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Materials Sciences and Applications 2018年第4期9卷 393-411页

作者： Seung-Hoon Nahm Hyun-Bo Shim Un-Bong Baek chang-min suh Korea Research Institute of Standards and Science Daejeon Republic of Korea School of Mechanical Engineering Yeungnam University Daegu Republic of Korea School of Mechanical Engineering Kyungpook Nat’l University Daegu Republic of Korea

The influence of hydrogen embrittlement on the fatigue behaviors of AISI 304 stainless steel is investigated. The fatigue endurance limits of the untreated and hydrogen-embrittled materials were almost the same at 400 MPa, and hydrogen embrittlement had little influence even though the sample contained about 8.1 times more hydrogen. Thus, the sensitivity of hydrogen gas in this material is very low. A surface crack initiation, growth, coalescence, and micro ridge model is proposed in this study. Slip line formation?⇒microcrack formation?⇒increases in the crack width, and blunting of the crack tip as it grows?⇒formation of many slip lines because of deformation in the shear direction?⇒growth of the crack in the shear direction, forming micro ridges, coalescence with adjacent cracks ⇒?continuous initiation, growth, coalescence, and ridge formation of surface cracks and specimen breakage.

关键词： Hydrogen-Embrittled Fatigue Behaviors Surface Crack Initiation Growth Coalescence Micro Ridge Formation VHCF (Very High Cycle Fatigue) Fracture Surface Analysis

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北师大版初中数学新教材的特色及变化分析

教学与管理 2025年第1期 44-48页

作者：常海斌宁依敏首都师范大学教育学院北京100048 华东师范大学数学科学学院上海200241

深刻理解和准确解读教材是有效使用教材的前提。北师大版初中数学新教材遵循“教育本位”的教材编写理念,在章首语、栏目设置、问题解决、习题设计和素材选取上各具特色;教材整体采用跨领域混编、螺旋式上升和小结整合式的编写模式,着... 详细信息

深刻理解和准确解读教材是有效使用教材的前提。北师大版初中数学新教材遵循“教育本位”的教材编写理念,在章首语、栏目设置、问题解决、习题设计和素材选取上各具特色;教材整体采用跨领域混编、螺旋式上升和小结整合式的编写模式,着重凸显课程内容的结构化和认知过程的进阶性;四个学习领域以“研究对象”的形式进行内容整合,具有重视代数推理、重构统计量的组合形式以及对综合与实践领域进行主题迭代和核心创变等变化。

关键词：初中数学新教材教材编写特色北师大版教材新教材变化分析

Embedded Surfaces for Symplectic Circle Actions

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Chinese Annals of Mathematics,Series B 2017年第6期38卷 1197-1212页

作者： Yunhyung CHO min Kyu KIM Dong Youp suh Department of Mathematics Education Sungkyunkwan UniversitySeoulRepublic of Korea. Department of Mathematics Education Gyeongin National University of EducationSan 59-12Gyesan-dongGyeyang-guIncheon 407-753Republic of Korea. Department of IVIathematieal Sciences KAIST335 GwahangnoYu-sung GuDaejeon 305-701Republic of Korea.

The purpose of this article is to characterize symplectic and Hamiltonian circle actions on symplectic manifolds in terms of symplectic embeddings of Riemann *** precisely, it is shown that(1) if(M, ω) admits a Hamiltonian S^1-action, then there exists a two-sphere S in M with positive symplectic area satisfying c1(M, ω), [S] > 0,and(2) if the action is non-Hamiltonian, then there exists an S^1-invariant symplectic2-torus T in(M, ω) such that c1(M, ω), [T] = 0. As applications, the authors give a very simple proof of the following well-known theorem which was proved by Atiyah-Bott,Lupton-Oprea, and Ono: Suppose that(M, ω) is a smooth closed symplectic manifold satisfying c1(M, ω) = λ· [ω] for some λ∈ R and G is a compact connected Lie group acting effectively on M preserving ω. Then(1) if λ 0, then the G-action is Hamiltonian.

关键词： Symplectic geometry Hamiltonian action

Cluster Structures in 2-Calabi-Yau Triangulated Categories of Dynkin Type with Maximal Rigid Objects

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Acta Mathematica Sinica,English Series 2017年第12期33卷 1693-1704页

作者： Hui min chang Department of Mathematical Sciences Tsinghua University Beijing 100084 P. R. China Department of Applied Mathematics School of Education The Open University of China Beijing 100039 Po R. China

