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Discovery and significance of microfossils from Qinbaikouian Dazhuang Formation in Luonan, Shaanxi Province

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Chinese Science Bulletin 1997年第3期42卷 243-245页

作者： chen, z Hua, H Jian, wC Hu, YX Department of Geology Northwest University Xi’an China Xi’an Institute of Geology and Mineral Resources Chinese Academy of Geological Sciences Xi’an China

THE microfossils were obtained by using 5%—7% HF acid from Qingbaikouian Dazhuang Formation in Luonan County, Shaanxi Province, with an age of 800—1000 Ma. The fossils may be one type of the oldest skeletal mierofos... 详细信息

关键词： microfossil Qinbaikouian Dazhuang Formation Shaanxi Province.

Effect of 2–6 at.% Mo addition on microstructural evolution of Ti-44Al alloy

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Journal of Materials Science & Technology 2018年第7期34卷 1196-1204页

作者： S.z.zhang z.w.Song J.C.Han C.J.zhang P.Lin D.D.zhu F.T.Kong Y.Y.chen School of Materials Science and Engineering Taiyuan University of Technology Shanxi Key Laboratory of Advanced Magnesium-Based Materials Taiyuan University of Technology School of Mechanical Engineering Taiyuan University of Technology School of Mechanical Engineering Quzhou University State Key Laboratory for Advanced welding and Jointing Harbin Institute of Technology

In order to understand the effect of Mo alloying on the microstructural evolution of TiAl alloy, the as-cast microstructure, heat treated microstructure characteristic, and hot compression microstructure evolution of Ti-44Al alloy have been studied in this work. The as-cast microstructure morphology changes from （γ＋α2） lamellar colony and β/β0＋γ mixture structure to β/β0 phase matrix widmannstatten structure, when Mo content increases from 2 at.% to 6 at.%. Affected by the relationship between β phase and α90℃phase, the angles between the lamellar orientation and the block β/β0 phase are roughly at 0℃, 45℃ and 90℃. Comparing with heat treatment microstructure, the hot compression microstructure contains less β/β0 phase, however, theβ/β0 phase containing 2Mo alloy and 3Mo alloy hot compressed at 1275 ℃ has the inverse tendency. In addition, （α2 ＋γ） colony is decomposed by the discontinuous transformation.2017 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science ＆ Technology.

关键词： Phase transformation Titanium aluminides Heat treatment Microstructure evolution,β/βo phase

Enhanced Mechanical Properties of Friction Stir welded 5083Al-H19 Joints with Additional water Cooling

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Journal of Materials Science & Technology 2017年第9期33卷 1009-1014页

作者： B.B.wang F.F.chen F.Liu w.G.wang P.Xue z.Y.Ma School of Mechanical Engineering Liaoning Shihua University Shenyang National Laboratory for Materials Science Institute of Metal ResearchChinese Academy of Sciences

3-mm-thick 5083Al-H19 rolled plates were friction stir welded(FSw) at tool rotation rates of 800 and200 rpm with and without additional water cooling. with decreasing the rotation rate and applying water cooling, softening in the FSw joint was significantly reduced. At a low rotation rate of 200 rpm with additional water cooling, almost no obvious softening was observed in the FSw joint, and therefore a FSw5083Al-H19 joint with nearly equal strength to the base material(BM) was obtained. Furthermore, the grains in the nugget zone were considerably refined with reducing the heat input and ultrafine equiaxed grains of about 800 nm were obtained in the lowest heat input condition. This work provides an effective method to achieve high property FSw joints of precipitate-hardened and work-hardened Al alloys.

关键词： Friction stir welding Aluminum alloy water cooling Microstructure Mechanical property

Effects of diurnal adjustment on biases and trends derived from inter-sensor calibrated AMSU-A data

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Frontiers of Earth Science 2018年第1期12卷 1-16页

作者： H. chen X. zOU z. QIN Department of Atmospheric and Oceanic Sciences University of Colorado Boulder Colorado CO 80309 USA Earth System Science Interdisciplinary Center (ESSIC) University of Maryland College Park Maryland MD 20742 USA Joint Center for Data Assimilation Research and Applications Nanjing University of Information Science and Technology Nanjing 210044 China

