15 January 2018, Volume 58 Issue 1

    

• Select all
  |

COMPUTER SCIENCE AND TECHNOLOGY
• Select
  Design and implementation of an evaluation platform for NDN name lookup algorithms

  ZHANG Ting, WANG Yi, YANG Tong, LU Jianyuan, LIU Bin

  Journal of Tsinghua University(Science and Technology). 2018, 58(1): 1-7. https://doi.org/10.16511/j.cnki.qhdxxb.2018.22.001

  Abstract ( ) Download PDF ( )   Knowledge map   Save

  Many name lookup algorithms have been proposed for named data networking (NDN). These algorithms need to be evaluated based on their reachable speed, scalability, and update performance. However, NDN is still in the research stage so there are no large NDN networks and no large real name routing tables or NDN traffic. This paper presents a software test platform, NDNBench, to evaluate, compare and test different name lookup algorithms. NDNBench consists of a seed forwarding information base (FIB) analyzer, an FIB generator, a name trace generator and an update generator. Tests show that the name table and traffic characteristics greatly influence the NDN name lookup algorithm performance. The platform extracts these features, forms quantifiable parameters and provides them to the user. The parameters of NDNBench can be adjusted to obtain various FIBs and traces with structure and size diversity to test the lookup algorithms. This paper also evaluates some existing name lookup algorithms.
  
• Select
  Pricing strategy and revenue allocation between service providers in mobile sponsored markets

  SU Hui, TAN Qi, ZHAO Yi, XU Ke

  Journal of Tsinghua University(Science and Technology). 2018, 58(1): 8-13. https://doi.org/10.16511/j.cnki.qhdxxb.2018.22.002

  Abstract ( ) Download PDF ( )   Knowledge map   Save

  The virtual Internet service providers (ISPs) have changed the connection and economic relationships among ISPs in mobile Internet sponsored markets. Game theory is used to develop a model to study the competition among ISPs and to analyze data allocation, pricing and utility issues for cooperative and non-cooperative games for ISPs in the mobile sponsored market. This paper also presents a revenue allocation mechanism and solves for the optimal allocation factor using the Nash bargaining solution. The results show that the price difference between ISPs increases with the sponsored level and the revenue allocation mechanism encourages the ISPs to adjust their optimized purposes to maximize the social welfare.
• Select
  Synchronization control of cyber physical systems during malicious stochastic attacks

  GAO Yang, MA Yangyang, ZHANG Liang, WANG Meilin, WANG Weiping

  Journal of Tsinghua University(Science and Technology). 2018, 58(1): 14-19. https://doi.org/10.16511/j.cnki.qhdxxb.2018.22.003

  Abstract ( ) Download PDF ( )   Knowledge map   Save

  Cyber physical systems (CPSs) exist in many modern infrastructure systems, such as the future smart grid, smart transportation networks, and public health systems. CPS security is critical for normal operation of our society. The physical layer networks and the cyber layer networks are all complex networks that are interdependent. A mathematical model is given for the interdependent systems during stochastic malicious attacks, which exist in both the physical layer networks and the cyber layer networks. In addition, an adaptive nonlinear controller is given to synchronize interdependent CPSs during malicious stochastic attacks. The controller uses the properties of a Weiner process for the physical layer networks to synchronize the interdependent CPSs. Numerical simulations show the effectiveness of the theoretical results.
• Select
  Abnormal traffic flow identification for a measurement and control network for launch vehicles

  XU Hongping, LIU Yang, YI Hang, YAN Xiaotao, KANG Jian, ZHANG Wenjin

  Journal of Tsinghua University(Science and Technology). 2018, 58(1): 20-26,34. https://doi.org/10.16511/j.cnki.qhdxxb.2018.22.004

  Abstract ( ) Download PDF ( )   Knowledge map   Save

  The measurement and control network of a launch vehicle is an important national defense information infrastructure for remote measurements and launch control. This network provides a key measure to detect abnormal behavior and ensure information security through accurate analysis of the traffic. This paper describes a network strategy using the port mapping method, payload matching, and support vector machine (SVM) learning algorithm. The training samples are produced by the port mapping and payload matching method. Then, the key features are selected based on the information gain. Next, the SVM model is built with these features and trained by the training samples. The traffic data is then analyzed by the voting mechanism. Actual data from the network is used to verify the method with the results showing that this method has an accuracy of 99.1% with far fewer manual analyses.
AUTOMOTIVE ENGINEERING
• Select
  Dual-mode hybrid track-type vehicle powertrain design using planetary gear sets

  QIN Zhaobo, LUO Yugong, XIE Laiqing, CHEN Wenqiang, LI Keqiang

  Journal of Tsinghua University(Science and Technology). 2018, 58(1): 27-34. https://doi.org/10.16511/j.cnki.qhdxxb.2018.22.005

