Johnson-Cook dynamic constitutive relationship for TC16 titanium alloy

The true stress-strain curves of TC16 alloy with a wide range of strain rates were investigated under uniaxial quasi-static tension and uniaxial dynamic compression with the Instron 8032 test machine and the split Hopkinson bar respectively. The results indicate that the true stress increases with increasing strain rate,while decreases with increasing temperature. Under the 105 s-1 high strain rate and temperature higher than 673 K,the true stress would even be less than that under quasi-static condition. A new method incorporating TC16's stress-strain curve developing item was proposed to determine the coefficients in J-C model easily and to avoid the estimation of the adiabatic temperature rising. The Johnson-Cook dynamic constitutive relationship for TC16 was obtained for the first time. Good agreement was obtained between the model prediction and the experimental stress-strain curves for TC16 under both quasi-static and dynamic loadings.

A review of extractive distillation from an azeotropic phenomenon for dynamic control

Extractive distillation is an effective method for separating azeotropic or close boiling point mixtures by adding a third component.Various technologies for performing the extractive distillation process have been explored to protect the environment and save resources.This paper focuses on the improvement of these advanced technologies in recent years.Extractive distillation is retrieved and analyzed from the view of phase equilibrium,selection of solvent in extractive distillation,process design,energy conservation,and dynamic control.The quantitative structure–property relationship used in extractive distillation is discussed,and the future development of extractive distillation is proposed to determine how the solvent affects the relative volatility of the separated mixture.In the steady state design,the relationship between the curvature of the residue curve and parameters of the optimal steady state is also highlighted as another field worthy of further study to simplify the distillation process.

A Train-Bridge Dynamic Interaction Analysis Method and Its Experimental Validation

The train-bridge dynamic interaction problem began with the development of railway technology, and requires an evaluation method for bridge design in order to ensure the safety and stability of the bridge and the running train. This problem is studied using theoretical analysis, numerical simulation, and experimental study. In the train-bridge dynamic interaction system proposed in this paper, the train vehicle model is established by the rigid-body dynamics method, the bridge model is established by the finite element method, and the wheel/rail vertical and lateral interaction are simulated by the corresponding assumption and the Kalker linear creep theory, respectively. Track irregularity, structure deformation, wind load, collision load, structural damage, foundation scouring, and earthquake action are regarded as the excitation for the system. The train-bridge dynamic interaction system is solved by inter-history iteration. A case study of the dynamic response of a CRH380BL high-speed train running through a standard-design bridge in China is discussed. The dynamic responses of the vehicle and of the bridge subsystems are obtained for speeds ranging from 200 km-b-1 to 400 km.h-1, and the vibration mechanism are analyzed.

Experimental investigation on static and dynamic resilient moduli of compacted fine soil

To investigate the static and dynamic resilient modulus of fine soil,and adapting to the new design code and maintenance system of highway subgrade in China,a series of static and dynamic tests were carried out according to the standard laboratory test methods(JTG E40-2007 and JTG D30-2015,respectively).The effects of initial water content,compactness and freeze-thaw cycles on the static and dynamic resilient moduli of fine soil were investigated and analyzed.Experimental test results show that with increasing water content,dry density and freeze-thaw cycles,the static moduli reduces about10.2%~40.0%,14.4%~45.5%,and 24.0%~50.3%,and dynamic moduli reduces about 10.9%~90.8%,2.5%~38.4%,and0.0%~46.0%,respectively.Then,the empirical mathematical relationship between static and dynamic resilient moduli was established under different water content,dry density and freeze-thaw cycles.The investigation results can be used to determine the dynamic modulus of fine soil by widely used static modulus,which could meet the requirement of adopting dynamic modulus index in new specification.

