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百年期刊
ISSN 1000-0585
CN 11-1848/P
Started in 1982
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Table of Content
, Volume 57 Issue 6
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COMPUTER SCIENCE AND TECHNOLOGY
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Provenance dependency path pattern mining algorithm based on grammar induction
PEI Jisheng, YE Xiaojun
Journal of Tsinghua University(Science and Technology). 2017,
57
(6): 561-568. DOI: 10.16511/j.cnki.qhdxxb.2017.26.019
Abstract
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Provenance dependency path patterns are the foundations of many provenance based cloud data security measures. This article analyzes the importance of provenance dependency path pattern mining in provenance based security system with a linearization algorithm for provenance graphs that enables grammar induction and parsing of provenance data using automata models. A similarity measurement method is given for dependency paths based on grammar parsing with a dependency path pattern mining algorithm to reduce reliance on the domain knowledge and support automatic provenance rule learning. The feasibility and effectiveness of the approach are demonstrated by experiments.
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Data storage and access framework for business models in distributed environments
CAI Hongming, JIANG Zuhai, JIANG Lihong
Journal of Tsinghua University(Science and Technology). 2017,
57
(6): 569-574. DOI: 10.16511/j.cnki.qhdxxb.2017.26.020
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Business models can be used in model driven service development to rapidly construct and execute service applications in cloud platforms. However, a united model management is different to construct due to the massive amount of heterogeneous data. Therefore, a distributed model storage and accessing framework was developed to support the different stages of the full lifecycle of services, such as business modeling, service transformation, service configuration, service deployment and service monitoring. First, relational databases and a NoSQL database were integrated to efficiently store and access structured data.Then, a file repository based on Hadoop was built to manage unstructured model files in a comprehensive database management model for unified management of business models. RESTful services were generated for applications based on resource descriptions in the business models. Finally, a cloud-based business model library was built for verification. Tests show that the framework provides an effective data storage and access model for service applications and reduces development and maintenance costs. The tests also validate the framework's capabilities.
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Semantic relevancy between sentences for Chinese reading comprehension on college entrance examinations
GUO Shaoru, ZHANG Hu, QIAN Yili, LI Ru, YANG Zhizhuo, GU Zhaojun, MA Shuhui
Journal of Tsinghua University(Science and Technology). 2017,
57
(6): 575-579,585. DOI: 10.16511/j.cnki.qhdxxb.2017.26.021
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Multiple-choice reading comprehension questions in the Chinese College Entrance Examination are based on the given background material with the reader selecting the best option from a number of options. The answer may not be directly found in the background material since the passage is relatively short and the key information is hidden. Thus, information mining from the background material and semantic relevancy analyses with options are keys to solving the problem, with sentence level semantic relevancy analysis as the foundation. This paper presents an algorithm to calculate the semantic relevancy between sentences based on Multi-Dimension Voting by analyzing large numbers of multiple-choice questions from Chinese scientific article text understanding questions from college entrance examinations. The method utilizes the voting algorithm to take advantage of different size metrics to select the best option. The algorithm accuracy for the national college entrance examination of Beijing text understanding questions is 53.84%, which verifies the validity of the method.
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Improved pairing-free constant round certificateless authenticated group key agreement protocol
SHAN Chun, HU Kangwen, XUE Jingfeng, HU Changzhen, ZHAO Xiaolin
Journal of Tsinghua University(Science and Technology). 2017,
57
(6): 580-585. DOI: 10.16511/j.cnki.qhdxxb.2017.26.022
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Current certificateless group key agreement protocols are not secure when adversaries can replace the participants' public keys or the key generation center (KGC) master secret key is known. An improved protocol appends a signature in the second round to eliminate this weakness. The signature is related to the group identity, the broadcast messages in the first round and the computed message in the second round, to ensure the protocol freshness and the entity authenticity. The message in the second round guarantees that the adversary cannot attack the protocol by corrupting neighboring entities. The improved protocol is resilient to these two attacks and is more efficient other certificateless group protocols.
