Chinese  |  English

Top access

  • Published in last 1 year
  • In last 2 years
  • In last 3 years
  • All

Please wait a minute...
  • Select all
    |
  • COMPUTER SCIENCE AND TECHNOLOGY
    WANG Yun, HU Min, TA Na, SUN Haitao, GUO Yifeng, ZHOU Wuai, GUO Yu, ZHANG Wanzhe, FENG Jianhua
    Journal of Tsinghua University(Science and Technology). 2024, 64(4): 649-658. https://doi.org/10.16511/j.cnki.qhdxxb.2023.26.042
    Abstract (2634) PDF (994) HTML (50)   Knowledge map   Save CSCD(9)
    [Significance] Since the turn of the 21st century, artificial intelligence (AI) has advanced considerably in many domains, including government affairs. Furthermore, the emergence of deep learning has taken the development of many AI fields, including natural language processing (NLP), to a new level. Language models (LMs) are key research directions of NLP. Referred to as statistical models, LMs were initially used to calculate the probability of a sentence; however, in recent years, there have been substantial developments in large language models (LLMs). Notably, LLM products, such as the generative pretrained transformer (GPT) series, have driven the rapid revolution of large language research. Domestic enterprises have also researched LLMs, for example, Huawei’s Pangu and Baidu's enhanced language representation with informative entities (ERNIE) bot. These models have been widely used in language translation, abstract construction, named-entity recognition, text classification, and relationship extraction, among other applications, and in government affairs, finance, biomedicine, and other domains. [Progress] In this study, we observe that improving the efficiency of governance has become one of the core tasks of the government in the era of big data. With the continuous accumulation of government data, traditional statistical models relying on expert experience and local features gradually suffer limitations during application. However, LLMs, which offer the advantages of high flexibility, strong representation ability, and effective results, can rapidly enhance the intelligence level of government services. First, we review the research progress on early LMs, such as statistical LMs and neural network LMs. Subsequently, we focus on the research progress on LLMs, namely the Transformers series, GPT series, and bidirectional encoder representations from transformers (BERT) series. Finally, we introduce the application of LLMs in government affairs, including government text classification, relationship extraction, public opinion risk identification, named-entity recognition, and government question answering. Moreover, we propose that research on LLMs for government affairs must focus on multimodality, correctly benefit from the trend of “model as a service,” focus on high data security, and clarify government responsibility boundaries. Additionally, a technical path for studying LLMs for government affairs has been proposed. [Conclusions and Prospects] The application of LLMs in government affairs mainly focuses on small-scale models, lacking examples of application in large-scale models. Compared with smaller models, large models offer many advantages, including high efficiency, broader application scenarios, and more convenience. These advantages can be understood as follows. In terms of efficiency, large models are usually trained on a large amount of heterogeneous data, thus delivering better performance. In terms of application scenarios, large models gradually support multimodal data, resulting in more diverse application scenarios. In terms of convenience, we emphasize the “pretraining + fine-tuning” mode and the invocation method of interfaces, making LLMs more convenient for research and practical applications. This study also analyzes the issues suffered by LLMs, specifically from the technological and ethical perspectives, which have resulted in a panic to a certain extent. For example, ChatGPT has generated many controversies, including whether the generated files are novel, whether using ChatGPT will lead to plagiarism and ambiguity as to who are property rights owners for the generated files. Overall, it can be said that LLMs are in the stage of vigorous development. As the country promotes research on AI and its application in government affairs, LLMs will play an increasingly crucial role in the field.
