Effect of Stokes drift on upper ocean mixing

Stokes drift is the main source of vertical vorticity in the ocean mixed layer. In the ways of Coriolis - Stokes forcing and Langmuir circulations, Stokes drift can substantially affect the whole mixed layer. A modified Mellor-Yamada 2. 5 level turbulence closure model is used to parameterize its effect on upper ocean mixing conventionally. Results show that comparing surface heating with wave breaking, Stokes drift plays the most important role in the entire ocean mixed layer, especially in the subsurface layer. As expected, Stokes drift elevates both the dissipation rate and the turbulence energy in the upper ocean mixing. Also, ilffluence of the surface heating, wave breaking and wind speed on Stokes drift is investigated respectively. Research shows that it is significant and important to assessing the Stokes drift into ocean mixed layer studying. The laboratory observations are supporting numerical experiments quantitatively.

Revisiting Effect of Ocean Diapycnal Mixing on Atlantic Meridional Overturning Circulation Recovery in a Freshwater Perturbation Simulation

The effects of ocean density vertical stratification and related ocean mixing on the transient response of the Atlantic meridional overturning circulation （AMOC） are examined in a freshwater perturbation simulation using the Bergen Climate Model （BCM）. The results presented here are based on the model outputs of a previous freshwater experiment： a 300-year control integration （CTRL）, a freshwater integration （FW1） which started after 100 years of running the CTRL with an artificially and continuously threefold increase in the freshwater flux to the Greenland-Iceland-Norwegian （GIN） Seas and the Arctic Ocean throughout the following 150-year simulation. In FW1, the transient response of the AMOC exhibits an initial decreasing of about 6 Sv （1 Sv=106 m3 s^-1） over the first 50-year integration and followed a gradual recovery during the last 100-year integration. Our results show that the vertical density stratification as the crucial property of the interior ocean plays an important role for the transient responses of AMOC by regulating the convective and diapycnal mixings under the enhanced freshwater input to northern high latitudes in BCM in which the ocean diapycnal mixing is stratification-dependent. The possible mechanism is also investigated in this paper.

RESPONSE OF THE OCEAN UPPER MIXED LAYER TO ATMOSPHERIC FORCING

Using a one-dimension Turbulence Kinetic Energy(TKE)mixed layer model based on a simple eddyKinetic energy parameterization of the ocean upper mixed layer,some numerical examinations are intro- duced in this paper.These examination results show that the TKE ocean mixed layer model can respondwell to the effect of atmospheric forcing on the ocean upper mixed layer.The joint effect of wind stressand heat exchange on the ocean upper layer has nonlinear characteristics.The adjustment time of the re-sponse of the ocean upper mixed layer to the atmospheric forcing is about 12 hours in this model.

Model Analysis of Influences of Aerosol Mixing State upon Its Optical Properties in East Asia

The air quality model system RAMS （Regional Atmospheric Modeling System）-CMAQ （Models-3 Com- munity Multi-scale Air Quality） coupled with an aerosol optical/radiative module was applied to investigate the impact of different aerosol mixing states （i.e., externally mixed, half externally and half internally mixed, and internally mixed） oil radiative forcing in East Asia. The simulation results show that the aerosol optical depth （AOD） generally increased when the aerosol mixing state changed from externally mixed to internally mixed, while the single scattering albedo （SSA） decreased. Therefore, the scattering and absorption proper- ties of aerosols can be significantly affected by the change of aerosol mixing states. Comparison of simulated and observed SSAs at five AERONET （Aerosol Robotic Network） sites suggests that SSA could be better estimated by considering aerosol particles to be internally mixed. Model analysis indicates that the impact of aerosol mixing state upon aerosol direct radiative forcing （DRF） is complex. Generally, the cooling effect of aerosols over East Asia are enhanced in the northern part of East Asia （Northern China, Korean peninsula, and the surrounding area of Japan） and are reduced in the southern part of East. Asia （Sichuan Basin and Southeast China） by internal mixing process, and the variation range can reach ＋5 W m 2. The analysis shows that the internal mixing between inorganic salt and dust is likely the main reason that the cooling effect strengthens. Conversely, the internal nfixture of anthropogenic aerosols, including sulfate, nitrate, ammonium, black carbon, and organic carbon, could obviously weaken the cooling effect.

