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Dinosaur-associated Poaceae epidermis and phytoliths from the Early Cretaceous of China

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National Science Review 2018年第5期5卷 721-727页

作者： Yan Wu Hai-Lu You xiao-qiang li Key Laboratory of Vertebrate Evolution and Human Origins of Chinese Academy of Sciences Institute of Vertebrate Paleontology and PaleoanthropologyChinese Academy of Sciences CAS Center for Excellence in life and Paleoenvironment College of Earth Sciences University of Chinese Academy of Sciences

Grasses(Poaceae) are human’s most important crop plants and among the most important extant clades of vascular plants. However, the origin and early evolution of grasses are controversial, with estimated ages from molecular dating ranging between 59 and 129 Ma(million years ago). Here we report the discovery of basalmost grasses from the late Early Cretaceous(Albian, 113-101 Ma) of China based on microfossils(silicified epidermal pieces and phytoliths) extracted from a special structure along the dentition of a basal hadrosauroid(duck-billed dinosaur). Thus, this discovery represents the earliest known grass fossils, and is congruent with previous estimations on grass origin and early evolution calibrated by oldest known fossil grasses, highlighting the role of fossils in molecular dating. This discovery also indicates deep-diverging grasses probably gained broad distribution across both Laurasian and Gondwanan continents during the Barremian(129-125 Ma).

关键词： Poaceae dinosaur phytolith epidermis Early Cretaceous

Research on temperature field of non-uniform heat source model in surface grinding by cup wheel

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Advances in Manufacturing 2019年第3期7卷 326-342页

作者： Shi-Jie Dai xiao-qiang li Hui-Bo Zhang State Key Laboratory of Reliability and Intelligence of Electrical Equipment Hebei University of TechnologyTianjin 300130People's Republic of China School of Mechanical Engineering Hebei University of TechnologyTianjin 300130People's Republic of China Hebei Key Laboratory of Robot Perception and Human-Robot Interaction Tianjin 300130People's Republic of China

To address the problems of thermal damage to a workpiece surface caused by the instantaneous high temperature during grinding and the difficulty in monitoring temperature in real time,the temperature field in the case of composite surface grinding by a cup wheel is *** order to predict the grinding temperature,considering material removal and grinding force distribution,a nonuniform heat source model with different function distributions in the circumferential and radial directions in the cylindrical coordinate system is first proposed;then,the analytical model is deduced and the numerical model of the temperature field is established based on the heat source *** validation experiments for grinding temperature field are carried out using a high-definition infrared thermal imager and an artificial *** to the temperature field based on the uniform heat source model,the results based on the non-uniform heat source model are in better agreement with the actual temperature field,and the temperature prediction error is reduced from approximately 23% to 6%.Thus,the present study provides a more accurate theoretical basis for preventing bums in cup wheel surface grinding.

关键词： Non-uniform heat source Temperature filed Surface grinding Cup wheel

Preparation of in situ and ex situ reinforced Fe–10Cr–1Cu–1Ni–1Mo–2C containing NbC particles by milling and hot pressing

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International Journal of Minerals,Metallurgy and Materials 2015年第2期22卷 157-166页

作者： xiao-qiang li Zi-yang li Yong-quan Ye Ke Hu School of Mechanical and Automotive Engineering South China University of Technology

An in situ and ex situ reinforced powder metallurgy （PM） steel was prepared by the combination of high-energy ball milling and subsequent hot pressing of elemental mixed powders of Fe-10Cr-1Cu-1Ni-1Mo-2C by mass with the addition of NbC particles. A 40-h milling pretreatment makes the powder particles nearly equiaxed with an average diameter of-8 μm, and the ferrite grain size is refined to -6 nm. The sintered density reaches 99.0%-99.7% of the theoretical value when the sintering is conducted at temperatures greater than 1000℃ for 30 min. In the sintered bulk specimens, the formation of an in situ M7C3 （M = Cr, Fe, Mo） phase is confirmed. MTC3 carbides with several hundred nanometers in size are uniformly distributed in the matrix. Some ultra-fine second phases of 50-200 nm form around the ex situ NbC and in situ M7C3 particles. The sintered steel exhibits an excellent combination of hardness （〉 Hv 500） and compressive strength （2100-2420 MPa）.

