检索结果-南通市图书馆

Graphene effectively activating "dead" water molecules between manganese dioxide layers in potassium-ion battery

维普期刊数据库评论

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Journal of Energy Chemistry 2024年第6期93卷 306-315,I0008页

作者： Xinhai Wang Wensheng yang Shengshang Lu Shangshu Peng Tong Guo Quan Xie Qingquan Xiao yunjun Ruan Institute of Advanced Optoelectronic Materials and Technology College of Big Data and Information EngineeringGuizhou UniversityGuiyang 550025GuizhouChina

Aqueous potassium-ion batteries(APIBs),recognized as safe and reliable new energy devices,are considered as one of the alternatives to traditional batteries.Layered MnO_(2),serving as the main cathode,exhibits a lower specific capacity in aqueous electrolytes compared to organic systems and operates through a different reaction mechanism.The application of highly conductive graphene may effectively enhance the capacity of APIBs but could complicate the potassium storage environment.In this study,a MnO_(2) cathode pre-intercalated with K~+ions and grown on graphene(KMO@rGO) was developed using the microwave hydrothermal method for APIBs.KMO@rGO achieved a specific capacity of 90 mA h g^(-1) at a current density of 0.1 A g^(-1),maintaining a capacity retention rate of>90% after 5000 cycles at 5 A g^(-1).In-situ and exsitu characterization techniques revealed the energy-storage mechanism of KMO@rGO:layered MnO_(2)traps a large amount of "dead" water molecules during K~+ions removal.However,the introduction of graphene enables these water molecules to escape during K~+ ions insertion at the cathode.The galvanostatic intermittent titration technique and density functional theory confirmed that KMO@rGO has a higher K~+ions migration rate than MnO_(2).Therefore,the capacity of this cathode depends on the interaction between dead water and K~+ions during the energy-storage reaction.The optimal structural alignment between layered MnO_(2) and graphene allows electrons to easily flow into the external circuit.Rapid charge compensation forces numerous low-solvent K~+ions to displace interlayer dead water,enhancing the capacity.This unique reaction mechanism is unprecedented in other aqueous battery studies.

关键词： Graphene K-ion batteries Mn-based layered oxide Water molecules Density functional theory

Adaptive Trajectory Tracking Control for Nonholonomic Wheeled Mobile Robots:A Barrier Function Sliding Mode Approach

在线全文

学校读者我要写书评

暂无评论

IEEE/CAA Journal of Automatica Sinica 2024年第4期11卷 1007-1021页

作者： yunjun Zheng Jinchuan Zheng Ke Shao Han Zhao Hao Xie Hai Wang the School of Mechanical Engineering Hefei University of TechnologyHefei 230009China the School of Science Computing and Engineering TechnologiesSwinburne University of TechnologyHawthorn VIC 3122Australia the School of Civil Aviation Northwestern Polytechnical UniversityXi’an 710072China the Shanghai Aerospace Control Technology Institute Shanghai 201109 the School of Automation Science and Electrical Engineering Beihang UniversityBeijing 100191China the College of Science HealthEngineering and EducationMurdoch UniversityPerth WA6150Australia

The trajectory tracking control performance of nonholonomic wheeled mobile robots(NWMRs)is subject to nonholonomic constraints,system uncertainties,and external disturbances.This paper proposes a barrier function-based adaptive sliding mode control(BFASMC)method to provide high-precision,fast-response performance and robustness for NWMRs.Compared with the conventional adaptive sliding mode control,the proposed control strategy can guarantee that the sliding mode variables converge to a predefined neighborhood of origin with a predefined reaching time independent of the prior knowledge of the uncertainties and disturbances bounds.Another advantage of the proposed algorithm is that the control gains can be adaptively adjusted to follow the disturbances amplitudes thanks to the barrier function.The benefit is that the overestimation of control gain can be eliminated,resulting in chattering reduction.Moreover,a modified barrier function-like control gain is employed to prevent the input saturation problem due to the physical limit of the actuator.The stability analysis and comparative experiments demonstrate that the proposed BFASMC can ensure the prespecified convergence performance of the NWMR system output variables and strong robustness against uncertainties/disturbances.