Cyclic testing of moment-shear force interaction in reinforced concrete shear wall substructures

Previous quasi-static cyclic tests of shear walls,which routinely used an incremental lateral displacement test protocol with a constant axial load,failed to reflect the character of moment-shear force interaction of prototype buildings.To study the effect of the moment-shear force interaction on the seismic performance of shear walls,three identical 2-story shear wall specimens with different loading patterns were constructed at 1/2 scale,to represent the lower portion of an 11-story high-rise building,and were tested under reversed cyclic loads.The axial force,shear force and bending moment were simultaneously applied to simulate the effects of gravity loads and earthquake excitations on the prototype.The axial force and bending moment delivered from the upper structure were applied to the top of the specimens by two vertical actuators,and the shear force was applied to the specimens by two horizontal actuators.A mixed force-displacement control test program was adopted to ensure that the bending moment and the lateral shear were increased proportionally.The experimental results show that the moment-shear force interaction had a significant effect on the failure pattern,hysteretic characteristics,ductility and energy dissipation of the specimens.It is recommended that moment-shear force interaction should be considered in the loading condition of RC shear wall substructures cyclic tests.

Further Laboratory Experiments on Aerosol Scavenging in Mixed Clouds to Assess the Role of Phoretic Forces and Particle Solubility

Scavenging experiments have been performed in a cloud chamber inside a cold room with different aerosol particles: Paraffin particles, NaCl particles, Magnesium oxide particles, Carbon particles, Sahara dust particles. Essentially the experimental tests were carried on following the sequence of operations: the generation of the aerosol particles, their injection in the lower part of the cloud chamber, injection of water droplets in the whole chamber volume, nucleation of ice crystals, collection of ice crystals and their examination as for resulting scavenging efficiency. Evidence is given of the peculiar behaviour of soluble particles, individual and eventually inside mixed particles, leading to very much important scavenging efficiency, probably to be ascribed to aerodynamic capture. The evident peculiar behaviour of deliquescent particles can be oriented towards applications to an efficient abatement of specific effluents, on one side, and to weather modification experiments, both rain enhancement and hail prevention experiments.

The influence of explicit tidal forcing in a climate ocean circulation model

The eight main tidal constituents have been implemented in the global ocean general circulation model with approximate 1° horizontal resolution.Compared with the observation data,the patterns of the tidal amplitudes and phases had been simulated fairly well.The responses of mean circulation,temperature and salinity are further investigated in the global sense.When implementing the tidal forcing,wind-driven circulations are reduced,especially those in coastal regions.It is also found that the upper cell transport of the Atlantic meridional overturning circulation（AMOC） reduces significantly,while its deep cell transport is slightly enhanced from 9×106m3/s to 10×106 m3/s.The changes of circulations are all related to the increase of a bottom friction and a vertical viscosity due to the tidal forcing.The temperature and salinity of the model are also significantly affected by the tidal forcing through the enhanced bottom friction,mixing and the changes in mean circulation.The largest changes occur in the coastal regions,where the water is cooled and freshened.In the open ocean,the changes are divided into three layers：cooled and freshened on the surface and below 3 000 m,and warmed and salted in the middle in the open ocean.In the upper two layers,the changes are mainly caused by the enhanced mixing,as warm and salty water sinks and cold and fresh water rises;whereas in the deep layer,the enhancement of the deep overturning circulation accounts for the cold and fresh changes in the deep ocean.

Topography and soil content contribute to plant community composition and structure in subtropical evergreen-deciduous broadleaved mixed forests

