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On a general theory.for compressing process and aeroacoustics:linear analy.is

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Acta Mechanica Sinica 2010年第3期26卷 355-364页

作者： E .Mao y. P. shi J. Z. Wu State Key.Laboratory.for Turbulence and Complex Sy.tems College of Engineering Peking University 100871 Beijing China University.of Tennessee Space Institute Tullahoma TN 37388 USA

Of the three mutually.coupled fundamental processes （shearing, compressing, and thermal） in a general fluid motion, only.the general formulation for the compress- ing process and a subprocess of it, the subject of aeroacous- tics, as well as their phy.ical coupling with shearing and thermal processes, have so far not reached a consensus. This situation has caused difficulties for various in-depth complex multiprocess flow diagnosis, optimal configuration design, and flow/noise control. As the first step toward the desired formulation in fully.nonlinear regime, this paper employ. the operator factorization method to revisit the analy.ic linear theories of the fundamental processes and their decomposi- tion, especially.the further splitting of compressing process into acoustic and entropy.modes, developed in 1940s-1980s. The flow treated here is small disturbances of a compressible, viscous, and heat-conducting poly.ropic gas in an unbounded domain with arbitrary.source of mass, external body.force, and heat addition. Previous results are thereby.revised and extended to a complete and unified theory. The theory.pro- vides a necessary.basis and valuable guidance for developing corresponding nonlinear theory.by.clarify.ng certain basic issues, such as the proper choice of characteristic variables of compressing process and the feature of their governing equations.

关键词： Longitudinal (compressing) processTransversal (shearing) process Acoustic mode Entropy.mode Aeroacoustics

Suppression of grain boundary.migration at cry.genic temperature in an extremely.fine nanograined Ni-Mo alloy

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Journal of Materials Science & Technology 2020年第22期54卷 65-69页

作者： J.Hu J.X.Li y.-N.shi Sheny.ng National Laboratory.for Materials Science Institute of Metal ResearchChinese Academy of SciencesShenyang 110016China Institute of Advanced Materials East China JiaoTong UniversityNanchang 330013China School of Materials Science and Engineering University of Science and Technology of ChinaHefei 230026China

Microindentation creep tests on an electrodeposited extremely.fine(4.9 nm) nanograined(ng) Ni-14.2 at.% Mo(Ni-14.2 Mo) at both room temperature(RT) and liquid nitrogen temperature(LNT) demonstrated that lowering temperature retarded softening in the ng Ni-Mo alloy. The obtained strain rate sensitivity.at LNT was one order of magnitude lower than that at RT. Microstructural characterization revealed that mechanically.driven grain boundary.GB) migration was greatly.suppressed by.lowering temperature,which might be ascribed to the presence of solute Mo atoms that significantly.retarded coupled GB motion at LNT. Deformation was instead carried by.shear bands.

关键词： Extremely.fine nanograined metals Mechanically.driven grain boundary.migration Cry.genic temperature Shear bands Solute atoms

Healing Process of Casting Pores in a Ni-based Superalloy.by.Hot Isostatic Pressing

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Journal of Materials Science & Technology 2015年第11期31卷 1151-1157页

作者： X.G.Zheng y.-N.shi L.H.Lou Sheny.ng National Laboratory.for Materials Science Institute of Metal Research Chinese Academy of Sciences Superalloy.Division Institute of Metal Research Chinese Academy of Sciences

Hot isostatic pressing （HIP） with a pressure of 180 MPa at a temperature of 1170 ℃ was introduced to an investment cast Ni-based superalloy.（Mgl） turbocharger blade to explore the healing process of casting pores generated during investment casting. Optical micrograph and scanning electron naicroscopy.（SEM） observations indicate that eutectic pores are the main cast defects in the as-cast blade before HIP. These pores normally.locate at the solidification front of γ/γ＇ eutectic with a size of a few micrometers to a few tens of micrometers. After HIP for 4 h, most of the pores were closed. Based on phase characteristics, these pores were healed by.the formation of γ matrix with finer and irregular-shaped γ＇ precipitates. Healing interface can be easily.distinguished by.SEM. Line scan by.using energy.dispersive X-ray.spectroscopy.（EDS） reveals a much higher Ti and Al concentration in the healing interface. It is proposed that solute diffusion toward the casting pores during HIP results in the formation of γ, and the much higher concentration of γ＇-forming elements Al and Ti near the healing interface contributes to the precipitation of γ＇ in the healed region in the succeeding cooling process after HIP.

