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耕地细碎化对粮食生产技术效率的非线性影响研究——基于农户兼业的中介效应分析

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中国农业资源与区划 2024年第2期45卷 38-48页

作者：申淑虹牛文浩李贤靳亚亚张蚌蚌西北农林科技大学经济管理学院陕西杨凌712100

[目的]理清耕地细碎化对粮食生产技术效率的非线性影响及其作用机制,对提高粮食产量、保障中国粮食安全具有重要意义。[方法]文章基于陕西省603户农户的实地调研数据,运用数据包络分析模型(DEA)测算了农户粮食生产技术效率,借助Tobit模... 详细信息

[目的]理清耕地细碎化对粮食生产技术效率的非线性影响及其作用机制,对提高粮食产量、保障中国粮食安全具有重要意义。[方法]文章基于陕西省603户农户的实地调研数据,运用数据包络分析模型(DEA)测算了农户粮食生产技术效率,借助Tobit模型分析了耕地细碎化对粮食生产技术效率的非线性影响,并进一步运用中介效应模型探讨了农户兼业在其中的中介作用。[结果](1)调研地区全体农户的平均粮食生产技术效率值偏低且分化严重;(2)耕地细碎化对粮食生产技术效率影响呈现弱显著的倒U型关系;(3)农户兼业程度对粮食生产技术效率影响的总效应呈现显著的U型关系;(4)农户兼业在耕地细碎化对粮食生产技术效率的影响中发挥了部分中介效应。[结论](1)多管齐下解决耕地细碎化问题,推行适度规模经营;(2)依托个体农户特征差异,针对性引导农户职业合理分化。

关键词：耕地细碎化农户兼业生产技术效率 DEA-Tobit模型中介效应

城市化背景下粤港澳大湾区生态风险时空演变及生态分区识别研究

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环境工程技术学报 2024年第2期14卷 562-573页

作者：李超牛文浩黄怀玉姚顺波龚直文西北农林科技大学经济管理学院西北农林科技大学资源经济与环境管理研究中心

为揭示粤港澳大湾区城市群30年间土地利用类型转移变化规律,基于1990—2020年共4期Landsat遥感影像,分析研究区生态系统服务价值(ESV)及生态风险值时空演变特征并构建生态功能分区。结果表明:30年间,粤港澳大湾区建设用地面积累计增加56... 详细信息

为揭示粤港澳大湾区城市群30年间土地利用类型转移变化规律,基于1990—2020年共4期Landsat遥感影像,分析研究区生态系统服务价值(ESV)及生态风险值时空演变特征并构建生态功能分区。结果表明:30年间,粤港澳大湾区建设用地面积累计增加5616 km^(2),增幅达179%,主要源于林地和耕地的转移变化;ESV在时间上总体呈先增加后减少趋势,在空间上呈中部低、四周高特征;生态风险在时间上呈不断增加趋势,风险等级向中高风险类型转移,在空间上呈中部高、四周低分布特征且表现出一定的空间集聚现象;根据ESV与生态风险值分布,可将研究区划分为严格管控区、重点管控区、一般管控区与生态保护区4种功能生态分区,其中严格管控区面积呈扩大趋势,重点管控区面积呈先增后减趋势,而生态保护区面积呈持续缩小趋势。

关键词：城市群土地利用变化生态系统服务价值生态风险生态分区粤港澳大湾区

Photochemical microfluidic synthesis of vitamin D_3 by improved light sources with photoluminescent substrates

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Chinese Journal of Chemical Engineering 2021年第1期34卷 204-211页

作者： wenhao niu Yuanzhi Zheng Ying Li Le Du Wei Liu The State Key Laboratory of Chemical Resource Engineering Beijing Key Laboratory of Membrane Science and TechnologyBeijing University of Chemical TechnologyBeijing 100029China

This study presents a novel technique for the controllable preparation of photoluminescent substrates to enhance the photochemical microfluidic synthesis of vitamin D_*** dip-coating method to prepare the substrates was experimentally optimized,and the corresponding emission behaviors were systematically *** substrates were successfully used to enhance the ultraviolet B(UVB) emission of a low-power light source(e.g.,an 8 W lamp),whose UVB emission intensity was increased by approximately 11 *** virtue of the novel light source,the productivity of a single set of photochemical microreactor with a 12-meter-long channel(0.6 mm i.d.) was increased to 1.83 kg·a^(-1),which was 42% higher than that of a 100 W lamp,and no cooling devices were *** method is simple and has great potential to replace traditional medium-pressure mercury lamps for UVB-irradiated photochemical reactions.