  Abstract ( ) Download PDF ( )   Knowledge map   Save

  This paper presents a powertrain design for hybrid track-type vehicles based on planetary gear sets. The design uses a three planetary gear set structure with two operating modes for the best fuel efficiency while improving the straight driving performance and the steering performance. This design eliminates the complex steering shaft while ensuring the steering index and improving steering efficiency compared with current powertrain designs. An automated modelling method is used to analyze all the candidate designs. The designs are screened using dynamic programming to analyze the fuel economy to select the best one with the least fuel consumption. Simulations indicate that the design has better performance and fuel economy than the current series hybrid benchmark for the track-type vehicle powertrain design.
• Select
  Simulations of the unsteady fluid-structure coupling characteristics of a conical orifice valve

  LÜ Zhenhua, LI Ming

  Journal of Tsinghua University(Science and Technology). 2018, 58(1): 35-42. https://doi.org/10.16511/j.cnki.qhdxxb.2018.22.006

  Abstract ( ) Download PDF ( )   Knowledge map   Save

  The dynamics of a conical orifice valve in a heavy-duty vehicle damper were analyzed using 3-D fluid-structure coupling finite element models solved using the direct coupling computational method. The results show the internal 3-D transient fluid pressure and velocity distributions for transient inlet flow rates and the unsteady high-frequency fluctuations of the valve opening and the forces on the valve. The dynamic responses are given for various compression spring characteristics, valve structure parameters and inlet flow rates to understand the fluid-structure coupling self-excited vibrations of the valve. The results show that heavily preloaded valve springs and small inlet flow rates lead to high-frequency fluctuations of the valve opening and collisions of the core onto the seat. In addition, a zero preload of the valve spring eliminates the fluid-structure coupling vibrations and large inlet flow rates reduce the unsteady opening fluctuations. These conclusions are important for understanding fluid-structure coupling self-excited vibration problems in valves.
  
• Select
  Verification of a cathode pressure drop model for single phase flow in a proton exchange membrane fuel cell

  LI Yuehua, PEI Pucheng, WU Ziyao, JIA Xiaoning

  Journal of Tsinghua University(Science and Technology). 2018, 58(1): 43-49. https://doi.org/10.16511/j.cnki.qhdxxb.2018.22.007

  Abstract ( ) Download PDF ( )   Knowledge map   Save

  The single phase flow pressure drop through the cathode in a proton exchange membrane fuel cell is an important benchmark for online water management. However, there are few models of this pressure drop applicable to all operating conditions. The cathode pressure drop is found here to be a quadratic function of the current and stoichiometric ratio using experimental data for a 156 W fuel cell. Five parameters influencing the pressure drop are the current, stoichiometric ratio, stack temperature, inlet pressure, and inlet relative humidity. A model for this pressure drop is then developed that agrees within 10% with experiment results. This model can guide online diagnosis of water related faults.
• Select
  Crack detection algorithm for fluorescent magnetic particle inspection based on shape and texture features

  MA Tao, SUN Zhenguo, CHEN Qiang

  Journal of Tsinghua University(Science and Technology). 2018, 58(1): 50-54. https://doi.org/10.16511/j.cnki.qhdxxb.2018.22.008

  Abstract ( ) Download PDF ( )   Knowledge map   Save

  This paper introduces an algorithm based on shape and texture features to recognize cracks from fluorescent magnetic particle inspection images. The algorithm detects ridge lines in the images that represent candidate cracks, extracts the local texture features of each ridge point using a scale-invariant feature transform (SIFT) descriptor, and averages those from the same line to form the texture features of the ridge line. A support vector machine classifier is then used to detect the cracks. Tests show that this algorithm more accurately distinguishes the cracks from non-defects than conventional shape-based algorithms or texture-based algorithms. The combined shape and local textures improve the crack detection accuracy.
AUTOMATION
• Select
  Transfer learning for acoustic modeling of noise robust speech recognition

  YI Jiangyan, TAO Jianhua, LIU Bin, WEN Zhengqi

  Journal of Tsinghua University(Science and Technology). 2018, 58(1): 55-60. https://doi.org/10.16511/j.cnki.qhdxxb.2018.21.001

  Abstract ( ) Download PDF ( )   Knowledge map   Save

  Speech recognition in noisy environments was improved by using transfer learning to train acoustic models. The training of an acoustic model trained with noisy data (student model) is guided by an acoustic model trained with clean data (teacher model). This training process forces the posterior probability distribution of the student model to be close to the teacher model by minimizing the Kullback-Leibler (KL) divergence between the posterior probability distribution of the student model and that of the teacher model. Tests on the CHiME-2 dataset show that this method gives a 7.29% absolute average word error rate (WER) improvement over the baseline model and 3.92% absolute average WER improvement over the best CHiME-2 system.
• Select
  Automatic prosodic boundary labeling based on fusing the silence duration with the lexical features

