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Microstructural evolution of aluminum alloy during friction stir welding under different tool rotation rates and cooling conditions

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Journal of Materials Science & Technology 2019年第6期35卷 972-981页

作者： X.h. Zeng P. Xue l.h. wu D.R. Ni B.l. Xiao K.S. Wang Z.Y. Ma Shenyang National laboratory for Materials Science Institute of Metal Research Chinese Academy of Sciences Shenyang 110016 China University of Chinese Academy of Sciences Beijing 100049 China School of Metallurgical Engineering Xi'an University of Architecture and Technology Xi'an 710055 China

The microstructural evolution during friction stir welding(FSW) has long been studied only using one single welding parameter. Conclusions were usually made based on the final microstructure observation and hence were one-sided. In this study, we used the "take-action" technique to freeze the microstructure of an Al-Mg-Si alloy during FSW, and then systematically investigated the microstructures along the material flow path under different tool rotation rates and cooling conditions. A universal characteristic of the microstructural evolution including four stages was identified, i.e. dynamic recovery(DRV), dislocation multiplication, new grain formation and grain growth. however, the dynamic recrystallization(DRX)mechanisms in FSW depended on the welding condition. For the air cooling condition, the DRX mechanisms were related to continuous DRX associated with subgrain rotation and geometric DRX at high and low rotation rates, respectively. Under the water cooling condition, we found a new DRX mechanism associated with the progressive lattice rotation resulting from the pinning of the second-phase *** on the analyses of the influencing factors of grain refinement, it was clearly demonstrated that the delay of DRV and DRX was the efficient method to refine the grains during FSW. Besides, ultra-high strain rate and a short duration at high temperatures were the key factors to produce an ultrafine-grained material.

关键词： Aluminum alloys Grain refinement Dynamic recrystallization Severe plastic deformation Friction stir welding

Secure beamforming and deployment design for rate-splitting multiple access-based UAV communications

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Science China(Information Sciences) 2025年第1期68卷 342-356页

作者： Bing WANG Xiaofeng TAO Shujun hAN huici wu Kai YANG Zhu hAN National Engineering Research Center of Mobile Network Technologies Beijing University of Posts and Telecommunications Peng Cheng laboratory Department of Electrical and Computer Engineering University of Houston

Rate-splitting multiple access(RSMA) has recently gained attention as a potential robust multiple access(MA)scheme for upcoming wireless networks. Given its ability to efficiently utilize wireless resources and design interference management strategies, it can be applied to unmanned aerial vehicle(UAV) networks to provide convenient services for large-scale access ground users. however, due to the line-of-sight(loS) broadcast nature of UAV transmission, information is susceptible to eavesdropping in RSMA-based UAV networks. Moreover, the superposition of signals at the receiver in such networks becomes complicated. To cope with the challenge, we propose a two-user multi-input single-output(MISO) RSMA-based UAV secure transmission framework in downlink communication networks. In a passive eavesdropping scenario, our goal is to maximize the sum secrecy rate by optimizing the transmit beamforming and deployment location of the UAV-base station(UAV-BS),while considering quality-of-service(QoS) constraints, maximum transmit power, and flight space limitations. To address the non-convexity of the proposed problem, the optimization problem is first decoupled into two subproblems. Then, the successive convex approximation(SCA) method is employed to solve each subproblem using different propositions. In addition, an alternating optimization(AO)-based location RSMA(l-RSMA) beamforming algorithm is developed to implement joint optimization to obtain the suboptimal solution. Numerical results demonstrate that(1) the proposed l-RSMA scheme yields a28.97% higher sum secrecy rate than the baseline l-space division multiple access(SDMA) scheme;(2) the proposed l-RSMA scheme improves the security performance by 42.61% compared to the l-non-orthogonal multiple access(NOMA) scheme.

