检索结果-南通市图书馆

Effect of Substitutional Sr Ion on Mechanical Properties of Calcium Phosphate Bone Cement

在线全文

同方期刊数据库

学校读者我要写书评

暂无评论

Journal of Wuhan University of Technology(Materials Science) 2013年第4期28卷 741-745页

作者：陶艳 li dongxu li Yanbao State Key Laboratory of Materials-Oriented Chemical Engineering School of Materials Science and Engineering Nanjing University of Technology

A novel calcium phosphate cement was developed by adding different amount of SrO to tetracalcium phosphate during the fabrication process. The experimental results show that compressive strength of cements based on tetracalcium phosphate doped with SrO significantly increases with the increase of SrO content, approximately 60 MPa, whilst the mechanical behavior of CPC slightly decreases if 0.7wt% SrO is added. X-ray diffraction measurement confirms the setting reaction of doped cements is similar to that of pure calcium phosphate cement （CPC）. Low crystalline hydroxyapatite （HA） is found to be the main constituent of set cement. A mechanical reinforcement effect is resulted from the substitution of Sr ion to Ca2＋ in tetracalcium phosphate （TTCP）, accelerating HA crystal formation and a more cross-linked cement structure. In vitro bioactivity tests showed that CPC added with 0.5wt% SrO had a more rapid degradation compared with pure CPC.

关键词： calcium phosphate cement SrO compressive strength bioactivity

The Mechanical Properties and Hydration Characteristics of Cement Pastes Containing Added-calcium Coal Gangue

在线全文

学校读者我要写书评

暂无评论

Journal of Wuhan University of Technology(Materials Science) 2008年第2期23卷 254-258页

作者： li dongxu SONG Xuyan College of Material Science EngineeringNanjing University of Technology Nanjing 210009 China Department of Civil Engineering University of Science and Technology and Suzhou 215011 China

The mechanical properties of several kinds of coal gangue calcined with limestone were Researched so as to find the optimum way of calcinations with limestone. Microstructure and property of hydration process of cement pastes containing added-calcium coal gangue were analyzed by means of scanning electron microscope （SEM） and method of mercury in trusion poremeasurement （MIP）, etc. The experiment can approve those results： when proper amounst of gypsum and fluorite were taken as mineralizers in the course of calcinations of added-calcium coal gangue, activity of coal gangue can be effectively improved. The results of mechanical property and structural characteristic such as hydration process, hydration product and microstructure etc. of cement pastes containing added-calcium coal gangue are consistent.

关键词： coal gangue calcinations with limestone scanning electron microscope pore structure study

Vibration control for the solar panels of spacecraft: Innovation methods and potential approaches

在线全文

学校读者我要写书评

暂无评论

International Journal of Mechanical System Dynamics 2023年第4期3卷 300-330页

作者： dongxu li Wang liu College of Aerospace Science National University of Defense TechnologyChangshaChina

Solar panels on spacecraft are typical kinds of flexible ***‐frequency and large‐amplitude vibrations usually occur due to the inevitable disturbances of deployment impact,attitude/orbit maneuver,separation/docking impact,and so *** vibrations degrade the stability of the spacecraft platform,leading to a reduction in imaging quality and pointing direction *** control is obligatory during flight ***,we summarize the researches on vibration control of the solar ***,typical solar panels used in spacecraft and the specific difficulties in dynamic modeling and control design are ***,the researches on dynamic modeling methods,decentralized vibration control strategy,and in‐orbit vibration controller design technologies are presented ***,a practical example where our method was successfully applied in‐orbit is *** conclusion,the theories,methods,and technologies presented in this review hold significant value for achieving high‐precision performance in large spacecraft.

关键词： solar panels dynamic modeling decentralized vibration control engineering application technology

Analysis and Testing of Microvibrations Produced by Momentum Wheel Assemblies

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

Chinese Journal of Aeronautics 2012年第4期25卷 640-649页

作者： ZHOU Weiyong li dongxu LUO Qing liU Kun College of Aerospace and Material Engineering National University of DeJense TechnologyChangsha 410073China

The microvibrations produced by momentum wheel assemblies（MWA） can degrade the performance of instruments with high pointing precision and stability on *** paper concentrates on analyzing and testing the microvibrations produced by *** analyze the disturbance sources produced by mass imbalance,structural mode,bearing irregularity and nonlinear stiffness,and random noise;then,test a well-balanced MWA by a highly sensitive measurement system consisting of a Kistler table and an optical *** results show that the test system has a resolution of less than 0.003 N in the frequency range of 3-300 *** dynamic imbalance of the MWA cannot excite the radial rocking mode,but there are dynamic amplifications when the poly-harmonic disturbances intersect with the structural *** at high rotational speed（〉3 000 rev/min）,the main disturbance sources of the MWA come from the bearing irregularity interacting with radial translation mode in the high frequency ***,bearing noise deserves more attention for the well-balanced MWA,and alternative of high quality bearings are proposed to reduce the microvibrations.