  FU Ruibo, TAO Jianhua, LI Ya, WEN Zhengqi

  Journal of Tsinghua University(Science and Technology). 2018, 58(1): 61-66,74. https://doi.org/10.16511/j.cnki.qhdxxb.2018.21.003

  Abstract ( ) Download PDF ( )   Knowledge map   Save

  Automatic prosodic boundary labeling is important in the construction of a speech corpus for speech synthesis. Automatic labeling of prosodic boundaries gives more consistent results than manual labeling of prosodic boundaries which is time consuming and inconsistent. Manual labeling method is modelled here using a recurrent neural network to train two sub-models which use lexical features and acoustic features to label the prosodic boundaries. Model fusion is then used to combine the outputs of the two sub-models to obtain the optimal labeling results. The silence durations for each word give clearer physical meanings and better correlations with the prosodic boundaries than the acoustic features used in traditional methods extracted frame-by-frame. Tests show that the silence durations extracted using the current acoustic features and the model fusion method improve the prosodic boundary labeling compared with previous feature fusion methods.
ELECTRICAL ENGINEERING
• Select
  Lumped parameter thermal circuit method combined with temperature field and flow field analyses for temperature predictions of permanent magnets in motors

  ZENG Yingyu, JIANG Xiaohua

  Journal of Tsinghua University(Science and Technology). 2018, 58(1): 67-74. https://doi.org/10.16511/j.cnki.qhdxxb.2018.22.009

  Abstract ( ) Download PDF ( )   Knowledge map   Save

  Sintered Nd-Fe-B permanent magnets (PM) have high electrical conductivity, but eddy currents in the PMs may cause thermal demagnetization, so the temperatures of the PMs in motors must be known. A lumped parameter thermal circuit method is presented in this paper to predict the temperature rise in the PMs using an equivalent thermal circuit for the stator obtained by a temperature field analysis, and the air gap thermal resistance obtained by a computational fluid dynamics analysis including the stator slot opening. The PM temperature of a 30-kW 4-pole motor is analyzed by this method. The predictions compare well with measurement by an infrared sensor for a pulse width modulation (PWM) voltage excitation case with significant eddy current losses in the PM with less than 3.7% error in the temperature difference between the PM and the outer stator surface. The PM temperature in the motor can be well predicted by this method from the temperature of the outer stator surface.
• Select
  Multipath detection based on signal amplitude oscillations with circularly rotating antenna

  XIE Lin, CUI Xiaowei, LU Mingquan

  Journal of Tsinghua University(Science and Technology). 2018, 58(1): 75-80. https://doi.org/10.16511/j.cnki.qhdxxb.2018.22.010

  Abstract ( ) Download PDF ( )   Knowledge map   Save

  Multipath interference is the main error source in high-precision global navigation satellite system (GNSS) applications. The geosynchronous earth orbit (GEO) satellite in the BeiDou navigation satellite system (BDS) has extremely low fading frequencies on the multipath signals, so most measurement based multipath detection techniques are ineffective. This paper describes a multipath detection method based on a circularly rotating antenna. The rotating parameters are controlled to increase the multipath fading frequency so that it is separated from the spectrum of the received signals to facilitate detection. Tests use a GNSS signal generator to create the multipath environment. This method successfully detects a short delay multipath signal that is 30 dB lower than the direct signal. Its signal detection ability is then better than the carrier to noise ratio (CNR) and code minus carrier (CMC)-based multipath detection methods. This method dramatically reduces the detection time and solves the GEO multipath detection problem.
CHEMISTRY AND CHEMICAL ENGINEERING
• Select
  Dynamic adjustment interval identification of hydrocracking based on principal component derivative feature clustering

  CHEN Xiaofang, QIAN Yingcan, WANG Yalin, YANG Chunhua

  Journal of Tsinghua University(Science and Technology). 2018, 58(1): 81-86. https://doi.org/10.16511/j.cnki.qhdxxb.2018.22.011

