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Mapping aboveground biomass by integrating geospatial and forest inventory data through a k-nearest neighbor strategy in North Central Mexico

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j.urnal of Arid land 2014年第1期6卷 80-96页

作者： Carlos A AGUIRRE-SAlADO Eduardo j.TREVIO-GARzA Oscar A AGUIRRE-CAlDERóN j.vier j.MNEz-Prez Marco A gonzl.z-TAGlE j.sé R VAlDz-l.zAlDE Guillermo SNCHEz-DíAz Reij. HAAPANEN Alej.ndro I AGUIRRE-SAlADO liliana MIRANDA-ARAGóN Faculty of Forest Sciences Autonomous University of Nuevo Leon Faculty of Engineering Autonomous University of San Luis Potosi Forestry Program Postgraduate College Haapanen Forest Consulting Faculty of Agronomy and Veterinary Autonomous University of San Luis Potosí

As climate change negotiations progress,monitoring biomass and carbon stocks is becoming an important part of the current forest ***,national governments are interested in developing forest-monitoring strategies using geospatial *** statistical methods for mapping biomass,there is a nonparametric approach called k-nearest neighbor(kNN).We compared four variations of distance metrics of the kNN for the spatially-explicit estimation of aboveground biomass in a portion of the Mexican north border of the intertropical *** derived,climatic,and topographic predictor variables were combined with the Mexican National Forest Inventory(NFI)data to accomplish the *** of distance metrics applied into the kNN algorithm was evaluated using a cross validation leave-one-out *** results indicate that the Most Similar Neighbor(MSN)approach maximizes the correlation between predictor and response variables(r=0.9).Our results are in agreement with those reported in the *** findings confirm the predictive potential of the MSN approach for mapping forest variables at pixel level under the policy of Reducing Emission from Deforestation and Forest Degradation(REDD+).

关键词： k-nearest neighbor Mahalanobis most similar neighbor MODIS BRDF-adj.sted reflectance forest inventory the policy of Reducing Emission from Deforestation and Forest Degradation

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Simulations of deformation and damage processes of SiCp/Al composites during tension

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j.urnal of Materials Science & Technology 2018年第4期34卷 627-634页

作者： j.F.zhang X.X.zhang Q.z.wang B.l.Xiao z.Y.Ma Shenyang National laboratory for Materials Science Institute of Metal ResearchChinese Academy of SciencesShenyang 110016China University of Chinese Academy of Sciences Beijing 100049China

The deformation, damage and failure behaviors of 17 vol.% SiCp/2009AI composite were studied by micro- scopic finite element （FE） models based on a representative volume element （RVE） and a unit cell. The RVE having a 3D realistic microstructure was constructed via computational modeling technique, in which an interface phase with an average thickness of 50 nm was generated for assessing the effects of interracial properties. Modeling results showed that the RVE based FE model was more accurate than the unit cell based one. Based on the RVE, the predicted stress-strain curve and the fracture morphology agreed well with the experimental results. Furthermore, lower interface strength resulted in lower flow stress and ductile damage of interface phase, thereby leading to decreased elongation. It was revealed that the stress concentration factor of SiC was -2.0： the average stress in SiC particles reached -1200 MPa, while that of the composite reached -600 MPa.

关键词： Metal matrix composites (MMCs) Fracture Finite element (FE) analysis Interfacial strength Tensile strength Representative volume element (RVE)

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THEORETICAl ANAlYSIS FOR THE MOTION AND TEMPERATURE OF MElT DROPlETS IN SPRAY DEGASSING PROCESS

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Acta Metallurgica Sinica(English letters) 2007年第3期20卷 193-198页

作者： R.z. Wu z.K. Qu B.D. Sun D. Shu j. Wang College of Materials Science ＆ Chemical Engineering Harbin Engineering University Harbin 150001 China State Key laboratory of Metal Matrix Composites Shanghai Jiao Tong University Shanghai 200030 China Department of Chemistry Harbin Normal University Harbin 150025 China

The motion of melt droplets in spray degassing process was anal.zed theoretically. The height of the treatment tank in spray degassing process couM be determined by the results of theoretical calculation of motion of melt droplets. To know whether the melt droplets wouM solidify during spraying process, the balance temperature of melt droplets was also theoretically anal.zed. Then proof experiments for theoretical results about temperature of melt droplets were carried. In comparison, the experimental results were nearly similar to the calculation results,

