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ISSN 1000-0585
CN 11-1848/P
Started in 1982
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  • Table of Content
      , Volume 58 Issue 2 Previous Issue   
    For Selected: View Abstracts Toggle Thumbnails
    COMPUTER SCIENCE AND TECHNOLOGY
    Remote sensing image recognition based on generalized regularized auto-encoders
    YANG Qianwen, SUN Fuchun
    Journal of Tsinghua University(Science and Technology). 2018, 58 (2): 113-121.   DOI: 10.16511/j.cnki.qhdxxb.2018.25.006
    Abstract   PDF (2250KB) ( 470 )
    This paper addresses the problem of sample scarcity in SAR (synthetic aperture radar) images, which are very useful remote sensing sources but are very costly to obtain. SAR images have limited samples which makes it hard to get a standardized “good” model for even simple classification tasks. Then, the limited samples are expanded via generalization of the sample space using prior and a priori information including labels. Then, auto-learning models, regularized auto-encoders, are used to extract useful features from the generalized sample space. A regularization term is used to penalize generalized samples in an image recognition algorithm. The method produces good results on limit-sized subsets from the MNIST database and the SAR MSTAR image dataset. With limited input samples, the method gives better reconstruction errors and recognition accuracies in the SAR ship images than the state-of-art methods. Thus, this algorithm is shown to be successful in both theoretical analyses and tests.
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    Microblog sentiment analysis method based on a double attention model
    ZHANG Yangsen, ZHENG Jia, HUANG Gaijuan, JIANG Yuru
    Journal of Tsinghua University(Science and Technology). 2018, 58 (2): 122-130.   DOI: 10.16511/j.cnki.qhdxxb.2018.22.015
    Abstract   PDF (2574KB) ( 1619 )
    Microblog sentiment analysis is used to get a user's point of view. Most sentiment analysis methods based on deep learning models do not use emotion symbols. This study uses a double attention model for microblog sentiment analysis that first constructs a microblog emotion symbol knowledge base based on existing emotional semantic resources including emotion words, degree adverbs, negative words, microblog emoticons and common Internet slang. Then, bidirectional long short-term memory and a full connection network are used to encode the microblog text and the emotion symbols in the text. After that, an attention model is used to construct the semantic representations of the microblog text and emotion symbols which are combined to construct the final semantic expression of the microblog text. Finally, the emotion classification model is trained on these semantic representations. The combined attention model and emotion symbols enhance the ability to capture the emotions and improve the microblog sentiment classification. This model gives the best accuracy for many sentiment classification tasks on the Natural Language Processing and Chinese Computing (NLPCC) microblog sentiment analysis task datasets. Tests on the 2013 and 2014 NLPCC datasets give F1-scores for the macro and micro averages that are 1.39% and 1.26% higher than the known best model for the 2013 dataset and 2.02% and 2.21% higher for the 2014 dataset.
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    Credit index measurement method for Android application security based on AHP
    XU Junfeng, WANG Jiajie, ZHU Kelei, ZHANG Puhan, MA Yufei
    Journal of Tsinghua University(Science and Technology). 2018, 58 (2): 131-136.   DOI: 10.16511/j.cnki.qhdxxb.2018.26.007
    Abstract   PDF (1355KB) ( 644 )
    The openness and popularity of Android systems has resulted in, Android applications facing serious security risks such as malicious injection and re-packaging. The traditional measurement methods of Android software security can generally determine its security level for its security index measurement accuracy, but they cannot provide accurate software credit measurements and security index sorting. This paper assigns a safety coefficient to indicate the scope of security after a reverse analysis of the Android software for the security classification. Then, the analytic hierarchy process (AHP) evaluation model is used for a preliminary safety score of the Android software. Meanwhile, the Android software certification strength and the violation records in the external application market are used to calculate the final AHP security index twice. Tests show that this measurement method can accurately measure the security index of Android software products.
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    K-means based feature reduction for network anomaly detection
    JIA Fan, YAN Yan, ZHANG Jiaqi
    Journal of Tsinghua University(Science and Technology). 2018, 58 (2): 137-142.   DOI: 10.16511/j.cnki.qhdxxb.2018.26.005
    Abstract   PDF (1241KB) ( 550 )
    Although the basic K-means test was used for anomaly detection in the KDD 99 attack dataset, its accuracy and efficiency for detecting rare attacks needs to be improved. Rare attacks, which are usually greater threats, are easily hidden by common threats so the rare attacks can be more easily identified by removing common attacks. An improved hierarchical iterative K-means method was developed based on this finding to detect all kinds of anomalies using feature reduction through correlations to decrease classification the dimensions. The algorithm is able to detect almost every rare attack with a 99% succesful classification rate and for nearly real-time detection with 90% less computations on the KDD 99 data compared with the basic K-means algorithm.