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Multi-dimensional Hash table structure for massive data applications
WU Quanyuan, PENG Can, ZHENG Yi, BU Junli
Journal of Tsinghua University(Science and Technology). 2017,
57
(6): 586-590. DOI: 10.16511/j.cnki.qhdxxb.2017.26.023
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Traditional Hash table can quickly locate the target by calculating the Hash value of the target data to enable fast data access and retrieval. Good storage performance requires that the Hash table maintains a loose state by sacrificing 10%-25% of the space. This is a tremendous waste of space in massive data storage systems. This paper presents a multi-dimensional Hash table structure that by increasing the logical dimension of the Hash table to significantly reduce the collision rate in the Hash table for satisfactory performance with a high filling rate. Tests show that with ten million entries, the collision rate of a two-dimensional Hash table is 2-4 orders of magnitude lower than a traditional Hash table and the overall performance is improved by 1 order of magnitude. In addition, a failure rate concept is proposed to improve Hash table performance evaluations.
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MECHANICAL ENGINEERING
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Predictive model for the interlayer burr height during drilling of stacked aluminum plates
WU Dan, HUANG Shijian, GAO Yuhao, DONG Yunfei, MA Xinguo
Journal of Tsinghua University(Science and Technology). 2017,
57
(6): 591-596,603. DOI: 10.16511/j.cnki.qhdxxb.2017.26.024
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The drilling of stacked components tends to form interlayer burrs, which reduce machining quality and the production efficiency. This study analyzes the formation and height of interlayer burrs and presents an effective processing method to control interlayer burrs. An empirical formula was developed for the thrust force during drilling for an finite element analysis (FEA) model of the drilling process to product the single plate deformations and to find the initial burr formation position. Then, the energy method is used in a mechanical model to product the interlayer burr height. The predictions agree well with drilling experiments with stacked aluminum plates and a carbide drill. The results show the effects of the feed rate and the interlayer gap on the interlayer burr formation to optimize the processing parameters of stacked components.
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Foot-wheel driven exoskeleton for rehabilitation training of paraplegic patients
MA Qingchuan, JI Linhong, WANG Rencheng, LI Wei
Journal of Tsinghua University(Science and Technology). 2017,
57
(6): 597-603. DOI: 10.16511/j.cnki.qhdxxb.2017.26.025
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Paraplegic patients must rely on assistive devices for movement with upright walking as their most pressing need. A powered lower-limb exoskeleton with mechanical structure is introduced in this study, which enables the patients to walk alternatively and further benefit their engagement in the rehabilitation training. The system includes a foot-wheel driven exoskeleton and wireless control crutches. The exoskeleton is driven by a hub motor at the bottom of the exoskeleton's foot. The crutches act as auxiliary devices to support the walking and control the exoskeleton motion by the embedded wireless controller. Alternative pressing of button on the crutch enables the continued walking with the whole walking procedure was fully controlled by the user in real-time. An automatic brake and mechanical limitations of the maximum step length were both designed to provide operational safety. The gait of a healthy subject with and without the exoskeleton were analyzed in a 3D gait analysis system. The spatio-temporal parameters and kinematic figures show that the exoskeleton can assist the user to complete secure, stable walk in a standing posture.
