期刊文献+
共找到12篇文章
< 1 >
每页显示 20 50 100
Femtosecond electron pulse compression by using the time focusing technique in ultrafast electron diffraction 被引量:3
1
作者 温文龙 雷晓红 +7 位作者 胡昕 徐向晏 王俊锋 曹希斌 刘虎林 王超 党利宏 田进寿 《Chinese Physics B》 SCIE EI CAS CSCD 2011年第11期228-232,共5页
We present a new model of an electron gun for generating subrelativistic femtosecond (fs) electron pulses. The basic idea is to utilize a dc acceleration stage combined with a time focusing region, the time focusing... We present a new model of an electron gun for generating subrelativistic femtosecond (fs) electron pulses. The basic idea is to utilize a dc acceleration stage combined with a time focusing region, the time focusing electrode generates an electron energy chirp for bunching at the target. Without considering the space charge effects, simulations of the electron gun were carried out under the conditions of different dc voltages and various slopes of the voltage added on the time focusing electrode. Tracing and simulating large numbers of photoelectrons through Monte-Carlo and finite difference methods, the electron pulses with 1 ps can be compressed to 55 fs, which will allow significant advances in the field of ultrafast diagnosis. 展开更多
关键词 time focusing technique temporal pulse compressing time-dependent electric field Monte Carlo method
下载PDF
Locally Minimum Storage Regenerating Codes in Distributed Cloud Storage Systems 被引量:2
2
作者 Jing Wang Wei Luo +2 位作者 Wei Liang Xiangyang Liu Xiaodai Dong 《China Communications》 SCIE CSCD 2017年第11期82-91,共10页
In distributed cloud storage systems, inevitably there exist multiple node failures at the same time. The existing methods of regenerating codes, including minimum storage regenerating(MSR) codes and minimum bandwidth... In distributed cloud storage systems, inevitably there exist multiple node failures at the same time. The existing methods of regenerating codes, including minimum storage regenerating(MSR) codes and minimum bandwidth regenerating(MBR) codes, are mainly to repair one single or several failed nodes, unable to meet the repair need of distributed cloud storage systems. In this paper, we present locally minimum storage regenerating(LMSR) codes to recover multiple failed nodes at the same time. Specifically, the nodes in distributed cloud storage systems are divided into multiple local groups, and in each local group(4, 2) or(5, 3) MSR codes are constructed. Moreover, the grouping method of storage nodes and the repairing process of failed nodes in local groups are studied. Theoretical analysis shows that LMSR codes can achieve the same storage overhead as MSR codes. Furthermore, we verify by means of simulation that, compared with MSR codes, LMSR codes can reduce the repair bandwidth and disk I/O overhead effectively. 展开更多
关键词 distributed cloud storage systems minimum storage regenerating(MSR) codes locally repairable codes(LRC) repair bandwidth overhead disk I/O overhead
下载PDF
Recent Advances in Selective Maintenance from 1998 to 2014 被引量:1
3
作者 徐庆征 郭乐勐 +1 位作者 王娜 费蓉 《Journal of Donghua University(English Edition)》 EI CAS 2015年第6期986-994,共9页
The selective maintenance is a new branch and significant breakthrough of reliability and maintenance theory.In the original selective maintenance problem,a subset of maintenance activities is performed on selected co... The selective maintenance is a new branch and significant breakthrough of reliability and maintenance theory.In the original selective maintenance problem,a subset of maintenance activities is performed on selected components during the finite break so that the system is able to maximize the next mission reliability.It is a fast growing research field over the past ten years,in which a variety of mathematical models and solution methodology have been proposed for dealing with more complex and significant problems.An overview of some recent advances in selective maintenance modeling and treatment methods is provided in this paper.A number of challenges that can be undertaken to help move the field forward are also discussed according to the current state of the selective maintenance approach. 展开更多
关键词 selective maintenance mathematical model solution methodology RELIABILITY preventive maintenance maintenance resource
下载PDF
Model of Autonomous Positioning Through Associating Environment Memory Information
4
作者 Du Jia Wu Dewei Zhou Yang 《Transactions of Nanjing University of Aeronautics and Astronautics》 EI CSCD 2016年第5期584-594,共11页