  • LOW-CARBON TRANSPORTATION & GREEN DEVELOPMENT
    WANG Yan, OU Guoli
    Journal of Tsinghua University(Science and Technology). 2023, 63(11): 1693-1706. https://doi.org/10.16511/j.cnki.qhdxxb.2023.26.033
    Abstract (2000) PDF (695) HTML (30)   Knowledge map   Save
    [Significance] The issue of climate change is extremely complex and encompasses multiple factors such as the environment, economy, society, and related aspects. With the ongoing maturation of complex system modeling technology, low-carbon transportation research using the computable general equilibrium (CGE) model presents a new approach to policy evaluation. The CGE model has three primary advantages for analyzing the economic challenges of transitioning to low-carbon transportation. First, the approach has a solid microeconomic foundation that can directly reflect the mechanism and influence of economic subjects' behavior under the assumption of a rational economic player. Second, CGE models are capable of fully simulating the connections of different economic sectors, which can uncover the transmission effect of transportation policy impact among various sectors, as well as the response of various sectors to the policy impact. Third, the model has two major types, static and dynamic CGE models, which can analyze the short- and long-term impact of different policies, respectively. As an essential prediction tool for policy impact and trend analysis, CGE models can comprehensively reveal the interaction characteristics between the transportation industry and the whole national economy, enabling the prediction of the economic and social impact of low-carbon transportation policies. [Progress] This study investigates contemporary research on transportation policies based on the CGE model. A total of 78 relevant empirical studies are collected from the Web of Science, Science Direct, and China National Knowledge Infrastructure, of which more than 50% focus on predicting the impact of low-carbon transportation policies, indicating that the investigation of traffic-related carbon emissions has gradually become a popular topic of empirical analysis using CGE models. The research topics include: (1) The influence of low-carbon transportation economic incentives, such as carbon tax, emission trading scheme, and transportation subsidies. (2) The application effect of low-carbon technologies, such as electric vehicles and carbon capture and storage. (3) The effect of low-carbon transportation urban planning, including land use, vehicle speed limits, walking-oriented urban design, and bicycle-oriented urban space development. (4) Predicting the economic and social impact of the implementation of nationally determined contributions and fuel economy standards. Previous research establishes a solid foundation for prediction and policy analysis in low-carbon transportation research; however, in the context of China's 2030 carbon peak and 2060 carbon neutrality goals, some issues remain that require further exploration and investigation. [Conclusions and Prospects] First, regarding emissions reduction policies, differing transportation needs, transportation structure, energy structure, technical level, and macropolicies will affect transportation carbon emissions. The carbon emissions reduction potential of various policies requires further study, and it is essential to propose structured solutions referencing the prediction and design of composite system transportation emissions reduction policies. Based on China's 1+N policy system for advancing the dual carbon goals, this study constructs a low-carbon transportation policy matrix based on the “avoid/shift/improve-planning/regulatory/economic/information/technological (ASI-PREIT)” structure, producing a proposed “policy basket” for low-carbon transportation CGE modeling. This policy matrix will comprehensively reveal the correlation between policy tools for low-carbon transportation CGE modeling and help put forward structured low-carbon solutions. Second, in terms of model construction, accessibility is the most intuitive factor for transportation. As with other sectors, treating the transportation sector simply as a product production sector risks neglecting network and external benefits; therefore, this study proposes the inclusion of transportation accessibility factors in low-carbon transportation CGE models as spatial computable general equilibrium model to identify regional economic correlations and regional product flow. Third, in terms of synergies, carbon emissions reduction in transportation is crucial to achieving China's dual carbon goals and can advance innovation and economic growth, leveraging a wide range of synergies, including sustainable development, improving public health, and enhancing the overall quality of life. Currently, increasingly severe ecological and environmental challenges are forcing global economies to reassess the GDP-centered development model, seeking balanced and sustainable development strategies that include environment, economy, and society. This study proposes the development of a comprehensive low-carbon transportation CGE model to compare and analyze the optimal solutions for balancing the co-benefits of environment-economy-society from a global perspective and design low-carbon transportation policy combinations to advance sustainable development. In summary, this study endeavors to systematically review the empirical research applying CGE models in the field of low-carbon transportation, provide a reference for expanding the research on low-carbon transportation, and help policymakers and the transportation sector achieve China's dual carbon goals.
