15 November 2015, Volume 55 Issue 11

    

• Select all
  |

AUTO MATION
• Select
  Measurements of the competitive characteristics of multi-topic propagation in online social networks

  SUN Liyuan, GUAN Xiaohong

  Journal of Tsinghua University(Science and Technology). 2015, 55(11): 1157-1162. https://doi.org/10.16511/j.cnki.qhdxxb.2015.21.006

  Abstract ( ) Download PDF ( )   Knowledge map   Save

  Online social networks have many topics but people's attention spans are very limited, so the many topics compete for the scarce user attention spans. This competitive relationship affects the propagation of information and the formation of public opinions. Most existing research has focused on the spread of individual topics. This study investigates the spread of multiple topics and methods to quantitatively describe the competitive characteristics. Topic and user level methods are developed to measure resource changes, topic competition intensity, user attention transitions and topic relevance. Metrics are developed for the resource variation rate and the user attention transition rate. Measurements of the actual data collected from Sina Weibo show that the total user attention level is almost stable with most user attention transitions moving from existing topics to newly appearing topics and between similar topics. These measurements provide modeling of the multi-topic propagation processes.
• Select
  Modeling of the forwarding behavior in microblogging with adaptive interest

  ZHOU Cangqi, ZHAO Qianchuan, LU Wenbo

  Journal of Tsinghua University(Science and Technology). 2015, 55(11): 1163-1170. https://doi.org/10.16511/j.cnki.qhdxxb.2015.21.007

  Abstract ( ) Download PDF ( )   Knowledge map   Save

  The emergence of social media has given rise to research on how online users behave. This paper describes how users forward messages in microblogging services. The results shed light on the factors affecting user decisions. A precise description of user forwarding behavior can also support the intervention and control of information spreading. The lengths of activity periods in existing human dynamic models with adaptive interest were used to develop a modified model to describe user forwarding dynamics in microblogging services. This model takes into account both the differences in the durations of the activity cycles and the effect of circadian rhythms. The distribution of the time intervals between successive forwarding activities is heavy-tailed in the real data. The simulation results are consistent with the distribution in the real data which demonstrates the effectiveness and flexibility of this model.
  
• Select
  Analysis and suppression for shaft torsional vibrations in large wind turbines with MPPT control

  YANG Wentao, GENG Hua, XIAO Shuai, YANG Geng

  Journal of Tsinghua University(Science and Technology). 2015, 55(11): 1171-1177. https://doi.org/10.16511/j.cnki.qhdxxb.2015.21.018

  Abstract ( ) Download PDF ( )   Knowledge map   Save

  As wind turbines become larger and lighter, they are experiencing more severe shaft torsional vibrations. Therefore, the suppression of turbine shaft torsional vibrations is becoming more important. This paper compares three common maximum power point tracking(MPPT) control algorithms. All three methods use generator speed feedback to enhance the drive shaft damping. An advanced conventional MPPT control method was then developed with an extra order added to the MPPT command to suppress shaft torsional vibrations. The result suppresses the torsion vibrations of the drive shaft, while ensuring that the wind turbines work at the maximum power point. Simulations verify the effectiveness of the theoretical analyses and this method.
• Select
  Cluster analysis of a price index series based on the hierarchical division algorithm

  CHU Hongyang, CHAI Yueting, LIU Yi

  Journal of Tsinghua University(Science and Technology). 2015, 55(11): 1178-1183. https://doi.org/10.16511/j.cnki.qhdxxb.2015.21.010

  Abstract ( ) Download PDF ( )   Knowledge map   Save

  At present, e-commerce trade is not included in the consumer price index published by the National Bureau of Statistics of China. With the rapid development of e-commerce, the development of an online consumer price index(CPI) has become an urgent problem. Online transaction data supports real-time access and corresponds to actual transactions. Therefore, an online CPI should be more real-time and more accurate than the traditional CPI. However, the calculation of a classification price index requires classification of elementary price indexes, because there are differences in the classification standards used by different enterprises. This paper describes a hierarchical division algorithm for cluster analyses of price index series, which uses a correlation coefficient based distance and the Manhattan distance to measure the distances between price index series and then divides the series by two steps. The method uses ending conditions to stop the divisions, so that the cluster count need not be preset. Finally, the method is applied to practical cases with 219 of 226 price index series effectively divided, which indicates a good clustering result.
• Select
  Chemical reaction optimization algorithm for the distributed permutation flowshop scheduling problem

  SHEN Jingnan, WANG Ling, WANG Shengyao

  Journal of Tsinghua University(Science and Technology). 2015, 55(11): 1184-1189,1196. https://doi.org/10.16511/j.cnki.qhdxxb.2015.21.009

