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15 April 2017, Volume 57 Issue 4
    

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    HYDRAULIC ENGINEERING
  • XU Mengzhen, LI Yanfu, LI Zhiwei, WANG Zhaoyin, HAN Lujie
    Journal of Tsinghua University(Science and Technology). 2017, 57(4): 337-344. https://doi.org/10.16511/j.cnki.qhdxxb.2017.25.001
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    Field investigations and samplings in typical aeolian erosion areas in Sanjiangyuan were taken to study the features of sediment particles. The sediment composition distributions of active, semi-fixed, and fixed sand dunes were analyzed to identify the components of blowing sand when eroded by wind. The content of the blowing sand then influences the desertification. A desertification risk index which indicates the risk of desertification for an area was defined and applied to assess the desertification risk of the aeolian erosion areas. The desertification risk index of the sampled areas was correlated with the blowing sand percentage. Desertification is unlikely when the blowing sand percentage was less than 50%, with the desertification risk increasing exponentially as the blowing sand percentage increased for percentages over 60%. Therefore, the blowing sand percentage is recommended as an index for indicating the desertification risk of a region. Strategies to reduce the proportion of blowing sand and promoting vegetation coverage are recommended for preventing desertification in the Sanjiangyuan region.
  • SHI Jie, LI Qingbin
    Journal of Tsinghua University(Science and Technology). 2017, 57(4): 345-350. https://doi.org/10.16511/j.cnki.qhdxxb.2017.25.002
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    Similarity model test results cannot be simply converted to the prototype without consideration of the size effect. The extended finite element method (XFEM) was used to analyze the failure mechanism and overall structure strength of a type of prenotched gravity dam. The size effect was investigated by analyzing the nominal strength of geometrically similar prenotched gravity dams with various sizes. The nominal strength and failure mechanism were analyzed for two sets of models with an extra centrifugal force and a self-weight force. The results show that the structural strength in the centrifugal models decreases exponentially and tends to be stable for larger sizes, while in gravitational models the strength decreases exponentially up to a critical height and then increases gradually due the self-weight contribution. The relative length of the fracture process zone is an intrinsic factor while the self-weight stress is an external loading factor for the effect of size on the structural strength.
  • ZHENG Hang, CHEN Ben, LIN Mu
    Journal of Tsinghua University(Science and Technology). 2017, 57(4): 351-356. https://doi.org/10.16511/j.cnki.qhdxxb.2017.25.003
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    China is developing its water rights drawing system based on water trading which is an important method to optimize allocations through the market mechanism. This article describes the mathematical model for pooled water trading and analyzes trader bidding behavior in the market. The trader income is also calculated based on balancing the trading risk and benefit. The best bidding strategy is selected to give the optimal income. Split bidding was also analyzed to show that split bidding increases the trader income. Furthermore, the effect of information transparency was also studied by solving for the game equilibrium between buyers with the result showing that increasing information disclosure improves the price discovery effectiveness in the market.
  • LIN Xu, ZHAO Jianshi, LEI Xiaohui, WANG Hao
    Journal of Tsinghua University(Science and Technology). 2017, 57(4): 357-361. https://doi.org/10.16511/j.cnki.qhdxxb.2017.25.004
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    The economic cost of pollutant control was quantified to find the minimum economic cost of implementing a water quality red line. Current studies have few quantitative analysis tools. This study analyzes both the economic value added and the pollutant emission effects to develop a function for the economic value of additional pollutant emissions. This function can be used for quantitative analyze of the additional economic value and the pollutants emitted to rivers in a river basin. This function is used to analyze the effects in the Weihe Basin in Shaan Xi province. The results are accurate and suitable for quantitative analyze for river basin management.
  • CIVIL ENGINEERING
  • GUO Mengwu, ZHONG Hongzhi
    Journal of Tsinghua University(Science and Technology). 2017, 57(4): 362-368. https://doi.org/10.16511/j.cnki.qhdxxb.2017.25.005
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    For model verification which is mainly focused on the control of discretization errors of numerical results, a posteriori error estimation plays an important role in various numerical tools such as the finite element method. The outputs of interest are usually converted into integral functionals over the problem domain for a posteriori error analysis. Among the available techniques for goal-oriented error estimation, only two approaches, the constitutive relation error estimation and the constrained optimization method with convex objective functions, have been claimed to be able to offer guaranteed strict upper and lower bounds for the errors in quantities of interest. The two approaches are briefly reviewed and the equivalence of their formulation and principle is given. Both approaches are shown to be essentially based on the complementary energy theorem. The equivalence of the two approaches is instrumental in simplification of error estimation and extension of applications into more complex problems.