  • AEROSPACE ENGINEERING
    LIN Weiquan, XU Hangrui, LAN Xudong
    Journal of Tsinghua University(Science and Technology). 2024, 64(9): 1521-1535. https://doi.org/10.16511/j.cnki.qhdxxb.2024.27.024
    Abstract (1977) PDF (1684) HTML (36)   Knowledge map   Save CSCD(2)
    [Significance] With the rapid advancements in aerospace engineering technology, the performance requirements for aircraft are increasingly escalating. At present, there are numerous goals for aircraft utilization in military, transportation, and other sectors. Hypersonic aircraft, which operate under multiple operating conditions and across a wide velocity range, have become a hot research topic in many countries. A critical component of such high-performance aircraft is their power system. A high-performance aircraft must have a high-performance power system to match it. Existing mature power systems have limitations in terms of working conditions and performance. Therefore, the development trend has shifted toward combined power systems. Currently, prominent combined engines include rocket-based combined cycle (RBCC), turbine-based combined cycle (TBCC), air turborocket, and precooled engines. When considering factors like cost, performance, and safety, TBCC engines emerge as the most promising power system for hypersonic aircraft within the near space range of 20-100 km because of their flight envelope width, reusable, large unit thrust, and other advantages. Therefore, summarizing the key TBCC technologies and exploring their development path is crucial. [Progress] The United States, Japan, and the United Kingdom are pioneers in combined power research. These countries have achieved significant technical achievements, possess mature technologies, and have completed the entire research and development cycle for combined engine products. They are at the forefront of this field. In the future research and development strategy, the United States focuses on system-wide research of TBCC and RBCC technologies. Following the completion of the HYPR90 program, Japan has conducted an in-depth study into the precooled engine ATREX. Meanwhile, the UK continues its extensive research on SABRE, aiming to deploy it in future single-stage spacecraft. Other countries, such as Germany, Russia, and China, are also engaged in large-scale TBCC research, accumulating a large number of technologies to achieve breakthroughs from theory to engineering application in the future. In terms of TBCC key technologies, this paper analyzes and summarizes advancements in propulsion system technology and subsystem technology. For subsystems, current TBCC inlet forms are reviewed, with advanced mixed rectangular divergent and integrated multidimensional cross-sectional configurations being analyzed. The future direction points toward the development of 3D internal contraction inlets. The advantages and disadvantages of series and parallel exhaust systems are analyzed alongside the basic theory of the exhaust process, emphasizing the need for more theoretical support for exhaust systems. Numerous achievements in modal conversion control technology are listed, highlighting that future research should focus on integrating strongly coupled flight control with modal control technology. Regarding propulsion system technology, a comprehensive theoretical model for aircraft-engine integration is presented, pointing out the defects of the traditional separate design approach for aircraft and engines. This paper reviews the development of performance simulation and testing technologies domestically and internationally, suggesting that future assignments should involve developing sophisticated simulation software and building new test benches. [Conclusions and Prospects] The combined engine essentially integrates four types of engines: turbine, rocket, ramjet and precooled. This paper summarizes the key technologies of TBCC and explores their development routes while also providing three prospects for the future form of combined engines: combining new basic power forms, adopting new energy sources, and incorporating the external drive platforms.
  • BIG DATA
    ZHAO Xingwang, HOU Zhedong, YAO Kaixuan, LIANG Jiye
    Journal of Tsinghua University(Science and Technology). 2024, 64(1): 1-12. https://doi.org/10.16511/j.cnki.qhdxxb.2024.21.001
    Abstract (1962) PDF (705) HTML (36)   Knowledge map   Save
    [Objective] Multiview graph clustering aims to investigate the inherent cluster structures in multiview graph data and has received quite extensive research attention over recent years. However, there are differences in the final quality of different views, but existing methods treat all views equally during the fusion process without assigning the corresponding weights based on the received quality of the view. This may result in the loss of complementary information from multiple views and go on to ultimately affect the clustering quality. Additionally, the topological structure and attribute information of nodes in multiview graph data differ significantly in terms of content and form, making it somewhat challenging to integrate these two types of information effectively. To solve these problems, this paper proposes two-stage fusion multiview graph clustering based on an attention mechanism.