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Acta Mechanica Solida Sinica 2021年第2期34卷 263-273页

作者： Kai Zhang Mingchuan Wang weijie liu Jianlin liu College of Pipeline and Civil Engineering China University of Petroleum(East China)Qingdao 266580China Sino-French Engineer School Nanjing University of Science and TechnologyNanjing 210094China Institute of Applied Physics and Computational Mathematics Beijing 10094China

In this study,the numerical simulations of sheet metal forming processes are performed based on a fully coupled elastoplastic damage *** effects of stress triaxiality and Lode angle are introduced into the damage evolution law to capture the loading-path-dependent *** proposed constitutive model is implemented into the finite element(FE)code ABAQUS/Explicit via the user-defined subroutine(VUMAT).Next,the identification procedure for DP780 based on the hybrid experimental-numerical method is presented in *** numerical results of simple tests are compared with the experiments,and obvious improvement is observed for the proposed model under various loading ***,the model is applied to predict the edge fracture during sheet blanking *** predicted global load–displacement responses and crack paths have a good agreement with the experimental results,indicating that the model holds great potentials in simulation of metal forming processes.

关键词： Ductile damage Full coupling Stress state Numerical simulation Edge fracture

High performance low cost steels with ultrafine grained and multi-phased microstructure

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Science China(Technological Sciences) 2009年第8期52卷 2245-2254页

作者： liu XiangHua LAN HuiFang DU LinXiu liu weijie State Key Laboratory of Rolling and Automation Northeastern UniversityShenyang 110004China Graduate Institute of Ferrous Technology Pohang University of Science and TechnologyPohang790-784Korea

Ultrafine grained ferrite was obtained through tempering cold rolled martensite with an average grain size of 200―400 nm in a low carbon and a microalloyed steel. Thermal and mechanical stability of the two steels was studied. Due to the pinning effect of microalloyed precipitates on the movement of dislocations and grain boundaries, the recrystallization and grain growth rate were retarded, and the thermal stability of ultrafine grained microstructure was improved. The ultrafine grained ferritic steel was strengthened, but its strain hardening rate was reduced. It seems that the tiny carbide precipitates have no significant effect on work hardening rate. The ultrafine grained ferrite+martensite dual phase microstructure was obtained in the microalloyed steel through intercritically annealing cold rolled martensite. The resulting multiphase microstructure has a tensile strength higher than 1.0 GPa with a yield ratio lower than 0.7. Another type of multiphase microstructure with nanoscaled lath bainite+ retained austenite was obtained through an isothermal heat treatment in low temperature bainite transformation region in high carbon steel. The tensile strength was as high as 1.64 GPa with a yield ratio of 0.84.

关键词： ultrafine grained steel multiphase high strength yield ratio

Memway:In-Memory Waylaying Acceleration for Practical Rowhammer Attacks Against Binaries

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Tsinghua Science and Technology 2019年第5期24卷 535-545页

作者： Lai Xu Rongwei Yu Lina Wang weijie liu the Key Laboratory of Aerospace Information Security and Trusted Computing Ministry of Education School of Cyber Science and Engineering Wuhan University

The Rowhammer bug is a novel micro-architectural security threat, enabling powerful privilege-escalation attacks on various mainstream platforms. It works by actively flipping bits in Dynamic Random Access Memory(DRAM) cells with unprivileged instructions. In order to set up Rowhammer against binaries in the Linux page cache, the Waylaying algorithm has previously been proposed. The Waylaying method stealthily relocates binaries onto exploitable physical addresses without exhausting system memory. However, the proof-of-concept Waylaying algorithm can be easily detected during page cache eviction because of its high disk I/O overhead and long running time. This paper proposes the more advanced Memway algorithm, which improves on Waylaying in terms of both I/O overhead and speed. Running time and disk I/O overhead are reduced by 90% by utilizing Linux tmpfs and inmemory swapping to manage eviction files. Furthermore, by combining Memway with the unprivileged posix fadvise API, the binary relocation step is made 100 times faster. Equipped with our Memway+fadvise relocation scheme,we demonstrate practical Rowhammer attacks that take only 15–200 minutes to covertly relocate a victim binary,and less than 3 seconds to flip the target instruction bit.

关键词： Rowhammer bug Waylaying algorithm in-memory swapping page cache eviction

Petahertz communication:Harmonizing optical spectra for wireless communications

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Digital Communications and Networks 2021年第4期7卷 605-614页

作者： Zhengyuan Xu weijie liu Zhaocheng Wang Lajos Hanzo Wireless-Optical Communications Key Laboratory of CAS University of Science and Technology of ChinaHefei230027China Department of Electronic Engineering Tsinghua UniversityBeijing100084China School of Electronics and Computer Science University of SouthamptonSouthamptonS0171BJUK

With the rapid deployment of Next-Generation Networks(NGN),the research community has initiated discussions on an entirely new suite of optical enabling *** pave the way for the development of future wireless networks,this article aims to unify the existing infrared,visible light,and ultraviolet subbands while also exploring the potential of the Petahertz(PHz)band to support extremely bandwidth-thirsfy telepresence style *** focus is on the emerging Petahertz Communication(PetaCom)framework,scenario-dependent propagation channels,modulation schemes,system performance,multiple access techniques,and *** conclude with a range of PetaCom challenges and open research issues.

