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Second Generation Wavelet Finite Element and Rotor Cracks Quantitative Identification Method

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Chinese Journal of Mechanical Engineering 2010年第2期23卷 195-199页

作者： CHEN xuefeng li Bing HE Yuming HE Zhengjia State Key Laboratory for Manufacturing Systems Engineering Xi ＇an Jiaotong University Xi ＇an 710049 China

The presence of cracks in the rotor is one of the most dangerous and critical defects for rotating machinery. Defect of fatigue cracks may lead to long out-of-service periods, heavy damages of machines and severe economic consequences. With the method of finite element, vibration behavior of cracked rotors and crack detection was received considerable attention in the academic and engineering field. Various researchers studied the response of a cracked rotor and most of them are focused on the crack detection based on vibration behavior of cracked rotors. But it is often difficult to identify the crack parameters quantitatively. Second generation wavelets （SGW） finite element has good ability in modal analysis for singularity problems like a cracked rotor. Based on the fact that the feature of SGW could be designed depending on applications, a multiresolution finite element method is presented. The new model of SGW beam element is constructed. The first three natural frequencies of the rotor with different crack location and size were solved with SGW beam elements, and the database for crack diagnosis is obtained. The first three metrical natural frequencies are employed as inputs of the database and the intersection of the three frequencies contour lines predicted the normalized crack location and size. With the Bently RK4 rotor test rig, rotors with different crack location and size are tested and diagnosed. The experimental results denote the cracks quantitative identification method has higher identification precision. With SGW finite element method, a novel method is presented that has higher precision and faster computing speed to identify the crack location and size.

关键词： second generation wavelet finite element fault diagnosis crack

Image-based numerical study of three-dimensional meso-structure effects on damage and failure of heterogeneous coal-rock under dynamic impact loads

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Particuology 2020年第4期18卷 132-141页

作者： Kehong Zheng Bingjing Qiu Zhenyu Wang xuefeng li Jianping li Kuidong Gao College of Civil Engineering and Architecture Zhejiang UniversityHangzhou 310058China School of Energy and Mechanical Engineering Nanjing Normal UniversityNanjing 210000China College of Mechanical and Electrical Engineering China University of Mining and Technology Xuzhou 221116China College of Mechanical&Electrical Engineering Shandong University of Science&Technology Qingdao 266000China

This paper proposes a numerical three-dimensional(3D)mesoscopic approach based on the discrete element method combined with X-ray computed tomography(XCT)images to characterize the dynamic impact behavior of heterogeneous coal-rock(HCR).The dynamic impact loading in three directions was modelled to investigate the effects of the 3D meso-structure on the failure patterns and fracture mechanism,with different impact *** XCT image-based discrete element model of HCR was calibrated through appropriate standard uniaxial compression *** simulations were carried out to investigate how the breakage behaviors are affected by different loading directions with different impact *** loading direction,input energy,and spatial distribution of the mineral phase had a remarkable influence on the failure patterns and load-carrying *** shape of the gangue phase and the approximate location of the gangue interfaces are key parameters to consider when investigating the failure patterns and fracture mechanism of heterogeneous rock *** damage and fracture tended to propagate from the surfaces to the HCR *** gangue phase area contacting the loading wall,growth direction of the strong gangue interfaces,and loading directions greatly influenced the failure patterns of the heterogeneous rock materials.

关键词： Heterogeneous coal-rock Impact loads X-ray computed tomography(XCT) 3D image-based discrete element modelling Failure pattern

Nitrogen isotope stratigraphy of the Early Cambrian successions in the Tarim Basin:Spatial variability of nitrogen cycling and its implication for paleo-oceanic redox conditions

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Acta Geochimica 2024年第4期43卷 785-801页

作者： Bi Zhu xuefeng li Lu Ge Yongquan Chen Institute of Earth’s Critical Zone School of Earth Sciences and EngineeringHohai UniversityNanjing 210098China Research Institute of Exploration and Development Tarim Oil Field CompanyPetroChinaKorlaChina