关键词： Adaptive sliding mode barrier function nonholonomic wheeled mobile robot(NWMR) trajectory tracking control

Numerical studies of undulation control on dynamic stall for reverse flows

在线全文

学校读者我要写书评

暂无评论

Acta Mechanica Sinica 2020年第2期36卷 290-305页

作者： Biao Wang Jian Liu yunjun yang Zhixiang Xiao School of Aerospace Engineering Tsinghua UniversityBeijing 100084China China Aerodynamics Research and Development Center Mianyang 621000China China Academy of Aerospace Aerodynamics Beijing 100074China

The delayed detached-eddy simulation with adaptive coefficient(DDES-AC)method is used to simulate the baseline and leading-edge undulation control of dynamic stall for the reverse flow past a finite-span wing with NACA0012 airfoil.The numerical results of the baseline configuration are compared with available measurements.DDES and DDES-AC perform differently when predicting the primary and secondary dynamic stalls.Overall,DDES-AC performs better owing to the decrease of grey area between the strong shear layer and the fully three-dimensional separated flow.Moreover,the effects of the undulating leading-edge on the forces,lift gradients,and instantaneous flow structures are explored.Compared with the uncontrolled case,the lift gradient in the primary dynamic stall is reduced from 18.4 to 8.5,and the secondary dynamic stall disappears.Therefore,periodic unsteady air-loads are also reduced.Additionally,the control mechanism of the wavy leading edge(WLE)is also investigated by comparison with the straight leading edge(SLE).No sudden breakdown of strong vortices is the main cause for WLE control.

关键词： DDES-AC model Dynamic stall Reverse flow Undulating leading edge Flow control

Magnetic resonance perfusion imaging evaluation in perfusion abnormalities of the cerebellum after supratentorial unilateral hyperacute cerebral infarction

维普期刊数据库评论

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Neural Regeneration Research 2012年第12期7卷 906-911页

作者： Pan Liang yunjun yang Weijian Chen Yuxia Duan Hongqing Wang Xiaotong Wang Department of Radiology First Affiliated Hospital of Wenzhou Medical College Wenzhou 325000 Zhejiang Province China Second Affiliated Hospital of Wenzhou Medical College Wenzhou 325000 Zhejiang Province China

Magnetic resonance imaging （MRI） data of 10 patients with hyperacute cerebral infarction （≤6 hours） were retrospectively analyzed.Six patients exhibited perfusion defects on negative enhancement integral maps,four patients exhibited perfusion differences in pseudo-color on mean time to enhance maps,and three patients exhibited perfusion differences in pseudo-color on time to minimum maps.Dynamic susceptibility contrast-enhanced perfusion weighted imaging revealed a significant increase in region negative enhancement integral in the affected hemisphere of patients with cerebral infarction.The results suggest that dynamic susceptibility contrast-enhanced perfusion weighted imaging can clearly detect perfusion abnormalities in the cerebellum after unilateral hyperacute cerebral infarction.

关键词： magnetic resonance imaging magnetic resonance-perfusion-weighted imaging cerebral infarction cerebral perfusion functional neurological deficit

在线全文

学校读者我要写书评

暂无评论

倾转机翼/旋翼机过渡姿态规划分析

兵器装备工程学报 2024年第1期45卷 20-26,58页

作者：王宗辉杨云军中国航天空气动力技术研究院北京100074 彩虹无人机科技有限公司北京100074

针对带有倾转机翼段的新构型倾转旋翼机复杂的倾转过渡变构型过程,提出一种基于动量叶素理论的高速段倾转走廊边界计算方法。通过低速时机翼失速限制和高速时旋翼可用功率限制建立倾转过渡走廊计算模型,对比了传统构型倾转旋翼机和倾转... 详细信息

