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新冠肺炎全球大流行下非洲的抗疫和中非合作

国际政治研究 2020年第3期41卷 73-83,M0003,M0004页

作者：刘海方北京大学国际关系学院 100871

新冠肺炎疫情暴发后,非洲国家尽管在整体上也面临实现保障民生和疫情防控的两难选择,但它们还是采取积极举措应对疫情。非洲联盟和成员国建立起二级联动抗击新冠肺炎疫情机制;教育公众做好群防群控和改善社区诊所,使防疫"下沉到社区";... 详细信息

新冠肺炎疫情暴发后,非洲国家尽管在整体上也面临实现保障民生和疫情防控的两难选择,但它们还是采取积极举措应对疫情。非洲联盟和成员国建立起二级联动抗击新冠肺炎疫情机制;教育公众做好群防群控和改善社区诊所,使防疫"下沉到社区";民间和社区也自发产生各种创新性应对行动。这些区域间团结合作方式有效地延缓了疫情在非洲的发展。同时,为因应此次疫情,中国与非洲都表现出团结互助精神,中国在已有卫生合作基础上,向非洲派出抗疫专家医疗队,传递抗击新冠病毒的信心和防疫知识与技术。新冠肺炎疫情远未结束,中国在与非洲携手抗疫的过程中重申团结精神,积极探索建设中非卫生健康共同体。

关键词：非传统安全新冠肺炎疫情全球公共卫生非盟中非合作中国援非医疗队

Distribution control and formation mechanism of gas inclusions in directionally solidified Al2O3-Er3Al5O12-ZrO2 ternary eutectic ceramic by laser floating zone melting

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Journal of Materials Science & Technology 2021年第7期66卷 21-27页

作者： Haijun Su Yuan liu Qun Ren Zhonglin Shen haifang liu Di Zhao Guangrao Fan Min Guo Jun Zhang Lin liu Hengzhi Fu Research&Development Institute of Northwestern Polytechnical University in Shenzhen Shenzhen518057China State Key Laboratory of Solidification Processing Northwestern Polytechnical UniversityXi'an710072China

Distribution control and formation mechanism of gas inclusions formed in directionally solidified Al2O3-Er3Al5O12-ZrO2 eutectic ceramic rods are explored during laser floating zone melting. In atmospheric environment, highly-dense bubble-free eutectic rods are well fabricated at low solidification rate(<25μm/s). Gas inclusions form intermittently when the solidification rate is in the range of 25-50 μm/s,but produce continuously at higher solidification rates(100-200 μm/s). The gas inclusions exhibit an elongated finger-like pattern along the growth direction, which of the maximum value of diameter first increases and then decreases with increasing the solidification rate. Meanwhile, the volume fraction of gas inclusions increased gradually with the solidification rate. Based on the effect of surface tension gradient, heterogeneous nucleation of gas bubbles is evaluated to be the primary formation mechanism of gas inclusions.

关键词： Directional solidification Gas inclusions Eutectic oxide Laser floating zone melting Formation mechanism

Preparation of large-size Al_(2)O_(3)/GdAlO_(3)/ZrO_(2)ternary eutectic ceramic rod by laser directed energy deposition and its microstructure homogenization mechanism

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Journal of Materials Science & Technology 2021年第26期85卷 218-223页

作者： haifang liu Haijun Su Zhonglin Shen Di Zhao Yuan liu Yinuo Guo Min Guo Jun Zhang Lin liu Hengzhi Fu State Key Laboratory of Solidification Processing Northwestern Polytechnical UniversityXi’an710072China

Laser 3D printing based on melt growth has great potential in rapid preparation of Al_(2)O_(3)-based eutectic ce *** this work,la rge-scale Al_(2)O_(3)/GdAlO_(3)/ZrO_(2)ternary eutectic ceramic rod with diameter of 4-5 mm and height higher than 250 mm was additively manufactured by laser directed energy ***,heat treatment was applied to eliminate the microstructure heterogeneity in the as-deposited eutectic ceramic,and the microstructure homogenization mechanism was studied in *** results indicate that colonies and banded structures completely disappear after the heat treatment,producing a homogeneous network eutectic *** microstructure homogenization is revealed to experience three stages of discontinuous coarsening,continuous coarsening and microstructure ***,it is found that the eutectic spacing linearly increases with the heat treatment time,meaning that the coarsening behavior of the laser 3D-printed Al_(2)O_(3)/GdAlO_(3)/ZrO_(2)eutectic ceramic satisfies well with the Graham-Kraft model.

关键词： Oxide eutectic ceramic Laser 3D printing Melt growth Heat treatment Microstructure homogenization

Formation mechanism and roles of oxygen vacancies in melt-grown Al_(2)O_(3)/GdAlO_(3)/ZrO_(2) eutectic ceramic by laser 3D printing

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Journal of Advanced Ceramics 2022年第11期11卷 1751-1763页

作者： haifang liu Haijun SU Zhonglin SHEN Hao JIANG Di ZHAO Yuan liu Yinuo GUO Xiang LI Min GUO Jun ZHANG Lin liu Hengzhi FU State Key Laboratory of Solidification Processing Northwestern Polytechnical UniversityXi’an 710072China Shenzhen Research Institute of Northwestern Polytechnical University Shenzhen 518057China