The Early Cambrian represents a critical time period characterized by extraordinary biological innovations and dynamic redox conditions in *** isotopic signatures of ancient sediments have the potential to elucidate the evolutionary path of marine redox states and the biogeochemical nitrogen cycle within the water column of the Early Cambrian *** existing research on this topic has predominantly focused on South China,the exploration of other continental margins has been limited,leaving contradictory hypotheses *** this study,pairedδ^(15)N andδ^(13)C org analyses were performed on the Lower Cambrian successions from the Shiairike section(inner ramp)and Well Tadong 2(deep shelf/basin)in the northwestern and eastern Tarim Basin,*** data from the Shiairike section reveal a discernible shift in the operation of different nitrogen cycles for the black chert-shale unit,also referred to as the black rock series in Chinese literature,of the Yurtus Formation(Fortunian stage to lower Stage 3).Oscillatingδ^(15)N values for its lower part are suggestive of alternating anaerobic assimilation of NH 4+and denitrification/*** is likely attributed to a shallow,unstable chemocline consistent with the upwelling and incursion of deep,anoxic waters during a major *** contrast,aerobic nitrogen cycling,indicated by positiveδ^(15)N values of>2‰,dominated the upper part alongside a reduction in upwelling *** the other hand,theδ^(15)N signatures of Xishanbulake and Xidashan Formations of Well Tadong 2,which encompass a time interval from the Cambrian Fortunian Age to Age 4,are indicative of N_(2)fixation by diazotrophs as the major nitrogen *** two studied intervals,although not time-equivalent,exhibit separated states of nitrogen cycling at least during the deposition of the Yurtus black rock *** spatially different nitrogen cycling of the studied sections is compatible with a redox-stratified ocean dur

关键词： Nitrogen isotopes Early Cambrian Tarim Black rock series

An inverse method for characterization of dynamic response of 2D structures under stochastic conditions

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Chinese Journal of Aeronautics 2024年第3期37卷 440-455页

作者： xuefeng li Abdelmalek ZINE Mohamed ICHCHOU Noureddine BOUHADDI Pascal FOSSAT Laboratory of Tribology and Systems Dynamic Central School of LyonEcully 69134France Institut Camille Jordan Central School of LyonEcully 69134France Department of Applied Mechanics University of Burgundy Franche-ComtéBesancon 25000France

The reliable estimation of the wavenumber space(k-space)of the plates remains a longterm concern for acoustic modeling and structural dynamic behavior *** current analyses of wavenumber identification methods are based on the deterministic *** this end,an inverse method is proposed for identifying wave propagation characteristics of twodimensional structures under stochastic conditions,such as wavenumber space,dispersion curves,and band *** proposed method is developed based on an algebraic identification scheme in the polar coordinate system framework,thus named Algebraic K-Space Identification(AKSI)***,a model order estimation strategy and a wavenumber filter are proposed to ensure that AKSI is successfully *** main benefit of AKSI is that it is a reliable and fast method under four stochastic conditions:(A)High level of signal noise;(B)Small perturbation caused by uncertainties in measurement points’coordinates;(C)Non-periodic sampling;(D)Unknown structural *** validate the proposed method,we numerically benchmark AKSI and three other inverse methods to extract dispersion curves on three plates under stochastic *** experiment is then performed on an isotropic steel *** investigations demonstrate that AKSI is a good in-situ k-space estimator under stochastic conditions.

关键词： Inverse method Dispersion relation Wavenumber space Periodic plates Stochastic conditions Wave propagation characterization

miRNAs reshape immunity and inflammatory responses in bacterial infection

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Signal Transduction and Targeted Therapy 2018年第1期3卷 199-211页

作者： Xikun Zhou xuefeng li Min Wu Department of Biomedical Sciences University of North DakotaGrand ForksND 58202-9037USA

Pathogenic bacteria cause various infections worldwide,especially in immunocompromised and other susceptible individuals,and are also associated with high infant mortality rates in developing ***(miRNAs),small non-coding RNAs with evolutionarily conserved sequences,are expressed in various tissues and cells that play key part in various physiological and pathologic *** evidence implies roles for miRNAs in bacterial infectious diseases by modulating inflammatory responses,cell penetration,tissue remodeling,and innate and adaptive *** review highlights some recent intriguing findings,ranging from the correlation between aberrant expression of miRNAs with bacterial infection progression to their profound impact on host immune *** of dysregulated miRNAs in bacterial infection may be an approach to improving the diagnosis,prevention and therapy of infectious diseases.

关键词： immunity infection prevention

Temperature-induced dissociation reaction and dynamics of light-harvesting complex II isolated from purple photosynthetic bacterium ***

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Chinese Science Bulletin 2007年第8期52卷 1029-1035页

作者： FENG Juan li xuefeng liU Yuan School of life Science and Technology University of Electronic Science & Technology of China Chengdu 610054 China

Steady-state absorption spectroscopy,circular dichroism,and resonance Raman spectroscopy have been used to investigate the thermal stability of LH2 complex isolated from purple photosynthetic bacterium *** results show that:1)upon increasing the temperature,a transition from B800 and B850 to free bacteriochlorophyll(B780)happens;2)a gradual decrease and disappearance of CD signal in visible region occur;3)a shift of the frequency,belonging to C==C and C—C stretching vibration,to higher wavenumber takes *** is suggested that LH2 complex can be dissociated in the presence of B800,B850 and carotenoids ***-exponential fitting on the dynamic decay curves gives the apparent time constants of hundreds of minutes for various pigments.