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    Multi-user fully homomorphic encryption scheme based on proxy re-encryption for cloud computing
    LI Taoshen, LIU Qing, HUANG Ruwei
    Journal of Tsinghua University(Science and Technology). 2018, 58 (2): 143-149.   DOI: 10.16511/j.cnki.qhdxxb.2018.26.009
    Abstract   PDF (1284KB) ( 821 )
    Cloud computing involves multi-user sharing, user privacy and security, and ciphertext evaluation. This paper presents a multi-user, fully homomorphic encryption scheme based on proxy re-encryption for cloud computing. The scheme uses different public keys to encrypt the ciphertexts of different users, so different user ciphertexts provide ciphertext independence and indiscernibility. When a ciphertext is uploaded to the cloud, the ciphertext of one user is re-encrypted by the cloud service provider (CPS) as the agent and converted into a ciphertext for the same user. This allows the ciphertext calculation between the two users to meet the fully homomorphic computing requirements. A security analysis shows that the security of the this scheme is based on the harder problem of learning with errors (LWE) and can resist the chosen plaintext attack (in the generic bilinear group radom oracal model). Tests show that this scheme efficiently implements fully homomorphic evaluations of different user ciphertexts and supports multi-user sharing.
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    User privacy-preserving cloud storage scheme on CP-ABE
    CAO Laicheng, LIU Yufei, DONG Xiaoye, GUO Xian
    Journal of Tsinghua University(Science and Technology). 2018, 58 (2): 150-156.   DOI: 10.16511/j.cnki.qhdxxb.2018.26.006
    Abstract   PDF (1351KB) ( 720 )
    A ciphertext-policy attribute based encryption (CP-ABE) user privacy-preserving cloud storage (UPCS) scheme was developed to protect user privacy in cloud storage environments. The data owner sets different access right attributes on different data files. The CP-ABE scheme has the trusted third-party embed the access right attributes into a ciphertext wich can be decrypted only when the user's attributes satisfy the access attributes of the ciphertext. The computational times of the data owner and users are reduced by authorizing some data owner and user operations to a distributed proxy server. Tests show that this scheme can effectively guarantee the user data and keyword privacy and reduce the data owner and user computational times.
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    CONSTRUCTION MANAGEMENT
    Path analysis attack prediction method for electric power CPS
    XIA Zhuoqun, LI Wenhuan, JIANG Lalin, XU Ming
    Journal of Tsinghua University(Science and Technology). 2018, 58 (2): 157-163.   DOI: 10.16511/j.cnki.qhdxxb.2018.26.012
    Abstract   PDF (1661KB) ( 762 )
    The electric power industry needs to defend against multi-step cross-domain attacks seeking to damage electric power CPS. This paper presents path analysisa electric power CPS attack prediction method that defines a common attack graph based on a probability attack graph model. The Cross-origin attack probability and the cross-origin mean time to compromise are used to quantify the exploit difficulty and the attacker proficiency for offensive and defensive actions to protect the power infrastructure. When attacks are detected in real time, the improved Dijkstra algorithm will enumerate possible follow-up attack paths. The two quantitative indicators are combined to predict the greatest threat attack path. Simulations show that this method can more effectively predict the attack path as a good defensive strategy for electric power CPS security management.
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    ELECTRONIC ENGINEERING
    OpenFlow based software overlay router
    ZHAO Jun, BAO Congxiao, LI Xing
    Journal of Tsinghua University(Science and Technology). 2018, 58 (2): 164-169.   DOI: 10.16511/j.cnki.qhdxxb.2018.25.004
    Abstract   PDF (1075KB) ( 415 )
    More and more network services use overlay networks with physical links between geographically distributed data centers with various kinds of tunnelling technologies to make full use of link resources between data centers. This paper presents an OpenFlow based software overlay router (SOR) to construct a flexible traffic overlay network. The system uses open sourced and widely used software packages, Open vSwitch and OpenVPN, for rapid deployment and low cost software development and maintenance. The system then leverages an OpenFlow based stateful traffic engineering of multi tunnels (TEOFMT) algorithm, to maintain a four tuple mapping relationship between TCP/UDP packets, to modify the packets according to the mapping relationship, and to forward the modified packets to the desired tunnel based on a kernel routing table for flexible traffic transmission scheduling. An overlay network was built using this router with the bandwidth measurement tools, iPerf and DVTS-SASM (digital video transport system- scalable application specific measurement), used to measure the link bandwidth in the network. The results indicate that this router greatly improves the utilization rate.