Topography and soil factors are known to play crucial roles in the species composition of plant communities in subtropical evergreen-deciduous broadleaved mixed forests.In this study,we used a systematic quantitative approach to classify plant community types in the subtropical forests of Hubei Province(central China),and then quantified the relative contribution of drivers responsible for variation in species composition and diversity.We classified the subtropical forests in the study area into 12 community types.Of these,species diversity indices of three communities were significantly higher than those of others.In each community type,species richness,abundance,basal area and importance values of evergreen and deciduous species were different.In most community types,deciduous species richness was higher than that of evergreen species.Linear regression analysis showed that the dominant factors that affect species composition in each community type are elevation,slope,aspect,soil nitrogen content,and soil phosphorus content.Furthermore,structural equation modeling analysis showed that the majority of variance in species composition of plant communities can be explained by elevation,aspect,soil water content,litterfall,total nitrogen,and total phosphorus.Thus,the major factors that affect evergreen and deciduous species distribution across the 12 community types in subtropical evergreendeciduous broadleaved mixed forests include elevation,slope and aspect,soil total nitrogen content,soil total phosphorus content,soil available nitrogen content and soil available phosphorus content.

Influence of liquid bridge force on physical stability during fuel storage and transportation

The physical stability of solid-liquid fuel is a factor that needs to be considered for fuel product practicability for storage and transportation. To determine the Influence of liquid bridge force on physical stability, two detection devices were designed. The laws obtained from microscopic experiments are used to verify the physical stability of fuel under different component ratios. The liquid bridge force is found to increase with the droplet volume. Multiliquid bridges above one critical saturation can generate significant resultant forces compared to single-liquid bridges of the same volume. There exist four states of solid-liquid mixed fuel with increasing liquid saturation rate. The liquid bridge force between the solid and liquid plays a dominant role in the physical stability of the first three states. There may be two stages involved in the stratification process for state 4 fuel, and the liquid viscosity is another factor that cannot be ignored. In the process of selecting a fuel ratio, a larger liquid bridge force between the components can be obtained by properly improving the wetting effect so that the fuel shows better physical stability.

Hybrid H_2/H_∞ force/position control based on neural networks

A neural network control scheme with mixed H2/H∞performance was proposed for robot force/position control under parameter uncertainties and external disturbances. The mixed H2/H∞tracking performance ensures both robust stability under a prescribed attenuation level for external disturbance and H2optimal tracking. The neural network was introduced to adaptively estimate nonlinear uncertainties, improving the system’s performance under parameter uncertainties as well as obtaining the H2/H∞tracking performance. The simulation shows that the control method performs better even when the system is under large modeling uncertainties and external disturbances.

A Multiphase Mixed Methods Approach to the Internationalization of Higher Education in South Africa:Outline of a Discursive Research Framework

Higher education internationalization(HEI)has become an important priority for global decision makers and education providers.Persuaded by globalization,HEI is a political strategy and economic prospect for countries,governments,and universities to position themselves in global markets.The purpose of this paper is to provide a methodological pathway to develop a dynamic,reformed South African HEI framework based on the transformative drive(i.e.,adjustment of change,learning,shared knowledge,internationalization,globalization an institutionalized memory)of HEI in China.The interpretivist paradigm constitutes the basic research approach.Quantitative and qualitative data will be collected,analyzed,and integrated using a multiphase mixed methods approach.This approach consists of three phases including content analysis(Phase I),in-depth interviews(Phase II),and surveys(Phase III),which answers the focal research question.The significance of this research includes creating a better understanding of South African higher education(HE)policy issues from a transformational perspective,contributing to theory on how internationalization affects HE’s position in economic and social development and broadening knowledge and understanding of the unique circumstances and challenges of HEI in developing countries,particularly in countries seeking to position themselves in the globalized knowledge economy.

混合所有制改革与新质生产力——基于中国上市公司的微观证据

混合所有制改革是促进企业新质生产力发展进而实现企业高质量发展的重要举措。以2013—2020年中国沪深A股非ST类、非金融类上市公司为样本,考察了混合所有制改革对企业新质生产力的影响效应及作用机制。研究发现:①混合所有制改革显著促进了企业新质生产力发展,且经过稳健性检验及内生性检验后,该研究结论仍然成立;②影响机制检验结果表明,混合所有制改革主要通过增强企业融资能力与提升公司治理水平的双重机制促进企业新质生产力发展;③异质性分析结果表明,混合所有制改革对企业新质生产力的促进效应在高竞争程度行业、高数字化程度行业及高创新活跃度行业中更为明显。研究结论为驱动企业新质生产力发展和深化混合所有制改革提供了经验启示。

