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.

Mass‑Spring‑Damping Theory Based Equivalent Mechanical Model for Cylindrical Lithium‑ion Batteries under Mechanical Abuse

An equivalent mechanical model with the equivalent physical meaning of mass-spring-damping is proposed for cylindrical lithium-ion batteries through experiments and theory.The equivalent mechanical model of a cylindrical lithium-ion battery consists of a spring-damping parallel unit.Therefore,a spring-damping parallel unit connecting a damping unit in series is selected to construct the constitutive characteristics of the battery under mechanical abuse.Comparison results show that the equivalent mechanical model can more effectively describe the mechanical properties of the batteries than most cubic fitting models,of which the average relative error of the equivalent mechanical model under different states-of-charge is less than 6.75%.Combined with the proposed equivalent mechanical model,the failure process of the batteries was simulated and analyzed using LS-Dyna and HyperWorks.Under rigid rod tests,failure occurred at the core and bottom of the batteries;under hemispherical punch tests,failure occurred at the core and top,consistent with the experimental results.The average prediction error for the failure displacement under different abuse conditions is less than 4%in the simulations.The equivalent mechanical model requires only a few parameters and can be recognized easily.In the future,the model can be used in safety warning devices based on mechanical penetration.

Refined model analysis of basement rock degradation mechanism of heavy-haul railway tunnel

This study investigated the degradation mechanism of the surrounding rock of a heavy-haul railway under a water-rich condition,based on the construction of the Taihangshan tunnel for the Wari Railway,a heavy-haul railway that used standard construction practices for axle loads of 30 t.Remote monitoring demonstrated that the coupling effect between the dynamic load of a heavy-haul train and the groundwater leads to the deterioration and hollowing of the surrounding rock.This study clarified the void evolution process and deterioration mechanism of the basement rock under the comprehensive influence of the groundwater–train dynamic load using a refined discrete element numerical simulation.The results revealed that the groundwater was the primary influencing factor in the deterioration of the lower part of the heavy-haul railway tunnel.Rock particles were gradually lost under the effects of long-term erosion due to groundwater and heavy-haul trains,which inevitably damaged the basement rock after the construction was completed.Based on this observation,the critical conditions for the deterioration and attenuation law of the physical parameters of the basement rock were obtained.The results of this study can provide ideas and serve as a reference for the forecasting and disaster treatment of basement rock damage in heavy-haul railway tunnels.

Effect of high intensity conditioning on aggregate size of fine sphalerite

High intensity conditioning(HIC)was used as a model to study the fundamental of fine sulphide particle flotation.The effect of impeller design,mechanical energy input,and agitation speed on aggregate size of fine sphalerite was tested.The aggregate size of fine sphalerite was measured with the Malvern Hydro 2000 Mastersizer.The results show that the size of aggregates of sphalerite particles ground for 3 min can be enlarged significantly with the activator and collector addition in HIC using the high energy impeller.The improved particle aggregation by using the high energy impeller is not directly related to a higher energy input into the system.With the same energy input into HIC,the aggregate size obtained with the high energy impeller is much coarser than that obtained with the low energy impeller.With the new impeller in HIC,the sphalerite aggregate size decreases with increasing agitation speed from 700 to 2 500 r/min.However,the recovery does not decrease until the agitation speed reaches 2 500 r/min.

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。

2022年末安徽一次大气重污染过程特征及成因分析

综合利用多源数据,应用HYSPLIT4轨迹分析、颗粒物区域传输分析等方法对2022年末安徽一次大气重污染过程变化特征及成因进行分析。结果表明:污染前期,受弱冷空气影响,有利于污染物输送至安徽地区;污染期间,地面处于弱气压场,混合层厚度较低,存在持续性逆温,且地面风速小、相对湿度较高、基本无降水,不利于污染物的扩散和清除,受区域输送叠加本地污染排放累积共同影响,污染程度加剧;2023年1月2日地面以东北、偏东风为主,风速增大、相对湿度下降、混合层厚度抬升,扩散条件转好,污染程度减轻。在此次污染过程中,山东、江苏、河南对安徽累积的区域输送贡献率占比为48.5%,高于安徽本地污染的贡献率(21.4%)。

基于Copula函数的多站洪水过程随机模拟研究

洪水过程随机模拟能够生成大量与历史洪水统计参数相似且形状各异的洪水过程,而水库群联合防洪调度需要结合流域内各水文站洪水过程统筹洪水资源的调度,实现洪水资源的科学调度,亟需发展多站洪水过程随机模拟方法。鉴于此,提出一种基于Copula函数的多站洪水过程随机模拟方法,该方法先利用二维Copula函数完成主站洪水过程的模拟,然后利用条件混合法构建三维Copula函数,依次模拟其余站的洪水过程。以长江中上游8处水文站为研究对象的结果表明,各站模拟洪水与历史洪水统计参数的相对误差较小,除了北碚和武隆站的最大值外,各水文站统计参数的相对误差在5%左右,能够反映历史洪水过程的统计特征,能够为水利工程防洪规划设计、水库群联合调度及防洪调度风险分析等工作提供支撑作用。

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。

语义和句法双增强的交互式方面级情感分析

针对目前研究存在的语义和句法信息提取不充分以及忽略二者交互的问题,提出一种利用交互注意力机制融合语义和句法信息的方面级情感分析模型。将方面间依赖关系与局部语义融合,获得综合的全局语义信息,将全局与局部信息进行交互得到更深层的语义信息;利用改进的图卷积网络增强模型提取上下文句法信息的能力;使用多头交互注意力完成方面词与上下文之间以及增强语义和句法之间的交互。为验证模型的有效性,在Laptop14、Restaurat14和Twitter基准数据集上进行实验,实验结果表明,所提模型取得的性能优于比较方法。

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。