Design and Dynamic Analysis of the Recirculating Planetary Roller Screw Mechanism

The recirculating planetary roller screw mechanism(RPRSM)is a transmission mechanism that engages the screw and nut threaded by multiple grooved rollers.In this paper,frstly,the design method of RPRSM nut threadless area is proposed,and the equations related to the structural parameters of nut threadless area are derived.On this basis,the cross-section design method of roller,screw and nut is constructed according to the actual situation of engagements between the screw/nut and the roller.By adjusting the gap between the two beveled edges and that between the arc and the beveled edge,the accuracy of the thread engagements between the screw/nut and the roller can be improved.Secondly,to ensure the engagements of the screw/nut and the roller,the distance equation from the center surface of the diferent rollers to the end surface of cam ring is given.Thirdly,combined with the working principle and structural composition of RPRSM,the component model is established according to its relevant structural parameters,and the virtual assembly is completed.Finally,the 3D model is imported into the ADAMS simulation software for multi-rigid body dynamics.The dynamic characteristic is analyzed,and the simulated values are compared with the theoretical values.The results show that the contact forces between the screw/nut and the roller are sinusoidal,mainly due to the existence of a small gap between the roller and the carrier.The maximum collision forces between the roller and cam ring are independent from load magnitude.Normally,the collision force between the roller and the carrier increases as the load increases.When RPRSM is in the transmission process,the roller angular speed in nut threadless area begins to appear abruptly,and the position of the maximum change is at the contact between the roller and the convex platform of cam ring.The design of the nut threadless area and the proposed virtual assembly method can provide a theoretical guidance for RPRSM research,as well as a reference for overall performance optimization.

Study on the Dynamic Behavior of Tungsten Alloy at Strain Rates up to 5 000 s^(-1)

The dynamic stress-strain curves of 93% tungsten (W) alloy in the forged state at strain rates up to (5 000 s^(-1)) and in the temperature range from 223 K to 473 K were measured with the split Hopkinson pressure bar (SHPB) technique. Based on the above experimental data a dynamic constitutive equation considering the effects of strain rate, temperature and the special microstructure of such a kind of W-alloy was proposed. The numerical simulation for the experimental process with this constitutive equation was also carried out, the results show that the constitutive relationship constructed in this paper is very satisfactory for representing the dynamic responsive behavior of material..

Dynamic trend analysis on relational effect of environmental protection industry in China

EPI （environmental protection indastry） and three industries constitute aur national economic structuse. By Grey System Theory and correlation effect analytical method for the first time, this paper analyzes the relatioaship degree between environmental protection industry and the three causes including industries involved in China in both qualitative and quantitotive aspects. Both the innate tale and the realistic reasons nf the relational degree are further analyzed by utilizing sastninoble development theory, circulating economy theol., ecological equilibrium theory, externality theory. industrial structure theory, and ecology prinrity rules. From all the analysts, this paper reveals the relationship between EPI and three industries. In addition, it offers suggestions to the feasibility of adjusting the industrial structure and developing the environmental protection industry in our country.

The relationship between attribute performance and customer satisfaction: an interpretable machine learning approach

Understanding the relationship between attribute performance(AP)and customer satisfaction(CS)is crucial for the hospitality industry.However,accurately modeling this relationship remains challenging.To address this issue,we propose an interpretable machine learning-based dynamic asymmetric analysis(IML-DAA)approach that leverages interpretable machine learning(IML)to improve traditional relationship analysis methods.The IML-DAA employs extreme gradient boosting(XGBoost)and SHapley Additive exPlanations(SHAP)to construct relationships and explain the significance of each attribute.Following this,an improved version of penalty-reward contrast analysis(PRCA)is used to classify attributes,whereas asymmetric impact-performance analysis(AIPA)is employed to determine the attribute improvement priority order.A total of 29,724 user ratings in New York City collected from TripAdvisor were investigated.The results suggest that IML-DAA can effectively capture non-linear relationships and that there is a dynamic asymmetric effect between AP and CS,as identified by the dynamic AIPA model.This study enhances our understanding of the relationship between AP and CS and contributes to the literature on the hotel service industry.

Vegetation-Climate Relationship and Its Application in the Division of Vegetation Zone in China

