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Semi-solid A3.6 alloy slurry for rheocasting prepared by a new process

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China Foundry 2013年第3期10卷 176-180页

作者： Liu zheng Liu Xiaomei Mao weimin Faculty of Mechanical and Electronic Engineering Jiangxi University of Science and Technology School of Material science and Engineering University of Science and Technology Beijing

To obtain the semi-solid slurry with uniform and fine structure morphology that satisfies the requirement of rheocasting process, a new process for preparing semi-solid AI alloy slurry was developed, in which local chilling was combined with low superheat pouring and slight electromagnetic stirring （LSPSEMS）. The morphology and the size of primary a-AI in the A3.6 alloy slurry prepared with the new process, i.e., LSPSEMS with local chilling, were investigated using MIAPS image analyzing software, and the grain refinement mechanism was discussed. The results indicate that the semi-solid primary phase consists of particle-like or globular-like a-AI, and the morphology and grain size of primary a-AI in the slurry can be markedly improved by the new process. The fine primary a-AI distributes uniformly in the slurry, which satisfies the requirement of rheocasting. Compared with the alloy prepared by LSPSEMS, the average equal-area-circle grain diameter of primary a-AI in semi-solid A3.6 alloy ingot prepared by the new process is decreased from 85.6μm to 68.8 μm at the central area, 112.6 μm to 77.6 μm at the transition area and is 84.7 μm in the edge area, respectively. The corresponding shape factor of primary a-AI is increased from 0.78 to 0.83. 0.54 to 0.77 and 0.28 to 0.59, respectively. In addition, the pouring temperature could be suitably raised from 620-63.℃ of the traditional process to 650℃ using this technique, which is convenient for practical operation. The mechanism of grain refinement, in the new process, is that the local chilling quickens up the temperature decrease in the center of the melt. The nuclei could not grow up in a short time so the finer grains are formed in the melt.

关键词： semi-solid A3.6 alloy new process rheocasting

Multi-Clock Snapshot Isolation Concurrency Control for NVM Database

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tsinghua science and technology 2022年第6期27卷 925-938页

作者： Xuyang Liu Kang Chen Mengxing Liu Shiyu Cai Yongwei Wu weimin zheng department of computer science and{3. Tsinghua UniversityBeijing 100084China

Multi-Clock Snapshot Isolation(MCSI)is a concurrency control mechanism that implements snapshot isolation on a single-layer Non-Volatile Memory(NVM)*** stores a single copy of data by using multi-version storage to ensure durability and runtime *** multi-clock transaction timestamp assignment,MCSI can efficiently generate snapshots with vector clocks and use per-thread transaction status arrays to identify uncommitted versions in *** evaluation,we compared MCSI with the PostgreSQL-style concurrency control used in the single-layer NVM database *** maximum transaction throughput of MCSI is 101%–195%higher than that of N2DB for the YCSB workloads,and 25%–49%higher for the TPC-C ***,the transaction latency of MCSI remains relatively stable as the thread count *** 18 worker threads,the average transaction latency of MCSI is 65%–84%lower than that of N2DB for the YCSB workloads and 16%–43.lower for the TPC-C workloads.

关键词： Non-Volatile Memory(NVM) snapshot isolation Multi-Version Concurrency Control(MVCC) vector clock

On Dynamic Channel Emulation in Sector MPAC for Over-the-Air Testing of Beamformed Massive MIMO Devices

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China Communications 2023年第4期20卷 41-56页

作者： Xiaochen Chen Heng Wang weimin Wang zheng Liu Yuanan Liu China Academy of Information and Communications technology Beijing 100191China beijing Key Laboratory of Work Safety Intelligent Monitoring Department of Electronic EngineeringBeijing University of Posts and TelecommunicationsBeijing 100876China

In this article,novel emulation strategies for the sectored multiple probe anechoic chamber(SMPAC)are proposed to enable the reliable evaluation of the massive multiple-input multiple-output(MIMO)device operating at beamforming mode,which requires a realistic non-stationary channel *** the dynamic propagation emulation,an efficient closed-form probe weighting strategy minimizing the power angular spectrum(PAS)emulation errors is derived,substantially reducing the associated computational *** the other hand,a novel probe selection algorithm is proposed to reproduce a more accurate fading *** standard channel models and setup configurations are comprehensively simulated to validate the capacity of the proposed *** simulation results show that more competent active probes are selected with the proposed method compared to the conventional ***,the derived closedform probe weighting strategy offers identical accuracy to that obtained with complicated numerical ***,a realistic dynamic channel measured in an indoor environment is reconstructed with the developed methodologies,and 95.6%PAS similarity can be achieved with 6 active *** satisfactory results demonstrate that the proposed algorithms are suitable for arbitrary channel emulation.

关键词： beamforming channel emulation massive MIMO device multiple probe anechoic chamber(MPAC) over-the-air testing

基于JavaCard的移动代理安全模型研究

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通信学报 2003年第11期24卷 27-33页

作者：王汝传孙开翠杨立扬郑晓燕南京邮电学院计算机科学与技术系中国科学院研究生院信息安全国家重点实验室北京100039

欲阻止恶意主机攻击移动代理,代理中的代码信息和数据信息必须被隐藏起来。同时,还要使它们对于执行环境来说是可访问和可执行的。现有措施大都采用软件方法(如密码技术),但并不足以解决恶意主机问题。一个完全不同的方法就是使用可信... 详细信息

欲阻止恶意主机攻击移动代理,代理中的代码信息和数据信息必须被隐藏起来。同时,还要使它们对于执行环境来说是可访问和可执行的。现有措施大都采用软件方法(如密码技术),但并不足以解决恶意主机问题。一个完全不同的方法就是使用可信赖的且可抵御攻击的JavaCard来保护移动代理。本文讨论用JavaCard保护移动代理的机理,同时给出我们所设计的一个JavaCard的安全模型。

关键词：移动代理 JavaCard 安全模型

Prediction of Interspecies Transmission for Avian Influenza A Virus Based on BP Neural Network

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Prediction of Interspecies Transmission for Avian Influenza ...