  Abstract ( ) Download PDF ( )   Knowledge map   Save

  An effective chemical reaction optimization(CRO) algorithm was developed to solve the distributed permutation flowshop scheduling problem(DPFSP). Four basic CRO algorithm operators were used in the solution to enrich the search behavior and ensure the population diversity. An effective local search procedure was developed based on the DPFSP characteristics to enhance the local exploitation ability of the algorithm. Finally, the effects of the parameter settings on the algorithm were investigated using the design-of-experiment method with the numerical results showing that this algorithm is effective.
COMPUTER SCIENCE AND TECHNOLOGY
• Select
  Experimental study of BGP routing-table-based inter-domain path characteristics

  YANG Jiahai, JIAO Liang, QIN Donghong, GE Liansheng

  Journal of Tsinghua University(Science and Technology). 2015, 55(11): 1190-1196. https://doi.org/10.16511/j.cnki.qhdxxb.2015.21.001

  Abstract ( ) Download PDF ( )   Knowledge map   Save

  The information stored in the routing table for the border gateway protocol(BGP) can reflect the scale of the Internet, the running state and the evolution of the architecture, which is important for basic research of the Internet. Previous studies of routing tables have mainly focused on the indicators that reflect the Internet scale, such as the routing table size, the Internet coverage, and the address consumption, but lack analyses of routing diversity. This paper introduces a characteristic analysis model for inter-domain paths and a path characteristic analysis framework based on the IPv4 routing table information in the BGP with statistical analyses of the AS scale and the inter-domain path characteristics. The results give information about the AS-level path attributes and their parameter distributions. The analyses show that the Internet currently has a rich diversity of routing paths with some best paths selected by BGP not the shortest paths in the routing table. The results provide guidance for future inter-domain route planning.
• Select
  Robust decoupling inner-loop control for a post-stall maneuverable fighter

  ZHOU Chijun, ZHU Jihong, LEI Humin, YUAN Xiaming, YIN Hang

  Journal of Tsinghua University(Science and Technology). 2015, 55(11): 1197-1207. https://doi.org/10.16511/j.cnki.qhdxxb.2015.21.011

  Abstract ( ) Download PDF ( )   Knowledge map   Save

  A robust decoupling control approach was developed for a strongly nonlinear and strongly coupled inner-loop system for post-stall maneuvers. The control process includes moment compensation, linear controller design and robust compensation. The aerodynamic moment, inertial coupling moment and additional moment caused by the thrust vector are first compensated through querying an aerodynamic database with the damping moment not included. A second-order reference model is then employed to determine the proportional and integral coefficients of the linear controller. A series of aerodynamic moment derivatives and thrust force parameter perturbations are then described by sine functions to get an analytical expression for the model uncertainty and a robust compensator based on the sliding mode control methodology. Simulations show that the energy consumption can be reduced when the aerodynamic damping moment is not included. Moreover, the Herbst maneuver and robust command tracking can be achieved, even with 60% parameter perturbations in the aerodynamic derivatives and 20% perturbations with the control derivatives.
  
• Select
  Wear-leveling method for PCM based on random mapping

  LIU Wei, WANG Yuping

  Journal of Tsinghua University(Science and Technology). 2015, 55(11): 1208-1215. https://doi.org/10.16511/j.cnki.qhdxxb.2015.21.005

  Abstract ( ) Download PDF ( )   Knowledge map   Save

  Phase change memory(PCM) uses a phase change material that is non-volatile, higher density, lower energy, and has better scalability than other methods. The main problem with PCM materials is the cell write limitation. Recent studies have focused on optimizing the write operations and wear-leveling, but cannot prevent malicious attacks to rapidly wear the PCM cells. This paper presents a PCM wear-leveling method which divides the whole PCM memory into two levels with separate random mapping tables to convert the logical cell addresses into physical addresses. The random mapping tables are updated dynamically according to the write count thresholds. This method not only implements PCM wear-leveling, but also resists malicious wearing-out attacks. Tests show that This method improves the wear-leveling by up to 87.5% over three existing wear-leveling methods with a system performance loss of less than 6% and additional storage overhead of less than 1‰ of the whole memory size.
• Select
  Number of round trips in LTP data block transmissions

  DONG Yangwei, LIN Chuang

  Journal of Tsinghua University(Science and Technology). 2015, 55(11): 1216-1220,1228. https://doi.org/10.16511/j.cnki.qhdxxb.2015.21.012

