏感性分析结果显示,纳入分析的工具变量不存在水平多效性及偏倚,并根据异质性分析结果使用对应的逆方差加权分析效应模型;③此次研究结果在饮食偏好与髋膝关节骨关节炎相关研究中提供了一定的参考价值,但仅纳入来自欧洲人群的人类全基因组关联研究数据,研究结果在其他种族中的有效性仍待检验;且并未进行性别、年龄及其他健康状态分层,研究结果难以完全排除来自人群分层的偏倚,未来仍需更大规模、更细化分类的样本数据开展相关因果关系研究。

关键词： Micropolar elasticity   Sliding friction   Size effect   Indentation   Singular integral equation  

摘要： In this study, the sliding friction contact problems associated with the indentation of an elastic half-plane by rigid cylindrical and flat punches were investigated within the context of the micropolar theory. The micropolar theory of elasticity introduces the characteristic material length and the dimensionless coupling number to describe the size effect. Coulomb's friction law is satisfied by a punch when it is subjected to both normal and tangential forces. Using the Fourier integral transformation technique, these mixed-boundary value problems were reduced to singular integral equations of the second kind in which the unknown quantity is the contact stress on the contact surface. The collocation method was utilized to solve the integral equations numerically. An extensive parametric study was conducted to investigate the effects of the friction coefficient, the characteristic material length, and the dimensionless coupling number on the normal and in-plane stresses. The results show that the contact stress predicted by the micropolar theory differs significantly from those predicted by the couple stress theory and the classical elasticity theory.

关键词： Volumetric locking   Mixed displacement-pressure formulation   EFG method   Irregular pressure node distribution   Hyperelastic materials  

摘要： Rubber-like materials that are commonly used in structural applications are modelled using hyperelastic material models. Most of the hyperelastic materials are nearly incompressible, which poses challenges, i.e., volumetric locking during numerical modelling. There exist many formulations in the context of the finite element method, among which the mixed displacement-pressure formulation is robust. However, such a displacement-pressure formulation is less explored in meshfree methods, which mitigates the problem associated with mesh distortion during large deformation. This work addresses this issue of alleviating volumetric locking in the element-free Galerkin method (EFGM), which is one of the popular meshfree methods. A two-field mixed variational formulation using the perturbed Lagrangian approach within the EFGM framework is proposed for modelling nearly incompressible hyperelastic material models, such as Neo-Hookean and Mooney-Rivlin. Taking advantage of the meshless nature of the EFGM, this work introduces a unique approach by randomly distributing pressure nodes across the geometry, following specific guidelines. A wide spectrum of problems involving bending, tension, compression, and contact is solved using two approaches of the proposed displacement-pressure node formulation involving regular and irregular pressure node distribution. It is observed that both approaches give accurate results compared to the reference results, though the latter offers flexibility in the pressure nodal distribution. (sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic). (sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic), (sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic) (sic)(sic)(sic)(sic), (sic)(sic)(sic)(sic)(sic)(sic). (sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic), (sic)(sic)(sic)(sic)(sic)(sic), (sic)(sic)(sic)(sic)(sic)(sic)-(sic)(sic)(sic)(sic)(sic)(si

关键词： Boussinesq problem   Finite elastic layer   Surface effect   Thickness effect   Analytical solution  

摘要： Both the thickness effect and surface effect should be important in nano-indentation behavior of coatings due to the finite thickness and small indentation size. As a basic solution, the two-dimensional Boussinesq problem of a finite elastic layer bonded to a rigid substrate is studied in this paper, employing the surface-energy-density-based elastic theory. The Airy stress function and Fourier integral transform methods are adopted to solve the problem. A nalytical solutions of both the stress and displacement fields are well achieved for a finite elastic layer under a concentrated force and a uniform pressure. Unlike the classical solutions, it is discovered that both the thickness effect and surface effect will show significant influences on the Boussinesq elastic behaviors. The surface effect would harden the finite elastic layer and induce a more uniformly distributing displacements and stresses. Only when the thickness is sufficiently large, the Boussinesq solution of an elastic half space may represent that of a finite elastic layer case. A generalized hardness is further defined to include the coupling effects of thickness and surface for the Boussinesq problem of a finite elastic layer. Such a study would assist in the design and property evaluation of coatings and micro-devices with layer-substrate structures.

关键词： 电磁感应   电容器   动态分析  

摘要： 电磁感应中含电容器电路简单模型在稍有不同条件时,其电路、动力学、能量的动态情况是有很大差异的,结果也不同。文中利用基本物理规律、物理思维方法以及数学方法,从电磁感应的简单含容电路模型入手,逐渐增加变化其条件,综合分析其各种情景下的电路情况、受力运动情况,并给出最终的结果。

关键词： 新工科   大学生   创新创业   人才培养  

摘要： 习近平总书记指出要进一步加强科学教育、工程教育,加强拔尖创新人才自主培养,为解决我国关键核心技术攻关提供人才支撑。新时代背景下,通过推动大学生创新创业培养出符合时代需求的新工科人才是我国高等工程教育实现创新和突破的重要抓手。文章通过调研,从学生角度分析了存在的问题,重点论述了国内高校开展双创工作的现状,探索了基于新工科人才需求的高校双创教育改革方向,以期为建设一流大学、培养一流人才提供参考。

关键词： 公安本科院校   公安学   公安人才   警察学院   一所   海警   职业院校   人才培养模式  

摘要： 2021年,海南省委、省政府通过有效整合海南政法职业学院(以下简称“海政”)等相关资源筹建海南警察学院(以下简称“海警院”)。海政是一所专业设置涵盖公安、司法、法律类专业的公办高等政法类职业院校。海警院拟办成一所专业涵盖法学、公安学、公安技术的省属公办公安本科院校,这与原来海政人才培养模式有较大不同。因此,对海警院公安人才培养模式进行研究,不仅能促进海政教师顺利转型,也能为培养自贸港所需的公安人才奠定扎实的师资基础。

关键词： 财经类高校   就业工作   就业特点   引导策略   国家战略需求  

摘要： 党的二十大报告首次单独成章对教育、科技、人才工作进行一体部署,尤其突出了教育在服务国家战略发展中的重要作用。通过分析我国三所“双一流”财经类高校就业数据,发现财经类高校毕业生在就业选择和去向上呈现一定特点,这些特点使得财经类高校毕业生在服务国家战略需求上形成“断裂”。分析就业规律和特点,探索其背后形成的原因,提出大力开拓就业新市场新领域,树立新财经人才培养目标,加强就业教育的引导策略,助力财经类高校实现“财经报国”的人才培养目标,进一步提升新时代背景下财经类高校就业工作服务国家战略发展的能力。

关键词： 劳动教育   劳动教育资源   协同供给  

摘要： 劳动教育资源协同供给是整合家庭、学校、社会等多方资源,通过协同合作与共同育人,创新教育方式,全面提升学生劳动素养和实践能力的综合实践活动。实现劳动教育资源协同供给,对于劳动教育资源建立有序供给的适配机制、建立系统供给的整体结构、塑造内在一体的文化载体、建构相互支持的整体关系具有重要意义。当前,劳动教育资源协同供给面临一系列挑战,包括制度支撑体系的不完善导致的资源分配不均、利益冲突阻碍供给结构的优化调整、劳动文化与社会主流期待的脱节,以及需求整体化与供给渠道碎片化之间的矛盾,为此,应构建制度支撑体系,建立利益协调机制,重塑劳动文化观念,整合供给渠道。