压缩空气储能地下储气库热力学改进模型研究

【目的】明晰地下储气库的热力学过程是压缩空气储能(compressed air energy storage,CAES)电站安全设计与运行调度的重要基础。【方法】现有地下储气库热力学模型在计算热量交换时,存在高压储气阶段热损失偏大和低压储气库阶段补热过多的不足。本文在全面分析地下储气库热力学模型理论基础合理性的前提下,先分析储气库热量计算偏差的形成根源;再提出改进模型。【结果】研究结果表明:现有的热力学计算解析模型忽略了CAES地下储气库在运行过程中温度分布的不均匀性,这种温度分布的不均匀导致储气室洞壁与压缩空气之间的对流换热模型失真,导致温度计算结果偏差大。考虑混合对流换热的改进模型二可以较好地解决储气阶段温度计算结果与真实结果之间偏差过大的问题。算例分析证明了改进模型二的合理性。【结论】本文的改进模型二可为CAES地下储气库容积优化设计与效率分析提供计算依据。

燃气轮机中心分级燃烧器天然气掺氢燃烧的受迫振荡特性

天然气掺氢燃烧是燃气轮机机组降低碳排放重要措施之一,但掺氢燃料的组分变化会导致燃烧室火焰结构及燃烧稳定性发生变化.为分析中心分级燃烧器掺氢燃烧条件下的燃烧不稳定性问题,通过试验研究了燃烧器入口速度扰动下,不同掺氢比对中心分级掺氢燃烧的瞬态火焰结构、压力以及热释放响应的影响,并利用本征正交分解(POD)法提取了火焰脉动的特征模态,发现其主要包含火焰干涉区强脉动和轴向扰动两种模态.试验结果表明,随着掺氢体积比从0%增大到30%,火焰前沿向上游移动,两级火焰间距缩短,火焰干涉对应的脉动模态的能量占比增大,加强了压力与热释放的耦合,导致燃烧室内的压力响应增大9%,热释放响应增大37%.

“80后”劳动力的失业风险及其影响因素研究

基于中国综合社会调查四期调查数据构建的混合截面数据,文章实证分析了“80后”劳动力的失业风险及其影响因素,并采用变量变换和倾向值匹配(PSM)检验模型估计结果的稳健性。研究发现,相对于全国平均水平而言,“80后”劳动力的失业风险较低且保持稳定态势。有失业风险的“80后”劳动力所占比例平均只有22.0%,不同调查年份所获得的“80后”劳动力失业风险的波动较小。受教育程度、工作经验与技能培训对“80后”劳动力的失业风险均有显著的影响,受教育程度越高、工作经验越多、参加职业技能培训的“80后”劳动力其失业风险越低。“80后”劳动力的失业风险,在性别、年龄、婚姻状况、是否签订劳动合同和是否参加失业保险的群体之间,呈现出显著的异质性特点。基于研究发现,文章提出了针对性政策建议和启示。

单绳缠绕式矿井提升机制动瞬态冲击抑制策略

在矿井提升机的制动控制中,制动瞬态冲击是影响矿井提升机安全可靠运行的关键问题。由于受到技术和经济成本的制约,目前包含贴闸/压紧的制动过程全程采用力闭环控制,这不可避免地导致闸瓦与闸盘刚性接触时的制动力瞬态冲击问题。针对矿井提升机制动瞬态冲击问题,文中提出了一种基于滞回切换原理的混合贴闸/压紧制动控制策略。首先,分别利用非奇异快速终端滑模控制和反步控制设计了贴闸和压紧控制器;其次,为达到快速贴闸的目的,设计了一种基于离散积分器的在线贴闸轨迹再规划方法,有效地减小了制动器贴闸时间;然后,为实现由贴闸控制到压紧控制的安全切换,利用滞回切换原理,制定了混合贴闸/压紧控制稳态切换策略,大大减小了制动力瞬态冲击;最后,为验证提出方法的有效性,选择传统全程力闭环控制策略C1与混合贴闸/压紧直接切换策略C2作为对比方法,在单绳缠绕式提升试验台进行了对比实验,从贴闸时间、制动力最大跟踪误差和提升钢丝绳最大张力3个方面对实验结果进行了分析。实验结果表明:相较于C1控制策略,提出制动控制策略的贴闸时间缩短了64.5%,钢丝绳张力峰值减小了41 N;相较于C2控制策略,提出制动控制策略的制动力冲击减小了90.3%,钢丝绳张力峰值减小了88 N。上述结果表明本文提出的方法能有效改善制动瞬态冲击,减小制动空动时间,提高制动系统安全性,同时本研究也为一类需要混合力/位置控制的电液伺服系统提供了一种有效的解决方法。

