An elasto-plastic constitutive model for soft rock considering mobilization of strength

A new elasto-plastic constitutive model is presented in the framework of plasticity theory. The strength characteristics of a diatomaceous soft rock is investigated. The friction angle and cohesion of soft rock are mobilized as a function of plastic strain. A hyperbolic hardening function for the mobilized friction and a mixed parabolic and exponential equation for the mobilized cohesion are proposed. In view of the unified strength theory and the mobilizations of strength components, a yield function is given. A plastic potential function is determined by using the non-associated plastic flow rule. An elasto-plastic constitutive model is developed and verified. The results indicate that the proposed model can predict the behavior of soft rock accurately. The advantages of the proposed constitutive model are analyzed. The evidences support that the proposed constitutive model is a mixed hardening/softening model. A hump hardening/softening function for mobilized friction is extended to a more generalized condition.

Inverted Modelling:An Effective Way to Support Motion Planning of Legged Mobile Robots

This paper presents an effective way to support motion planning of legged mobile robots—Inverted Modelling,based on the equivalent metamorphic mechanism concept.The difference from the previous research is that we herein invert the equivalent parallel mechanism.Assuming the leg mechanisms are hybrid links,the body of robot being considered as fixed platform,and ground as moving platform.The motion performance is transformed and measured in the body frame.Terrain and joint limits are used as input parameters to the model,resulting in the representation which is independent of terrains and particular poses in Inverted Modelling.Hence,it can universally be applied to any kind of legged robots as global motion performance framework.Several performance measurements using Inverted Modelling are presented and used in motion performance evaluation.According to the requirements of actual work like motion continuity and stability,motion planning of legged robot can be achieved using different measurements on different terrains.Two cases studies present the simulations of quadruped and hexapod robots walking on rugged roads.The results verify the correctness and effectiveness of the proposed method.

General mapping of one-dimensional non-Hermitian mosaic models to non-mosaic counterparts:Mobility edges and Lyapunov exponents

We establish a general mapping from one-dimensional non-Hermitian mosaic models to their non-mosaic counterparts.This mapping can give rise to mobility edges and even Lyapunov exponents in the mosaic models if critical points of localization or Lyapunov exponents of localized states in the corresponding non-mosaic models have already been analytically solved.To demonstrate the validity of this mapping,we apply it to two non-Hermitian localization models:an Aubry-Andre-like model with nonreciprocal hopping and complex quasiperiodic potentials,and the Ganeshan-Pixley-Das Sarma model with nonreciprocal hopping.We successfully obtain the mobility edges and Lyapunov exponents in their mosaic models.This general mapping may catalyze further studies on mobility edges,Lyapunov exponents,and other significant quantities pertaining to localization in non-Hermitian mosaic models.

Mobility edges in one-dimensional finite-sized models with large quasi-periodic disorders

We study the one-dimensional tight-binding model with quasi-periodic disorders,where the quasi-period is tuned to be large compared to the system size.It is found that this type of model with large quasi-periodic disorders can also support the mobility edges,which is very similar to the models with slowly varying quasi-periodic disorders.The energy-matching method is employed to determine the locations of mobility edges in both types of models.These results of mobility edges are verified by numerical calculations in various examples.We also provide qualitative arguments to support the fact that large quasi-periodic disorders will lead to the existence of mobility edges.

Analytical model of non-uniform charge distribution within the gated region of GaN HEMTs

A physics-based analytical expression that predicts the charge,electrical field and potential distributions along the gated region of the GaN HEMT channel has been developed.Unlike the gradual channel approximation(GCA),the proposed model considers the non-uniform variation of the concentration under the gated region as a function of terminal applied volt-ages.In addition,the model can capture the influence of mobility and channel temperature on the charge distribution trend.The comparison with the hydrodynamic(HD)numerical simulation showed a high agreement of the proposed model with numerical data for different bias conditions considering the self-heating and quantization of the electron concentration.The ana-lytical nature of the model allows us to reduce the computational and time cost of the simulation.Also,it can be used as a core expression to develop a complete physics-based transistorⅣmodel without GCA limitation.