[Methods] The algorithm can be divided into three stages:feature filtering based on graph filtering, feature fusion based on the attention mechanism, and topological fusion based on the attention mechanism. In the first stage, graph filters are applied to combine the attribute information with the topological structure of each view. In this process, a smoother embedding representation is achieved by filtering out high-frequency noise. In the second stage, the smooth representations of individual views are fused using attention mechanisms to obtain the consensus smooth representation, which incorporates information from all views. Additionally, a consensus Laplacian matrix is obtained by combining multiple views' Laplacian matrices using learnable weights. To obtain the final embedded representation, the consensus Laplacian matrix and consensus smooth representation are inputted into an encoder. Subsequently, the similarity matrix for the final embedded representation is computed. Training samples are selected from the similarity matrix, and the embedded representation and learnable weights of the Laplacian matrix are optimized iteratively to obtain a somewhat more compressed embedded representation. Finally, performing spectral clustering on the embedding representation yields the clustering results. The performance of the algorithm is evaluated using widely-used clustering evaluation metrics, including accuracy, normalized mutual information, an adjusted Rand index, and an F1-score, on three datasets:Association for Computing Machinery (ACM), Digital Bibliography & Library Project (DBLP), and Internet Movie Database (IMDB).[Results] 1) The experimental results show that the proposed algorithm is more effective in handling multiview graph data, particularly for the ACM and DBLP datasets, compared to extant methods. However, it may not perform as well as LMEGC and MCGC on the IMDB dataset. 2) Through the exploration of view quality using the proposed methods, the algorithm can learn weights specific to each view based on quality. 3) Compared to the best-performing single view on each dataset (ACM, DBLP, and IMDB), the proposed algorithm achieves an average performance improvement of 2.4%, 2.9%, and 2.1%, respectively, after fusing all views. 4) Exploring the effect of the number of graph filter layers and the ratio of positive to negative node pairs on the performance of the algorithm, it was found that the best performance was achieved with somewhat small graph filter layers. The optimal ratio for positive and negative node pairs was around 0.01 and 0.5.[Conclusions] The algorithm combines attribute information with topological information through graph filtering to obtain smoother representations that are more suitable for clustering. The attention mechanisms can learn weights from both the topological and attribute information perspectives based on view quality. In this way, the representation could get the information from each view while avoiding the influence of poor-quality views. The proposed method in this paper achieves the expected results, greatly enhancing the clustering performance of the algorithm.
  • CONSTRUCTION MANAGEMENT
    LI Enyuan, LIU Hongyu, ZHU Enwei
    Journal of Tsinghua University(Science and Technology). 2024, 64(2): 173-180. https://doi.org/10.16511/j.cnki.qhdxxb.2023.22.045
    Abstract (1740) PDF (600) HTML (33)   Knowledge map   Save
    [Objective] The land market plays a key role in achieving a stable and healthy market for real estate development and has a significant impact on macroeconomic conditions, government finances, and overall financial stability. However, many participants in the Chinese land market engage in blind expansion and irrational land acquisition, which interferes with achieving policy objectives such as price stability for land and housing, as well as the healthy development of the land market. This study analyzes market feedback of land auction participants and the factors influencing them. We use auction theory to examine the existence of the winner's curse phenomenon in the Beijing land market and provide policy recommendations for the government to regulate the land market. [Methods] This study is based on micro-level auction data from land sales in Beijing between 2013 and 2018 and from the Wind enterprise database. We first construct models to calculate cumulative abnormal returns for the auction participants' stock prices in the periods following land auctions. We then use an event study to explore the effects of participant, land, and auction characteristics on stock price changes. Particular attention is given to market feedback on the auction winners. The uniqueness of this study lies in the vast amount of data used. We consider factors that are crucial elements of market feedback but have been relatively unexplored in previous studies, such as participants' bidding premiums, past experiences in land auctions, and joint bidding. [Results] We find that:(1) The higher the final bidding premium of land auction participants, the more negative the market's reaction. Previous experience with repeated bidding and joint bidding enables participants to access more market information, helping mitigate irrational bidding. Variables such as land value, bidding intensity, and the frequency of winning bids on a single day that reflect a bidder's economic strength lead to more positive market evaluations. (2) Evidence of the winner's curse phenomenon is observed in the Beijing land market. Although cumulative abnormal returns do not show significant inter-group differences between winners and losers, results of controlling for the final bidding premium reveal that higher bidding premiums result in more negative market evaluations for the winners. Joint bidding helps winners to make rational bids, but the effect of repeated participation in the short term is not significant. (3) The market holds a significantly negative view of bidders who are active over an extended period, and this effect is more pronounced for the winners, providing additional evidence for the existence of the winner's curse phenomenon. [Conclusions] Based on these findings, we recommend the government to enact policies to encourage market participants to make rational bids. This could be achieved by promoting complementary advantages and sharing market information through joint bidding to some extent. The government should also enhance information disclosure through various means to alleviate information asymmetry in the market and strengthen supervision of active market participants' funds and the development and construction processes to reduce irrational bidding behavior.