  Abstract ( ) Download PDF ( )   Knowledge map   Save

  The Licklider transmission protocol(LTP) is a point-to-point protocol that is mainly used to transmit data between adjacent nodes in space networks. LTP achieves reliability by return acknowledgements and retransmissions. Typical applications have long distances between network nodes which result in large transmission delays. This delay is further multiplied by the acknowledgement and retransmission processes. Thus, the number of round trips(QoRT) needed to successfully transmit an LTP block needs to be investigated. This paper presents an analytical evaluation of the QoRT that gives the distribution function, mean and variance of the QoRT. The results also give more concise upper bounds, lower bounds and approximate means. Simulations verify the theoretical results.
• Select
  Sensitive information management system for un-trusted system platforms

  XIE Xuezhi, WANG Yuping, TAN Jianfeng, CHEN Qigeng

  Journal of Tsinghua University(Science and Technology). 2015, 55(11): 1221-1228. https://doi.org/10.16511/j.cnki.qhdxxb.2015.21.003

  Abstract ( ) Download PDF ( )   Knowledge map   Save

  The threats of backdoors and vulnerabilities in general-purpose operating systems complicate protection of sensitive information. This paper describes a sensitive memory management system(SMM) which protects sensitive information memory and prevents attackers from obtaining sensitive information by compromising the operating system kernel. Virtualization is used to set up different shadow page tables for the user-mode and the kernel-mode of the protected process and then controls access to the sensitive information so that only the proper applications can access the information and not the operating systems kernel. Tests show that the memory is protected with finer granularity and lower overhead than previous methods.
ELECTRONIC ENGINEERING
• Select
  Real-time system for detecting inter-domain routing man-in-the-middle attacks

  LI Song, DUAN Haixin, LI xing

  Journal of Tsinghua University(Science and Technology). 2015, 55(11): 1229-1234. https://doi.org/10.16511/j.cnki.qhdxxb.2015.21.017

  Abstract ( ) Download PDF ( )   Knowledge map   Save

  Man-in-the-middle attacks have become a new serious threat to inter-domain routing. This paper presents a real-time system for detecting inter-domain routing man-in-the-middle attacks based on an analysis of a threat model and key features in the control plane and the data plane. The detection system first monitors the anomalous route in the control plane and then probes the data plane to identify the inter-domain routing man-in-the-middle attack. Internet tests show that the detection system is light-weight and effectively detects probable man-in-the-middle attacks in inter-domain routing in real time.
• Select
  Mechanism of information distortion and its impact on optical networks for dynamic traffics

  LIU Haijiao, HUA Nan, LI Yanhe, ZHENG Xiaoping

  Journal of Tsinghua University(Science and Technology). 2015, 55(11): 1235-1240. https://doi.org/10.16511/j.cnki.qhdxxb.2015.21.014

  Abstract ( ) Download PDF ( )   Knowledge map   Save

  The impact of the network dynamics on network performance was analyzed to develop a distributed network noise(DNN) concept to efficiently suppress the effects of the network dynamics and increase the spectrum utilization. The analysis analyzes the mechanism of how information distortion influences the network performance. An analytical signaling blocking model is developed based on the DNN to indicate the influence of information distortion. The results show that the information distortion as well as the blocking probability increase with increasing origin arrival rate. The estimates derived from the analytical model agree well with experimental results.
• Select
  Mean physical-layer secrecy capacity in mobile communication systems

  LI Tao, ZHANG Yan, XU Xibin, ZHOU Shidong

  Journal of Tsinghua University(Science and Technology). 2015, 55(11): 1241-1245,1252. https://doi.org/10.16511/j.cnki.qhdxxb.2015.21.013

  Abstract ( ) Download PDF ( )   Knowledge map   Save

  The security of mobile communication systems depends on the mean physical-layer secrecy capacity as the user moves. In realistic propagation environments, the physical-layer secrecy capacity varies over a vast range because of the user motion. A mean physical-layer secrecy capacity of a legitimate user is defined to characterize the secure communication performance of the system. The distribution characteristics of the mean physical-layer secrecy capacity are derived based on the impact of the eavesdropper's position on the mean physical-layer secrecy capacity. A scheme is then given to improve the mean physical-layer secrecy capacity according to the distribution characteristics. The mean physical-layer secrecy capacity can be made to be not lower than a specified value by limiting the eavesdropper's positions. Theoretical and numerical results demonstrate that this scheme can effectively guarantee the mean physical-layer secrecy capacity in mobile communication systems.
• Select
  Detection of instant voice communication steganography using semi-supervised learning

  TU Shanshan, TAO Huaizhou, HUANG Yongfeng

  Journal of Tsinghua University(Science and Technology). 2015, 55(11): 1246-1252. https://doi.org/10.16511/j.cnki.qhdxxb.2015.21.016