Quantitative evaluation model of shale oil adsorption:A case study of the first member of Cretaceous Qingshankou Formation in northern Songliao Basin,NE China

A quantitative evaluation model that integrates kerogen adsorption and clay pore adsorption of shale oil was proposed,and the evaluation charts of adsorption-swelling capacity of kerogen(Mk)and adsorbed oil capacity of clay minerals(Mc)were established,taking the 1st member of Cretaceous Qingshankou Formation in the northern Songliao Basin as an example.The model and charts were derived from swelling oil experiments performed on naturally evolved kerogens and adsorbed oil experiments on clays(separated from shale core samples).They were constructed on the basis of clarifying the control law of kerogen maturity evolution on its adsorption-swelling capacity,and considering the effect of both the clay pore surface area that occupied by adsorbed oil and formation temperature.The results are obtained in four aspects:(1)For the Qing 1 Member shale,with the increase of maturity,Mk decreases.Given Ro of 0.83%–1.65%,Mk is about 50–250 mg/g.(2)The clay in shale adsorbs asphaltene.Mc is 0.63 mg/m^(2),and about 15%of the clay pore surface is occupied by adsorbed oil.(3)In the low to medium maturity stages,the shale oil adsorption is controlled by organic matter.When Ro>1.3%,the shale oil adsorption capacity is contributed by clay pores.(4)The oil adsorption capacity evaluated on the surface at room temperature is 8%–22%(avg.15%)higher than that is held in the formations.The proposed evaluation model reveals the occurrence mechanisms of shale oils with different maturities,and provides a new insight for estimating the reserves of shale oil under formation temperature conditions.

ILSM:Incorporated Lightweight Security Model for Improving QOS in WSN

In the network field,Wireless Sensor Networks(WSN)contain prolonged attention due to afresh augmentations.Industries like health care,traffic,defense,and many more systems espoused the WSN.These networks contain tiny sensor nodes containing embedded processors,TinyOS,memory,and power source.Sensor nodes are responsible for forwarding the data packets.To manage all these components,there is a need to select appropriate parameters which control the quality of service of WSN.Multiple sensor nodes are involved in transmitting vital information,and there is a need for secure and efficient routing to reach the quality of service.But due to the high cost of the network,WSN components have limited resources to manage the network.There is a need to design a lightweight solution that ensures the quality of service in WSN.In this given manner,this study provides the quality of services in a wireless sensor network with a security mechanism.An incorporated hybrid lightweight security model is designed in which random waypoint mobility(RWM)model and grey wolf optimization(GWO)is used to enhance service quality and maintain security with efficient routing.MATLAB version 16 andNetwork Stimulator 2.35(NS2.35)are used in this research to evaluate the results.The overall cost factor is reduced at 60%without the optimization technique and 90.90%reduced by using the optimization technique,which is assessed by calculating the signal-to-noise ratio,overall energy nodes,and communication overhead.

“低技能排斥”下的劳动力跨地区流动——产出效应与收入分配

在中国劳动力跨地区流动过程中,地方政府针对不同技能的劳动力制定了差异化的就业政策,不少地区基于缓解公共服务供需矛盾等方面的考虑,对低技能劳动力采取了排斥的态度。本文在量化空间一般均衡模型框架下刻画了高、低技能劳动力差异化的流动特征,使用2005年、2015年全国人口抽样调查微观数据,定量分析了“低技能排斥”下劳动力跨地区流动对收入分配的影响及产出效应。研究发现,第一,与高技能劳动力相比,低技能劳动力流动所面临的阻碍更大,使得低技能劳动力跨地区流动成本高于高技能劳动力。第二,“低技能排斥”下的劳动力跨地区流动,一定程度上抑制了高、低技能劳动力之间的技能互补,造成GDP损失。第三,全面破除“低技能排斥”,充分发挥高、低技能劳动力之间的技能互补性,将显著缩小地区之间劳动力的收入差距。因此,打破劳动力跨地区流动中的技能歧视,引导高、低技能劳动力畅通有序流动,优化劳动力配置效率的同时还有助于共同富裕战略目标的实现。