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Acoustic field characteristics of serrated ultrasonic phased array transducers
ZOU Cheng, CAI Dong, SUN Zhenguo, ZHANG Wenzeng, CHEN Qiang
Journal of Tsinghua University(Science and Technology). 2017,
57
(6): 604-608. DOI: 10.16511/j.cnki.qhdxxb.2017.26.026
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Serrated phased array transducers were used to detect longitudinal cracks on the outside surface of hollow shafts using electrical focus rotational scans. This paper describes the acoustic field characteristics of the serrated ultrasonic phased array transducers. The focus characteristics for a cylindrical fluid-solid interface was studied using the ray tracing method. Simulations with the finite element method (FEM) were used to evaluate the acoustic field in the shaft. Then, dynamic photoelastic experiments were used to study the focused transient acoustic field. Finally, detection experiments on a test block with artificial cracks showed that the serrated phased array transducers can rotationally scan the outside surface by using proper delayed time laws. The acoustic field energy was enhanced near the focus region, but decreased outside the focus region. The simulations matched the images acquired from the dynamic photoelastic experiment. The experiment shows that the crack signal was clear without interference from the back surface.
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PHYSICS AND ENGINEERING PHYSICS
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Terrorist attack vulnerability analysis of a natural gas network based on the Attacker-Defender game model
HUANG Lida, CHEN Jianguo, YUAN Hongyong, WANG Yan
Journal of Tsinghua University(Science and Technology). 2017,
57
(6): 609-613. DOI: 10.16511/j.cnki.qhdxxb.2017.26.027
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In recent years, terrorist attacks have become even more violent all over the world and terrorist forces have begun to spread to urban cities. Natural gas pipeline networks carrying hazardous materials in cities are easy targets for attacks. This study analyzes the vulnerability of a natural gas network to terrorist attacks. The adversary relationship between the attackers and defenders is modeled for a specfic natural gas transmission system using an attack-defense game based on game theory and the maximum-flow model of networks. The Nash equilibrium of the game strategy is used to analyze the optimal strategy choices of both parties. Monte Carlo simulations are used to compare the differences between random attacks and the optimal attack. The results show that the optimal attack targets differ for different numbers of pipelines, so it is impossible to rank the terrorist threat to pipelines. Additionally, most random attacks have little impact on the system. The conclusions in this paper can provide guidelines reference for government departments to mitigate the effects of terrorist attacks.
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Detailed eye model for adult Chinese males
ZHU Hongyu, QIU Rui, LI Junli, REN Li, LIU Huan, LI Chunyan, WU Zhen
Journal of Tsinghua University(Science and Technology). 2017,
57
(6): 614-619. DOI: 10.16511/j.cnki.qhdxxb.2017.26.028
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The human eye lens is sensitive to radiation. Thus, detailed eye models are needed to accurately assess the dose and radiation risk for the eye lens. A detailed eye model was build based on the characteristic parameters of Chinese adult males. The eye model includes nine main structures for the eyelids, scleral, choroid, retina, lens, iris, cornea, vitreous body and aqueous humor. The model was then used in an MCNP code to calculated the eye lens absorbed dose conversion coefficients for electrons for various irradiation conditions. The results compared with other studies show that the relatively deep anterior chamber of the Chinese male eye results in significant differences in the absorbed dose for electron energies between 0.6-1.2 MeV with a maximum relative difference of 98%. The detailed eye model in this paper provides a tool for accurate assessments of eye lens doses of Chinese adult males.
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ELECTRONIC ENGINEERING
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Detecting of fake accounts with hierarchical clustering
FANG Yong, LIU Daosheng, HUANG Cheng
Journal of Tsinghua University(Science and Technology). 2017,
57
(6): 620-624. DOI: 10.16511/j.cnki.qhdxxb.2017.26.029
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Since there are many malicious users on the Internet, popular online websites sometimes have millions of registered users. The system cannot easily distinguish between fake accounts and legitimate users. Fake accounts registered by a single malicious user often have similar profiles. This paper presents a new framework to find fake accounts in large numbers of users. The framework uses username string patterns to classify the original data and then calculates the similarity as measured by the Levenshtein distance between any two elements in one category. Hierarchical clustering with a proper threshold then finds groups of fake accounts hidden in the large amount of registration data. Tests demonstrate the effectiveness of this framework which algorithm relies less on data dimensions and features than other algorithms.