Distribution of vegetation is closely coupled with climate; the climate controls distribution of vegetation and the vegetation type reflects regional climates. To reveal vegetation_climate relationships is the foundation for understanding the vegetation distribution and theoretically serving vegetation regionalization. Vegetation regionalization is a theoretical integration of vegetation studies and provides a base for physiogeographical regionalization as well as agriculture and forestry regionalization. Based on a brief historical overview on studies of vegetation_climate relationships and vegetation regionalization conducted in China, we review the principles, bases and major schemes of previous vegetation regionalization and discuss on several contentious boundaries of vegetation zones in the present paper. We proposed that, under the circumstances that the primary vegetation has been destroyed in most parts of China, the division of vegetation zones/regions should be based on the distribution of primary and its secondary vegetation types and climatic indices that delimit distribution of the vegetation types. This not only reveals the closed relationship between vegetation and climate, but also is feasible practically. Although there still are divergence of views on the name and their boundaries of the several vegetation zones, it is commonly accepted that there are eight major vegetation regions in China, i.e. cold temperate needleleaf forest region, temperate needleleaf and broadleaf mixed forest region, warm temperate deciduous broadleaf forest region, subtropical evergreen broadleaf forest region, tropical monsoon forest and rain forest region, temperate steppe region, temperate desert region, and Qinghai_Xizang (Tibetan) Plateau high_cold vegetation region. Analyzing characteristics of vegetation and climate of major vegetation boundaries, we suggested that: 1) Qinling Mountain_Huaihe River line is an important arid/humid climatic, but not a thermal climatic boundary, and thus can not also be regarded as the northern limit of the subtropical vegetation zone; 2) the northern limit of subtropical vegetation zone in China is along the northern coast of the Yangtze River, from Hangzhou Bay, via Taihu Lake, Xuancheng and Tongling in Anhui Province, through by southern slope of the Dabie Mountains, to Wuhan and its west, coinciding with a warmth index ( WI ) value of 130-140 ℃·month; 3) the tropical region is limited in a very small area in southeastern Hainan Island and southern edge of Taiwan Island; and 4) considering a significant difference in climates between the southern and northern parts of the warm temperate zone, we suggested that the warm temperate zone in China is divided into two vegetation regions, deciduous broadleaf woodland region and deciduous and evergreen broadleaf mixed forest region, the Qinling Mountain_Huaihe River line being as their boundary. We also claimed that the zonal vegetation in North China is deciduous broadleaf woodland. Finally, we emphasized the importance of dynamic vegetation regionalization linked to climate changes.

To What Extent Are Cities Influenced by Rural Urban Relationships in Africa

If rural-urban relationship is treated as an open and unregulated process, cities serve as a sink for rural population, meaning that higher proportions of rural people migrate from rural areas to stay permanently in the cities. This process, which is commonly referred to as rural urban migration can be more evident if the urban system is maintained as an open system. This holds key to interpreting how cities attract and retain their populations, a process that is critical to understand the causes of deterioration of most cities in developing countries that still draw much of their population inputs from rural areas, as it is the case with Africa. Deducing from South African experience, if policies that regulate movement of people between rural areas and cities are politically inclined they tend to give a particular character to the evolution and development of cities. This has been found to be true for two sets of policies implemented inSouth Africa. Ones that were implemented during Apartheid, while they encouraged the migration of unskilled laborers from rural to urban areas, failed to promote settlement and adaptation of African communities in the cities and this led to an upsurge of informal settlements around many cities ofSouth Africa. One that have been implemented since the advent of Democracy, due to their relaxed nature have led to an influx of people of African descent into the city centers and the effect of this has been the deterioration of these areas. With these findings this study cautions that urban system needs to be treated as open, that is, be allowed to regulate itself through economic success and failures of people who aspire to live in urban areas by choosing to settle in the cities.

Seasonal Dynamics of Runoff-Sediment Relationship and Its Controlling Factors in Black Soil Region of Northeast China

以位于东北典型黑土区的黑龙江省乌裕尔河流域中上游为研究区,利用依安站31年的日水沙观测资料,对流域水沙的季节性动态特征进行了分析,对影响水沙关系的自然及人为因素进行了探讨。观测数据表明,7-9月的径流量占全年的64.7%,对本区的产流起主导作用;径流平均含沙量在4月融雪期和6月底到7月中旬明显高于其他时段,含沙量的季节变化与径流的变化明显不同。为描述各影响因素对含沙量变化的贡献,本文通过将含沙量的季节变化与其影响因素的变化进行关联,提出了一种从多因素联合影响中分离出单因素影响的思路,分析表明:冻融作用对裸地的径流含沙量影响剧烈,明显增加土壤侵蚀;在地表有无植被及耕作措施情况下,降雨侵蚀力的增加都将增加径流含沙量;植被的出现可以削弱降雨侵蚀力增大时的增沙效应,但7月降雨侵蚀力的增沙作用超过了作物覆盖的减沙作用。所提方法可方便地用于缺少对比观测实验地区的土地利用和管理措施水保效用评价。