针对带有倾转机翼段的新构型倾转旋翼机复杂的倾转过渡变构型过程,提出一种基于动量叶素理论的高速段倾转走廊边界计算方法。通过低速时机翼失速限制和高速时旋翼可用功率限制建立倾转过渡走廊计算模型,对比了传统构型倾转旋翼机和倾转机翼/旋翼机的倾转过渡走廊差别。对2种构型倾转旋翼机倾转过渡状态下前飞速度、机身迎角、旋翼桨距角姿态进行了对比分析。结果表明:带有倾转机翼段的倾转机翼/旋翼机具有更狭窄的倾转走廊,在短舱角0°状态,倾转机翼段占1/3展长的旋翼机相较于传统构型倾转旋翼机,倾转速度边界从39~57 m/s缩减到41.7~51.2 m/s,倾转操纵难度加大;在大于45°短舱角的倾转前期,同样的前飞速度和短舱倾转角状态下,倾转机翼/旋翼机机身迎角降低约2°,旋翼桨距角增大1°~4°,随着倾转过渡的完成,2种构型倾转旋翼机姿态差异逐渐变小。

关键词：倾转旋翼机倾转机翼倾转走廊倾转过渡姿态动量叶素理论

在线全文

学校读者我要写书评

暂无评论

含能热塑性弹性体推进剂研究进展

固体火箭技术 2024年第2期47卷 143-154页

作者：罗运军安梦婧北京理工大学材料学院北京100081 高能量密度材料教育部重点实验室北京100081

含能热塑性弹性体推进剂具有高能量、力学性能优异、可循环利用、可回收等优点,近年来成为固体推进剂发展的重要方向。总结了常见的含能热塑性弹性体的综合性能;论述了含能热塑性弹性体推进剂在高能、高燃速、钝感、低特征信号和富燃料... 详细信息

含能热塑性弹性体推进剂具有高能量、力学性能优异、可循环利用、可回收等优点,近年来成为固体推进剂发展的重要方向。总结了常见的含能热塑性弹性体的综合性能;论述了含能热塑性弹性体推进剂在高能、高燃速、钝感、低特征信号和富燃料推进剂等领域的研究进展;介绍了压延成型、模压成型、螺压成型和熔铸成型四种含能热塑性弹性体推进剂的制备工艺;综述了含能热塑性弹性体推进剂的重复加工性能和回收利用工艺;指出了目前该类推进剂存在的问题和不足,并对其未来发展方向进行了展望。

关键词：热塑性弹性体含能粘合剂固体推进剂制备工艺回收利用

在线全文

学校读者我要写书评

暂无评论

高效叠氮化方法研究进展

高等学校化学学报 2024年第5期45卷 10-27页

作者：龙磊韦伟罗运军李霄羽北京理工大学材料学院北京100081 湖北航天化学技术研究所襄阳441003

有机叠氮化合物是一类多功能化合物,是合成一系列治疗药物、生物活性化合物、功能材料及高能化合物有用的前驱体,被广泛应用于点击化学和Staudinger反应中.在过去的几十年里,研究人员开发了大量的合成策略来制备结构多样的有机叠氮化物... 详细信息

有机叠氮化合物是一类多功能化合物,是合成一系列治疗药物、生物活性化合物、功能材料及高能化合物有用的前驱体,被广泛应用于点击化学和Staudinger反应中.在过去的几十年里,研究人员开发了大量的合成策略来制备结构多样的有机叠氮化物,但不是所有的反应都能高效地进行.随着绿色化学的概念深入人心,安全性低、普适性低和效率低的传统叠氮化方法逐渐被淘汰,发展新的高效叠氮化方法迫在眉睫.本文综合评述了近年来制备脂肪族叠氮化合物及叠氮聚合物的高效合成方法,从碳碳多重键和碳氢键的叠氮化策略方面简述了脂肪族叠氮化物的合成,对叠氮聚合物的合成方法、潜在的新型合成策略进行了概述,并对未来叠氮化学的发展前景进行了展望.