A model of autonomous positioning through associating environment memory information is presented for unmanned combat aerial vehicle(UCAV).The representation strategy of environment by constructing place cells is used... A model of autonomous positioning through associating environment memory information is presented for unmanned combat aerial vehicle(UCAV).The representation strategy of environment by constructing place cells is used to produce the memory information,and the landmarks in memory are retrieved through perceiving and processing the environment.During UCAV′s flight,the landmarks are obtained in real-time and are matched with the landmarks in memory.Then,the idea of ranging positioning is adopted to calculate UCAV′s location based on the corresponding relationship between current obtained landmarks and the memorized landmarks.Simulation shows that the proposed model can realize autonomous positioning in the memorized environment,and the positioning performance is well when the sensor has a high precision. 展开更多
关键词 autonomous positioning environment memory environment representation landmarkst positioning feature point
下载PDF
Improved Computational Model of Grid Cells Based on Column Structure
5
作者 Yang Zhou Dewei Wu +1 位作者 Weilong Li Jia Du 《Journal of Harbin Institute of Technology(New Series)》 EI CAS 2016年第3期44-52,共9页
To simulate the firing pattern of biological grid cells,this paper presents an improved computational model of grid cells based on column structure.In this model,the displacement along different directions is processe... To simulate the firing pattern of biological grid cells,this paper presents an improved computational model of grid cells based on column structure.In this model,the displacement along different directions is processed by modulus operation,and the obtained remainder is associated with firing rate of grid cell.Compared with the original model,the improved parts include that:the base of modulus operation is changed,and the firing rate in firing field is encoded by Gaussian-like function.Simulation validates that the firing pattern generated by the improved computational model is more consistent with biological characteristic than original model.Besides,the firing pattern is badly influenced by the cumulative positioning error,but the computational model can also generate the regularly hexagonal firing pattern when the real-time positioning results are modified. 展开更多
关键词 GRID cells FIRING PATTERN BIONIC NAVIGATION
下载PDF
Dielectric barrier plasma dynamics for active aerodynamic flow control 被引量:6
6
作者 HAO JiangNan TIAN BaLin +3 位作者 WANG YuLin SONG YaHui PAN ShuCheng LI WenFeng 《Science China(Physics,Mechanics & Astronomy)》 SCIE EI CAS 2014年第2期345-353,共9页
The paper investigates the dynamics of a new multiple bipolar multiple Dielectric Barrier Discharges(DBD)actuator using in large-scale flow control.Particle image velocimetry experiments are performed to characteristi... The paper investigates the dynamics of a new multiple bipolar multiple Dielectric Barrier Discharges(DBD)actuator using in large-scale flow control.Particle image velocimetry experiments are performed to characteristic the effectiveness of the multiple bipolar DBD plasma actuator.The results show that the mutual interaction between the electrodes,one major disadvantage of traditional DBD characterized by reverse discharge can be entirely avoided,and a constantly accelerating electric wind velocity can be obtained by using the new multiple bipolar DBD plasma actuator. 展开更多
关键词 plasma actuator flow control PIV
原文传递
New Constructions of Identity-Based Threshold Decryption 被引量:1
7
作者 ZHANG Leyou HU Yupu +1 位作者 TIAN Xu'an YANG Yang 《Wuhan University Journal of Natural Sciences》 CAS 2010年第3期222-226,共5页
In this paper, based on the verifiable pair and identity-based threshold cryptography, a novel identity-based (ID-based) threshold decryption scheme (IDTDS) is proposed, which is provably secure against adaptive c... In this paper, based on the verifiable pair and identity-based threshold cryptography, a novel identity-based (ID-based) threshold decryption scheme (IDTDS) is proposed, which is provably secure against adaptive chosen cipbertext attack under the computational bilinear Diffie-Hellman (CBDH) problem assumption in the random oracle. The pubic cheekability of ciphertext in the IDTDS is given by simply creating a signed E1Gamal encryption instead of a noninteractive zero-knowledge proof. Furthermore, we introduce a modified verifiable pairing to ensure all decryption shares are consistent. Our scheme is more efficient in verification than the schemes considered previously. 展开更多
关键词 ID-Based threshold decryption verifiable pair computational bilinear Diffie-Hellman (CBDH) problem provable security
原文传递
Joint Resource Allocation for Lifetime-aware Cooperative Multi-carrier DF System
8
作者 Chao-Ping Guo Kun Han +1 位作者 Xiao-Long Zhang Hai-Lin Zhang 《International Journal of Automation and computing》 EI CSCD 2014年第1期87-92,共6页
In this paper,we study the problem of optimal resource allocation for lifetime maximization in an orthogonal-frequencydivision multiplexing(OFDM)system with decode-and-forward relay.The goal is to minimize total energ... In this paper,we study the problem of optimal resource allocation for lifetime maximization in an orthogonal-frequencydivision multiplexing(OFDM)system with decode-and-forward relay.The goal is to minimize total energy cost of the system by jointly optimizing power allocation,subcarrier pairing and relay selection.We present a heuristic solution that is composed of two parts.The first part is an optimal power allocation approach to allocate power to a subcarrier pair of the source and the relay.The second part is a modified Hungarian algorithm to make subcarrier pairing and relay selection.Evaluations show that the presented scheme outperforms other schemes in the total transmitted data and the network lifetime. 展开更多
