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Design of a novel side-mounted leg mechanism with high flexibility for a multi-mission quadruped earth rover BJTUBOT

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机械工程前沿:英文版 2023年第2期18卷 115-142页

作者： Yifan WU Sheng GUO Luquan LI lianzheng niu Xiao LI School of Mechanical Electronic and Control EngineeringBeijing Jiaotong UniversityBeijing 100044China

Earth rover is a class of emerging wheeled-leg robots for nature exploration.At present,few methods for these robots’leg design utilize a side-mounted spatial parallel mechanism.Thus,this paper presents a complete design process of a novel 5-degree-of-freedom(5-DOF)hybrid leg mechanism for our quadruped earth rover BJTUBOT.First,a general approach is proposed for constructing the novel leg mechanism.Subsequently,by evaluating the basic locomotion task(LT)of the rover based on screw theory,we determine the desired motion characteristic of the sidemounted leg and carry out its two feasible configurations.With regard to the synthesis method of the parallel mechanism,a family of concise hybrid leg mechanisms using the 6-DOF limbs and an L1F1C limb(which can provide a constraint force and a couple)is designed.In verifying the motion characteristics of this kind of leg,we select a typical(3-UPRU&RRRR)&R mechanism and then analyze its kinematic model,singularities,velocity mapping,workspace,dexterity,statics,and kinetostatic performance.Furthermore,the virtual quadruped rover equipped with this innovative leg mechanism is built.Various basic and specific LTs of the rover are demonstrated by simulation,which indicates that the flexibility of the legs can help the rover achieve multitasking.

关键词： design synthesis parallel mechanism hybrid leg mechanism screw theory quadruped robot

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 tumors.One prominent charac-teristic of GBM is the presence of abnormal microvessels.A significant correlation between angiogenesis and prognosis has been observed.Accurately reconstructing this neovascula-rization and tumor microenvironment through personalized in vitro disease models presents a significant challenge.However,it is crucial to develop new anti-angiogenic therapies for GBM.In 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

Modeling tuberous sclerosis complex with human induced pluripotent stem cells

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World Journal of Pediatrics 2024年第3期20卷 208-218页

作者： Weibo niu Benjamin Siciliano Zhexing Wen Department of Psychiatry and Behavioral Sciences Emory University School of MedicineWhitehead Research Building 447615 Michael StreetAtlantaGA 30322USA The Graduate Program in Molecular and Systems Pharmacology Laney Graduate SchoolEmory UniversityAtlanta.GA 30322.USA Department of Cell Biology Emory University School of MedicineWhitehead Research Building 447615 Michael StreetAtlantaGA30322USA Department of Neurology Emory University School of MedicineWhitehead Research Building 447.615 Michael StreetAtlantaGA 30322USA

Background Tuberous sclerosis complex(TSC)is an autosomal dominant genetic disorder with a birth incidence of I:6000 in the United States that is characterized by the growth of non-cancerous tumors in multiple organ systems including the brain,kidneys,lungs,and skin.Importantly,TSCis also associated with signicant neurological manifestations including epilepsy TSC-associated neuropsychiatric disorders,intellectual disabilities,and autism spectrum disorder.Mutations in the TSCI or TSC2 genes are well-established causes of TSC,which lead to TSC1/TSC2 deficiency in organs and hyper-activation of the mammalian target of rapamycin signaling pathway.Animal models have been widely used to study the effect of TSCl/2 genes on the development and function of the brain.Despite considerable progress in understanding the molecular mechanisms underlying TSC in animal models,a human-specific model is urgently needed to investigate the effects of TSCl/2 mutations that are unique to human neurodevelopment.Data sources Literature reviews and research articles were published in PubMed-indexed journals.Results Human-induced pluripotent stem cells(iPSCs),which capture risk alleles that are identical to their donors and have the capacity to differentiate into virtually any cell type in the human body,pave the way for the empirical study of previously inaccessible biological systems such as the developing human brain.Conclusions In this review,we present an overview of the recent progress in modeling TSC with human iPSC models,the existing limitations,and potential directions for future research.

关键词： Induced pluripotent stem cells Three-dimensional cultures Tuberous sclerosis complex Two-dimensional cultures

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

RNA interference in insects:the link between antiviral defense and pest control

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Insect Science 2024年第1期31卷 2-12页

作者： Jinzhi niu Ruoyu Chen Jin-Jun Wang Key Laboratory of Entomology and Pest Control Engineering College of Plant ProtectionSouthwest UniversityChongqingChina Key Laboratory of Agricultural Biosafety and Green Production of Upper Yangtze River(Ministry of Education) Southwest UniversityChongqingChina

RNA interference(RNAi)is a form of gene silencing triggered by double-stranded RNA(dsRNA)that operates in all eukaryotic cells.RNAi has been widely investigated in insects to determine the underlying molecular mechanism,to investigate its role in systemic antiviral defense,and to develop strategies for pest control.When insect cells are infected by viruses,viral dsRNA signatures trigger a local RNAi response to block viral replication and generate virus-derived DNA that confers systemic immunity.RNAi-based insect pest control involves the application of exogenous dsRNA targeting genes essential for insect development or survival,but the efficacy of this approach has limited potency in many pests through a combination of rapid dsRNA degradation,inefficient dsRNA uptake/processing,and ineffective RNAi machinery.This could be addressed by dsRNA screening and evaluation,focusing on dsRNA design and off-target management,as well as dsRNA production and delivery.This review summarizes recent progress to determine the role of RNAi in antiviral defense and as a pest control strategy in insects,addressing gaps between our fundamental understanding of the RNAi mechanism and the exploitation of RNAi-based pest control strategies.

