Influence of Al_2O_3 particles on the microstructure and mechanical properties of copper surface composites fabricated by friction stir processing

The influence of three factors, such as volume percentage of reinforcement particles(i.e. Al2O3), tool tilt angle and concave angle of shoulder, on the mechanical properties of Cue Al2O3 surface composites fabricated via friction stir processing was studied. Taguchi method was used to optimize these factors for maximizing the mechanical properties of surface composites. The fabricated surface composites were examined by optical microscope for dispersion of reinforcement particles. It was found that Al2O3 particles are uniformly dispersed in the stir zone. The tensile properties of the surface composites increased with the increase in the volume percentage of the Al2O3 reinforcement particles.This is due to the addition of the reinforcement particles which increases the temperature of recrystallization by pinning the grain boundaries of the copper matrix and blocking the movement of the dislocations. The observed mechanical properties are correlated with microstructure and fracture features.

The mechanical response of multi-tower continuous-span suspension bridge deck pavement based on whole bridge analysis

The effect of multiple span suspension structure on the mechanical response of bridge deck pavement was studied, and finite element analysis (FEM) of stress and strain of pavement according to the bridge floor system features of super-long and high flexibility was made. Meanwhile, the FEM results were compared with those of the single span suspension structure. Three-stage analytic hierarchy process (AHP) is developed to analyze the mechanical response including whole bridge analysis, partial beams section analysis and orthotropic plate analysis. The most unfavorable load position was determined by the numerical solutions acquired from each stage to study the main mechanical index of multiple span suspension structure. The FEM results showed that the mechanical response numerical solutions by using the three-stage AHP are greater than those by simplified boundary condition, and the force condition of multiple span suspension structure is worse than that of the single span suspension structure.

A preliminary analysis of physical mechanism of transformation process from a landed typhoon into an extratropical cyclone

A diagnostic study is performed in the paper on the process of typhoon Norris (1980) transforming into an ex-tratropical cyclone after its landing over Southeast China. The main findings are as follows:The changes of kinetic energy are mainly attributed to the generation due to non-divergent wind. During the early stage of the typhoon landing, there exits only a small quantity of kinetic energy exchanging with the environment. And after it is transformed into an extratropical cyclone, a large amount of kinetic energy is exported from the system toward the environment.The horizontal and vertical flux-divergence terms of eddy available potenlial energy are the prominent sinks in the budgets of eddy kinetic energy. The generations of eddy kinetic energy due to both the barotropic and baroclinic processes are source terms. The former is remarkable during the initial stage. But after the depression is transformed into an extratropical cyclone, the roles of the generation by the barotropic and baroclinic processes are reversed, 1. e. , the latter has become more significant than the former.Diabatic heating is the most dominant heat source. The terms of vertical heat flux by cumulus and large-scale motion are the major sinks. And the latter is prominent after the system is transformed into an extratropical cycfone.

Synthesis mechanism of Pr doped BaTi_4O_9 powder by sol-gel process

Pr Doped BaTi4O9 gel was prepared by sol-gel method using Ti(OC4H9)4, Ba(CH3COO)2, CH3COOH and CH3OCH2CH2OH as raw materials. Through analyzing dry gel thermal treated at different temperatures, the possible synthesis mechanism of Pr doped BaTi4O9 powder was discussed. At first, Ti(OC4H9)4 hydrolyzes and three dimensional networks form, in which Ba2+ and CH3COO- are mostly in the form of ions; organic solvent is gradually volatilized through calefaction at 700 ℃, then the offspring is turned into BaTi5O11. With the temperature increasing to 850 ℃, BaTi5O11 begins resolving partly and forming BaTi4O9, and at 1000℃ Ba4Ti13O22 forms partly, but BaTi4O9 is the main crystal phase. BaTi5O11 and Ba4Ti13O30 decomposes completely at 1200℃ and forms single-phase BaTi4O9. The infrared (IR) analysis also shows that the absorbing peak of Ti-O bond is not in the characteristic absorption range of Ti-O-Ti (700-900 cm-1), but slightly shifted to the higher end (908 cm-1). It is probably because that doping Pr enters into the crystal lattice and causes the abnormal absorption of Ti-O bond.

APPLICATION OF STOCHASTIC FINITE ELEMENT METHOD TO STRENGTH AND STABILITY ANALYSIS OF EARTH DAMS

This paper applies the stochastic finite element method to analyse the statistics of stresses in earth dams and assess the safety and reliability of the dams. Formulations of the stochastic finite element method are briefly reviewed and the procedure for assessing dam's strength and stability is described. As an example, a detailed analysis for an actual dam Nululin dam is performed. A practical method for studying built-dams based on the prototype observation data is described.