An Online computer Vision System for Worm’s Quantitative Locomotion Analysis

2009 Fourth International Conference on Bio-Inspired Computing:Theories and Applications(BIC-TA2009)

作者： Xiaoli Qiang1,zheng Kou2 School of Electronic Engineering and computer science,Peking{3.,beijing 100871,P.R.China Key laboratory of High Confidence Software Technologies of Ministry of Education,Peking{3.,beijing 100871,P.R.China State Key Laboratory of Virology,Wuhan Institute of Virology,Chinese Academy of sciences,Wuhan 43.071,China

The prediction of the transmissibility of avian influenza A viruses from birds to humans is very important for the public ***,two categories of molecular patterns,which were associated with the phenotype of interspecies transmission,were found to exist among avian influenza A viruses with different *** the paper,we used the similar method based on wavelet packet decomposition to transform the viral sequences and used the energy features of viral genome as input to train BP neural *** good results of experimentation were got to discriminate the two categories of molecular patterns.A novel method was constructed to predict the transmissibility of avian influenza A viruses.

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An Online Computer Vision System for Worm’s Quantitative Lo...

Performance Analysis for Multimedia Communication Systems with a Multilayer Queuing Network Model

第十一次中国生物物理学术大会暨第九届全国会员代表大会

作者： Hai-ning Zhang1,zheng-xing Wu 1,An-lian Qu 1,Tao Xu 2 1 Huazhong university of science and{3.,Wuhan 43.074,P.R.China 2 Institute of Biophysics,Chinese Academy of sciences,beijing 100101,P.R.China

＜正＞Background:The small nematode Caenorhabditis elegans（***）is an excellent model organism for studying the molecular and cellular basis of nervous system *** it

关键词： online analysis C.elegans computer vision locomotion

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China Communications 2018年第8期15卷 67-76页

作者： Xuehua Tang Zhongyuan Wang Xiaojun Li Zhen Han zheng He Youming Fu School of Remote Sensing and Information Engineering Wuhan UniversityWuhan 430079China Research Institute of Wuhan university in Shenzhen Shenzhen 518000China School of computer science Wuhan UniversityWuhan 430072China State Grid Economic and Technological Research Institute CO. LTDBeijing 102209China

Software performance evaluation in multimedia communication systems is typically formulated into a multi-layered client-server queuing network(MLCSQN) problem. However, the existing analytical methods to MLCSQN model cannot provide satisfactory solution in terms of accuracy, convergence and consideration of interlocking effects. To this end, this paper proposes a heuristic solving method for MLCSQN model to boost the performance prediction of distributed multimedia software systems. The core concept of this method is referred to as the basic model, which can be further decomposed into two sub-models: client sub-model and server sub-model. The client sub-model calculates think time for server sub-model, and the server sub-model calculates waiting time for client sub-model. Using a breadthfirst traversal from leaf nodes to the root node and vice versa, the basic model is then adapted to MLCSQN, with net sub-models iteratively resolved. Similarly, the interlocking problem is effectively addressed with the help of the basic model. This analytical solver enjoys advantages of fast convergence, independence on specific average value analysis(MVA) methods and eliminating interlocking *** experimental results on accuracy and computation efficiency verify its superiority over anchors.

关键词： multimedia communication system queuing network performance evaluation

Garbage Collection and Data Recovery for N2DB

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tsinghua science and technology 2022年第3期27卷 630-641页

作者： Shiyu Cai Kang Chen Mengxing Liu Xuyang Liu Yongwei Wu weimin zheng department of computer science and{3. Tsinghua UniversityBejing 100084China

Non-Volatile Memory(NVM) offers byte-addressability and persistency. Because NVM can be plugged into memory and provide low latency, it offers a new opportunity to build new database systems with a single-layer storage design. A single-layer NVM-Native DataBase(N2 DB) provides zero copy and log freedom. Hence, all data are stored in NVM and there is no extra data duplication and logging during execution. N2 DB avoids complex data synchronization and logging overhead in the two-layer storage design of disk-oriented databases and in-memory databases. Garbage Collection(GC) is critical in such an NVM-based database because memory leaks on NVM are durable. Moreover, data recovery is equally essential to guarantee atomicity, consistency, isolation, and durability properties. Without logging, it is a great challenge for N2 DB to restore data to a consistent state after crashes and recoveries. This paper presents the GC and data recovery mechanisms for N2 DB. Evaluations show that the overall performance of N2 DB is up to 3.6 higher than that of InnoDB. Enabling GC reduces performance by up to 10%,but saves storage space by up to 67%. Moreover, our data recovery requires only 0:2% of the time and half of the storage space of InnoDB.

关键词： Non-Volatile Memory(NVM) Garbage Collection(GC) data recovery

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信息系统的功能重组及其集成化安全管理

计算机工程与应用 1999年第11期35卷 41-43页

作者：王忠民郑利强万军涂序彦北京科技大学计算机系北京100083

文中提出对应用系统进行分解组合的设计思想，即利用软件单元实现动态的功能重组，适应需求的变化，延长软件使用寿命。同时提出了一种适用于功能重组系统的、可靠的集成化安全管理方案，以便简化安全管理工作。

关键词：集成化安全管理功能重组管理信息系统