  Abstract ( ) Download PDF ( )   Knowledge map   Save

  Hydrocracking is a complicated long-term process resulting from many coupled variables that affect manufacturing schedule and create loud noises. This paper presents a dynamic interval identification method for hydrocracking based on principal component derivative feature clustering to accurately identify the dynamic changes from data. Firstly, a principal component analysis (PCA) is used to extract the principal components of the key hydrocracking operating parameters. Then, the first-order derivatives are obtained from fitting polynomials of the principal components with sliding windows. After that, the K-means algorithm is used to identify the dynamic adjustment intervals for the principal component derivative feature clustering with the density peak technique used to determine the initial centers. The flexibility and effectiveness of this method are validated on an industrial petrochemical process. The results show that this method can avoid the influence of variable errors and accurately identify the dynamic adjustment intervals without priori knowledge.
PRECISION INSTRUMENT
• Select
  Design of a resonator vibration control system based on parametric drive

  SONG Mingliang, ZHOU Bin, ZHANG Rong

  Journal of Tsinghua University(Science and Technology). 2018, 58(1): 87-93. https://doi.org/10.16511/j.cnki.qhdxxb.2018.22.012

  Abstract ( ) Download PDF ( )   Knowledge map   Save

  Resonator vibration control based on parametric drive is a time-varying control method which has important applications in micro-electro-mechanical system (MEMS) sensors. This paper presents the design of a closed-loop parametric drive resonator vibration control system. The mathematical models of the parametric drive resonator and the control loops are derived theoretically. The system stability is analyzed with criteria for selecting the control loop parameters. Numerical simulations verify the theoretical analysis and the influences of the control loop parameters on the system performance. The analysis is then used to design a parametric drive vibration control for a MEMS resonator. The settling time of the starting process is less than 0.2 s and the variance of the amplitude at steady state is 0.04 mV. The research provides an important reference for the design of closed-loop parametric drive resonator vibration control systems.
AEROSPACE AND ENGINEERING MECHANICS
• Select
  Optimization of acoustic sensor arrays for wind tunnel measurements

  JI Jianchao, ZHANG Yu, WANG Mingxin

  Journal of Tsinghua University(Science and Technology). 2018, 58(1): 94-100. https://doi.org/10.16511/j.cnki.qhdxxb.2018.21.002

  Abstract ( ) Download PDF ( )   Knowledge map   Save

  Acoustic sensor arrays used in wind tunnels for acoustic measurements are affected by channel and background noise which can be greater than the signal sources. The noise is mainly related to the wind tunnel parameters, interactions between the wind and the wall, and the acoustic sensor. This study combines channel signal filtering with processing of the cross spectral matrix (CSM) diagonal elements to recover the signal of interest from the channel noise with an extended Kalman filter to track the phase difference of the background noise to optimize the coherent background noise. Simulations show that this method effectively reduces the number of side lobes, suppresses the side lobe level, reduces the influence of noise on the beamforming results, and greatly improves the imaging by the acoustic sensor array.
HYDRAULIC ENGINEERING
• Select
  Numerical simulations of the wind energy resources in the Yalong River area

  YANG Mingxiang, WANG Hao, JIANG Yunzhong, LEI Xiaohui, SONG Jianjiao

  Journal of Tsinghua University(Science and Technology). 2018, 58(1): 101-107. https://doi.org/10.16511/j.cnki.qhdxxb.2018.22.013

  Abstract ( ) Download PDF ( )   Knowledge map   Save

  Large scale wind energy resources are difficult to accurately assess. This study uses a numerical weather prediction model and wind data from 2000 to 2016 to calculate the wind speeds in the Yalong River area for about 17 years. The wind energy resources in the Yalong River area are assessed in terms of the spatial distribution of the average wind speed, the spatial distribution of the wind energy density, the annual distribution of the wind speed, and the temporal and spatial distribution of the annual exploitable wind energy. The analyses give the temporal and spatial features of the wind energy resources in the Yalong River area. There are several wind resource rich regions in the Yalong River area, such as the region near the longitude line of Ganzi, the region between the Ninglang River and the Ganyu River, and the Anning River valley. These results can be used for site selection for wind energy resources.
ECONOMICS AND MANAGEMENT
• Select
  Influence of the downward revision clause on Chinese convertible bond pricing

  WANG Yintian, MOON Jiyoung

  Journal of Tsinghua University(Science and Technology). 2018, 58(1): 108-112. https://doi.org/10.16511/j.cnki.qhdxxb.2018.22.014

  Abstract ( ) Download PDF ( )   Knowledge map   Save

  Chinese convertible bond market prices are higher than model prices, indicating "market premiums" in the market. The paper shows that the downward revision clause may increase the accuracy of model prices and reduce the "market premium". The Tsiveriotis and Fernandes pricing model is used with trigger conditions for the downward revision, call, put and conversion clauses. The downward revision clause reduces the "market premium". High conversion ratio, moneyness and stock volatility in a bull market increase the option value of convertible bonds and reduce the pricing error. Years-to-maturity and market timing are related with the market premiums and affect the pricing error.