A retrospective view on the history of natural sciences in XX-XXI

The presented paper is dedicated to a new ret-rospective view on the history of natural sci-ences in XX-XXI cc, partially including the sci-ence philosophy (mainly, the problems of the scientific realism, i.e. the correspondence of science to reality) and also a novel scheme for different classes of sciences with different ob-jects and paradigms. There are analyzed the chosen “great” and “grand” problems of phys-ics (including the comprehension of quantum mechanics, with a recently elaborated new chapter, connected with time as a quantum obs- ervable and time analysis of quantum processes) and also of natural sciences as a whole. The particular attention is paid to the interpretation questions and slightly to the aspects, inevitably connected with the world- views of the res- earchers (which do often constitute a part of the interpretation questions).

基于交替注意力机制和图卷积网络的方面级情感分析模型

方面级情感分析旨在预测给定文本中特定目标的情感极性。针对忽略方面词和上下文之间的句法关系和平均池化带来的注意力差异性变小的问题,提出一种基于交替注意力(AA)机制和图卷积网络(GCN)的方面级情感分析模型(AA-GCN)。首先,利用双向长短期记忆(Bi-LSTM)网络对上下文和方面词进行语义建模;其次,通过基于句法依存树的GCN学习位置信息和依赖关系,再利用AA机制进行多层次交互学习,自适应地调整对目标词的关注度;最后,拼接修正后的方面特征和上下文特征,得到最终的分类依据。相较于基于目标依赖的图注意力网络(TDGAT),所提模型在4个公开数据集上准确率提升了1.13%~2.67%,在5个公开数据集上F1值提升了0.98%~4.89%,验证了利用句法关系和提升关键词关注度的有效性。

基于TF-IDF和多头注意力Transformer模型的文本情感分析

文本情感分析旨在对带有情感色彩的主观性文本进行分析、处理、归纳和推理,是自然语言处理中一项重要任务。针对现有的计算方法不能充分处理复杂度和混淆度较高的文本数据集的问题,提出了一种基于TF-IDF(Term Frequency-Inverse Document Frequency)和多头注意力Transformer模型的文本情感分析模型。在文本预处理阶段,利用TF-IDF算法对影响文本情感倾向较大的词语进行初步筛选,舍去常见的停用词及其他文本所属邻域对文本情感倾向影响较小的专有名词。然后,利用多头注意力Transformer模型编码器进行特征提取,抓取文本内部重要的语义信息,提高模型对语义的分析和泛化能力。该模型在多领域、多类型评论语料库数据集上取得了98.17%的准确率。

一种新型6-DOF串并混联拟人机械臂及其位置分析

提出了一种新型6-DOF串并混联拟人机械臂,这种机械臂主要包括肩、上臂和前臂三部分,其中,肩采用球面三自由度并联机构为机构原型,上臂采用五杆二自由度并联机构为机构原型,前臂采用四杆机构为机构原型,结合这种机械臂的结构布局特点,求得其位置正解的封闭解,使用Bezout消元法求得这种拟人机械臂的位置反解的封闭解。

EOF分析在海岸地貌与沉积学研究中的应用进展

海岸地貌形成演化的过程和机制是当今海岸地貌与沉积学研究的核心任务。但是,对于海岸带这样高维数非线性系统行为的认识与研究还很有限,因而预测海岸地区地貌演变与沉积物输运就变得比较困难,尤其是动力数值模型在较大时空尺度上的模拟并不理想。数据驱动模型可以一定程度上解决这一问题,并且在数据驱动模型构建之前,经验正交函数(EOF)分析技术能够有效提取、定量表达数据中的主要型式与它们的时空演变,以及不同型式之间是如何相互联系的。这不但有助于构建数据驱动模型进行模拟,更有益于理解这些主控因素是如何影响海岸地貌演化的,进而不断丰富对于海岸地貌演化的过程与机制的认识。故本文在系统整理大量国内外文献的基础上,首先简要介绍了EOF分析的基本原理,然后从砂质和淤泥质海岸剖面的时空变化特征、河口近岸海底冲淤变化的时空演变特征和预测、海岸海洋地区沉积物粒度分布特征和输运等几个方面综述EOF分析在这些研究中的应用进展,同时比较分析研究实例中的问题,进而分析当前研究中的不足,提出应该主要从提高海岸地貌与沉积数据的野外获取手段与时空分辨率,拓宽可供EOF分析的时间或非时间序列的数据类型;深入挖掘EOF分析结果所显示出的海岸地貌与沉积现象中的物理过程与机制,以期为特定时空尺度的海岸地貌与沉积数值模拟提供有价值的参考信息;多与其他线性或非线性分析技术联合使用以作深入分析解释或模拟这三方面来做进一步改进,为实现EOF分析在海岸地貌与沉积学研究中的深入应用与发展提供借鉴。