Laser three-dimensional(3D)printing has become a significant technique to fabricate high-performance Al_(2)O_(3)-based eutectic ceramics based on melt ***,oxygen vacancies are inevitable crystal defects during this process,and their formation mechanism and roles in the as-deposited ceramics are still *** this paper,Al_(2)O_(3)/GdAlO_(3)/ZrO_(2) ternary eutectic ceramics were prepared by laser 3D printing,and the formation mechanism of the oxygen vacancies was revealed by conducting a well-designed annealing *** addition,the effects of the oxygen vacancies on the structure and mechanical property of the as-solidified eutectic ceramic were *** formation of oxygen vacancies is revealed to be a result of the transfer of oxygen atoms from the oxide ceramic to the oxygen-deficient atmosphere by means of vacancy migration ***,the presence of oxygen vacancies has no obvious effects on crystalline structure and microstructure of the additively manufactured eutectic ***,the chemical bond property changes to some extent due to the formation of these crystal defects,which may affect the mechanical property of the as-deposited eutectic *** is found that the hardness decreases by 3.9%,and the fracture toughness increases by 13.3%after removing the oxygen *** results may provide a potential strategy to regulate the mechanical property of the oxide ceramic materials.

关键词： oxide eutectic ceramic laser three-dimensional(3D)printing oxygen vacancy microstructure mechanical property

Enhanced comprehensive properties of stereolithography 3D printed alumina ceramic cores with high porosities by a powder gradation design

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Journal of Materials Science & Technology 2022年第36期131卷 264-275页

作者： Xiang Li Haijun Su Dong Dong Di Zhao Yuan liu Zhonglin Shen Hao Jiang Yinuo Guo haifang liu Guangrao Fan Wenchao Yang Taiwen Huang Jun Zhang Lin liu Hengzhi Fu State Key Laboratory of Solidification Processing Northwestern Polytechnical UniversityXi’an 710072China Research and Development Institute of Northwestern Polytechnical University in Shenzhen Shenzhen 518057China

Ceramic cores with complex structures and optimized properties are critical for hollow turbine blades applied in *** to traditional methods,additive manufacturing(AM)presents great advantages in forming complex ceramic cores,but how to balance the porosity and strength is an enormous *** this work,alumina ceramic cores with high porosity,moderate strength,and low high-temperature deflection were prepared using stereolithography(SLA)3D printing by a novel powder gradation design *** contradiction between porosity and flexural strength is well adjusted when the mass ratio of the coarse,medium,and fine particles is 2:1:1 and the sintering temperature is 1600℃.The fracture mode of coarse particles in sintered SLA 3D printing ceramic transforms from intergranular fracture to transgranular fracture with the increase of sintering temperature and the proportion of fine powders in powder *** sintered porosity has a greater influence on the high-temperature deflection of SLA 3D printed ceramic cores than grain *** this basis,a"non-skeleton"microstructure model of SLA 3D printed alumina ceramic cores is created to explain the relationship between the sintering process and *** a result,high porosity(36.4%),appropriate strength(50.1 MPa),and low high-temperature deflection(2.27 mm)were achieved by optimizing particle size gradation and sintering process,which provides an insight into the important enhancement of the comprehensive properties of SLA 3D printed ceramic cores.

关键词： Ceramic cores Stereolithography(SLA) Powder gradation design Sintering temperature Comprehensive properties

Hosting Africans-What are China's Concerns,If any?

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Hosting Africans-What are China's Concerns,If any?

作者： liu haifang Institute for West Asian and African Studies

"China’s demand for resources has thus underwritten African growth in recent years."Towards the end of 2008,amid the severe winter of the global financial crisis,the presence of thousands of homesick African students was testing China’s *** a responsible power,as it claims to have become in recent years,is China ready to host ever increasing African students,emerging businessmen and traders,besides the already resident diplomatic and commercial African expatriate population?

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Chinese Song of 'Chimurenga'A Chinese descendant has grown into the first Chinese female Minister of Zimbabwe

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Chinese Song of 'Chimurenga'A Chinese descendant has grown i...

作者： liu haifang School of International Studies Peking University

More than a century ago,in 1904,a 17-year-old young Chinese,leaving behind his wife and new-born son,came to Rhodesia(now Zimbabwe)to make a living,as he had no chance of getting a share of his ancestral property,being the youngest among the five boys of a peasant family in Nanpan Village near *** 18years,his illiterate village wife adventured into Africa all by herself to join him,

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The untold story of Chinese perceptions of Angola

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The untold story of Chinese perceptions of Angola

作者： liu haifang Center for African Studies Peking University(PKUCAS)

Introduction The China-Angola relationship has become an extremely topical subject worldwide since 2004 when the two countries signed a multi-billion dollar loan agreement.1 Campos and Vines discuss the idea of China and Angola’s special relationship constituting’a perfect marriage’and examine the idea that Sino-Angolan

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Africa's Emerging Endogenous Dynamics and New Thoughts on SinoAfrican Cooperation

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Africa's Emerging Endogenous Dynamics and New Thoughts on Si...

作者： liu haifang School of International Studies and Deputy Director & Secretary-General of Center for African Studies Peking University

THE FIRST DECADE of the 21st century,especially the years after the outbreak of financial crisis in 2008,saw impressive overall economic performance in *** as the term"Asian Tigers"was used to describe the emerging economies of Southeast Asian nations,the term"African Lions"is rapidly becoming a global ***2010,6 African nations were listed among the world’s 10 fastestgrowing economies,with Africa’s overall growth rate surpassing 5percent,a sharp contrast to Europe’s and North America’s sluggish

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