关键词： rate-splitting multiple access UAV communication precoding optimization deployment location physical layer security

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Preparation of Co/S co-doped carbon catalysts for excellent methylene blue degradation

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International Journal of Minerals,Metallurgy and Materials 2025年第1期32卷 169-181页

作者： haixu li haobo he Tiannan Jiang Yunfei Du Zhichen wu liang Xu Xinjie Wang Xiaoguang liu Wanhua Yu Wendong Xue School of Materials Science and Engineering University of Science and Technology BeijingBeijing 100083China Beijing Jinyu Tongda Refractory Technologies Co. Ltd.Beijing 100085China

S and Co co-doped carbon catalysts were prepared via pyrolysis of MOF-71 and thiourea mixtures at 800℃at a mass ratio of MOF-71 to thiourea of 1:0.1 to effectively activate peroxymonosulfate(PMS)for methylene blue(MB)*** effects of two different mixing routes were identified on the MB degradation ***,the catalyst obtained by the alcohol solvent evaporation(MOF-AEP)mixing route could degrade 95.60%MB(50 mg/l)within 4 min(degradation rate:K=0.78 min^(-1)),which was faster than that derived from the direct grinding method(MOF-DGP,80.97%,K=0.39 min^(-1)).X-ray photoelectron spectroscopy revealed that the Co-S content of MOF-AEP(43.39at%)was less than that of MOF-DGP(54.73at%),and the proportion of C-S-C in MOF-AEP(13.56at%)was higher than that of MOF-DGP(10.67at%).Density functional theory calculations revealed that the adsorption energy of Co for PMS was -2.94 eV when sulfur was doped as C-S-C on the carbon skeleton,which was higher than that when sulfur was doped next to cobalt in the form of Co-S bond(-2.86 eV).Thus,the C-S-C sites might provide more contributions to activate PMS compared with ***,the degradation parameters,including ph and MOF-AEP dosage,were ***,radical quenching experiments and electron paramagnetic resonance(EPR)measurements revealed that ^(1)O_(2)might be the primary catalytic species,whereas·O~(2-)might be the secondary one in degrading MB.

关键词： advanced oxidation process alcohol solvent evaporation hydrogen bond S and Co co-doped carbon catalysts wastewater remediation

Boosting cationic and anionic redox activity of li-rich layered oxide cathodes via li/Ni disordered regulation

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Journal of Energy Chemistry 2025年第1期100卷 533-543页

作者： Zewen liu Zhen wu hao Wang Xudong Zhang Yuanzhen Chen Yongning liu Shengwu Guo Shenghua Chen Yanli Nan Yan liu State Key laboratory for Mechanical Behavior of Materials Xi'an Jiaotong University School of Materials Science and Engineering Xi'an University of Architecture and Technology hefei Advanced Computing Center Operation Management Corp ltd Network Information Center Xi'an Jiaotong University

lithium-rich layered oxides （llOs） are increasingly recognized as promising cathode materials for nextgeneration high-energy-density lithium-ion batteries （lIBs）.however,they suffer from voltage decay and low initial Coulombic efficiency （ICE） due to severe structural degradation caused by irreversible O ***,we introduce a three-in-one strategy of increasing Ni and Mn content,along with li/Ni disordering and TM–O covalency regulation to boost cationic and anionic redox activity simultaneously and thus enhance the electrochemical activity of *** target material,li1.2Ni0.168Mn0.558Co0.074O2（l1）,exhibits an improved ICE of 87.2%and specific capacity of 293.2 mA h g-1and minimal voltage decay of less than 0.53 m V cycle-1over 300 cycles at 1C,compared to li1.2Ni0.13Mn0.54Co0.13O2（ls）(274.4 mA h g-1for initial capacity,73.8%for ICE and voltage decay of 0.84 mV/cycle over 300 cycles at 1C).Theoretical calculations reveal that the density of states （DOS） area near the Fermi energy level for l1 is larger than that of ls,indicating higher anionic and cationic redox reactivity than ***,l1 exhibits increased O-vacancy formation energy due to higher li/Ni disordering of 4.76%（quantified by X-ray diffraction Rietveld refinement） and enhanced TM–O covalency,making lattice O release more difficult and thus improving electrochemical *** increased li/Ni disordering also leads to more Ni2+presence in the li layer,which acts as a pillar during li+de-embedding,improving structural *** research not only presents a viable approach to designing low-Co llOs with enhanced capacity and ICE but also contributes significantly to the fundamental understanding of structural regulation in high-performance lIB cathodes.