Measurements of brightness temperatures from Advanced Microwave Sounding Unit-A （AMSU-A） temperature sounding instruments onboard NOAA Polar- orbiting Operational Environmental Satellites （POES） have been extensively used for studying atmospheric temperature trends over the past several decades. Inter- sensor biases, orbital drifts and diurnal variations of atmospheric and surface temperatures must be considered before using a merged long-term time series of AMSU-A measurements from NOAA- 15, - 18, - 19 and MetOp-A. we study the impacts of the orbital drift and orbital differences of local equator crossing times （LECTs） on temperature trends derivable from AMSU-A using near-nadir observa- tions from NOAA-15, NOAA-18, NOAA-19, and MetOp-A during 1998 - 2014 over the Amazon rainforest. The double difference method is firstly applied to estimation of inter-sensor biases between any two satellites during their overlapping time period. The inter-calibrated observations are then used to generate a monthly mean diurnal cycle of brightness temperature for each AMSU-A channel. A diurnal correction is finally applied each channel to obtain AMSU-A data valid at the same local time. Impacts of the inter-sensor bias correction and diurnal correction on the AMSU-A derived long-term atmospheric temperature trends are separately quantified and compared with those derived from original data. It is shown that the orbital drift and differences of LECT among different POESs induce a large uncertainty in AMSU-A derived long-term warming/cooling trends. After applying an inter-sensor bias correction and a diurnal correction, the warming trends at different local times, which are approximately the same, are smaller by half than the trends derived without applying these corrections.

关键词： AMSU-A diurnal adjustment decadal tem-perature trend

Elite capture,the“follow-up checks”policy,and the targeted poverty alleviation program:Evidence from rural western China

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Journal of Integrative Agriculture 2021年第4期20卷 880-890页

作者： chenG Xiao-yu wANG Jian-ying Kevin z.chen Institute of Agricultural Economics and Development Chinese Academy of Agricultural SciencesBeijing 100081P.R.China School of Economics Zhejiang University of Finance&EconomicsHangzhou 310018P.R.China China Academy for Rural Development Zhejiang UniversityHangzhou 310058P.R.China International Food Policy Research Institute WashingtonD.C.20005USA

Decentralized methods for targeting poverty are widely adopted in developing countries to improve the performance of various poverty alleviation programs.A common challenge for implementing successful decentralized targeting is the existence of elite *** has recently implemented a nationwide decentralized poverty targeting program,the targeted poverty alleviation(TPA)policy,to achieve the national goal of eliminating absolute poverty by the end of *** the largest decentralized poverty targeting program in the world,TPA's successful implementation was believed to be threatened by elite capture in some earlier *** 2015,a targeting correction mechanism,called"follow-up checks"policy,has been *** the"follow-up checks"policy,the elites and other ineligible households who receive benefits under TPA were removed from the *** paper investigates the elite capture phenomenon in TPA using village census data from a poverty-stricken county in 2017-two years after implementing the"follow-up checks"*** find no evidence of elite capture in *** elites are unlikely to become beneficiaries or receive more benefits than *** results contradict earlier findings that reported elite capture in *** argue that the reason is the accountability emphasized by the central government in the"follow-up checks"*** findings imply that having proper accountability is critical for improving targeting performance by global antipoverty initiatives.

关键词： elite capture decentralized poverty targeting targeted poverty alleviation the"follow-up checks"policy accountability

Modulators for Terahertz Communication: The Current State of the Art

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Research 2019年第1期2019卷 895-916页

作者： z.T.Ma z.X.Geng z.Y.Fan J.Liu H.D.chen College of Science Minzu University of ChinaBeijing 100081China School of Information Engineering Minzu University of ChinaBeijing 100081China State Key Laboratory for Integrated Optoelectronics Institute of SemiconductorsChinese Academy of SciencesBeijing 100083China State Key Laboratory of Superlattices and Microstructures Institute of SemiconductorsChinese Academy of SciencesBeijing 100083China

with the increase of communication frequency,terahertz(THz)communication technology has been an important research feld;particularly the terahertz modulator is becoming one of the core devices in THz communication *** modulation performance of a THz communication system depends on the characterization of THz *** modulators based on diferent principles and materials have been studied and ***,they are still on the way to practical application due to low modulation speed,narrow bandwidth,and insufcient modulation ***,we review the research progress of THz modulator in recent years and evaluate devices critically and *** focus on the working principles such as electric,optical,optoelectrical,thermal,magnetic,programmable metamaterials and nonlinear modulation methods for THz wave with semiconductors,metamaterials,and 2D materials(such as graphene,molybdenum disulfde,and tungsten disulfde).Furthermore,we propose a guiding rule to select appropriate materials and modulation methods for specifc applications in THz communication.

