THE APPLICATION OF MICROELECTRODE TO THE STUDY OF MULTISTEP ELECTRODE PROCESSES UNDER STEADY STATE CONDITIONS PART I EE MECHANISM

Under steady-state conditions, the general currents of EE reactions at disk,hemispherical and spherical microelectrodes are derived.From these equations, some electrode reaction parameters can be very simply obtained.

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.

Transport mechanism of eroded sediment particles under freeze-thaw and runoff conditions

Hydraulic erosion associated with seasonal freeze-thaw cycles is one of the most predominant factors,which drives soil stripping and transportation.In this study,indoor simulated meltwater erosion experiments were used to investigate the sorting characteristics and transport mechanism of sediment particles under different freeze-thaw conditions(unfrozen,shallow-thawed,and frozen slopes)and runoff rates(1,2,and 4 L/min).Results showed that the order of sediment particle contents was silt>sand>clay during erosion process on unfrozen,shallow-thawed,and frozen slopes.Compared with original soils,clay and silt were lost,and sand was deposited.On unfrozen and shallow-thawed slopes,the change of runoff rate had a significant impact on the enrichment of clay,silt,and sand particles.In this study,the sediment particles transported in the form of suspension/saltation were 83.58%–86.54%on unfrozen slopes,69.24%–84.89%on shallow-thawed slopes,and 83.75%–87.44%on frozen slopes.Moreover,sediment particles smaller than 0.027 mm were preferentially transported.On shallow-thawed slope,relative contribution percentage of suspension/saltation sediment particles gradually increased with the increase in runoff rate,and an opposite trend occurred on unfrozen and frozen slopes.At the same runoff rate,freeze-thaw process had a significant impact on the relative contribution percentage of sediment particle transport via suspension/saltation and rolling during erosion process.The research results provide an improved transport mechanism under freeze-thaw condition for steep loessal slopes.

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 （ OC4 H9 ） 4 hydrolyzes and three dimensional networks form, in which Ba^2＋ and CH3COO^- are mostly in the form of ions; organic solvent is gradually volatilized through ealefaetion at 700 ℃, then the offspring is turned into BaTi5O11. With the temperature increasing to 850 ℃, BaTi5O11 begins resolving partly and forming BaTi4Og, and at 1000℃ Ba4Ti13O22 forms partly, but BaTi409 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.

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 new classification of seepage control mechanisms in geotechnical engineering

Seepage flow through soils,rocks and geotechnical structures has a great influence on their stabilities and performances,and seepage control is a critical technological issue in engineering practices.The physical mechanisms associated with various engineering measures for seepage control are investigated from a new perspective within the framework of continuum mechanics;and an equation-based classification of seepage control mechanisms is proposed according to their roles in the mathematical models for seepage flow,including control mechanisms by coupled processes,initial states,boundary conditions and hydraulic properties.The effects of each mechanism on seepage control are illustrated with examples in hydroelectric engineering and radioactive waste disposal,and hence the reasonability of classification is demonstrated.Advice on performance assessment and optimization design of the seepage control systems in geotechnical engineering is provided,and the suggested procedure would serve as a useful guidance for cost-effective control of seepage flow in various engineering practices.

Thermal catalysis under dark ambient conditions in environmental remediation:Fundamental principles, development, and challenges

Thermal catalytic degradation of organic pollutants conducted in the dark at room temperature under atmospheric pressure without the need of external chemicals and energy sources has attracted a lot of attention over the last two decades. It provides unparalleled advantages over other advanced oxidation processes (AOPs) in treating domestic and industrial contaminated wastewater from the viewpoint of energy/chemical conservation and ease of operation. Rich knowledge has been accumulated in terms of the synthesis and application of thermal catalysts though controversies remain regarding their underlying mechanisms. This review sheds light on the proposed thermo- catalysis mechanism for the first time and presents the development of thermal catalysts under dark ambient conditions with a focus on catalyst materials, catalytic activity, and mechanism. The present review aims to provide mechanistic insights into the rational design of novel and efficient catalysts, and their underlying mechanisms as well as the emerging challenges and perspectives in thermo-catalysis under dark ambient conditions used for the practical and efficient treatment of contaminated wastewater.

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.

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.