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    Optimized deployment of broadcast cells based on the energy efficiency in a single frequency network
    CHEN Huangqing, ZHONG Xiaofeng, WANG Jing
    Journal of Tsinghua University(Science and Technology). 2018, 58 (2): 170-174.   DOI: 10.16511/j.cnki.qhdxxb.2018.26.002
    Abstract   PDF (1216KB) ( 538 )
    The multimedia broadcast/multicast service over a single frequency network (MBSFN) can significantly improve the spectral efficiency (SE) by conserving transmitting resources, while broadcasting popular data in the MBSFN mode. As more users demand the same data in all MBSFN area, the energy efficiency will improve. This paper uses a low computational complexity deployment algorithm to optimize the broadcast cells with MBSFN transmissions in stochastic geometry networks. Simulations show that broadcasting with this algorithm has better energy efficiency than both unicasting and broadcasting with point-to-multipoint (PTM) in each cell. The efficiency gain is very important to the user equipment distribution.
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    Analysis and modeling of the intonation of Chinese unmarked questions
    XU Xiaoying, LAI Wei, LI Ya, DING Xingguang, TAO Jianhua
    Journal of Tsinghua University(Science and Technology). 2018, 58 (2): 175-180.   DOI: 10.16511/j.cnki.qhdxxb.2018.26.001
    Abstract   PDF (1425KB) ( 473 )
    The identification of questions in speech needs a good understanding and accurate quantification of the intonation trends of questions. This paper uses a regression line of the pitch contour as an indicator of the intonation trend to analyze the intonation of experimental and natural questions. The slope of pitch contour regression line is an important prosodic feature for distinguishing questions from statements. This feature is influenced by factors such as sentence length and temporal domain of the sentence and differs for questions and statements. The inverse was then used to model changes of the intonation trend slope with a high goodness of fit as a reliable reference to predict and generate interrogative intonation.
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    NUCLEAR ENERGY AND NEW ENERGY
    Accurate continuum surface force model applicable to particle methods
    SUN Chen, JIANG Shengyao, DUAN Riqiang
    Journal of Tsinghua University(Science and Technology). 2018, 58 (2): 181-187.   DOI: 10.16511/j.cnki.qhdxxb.2018.25.002
    Abstract   PDF (1302KB) ( 611 )
    The continuum surface force (CSF) model was used to improve the accuracy of surface tension calculation using the particle method. A geometric method was developed to accurately detect the boundary particle with the curvature calculated from the surface divergence of the unit normal, which only depends on the boundary particles in the interaction domain. The surface tension was then calculated only on the boundary particle. Curvature calculation results using a circle and an ellipse showed that the curvature calculation is more accurate with the proper resolution and smoothing length. Two-dimensional, two single-phase models of square drop oscillations and two drops colliding with surface tension effects were simulated using the moving particle semi-implicit (MPS) method. The predicted oscillation periods agreed well with analytical results with reasonable shape and smooth surfaces. The results indicate that this improved CSF model can accurately simulate the surface tension effect in two-phase flows.
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    HTR-PM helium circulator motor cooling
    MO Fei, ZHANG Youjie, WANG Hong, ZHANG Qinzhao
    Journal of Tsinghua University(Science and Technology). 2018, 58 (2): 188-191.   DOI: 10.16511/j.cnki.qhdxxb.2018.25.005
    Abstract   PDF (1573KB) ( 521 )
    The helium circulator is an important part of the HTR-PM which uses helium as its working medium. Due to the limited space in the HTR-PM, the main helium fan uses a self-contained, air-cooled integrated structure to remove the motor heat. The auxiliary impeller design is then based on the flow characteristics and heat transfer characteristics of the motor cooling flow. Experiments using nitrogen as the working fluid were conducted to study the flow and heat transfer characteristics of the HTR-PM air-cooling system with the results extended to the helium working fluid. The experimental and theoretical results were used to optimize the cooling system design for the next HTR-PM main helium turbine auxiliary impeller design and optimization.
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    HYDRAULIC ENGINEERING
    Shaking table tests on the mitigation of liquefiable ground effects by well-point dewatering
    CHEN Yulong, ZHANG Ke
    Journal of Tsinghua University(Science and Technology). 2018, 58 (2): 192-197.   DOI: 10.16511/j.cnki.qhdxxb.2018.25.001
    Abstract   PDF (4334KB) ( 491 )
    The liquefaction resistance of saturated, sandy foundations can be improved by reducing the saturation. The well-point dewatering method was used to lower the saturation of the subsoil using vertical, horizontal, inclined and combined drainage pipes arrangements. The horizontal arrangement gave the best liquefaction resistance with the lowest induced excess pore pressure during the shaking. In engineering practice, the dewatering method can be used at regular intervals to reduce the liquefaction possibility.