关键词： Ice

Animal models for the study of hepatitis C virus infection and replication

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World Journal of Gastroenterology 2012年第23期18卷 2909-2913页

作者： Kristin l MacArthur Catherine h wu George Y wu Department of Medicine Beth Israel Deaconess Medical Center Boston MA 02215 United States Department of Medicine Division of Gastroenterology-Hepatology University of Connecticut Health Center Farmington CT 06030-1845 United States

hepatitis C virus (hCV) hepatitis, initially termed non-A, non-B hepatitis, has become one of the leading causes of cirrhosis and hepatocellular carcinoma worldwide. With the help of animal models, our understanding of the virus has grown substantially from the time of initial discovery. There is a paucity of available animal models for the study of hCV, mainly because of the selective susceptibility limited to humans and primates. Recent work has focused modification of animals to permit hCV entry, replication and transmission. In this review, we highlight the currently available models for the study of hCV including chimpanzees, tupaia, mouse and rat models. Discussion will include methods of model design as well as the advantages and disadvantages of each model. Particular focus is dedicated to knowledge of pathophysiologic mechanisms of hCV infection that have been elucidated through animal studies. Research within animal models is critically important to establish a complete understanding of hCV infection, which will ultimately form the basis for future treatments and prevention of disease.

关键词： hepatitis C virus Infection Replication Vac-cine hepatitis A virus

Fhl2 deficiency aggravates Candida albicans infection through decreased myelopoiesis

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Science China life Sciences 2025年

作者： Rongmei Gao Kanchao Chen Yimin Wang Rongxia Guo Xiaoyu Zhang Peng wu Weili Wang Qingxiang huang Xuemei Xie Shangda Yang Yanling lü Qian Ren Fei liu Song Chen Fengxia Ma Tao Cheng hui Cheng State Key laboratory of Experimental.h.matology National Clinical Research Center for Blood Diseases Haihe Laboratory of Cell Ecosystem Institute of Hematology & Blood Diseases Hospital Chinese Academy of Medical Sciences & Peking Union Medical College CAMS Center for Stem Cell Medicine PUMC Department of Stem Cell and Regenerative Medicine

hematopoiesis is a finely tuned process that generates all blood cell types through self-renewal and differentiation, which is crucial for maintaining homeostasis. Acute infections can prompt a hematopoietic response known as emergency myelopoiesis. In this study, using a Candida albicans (C. albicans) infection model, we demonstrated for the first time that disruption of Fhl2 led to increased fungal burden,heightened inflammatory response and reduced survival rates. Impaired myeloid hematopoiesis and immune cell production were evident, as proved by the decreased numbers of hematopoietic stem and progenitor cells (hSPCs) and granulocytes in the bone marrow of Fhl2-deficient mice. In conclusion, Fhl2 regulated emergency myelopoiesis in response to C. albicans, affecting the host’s defense against pathogens.

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Achieving superior mechanical properties in friction lap joints of copper to carbon-fiber-reinforced plastic by tool offsetting

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Journal of Materials Science & Technology 2018年第9期34卷 1628-1637页

作者： l.h.wu K.Nagatsuka K.Nakata Joining and Welding Research Institute Osaka University

It is a challenge to achieve a sound welded metal/carbon-fiber-reinforced thermoplastic（CFRTP） joint with high strength and few bubbles. In this study, sound lap joints of Cu and CFRTP were obtained by friction lap joining（FlJ） directly at rotation rates of 600-2000 rpm, with the welding tool at the joint center and offsetting the tool 7 mm away from the center toward the retreating side, respectively. Tool offsetting reduced the non-uniform temperature distribution in the lap joints resulting from the high conductivity of Cu, which not only enhanced the tensile shear force from 0.89-2.25 kN to 1.71-3.54 kN,with the maximum increasing rate of 135%, but also reduced the bubble area to only 19% of the original level of 2000 rpm. It is the first time to report a high-quality Cu/CFRTP joint with a high strength and few bubbles. The large increase of the strength after tool offsetting was attributed to the increase of the joining area, the decrease of bubbles and the decrease of the CFRTP degradation. The details on the generation,quantitative distribution and expulsion of the bubbles in the FlJ joints were discussed.