低出生率背景下省域学前教育资源供需关系与动态调配——基于对中部J省人口预测的分析

低出生率背景下研判省域学前教育资源供需关系的变化,对优化学前教育资源配置、实现学前教育优质均衡发展具有指导意义。本研究选择省域学前教育资源配置中低供给高需求类型的中部J省作为研究对象,运用PADIS-INT软件预测分析了J省2023—2035年低、中、高三种方案下城乡在园幼儿人数的变化,调查了J省学前教育人力资源与物力资源供给现状,进而预测分析了J省学前教育资源在供给动态变化与静态不变情况下的供需关系。结果发现,随着在园幼儿人数减少,学前教育资源需求将明显减少;现有人力资源供给存在结构性短缺,未来会出现城乡配置失衡;物力资源配备已达到高水平,未来会严重过剩。根据研究结果,建议地方政府根据资源供需关系的动态变化做好学前教育长期规划,控增量、调存量、疏余量;从结构与质量入手优化人力资源配置,稳定乡村教师队伍;谨慎增加办园条件投入,采用多种形式提升物力资源使用效益。

数字金融与区域经济发展的耦合协调性测度及其动态演进

以中国八大综合经济区为例,运用耦合协调度模型分析数字金融对区域经济发展的耦合协调关系,并基于Dagum基尼系数与Kernel核密度揭示数字金融与区域经济发展之间协调关系的地区差异及动态演进规律。结果表明:八大综合经济区的经济发展水平总体呈现稳定增长态势,具有“东高西低”阶梯形的异质性和阶段性特征;数字金融与区域经济发展之间协调发展水平逐年提升,八大综合经济区普遍由失调阶段跨入协调阶段;数字金融与区域经济发展之间协调关系存在明显的地区差异,沿海经济区的协调水平明显高于内陆经济区,但地区间协调程度的差距呈现逐渐缩小的演进态势。

浮动基多机悬吊系统动力耦合响应分析

为了研究浮动基多机悬吊系统在不规则波作用下的动力耦合关系,首先利用动量定理和动量矩定理建立了浮动基机器人动力学模型,其次利用达朗贝尔原理建立了悬吊系统的动力学模型,并提出了系统动力学的耦合关系分析步骤;最后结合实例,仿真分析了浮动基多机器人协调悬吊系统在不同波高、不同波长比和不同起吊速度下动力耦合响应过程。结果表明,该系统的理论研究进行了补充和完善,同时也为浮动基多机悬吊系统在实际的吊运过程中,判断安全的吊运环境提供技术支撑。

循环荷载下渭北地区黄土动力特性分析

为研究渭北地区的黄土动力学特性分析,通过TYS-20型土动三轴试验机,研究不同围压下黄土的动本构关系以及动骨干曲线,分析黄土的动剪模量比和阻尼比的关系,提出动剪切模量衰减模型和阻尼增长模型;研究不同围压对黄土动强度和残余应变的影响,从理论上解释黄土动力特性变化的原因,从而更好地保证黄土震陷对地下空间影响最小化;最后对比黄土震前震后微结构,并进行机理分析对该地区地下空间发展提供理论意义.研究结果显示:黄土的动本构关系符合双曲线模型;动剪模量比随动剪应变呈负指数衰减关系,而阻尼比随动剪应变呈对数关系增长;动强度和动强度指标受试验条件的影响较大,其中动强度随围压的增大而增大,表明动强度分析能较好地说明黄土的动力特性变化规律;根据电子显微镜对比土体震前震后微结构,并进行机理分析,为该地区地下空间发展提供理论支持.通过研究表明,渭北地区黄土在循环荷载作用下不易产生振动变形,属于轻微震陷区.