关键词： Microfluidics Photochemistry Composites UVB emission Vitamin D_3

西方选举民主与公民自治——基于“公民自治”观念的批判性研究

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当代世界与社会主义 2022年第2期 106-115页

作者：牛文浩南京师范大学公共管理学院

有观点认为,虽然西方选举民主制的治理绩效并不好,但能够更好地实现公民自治,所以还是比其他制度更具有民主性和正当性,是应效仿的“榜样”。对“公民自治”观念的考察发现,如果公民自治意味着“通过影响决策满足自身偏好”,那么由于大... 详细信息

有观点认为,虽然西方选举民主制的治理绩效并不好,但能够更好地实现公民自治,所以还是比其他制度更具有民主性和正当性,是应效仿的“榜样”。对“公民自治”观念的考察发现,如果公民自治意味着“通过影响决策满足自身偏好”,那么由于大规模集体决策中单个人的影响力对决策结果几乎不起作用,选举民主并不能够实现公民自治。如果将“对决策的最低限度反思”“无支配”等视为公民自治的实现,则会与人们关于公民自治的直觉相冲突,所以即使西方选举民主可以实现这些目标,也不能表明其可以实现公民自治。在代议制下,因为选民对民选官员所作决策的“理性无知”,以及利益集团对民选官员的“俘获”现象普遍存在,西方选举民主无法保证选举责任机制的实现,也就无法实现选民对决策的有效影响,从而无法保证决策结果满足选民的偏好,这会导致其进一步地偏离公民自治的目标。因此,即使公民自治是民主的核心价值及其正当性的重要基础,也并不意味着西方选举民主是民主的最佳实现方式,或者是更具正当性。

关键词：西方选举民主公民自治影响力无支配回应性

Design and Verification of Parallel Hip Exoskeleton Considering Output Torque Anisotropy

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Journal of Bionic Engineering 2024年第3期21卷 1305-1320页

作者： Jilong Xu Yunzhan niu Fucai Liu Engineering Research Center of the Ministry of Education for Intelligent Control System and Intelligent Equipment Yanshan UniversityQinhuangdao066004China Key Laboratory of Industrial Computer Control Engineering of Heibei Province Yanshan UniversityQinhuangdao066004China College of Mechanical Engineering Yanshan UniversityQinhuangdao066004China

In rehabilitation training,it is crucial to consider the compatibility between exoskeletons and human legs in ***,most exoskeletons today adopt an anthropomorphic serial structure,which results in rotational centers that are not precisely aligned with the center of the hip *** address this issue,we introduce a novel exoskeleton called the Parallel Hip Exoskeleton(PH-Exo)in this ***-Exo is meticulously designed based on the anisotropic law of output *** the friction of the drive components,a dynamic model of the human-machine complex is *** analysis demonstrates that PH-Exo not only exhibits outstanding torque performance but also achieves high controllability in both flexion/extension and adduction/abduction ***,a robust controller is designed to address model uncertainty,friction,and external *** experiments indicate that under the control of the robust controller,each motor achieves excellent tracking performance.

关键词： Hip exoskeleton Parallel mechanism Misalignment Anisotropy Output torque

An integrative mathematical model of microwave ion thruster for mHz-frequency thrust noise analysis

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Chinese Journal of Aeronautics 2024年第4期37卷 121-136页

作者： Xiang niu Hui LIU Daren YU Plasma Propulsion Laboratory Harbin Institute of TechnologyHarbin 150001China