机械加工过程中的切削力分析与控制策略研究

围绕“机械加工过程中的切削力分析与控制策略研究”展开研究,对不同材料和刀具参数下的切削力进行了系统测量,并建立了相应的力学模型。基于分析结果提出了一种有效的切削力控制策略,旨在优化加工过程中的力学性能。通过引入先进的控制算法和实时监测技术,实现了对切削力的精准调控,提高了加工效率和产品质量。最后通过仿真验证和实际应用测试,证明了所提策略在提高切削效能的同时,有效延长了工具寿命,为机械加工领域的自动化生产提供了可行的解决方案。

多方参与的北京传统居住院落保护实践运行机制解析

传统居住院落是北京老城保护的重点与难点,尽管保护实践不断开展,但风貌环境与居住条件仍普遍落后,亟需探究保护实践的运行机制,理解保护行动与保护结果之间的逻辑关系,以提升保护实践效果。为此,以北京雨儿胡同传统居住院落保护实践项目为例,从多方参与的过程性特点出发,构建“过程分析—效果评价—原因反思”的保护实践运行机制解析框架。研究发现:主体参与意愿和参与能力、项目目标设置、过程设计和机制保障共同影响实践效果。据此提出传统居住院落保护实践策略建议,为精细化设计多方参与保护实践运行机制提供参考。

平面并联2-DOF机构运动的计算机模拟逼近法

提出了用计算机模拟逼近法分析平面2-DOF机构的运动,运用该方法进行了运动分析。先采用CAD的几何约束、尺寸约束、尺寸方程和尺寸驱动技术,构造2-DOF机构的模拟机构。再用两个相同且彼此靠近的模拟机构,构造速度模拟机构,求解机构上确定点的速度和角速度。最后用两个相同且彼此靠近的速度模拟机构,构造加速度模拟机构,求解机构上确定点的加速度和角加速度。计算机模拟结果与解析法的结果比较表明,该方法具有简单、快捷、直观、求解精度高的优点,而且可以完成复杂机构的运动分析,为平面连杆机构运动分析提供了更有效的工具。

机械加工工艺技术误差及改进分析

为了有效改进机械加工过程中存在的误差问题,研究以某个零件加工案例为对象,对机械加工技术加工过程中存在的问题展开研究分析,深入探讨了机械加工技术的误差以及改进方法。先对零件加工过程中存在的变形问题、残余盈利以及磨削刚性误差以及装夹不合理等问题展开研究,从机械加工机床精度、刀具刃口以及工件装夹方法等方面为切入点,详细对机械加工工艺技术的误差展开探究,并提出了相应的改进方法。最后,经验证结果证明,改进后的机械加工工艺具有良好的效果,不仅能够有效提高加工的精度和效率,还能够为相关工作提供参考。

重卡驾驶室液压翻转机构性能参数的优化分析

重卡驾驶室液压翻转机构的性能是衡量整车性能的重要组成部分。为提升翻转机构的性能,建立翻转机构的数学模型,以顶出力系数、油压波动系数、翻转容量3个参数作为翻转机构的性能评价指标,将翻转机构的性能优化问题转化成有约束的多目标优化问题。采用线性加权法的评价函数对有约束的多目标问题进行优化,利用层次分析法(AHP)确定各项性能评价指标的加权系数,设置约束条件后对优化结果进行求解。针对某型重卡驾驶室翻转机构进行实例的优化分析,在MATLAB中对系统模型进行优化和求解,最后搭建AMESim模型进行仿真验证。结果表明:对加权系数的确定而言,AHP是一个稳定和有效的方法,且优化分析结果显示翻转机构的性能相比优化前提升了11.72%,与仿真结果近似。