中国人口流动的健康轨迹研究

人口的高流动性和流动人口快速老化已成为中国人口发展的显著特征。研究人口流动对我国城乡居民健康的影响及其变动趋势,对于理解和实现健康老龄化,改善人口健康水平具有重要意义。现有研究较多分析流动人口相比于城镇居民的健康状况,而对流动人口和农村居民的健康差异的研究相对缺乏;对于流动人口在老年阶段的健康状况与户籍人口的差异以及流动对人口健康的影响等关键问题尚没有确定结论。本文旨在探讨人口流动与个体健康的因果关系以及流动人口和城乡户籍人口之间随时间和年龄变化的健康差异。本文利用中国家庭动态追踪调查(CFPS)2010-2020年连续六次调查的面板数据,采用固定效应模型和线性回归模型分析人口流动的健康效应和年龄效应。研究发现2012-2020年流动对人口健康的总体影响为负,验证了流动具有健康损耗效应,存在“流行病学悖论”。从时期维度看,流动对人口健康的影响呈现由健康优势转为健康劣势的趋势,人口流动的健康选择效应和流动经历的内在健康损耗效应并存。初期流动人口具有健康优势,健康自评状况优于城乡户籍人口。随着时间推进,健康优势逐渐收敛,健康损耗效应逐渐显现。从年龄维度看,流动人口和城乡户籍人口的自评健康水平随着年龄增加都呈下降趋势,但流动人口的下降速度显著慢于城乡户籍人口,其健康优势在老年阶段逐渐消失。上述发现的政策含义是:在人口老龄化不断加深和流动人口规模保持高位,流动人口老化愈加明显的背景下,流动人口的健康老龄化成为重要挑战,在政策实践层面应关注流动经历对个体生命周期的持续影响,尤其是要重视城镇中的高龄流动人口返乡回流将健康风险转移到农村,从而增加农村整体的健康脆弱性和健康照护成本,应将人口流动因素作为优化城乡卫生健康资源配置的重要考量。

MaaS模式下城市路网异质出行者逐日流量分配模型

为研究出行即服务(MaaS)模式下的城市路网异质用户逐日路径选择行为和路网流量分配演变规律,将出行者分为选择MaaS服务的平台用户和自主决策的自由用户。建立了两类用户总量的逐日调整模型、自由用户的逐日选择模型及平台用户的系统最优分配模型,并利用不动点理论分析了模型稳定性。算例结果表明:若流量转移函数连续,则模型存在不动点,路径流量能收敛到稳定状态;异质用户路网能降低总出行时间,但达到稳态所需时间更长;高比例的平台用户路网总出行时间更小,更有利于路网优化;提升路网出行服务水平可以使路网稳定在最优态。

人体组织液特性对SAR值的影响及修正模型

比吸收率(specific absorption ratio,SAR)值测量所使用的组织液特性与规范标准中给出的组织液目标值会有一定偏差。此时,需要对SAR值的测量结果进行修正。针对此问题,提出了一种修正模型,修正模型基于电磁仿真的方法建立。通过在835 MHz频点与IEC 62209\IEEE 1528标准中的数据进行比较,对建模方法进行了验证。基于此建模方法,给出了3.5 GHz及28 GHz这2个下一代移动通信备选频段下的SAR值修正模型。使用此修正模型将减小SAR值测量的不确定度,进而提升各测量实验室间SAR符合性评定结果的一致性。使用此修正模型的另一个好处在于,该修正模型允许更大的组织液特性偏差,这将有助于降低SAR值测量的成本。