凝固剂及加工条件对豆腐凝胶形成及品质影响研究进展

豆腐的本质是一种蛋白质凝胶体,是大豆蛋白(主要是7S和11S球蛋白)在热处理下发生变性使蛋白质分子结构展开,再通过盐离子、氢离子或酶等凝固剂作用下发生聚集,形成致密均匀且具有网状结构蛋白凝胶。豆腐凝胶的形成及豆腐品质受多种因素的影响。本文从凝固剂种类(盐类、酸类和酶类凝固剂)以及加工条件(加工原料、制浆方法、豆浆体系pH、热处理条件)角度出发,阐明凝固剂及加工条件对豆腐凝胶形成以及品质的影响研究进展。以期为豆腐制品的工业化生产提供理论指导,为豆腐食品的研究开发与品质调控提供科学依据。

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。

基于主动激励的掘进机回转台振动抑制研究

悬臂式掘进机截割过程由于煤岩形状、硬度分布的随机性,当截割到硬岩时截割头会产生无规则的剧烈振动,瞬时高强度的冲击对掘进机关键受力部件回转台影响最大,其动态可靠性和寿命影响着截割效率和截割稳定性,为减弱截割过程回转台的振动,首先,基于截割现场回转台易失效损坏现象,建立截割过程回转台力学模型,推导回转台力学方程,研究回转台受力随截割参数变化规律;通过搭建截割试验台,测试截割过程回转台振动响应,结合有限元进行回转台振动模态分析,求解回转台前6阶固有频率及振型,分析回转台剧烈振动的原因。其次,基于工况路径分析理论,建立截割过程回转台工况传递路径分析模型,模拟回转台合成振动,分析各激励点对回转台振动贡献量及贡献程度,准确找到回转台主要激振源。最后,通过施加外部主动激励的方式,分析不同激励频率加载下回转台振动情况,探寻能够降低截割过程回转台振动的激励频段。试验结果表明:外部激振频率处于20~60 Hz,回转台振动幅值降低明显,此频段激励频率对回转台振动控制效果良好,有益于提高回转台寿命,且激振频率为40 Hz时回转台振动最小,回转台振动抑制效果最佳。研究结果有益于丰富回转台振动相关研究理论,实现在不改变机械结构基础上,降低回转台受力与结构变形,可为掘进机回转台的振动问题提供理论参考。

深部大理岩真三轴力学特性离散元和有限差分耦合分析

为了研究深部大理岩的动态力学特性,首先基于离散元PFC(particle flow code)和有限差分FLAC(fast Lagrangian analysis of continua)耦合法,对大理岩的细观参数进行标定。接着,对三维分离式霍普金森压杆(split Hopkinson pressure bar,SHPB)冲击模拟中的动态应力平衡条件及均匀性假设进行数值验证。最后,对真三轴应力环境下大理岩的应力-应变响应、破碎特征及能量演化机理等问题进行深入分析。结果表明:基于PFC-FLAC耦合理论的真三轴SHPB试验数值结果满足应力均匀性假设,模拟得到的应力-应变曲线与室内试验数据高度一致。峰值应力、峰值应变随着冲击方向上预压(下称“轴向压力”)的增大呈下降趋势。在轴向压力相同时,试样峰值应力增幅随入射应力的提高逐渐变小;当入射应力固定时,轴向压力对试样峰值应力有削弱作用,垂直于冲击方向的侧压则会提升试样的抗压强度。加载过程中声发射事件爆发期整体上发生在应力峰后段,并在此阶段试样内形成较明显的宏观破碎带。在真三轴动态压缩下,大理岩试样主要以拉伸裂纹居多,在总裂纹数中占比超过80%。试样从加载至破坏的过程伴随有能量的变化,达到应力峰值点时试样的应变储能达到极限,之后转化为以耗散能为主、颗粒动能等为辅的能量形式。

案例讨论式教学在力学课程中的探索

在土木工程专业力学课程教学中,探讨了“空手劈砖”案例的不同工况及力学知识。由学生分组开展分析与讨论,形成3种工况,并明确了相应的力学模型。在不同工况下,开展了砖的结构简图、内力分析、影响因素、危险截面、应力分析和动力分析。随着课程的逐步推进,学生逐步运用所学知识开展讨论,并分析了相关的力学现象。分析结果表明,工况3的效果最好,劈砖荷载约为608N,与相关文献吻合。该讨论式案例的引入调动了学生的兴趣,促进学生的思考、讨论、建模、分析和交流总结的能力,提升了课程的教学效果。

融合注意力机制的胶囊网络方面级情感分析

方面级情感分析旨在明确文本中关于特定方面的情感极性。针对句中方面词由复杂词组组成造成方面情感极性判断错误的问题,论文提出了一种融合注意力机制的胶囊网络方面级情感分析模型。模型首先通过双向长短时记忆网络(Bi-directional Long Short-Term Memory,BiLSTM)提取序列语义信息,使用N-gram模型对序列语义信息中的目标方面进行编码,然后利用交互注意力机制学习方面词和上下文之间的注意力,将最终生成的文本表示接入融合方面特征表示的胶囊网络进行分类,得到文本方面级的情感分类结果。模型利用胶囊网络有效提取部分与整体关系特征的能力,融合N-gram模型提取到的方面特征变换矩阵,改进了传统动态路由方法,增强了模型对方面情感极性的判断能力。该模型在SemEval-2014餐馆数据集和笔记本数据集上与多个模型进行了对比分析,实验结果显示该模型在两个数据集上的精确度达到了78.4%和72.4%,F1分数分别为0.687和0.668,证明融合交互注意力机制的胶囊网络模型在方面级情感分析任务方面具有较强的分类效果。