关键词 Cooperative communications resource allocation DECODE-AND-FORWARD orthogonal-frequency-division multiplexing(OFDM) subcarrier pairing power allocation relay selection
原文传递
Laser diffraction from capillary waves on liquid film surfaces
9
作者 朱峰 王宏 +1 位作者 陈利菊 张建航 《Optoelectronics Letters》 EI 2013年第1期65-68,共4页
A simple experiment for laser diffraction of capillary waves on liquid film surface (LFS) is realized. Steady and visible diffraction patterns are obtained. The dispersion relation of capillary waves on LFS is verifie... A simple experiment for laser diffraction of capillary waves on liquid film surface (LFS) is realized. Steady and visible diffraction patterns are obtained. The dispersion relation of capillary waves on LFS is verified by laser diffraction. In particular, both the relation between the wave number and the film thickness at a fixed angular frequency and the relation between the angular frequency and the wave number at a fixed film thickness are investigated. The theoretical and experimental results are in good agreement. 展开更多
关键词 激光衍射法 薄膜表面 毛细波 衍射图案 色散关系 LFS 角频率 膜厚度
原文传递
A novel multi-waveband dispersion compensating fiber based on hybrid photonic crystal fiber
10
作者 刘颖 李玉权 +2 位作者 汪井源 谢晓刚 李建华 《Optoelectronics Letters》 EI 2013年第1期53-56,共4页
In view of dispersion compensating in multiple wavebands at the same time, this paper proposes a novel multi-waveband dispersion compensating fiber (DCF) based on hybrid photonic crystal fiber (PCF). The proposed fibe... In view of dispersion compensating in multiple wavebands at the same time, this paper proposes a novel multi-waveband dispersion compensating fiber (DCF) based on hybrid photonic crystal fiber (PCF). The proposed fiber can compensate multiple wavebands at the same time. The mechanism of the multi-waveband dispersion compensation is analyzed, and the different material-filled structure is discussed numerically. The simulation results show that the multi-waveband DCF can compensate multiple wavelengths at the same time. By a reasonable design, this fiber can replace the multi-dispersion compensating system composed by cascaded multiple devices, and minimize the loads of the system in an efficient way. 展开更多
关键词 色散补偿光纤 光子晶体光纤 多波段 混合 色散补偿系统 基础 材料填充 仿真结果
原文传递
Multiple-frequency basestation RoF system based on po-larization multiplexed FWM in SOA
11
作者 向玉 张崇富 +2 位作者 尹树华 陈晨 邱昆 《Optoelectronics Letters》 EI 2012年第6期464-467,共4页
An approach of multiple-frequency millimeter-wave(mm-wave)signal generation is proposed for radio-over-fiber(RoF)system with multiple-frequency basestations(MFBSs).Two groups of orthogonally polarized signals are inje... An approach of multiple-frequency millimeter-wave(mm-wave)signal generation is proposed for radio-over-fiber(RoF)system with multiple-frequency basestations(MFBSs).Two groups of orthogonally polarized signals are injected into a semiconductor optical amplifier(SOA),and subsequently ten new different wavelengths are generated via four-wave mix-ing(FWM)effect.At each MFBS,different wavelengths are filtered out using demultiplexer and then input to a photodiode(PD)to generate the mm-wave signals with the frequencies from 52 GHz to 68 GHz at the interval of 2 GHz.Simulation results verify that the proposed multiple-frequency generation for MFBS RoF system can work properly. 展开更多
关键词 Base stations DIODES Millimeter waves Signal generators
原文传递
Research on Service-oriented Knowledge Management Model of Multi-campus College and University
12
作者 LI Dong LIU Xi-lin 《International Journal of Plant Engineering and Management》 2013年第4期212-216,共5页
Knowledge management theory is increasingly attracting the attention of colleges and universities, and has become a new perspective to the reform of college management. With the development of education informa tioniz... Knowledge management theory is increasingly attracting the attention of colleges and universities, and has become a new perspective to the reform of college management. With the development of education informa tionization, the service orientation will become the main direction in knowledge management. On the fact of many campuses in colleges and universities, this paper presents model based on serviceoriented idea and grid technology, campus university knowledge management. a university knowledge management system framework and discusses the processes of serviceoriented multi 展开更多
关键词 service oriented knowledge management multi-campus universities management mode
原文传递
上一页 1 下一页 到第
使用帮助 返回顶部