  Abstract ( ) Download PDF ( )   Knowledge map   Save

  Existing instant voice communication steganalysis schemes are mainly based on supervised learning classifiers. These kinds of methods need large amounts of pre-processing and training and their accuracy can be easily destroyed by differences between the distribution of the training and testing data sets. This paper describes a semi-supervised hybrid detection model to improve detection which removes the manually annotated training data set, so this model is simpler and gives better detection scopes. This paper also describes a self-learning, multi-criteria fusion module which can automatically generate pseudo-labelled sets and combines the confidence and representative levels to judge the performance of instant voice communication steganalysis. There is no distribution mismatch between the testing data and the training data in this method. Tests with common low bit-rate speech coding carriers show that this method is more accurate than the un-supervised method and the supervised method in mismatched conditions. When the distributions of the training and testing data sets differ, this method is less affected than the supervised method. The tests also show that this method can be deployed on different kinds of speech codecs.
ELECTRICAL ENGINEERING
• Select
  Operating characteristics of an electromagnetic coupler wind turbine generator system

  CHEN Jihe, LIN Yulong, CHAI Jianyun, LI Jie

  Journal of Tsinghua University(Science and Technology). 2015, 55(11): 1253-1257. https://doi.org/10.16511/j.cnki.qhdxxb.2015.21.015

  Abstract ( ) Download PDF ( )   Knowledge map   Save

  The electromagnetic coupler(EMC) wind turbine generator system(WTGS) is distinct from conventional wind turbines in that the synchronous generator is directly connected to the power gird and the output power is passed from the wind turbine gearbox via the EMC. The EMC with an inverter power supply can quickly and flexibly change the torque. This analysis includes additional torque control besides the wind turbine output torque to reduce the influence of system disturbances on the synchronous generator. WTGS and infinite power grid models are used to investigate the torque control and strategy for various system disturbances and fault conditions on the MATLAB Simulink platform. The results show that the additional torque control improves the generator system transient stability and dynamic response compared with only excitation and wind turbine pitch control. The system enables low voltage ride through(LVRT) that enhances the ability to support the grid voltage.
MECHANICAL ENGINEERING
• Select
  Linear motor acceleration estimation method based on grating signals

  LI Zhijun, LIU Chengying, MENG Fanwei, ZHOU Kai, ZHANG Zhi

  Journal of Tsinghua University(Science and Technology). 2015, 55(11): 1258-1263. https://doi.org/10.16511/j.cnki.qhdxxb.2015.21.008

  Abstract ( ) Download PDF ( )   Knowledge map   Save

  The performance of linear motor servo systems is greatly degraded by disturbances such as the cutting force, cogging force, and inertia variations. Acceleration control can effectively suppress disturbances, but such control requires accurate acceleration estimates with less phase lag. Optical encoders are widely used for position measurements in linear motor systems, so the acceleration can be easily estimated from the quantized positions. An acceleration estimation method is given here based on the constrained least squares polynomial fitting technique. The curve fitting is based on a least squares analysis of the historical position of the linear motor with the latest position of the linear motor on the resulting curve fit. Theoretical analyses and simulations both confirm that this method has less phase lag than the normal least squares polynomial fitting technique. This method works like a finite impulse response(FIR) filter for the acceleration estimate, which is convenient for real time control systems.
MICROELECTRONICS
• Select
  On-chip attenuator based on π-type polysilicon resistive network

  GUO Xin, LI Mengwei, GONG Zhuhao, LIU Zewen

  Journal of Tsinghua University(Science and Technology). 2015, 55(11): 1264-1268. https://doi.org/10.16511/j.cnki.qhdxxb.2015.21.002

  Abstract ( ) Download PDF ( )   Knowledge map   Save

  An on-chip 0~20 GHz attenuator was developed based on a π-type polysilicon resistive network as low cost attenuators with adjustable size that are compatible with other circuits. The sheet resistance(100~400Ω/sq) of the polysilicon resistor can be controlled by varying the boron-doping concentrations(5×10¹⁸~1.4×10²⁰ cm^-3) and post-annealing conditions(950~1050℃, 10~30 min). The resistance error was controlled less than 4%. The on-chip attenuator size can be set by selecting the sheet resistance for the on-chip 10 dB and 20 dB attenuating resistive networks. The devices were modelled in 3-D with HFSS with the simulation results showing excellent performance. The attenuation accuracies of the 10 dB and 20 dB attenuators were 0.26 dB and 0.04 dB over the entire frequency band(0~20 GHz), while the voltage standing wave ratios(VSWR) were less than 1.13 and 1.29, respectively. Both resistive networks were 265μm×270μm in size while both attenuators were less than 1000μm×800μm in size. These high accuracy attenuators can be used in microwave test instruments.