关键词： steel powder metallurgy reinforcement ball milling hot pressing

Adaptive NN Dynamic Surface Control for a Class of Uncertain Non-affine Pure-feedback Systems with Unknown Time-delay

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International Journal of Automation and computing 2016年第3期13卷 268-276页

作者： xiao-qiang li Dan Wang Zhu-Mu Fu Information Engineering College Henan University of Science and Technology Marine Engineering College Dalian Maritime University

Adaptive neural network （NN） dynamic surface control （DSC） is developed for a class of non-affine pure-feedback systems with unknown time-delay. The problems of ＂explosion of complexity＂ and circular construction of the practical controller in the traditional backstepping algorithm are avoided by using this controller design method. For removing the requirements on the sign of the derivative of function f~, Nussbaum control gain technique is used in control design procedure. The effects of unknown time-delays are eliminated by using appropriate Lyapunov-Krasovskii functionals. Proposed control scheme guarantees that all the signals in the closed-loop system are semi-globally uniformly ultimately bounded. Two simulation examples are presented to demonstrate the method.

关键词： Nonaffine pure-feedback systems dynamic surface control (DSC) time-delay neural network backstepping.

Microstructural evolution and mechanical properties of Alloy 718 fabricated by selective laser melting following different post-treatments

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Rare Metals 2021年第11期40卷 3222-3234页

作者： Hao Luo xiao-qiang li Cun-liang Pan Peng-Jiang He Ke-li Zeng National Engineering Research Center of Near-Net-Shape Forming for Metallic Materials South China University of TechnologyGuangzhou 510640China Institute of Materials and Processing Guangdong Academy of SciencesGuangzhou 510650China Dongguan Hyperpowder Co.Ltd. Dongguan 523808China

In this study,Alloy 718 specimens were fabricated via selective laser melting(SLM),and the effects of different post-treatments on microstructures and mechanical properties of the alloy were systematically *** post-treatment techniques investigated were solid solution+dual aging(SA) and hot isostatic pressing+solid solution+dual aging treatment(HIP+SA).The results indicate that the specimens treated using SA have a columnar crystal structure similar to the as-built sample,the microstructure is partially recrystallized,and the grain size increases ***,the grain morphology is dominated by equiaxed crystals in samples treated using HIP+SA,and the microstructure is completely recrystallized,with distinct grain coarsening and a large number of twins *** treated using SA and HIP+SA show high tensile strength and yield strength and excellent elongation at room temperature,which can be primarily attributed to the strengthening of the γ’ and γ "precipitated *** number of γ" precipitated phases are reduced due to the consumption of Nb to form a large amounts of δ phase and(Ti,Nb)C carbides,resulting in the strength of HIP+SA specimens being lower than that of SA specimens.

关键词： Selective laser melting Alloy 718 Post-treatments Microstructural evolution Mechanical properties

Atmospheric transmission algorithm for pulsed X-rays from high-altitude nuclear detonations based on scattering correction

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Nuclear Science and Techniques 2024年第3期35卷 40-52页

作者： Ding-Han Zhu Xiong Zhang xiao-qiang li Peng li Yan-Bin Wang Shuang Zhang State Key Laboratory of NBC Protection for Civilian Beijing 102205China

In high-altitude nuclear detonations,the proportion of pulsed X-ray energy can exceed 70%,making it a specific monitoring signal for such *** pulsed X-rays can be captured using a satellite-borne X-ray detector following atmospheric *** quantitatively analyze the effects of different satellite detection altitudes,burst heights,and transmission angles on the physical processes of X-ray transport and energy fluence,we developed an atmospheric transmission algorithm for pulsed X-rays from high-altitude nuclear detonations based on scattering *** proposed method is an improvement over the traditional analytical method that only computes direct-transmission *** traditional analytical method exhibits a maximum relative error of 67.79% compared with the Monte Carlo *** improved method reduces this error to within 10% under the same conditions,even reaching 1% in certain ***,its computation time is 48,000 times faster than that of the Monte Carlo *** results have important theoretical significance and engineering application value for designing satellite-borne nuclear detonation pulsed X-ray detectors,inverting nuclear detonation source terms,and assessing ionospheric effects.

关键词： High-altitude nuclear detonation Atmospheric transmission Pulsed X-rays Scattering correction Analytical method Monte Carlo method

Microstructure and mechanical properties of TiAl/Ni-based superalloy joints vacuum brazed with Ti-Zr-Fe-Cu-Ni-Co-Mo filler metal

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Rare Metals 2021年第8期40卷 2134-2142页

作者： Bao Wan xiao-qiang li Cun-liang Pan Dong-Yu li Sheng-Guan Qu Chao Yang National Engineering Research Center of Near-Net-Shape Forming for Metallic Materials South China University of TechnologyGuangzhou510640China