关键词：有机叠氮化合物有机合成脂肪族叠氮化物高能化合物

Apparent diffusion coefficient evaluation for secondary changes in the cerebellum of rats after middle cerebral artery occlusion

在线全文

学校读者我要写书评

暂无评论

Neural Regeneration Research 2013年第31期8卷 2942-2950页

作者： yunjun yang Lingyun Gao Jun Fu Jun Zhang Yuxin Li Bo Yin Weijian Chen Daoying Geng Department of Radiology Huashan Hospital Fudan University Department of Radiology First Affiliated Hospital of Wenzhou Medical University

Supratentorial cerebral infarction can cause functional inhibition of remote regions such as the cerebellum, which may be relevant to diaschisis. This phenomenon is often analyzed using positron emission tomography and single photon emission CT. However, these methods are expensive and radioactive. Thus, the present study quantified the changes of infarction core and remote regions after unilateral middle cerebral artery occlusion using apparent diffusion coefficient values. Diffu- sion-weighted imaging showed that the area of infarction core gradually increased to involve the cerebral cortex with increasing infarction time. Diffusion weighted imaging signals were initially in- creased and then stabilized by 24 hours. With increasing infarction time, the apparent diffusion co- efficient value in the infarction core and remote bilateral cerebellum both gradually decreased, and then slightly increased 3-24 hours after infarction. Apparent diffusion coefficient values at remote regions （cerebellum） varied along with the change of supratentorial infarction core, suggesting that the phenomenon of diaschisis existed at the remote regions. Thus, apparent diffusion coefficient values and diffusion weighted imaging can be used to detect early diaschisis.

关键词： neural regeneration brain injury cerebral ischemia cerebral infarction magnetic resonanceimaging apparent diffusion coefficient middle cerebral artery occlusion diffusion weighted imaging infarction core remote regions diaschisis grants-supported paper neuroregeneration

居民收入差距的主要来源发生转变了吗?——基于城乡二元结构的分解测算

在线全文

学校读者我要写书评

暂无评论

人口与经济 2024年第1期 1-15页

作者：熊云军谢海上海财经大学公共经济与管理学院上海200433 深圳大学中国经济特区研究中心广东深圳518060

如何缩小收入差距,实现人类共同富裕,成为广大学者关注的焦点。在现有研究中,如何测量居民收入差距,是分析收入差距问题的关键。随着越来越多的农村人口进城,居民收入差距的主要来源是否由过去的城乡收入差距发生了转变?鉴于此,通过分... 详细信息

如何缩小收入差距,实现人类共同富裕,成为广大学者关注的焦点。在现有研究中,如何测量居民收入差距,是分析收入差距问题的关键。随着越来越多的农村人口进城,居民收入差距的主要来源是否由过去的城乡收入差距发生了转变?鉴于此,通过分布函数加总的方法,从理论上将基尼系数按照农村与城镇的群组分解,得到基尼系数由农村内部、城镇内部、城乡之间与剩余项四部分组成。利用2005—2021年农村与城镇的收入分组数据测算了每一部分的基尼系数及其对居民收入差距的贡献度,并根据每一部分的贡献度来判断各时期居民收入差距的主要来源。主要结果显示,2012年之前中国居民的收入差距主要来源于城乡之间,而2012年之后的收入差距主要来源于城镇内部,这部分比重正随着城镇人口的增加不断扩大,并且工资性收入的不平等是城镇居民收入差距扩大的主要原因。针对结论提出了相应的政策建议:一方面,政府需要制定缩小工资性收入不平等性的政策,例如,深化工资制度改革,加强对部分行业工资总额和工资水平的双重调控,缩小城镇居民的工资水平差距;另一方面,加强对低收入人群转移性收入的政策性偏向,完善再分配调节机制。

关键词：居民收入差距主要来源基尼系数工资性收入