论中国共产党思想政治教育的四大模式

思想政治教育是中国共产党的优良传统和政治优势。百余年来,中国共产党思想政治教育围绕党和国家不同历史时期的中心任务和发展大局,综合运用社会动员、典型示范、文化育人和治理嵌入等模式服务国家、社会和人民,推动思想政治教育不断深化发展。具体来看,党和国家运用社会动员模式,在引导广泛参与中推动思想政治教育社会化;运用典型示范模式,在注重榜样引领中推动思想政治教育具象化;通过文化育人模式,在坚持成风化人中推动思想政治教育沉浸化;通过治理嵌入模式,在始终服务大局中推动思想政治教育制度化。

基于ROS-Matlab的移动机器人仿真研究

结合Linux下ROS系统高性能的仿真工具和跨平台兼容性,以及Matlab强大的计算能力、丰富的工具箱和函数库,通过建立ROS-Matlab的仿真控制系统,对移动机器人的关键技术进行研究。文中介绍了ROS-Matlab系统的框架和功能,首先,使用Gazebo构建2D仿真室内环境,通过Solidworks创建移动机器人模型,并将该模型以URDF文件形式导入ROS环境中;其次,利用SLAM_gmapping算法对仿真室内环境进行扫描建图,由Simulink发布目标点坐标和目标点导航话题,控制移动机器人完成导航任务;最后,由Simulink发布轨迹跟踪话题,控制移动机器人进行轨迹跟踪。通过仿真验证,由所建地图、目标点导航和轨迹跟踪曲线说明仿真系统的可行性,为机器人研究提供参考。

空空高速移动通信信号的频偏估计和跟踪算法

空空高速移动场景下飞行平台通信信号的多普勒频率范围大且变化快。针对现有频偏估计和跟踪算法难以兼顾估计精度和工程可实现性的难题,提出了低复杂度的新型高精度频偏估计和跟踪算法。首先根据空空高速移动场景下多普勒频率快速变化且具有时空相关性特征,在传统频偏模型的基础上构建适用于空空高速移动场景的时变频偏模型;然后基于此模型将相邻短前导的频偏估计值进行相互关联并处理,将频偏精度优化问题转化为经典的超定线性方程组的优化求解问题,最大限度地抑制了估计噪声,提高了频偏估计精度。仿真结果表明,该算法估计的残余频偏相对于经典算法大幅降低,当信噪比大于5 dB时,残余频偏的均方根误差控制在100 Hz范围内。针对该算法求解过程中存在的数值稳定性问题,给出了相应的工程可实现方法。该算法采用前馈补偿频偏跟踪方法,与传统的锁相环反馈跟踪方法相比,提高了系统的稳定性和时效性。

基于环境中移动运输代理的传感器网络建模

针对大型稀疏传感器网络中的数据获取,本文提出了一种利用环境中普遍存在的移动代理来连接稀疏传感器的网络体系结构和一种2-维网格随机游走分析模型;提出的传感器网络模型由3个抽象层构成,即由无线传感器构成的底层、由各种运输代理构成的中间层和由接入点/中央存储库构成的顶层。具体实现原理是位于中间层的移动运输代理从底层分布的无线传感器收集数据并缓冲数据,然后经过游走运输,最后将从底层的无线传感器收集的数据交付到顶层必要的接入点进行必要的存储和处理,从而实现整个传感器网络的数据获取;理论分析和仿真实验结果表明,提出的基于移动运输代理的传感器网络模型不仅具有较好的鲁棒性和可扩展性,而且相比于基站网络模型和Ad-hoc网络模型,在传感器功率消耗、数据成功率和基础设施投入成本方面有明显的优势。

基于喷泉码信息差异分簇的V2V协作数据分发方案

新兴车联网应用需要分发的数据量不断增加,车辆难以在一个RSU通信范围内收到完整数据,跨RSU通信完成率低,时效性差。针对此问题,提出一种基于喷泉码信息差异分簇的V2V协作数据分发方案。经过喷泉编码的数据由RSU广播;车辆通过XGBoots预测车速,以此计算V2V链路生存时间;链路可靠性和车辆的喷泉码信息差异构建引力模型来分簇,在簇内以V2V传输共享编码包,在保证完成率的前提下大幅降低数据分发延迟。仿真结果表明,与已有方案ECDS相比,对于不同大小的数据,该方案在保证完成率的基础上,平均时延降低了38%。

