15 November 2019, Volume 59 Issue 11

    

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CIVIL ENGINEERING
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  Assessing construction workers' unsafe behavior using a danger coefficient

  GUO Hongling, ZHANG Zhitian, YU Run

  Journal of Tsinghua University(Science and Technology). 2019, 59(11): 873-879. https://doi.org/10.16511/j.cnki.qhdxxb.2019.22.030

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  Traditional measures for managing workers' unsafe behavior are static, standardized methods that are only partially effective, which makes them difficult to use for managing dynamic unsafe behavior on site. Therefore, better methods are needed to assess the danger of unsafe behavior so as to take necessary countermeasures. This paper presents an assessment method for construction workers' unsafe behavior by introducing a danger coefficient. Firstly, various types of unsafe behavior are classified according to accident types and scenes. Then, the danger coefficients for various types of unsafe behavior are defined by combining the occurrence rate of an unsafe behavior, the possibility of various accidents caused by the behavior, and the consequences of the accidents. Resources can then be allocated to behavior management. A real case is given to show that this method can improve the effectiveness of unsafe behavior management to further improve construction site safety.
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  Price dispersion and information search behavior in a second-hand housing market

  ZHANG Hong, YU Lutong, LI Linjun, LI Vera

  Journal of Tsinghua University(Science and Technology). 2019, 59(11): 880-886. https://doi.org/10.16511/j.cnki.qhdxxb.2019.26.029

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  China's real estate market has entered the age of stock rooms and the second-hand housing market is bound to become more active in this stage. However, information asymmetry has led to large price discrepancies in the second-hand housing market, mainly because the second-hand housing transaction price can vary greatly. According to search theory, price discrepancies will lead to profitable information search behavior. The study of the relationship between the degree of discrepancies in second-hand housing prices and information search behavior has important implications for second-hand housing market information searches, improving the information search efficiency, and promoting the healthy development of the real estate intermediary industry and the second-hand housing market. This study uses information search theory to analyze the relationships among the price dispersion in the second-hand housing market, the number of information searches, and the information search cost, and proposes corresponding hypotheses to be tested. Then, a second-hand housing market is designed based on the key hypothesis for verification. A search experiment explores the relationship between the degree of price dispersion and the information search behavior. Finally, experimental data is used to complete the empirical analysis and test the hypothesis. The results show that increasing the price dispersion of the second-hand housing market will increase the number of buyer information searches. Increasing the number of buyer information searches then reduces the price dispersion in the second-hand housing market. Reducing the information search costs will increase the information for second-hand housing buyers. This research suggests that adjustments to the second-hand housing market should focus on reducing information search costs to stimulate increases in the number of information searches in the market which will reduce the degree of information asymmetry in the second-hand housing market and, thereby, reduce the price discrepancies in the second-hand housing market and lead to a more mature second-hand housing market.
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  Performance evaluation of the Allan variance method for ring laser gyroscope noise analyses

  LI Qi, BAI Zhengdong, ZHAO Sihao, DAI Dongkai, XING Haifeng

  Journal of Tsinghua University(Science and Technology). 2019, 59(11): 887-894. https://doi.org/10.16511/j.cnki.qhdxxb.2019.22.009

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  The Allan variance method for various types of gyroscopes in various conditions was evaluated for ring laser gyroscope (RLG) noise at room temperature (~25℃) and steady conditions with analyses of the minor RLG noise terms besides the 5 major noise terms. Tests of a Chinese RLG and the widely used MPU 9250 micro-electro-mechanical systems (MEMS) inertial measurement unit (IMU) for static and dynamic conditions show that the Allan variance method can be used to estimate the main noise terms of various types of gyroscopes for static conditions to set the Kalman filter parameters for integrated global navigation satellite system/inertial navigation system (GNSS/INS) with the parameter values depending on the degree of understanding of the gyroscope physics. Several conclusions are given to supplement the classical Allan variance method in the IEEE Standard Specification Format Guide and Test Procedure for Single Axis Interferometric Fiber Optic Gyros. The wide applicability of the Allan variance method is contrasted with some commonly used data analysis methods. The Allan variance method has been widely recognized for metrology of precise instruments to improve the design and manufacture of precise instruments and to improve the precision of inertial measurements.
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  Geometric design of an outdoor three-dimensional kinematic verification field for a position and orientation system

