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MECHANISM OF SOUND GENERATION By FLOW OVER TWO CAVITIES IN TWO DIMENSIONS

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Journal of Hydrodynamics 2001年第1期13卷 58-63页

作者： liu, X.Z. liu, y.Z. Miao, G.P. Sch. of Naval Archit. and Ocean Eng. Shanghai Jiaotong Univ. Shanghai 20030 China

The mechanism of sound generation by flow over two cavities in two dimensions is studied by examining the evolution of vorticity, pressure level, spectra and directivity of the generated sound. The study shows that the sound pressure level for two cavities is higher than that for a single cavity. When the distance between the two cavities is large, the interaction between vortices caused by cavities is weak enough to be negligible, so that the results from the acoustic analogy approach coincide with those from the superposition principle. When the distance between the two cavities is relatively small, however, the interaction between vortices becomes stronger and the results from acoustic analogy approach are then larger than those from the superposition principle. Regarding the nonlinear interaction of sound waves in the far field, high harmonic waves can occur when the dimensions of the two cavities are equal, while the sum and difference frequency waves besides the high harmonic waves appear when the dimensions of the two cavities are different.

关键词： Cavitation Computer simulation Hydrodynamics

Dispersion and Damage of Carbon Nanotubes in Carbon Nanotube/7055Al Composites During High-Energy Ball Milling Process

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Acta Metallurgica Sinica(English Letters) 2021年第2期34卷 196-204页

作者： S.Bi B.L.Xiao Z.H.Ji B.S.liu Z.y.liu Z.y.Ma Shi-changxu Innovation Center for Advanced Materials Institute of Metal ResearchChinese Academy of Sciences72 Wenhua RoadShenyang 110016China School of Material Science and Engineering University of Science and Technology of China72 Wenhua RoadShenyang 110016China AVIC Manufacturing Technology Institute Beijing 100024China

High-energy ball milling(HEBM)combined with powder metallurgy route was used to fabricate carbon nanotube(CNT)reinforced 7055 Al *** powder morphology evolution processes(HEBM-1 and HEBM-2)were designed to investigate the dispersion and damage of CNTs during HEBM ***-1 evolution process involved powder fl attening,cold-welding and fracture,while HEBM-2 evolution process consisted of powder fl attening and *** HEBM-1,the repetitive fracture and cold-welding process was effective for dispersing ***,the powder fl attening process in HEBM-2 was unsuccessful in dispersing CNTs due to two reasons:(1)the thickness of fl aky Al powders exceeded the critical value,and(2)the clustered CNTs embedded in fl aky Al powders could not be *** of the broadening of D band and the appearance of a new defect-related D’band,product of I D/I G and full width half maximum of D band,rather than I D/I G,was used to evaluate the actual damage of *** indicates that the damage of CNTs was severe in powder fl attening and fracture stages,while the damage of CNTs was small in powder cold-welding stage.

关键词： Metal matrix composites Carbon nanotubes Powder evolution Dispersion and damage Powder metallurgy

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城市水系统理论及其模型研制与应用

中国科学：地球科学 2024年第3期54卷 725-744页

作者：夏军张永勇佘敦先张世彦杨军吕明权张翔罗安琪吴胜军刘阳中国科学院地理科学与资源研究所陆地水循环及地表过程重点实验室北京100101 武汉大学水资源与水电工程科学国家重点实验室武汉430072 中国科学院城市环境研究所城市环境与健康重点实验室福建省流域生态重点实验室水生态健康研究组厦门361021 中国科学院重庆绿色智能技术研究院重庆400714

城市水系统理论是流域水系统科学在城市尺度的拓展,为解决城市化引起的人水关系失衡和突出水问题(内涝、黑臭和水污染、生态退化等)提供了新的系统化解决方案.现有城市水系统相关研究大多关注水循环单一过程,对水循环及其伴生的物质循... 详细信息