Many high-precision space missions need thrusters to produce thrust with low noise to compensate for disturbances and ensure satellite platform stability. Microwave ion thruster is characterized with a wide thrust range and potential for these missions. A cost-effective and accurate mathematical model is crucial for mHz-frequency thrust noise analysis and feedback controller design. The Particle-In-Cell(PIC) and global models are two common simulation tools. The PIC model is characterized with high accuracy but huge computation cost, which is difficult to analyze long-time performance characteristics. Now, the global model is only used for the discharge chamber with low accuracy and cannot reflect ion extraction properties. In this paper, an integrative mathematical model is built for a 1-cm microwave ion thruster and can reflect ion beamlet divergence and impingement on the Accelerator Grid(AG). Simulation results show good agreement with experiments at 0.06 sccm. However, the model demonstrates worse consistency with experiments when the flux increases to 0.1 sccm, which may be because the influence of neutral gas on the Electron Cyclotron Resonance(ECR) is not considered in the model. A long-time(1000 s) simulation is conducted with this model under 35 μN. It takes 3 hrs, and the thrust noise reaches 1 μN/Hz^(0.5) at 1 mHz.

关键词： Electric propulsion Microwave ion thruster Integrative model Sheath property Ion beamlet divergence Thrust noise Plasma

Vascularization ability of glioma stem cells in different three-dimensional microenvironments

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Regenerative Biomaterials 2024年第1期3卷 34-43页

作者： Xuanzhi Wang Tao Xu Chaoshi niu Department of Neurosurgery The First Affliated Hospital of USTCDivision of Life Sciences and MedicineUniversity of Science and Technology of ChinaHefeiAnhui230036China Department of Neurosurgery Sichuan Provincial People's HospitalUniversity of Electronic Science and Technology of ChinaChengdu 610072People's Republic of China Center for Bio-intelligent Manufacturing and Living Matter Bioprinting Research Institute of Tsinghua University in ShenzhenTsinghua UniversityShenzhen 518057People's Republicof China

Glioblastoma(GBM)is among the most common and aggressive adult central nervous system *** prominent charac-teristic of GBM is the presence of abnormal microvessels.A significant correlation between angiogenesis and prognosis has been *** reconstructing this neovascula-rization and tumor microenvironment through personalized in vitro disease models presents a significant ***,it is crucial to develop new anti-angiogenic therapies for *** this study,3D bioprinted glioma stem cell(GSC)-laden hydrogel scaffolds,hybrid Gsc hydrogels and ceil-free hydrogel scaffolds were manufactured to investigate the vas-cularization ability of GsCs in varying 3D microenvironments.

关键词： 3D bioprinting xenograft tumors GSC-laden hydrogel scaffold glioblastoma angiogenesis

Event-triggered sliding mode control of linear repetitive processes and its application in metal rolling process

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Science China(Information Sciences) 2024年第3期67卷 167-181页

作者： Xinyu LV Yugang niu James LAM Key Laboratory of Smart Manufacturing in Energy Chemical Process (East China University of Science and Technology) Ministry of Education Department of Mechanical Engineering The University of Hong Kong

This paper investigates the design problem of a sliding mode controller for linear repetitive processes(LRPs) with a finite pass length on each pass. Under limited communication resources, an eventtriggered mechanism is implemented from the sensors to the controller, whose triggered sequence is consistent with the evolution direction of LRPs. To periodically orchestrate communication between the controller and actuator, a round-robin scheduling mechanism is established based on the pass length. A sliding function involving the state and pass profile is constructed, and the sliding mode controller is designed using triggered states and pass profile signals. Feasible controller gains are attained to ensure the stability of the resultant closed-loop system. Finally, the proposed strategy is implemented for a multi-roll metal rolling process.

关键词： event-triggered mechanism linear repetitive processes metal rolling process round-robin scheduling sliding mode control

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Bilayer solid-electrolyte interphase structure enables a 440 Wh kg^(-1) lithium metal pouch cell to achieve 130 cycles

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Science China Chemistry 2024年第3期67卷 751-752页

作者： Xiong Liu Chaojiang niu School of Materials Science and Engineering Zhengzhou UniversityZhengzhou 450001China

Lithium(Li) metal has been considered one of the most promising anodes due to its high theoretical capacity, lightweight and low electrochemical potential. The cell-level energy density of rechargeable lithium metal batteries(LMBs) is expected to surpass 500 Wh kg^(-1) after replacing the graphite anode in lithium-ion batteries [1].

关键词： lithium electrolyte layer