  • WANG Shouqing, WU Di, PENG Wei, CUI Qingbin
    Journal of Tsinghua University(Science and Technology). 2017, 57(4): 369-375. https://doi.org/10.16511/j.cnki.qhdxxb.2017.25.006
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    PPP (public-private partnership) is a new financing mode that eases the financial pressure and promotes efficiency. The allocation of control rights in PPP projects is a critical success factor. The control allocation principles and mechanisms in PPP projects are examined using decision indexes to describe the control allocation and nationwide big data. A guiding index is developed to characterize the statistics in terms of the regions, decision-making processes and allocation entities. Then, the FMEA (failure mode and effects analysis) index was used with survey data for a correlation analysis to explain the allocation mechanism. The shortcomings of China's PPP practices are related to the lack of pertinent regulations, allocation monitoring, and industry and public participation. Finally, suggestions are then given based on this research and international experience.
  • FENG Ke, WANG Shouqing, XUE Yanguang
    Journal of Tsinghua University(Science and Technology). 2017, 57(4): 376-381. https://doi.org/10.16511/j.cnki.qhdxxb.2017.25.007
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    The equity structure of a public-private partnership (PPP) project directly affects the allocation of risk and interest among the project stakeholders. A reasonable equity allocation decision making model is important for a project's success. This paper first analyzes the equity allocation decision making principles of the main stakeholders. These principles and project financing characteristic were then used to define an optimization model to minimize a PPP projects' social costs while satisfying the objectives of the key PPP stakeholders, i.e., the debtors, the private companies and the governments. A genetic algorithm is used to solve the decision making problem with a Monte Carlo model to simulate the changes in the project revenues with an immunological memory cell to improve the algorithm convergence. The model is validated by companies with an actual urban rail transport project. The model can be used to provide reference data for public and/or private entities for equity structure decision making for other PPP projects.
  • ELECTRICAL ENGINEERING
  • SUN Jiasong, ZHANG Jingyun, YANG Yi
    Journal of Tsinghua University(Science and Technology). 2017, 57(4): 382-387. https://doi.org/10.16511/j.cnki.qhdxxb.2017.25.008
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    Key audio detection, an important form of audio retrieval, uses a query audio sample to search in an audio database but such searches are not very efficient or robust. This paper optimizes the pre-processing, fingerprint extraction and retrieval of the audio retrieval. The pre-processing uses endpoint detection based on the sub-band energy ratio with a modified window function and measurements of the sub-band divisions. The fingerprint extraction uses seed fragments and spectral sub-band centroids. The retrieval part uses a threshold for the hit counts to improve the efficiency. This system improves the precision and reduces the recall rate with good noise suppression. The retrieval efficiency and performance are effectively improved.
  • PEI Yukui, SUO Wanping
    Journal of Tsinghua University(Science and Technology). 2017, 57(4): 388-392,398. https://doi.org/10.16511/j.cnki.qhdxxb.2017.25.009
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    Phase noise can impair the BER performance of high-data-rate satellite communications. The influence of the phase noise varies in the two frequency bands in both the uncoded or low-density parity-check (LDPC) coded communication systems. This paper presents a simulation and then an iterative compensation algorithm for the LDPC codes for the phase noise in the higher frequency band, which significantly degrades the high order modulation systems performance. The algorithm first compares the phases of the receiving and after-decoding symbols, extracts the difference based on the low-pass and narrow-band characteristics of the phase noise, and their compensates for the losses in an iteration loop. Simulations show that the method improves the LDPC-coded systems performance when the phase noise significantly degrades the signal.