城市水系统理论是流域水系统科学在城市尺度的拓展,为解决城市化引起的人水关系失衡和突出水问题(内涝、黑臭和水污染、生态退化等)提供了新的系统化解决方案.现有城市水系统相关研究大多关注水循环单一过程,对水循环及其伴生的物质循环、水生态以及人文等过程互馈机制仍需进一步探索.本文以流域水系统科学和水循环理论为基础,发展了城市水系统的概念、理论和技术体系;以城市多种下垫面条件下时变增益降雨-径流模型为核心,耦合自然-社会水循环及其伴生的水环境、水生态等过程和多尺度海绵措施的影响,研发了城市水系统5.0模型,实现了源头降雨-径流-面源污染负荷、排水管网系统水量水质转输、末端调蓄和净化、社会经济水循环、水系统评估和调控等五大关键模拟功能,成果已在武汉市开展示范应用.结果表明:城市水系统应以城市及其联系的河湖为研究对象,探索城市自然-人工侧支水循环和外江调蓄等耦合,以及社会经济发展、海绵措施对水量-水质-水生态等过程的调控机制.研发的城市水系统5.0模型很好地模拟了城区降雨-径流过程、水体总氮和总磷浓度、社会经济发展特征指标等.与实测数据对比,所有降雨-径流场次的相关系数和纳什效率系数分别处于优秀和良好等级;78.1%的实测点位中总氮和总磷浓度模拟偏差均在良好等级,且相关系数均在0.90以上;在18个社会经济发展特征指标中, 100%、83.3%和69.4%的指标偏差、相关系数和纳什效率系数均在优秀等级.在此基础上,优选源头海绵措施、人工强化措施和源头削减-路径拦截-末端治理等分别明显改善了内涝、水体黑臭和湖泊富营养化.其中10年一遇降雨条件下最大内涝淹没面积削减达32.6%,黑臭水体去除率为65%,水体综合营养指数降低了37%,武汉市2020年绿色发展水平也由现状条件下的0.56提升到了0.67,在城市绿色发展评估体系的五个维度(资源利用、环境质量、生态保护、经济增长和绿色生活)中,生态保护维度改善最明显.本研究将进一步推动城市水文学、环境科学和生态学等多学科领域的交叉和发展,也为我国城市复杂水问题的解决和绿色发展等提供重要的理论和技术基础.

关键词：城市水系统人水关系水问题绿色发展理论基础数学模型

INVESTIGATION OF MULTI-STEP THERMO-MECHANICALTREATMENT OF CAN-FORGED TiAl-BASED ALLOy

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Acta Metallurgica Sinica(English Letters) 1997年第4期10卷 369-374页

作者： y.H. He B. y. Huang y. liu and y.X. liu (Powder Metallurgy Research Institute, Central South University of Technology, Changsha 410083, China) Central South Univ of Technology Changsha China

The effects of a new technology, multi-step thermo-mechanical treatment, on the microstructure, deformation substructure and mechanical properties at ambient and elevated tempemture of can-forged Ti-33 Al-3 Cr-0.5Mo (wt%) Alloy were *** results show that, after multi-step thermo-mechanical treatment of can-forged specimens, homogeneous, fine microstructures can be obtained in the whole TiAl-based alloy specimens. Furthermore, the specimen with homogeneous and fine full lamellae microstructure demonstrutes excellent comprehensive mechanical properties at ambient and elevated temperature.

关键词： TiAl-based alloy mechanical property heat treatment

基于ETCCDI的中国极端气温指数栅格数据集研发及评估

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全球变化数据学报（中英文） 2024年第1期8卷 67-75,V0067-V0075页

作者：陈秋沅张宇刘潇喻练秦来徐建军广东海洋大学南海海洋气象研究院湛江524088 广东海洋大学海洋与气象学院近海海洋变化与灾害预警技术实验室湛江524088 广东海洋大学陆架及深远海气候、资源与环境广东普通高校重点实验室湛江524088 广东海洋大学深圳研究院深圳518120

全球增暖背景下,极端天气和气候事件频发,为了统一不同国家和地区对极端气候事件的定义,世界气象组织(WMO)成立了气候变化检测和指数专家组(ETCCDI),给出了26个具有代表性的极端气温和降水指数,用于规范全球极端气候事件的研究。本文利... 详细信息

全球增暖背景下,极端天气和气候事件频发,为了统一不同国家和地区对极端气候事件的定义,世界气象组织(WMO)成立了气候变化检测和指数专家组(ETCCDI),给出了26个具有代表性的极端气温和降水指数,用于规范全球极端气候事件的研究。本文利用中国国家级地面气象站基本气象要素日值数据集(V3.0),计算了中国区域16个ETCCDI定义的极端气温指数,包括最大日最高气温(TXx)、最小日最高气温(TXn)、最大日最低气温(TNx)、最小日最低气温(TNn)、暖昼百分比(TX90p)、冷昼百分比(TX10p)、暖夜百分比(TN90p)、冷夜百分比(TN10p)、夏日日数(SU)、热夜日数(TR)、冰冻日数(ID)、霜冻日数(FD)、持续暖日日数(WSDI)、持续冷日日数(CSDI)、气温日较差(DTR)和生长期长度(GSL)等。为方便不同学科领域研究者使用,本文采用角距离加权插值方法,将台站数据插值成空间分辨率为0.25°×0.25°的经纬网格数据,存储格式为.NetCDF,时间跨度为1961–2020年,时间分辨率为逐年或逐月,包含16个年数据文件和13个月数据文件,数据总量为1.43 GB,压缩后为353.0 MB。该数据集命名为SimmEX_1961-2020_1.0,可为各类极端气温事件的研究提供数据支撑,同时,在环境、经济、能源等领域也有着广泛的应用前景。