关键词： Superalloy.Hot isostatic pressing (HIP) Healing

Neuroevolution-enabled adaptation of the Jacobi method for Poisson’s equation with density.discontinuities

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Theoretical & Applied Mechanics Letters 2021年第3期11卷 172-179页

作者： T.-R.Xiang X.I.A.y.ng y.-P.shi Mechanical Engineering Johns Hopkins UniversityMD 21218USA Department of Mechanics and Engineering Science Peking UniversityBeijing 100871China Mechanical Engineering Pennsylvania State UniversityPennsylvania 16802USA

Lacking labeled examples of working numerical strategies,adapting an iterative solver to accommodate a numerical issue,e.g.,density.discontinuities in the pressure Poisson equation,is non-trivial and usually.involves a lot of trial and ***,we resort to evolutionary.neural network.A evolutionary.neural network observes the outcome of an action and adapts its strategy.*** process requires no labeled data but only.a measure of a network’s performance at a *** neuro-evolution and adapting the Jacobi iterative method for the pressure Poisson equation with density.discontinuities,we show that the adapted Jacobi method is able to accommodate density.discontinuities.

关键词： Evolutionary.neural network Jacobi method

LITHIUM ORDERING IN CHEMICALLy.DELITHIATED Li_xCoO_2

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Acta Metallurgica Sinica(English Letters) 2006年第3期19卷 197-202页

作者： X. Liu W.H. Tian H.X. y.ng y. G. shi J. Q. Li Department of Materials Phy.ics and Chemistry University of Science and Technology Beijing Beijing 100083 China Beijing National Laboratory.for Gondensed Matter Phy.ics Institute of Physics The Chinese Academy of Sciences Beijing 100080 Ghina

Chemical delithiated LixCoO2 （x=1, 0.7, 0.66 and 0.57） has been sy.thesized by.using a strong oxidant, NaS2O8 .The structure investigations indicate that all the samples remain with hexagonal cells, which have expansion of c axis during Li extraction. Transmission electron microscopy.（TEM） observations revealed the presence of superstructures arising from intercalated U-ordering corresponding to first-principle calculations. The measurements of the phy.ical properties are also influenced by.Li concentration.

关键词： LixCoO2 delithiated Li-ordering

Ultrasonic-based surface patterning and interfacial reaction of ZrO_(2)ceramics

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Journal of Materials Science & Technology 2023年第24期155卷 202-210页

作者： H.J. Dong Z.L. Li X.G.Song J.C. Feng S.J. Wei J.H. Fu y. shi State Key.Laboratory.of Advanced Welding and Joining Harbin Institute of Technology Harbin 150001 China Shandong Provincial Key.Lab of Special Welding Technology Harbin Institute of Technology at Weihai Weihai 264209 China

We demonstrate a process to achieve selective surface metallization of ZrO_(2)ceramics using ultrasound technology.in atmospheric environments at 350℃,which bestows good weldability.of ZrO_(2)to achieve rapid and reliable connections with other metals as well as ceramic *** challenge is that brazing or diffusion welding processes to accomplish metallurgical connections for ZrO_(2) ty.ically.require holding at elevated temperatures for minutes to hours,while the selective ultrasonic metallization process requires only.a few seconds of processing without the application of covering films or solder *** this study.the selected Sn-2Ti alloy.could effectively.wet and spread on ZrO_(2)substrate under ultrasonication,and continuous interphase lay.rs were rapidly.formed in situ between ZrO_(2)and *** bonding strength for the ZrO_(2)/Sn-2Ti interface was well established with the highest shear strength of 37.1 MPa,and the fracture location occurred at the filler *** interfacial reaction lay.r thickened remarkably.with the prolongation of sonication,accompanied by.the partial cry.tallization of amorphous TiO and the formation of irregularly.striped Ti_(11.31)Sn_(3)O_(10)nanocry.tals.