关键词： spray degassing hydrogen removal aluminum melt motion temperature

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New method for oblique impact dynamics research of a flexible beam with large overall motion considering impact friction force

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Acta Mechanica Sinica 2016年第4期32卷 720-730页

作者： W.Yuan l.li D.G.zhang j.z.Hong School of Science Nanjing University of Science and Technology Department of Engineering Mechanics Shanghai Jiao Tong University

A flexible beam with large overall rotating motion impacting with a rigid slope is studied in this paper. The tangential friction force caused by the oblique impact is anal.zed. The tangential motion of the system is divided into a stick state and a slip state. The contact constraint model and Coulomb friction model are used respectively to deal with the two states. Based on this hybrid modeling method, dynamic equations of the system, which include all states（before, during, and after the collision）are obtained. Simulation results of a concrete example are compared with the results obtained from two other models： a nontangential friction model and a modified Coulomb model. Differences in the results from the three models are discussed. The tangential friction force cannot be ignored when an oblique impact occurs. In addition, the results obtained from the model proposed in this paper are more consistent with real movement.

关键词： collision oblique friction stick tangential considering Coulomb constraint coordinate rotating

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Partition method and experimental validation for impact dynamics of flexible multibody system

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Acta Mechanica Sinica 2018年第3期34卷 482-492页

作者： j.Y.Wang z.Y.liu j.z.Hong School of Naval Architecture Ocean and Civil EngineeringShanghai Jiao Tong University

The impact problem of a flexible multibody system is a non-smooth, high-transient, and strong-nonlinear dynamic process with variable boundary. How to model the contact/impact process accurately and efficiently is one of the main difficulties in many engineering applications. The numerical approaches being used widely in impact analysis are mainly from two fields： multibody system dynamics （MBS） and computational solid mechanics （CSM）. Approaches based on MBS provide a more efficient yet less accurate analysis of the contact/impact problems, while approaches based on CSM are well suited for particularly high accuracy needs, yet require very high computational effort. To bridge the gap between accuracy and efficiency in the dynamic simulation of a flexible multibody system with contacts/impacts, a partition method is presented considering that the contact body is divided into two parts, an impact region and a non-impact region. The impact region is modeled using the finite element method to guarantee the local accuracy, while the non-impact region is modeled using the modal reduction approach to raise the global efficiency. A three-dimensional rod-plate impact experiment is designed and performed to validate the numerical results. The principle for how to partition the contact bodies is proposed： the maximum radius of the impact region can be estimated by an analytical method, and the modal truncation orders of the non-impact region can be estimated by the highest frequency of the signal measured. The simulation results using the presented method are in good agreement with the experimental results. It shows that this method is an effec-rive formulation considering both accuracy and efficiency. Moreover, a more complicated multibody impact problem of a crank slider mechanism is investigated to strengthen this conclusion.

关键词： Partition method Impact dynamics Experimental investigation Efficiency and accuracy Partition principle

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Synergetic deformation mechanisms in an Mg-zn-Y-zr alloy with intragranular lPSO structures

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j.urnal of Magnesium and Alloys 2023年第5期11卷 1754-1768页

作者： z.z.Peng X.H.Shao z.M.liang D.l.Wang l.W.Wang X.l.Ma Hebei Key laboratory of Material Near-Net Forming Technology School of Materials Science and EngineeringHebei University of Science and TechnologyShijiazhuang 050018China Shenyang National laboratory for Materials Science Institute of Metal ResearchChinese Academy of Sciences72 Whenua RoadShenyang 110016China

Deformation kink is one of the important strengthening mechanisms of the long-period-stacking-ordered(lPSO)phase containing magnesium(Mg)alloys,while the deformation twin is generally *** optimize the mechanical properties of lPSO containing Mg alloy by simultaneously exciting kink and twin,we successfully prepared the Mg-zn-Y-zr alloy featuring intragranular lPSO phase and free grain boundary lPSO phase by *** unraveled the corresponding strengthening and toughening mechanisms through transmission electron microscopy characterization and theoretical *** high strength and good plasticity of the homogenized alloy benefit from the synergistic deformation mechanism of multiple kinking and twining in the *** the activation of kinking and twinning depends on the thicknesses of lPSO lamellae and their relative *** results may shed light on optimizing the design of Mg alloys regulating the microstructure of lPSO phases.