  • LOW-CARBON TRANSPORTATION & GREEN DEVELOPMENT
    SONG Yuanyuan, YAO Enjian, XU Honglei, HUANG Quansheng, WU Rui, WANG Renjie
    Journal of Tsinghua University(Science and Technology). 2023, 63(11): 1707-1718. https://doi.org/10.16511/j.cnki.qhdxxb.2023.26.021
    Abstract (1689) PDF (572) HTML (33)   Knowledge map   Save CSCD(4)
    [Significance] Climate change is the primary challenge that intensely affects sustainable human development. The transport sector has been one of the major sources of carbon emissions and is considerably affected by climate change. Because of the growth of China's economy and total transport demand, transport-related carbon emissions are also gradually increasing. Moreover, frequent complex and extreme climate events with clear regional differences have negatively affected the construction, maintenance, and operation of the transport infrastructure. Therefore, China's transport sector needs to reduce carbon emissions for green and low-carbon developments and improve its adaptability and resistance to various adverse climatic conditions. However, China's transport sector still faces many challenges in mitigating and adapting to climate change, and its policy tools, measures, and basic capacity to cope with climate change need to be enhanced. Therefore, transport sector-related strategies and routes to adapt to climate change need to be explored. [Progress] First, the policies and measures implemented in different countries to address climate change were introduced from the perspectives of mitigation and adaptation. Second, the advancements made by China's transport sector in mitigating climate change were summarized from the perspectives of the construction of green and low-carbon transport infrastructure, optimization of the transport structures, and promotions and applications of new and clean energy. The measures implemented to adapt to climate change in China's transport sector were summarized from the perspectives of improving the adaptability of the transport infrastructure, strengthening the monitoring and warning systems of climate change, and managing risk. Third, the interactions between each subfield and sublink of the transport system and climate change, as well as the main measures implemented to mitigate and adapt to climate change in the transport sector, were analyzed. Finally, key areas, strategies, and methods to mitigate and adapt to climate change were proposed. [Conclusions and Prospects] Analysis results are provided and discussed. First, the current plan for China's transport response to climate change needs improvement. The capacity to respond to climate change has not been planned at the subfield and sublink level of the transport system. For mitigating climate change, carbon emissions reduction measures, such as the promotion of new energy vehicles and ships, as well as the optimization of the transport structure, are inadequate. Furthermore, the assessment of the effects of the transport infrastructure on climate change is still in its infancy. Second, the direction of the transport system's development should be combined with the strategic requirements of mitigation and adaptation to climate change. Third, in the transport field, the infrastructure, equipment, and transport structure should be improved; moreover, the infrastructure should be adapted to climate change, and emergency support of transport equipment and transportation organization in extreme weather should be optimized to enhance the capability to adapt to climate change. Finally, the following measures are proposed: Mitigation and adaptation to climate change should be jointly and appropriately implemented to comprehensively address climate change in the transport sector. Greenhouse gases and air pollutants should be jointly controlled to realize the goal of “double carbon”. Adaptation to climate change should be applied in conjunction with ecological protection and restoration to strengthen the capacity of the transport sector to adapt to climate change.