关键词： hybrid joining Plastic Metal Carbon-fiber-reinforced plastic Properties

laser additive manufacturing of biodegradable Mg-based alloys for biomedical applications: A review

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Journal of Magnesium and Alloys 2022年第4期10卷 915-937页

作者： C.l.wu W.J.Xie h.C.Man Department of Industrial and Systems Engineering The Hong Kong Polytechnic UniversityHung HomKowloonHong KongChina

Metallic implants are widely used in internal fixation of bone fracture in surgical *** are mainly used for providing mechanical support and stability during bone reunion,which usually takes a few months to *** implants made of stainless steels,Ti-based alloys and CoCrMo alloys have been widely used for orthopedic reconstruction due to their high strength and high corrosion *** metallic implants will remain permanently inside the body after implantation,and a second surgery after bone healing is needed because the long-term presence of implant will lead to various *** implant removal surgery not only incurs expenditure,but also risk and psychological *** a consequence,studies on the development of biodegradable implants,which would degrade and disappear in vivo after bone reunion is completed,have drawn researchers’*** this connection,Mg-based alloys have shown great potentials as promising implant materials mainly due to their low density,inherent biocompatibility,biodegradability and mechanical properties close to those of ***,the high degradation rate of Mg-based implants in vivo is the biggest hurdle to *** from materials selection,a fixation implant is ideally tailor-made in size and shape for an individual case,for best surgical ***,laser additive manufacturing(lAM),with the advent of sophisticated laser systems and software,is an ideal process to solve these *** this paper,we reviewed the progress in lAM of biodegradable Mg-based alloys for biomedical *** effect of powder properties and laser processing parameter on the formability and quality was thoroughly *** microstructure,phase constituents and metallurgical defects formed in the lAMed samples were *** mechanical properties,corrosion resistance,biocompatibility and antibacterial properties of the lAMed samples were summarized and compared with samples fabricated by

关键词： laser additive manufacturing Magnesium alloys Implant Biomedical applications Mechanical properties Biodegradability

EFFECT OF TOOl WEAR ON MICROSTRUCTURE, MEChANICAl PROPERTIES AND ACOUSTIC EMISSION OF FRICTION STIR WElDED 6061 Al AllOY

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Acta Metallurgica Sinica(English letters) 2006年第1期19卷 9-19页

作者： W.M. Zeng h.l. wu J. Zhang East China University of Science and Technology Shanghai 200237 China The University of Texas at El Paso-MetaUurgy and Materials Engineering Texas 79902 USA

Tool condition is one of the main concerns in friction stir welding （FSW）, because the geometrical condition of the tool pin including size and shape is strongly connected to the microstrueture and mechanical performance of the weld. Tool wear occurs during FSW, especially for welding metal matrix composites with large amounts of abrasive particles, and high melting point materials, which significantly expedite tool wear and deteriorate the mechanical performance of welds. Tools with different pin-wear levels are used to weld 6061 Al alloy, while acoustic emission （AE） sensing, metallographic sectioning, and tensile testing are employed to evaluate the weld quality in various tool wear conditions. Structural characterization shows that the tool wear interferes with the weld quality and accounts for the formation of voids in the nugget zone. Tensile test analysis of samples verifies that both the ultimate tensile strength and the yield strength are adversely affected by the formation of voids in the nugget due to the tool wear. The failure location during tensile test clearly depends on the state of the tool wear, which led to the analysis of the relationships between the structure of the nugget and tool wear. AE signatures recorded during welding reveal that the AE hits concentrate on the higher amplitudes with increasing tool wear. The results show that the AE sensing provides a potentially effective method for the on-line manitoring of tool wear.

关键词： acoustic emission online monitoring tool wear 6061 Al alloy