关键词： momentum wheel assemblies microvibration bearing irregularity mass imbalance vibration analysis

Study on the description method of upper limb's muscle force levels during simulated in-orbit operations

在线全文

学校读者我要写书评

暂无评论

Science China(Physics,Mechanics & Astronomy) 2013年第3期56卷 651-657页

作者： ZHAO Yan li dongxu liU ZhiZhen liU liang College of Aerospace Science and Engineering National University of Defense Technology Science and technology on human factors engineering laboratory China Astronaut Research and Training Center

The dexterous upper limb serves as the most important tool for astronauts to implement in-orbit experiments and *** study developed a simulated weightlessness experiment and invented new measuring equipment to quantitatively evaluate the muscle ability of the upper *** maximum voluntary contractions(MVCs) and surface electromyography(sEMG) signals of right-handed pushing at the three positions were measured for eleven *** order to enhance the comprehensiveness and accuracy of muscle force assessment,the study focused on signal processing *** applied a combination method,which consists of time-,frequency-,and bi-frequency-domain ***-and frequency-domain analyses estimated the root mean square(RMS) and median frequency(MDF) of sEMG signals,*** order spectra(HOS) of bi-frequency domain evaluated the maximum bispectrum amplitude(Bmax),Gaussianity level(Sg) and linearity level(Sl) of sEMG *** showed that B max,S l,and RMS values all increased as force *** and S g values both declined as force *** research demonstrated that the combination method is superior to the conventional time-and frequency-domain *** method not only described sEMG signal amplitude and power spectrum,but also deeper characterized phase coupling information and non-Gaussianity and non-linearity levels of sEMG,compared to two conventional *** finding from the study can aid ergonomist to estimate astronaut muscle performance,so as to optimize in-orbit operation efficacy and minimize musculoskeletal injuries.

关键词： astronaut sEMG MVC Bi-frequency domain time domain frequency domain

Task space control of free-floating space robots using constrained adaptive RBF-NTSM

在线全文

同方期刊数据库

学校读者我要写书评

暂无评论

Science China(Technological Sciences) 2014年第4期57卷 828-837页

作者： GUO ShengPeng li dongxu MENG YunHe FAN CaiZhi College of Aerospace Science and Engineering National University of Defense Technology

Trajectory tracking control of space robots in task space is of great importance to space missions, which require on-orbit manipulations. This paper focuses on position and attitude tracking control of a tree-floating space robot in task space. Since nei- ther the nonlinear terms and parametric uncertainties of the dynamic model, nor the external disturbances are known, an adap- tive radial basis function network based nonsingular terminal sliding mode （RBF-NTSM） control method is presented. The proposed algorithm combines the nonlinear sliding manifold with the radial basis function to improve control performance. Moreover, in order to account for actuator physical constraints, a constrained adaptive RBF-NTSM, which employs a RBF network to compensate for the limited input is developed. The adaptive updating laws acquired by Lyapunov approach guar- antee the global stability of the control system and suppress chattering problems. Two examples are provided using a six-link free-floating space robot. Simulation results clearly demonstrate that the proposed constrained adaptive RBF-NTSM control method performs high precision task based on incomplete dynamic model of the space robots. In addition, the control errors converge faster and the chattering is eliminated comparing to traditional sliding mode control.