  • LOW-CARBON TRANSPORTATION & GREEN DEVELOPMENT
    HUANG Ailing, WANG Zijian, ZHANG Zhe, LI Mingjie, SONG Yue
    Journal of Tsinghua University(Science and Technology). 2023, 63(11): 1729-1740. https://doi.org/10.16511/j.cnki.qhdxxb.2023.26.034
    Abstract (1622) PDF (519) HTML (26)   Knowledge map   Save
    [Objective] In the airport ground-transport system, it is operationally important to match the evacuation requirement of passengers, and the capacity of multimodal transport vehicles is crucial. Numerous studies have investigated single-mode transport capacity allocation; however, research on multimode allocation is scarce. [Methods] To mitigate the difficulty in realizing an exact match between the evacuation demand of passengers and the capacity of multimodal transport, a bi-level programming model for multimodal transport resource allocation is proposed according to the analysis of the interaction between capacity allocation and passenger travel choice. A utility function of multiple travel modes, including airport buses, metro, taxis, and private cars, is formulated with the following four features: travel time, travel cost, punctuality, and comfort. The upper-level objective is to minimize the total enterprise-operation cost, passenger-waiting cost, and carbon emission cost for optimizing the headway of public transit and the taxi arrival rate, which is subject to the capacity of each transit mode, the range of each public-transit headway decided by fixed equipment, and the range of taxi arrival rate decided by the capacity of boarding location. Based on the output of the transport capacity allocation scheme used by the upper level, the low-level objective is to assign the passenger flow toward multiple travel modes according to a stochastic user equilibrium-logit model with a utility function. Furthermore, an improved genetic algorithm combined with method of successive algorithm (MSA) is designed to solve the proposed bi-level programming model. To improve the solving efficiency of the algorithm, a pre-search mechanism is proposed, in which the infeasible solution is filtered out using low-precision MSA to reduce the computational cost of repeatedly calling the low-level model. [Results] The Beijing Daxing International Airport was considered as a case study to illustrate the efficiency and effectiveness of the proposed bi-level programming model in optimizing transport capacity allocation in airport ground-transport centers. The transport capacity allocation scheme obtained via the proposed model reduced the average passenger-waiting time and the total carbon emission of the system by 14.08% and 6.21%, respectively, while increasing the operation cost by only 1.32%. Moreover, the optimized capacity allocation scheme resulted in the switching of 6.7% of passengers who availed taxis and private cars to buses and metro, which were more environmentally friendly. The proposed solution algorithm could efficiently solve the bi-level model. Under the pre-search mechanism, the generation time of the scheme was 217.6 s, which could meet the production demand within the acceptable time. [Conclusions] Results show that the optimized scheme obtained from the bi-level model and algorithms is considerably better than before. The proposed scheme reduces passenger-waiting time and the carbon emissions of the multimodal transport system at a negligible cost. Using the optimized scheme, the organizers of airport ground-transport centers can coordinate the capacities of landside multiple transport modes and guide passengers reasonably. This will reduce operation costs, improve airport landside traffic structure, and encourage green and low-carbon travel.
  • AEROSPACE ENGINEERING
    CHEN Zhongcan, ZHANG Kai, LI Feng, ZHAO Yue, WU Jianhui, HE Qilian, CHEN Min
    Journal of Tsinghua University(Science and Technology). 2024, 64(2): 318-336. https://doi.org/10.16511/j.cnki.qhdxxb.2023.26.047
    Abstract (1502) PDF (466) HTML (39)   Knowledge map   Save CSCD(4)
    [Significance] Aerospace vehicles have undergone significant modifications in terms of aerodynamic shape, flight speed, flight environment, and flight duration compared with conventional flight vehicles. They must withstand harsh aerodynamic thermal environments for long durations and maintain a sharp leading-edge shape with a high lift-to-drag ratio, imposing extremely stringent requirements on the temperature resistance, durability, structural efficiency, and reliability of the thermal protection system. Traditional thermal protection depends largely on passive methods such as heat insulation, heat sink, and radiation heat dissipation. Although the thermal protection performance of related technologies has improved, which is restricted by several constraints, such as ensuring that the prototype is safe under harsh conditions of extremely high heat flux and ultrahigh temperature along with structural stability, long-term operation, light-weight nature, and repeatability. Thus, a new active thermal protection technology is necessary. In this context, transpiration cooling technology offers the advantage of high thermal efficiency without requiring any changes in the prototype of a vehicle. It has been widely considered a potential active thermal protection technology. However, when transpiration cooling is used for thermal protection of a flight vehicle, some challenges related to the