  LI Qi, BAI Zhengdong, LI Qiong, WU Fei, CHEN Bobo, XIN Haohao, CHENG Yuhang

  Journal of Tsinghua University(Science and Technology). 2019, 59(11): 895-901. https://doi.org/10.16511/j.cnki.qhdxxb.2019.22.026

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  A three-dimensional test field was developed to verify the accuracy of a multi-sensor integrated position and orientation system (POS) with an improved kinematic testing method. This paper describes the POS kinematic testing method conditions, the geometric model for the outdoor three-dimensional kinematic verification field, and the limitations of the field design. Static and kinematic calibration tests of a multi-sensor integrated POS in the field are consistent with the field design parameters. Statistical analyses of the distance, horizontal and vertical errors using the classical variance, Allan variance, and other methods show that the short-term precision of the multi-sensor integrated POS is acceptable. This verification method can not only verify the position and orientation precision of the POS, but can also be used to develop specifications to improve POS designs.
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  Influence of long-term load and chlorine corrosion on reinforced concrete beam deflection

  HE Shiqin, CAO Zeyang, LIU Weijie, LI Pengfei

  Journal of Tsinghua University(Science and Technology). 2019, 59(11): 902-909. https://doi.org/10.16511/j.cnki.qhdxxb.2019.26.022

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  This study predicts the long-term deformation of reinforced concrete (RC) beams in corrosive environments which is important for ensuring the long-term strength and durability of structures. The long-term deformation of RC beams was measured for the coupling action of the load level and chloride corrosion environment. The long-term deflection of the beams was compared with predictions of the ACI209R model. The results show that the beam deflection when affected by load-chloride corrosion can be divided into four stages:the deflection increased rapidly in the first 10 d, the growth rate slowed after 10 d, the growth rate further decreased after 150 d, and the deflection rate started to increase again after 300 d. Alternating dry and wet environments caused the deflection rates to go up and down. The load level has an evident influence on the RC beam deflection in the corrosive environment. The ACI209R prediction model does not accurately predict the test results because it does not consider the coupled effect of the reinforcement corrosion.
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  Interfacial shearing of anchored rock slopes with a weak layer under earthquake loading

  YAN Zhixin, LI Yapeng, LONG Zhe, ZHAI Juyun, JIN Feifei

  Journal of Tsinghua University(Science and Technology). 2019, 59(11): 910-916. https://doi.org/10.16511/j.cnki.qhdxxb.2019.26.011

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  The bolt-grout and grout-rock interfaces of rock slopes anchored by full-length bonded bolts experience significant shear stresses during earthquakes which can lead to failures. This paper presents a numerical model of an anchored rock slope with a weak layer to predict these shear stresses using solid and interface elements in the FLAC^3D software. The model is used to predict the distributions of the anchorage interface shearing action and the anchor axial forces and how they evolve over time for a horizontal simple harmonic wave. The results show that solid elements can be combined with interface elements for modeling. The model can accurately predict the shear and debonding failure of the anchorage interface. The shear stresses at the two anchorage interfaces and the anchor axial force are not the same and the shear stress at the weak layer is zero while the axial force is the largest force. As the ground motion continues, the shear stresses at the two anchorage interfaces and the anchor axial force all increase. Debonding then occurs at the anchorage interface and develops toward both ends of the bolt and the anchorage interface far from the neutral point and the peak shear stress location moves to both ends of the bolt. The results show the failure mechanism of an anchored bedding rock slope with a weak layer during an earthquake, which is of great significance for designing geotechnical anchorage systems.
AUTOMATION
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  Mining and predicting of cold start service collaboration relationships in service systems

  HAO Yushi, FAN Yushun

  Journal of Tsinghua University(Science and Technology). 2019, 59(11): 917-924. https://doi.org/10.16511/j.cnki.qhdxxb.2019.22.022

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  Services that have never been used and newly released services in Web service systems are called cold start services. A cold start service collaboration relationship mining and predicting method is developed to help service composition developers identify the characteristics of cold start services, increase attention to and usage of cold start services, and enhance the element diversity and robustness of service systems. The method first establishes a functional vector for each service using service description reconstruction and a functional topic analysis. Next, the method builds a collaborative vector for each non-cold start service based on its historical collaboration record and functional vector. Finally, the method compares the functional vectors of cold start services with the collaborative vectors of non-cold start services to predict the collaboration relationships for cold start services. Tests on real-world data show that this method more effectively predicts the relationships than state-of-the-art methods.
  