生育水平与女性劳动参与率的动态关系研究

生育水平变动会影响未来劳动年龄人口供给,但生育水平与女性劳动参与率的相关性研究结论尚有争议。基于我国1970—2021年生育率水平和女性劳动参与率时间序列数据,通过平稳性检验、协整检验以及格兰杰因果检验后,建立向量自回归(VAR)模型对两者之间的变动关系进行实证分析和检验,从宏观角度揭示生育水平变动与女性劳动参与率变化的动态关联性。研究发现,我国生育水平与女性劳动参与率的相关性由1979—1990年的负相关转变为1991—2021年的正相关,生育水平与女性劳动参与率存在长期稳定的均衡关系,总和生育率与女性劳动参与率已总体呈现出一定的格兰杰因果关系;1991—2021年我国总和生育率与女性劳动参与率的互动响应关系显著,女性劳动参与率变动对总和生育率变动的冲击影响呈现滞后性,且影响程度没有总和生育率对女性劳动参与率的冲击影响大。因此,在生育政策调整背景下,我国应充分重视生育水平与女性劳动参与率的互动影响和冲击响应关系,有效保障女性生育和劳动权益,推进性别平等的生育支持体系建设,在提振社会生育水平的同时稳定女性劳动参与率。

岩石爆破基础理论研究进展与展望Ⅱ—动静关系

炸药爆炸做功与岩体破碎耗能的耦合作用机理、炸药能量释放与爆炸裂纹扩展的精细控制原理,是岩石爆破基础理论需要解决的两个关键科学问题;“动静关系”研究是解决关键科学问题的重要途径之一.本文采用文献综述分析方法对2000年—2023年期间在中国知网数据库(CNKI)和科学引文索引数据库(WOS)收录的期刊论文进行了主题检索和分析,将岩石爆破“动静关系”研究划分为三个不同阶段:第Ⅰ阶段(2006年之前)、第Ⅱ阶段(2007年—2015年)和第Ⅲ阶段(2016年至今).确定了对“动静关系”研究有重要贡献的作者和研究机构,揭示了关键词及其共现关系,突出了研究的重点和趋势.通过对已有研究的系统梳理,结合作者团队已经开展的研究工作和成果,明确了新时期“动静关系”的研究方向,即爆炸应力波与爆生气体的动静能量分布与高效利用、考虑岩石爆破破裂真实物理过程的数值模拟算法、爆炸应力波与爆生气体动静破岩效果的量化调控.“动静关系”的深入研究将推动爆破工程从“经验主导”走向“理论指导”,从“粗放式”走向“精细化”.

水平作用下古建筑木柱受力性能影响因素分析

由于柱脚的平摆浮搁布置,古建筑木柱在水平作用下的受力性能对整体结构的抗震性能具有重要影响.为探究水平作用下古建筑木柱受力性能的影响因素,基于木柱在水平作用下的力学模型,从静力和动力两个方面,分别讨论弹性模量、高径比、轴压比、圆频率和加速度幅值等因素对木柱受力性能的影响.结果表明:在静态下,古建筑木柱的受力行为由柱脚节点的受力性能体现.更大的弹性模量、更小的高径比和更高的轴压比能够增加柱脚节点的刚度和恢复力矩,使木柱保持稳定.在动态下,木柱的动力响应表现为滑移和倾斜.相比于水平作用的振幅,频率对木柱的动力响应影响更大.柱脚的滑移量有限,木结构的倒塌更大来自于木柱的倾斜角度过大.该研究成果可为古建筑木柱的抗震加固提供理论支撑.

动态化学交联聚烯烃类弹性体研究进展

聚烯烃类弹性体是由乙烯与丙烯或其他高碳α-烯烃共聚而成的高端聚烯烃材料,具有出色的化学稳定性、耐候性和电绝缘性,广泛应用于光伏、汽车、电缆等领域。通过动态化学交联可在保证其加工性的前提下,进一步提高其力学性能与热稳定性,拓展应用范围。综述了动态化学交联聚烯烃弹性体的制备工艺,包括一步法直接交联和功能化后再交联(多步法)。详细介绍了后功能化、乙烯与功能化单体共聚等功能化方法。讨论了动态化学交联聚烯烃类弹性体的表征手段及其链结构、聚集态结构和性能之间的关系。展望了动态交联聚烯烃类弹性体的未来发展。为动态化学交联聚烯烃类弹性体的可控制备、构效关系研究以及高值应用提供理论指导与技术支持,推动高端聚烯烃材料的创新和发展。