关键词： Selective ultrasonic metallization Zirconia surface patterning Low temperature connection Sono-oxidation Interfacial reaction

Towards Auction-Based HPC Computing in the Cloud

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Computer Technology.and Application 2012年第7期3卷 499-509页

作者： Moussa Taifi Justin y. shi Abdallah Khreishah Computer and Information Sciences Department Temple University Philadelphia PA 19122 USA

Cloud computing is expanding widely.in the world of IT infrastructure. This is due partly.to the cost-saving effect of economies of scale. Fair market conditions can in theory.provide a healthy.environment to reflect the most reasonable costs of computations. While fixed cloud pricing provides an attractive low entry.barrier for compute-intensive applications, both the consumer and supplier of computing resources can see high efficiency.for their investments by.participating in auction-based exchanges. There are huge incentives for the cloud provider to offer auctioned resources. However, from the consumer perspective, using these resources is a sparsely.discussed challenge. This paper reports a methodology.and framework designed to address the challenges of using HPC （High Performance Computing） applications on auction-based cloud clusters. The authors focus on HPC applications and describe a method for determining bid-aware checkpointing intervals. They.extend a theoretical model for determining checkpoint intervals using statistical analy.is of pricing histories. Also the latest developments in the SpotHPC framework are introduced which aim at facilitating the managed execution of real MPI applications on auction-based cloud environments. The authors use their model to simulate a set of algorithms with different computing and communication densities. The results show the complex interactions between optimal bidding strategies and parallel applications performance.

关键词： Auction-based cloud computing fault tolerance cloud HPC (high performance computing)

SIMULATON ON WELDING PROCESS OF T - JOINTS

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Acta Metallurgica Sinica(English Letters) 2000年第1期13卷 205-211页

作者： H. y. Zhao A. L. Lu Q. y. shi and F. y.n (Welding Division, Department of Mechanical Engineering,Tsinghua University. Beijing 100084, China)

T-joints are widely.used in ship manufacturing and other welding *** welding residual stress and deformation hare significant influence on failure and service life in welding *** us- ing of 3D thermal elasto - plastic FEM, the temperature fields,stress fields and deformation of weld- ing processes on T - joints are analy.ed in this *** moving heat source is considered in the com- putation. Moreover, weld metal filling and multiple - pass welding are simulated using activate/deac- tivate *** avoiding 'locking' in full integration elements of welding computation,the re- duced intergration elements are used in weld *** nonlinear FEM analy.is program MARC is used to complete the computations, as well as its user subroutines that are programmed to develop the special techniques needed in the simulation of welding *** different welding procedures are com- pared, and the welding residual stress and deformation are discussed in details.

关键词： welding,FEM three dimension,temperature field,residual stress

LASER LIFT-OFF OF GaN THIN FILMS FROM SAPPHIRE SUBSTRATES

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Acta Metallurgica Sinica(English Letters) 2001年第6期14卷 448-452页

作者： J. Xu, R. Zhang, y.P. Wang, X.Q. Xiu, S.L. Gu, B. Shen, y. shi, Z.G. Liu and y.D. Zheng (Department of Phy.ics and National Laboratory.of Solid State Microstructures, Nanjing University. Nanjing 210093, China) Department of Phy.ics and National Laboratory.of Solid State Microstructures Nanjing University

Gallium Nitride film was successfully.separated from sapphire substrate by.laser radiation. The absorption of the 248 nm radiation by.the GaN at the interface results in rapid thermal decomposition of interfacial lay.r, y.elding metallic Ga and N2 gas. The substrate can be easily.removed by.heating above the Ga melting point (29°C). X-ray.diffraction, atomic force microscopy.and photoluminescence of GaN before and after lift-off process have been performed, which demonstrated that the separation and transfer process do not alter the structural quality.of the GaN films. And further discussions on the threshold energy.and crack-free strategies of laser lift-off process have also been presented.

关键词： Gallium compounds Laser beam effects Nitrides Sapphire Separation