关键词： Petahertz communication Petahertz spectrum harmonization Optical spectrum Optical wireless communication

Flow field control for 2-meter high-speed free-jet wind tunnel

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Chinese Journal of Aeronautics 2023年第10期36卷 77-89页

作者： Jiayi TIAN Zhongwei LING weijie liu Jianhua Qin Neng XIONG China Aerodynamics Research and Development Center Mianyang 621000China

The 2-meter High-speed Free-jet Wind Tunnel(2 m HFWT)is China’s first large-scale open-jet trisonic wind *** to traditional closed high-speed wind tunnels,this wind tunnel is endowed with remarkable advantages of ample test chamber space,less interference from the tunnel wall,flexible model support mode,and adjustable continuous variation of the Mach ***,its unique structure makes traditional wind tunnel control methods difficult to apply and brings significant challenges to wind tunnel flow field *** this paper,a flow field control system is designed for the 2 m HFWT by comprehensively using advanced control technologies such as neural network,gain scheduling,feedforward control,and adaptive *** practical application tests,it is proved that the proposed control system successfully solves the problem of high-precision flow field control under continual depletion of storage tank pressure,and realizes distinctive functions of adaptive static pressure matching and continuously varying Mach number at supersonic *** addition,due to the application of workflow technology,the flow field control system can flexibly adapt to the implementation of tests of different types and operation conditions,thus fully satisfying the needs of conducting various conventional and special tests in the 2 m HFWT.

关键词： Continuously varying Mach number Wind tunnel Flow field control Neural network Static pressure matching Feedforward control

Design and Implementation of a Time Synchronization Method for UOWC Networks

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Journal of Communications and Information Networks 2024年第1期9卷 56-63页

作者： weijie liu Jingyi Zhang Nuo Huang Zhengyuan Xu CAS Key Laboratory of Wireless-Optical Communications School of Information Science and TechnologyUniversity of Science and Technology of ChinaHefei 230027China

Underwater optical wireless communication (UOWC) technology facilitates high-speed data transmission among multiple nodes in underwater networks. Nevertheless, the absence of a common clock poses a challenge to achieving systematic and reliable access for multiple nodes within these networks. This paper presents a time synchronization method for UOWC networks to ensure the successful execution of the media access control (MAC) protocol. In this method, the node obtains timestamps by exchanging messages with the optical access point (OAP). Subsequently, the node calculates the clock drift relative to the OAP and the propagation time,ensuring that transmitted data packets can arrive approximately at the time specified by the OAP. To validate the effect of the proposed method, an experimental UOWC prototype, including the OAP and nodes, is implemented using field programmable gate array (FPGA). The experimental results demonstrate that the maximum difference between the actual arrival times of two data packets that are expected to reach the OAP simultaneously according to the MAC protocol meets the requirements of the quasi-synchronous code division multiple access (QS-CDMA) system, thereby substantiating the effectiveness of this synchronization method.

关键词： UOWC time synchronization MAC FPGA QS-CDMA

MDKB-Bot:A Practical Framework for Multi-Domain Task-Oriented Dialogue System

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Data Intelligence 2019年第2期1卷 176-186页

作者： Yadi Lao weijie liu Sheng Gao Si Li Pattern Recognition and Intelligence System Laboratory Beijing University of Posts and TelecommunicationsBeijing 100876China

One of the major challenges to build a task-oriented dialogue system is that dialogue state transition frequently happens between multiple domains such as booking hotels or ***,the encoder-decoder model based on the end-to-end neural network has become an attractive approach to meet this ***,it usually requires a sufficiently large amount of training data and it is not flexible to handle dialogue state *** paper addresses these problems by proposing a simple but practical framework called Multi-Domain KB-BOT(MDKB-BOT),which leverages both neural networks and rule-based strategy in natural language understanding(NLU)and dialogue management(DM).Experiments on the data set of the Chinese Human-Computer Dialogue Technology Evaluation Campaign show that MDKB-BOT achieves competitive performance on several evaluation metrics,including task completion rate and user satisfaction.