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Phonatory characteristics of the vibrato voice in Young woman roles in Kunqu Opera
DONG Li, KONG Jiangping
Journal of Tsinghua University(Science and Technology). 2017,
57
(6): 625-630. DOI: 10.16511/j.cnki.qhdxxb.2017.26.030
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The vibrato characteristics of two professional Kunqu Opera singers playing Young woman roles were measured using three EGG parameters for the fundamental frequency (F0), contact quotient (CQ) and speed quotient (SQ). The F0 in the Young woman role's singing showed a slow vibrato rate and a low vibrato amplitude as with their gentle voice. CQ and SQ changed periodically during vibrato singing. For most vibrato periods, the CQ and SQ vibrato rates were equal to the F0 vibrato rate. The vibrato phases of the three parameters showed no differences or a 180°difference, depending on the phonation type. The singers vibrate their larynx to producing the vibrato.
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AUTOMATION
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Dual channel spacecraft attitude control method based on an external disturbance observer
XU Limin, ZHANG Tao
Journal of Tsinghua University(Science and Technology). 2017,
57
(6): 631-636. DOI: 10.16511/j.cnki.qhdxxb.2017.26.031
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A dual channel attitude control method was developed for rigid body spacecraft based on a disturbance state observer. A linearized attitude control dynamics and kinematics model of the spacecraft was incorporated into a dual channel control system with a stabilization compensator controller and a servo compensator to adjust the control variables for servo tracking. The system poles are reassigned by state feedback to satisfy the given dynamic and static indicators, while estimated values of the interference obtained by the disturbance state observer are fed back via a compensating channel to the input to suppress disturbances. Simulations confirm that this control method has excellent static and dynamic properties and strong anti-interference ability.
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ELECTRICAL ENGINEERING
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Grid voltage synchronization algorithms for grid-connected power converters
WEN Wusong, ZHANG Yingchao, WANG Lu, ZHAO Zhengming, NIE Jintong
Journal of Tsinghua University(Science and Technology). 2017,
57
(6): 637-643. DOI: 10.16511/j.cnki.qhdxxb.2017.26.032
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An accurate and fast detection of the amplitude, frequency and phase angle of the grid voltage is crucial to assure the steady-state and dynamic performance of grid-connected power converters. This paper describes the classification of grid voltage synchronization algorithms, the principles and characteristics of phase-locked-loop (PLL) controllers, and the serious problems of PLL controllers such as frequency variations, unbalanced and distortied conditions, direct-current (DC) bias and phase-angle jumps with suppression methods to reduce these effects. The results show that PLL controllers based on synchronous reference frames or resonant controller are now widely used to track the grid voltage with multichannel-decoupling to suppress the harmonics and frequency fluctuations. A single-phase controller can be equivalent to a three-phase controller with new synchronization systems being more accurate, fast and robust.
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HYDRAULIC ENGINEERING
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Partnering to enhance interface management in international EPC projects
SHEN Wenxin, TANG Wenzhe, ZHANG Qingzhen, WANG Shuli
Journal of Tsinghua University(Science and Technology). 2017,
57
(6): 644-650. DOI: 10.16511/j.cnki.qhdxxb.2017.26.033
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Enhancing interface management in international engineering-procurement-construction (EPC) projects will help Chinese contractors better achieve project objectives and improve project performance and core competence. Questionnaires, interviews, case studies and social network analyse were used to construct and test an interface management model for international EPC projects to show the relationships among trust, openness, communication, and interface management performance. The results demonstrate that EPC contractors and designers have the best interface management performance, and trust improves interface management through enhanced inter-organizational openness and communication. The social network analyse and case studies confirm the important roles of suppliers and designers in the EPC contractors network.