For the purpose of elevated temperature service and weight reduction in aerospace vehicle applications,a novel Ti-Zr-Fe-Cu-Ni-Co-Mo filler metal was employed to join TiAl to Ni-based superalloy(GH536).The effects of brazing temperature on interfacial microstructure and chemical composition of the joints were *** representative joint microstructure from TiAl substrate to GH536 substrate was primarily composed of four characteristic layers in order:B_(2);Al_(3)NiTi_(2);AlNi_(2)Ti containing Cr-rich(Cr,Ni,Fe)_(ss)(subscript ss represents solid solution),Ni-rich(Ni,Cr,Fe)_(ss) and TiNi3;Cr-rich(Cr,Ni,Fe)_(ss)containing AlNi_(2)Ti,Ni-rich(Ni,Cr,Fe)_(ss) and *** IV has the majority of the brazing seam,while LayerⅡwas the *** the thickness of LayerⅡwas not affected by brazing *** the increase in brazing temperature in the range of 1110-1170℃,both the shear strength and the thickness of brazing seam firstly increased and then *** joint performance was jointly controlled by the thickness of brazing seam,the amounts of microcracks and intermetallic compounds formed in brazing *** maximum shear strength of 183 MPa at room temperature was obtained together with a peak thickness when the joint was brazed at 1150℃for 10 min and the shear fracture mainly occurred in the thinnest LayerⅡAl_(3)NiTi_(2).

关键词： TiAl alloy Ni-based superalloy Brazing Microstructure Shear strength

Vegetation and Climate Variations at Taibai, Qinling Mountains in Central China for the Last 3 500 cal BP

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Journal of Integrative Plant Biology 2005年第8期47卷 905-916页

作者： xiao-qiang li John DODSON Jie ZHOU Su-Min WANG Qian-li SUN State Key Laboratory of Loess and Quaternary Geology Institute of Earth Environment the Chinese Academy of Sciences Xi＇an 710075 China Institute for the Environment Brunel University Uxbridge Middlesex UB8 3PH UK Nanjing Institute of Geography and limnology the Chinese Academy of Sciences Nanjing 210008 China

Pollen records of two swamp sections, located at Taibai Mountain, the highest peak in the Qinling Mountains of central China, show variations of vegetation and climate for the last 3 500 cal BP. The pollen assemblage at the Foyechi and Sanqingchi sections and the surface soil pollen allowed us to reconstruct a high-altitude vegetation history at Taibai Mountain for the first time. The data indicated that there was a cold-dry climate interval between 3 500 and 3 080 cal BP and a relatively warm and wet period compared with the present from 3 080 to 1 860 cal BE The warmest period in the late Holocene on Taibai Mountain was from 1 430 to 730 cal BP, with an approximate 2 ~C increase in mean annual temperature compared with today. There was a relatively cool-dry climate interval from 730 to 310 cal BE After 310 cal BE a mountain tundra vegetation developed again and the position of the modern tree line was established.

关键词： climate variation Late Holocene pollen Taibai Mountain vegetation.

The influence of ultrasonic vibration on parts properties during incremental sheet forming

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Advances in Manufacturing 2021年第2期9卷 250-261页

作者： Yan-Le li Zi-Jian Wang Wei-Dong Zhai Zi-Nan Cheng Fang-Yi li xiao-qiang li Key Laboratory of High Efficiency and Clean Mechanical Manufacture Ministry of EducationSchool of Mechanical EngineeringShandong UniversityJinan 250061People’s Republic of China National Demonstration Center for Experimental Mechanical Engineering Education Shandong UniversityJinan 250061People’s Republic of China School of Mechanical Engineering and Automation Beihang UniversityBeijing 100083People’s Republic of China

The integration of ultrasonic vibration into sheet forming process can significantly reduce the forming force and bring benefits including the enhancement of surface quality,the enhancement of formability and the reduction of ***,the influencing mechanisms of the high-frequency vibration on parts properties during the incremental sheet forming(ISF)process are not well known,preventing a more efficient forming *** paper comprehensively investigates the effects of different process parameters(vibration amplitude,step-down size,rotation speed and forming angle)on the micro-hardness,minimum thickness,forming limit and residual stress of the formed ***,a series of truncated pyramids were formed with an experimental platform designed for the ultrasonic-assisted incremental sheet ***,microhardness tests,minimum thickness measurements and residual stress tests were performed for the formed *** results showed that the surface micro-hardness of the formed part was reduced since the vibration stress induced by the ultrasonic vibration within the material which eliminated the original internal *** superimposed University,Beijing 100083,People’s Republic of China ultrasonic vibration can effectively uniform the residual stress and thickness distribution,arid improve the forming limit in the case of the small deformation *** addition,through the tensile fracture analysis of the formed part,it is shown that the elongation of material is improved and the elastic modulus and hardening index are *** findings of the present work lay the foundation for a better integration of the ultrasonic vibration system into the incremental sheet forming process.

关键词： Incremental sheet forming(ISF) Ultrasonic vibration Residual stress Forming limit