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  Model-driven MOE method for weapon systems

  WEI Hailong, LI Qing, HUANG Shisheng, XU Zhiyong, PU Yudi, YANG Shaobo

  Journal of Tsinghua University(Science and Technology). 2019, 59(11): 925-933. https://doi.org/10.16511/j.cnki.qhdxxb.2019.21.023

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  Modern weapon systems are expensive and complex. The current measure of effectiveness (MOE) method is also expensive many complex relationships among the layers. The paper uses model-based systems engineering (MBSE) to construct a model-driven MOE method with system modeling to support the acquisition of MOE data through model analyses and simulations. This method is less expensive and more useful than traditional methods, which improves the system design optimization and development decision making. The system closely links the method and the system design, so it is applicable to all stages of the life cycle of the development and construction of weapon systems and can be refined to various granularity system levels. The MOE method is verified through analysis of a damage control system (DCS) as an example.
ECONOMICS AND MANAGEMENT
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  Macroeconomic effects of China's Western Development Program: Analysis of co-movements among different regions based on the Bayesian dynamic latent factor model

  LIU Chun, ZHANG Jian

  Journal of Tsinghua University(Science and Technology). 2019, 59(11): 934-939. https://doi.org/10.16511/j.cnki.qhdxxb.2019.25.002

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  The influence of state-level and regional economic fluctuations on regional economic growth was analyzed using a Bayesian dynamic latent factor model based on the different economic development rates in different regions of China. This method decomposes the fluctuations of the macroeconomic aggregates in China into the state factor, the regional factors and the idiosyncratic errors specific to each aggregate variable. The dynamics of the macroeconomic variables were analyzed from 1980 to 2015 to show that the regional output and investment are mainly influenced by the state factor, while regional consumption is mainly influenced by the regional factor. Furthermore, the study finds that after implementation of China's Western Development Program, the state factor has more significant influence on the fluctuations of all the economic variables in the western region with the greatest influence on investment.
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  Fiscal decentralization, fiscal squeeze and local government revenue and expenditure restructuring

  ZHANG Yuan, WU Binzhen

  Journal of Tsinghua University(Science and Technology). 2019, 59(11): 940-952. https://doi.org/10.16511/j.cnki.qhdxxb.2019.22.035

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  This study investigates how local governments restructure their revenue and expenditure in response to fiscal stress resulting from changes in fiscal decentralization. The exogenous policy shock of income tax sharing in 2002 is analyzed using the difference-in-difference method to solve the endogeneity problem. The results show that prefectural governments faced with increasing fiscal stresses tend to maintain their revenue and expenditure levels by various revenue tools but they change their expenditure structures. Prefectural governments with larger income losses increase their reliance on non-income taxes and government funds and prefer to increase their infrastructure expenditures.
ENGINEERING MECHANICS
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  Accuracy evaluation and correction of the element integration based on a geometric index in the boundary element method

  HUANG Junhao, CHEN Yongqiang

  Journal of Tsinghua University(Science and Technology). 2019, 59(11): 953-960. https://doi.org/10.16511/j.cnki.qhdxxb.2019.22.012

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  This paper presents a scheme to evaluate the element integration accuracy for the boundary element method based on a singular geometric index to improve the accuracy of the final solution. The singular geometric index is defined as the ratio of the shortest distance from the source point to the integral element to the element length. For a discretized boundary mesh, the upper bound of the quadrature error is used to obtain the relationship between the singular geometric index and the element integration accuracy with the integrated accuracies of all the elements estimated from the node geometries. Furthermore, the maximum relative error of the solution which is a global precision index is estimated from the matrix error transfer formula. If the index is larger than a threshold, some of the element integrals are not accurate and should be corrected to improve the solution accuracy. This method uses the sinh transformation method to correct the element integrals of low accuracy elements. Numerical results show that this method can guarantee the accuracy of the overall stiffness matrix coefficient of the boundary element method and the final solution accuracy using only the geometric node information. This scheme does not need to change the original calculation, requires little additional computational cost, and can be easily implemented.