In this paper, we consider two kinds of 2-Calabi-Yau triangulated categories with finitely many indecomposable objects up to isomorphisms, called An,t =D^b（KA（2t＋1）（n＋1）-3）/τ^t（n＋1）-1[1], where n,t ≥ 1, and Dn,t = Db（KD2t（n＋1））/τ^（n＋1）φ^n, where n,t ≥ 1, and φ is induced by an automorphism of D2t（n＋1） of order 2. Except the categories An,1, they all contain non-zero maximal rigid objects which are not cluster tilting. An,1 contain cluster tilting objects. We define the cluster complex of An,t （resp. Dn,t） by using the geometric description of cluster categories of type A （resp. type D）. We show that there is an isomorphism from the cluster complex of An,t （resp. Dn,t） to the cluster complex of root system of type Bn. In particular, the maximal rigid objects are isomorphic to clusters. This yields a result proved recently by Buan-Palu-Reiten： Let RAn,t, resp. RDn,t, be the full subcategory of An,t, resp. Dn,t, generated by the rigid objects. Then RAn,t≈RAn,1 and TDn,t≈TAn,1 as additive categories, for all t 〉 1.

关键词： 2-Calabi-Yau triangulated category cluster structure cluster complex

A learning framework based on weighted knowledge transfer for holiday load forecasting

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Journal of Modern Power Systems and Clean Energy 2019年第2期7卷 329-339页

作者： Pan ZENG chang SHENG min JIN College of Computer Science and Electronic Engineering Hunan University

Since the variation pattern of load during holidays is different than that of non-holidays, forecasting holiday load is a challenging task. With a focus on this problem, we propose a learning framework based on weighted knowledge transfer for daily peak load forecasting during ***,we select source cities which can provide extra hidden knowledge to improve the forecast accuracy of the load of the target city. Then, all the instances which are from source cities and the target city will be weighted and trained by the improved weighted transfer learning algorithm which is based on the TrAdaBoost algorithm and can decrease negative transfer. We evaluate our method with the classical support vector machine method and a method based on knowledge transfer on a real data set, which includes eleven cities in Guangdong province of China,to illustrate the performance of the method. To solve the problem of limited historical holiday load data, we transfer the data from nearby cities based on the fact that nearby cities in Guangdong province of China have a similar economic development level and similar load variation pattern. The results of comparative experiments show that the framework proposed by this paper outperforms these methods in terms of mean absolute percent error and mean absolute scaled error.

关键词： Load forecasting Holiday effect Sparse data Weighted knowledge transfer

Effect of Al addition on corrosion behavior of high-purity Mg in terms of processing history

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Journal of Magnesium and Alloys 2023年第3期11卷 851-868页

作者： Sang Kyu Woo Byeong-Chan suh Ha Sik Kim chang Dong Yim Helmholtz Zentrum Hereon Max-Planck-Straße 1Geesthacht D-21502Germany Korea Institute of Materials Science 797 Changwondae-roSeongsan-guChangwonGyeongnam 51508Republic of Korea University of Science and Technology 217 Gajeong-roYuseong-guDaejeon 34113Republic of Korea

In this study,the effects of Al addition on the corrosion behavior of pure Mg with controlled impurity contents were systematically analyzed according to the processing *** results revealed that the corrosion behavior of high-purity Mg-Al alloys is strongly related to changes in the microstructure,including theβphase and Al-Mn or Al-Fe phases,and the protectiveness of the surface film according to the Al content and processing *** the as-cast alloys,the corrosion rate increased due to the increase ofβphase as the Al content increased,but in the as-extruded alloys,the corrosion rate,which was high due to intermetallic compounds caused by impurities in the low Al alloy,decreased as the Al content increased,and then increased *** is due to the combined effect of the increase of theβphase and decrease of the impurity effect,and the increase of the dissolved Al *** results suggest that it is necessary to analyze the effect of alloying elements on the corrosion behavior of pure Mg with information concerning the impurity content and processing history.

关键词： Mg High purity Mg-Al alloys Processing history Micro-galvanic Surface film

Performance analysis and flow mechanism of channel wing considering propeller slipstream

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Chinese Journal of Aeronautics 2023年第11期36卷 165-184页

作者： Xiaoxuan MENG Ziyi XU min chang Junqiang BAI School of Aeronautics Northwestern Polytechnical UniversityXi’an 710072China Unmanned System Research Institute Northwestern Polytechnical UniversityXi’an 710072China Shenzhen Research Institude of Northwestern Polytechnical University Shenzhen 518057China

The development of the Urban Air Mobility concept has proposed stringent requirements for the fixed-wing vehicle’s Short/Vertical Take-Off and Landing(S/VTOL)*** its lift-enhancing impact,the channel wing,can improve aircraft low-speed performance and Short Take-Off and Landing(STOL)*** is critical for the performance analysis and flow mechanism study of a channel wing that considers the influence of propeller slipstream to guide the design of S/VTOL *** law and mechanism for the effect of the enclosing angle of the arc wing,the phase angle of the propeller,the tip clearance,the rotational speed and the chordwise position of the propeller on the channel wing are explored utilizing the quasi-steady multi reference frame method.A channel wing with a larger enclosing angle has a better ability to enhance lift and reduce drag using propeller *** effect of propeller phase angle on channel wing aerodynamic forces is periodic and *** propeller rotational speed is helpful to enhance lift and resist flow separation for channel *** can reduce drag for tractor configuration but increase drag for pusher ***,the nose-down pitching moment of a channel wing will grow dramatically,making longitudinal trimming in aircraft layout design challenging.