基于数学模型的造纸机水针移动控制系统优化研究

为有效应对造纸机水针移动惯性所造成的定位偏差,确保水针精准且快速移动,以拟合优化方法构建了造纸机水针移动控制数学模型。采取变速双控制中性区方法,以反复测试寻找控制中性区数值的合理范围,并针对性建立水针移动与中性区数值的数学模型,以求解控制中性区数值。实际应用验证结果表明,变速双控制中性区方法的引进使造纸机水针移动曲线变化趋向于平缓,且终止位置与设定位置误差控制于0.79%,精确度非常高;相比传统变速单控制中性区方法,水针移动响应时间缩短了25s。

中国与OECD国家留学生流动网络的空间格局与影响机制

构建和推动高质量人才环流是中国国际人才培养和人才磁石型国家建设的重要途径。本文基于2019年中国与38个经济合作与发展组织(OECD)成员国之间高等学校留学生流动数据,构建有向加权的国际人才流动网络,并运用社会网络分析探讨国际人才流动的空间格局与影响机制。结果显示:① 39个国家之间留学生交流密切,区域组团明显,形成北美亚太组团、南美欧洲组团、北欧波罗的海组团、捷克斯洛伐克组团。中国和美国是国际人才交流的中心,同时中国、英国、德国、美国、法国也是人才流动的门户与枢纽。②各国家在输出和接收留学生上存在非对称性。中国留学生流出量占总网络的近50%,而OECD各国输出量相对均衡。美国、英国、澳大利亚成为留学生流入量排名前3,中国以7.17%的占比居第四。③国家的开放程度、教育质量、经济水平对留学生流动的影响均存在发送者效应和接收者效应,地理、语言文化、贸易方面的邻近可促进留学生流动。结构依赖是留学生流动的重要驱动力,其中互惠效应、择优依附效应与传递闭合效应最为显著,对于外生动力具有一定的替代性。中国与OECD国家间的人才联系仍有较大的提升空间,需从个体属性、多维邻近性和结构内生性方面进行优化,促进区域内人才更加扁平化多元化交流发展。

教育机会公平对劳动力流入地选择的影响--基于代际流动视角

利用中国劳动力动态调查数据构造城市层面的教育机会公平衡量指标,并结合中国流动人口动态调查以及相关城市特征数据,采用条件Logit模型探讨了教育机会公平如何影响劳动力的流动决策。研究发现,不同城市间教育机会公平的差异是影响劳动力流入地选择的重要因素。具体而言,劳动力倾向于流入教育机会公平程度高的城市,但这一偏好会随着城市落户门槛的提高而减弱。进一步分析表明,教育机会公平对劳动力的吸引作用存在明显的个体特征异质性,高教育水平、新生代、具有正规就业身份和已婚的劳动力群体更看重地区教育机会公平程度。文章结论对如何引导劳动力合理有序流动、优化地区人力资本配置有重要的参考意义。

中国劳动力流动对城乡融合发展影响的异质性研究

文章通过构建中国劳动力、城市部门与农村部门的演化博弈模型,探讨劳动力流动对城乡融合发展影响的内在机理,并基于2002-2020年中国31个省级面板数据,考察劳动力流动与城乡融合发展演进的特征事实,实证分析劳动力流动对城乡融合发展影响的效应及其时空异质性。研究发现:城乡融合发展水平与劳动力流动水平均稳步上升,且均存在地区差异;就全国层面而言,劳动力流动对城乡融合发展具有显著的促进作用;在时间维度上,劳动力流动对城乡融合发展的边际影响逐渐降低;在空间维度上,劳动力流动对城乡融合发展的影响在东部地区更为显著。因此,提高劳动力的区际流动水平,着重解决劳动力要素区域错配问题,是提高城乡融合发展水平的关键举措。