关键词： RNAi response systemic RNAi insecticidal dsRNA biological control off-targets

Highly Thermoconductive,Strong Graphene‑Based Composite Films by Eliminating Nanosheets Wrinkles

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Nano-Micro Letters 2024年第1期16卷 328-340页

作者： Guang Xiao Hao Li Zhizhou Yu Haoting niu Yagang Yao College of Engineering and Applied Sciences Jiangsu Key Laboratory of Artificial Functional Materialsand Collaborative Innovation Center of Advanced MicrostructuresNational Laboratory of Solid State MicrostructuresNanjing UniversityNanjing 210093People’s Republic of China Institute of Laser Manufacturing Henan Academy of SciencesZhengzhou 450052People’s Republic of China Center for Quantum Transport and Thermal Energy Science School of Physics and TechnologyNanjing Normal UniversityNanjing 210023People’s Republic of China

Graphene-based thermally conductive composites have been proposed as effective thermal management materials for cooling high-power electronic devices.However,when flexible graphene nanosheets are assembled into macroscopic thermally conductive composites,capillary forces induce shrinkage of graphene nanosheets to form wrinkles during solution-based spontaneous drying,which greatly reduces the thermal conductivity of the composites.Herein,graphene nanosheets/aramid nanofiber(GNS/ANF)composite films with high thermal conductivity were prepared by in-plane stretching of GNS/ANF composite hydrogel networks with hydrogen bonds andπ-πinteractions.The in-plane mechanical stretching eliminates graphene nanosheets wrinkles by suppressing inward shrinkage due to capillary forces during drying and achieves a high in-plane orientation of graphene nanosheets,thereby creating a fast in-plane heat transfer channel.The composite films(GNS/ANF-60 wt%)with eliminated graphene nanosheets wrinkles showed a significant increase in thermal conductivity(146 W m^(−1)K^(−1))and tensile strength(207 MPa).The combination of these excellent properties enables the GNS/ANF composite films to be effectively used for cooling flexible LED chips and smartphones,showing promising applications in the thermal management of high-power electronic devices.

关键词： Graphene Aramid nanofiber Wrinkles elimination In-plane stretching Thermal conductivity

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

Intraspecific floral colour variation in three Pedicularis species

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Plant Diversity 2024年第2期46卷 274-279页

作者： Qiu-Yu Zhang Zhe Chen Hang Sun Yang niu State Key Laboratory of Plant Diversity and Specialty Crops Kunming Institute of BotanyChinese Academy of SciencesKunming 650201YunnanChina University of Chinese Academy of Sciences Beijing 100049China

Flower constancy describes the phenomenon that pollinators tend to successively visit flowers of a single species during foraging,reducing reproductive interference in natural communities.The extent of flower constancy is largely determined by the floral traits of co-flowering species.Both higher inter-specific and lower intraspecific differences of floral traits should contribute to a higher level of flower constancy.However,previous studies mainly focused on interspecific difference,and the intraspecific variation(consistency)of floral traits received much less attention.We hypothesise that selection may favour lower intraspecific floral trait variation in communities composed of multiple co-flowering congeners.We investigated the floral colour variation of three focal Pedicularis species that share pollinators in 19communities composed of either single or multiple Pedicularis species.Colour was quantified using image-based colour analysis as perceived by pollinators.We found that most of the intrapopulation floral colour variation was below the colour discrimination threshold of bumblebees,implying strongly constrained by the visual selection by pollinators.Contrary to the hypothesis,there is no significant difference in intraspecific floral colour variation between different community contexts.It may be due to the relatively large interspecific floral colour differences of most co-flowering species.The influence of community context on intraspecific variation may be reflected in floral traits other than colours.

关键词： Flower constancy Floral colour variation Plantepollinator interactions Pollinator vision

An Asynchronous Variational Integrator for Contact Problems Involving Elastoplastic Solids

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Acta Mechanica Solida Sinica 2024年第2期37卷 305-315页

作者： Zongwu niu Zixiao Wang Yongxing Shen University of Michigan-Shanghai Jiao Tong University Joint Institute Shanghai Jiao Tong UniversityShanghai200240China School of Agriculture and Biology Shanghai Jiao Tong UniversityShanghai200240China Department of Biostatistics Johns Hopkins Bloomberg School of Public HealthBaltimoreMaryland21205USA

Simulations of contact problems involving at least one plastic solid may be costly due to their strong nonlinearity and requirements of stability.In this work,we develop an explicit asynchronous variational integrator(AVI)for inelastic non-frictional contact problems involving a plastic solid.The AVI assigns each element in the mesh an independent time step and updates the solution at the elements and nodes asynchronously.This asynchrony makes the AVI highly efficient in solving such bi-material problems.Taking advantage of the AVI,the constitutive update is locally performed in one element at a time,and contact constraints are also enforced on only one element.The time step of the contact element is subdivided into multiple segments,and the fields are updated accordingly.During a contact event,only one element involving a few degrees of freedom is considered,leading to high efficiency.The proposed formulation is first verified with a pure elastodynamics benchmark and further applied to a contact problem involving an elastoplastic solid with non-associative volumetric hardening.The numerical results indicate that the AVI exhibits excellent energy behaviors and has high computational efficiency.

关键词： Asynchronous variational integrator Plasticity Contact Computational efficiency Finite element method