关键词：气候变化 ETCCDI 极端气候指数 SimmEX

PREPARATION AND XRD STUDy OF LITHIUM DEFICIENT LiB COMPOUND

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Acta Metallurgica Sinica(English Letters) 2004年第5期17卷 667-671页

作者： Z.J.liu B.y.Huang Z.y.Li StateKeyLaboratoryforPowderMetallurgy CentralSouthUniversityChangsha410083China

The LiB compounds in lithium deficient state were prepared by three methods and its crystal structure was investigated by using XRD. It is found that the lattice constant c of the compound will increase step by step with decreasing Li content from 0.2796nm of the normal LiB to 0.2886, 0.2981 and 0.3118nm of the lithium deficient LiB. The change of the lattice constant is reversible.

关键词： LiB compound crystal structure electrode materials X-ray diffraction

Effect of Carbon Nanotube Orientation on Mechanical Properties and Thermal Expansion Coefficient of Carbon Nanotube-Reinforced Aluminum Matrix Composites

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Acta Metallurgica Sinica(English Letters) 2014年第5期27卷 901-908页

作者： Z.y.liu B.L.Xiao W.G.Wang Z.y.Ma School of Materials Science and Engineering Dalian University of Technology Shenyang National Laboratory for Materials Science Institute of Metal ResearchChinese Academy of Sciences School of Mechanical Engineering Liaoning Shihua University

Carbon nanotube-reinforced 2009Al （CNT/2009Al） composites with randomly oriented CNTs and aligned CNTs were fabricated by friction stir processing （FSP） and FSP-rolling, respectively. The CNT/2009A1 composites with aligned CNTs showed much better tensile properties at room temperature and elevated temperature compared with those with the randomly oriented CNTs, which is mainly attributed to larger equivalent aspect ratio of the CNTs and avoidance of preferential fracture problems. However, much finer grain size was not beneficial to obtaining high strength above 473 K. The aligned CNTs resulted in tensile anisotropy, with the best tensile properties being achieved along the direction of CNT aligning. As the off-axis angle increased, the tensile properties were reduced due to the weakening of the load transfer ability. Furthermore, aligned CNTs resulted in much lower coefficient of thermal expansion compared with randomly oriented CNTs.

关键词： Carbon nanotubes Metal matrix composites Mechanical properties Coefficient of thermalexpansion Friction stir processing

The Credit-Risk Decision Mechanism on Fixed Loan Interest Rate with Imperfect Information

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Journal of Systems Engineering and Electronics 2001年第3期12卷 20-24页

作者： Pang, S. liu, y. Wang, y. yao, H. Department of Mathematics Jinan University Guangzhou 510632 China

In this paper, decision mechanism of credit-risk for banks is studied when the loan interest rate is fixed with asymmetry information in credit market. We give out the designs of rationing and non-rationing on credit risky decision mechanism when collateral value provided by an entrepreneur is not less than the minimum demands of the bank. It shows that under the action of the mechanism, banks could efficiently identify the risk size of the project. Finally, the condition of the project investigation of bank is given over again.

关键词： Classification (of information) Financial data processing Risk assessment

Tensile Strength and Electrical Conductivity of Carbon Nanotube Reinforced Aluminum Matrix Composites Fabricated by Powder Metallurgy Combined with Friction Stir Processing

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Journal of Materials Science & Technology 2014年第7期30卷 649-655页

作者： Z.y.liu B.L.Xiao W.G.Wang Z.y.Ma Shenyang National Laboratory for Materials Science Institute of Metal ResearchChinese Academy of Sciences Dalian University of Technology Liaoning Shihua University

A route combining powder metallurgy and subsequent friction stir processing was utilized to fabricate carbon nanotube （CNT） reinforced AI （CNT/AI） and 6061AI （CNT/6061AI） composites. Microstructural observations indicated that CNTs were uniformly dispersed in the matrix in both CNT/AI and CNT/6061AI composites. Mg and Si elements tended to segregate at CNT-AI interfaces in the CNT/6061AI composite during artificial aging treatment. The tensile properties of both the AI and 6061AI were increased by CNT incorporation. The electrical conductivity of CNT/AI was decreased by CNT addition, while CNT/6061AI exhibited an increase in electrical conductivity due to the Mg and Si segregation.

关键词： Carbon nanotubes Metal matrix composites Mechanical properties Electrical properties Friction stir processing