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    Chloride permeability in cement-based materials based on DC/AC methods
    QIAN Peng, XU Qianjun
    Journal of Tsinghua University(Science and Technology). 2018, 58 (2): 198-203.   DOI: 10.16511/j.cnki.qhdxxb.2018.25.003
    Abstract   PDF (1581KB) ( 390 )
    The chloride permeability of cemented materials saturated with solutions of deionized water or 1 mol/L NaCl was measured using the rapid chloride permeability test (RCPT) and electrical impedance spectroscopy (EIS). The results show that as the water-cement ratio increases, the passed charge and the resistance of continuous conduction paths (R1) increase, indicating that a reduced anti-chloride penetration ability. The RCPT tests showed that the passed charge and temperature rise of the specimens saturated with different solutions were almost the same for a given water-cement ratio. However, the EIS tests showed that the initial currents in the NaCl saturated samples were higher than in the water saturated samples. DC/AC tests showed a strong power relation between R1 and the passed charge and a linear relationship between R1 and the passed initial current. Thus, the initial current can be used to calculate the chloride diffusion coefficient and to evaluate the permeability more accurately with the passed charge.
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    MECHANICAL ENGINEERING
    Characteristics of controllable stiffness for cable-driven parallel robots
    CUI Zhiwei, TANG Xiaoqiang, HOU Senhao, XIANG Chengyuan
    Journal of Tsinghua University(Science and Technology). 2018, 58 (2): 204-211.   DOI: 10.16511/j.cnki.qhdxxb.2018.26.010
    Abstract   PDF (1931KB) ( 974 )
    Human-robot interaction include some safety threats to people or products from the robots due to their stiffness. The characteristics of controllable stiffness for cable-driven parallel robots are studied using a static stiffness analysis and cable tension distribution method. The robot kinematics and statics equations are used for the force analysis with the three-dimensional Hessian matrix of the structural matrix to position differential is deduced by introducing a line vector and a differential transform. Then, the static stiffness model is derived for the relationship between the cable tension and the robot stiffness. The robots stiffness is then controlled by analyzing the cable tension polygon and the cable tension distribution. Simulations show that this method can effectively control the robot stiffness.
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    AUTOMOTIVE ENGINEERING
    Simulation of a multi-axial loading fatigue test of the rear drive axle of a minivan
    DONG Zhichao, WANG Xiaofeng, LOU Weipeng, HUANG Yuanyi, ZHONG Ming
    Journal of Tsinghua University(Science and Technology). 2018, 58 (2): 212-216.   DOI: 10.16511/j.cnki.qhdxxb.2018.26.004
    Abstract   PDF (2083KB) ( 572 )
    When a vehicle is running, its suspension is heavily loaded due to the motion. The durability is then one of the key problems in vehicle design. Multi-axial loading laboratory fatigue tests are widely used to shorten the development process, reduce costs and enhance market competitiveness. This paper presents a practical method for simulating multi-axial fatigue tests of a rear axle using a dynamic finite element model of the rear axle and data processing in MATLAB. The simulation of the laboratory fatigue tests includes system identification, calculation of the input dynamic loads for the finite-element model and calculation of the stress-strain response reproduced and compared with the measured stress-strain response. With the errors of less than 5% with the critical fatigue areas in the rear axle located where the section sizes change.
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    CIVIL ENGINEERING
    Relationship between CaO hydration activity and its expansive characteristics in C4A3$-CaSO4-CaO systems
    HAN Jianguo, YAN Peiyu, ZHANG Youhai
    Journal of Tsinghua University(Science and Technology). 2018, 58 (2): 217-224.   DOI: 10.16511/j.cnki.qhdxxb.2018.26.003
    Abstract   PDF (2106KB) ( 394 )
    The effects of two C4A3$-CaSO4-CaO (CCC) systems were evaluated to explain the cause of water-loss-expansion of CCC systems introduced into concrete. This study measures the influences of two CCC systems on the concrete workability, compressive strength, autogenous shrinkage, dry shrinkage, hydration heat and XRD pattern. The results show that the CCC system can significantly compensate for concrete autogenous shrinkage and drying shrinkage, and that the CaO component of the CCC system is responsible for the water-loss-expansion behavior during drying. The dead burn during manufacturing or hindered hydration in low water-to-binder concrete allowed the CaO to continue to hydrate for unsaturated conditions while resulted in in-situ hydration and expansion. The results show the relationship between the CCC component activity and the expansive characteristics. Thus, CaO dead burn should be avoided and the CCC concentration should be reduced in low water-to-binder concrete.
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