  • ABULIZI Abudukelimu, JIANG Minghu, YAO Dengfeng, ABUDUKELIMU Halidanmu
    Journal of Tsinghua University(Science and Technology). 2017, 57(4): 393-398. https://doi.org/10.16511/j.cnki.qhdxxb.2017.25.010
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    Event-related potentials (ERPs) were used to investigate electrophysiological correlates of Uyghur morphological word processing in lexical decision paradigms. Four stimuli were used with monomorphemic words, bimorphemic inflected nouns (case suffix is added to the stem), monomorphemic pseudowords (changing one or two letters in monomorphemic nouns) and inflected pseudowords (changing one or two letters in stems). The mean phonemic length of all the words was controlled to be six letters long. EEG data showed N400 effects for the bimorphemic complex words and pseudowords in the 350-550 time windows. The N400 effects for the bimorphemic pseudoword were demonstrated that subjects failed all lexical searches when processing bimorphemic pseudowords. The effect for the bimorphemic complex words most probably reflects the access and possible interaction of the stems and suffixs. The EEG data also showed the differences in the neurocognitive underpinning that supports monomorphemic words, bimorphemic inflected words and both types of pseudoword processing. The mean amplitudes for bimorphemic words are more negative in the right hemisphere electrodes than for monomorphemic words. The experimental results reveal that native Uyghur speakers represent and access inflected Uyghur words in a morphologically decomposed form, while monomorphemic words are accessed as a single form.
  • NUCLEAR ENERGY AND NEW ENERGY
  • ZHOU Shuqiao, LI Duo
    Journal of Tsinghua University(Science and Technology). 2017, 57(4): 399-404. https://doi.org/10.16511/j.cnki.qhdxxb.2017.25.011
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    Redundant controllers are widely used in control systems of nuclear-powered facilities requiring high reliability. The reliability of dual-redundant controllers is improved by analyzing the controllers' possible working states in a state transition diagram. The two critical circumstances where the reliability is impaired are failures caused by dual-master collisions and the loss of redundancy resulting from the failure of a stand-by unit. To avoid these critical circumstances, this paper presents a redundant controller scheme with dual dedicated communication paths using heartbeat double checking and slave reporting. A Markov-chain model was developed to evaluate the reliability of redundant controllers and the effectiveness of this scheme. The results show that this redundant controller design significantly improves the reliability with a three orders of magnitude reduction of the failure rate.
  • ZHANG Jingyu, LI Fu, SUN Yuliang
    Journal of Tsinghua University(Science and Technology). 2017, 57(4): 405-409. https://doi.org/10.16511/j.cnki.qhdxxb.2017.25.012
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    During the building of the first core of the pebble bed high-temperature gas-cooled reactor (PBR), the ratio between the fuel spheres and graphite spheres, the fill material in the gaps in the core and the cavity height above the pebble bed will change. Thus, the neutronics design of the first core using the deterministic VSOP code needs some special treatments. The approximations for the first are an evaluated using a more detailed model of the first core analyzed by a general Monte Carlo code. Comparisons of the predictions of the two codes show that the special treatments for the first core used with the VSOP code will not cause significant errors include using the equivalent sphere model to calculate the thermal spectrum, calculating the reactivity of the gap fill material using the streaming correction method, heating the helium atmosphere as a vacuum, and using anisotropic diffusion coefficients to model the large top cavity. Thus, these special treatments for the first core used by the VSOP code are acceptable.
  • LI Junfeng, QIU Yu, WANG Jianlong
    Journal of Tsinghua University(Science and Technology). 2017, 57(4): 410-414. https://doi.org/10.16511/j.cnki.qhdxxb.2017.25.013
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    The radiation stability of the cementation matrix for spent radioactive resin when exposed to high radioactive fluxes was investigated using a sulfoaluminate cementation matrix for radioactive waste. The variation of the compressive strength after irradiation, the strength losses after freezing and the leach rate were compared for various γ-ray radiation doses. The microstructures of the hydration products in the irradiated cementation matrix were observed using an SEM. The results show that the radiation reduces the compressive strength of the cementation matrix with the losses increasing with the dose. The strength losses after freezing were also increased by the radiation. The adsorption of leaching ions was reduced. The aluminium micelles in the microstructure were reduced. The radiation may cause the decomposition of the aluminium micelles, which may led to the increased radionuclide leach rate. The results also showed that the matrix stability was not affected by the radiation when the total absorbed dose was below 105Gy.
  • ECONOMIC AND PUBLIC MANAGEMENT
  • ZHANG Hong, CHEN Jiawei, LI Vera
    Journal of Tsinghua University(Science and Technology). 2017, 57(4): 415-420. https://doi.org/10.16511/j.cnki.qhdxxb.2017.25.014
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    As the internet develops, more and more people are paying attention to disintermediation on the second-hand house market. This paper studies the difference between markets with automated trading platforms and those with broker information services using experimental economics. The results show that the problem of asymmetric information is worse in a market with automated trading platforms than with broker information services. Markets with broker information services are closer to the Pareto equilibrium than with automated trading platforms. Markets are less efficient with automated trading platforms than with broker information services. Thus, internet self-help trading platforms can not replace broker information services. Brokers should improve information quality to improve market efficiency.