关键词：紫色光合细菌沼泽红假单胞菌温度诱导离解反应反应动力学捕光配合物Ⅱ

Physical, Antioxidant and Thermal Shock Properties of Cu/Ti_2AlC Conductive Composites

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Journal of Wuhan University of Technology(Materials Science) 2013年第3期28卷 504-507页

作者：严明 ZENG Chengwen li Zongyu li xuefeng 陈艳林 School of Materials Science & Engineering Hubei University of Technology Huber Provincial Key Laboratory of Green Materials for light Industry Hubei University of Technology

Cu/Ti2AlC composites were fabricated by vacuum hot-pressing technique. Phase composition was analyzed by XRD and morphology of fracture was observed by SEM. Physical performance such as density, resistivity, hardness and friction coefficient with different volume fraction of Cu/Ti2AlC composites were studied. When the content of Ti2AlC increased from 10% to 70%, the relative density reduced from 99.38% to 90.56% and the resistivity increased significantly. Hardness reached the maximum value when Ti2AlC was at 60% and friction coefficient declined with the increasing of Ti2AlC. Cu/Ti2AlC composites, showing good conductivity properties and friction performance. Oxidation resistance enhanced obviously with the content of Ti2AlC increasing. Cu-60%Ti2AlC sample possessed optimum thermal shock resistance, and no cracking was found at 600 ℃ cycled for 10 times and 900 ℃ cycled for 1 time.

关键词： Cu-based composites Ti2AlC hot-pressing technique properties

An MYB Transcription Factor from Malus xiaojinensis Has a Potential Role in Iron Nutrition

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Journal of Integrative Plant Biology 2008年第10期50卷 1300-1306页

作者： Jie Shen xuefeng Xu Tianzhong li Dongmei Cao ZhenhaiHan Institute for Horticultural Plants China Agricultural University Beijing 100094 China

Regulation of iron uptake and use is critical for plant survival and growth. We isolated an MYB gene from Malus xiaojinensis named MxMYB1, which is induced under Fe-deficient conditions. Expression of MxMYB1 was upregulated by Fe starvation in the roots but not in leaves, suggesting that MxMYB1 might play a role in iron nutrition in roots. Transgenic Arabidopsis plants expressing MxMYB1 exhibited lower iron content as compared with wild type plants under both Fe-normal （40 μM） and Fe-deficient conditions （Fe omitted and Ferrozine 300 μM）. However, the contents of Cu, Zn and Mn were not changed in these transgenic plants. Gene chip and real-time polymerase chain reaction analyses indicated that the expression of two Fe-related genes encoding an iron transporter AtlRT1 and an iron storage protein ferritin AtFER1 might be negatively regulated by MxMYB1 as the expression levels of these genes were lower in MxMYB1 expressing transgenic Arabidopsis plants as compared with wild type plants under both Fe-normal and Fe-deficient conditions. These results suggest that MxMYB1 may function as a negative regulator of iron uptake and storage in plants.

关键词： Fe Malus xiaojinensis MxMYB transgenic Arabidopsis.

Triaxial test on glass beads simulating coarse-grained soil

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Research in Cold and Arid Regions 2022年第4期14卷 274-280页

作者： WenDong Xu xuefeng li WenWei Yang HongJin Jia School of Civil and Hydraulic Engineering Ningxia UniversityYinchuanNingxia 750021China Solid Mechanics Institute Ningxia UniversityYinchuanNingxia 750021China Ningxia Center for Research on Earthquake Protection and Disaster Mitigation in Civil Engineering YinchuanNingxia 750021China School of Physics and Electronic-Electrical Engineering Ningxia UniversityYinchuanNingxia 750021China

It is feasible to study the mechanical characteristics of coarse-grained soil by simulated granular materials such as glass *** this paper,3 mm diameter glass beads are used to conduct drained and undrained triaxial tests under different confining pressures to explore their strength,deformation and critical state ***,the influence of drainage and confining pressure on the stick-slip phenomenon of glass beads is *** experimental findings from triaxial tests show that the stress-strain relationship of glass beads softens when the confining pressure is *** the undrained condition,the initial modulus increases with the increase in the confining *** contrast,it is not significantly affected by the confining pressure in the drained *** is quite evident that the glass beads hardly contract during the shearing process,and their stress path is approximately a segmented straight *** slope of the critical state line under the undrained condition is greater than that under the drained condition,and the friction angle of the glass beads under the undrained and drained conditions is calculated to be 28.1and 29.5,*** phenomenon of stick-slip has been depicted for the different test conditions,and the stick-slip amplitude linearly increases with the confining pressure,especially in the undrained *** is also found that the maximum energy released from the phenomenon of stick-slip increases linearly with the confining pressure.

关键词： Triaxial test Glass beads Strength Critical state Stick-slip