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。

重塑条件对红黏土力学特性影响试验研究

重塑条件是影响重塑土样相关力学特性的重要因素,为分析堤防建设的土工试验中各重塑条件对重塑土力学特性的影响,采用不固结不排水三轴试验研究了不同重塑条件(碎土方式、含水率和制样方式)对重塑红黏土力学特性的影响,并结合扫描电镜图像揭示了相关重塑条件对力学强度特性的影响机理。结果表明:在含水率较低时,影响红黏土重塑样强度的主要因素为制样方式;当含水率升高后,碎土方式成为主要的控制因素;结合微观试验进一步说明不同碎土方式得到不同级配的土粒,机械碎土方式会使得土颗粒集聚成不同数量的“粗颗粒”,改变土粒级配从而影响相关力学特性;不同制样方式导致土颗粒发生不同的有序排列,进而使得土体抗剪强度发生变化。

基于3D卷积视频分析的猪步态评分方法

【目的】猪肢蹄病是种猪淘汰的重要原因之一,给养殖场带来巨大的经济损失。猪蹄疾病判断通常依赖人工肉眼观察猪只步态进行排查,存在效率低、人力成本高等问题。本文旨在实现自动化猪步态评分,高效判断猪只肢蹄健康状况。【方法】本文提出一种“端到端”的猪步态评分方法,在单头种猪经过测定通道时采集视频,并制作四分制步态数据集。采用深度学习技术分析视频,设计了一种基于3D卷积网络的时间注意力模块(Time attention module,TAM),有效提取视频帧图像之间的特征信息。将TAM与残差结构结合,构建猪步态评分模型TA3D,对步态视频进行特征提取与步态分类评分。为进一步提升模型性能并实现自动化处理,本文设计了步态关注模块(Gait focus module,GFM),能够自动从实时视频流中提取有效信息并合成高质量步态视频,在提高模型性能的同时降低计算成本。【结果】试验结果表明,GFM可以实时运行,步态视频大小可以减少90%以上,显著降低存储成本,TA3D模型步态评分准确率达到96.43%。与其他经典的视频分析模型的对比测试结果表明,TA3D的准确率和推理速度均达到最佳水平。【结论】本文提出的方案可应用于猪只步态自动评分,为猪肢蹄病的自动检测提供参考。

违实条件句前件小句语义表征加工机制的ERP研究

本研究采用ERP技术,通过操纵汉语违实条件句和因果条件句前件小句中语义信息与语境信息的一致性,对违实条件句前件小句语义表征加工的时间进程进行了考察。研究发现:1)在句首连词位置,“要是”比“因为”引发了更大的P3a成分和P600成分;2)在前件小句句中动词位置,语境不一致条件引发了更大的P600成分;3)在前件小句句末名词位置,在因果条件句中,语境不一致条件比一致条件诱发了更大的N400成分,而在违实条件句中该效应并未出现。结果表明,读者对汉语违实条件句前件小句中语义表征的加工分为三个阶段:首先,假设连词“要是”作为违实成分,引发了违实语境的建立;之后,读者建构并加工假设表征;最后读者建构起事实表征,并对假设表征和事实表征共同加工。本研究支持并扩展了双重表征理论。

小型集材挂车满载工况下的有限元建模与分析

小型集材挂车于林间作业存在多种工况,包括满载弯曲、满载扭转、紧急制动和急速转弯。为解决挂车在满载工况下车载系统的可靠性与安全性较差的问题,建立小型集材挂车的三维装配模型,进行静态分析。通过有限元分析,研究挂车在4种典型工况下的结构变形和应力分布。研究表明,满载弯曲工况下,最大位移为4.5177 mm,最大应力为115.19 MPa,安全系数为3.08;满载扭转工况下,最大位移为0.98448 mm,最大应力为71.929 MPa,安全系数为4.935;满载制动工况下,最大位移为4.9946 mm,最大应力为120.05 MPa,安全系数为2.957;紧急转弯工况下,最大位移为4.3658 mm,最大应力为104.64 MPa,安全系数为3.39。结果显示研究设计的小型集材挂车在林间作业时满载工况下稳定性较强,确保木材的可靠采集和运输。基于该结果可进一步优化挂车设计和性能,以适应不断变化的需求和环境要求。