基于自抗扰控制的机械臂末端力/位置控制

针对机械臂末端力/位置控制问题,提出一种基于自抗扰控制(ADRC)的间接力/位置混合阻抗控制方案,将间接力/位置混合控制与阻抗控制相结合,在机械臂未与环境接触时采用位置控制,在与环境接触后切换为间接力控制,并体现出阻抗特性。该方案将混合阻抗控制与ADRC相结合,根据机械臂与环境接触时的阻抗模型建立ADRC控制器,并将阻抗参数视为系统总扰动的一部分,利用扩张状态观测器进行估计补偿,实现在无需计算阻抗参数的情况下使间接力/位置混合阻抗控制器在面对扰动时有较好的稳定性和鲁棒性。完成二自由度机械臂模型的仿真,并与传统阻抗控制器进行了比较,结果验证了所提出的基于ADRC的间接力/位置混合阻抗控制方案的有效性。

紫外老化对温拌沥青纳观黏附力及分子量的影响

为探究隔氧/有氧紫外老化对温拌沥青纳观黏附力和分子量的影响,选择3种基质沥青和不同掺量的两种温拌剂制备了不同类型的温拌沥青,进行200 h隔氧紫外老化试验;同时,进行RTFOT、长期压力老化(PAV)试验和不同老化时间的光氧老化试验。在此基础上,对不同老化状态的温拌沥青进行原子力显微镜(AFM)试验和渗透凝胶色谱(GPC)试验。结果表明:隔氧紫外老化下,温拌SK沥青制备的纳观黏附力最大;Evotherm增强了温拌沥青纳观黏附力,而Sasobit中的蜡降低了温拌沥青的纳观黏附力。隔氧紫外老化200 h对温拌沥青的黏附力和分子量影响程度显著大于PAV老化方式的影响程度,紫外老化200 h温拌沥青的纳观黏附力小于PAV老化温拌沥青,而大粒径分子的含量显著大于PAV老化温拌沥青。隔氧与不隔氧紫外老化方式下,温拌沥青纳观黏附力和分子量变化规律相差较大,老化初期,光氧老化对温拌沥青纳观黏附力和分子量影响更为显著;光氧老化后温拌沥青的纳观黏附力和大粒径分子的决定系数为0.896,两者的相关性较好。

软土基坑强制搅拌斜向支撑桩的应用

文中以某基坑工程为例,对软土地区强制搅拌斜向支撑桩的设计及施工进行分析,并对施工效果进行评价。结果表明,上部放坡开挖、下部双排法组合钢管桩结合强制搅拌斜向支撑桩,随着深度的增加,土体水平位移不断降低,基坑最大水平位移11.4mm,各个环节的检测值均未超过预警值,表明强制搅拌斜向支撑桩施工效果良好,有效控制施工过程中的变形。强制搅拌斜向支撑桩经济成本低,施工周期短,具有良好的推广应用价值。

医用防护服粉碎装置设计

为提升粉碎装置对医用防护服混合物的粉碎性能,需对粉碎装置进行优化设计。采用模块化设计与粉碎过程分析的方法,对医用防护服粉碎装置的动刀安装角度与刀架安装布局进行改进设计,使用ADAMS对优化前后的粉碎装置进行仿真模拟。结果表明:将粉碎动刀的安装角度由水平安装提升至与水平方向呈60.8°的夹角后,粉碎装置对医用防护服的剪切力提升了34%;动刀刀架以间隔15°的方式进行布局,刀架工作时所受到的应力由3960 N下降至660 N;对医用防护服混合物剪切时,优化后的单辊式粉碎机刀架布局角速度波动范围由625~820°/s降低至700~800°/s,角加速度无明显波动,振动明显降低。