关键词： Mg alloy lPSO distribution Kink Twin Transmission electron microscopy

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Anisotropic Inter-granular Corrosion Behaviors and Microstructures of AlMgSiCu Alloy Sheets Made by Thermal–Mechanical Treatments

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Acta Metallurgica Sinica(English letters) 2022年第2期35卷 275-284页

作者： l.M.liu Y.X.lai C.l.Wu z.zhang j.H.Chen Center for High-Resolution Electron Microscopy College of Materials Science and EngineeringHunan UniversityChangsha 410082China

This study investigates the microstructure and local corrosion behavior of an Al-Mg-Si-Cu alloy,which has been subj.cted to cold-rolling with different deformation strain ratios(DSRs)and followed by artificial *** corrosion tests show that peak-aged samples with a small DSR(5-10%)are sensitive to inter-granular corrosion(IGC)along both the normal and rolling *** the DSR increases to medium strength(20-40%),IGC sensitivity decreases along both directions and corrosion propagates *** the DSR is 60-80%,IGC sensitivity along the normal direction continues to decrease,but increases along the rolling direction,indicating pronounced corrosion *** characterization reveals the decreased IGC sensitivity is mainly attributed to a reduction in element segregation at high-angle grain boundaries and the kinked and discontinuous grain boundary corrosion *** increased IGC sensitivity along the rolling direction could be related to the significantly flattened grains.

关键词： Al alloys local corrosion Anisotropy Transmission electron microscopy(TEM) Electron backscattering diffraction(EBSD)

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Coercivity Enhancement of Nd-Fe-B Thin Film Magnets through Dy Surface Diffusion Process

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j.urnal of Materials Science & Technology 2011年第9期27卷 826-830页

作者： C.Y. You j. zhu N. Tian z.X. lu State Key laboratory for Advanced Metals and Materials University of Science and Technology Beijing Beijing 100083 China School of Materials Science and Engineering Xi＇an University of Technology Xi＇an 710048 China

The Dy capping layer was deposited at different temperatures on the Nd-Fe-B thin films to investigate the mechanism of the coercivity enhancement through the Dy surface diffusion. The highest coercivity of 2005 kA/m （25.2 kOe） was obtained at the Dy deposition temperature of 460℃, which was significantly higher than the value of 1297 kA/m （16.3 kOe） without Dy capping layer. By performing the transmission electron microscopy （TEM） analysis, it was found that some of the grain boundaries were enriched with Nd element, which could be partly ascribed to the promotion by the Dy surface diffusion. In comparison to the evolution of the spin reorientation temperature of Nd2Fe14B phase after the deposition of the Dy capping layer, it is concluded that structural modification plays a significant role in the coercivity enhancement due to the Dy surface diffusion.

关键词： Nd-Fe-B thin film Coercivity enhancement Dy layer Microstructure

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TRANSFORMATION BEHAVIOR OF Ti_(50-x/2)Ni_(50-x/2)Cu_x AllOYS

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Acta Metallurgica Sinica(English letters) 2006年第6期19卷 391-396页

作者： j. Wang W. j.n M.z. Cao R. Yang Institute of Metal Research Chinese Academy of Sciences Shenyang 110016 China Institute of Metal Research Chinese Academy of Sciences Shenyang 110016 China Institute of Metal Research Chinese Academy of Sciences Shenyang 110016 China Institute of Metal Research Chinese Academy of Sciences Shenyang 110016 China

Phase transformation behavior of Ti50-x/2Ni50-x/2Cux (x=2, 5, 15) alloys was investigated using differential scanning calorimetry (DSC). The results show that Ti50-x/2Ni50-x/2Cux alloys undergo a two-stage martensitic transformation on cooling and transform reversely in one stage on heating when treated at 823K for 5 hours. Heat treatment has no effect on the transformation behavior of Ti49Ni49Cu2 alloy but does influence that of Ti47.5Ni47.5Cu5 alloy and Ti42.5Ni42.5Cu15 alloy. Effect of heat treatment is related with precipitation of CuNiTi phase. The maximum recoverable elongation of Ti49Ni49Cu2 wire is about 6%.

关键词： microstructure transformation shape memory Ti-Ni-Cu

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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 anal.ze 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

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