关键词： Dialogue system Knowledge base Natural language understanding Slot filling Natural language generation

CAPT:Context-Aware Provenance Tracing for Attack Investigation

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China Communications 2018年第2期15卷 153-169页

作者： Cheng Tan Lei Zhao weijie liu Lai Xu Lina Wang School of Computer Wuhan University Key Laboratory of Aerospace Information Security and Trusted Computing Ministry of Education Wuhan University

APT attacks are prolonged and have multiple stages, and they usually utilize zero-day or one-day exploits to be penetrating and stealthy. Among all kinds of security tech- niques, provenance tracing is regarded as an important approach to attack investigation, as it discloses the root cause, the attacking path, and the results of attacks. However, existing techniques either suffer from the limitation of only focusing on the log type, or are high- ly susceptible to attacks, which hinder their applications in investigating APT attacks. We present CAPT, a context-aware provenance tracing system that leverages the advantages of virtualization technologies to transparently collect system events and network events out of the target machine, and processes them in the specific host which introduces no space cost to the target. CAPT utilizes the contexts of collected events to bridge the gap between them, and provides a panoramic view to the attack investigation. Our evaluation results show that CAPT achieves the efi＇ective prov- enance tracing to the attack cases, and it only produces 0.21 MB overhead in 8 hours. With our newly-developed technology, we keep the run-time overhead averages less than 4%.

关键词： attack investigation provenance tracing context-aware virtualization technol-ogies APT attacks panoramic view

Application of a novel backwashing process in upflow biological aerated filter

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Journal of Environmental Sciences 2010年第3期22卷 362-366页

作者： Jinshui Yang weijie liu Baozhen Li Hongli Yuana Meiping Tong Jinsong Gao State Key Laboratory for A grobiotechnology College of Biological Sciences Key Laboratory of Agro-Microbial Resource and Application Ministry of Agriculture China Agricultural University Beijing 100193 China. The key Laboratory of Water and Sediment Sciences Ministry of Education Department of Environmental Engineering Peking University Beijing 100871 China Changsha Medical College Changsha 410219 China

To improve the efficiency of backwashing in upflow biological aerated filter （BAF）, a novel backwashing process named air-water siphon backwashing （AWSB） was proposed and applied on laboratory scale. The effects of backwashing on turbidity and suspended solid （SS） in backwashing efluent using this new backwashing process were compared with those of traditional backwashing process, namely air-water backwashing （AWB）. In AWB, the turbidity of backwashing efluent maintained 100 NUT when consumed 60 min and 10.5 L water. However, in AWSB, it declined to 44 NUT, consumed 40 min, and 7 L water. The COD removal of BAF after backwashing was also analyzed. The average removal rate of COD in the reactor backwashed by AWB and AWSB was 89.34% and 90.91%, respectively. Compared with AWB, the backwashing interval had been prolonged 35%. The volume of backwashing water in that AWSB was only 66.7% of that in AWB. The results demonstrated that AWSB required less water and took shorter backwashing timerelative to AWB to achieve the same turbidity of backwashing efluent, and AWSB was more effective in removing fouling than that of AWB. More significant advantage of AWSB was that the backwashing interval was effectively prolonged

关键词： biological aerated filter air-water siphon backwashing chemical oxygen demand

Bi-functions of titanium and lanthanum co-doping to enhance theelectrochemical performance of spinel LiNi_(0.5)Mn_(1.5)O_(4)cathode

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Journal of Materiomics 2019年第2期5卷 156-163页

作者： Xueying Zheng weijie liu Qunting Qu Honghe Zheng Yunhui Huang School of Materials Science and Engineering Tongji UniversityShanghai201804China College of Energy&Collaborative Innovation Center of Suzhou Nano Science and Technology Soochow UniversitySuzhouJiangsu215006PR China

Spinel LiNi_(0.5)Mn_(1.5)O_(4)(LNMO)cathode material doped with Ti and La co-doping were synthesized through a solid-state *** bi-functions of the Ti and La co-doping is *** the one hand,the stability of the LiNi_(0.5)Mn_(1.5)O_(4)crystal structure is enhanced and the Mn3t interference inside the material is reduced by the Ti *** the other hand,the co-doped La contributes to the formation of Li_(0.5)La_(0.5)TiO_(3)(LLTO)superionic conductor incorporated in the bulk LiNi_(0.5)Mn_(1.5)O_(4)phase,thereby enhancing the Li *** the help of XRD,FTIR,SEM and STEM techniques,La and Ti in the crystallographic structure and the dispersion of the LLTO superionic conductor in the bulk LNMO spinel are *** the optimized molar ratio of 20:1 between LNMO and LLTO,the composite exhibits the best electrochemical performances in terms of the reversible capacity,rate capability and cycling *** lithium ion diffusion coefficient in the bulk LNMO phase is tripled by the LLTO superionic conductor incorporation.

关键词： Lithium ion batteries Spinel LiNi_(0.5)Mn_(1.5)O_(4) Li0.5La0.5TiO3 Co-doping Superionic-conductor