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BIOLOGICAL SCIENCE AND ENGINEERING
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Autofluorescence of chloroplasts measured by a laser scanning confocal microscope
FENG Qianqian, WANG Wenjuan, LI Haidong, PAN Xun
Journal of Tsinghua University(Science and Technology). 2017,
57
(6): 651-654,660. DOI: 10.16511/j.cnki.qhdxxb.2017.26.034
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The autofluorescence of nicotiana benthamiana chloroplasts was studied using a laser scanning confocal microscope. The chloroplast autofluorescence was obtained by spectral scanning with various excitation wavelengths. Then, chloroplast autofluorescence images were obtained using laser scanning confocal microscopy with various excitation wavelengths with intensity quantification. Finally, nicotiana benthamiana chloroplasts were illuminated with 488 nm light to test the autofluorescence stability. 488 nm light has the highest excitation efficiency for chloroplast autofluorescence, while 561 nm light has the lowest excitation efficiency. The autofluorescence chloroplast emission spectrum starts from 637 nm and peaks at 681 nm. The measurements show that the chloroplast autofluorescence is very stable and that laser scanning confocal microscopy can accurately measure chloroplasts autofluorescence. This work will facilitate improved plant tissue imaging chloroplast genetic engineering research.
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ENVIRONMENTAL SCIENCE AND ENGINEERING
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Carbon emissions and trading in Hebei Province for Beijing-Tianjin-Hebei collaborative development
HUANG Sheng, LI Xingguo
Journal of Tsinghua University(Science and Technology). 2017,
57
(6): 655-660. DOI: 10.16511/j.cnki.qhdxxb.2017.26.035
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This study analyzes how carbons emissions cross between provinces and the effect on the carbon trading market development model. The carbon emissions of Hebei Province account for more than 70% of the total emissions in the Beijing-Tianjin-Hebei (Jing-Jin-Ji) area and the trend is increasing. The steel industry in Hebei is a major carbon emitter in the Jing-Jin-Ji area with more than 20% of the emissions each year. Thus, measures are needed to upgrade the industry and reduce carbon emissions. The measures include establishing carbon trading markets in the Jing-Jin-Ji area, developing carbon financing strategies, reducing carbon production, training carbon experts and improving the carbon trading supervision system.
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CONSTRUCTION MANAGEMENT
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Minimum revenue guarantee mechanism design for toll road PPP projects
LIU Ting, WANG Shouqing, FENG Ke
Journal of Tsinghua University(Science and Technology). 2017,
57
(6): 661-666. DOI: 10.16511/j.cnki.qhdxxb.2017.26.036
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This article describes the principles and methodology used to design the minimum revenue guarantee (MRG) mechanism to improve revenue risk allocation for toll road PPP projects. A literature review shows five critical principles for MRG design which are used in a stochastic model to find the optimal upper and lower revenue thresholds. A case study shows the application and effectiveness of this methodology. This research shows that a minimum revenue threshold determined by the target capital structure significantly reduces the bankruptcy probability of the project company. A maximum revenue threshold jointly determined by a target rate of investment return and a bidding process will prevent the private sector from obtaining excessive profits from the PPP project. These method and models will help with quantitative evaluations of the impacts of an MRG on a PPP project's financial status and the government's contingent liabilities to further improve project evaluations and fiscal sustainability assessments as well as budgeting for PPPs.
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ECONOMIC AND PUBLIC MANAGEMENT
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Export and corporate tax avoidance
WANG Rui, LU Yao, SHI Xinzheng
Journal of Tsinghua University(Science and Technology). 2017,
57
(6): 667-672. DOI: 10.16511/j.cnki.qhdxxb.2017.25.020
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The Asian financial crisis in 1997 is used as a natural test of how an exogenous exchange rate shock impacts corporate tax avoidance. This paper constructs a firm level exchange rate shock model from export destination information in the 1995 industry survey. An empirical analysis shows that firms whose export destinations experience greater currency depreciation have slower export growth and stronger incentives to engage in tax avoidance. This paper also demonstrates that weaker supervision induced by exporting to poor countries motivates firms to avoid income taxes.
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