关键词： Channel wing Computational fluid dynamics Flow interactions Mechanisms Slipstream effect

Dynamic recrystallization behaviour of H13-mod steel

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Journal of Iron and Steel Research International 2020年第9期27卷 1073-1086页

作者： chang-min Li Yuan-biao Tan Fei Zhao College of Materials and Metallurgy Guizhou UniversityGuiyang 550025GuizhouChina

H13-mod steel developed after optimizing the composition and heat treatment process exhibits good hardness and impact toughness and can be used as a shield machine *** on the Avrami equation,the dynamic recrystallization(DRX)behaviour of H13-mod steel during hot compression was studied in the temperature of 900-1150°C and strain rate ranges of 0.01-10 s^-1.A DRX model and finite element software were used to study DRX behaviour of H13-mod *** DRX was found at both low and high strain *** backscatter diffraction and optical microscopy analyses found different DRX nucleation mechanisms at low and high strain rates under different *** a low strain rate,the nucleation was dominated by the strain-induced grain boundary migration,whereas the subgrain coalescence mechanism was dominant at a high strain ***,dynamic recovery occurred in both *** addition,it was easier to obtain small and uniform equiaxed grains at high strain rates than at low strain rates.

关键词： H13-mod steel Dynamic recrystallization Dynamic recrystallization volume fraction model Finite element simulation Nucleation mechanism

Cuticle and skin cell walls have common and unique roles in grape berry splitting

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Horticulture Research 2021年第1期8卷 2428-2438页

作者： Ben-min chang Markus Keller Department of Horticulture Irrigated Agriculture Research and Extension CenterWashington State UniversityProsserWAUSA

The skin protects a fruit from environmental stresses and supports the fruit’s *** of the skin leads to fruit splitting and may compromise commercial production for fruit *** mechanical properties of the cuticle and skin cell walls might influence the splitting susceptibility of fleshy *** shell theory and fracture mechanics were utilized in this study to target the potential factors contributing to splitting *** study analyzed the structure of the cuticle and epidermis in ripening grape berries and examined the temporal dynamics of berry *** waxes were partially removed,and skin cell walls were manipulated using wall stiffening and loosening solutions that altered reactions involving hydrogen peroxide.A more than twofold difference in cuticle thickness among grape cultivars did not account for their differences in splitting ***,while removing predominantly epicuticular wax did not alter the berries’splitting resistance,their surface appearance and increasing yield strength following partial wax removal support the notion that cuticular waxes contribute to berry mechanical *** berries in H 2 O 2-based cell wall loosening solutions increased the splitting probability and accelerated berry splitting,whereas cell wall stiffening solutions decreased the splitting probability and delayed berry *** results showed that both cuticle and skin cell walls contribute to the mechanical properties of grape berries and to their splitting *** results also suggest that the two current explanations for fruit splitting,the critical turgor model and the zipper model,should be viewed as complementary rather than incompatible.

关键词： walls splitting Cut

Reduced graphene oxide-based materials for electrochemical energy conversion reactions

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Carbon Energy 2019年第1期1卷 85-108页

作者： Seokhoon Choi changyeon Kim Jun min suh Ho Won Jang Department of Materials Science and Engineering Seoul National UniversitySeoulRepublic of Korea

There have been ever-growing demands to develop advanced electrocatalysts for renewable energy conversion over the past *** a promising platform for advanced electrocatalysts,reduced graphene oxide(rGO)has attracted substantial research interests in a variety of electrochemical energy conversion *** versatile utility is mainly attributed to unique physical and chemical properties,such as high specific surface area,tunable electronic structure,and the feasibility of structural modification and ***,a comprehensive discussion is provided upon recent advances in the material preparation,characterization,and the catalytic activity of rGO-based electrocatalysts for various electrochemical energy conversion reactions(water splitting,CO2 reduction reaction,N2 reduction reaction,and O2 reduction reaction).Major advantages of rGO and the related challenges for enhancing their catalytic performance are addressed.

关键词： CO2 reduction reaction electrocatalysis N2 reduction reaction O2 reduction reaction reduced graphene oxide water splitting