油茶果脱壳的果壳力学-损伤与仿真研究

油茶果脱壳由手工转向机械化脱壳是现代化加工的必然趋势,油茶果脱壳加工不同参数下果壳力学与组织结构变化,是脱壳装备结构与作业参数优化的基础。本文搭建了原位观测实验平台,分析了不同压缩速率、果壳区域、温度、含水率等作用因素下油茶果壳的力学特性,深入分析了不同工况下的果壳组织结构变化。通过建立果壳压缩力学模型,对果壳压缩过程中的损伤进行分析。结果表明:在压缩过程中,果壳损伤阶段可分为:外果皮塑性、中果皮塑性形变;随着压缩速率的增大,压缩峰值力先增后减;在压缩速率1.0 mm/s时,压缩峰值力达到最大值,腹部(14.7 N)>底部(13.3 N)>顶部(12.8 N);果壳样品含水率降低,使得外果皮硬度增加,外果皮峰值力上升,压缩峰值力下降;当温度升高时,果壳结构变化明显,失水硬化,压缩峰值力呈类抛物线上升;有限元仿真深入揭示了压缩过程应力分布及裂纹状态。

平面3-DOF混联机构构型综合及其同构分析

通过应用Assur杆组法及图论理论对平面3-DOF全转动副机构进行了构件分类和构件组合,得到了一种最基本的3条支链对称的运动链结构。然后运用拓扑胚图插点法画出了其拓扑胚图,对其支链进行分类并插入拓扑胚图中,再进行同构分析得到了6种运动链构型。最后,运用一种新的基于构件关系的图论描述方法推导出了此机构的混联构型,并对其进行了应用研究。这些为以后非全转动副平面3-DOF机构的研究打下了基础。同时,通过研究平面3-DOF机构也更加有利于空间少自由度机构的研究。

大断面隧道仰拱底鼓破坏模式探析

为了提升隧道的设计水平,分析了大断面隧道仰拱底鼓的影响因素,基于薄板压曲微分方程推导了仰拱底鼓临界平衡公式。随后,依托某高速公路隧道,利用ABAQUS软件建立有限元模型,探讨了大断面隧道底鼓的破坏过程和变形机理,同时提出了大断面隧道在施工和运营期间的仰拱底鼓控制措施。

基于荧光显微量化分析的SBS改性沥青溶胀行为表征

SBS是改性沥青中最常用的改性剂,其溶胀状态对沥青性能具有显著影响。通过针入度、软化点、延度等试验研究了SBS改性沥青的宏观性能;基于荧光显微技术,研究了对不同剪切时间下SBS改性沥青中SBS相场分布和溶胀状态,并对SBS的溶胀发育行为进行了量化表征;建立了宏观性能与显微形态参数的线性关系模型,并分析显微形态参数对宏观性能的影响规律。分析结果表明:剪切时间对SBS改性沥青的物理性能有显著影响。随着剪切时间的增加,SBS颗粒的数量、长短轴比、圆形度、面积比和平均面积均发生了变化。剪切时间由5 min增加至55 min,SBS颗粒数量增加了68%;长短轴比值增加了47%,颗粒形状由椭圆趋向长条状变化;SBS颗粒面积比增加了40.88%,平均面积增大了24.93倍。剪切60~90 min,SBS颗粒继续溶胀发育,SBS颗粒数重复剪切5~55 min的变化过程。SBS颗粒的面积比和平均面积与宏观性能中的软化点存在显著的线性关系。

Co-inhibition of methanogens for methane mitigation in biodegradable wastes

The inhibition effects and mechanisms of chlorinated methane and acetylene on methanogenesis in the anaerobic digestion process of the biodegradable wastes were investigated.It was found that both chloroform and acetylene could effectively inhibit methanogens while the biodegradability of the wastes was not affected.Acetylene inhibited the activity of methanogens,while chloroform inhibited metabolic process of methanogenesis.A central composite design（CCD） and response surface regression analysis（RSREG） were employed to determine the optimum conditions and interaction effects of chloroform and acetylene in terms of inhibition effciency,production of volatile fatty acids（VAF） and molar ratio of propionic acid to acetic acid.Chloroform had significant effect on enhancing the production of VFA（F = 121.3;p 〈 0.01）,and acetylene promoted the inhibition effciency（F = 99.15;p 〈 0.05） more effectively than chloroform（F = 9.72;p 〉 0.05）.In addition,a maximum molar ratio of propionic acid to acetic acid of 1.208 was estimated under the optimum conditions of chloroform concentration of 9.05 mg/kg and acetylene concentration of 3.6×10^-3（V/V）.Hence,methanogens in the wastes can be inhibited while the stabilization process of the biodegradable wastes can still work well,as propionic acid generated during the inhibition process could hardly be utilized by methanogens.