  • ZHANG Hong, LI Linjun, LI Vera
    Journal of Tsinghua University(Science and Technology). 2017, 57(4): 421-425,431. https://doi.org/10.16511/j.cnki.qhdxxb.2017.25.015
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    Experimental economics was used to study the effect of broker price information mastering on resale housing bargaining efficiency. The formulae for broker price information mastering and resale housing bargaining efficiency were developed with experiments then run to study the relationship between the broker price information mastering and resale housing bargaining efficiency. The results show that the broker price information mastering has no significant impact on the buyer bargaining efficiency and that improving the broker price information mastering increases the seller's bargaining efficiency by 2.27%, the broker's bargaining efficiency by 0.69% and the overall bargaining efficiency by 0.73%.
  • ELECTRONIC ENGINEERING
  • ZHAO Yangyang, CHAI Jianyun, SUN Xudong, BI Daqiang
    Journal of Tsinghua University(Science and Technology). 2017, 57(4): 426-431. https://doi.org/10.16511/j.cnki.qhdxxb.2017.25.016
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    The self-startup of a vanadium battery consists of the following steps. Firstly, the electrolyte circulation system is started. After the main switch is closed to connect the cell stack with the converter, the conventional charging and discharging operations are then started. However, the voltage difference can be extremely large between the electrodes in the stack and the required input voltage in the circulation system, especially when the stack is at low capacity. This large voltage difference will lead to a large current transient between the converter and the vanadium battery. Thus, when the converter is using current limit control, the circulation system input voltage should be carefully selected to avoid self-startup failure. This paper presents a two-stage DC/DC converter with a high frequency transformer for the vanadium battery self-startup process with its control principle. A self-startup test with a 5 kW vanadium battery module showed that the converter worked during the self-startup and charge/discharge processes.
  • COMPUTER SCIENCE AND TECHNOLOGY
  • LI Yu, ZHAO Yong, GUO Xiaodong, LIU Guole
    Journal of Tsinghua University(Science and Technology). 2017, 57(4): 432-436. https://doi.org/10.16511/j.cnki.qhdxxb.2017.25.017
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    An access control points in cloud computing are difficult to link. An assurance model for access control on the whole system was developed based on formal definitions of the access request equivalence relation and the support relation, the analysis formally proves that the assurance algorithm can ensure the credibility of access requests. The implementation methods are given for the network layer, application layer and operating system kernel layer in cloud computing. An access semantic encapsulation shows that the algorithm meets the access control linkage requirements and can ensure the credibility of access requests.
  • INDUSTRIAL ENGINEERING
  • YANG Xiaofang, WANG Zhe, JIANG Hai
    Journal of Tsinghua University(Science and Technology). 2017, 57(4): 437-442. https://doi.org/10.16511/j.cnki.qhdxxb.2017.25.018
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    The online air-ticket agent can significantly improve an air-ticket search system for online travel search engines. The paper analyzes the air-ticket agent behavior based on user air-ticket searches and booking data from an online travel search engine. A multinomial logit model is used to analyze the effects of the agents' quote, grades, value-added services, positions on the page and market shares to build a log-price multinomial logit model for user online air-ticket agent choices. The results show that the price quotes are the principal user concern and that including insurance and fewer raters lead to fear selections of the agent which value-added services and higher grades attract user attention. Users are more inclined to choose the agents showed on the front of the page and then the agents listed at the bottom. Agents with large market shares significantly influence the choice. Tests show that the predictions of this model are better than those using historical data.
  • ENVIRONMENTAL SCIENCE AND ENGINEERING
  • ZHANG Hongjun, WANG Lining, CHEN Wenying
    Journal of Tsinghua University(Science and Technology). 2017, 57(4): 443-448. https://doi.org/10.16511/j.cnki.qhdxxb.2017.25.019
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    The road and rail transport sectors are important sources of CO2 emissions. A contribution-based residual distribution Laspeyres index (CRDLI) was developed to analyze the CO2 emissions from road and rail transport systems in China and six other countries. Transport turnover has an important influence on CO2 emissions, while energy intensity and energy structure are keys to mitigating CO2 emissions. GDP per capita is the main driver that increases transport turnover with reducing the turnover rate caused by GDP increases an important way to slow the increase in the transport turnover and further reduce CO2 emissions.