关键词： modulator communication narrow

STUDY ON THE NUMERICAL SIMULATION OF MULTI-STAGE ROTARY FORGING OF A NON-AXISYMMETRIC PART AND THE CAE ANALYSIS OF THE DIE STRENGTH

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Acta Metallurgica Sinica(English Letters) 2005年第5期18卷 627-634页

作者： H. Tian J. wang w.P. Dong J. chen z. zhao G.M. wu National Die ＆ Mold CAD Engineering Research Center Shanghai Jiaotong UniversityShanghai 200030 China

Traditionally a rotary forging process is a kind of metal forming method where a conic upper die, whose axis is deviated an angle from the axis of machine, forges a billet continuously and partially to finish the whole deformation. For the rotary forging process simulation, more researches were focused on simulating the simple stage forming process with axisymmetric part geometry. whereas in this paper, the upper die is not cone-shaped, and the billet is non-axisymmetric. So the movement of the punch is much more complicated than ever. The 3D FEM simulation models for the preforming ＆ final forming processes are set up aider carefully studying the complicated movement pattern. Deform-3D is used to simulate the material flow, and the boundary nodal resisting forces calculated by the final stage process simulation is used to analyze the final forming die strength. The CAE analysis of the die shows that the design of the final forming die is not reasonable with lower pre-stress which is easy to crack at the critical corners. An optimum die design is also provided with higher pre-stress, and verified by CAE analysis.

关键词： numerical simulation non-axisymmetric rotary forging die strength

Interface dominated deformation transition from inhomogeneous to apparent homogeneous mode in amorphous/amorphous nanolaminates

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Journal of Materials Science & Technology 2022年第4期99卷 178-183页

作者： z.Q.chen M.C.Li J.S.Cao F.C.Li S.w.Guo B.A.Sun H.B.Ke w.H.wang Songshan Lake Materials Laboratory Dongguan 523808PR China Institute of Physics Chinese Academy of SciencesBeijing 100190PR China Institute of Materials Engineering Nanjing UniversityNantong 226019PR China School of Physics Science and Technology Xinjiang UniversityXinjiang 830046PR China School of Physical Sciences University of Chinese Academy of SciencesBeijing 100049PR China State Key Laboratory for Mechanical Behavior of Material Xi'an Jiaotong UniversityXi’an 710049PR China

The amorphous/amorphous nanolaminates(A/ANLs)have aroused great attentions owing to their tunable structure and enhanced mechanical ***,the plastic deformation mechanism of A/ANLs have yet been ***,we systematically examined the mechanical properties and deformation behavior of series of NiNb/zrCuNi Al A/ANLs via nanoindentaion *** was found that both the amount and morphology of amorphous/amorphous interface(A/AIs)played crucial roles in the plastic deformation of A/*** and straighter A/AIs facilitated multiple shear banding deformation,of which the hardness increased with decreasing layer thickness,as the A/AIs hindered the propagation of shear bands(SBs).whilst,more and wavier A/AIs promoted homogeneous deformation,of which the hardness stayed at a much lower value and was relatively irrelevant with the layer thickness,for the promoted activation of shear transformation zones by A/*** results provide guidance for modifying the mechanical properties of amorphous alloys with interface engineering design.

关键词： Amorphous alloys Nanolaminates Shear bands Hardness Interface

Magneto optics and time resolved terahertz spectrocopy

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Chinese Physics B 2018年第7期27卷 112-119页

作者： T Dong z G chen N L wang International Center for Quantum Materials School of PhysicsPeking UniversityBeijing 100871China Institute of Physics Chinese Academy of SciencesBeijing 100190China

Exploring, manipulating, and understanding new exotic quantum phenomena in condensed-matter systems have gen- erated great interest in the scientific community. Static and time resolved optical spectroscopies after photoexcitations are important experimental tools for probing charge dynamics and quasiparticle excitations in quantum materials. In Syner- getic Extreme Condition User Facility （SECUF）, we shall construct magneto-infrared and terahertz measurement systems and develop a number of ultrafast femtosecond laser based systems, including intense near to mid-infrared pump terahertz probe. In this article, we shall describe several systems to be constructed and developed in the facilities, then present some examples explaining the application of magneto optics and time resolved spectroscopy techniques.

关键词： magneto-optics infrared spectroscopy mid-infrared pump terahertz probe