关键词： free-floating space robots task space radial basis function nonsingular terminal sliding mode

Synthesis,structure and bonding of the hypoelectronic cluster compound Sr_3Tl_5

在线全文

学校读者我要写书评

暂无评论

Science China Chemistry 2012年第1期55卷 131-137页

作者： li dongxu LUO GengGeng XIAO ZiJing DAI JingCao Institute of Materials Physical Chemistry Huaqiao UniversityXiamen 361021China

The Sr3Tl5 phase was prepared by high temperature synthesis techniques through reaction of the high purity elements in the welded Nb *** structure established through X-ray structural analysis shows the compound is a good hypoelectronic trielide example of the Pu3Pd5 structural type in which skeletal electron count is lower than in a traditional Zintl phase(Cmcm,Z = 4;a = 10.604(2) ,b = 8.675(2) ,and c = 10.985(2) ;V = 1010.5(3) 3).The strontium size and the compound's polarity appear responsible for this thallium phase crystallization in the Pu3Pd5 family type rather than the isoelectronic Sr3In5 version.A first-principle electronic structure calculation(LMTO) demonstrates that the strontium atoms participate substantially in Sr-Tl bonding in the structure.

关键词： Zintl phases hypoelectronic cluster polar intermetallics LMTO calculations

Placement optimization of actuator and sensor and decentralized adaptive fuzzy vibration control for large space intelligent truss structure

在线全文

学校读者我要写书评

暂无评论

Science China(Technological Sciences) 2011年第4期54卷 853-861页

作者： li dongxu liU Wang JIANG JianPing XU Rui College of Aerospace and Material Engineering National University of Defense TechnologyChangsha 410073China

Large space truss structure is widely used in *** vibration of this kind of structure will cause some serious *** instance,it will disturb the work of the payloads which are supported on the truss,even worse,it will deactivate the ***,it is highly in need of executing vibration control for large space truss *** space intelligent truss system(LSITS) is not a normal truss structure but a complex truss system consisting of common rods and active rods,and there are at least one actuator and one sensor in each active *** of the key points in the vibration control for LSITS is the location assignment of actuators and *** positions of actuators and sensors will directly determine the properties of the control system,such as stability,controllability,observability,*** this paper,placement optimization of actuators and sensors(POAS) and decentralized adaptive fuzzy control methods are presented to solve the vibration control *** electro-mechanical coupled equations of the active rod are established,and the optimization criterion which does not depend upon control methods is *** optimal positions of actuators and sensors in LSITS are obtained by using genetic algorithm(GA).Furthermore,the decentralized adaptive fuzzy vibration controller is designed to control *** LSITS dynamic equations with considering those remaining modes are *** adaptive fuzzy control scheme is improved via sliding control *** T-typed truss structure is taken as an example and a demonstration experiment is carried *** experimental results show that the GA is reliable and valid for placement optimization of actuators and sensors,and the adaptive fuzzy controller can effectively suppress the vibration of LSITS without control spillovers and observation spillovers.

关键词： large space intelligent truss system placement optimization of actuators and sensors genetic algorithm adaptive fuzzy control decentralized control

Learning Sequential and Structural Dependencies Between Nucleotides for RNA N6-Methyladenosine Site Identification

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10期11卷 2123-2134页

作者： Guodong li Bowei Zhao Xiaorui Su dongxu li Yue Yang Zhi Zeng Lun Hu Xinjiang Technical Institute of Physics and Chemistry Chinese Academy of ScienceUrumqi 830011China College of Computer Xi’an Jiaotong UniversityXi’an 710049China IEEE

N6-methyladenosine(m6A)is an important RNA methylation modification involved in regulating diverse biological processes across multiple ***,the identification of m6A modification sites provides valuable insight into the biological mechanisms of complex diseases at the post-transcriptional *** a variety of identification algorithms have been proposed recently,most of them capture the features of m6A modification sites by focusing on the sequential dependencies of nucleotides at different positions in RNA sequences,while ignoring the structural dependencies of nucleotides in their threedimensional *** overcome this issue,we propose a cross-species end-to-end deep learning model,namely CR-NSSD,which conduct a cross-domain representation learning process integrating nucleotide structural and sequential dependencies for RNA m6A site ***,CR-NSSD first obtains the pre-coded representations of RNA sequences by incorporating the position information into single-nucleotide states with chaos game representation *** then constructs a crossdomain reconstruction encoder to learn the sequential and structural dependencies between *** minimizing the reconstruction and binary cross-entropy losses,CR-NSSD is trained to complete the task of m6A site *** experiments have demonstrated the promising performance of CR-NSSD by comparing it with several state-of-the-art m6A identification ***,the results of cross-species prediction indicate that the integration of sequential and structural dependencies allows CR-NSSD to capture general features of m6A modification sites among different species,thus improving the accuracy of cross-species identification.

关键词： Cross-domain reconstruction cross-species prediction N6-methyladenosine(m6A)modification site RNA sequence sequential and structural dependencies