complexity of the system, a mismatch between coolant supply and demand, unstable control of the operation, and development of a high-precision prediction model etc., arise. [Progress] Research on transpiration cooling primarily focused on quick evaluation of performance, numerical simulation of flow and heat transfer, evaluation of cooling mechanism performance, development of optimal control algorithm for efficiency, and optimization of structure form and yielded beneficial results. However, several fundamental scientific issues needed to be urgently addressed to fully realize the engineering application of this technology in aerospace vehicles. In the context of numerical simulation, the accuracy and adaptability of the heat and mass transfer model should be improved. Most existing studies had mathematically described and solved the physical process of heat and mass transfer in porous media at the macroscale. But some parameters related to specific phase change heat and mass transfer (such as evaporation/condensation coefficient and fluid-solid convection heat transfer coefficient) that affect the model's accuracy must be modified through experiments, and the adaptation was partially successful. Most existing models assumed that the temperature of porous media, liquid phases, and gas phases were equal. Although a few models explored the nonequilibrium effect between porous media and fluids, they did not consider the nonequilibrium effect between gas and liquid phases. There were few flight experiments in the research and a large gap between the ground experimental test and practical use conditions. Furthermore, extreme effects related to high-temperature, real, and rarefied gases and shock wave/boundary layer interference during high-speed flight could not be effectively reproduced on the ground. Moreover, there was a lack of experimental data that could be used to verify the accuracy of the heat and mass transfer model. The experimental test method was relatively simple, and the flow and heat transfer process of the liquid in the porous medium could not be obtained. It was challenging to effectively obtain the boundary layer flow law of the liquid when it entered the high-speed mainstream flow from the porous medium. In terms of control strategy, the present research on transpiration cooling control systems lacked a transient simplified mathematical model that could be quickly established, particularly for liquid phase change transpiration cooling with the multiphase flow and phase change process. Simultaneously, there were few transpiration cooling control systems with practical engineering values based on modern control theory, which made it difficult to achieve optimal performance in practical engineering applications. Some adaptive and self-driven transpiration cooling systems had been proposed as new forms of transpiration cooling structures; however, they were still at the mechanism verification stage, and the engineering application effect needed to be verified. [Conclusions and Prospects] Follow-up research will focus on the micro/mesoscale fine numerical calculation model, advanced visual experimental testing methods, rapid response-precise control strategies, self-driven and adaptive structural engineering systems, and combined active and passive thermal protection.
  • LOW-CARBON TRANSPORTATION & GREEN DEVELOPMENT
    WANG Yue, YAO Enjian, HAO He
    Journal of Tsinghua University(Science and Technology). 2023, 63(11): 1741-1749. https://doi.org/10.16511/j.cnki.qhdxxb.2023.26.024
    Abstract (1417) PDF (484) HTML (25)   Knowledge map   Save CSCD(3)
    [Objective] Optimising travel structure, improving travel efficiency, and reducing transport carbon emissions are essential paths to green and low-carbon transport development. Research into fine-grained carbon management has received much attention in recent years. However, the implementation is complex, and setting a price on carbon estimation tends to elicit negative feelings from travellers. [Methods] In the concept of mobility as a service (MaaS), the service can provide an end-to-end travel service by the combination of multi-transport modes, including roads and public transport, as well as many new forms of transportation. Thus, the service provider can realise flexible price adjustments for multi-transport modes and sections in a single trip. Consequently, this paper proposes a low-carbon-oriented pricing strategy for the service provider. From the different perspectives of the MaaS servicer, travellers and the environment, we propose a multi-objective optimisation model. The object includes maximising service providers' revenue and minimising network travel time and transportation network carbon emissions. The model is a two-layer planning model. The upper layer of the model is the process of finding decision variables to calculate the objective function. The lower layer is the joint traffic mode and route choice process, as well as traffic equilibrium allocation in a multi-modal transportation network. In this model, the joint choice of mode and route of travellers depends on the upper-layer decision variables. Then, to solve the above optimisation problem, the reference point based non-dominated sorting genetic algorithm (NSGA-Ⅲ) and the method of successive algorithm (MSA) are introduced. [Results] The case study was conducted on an example network with 1 origin-destination pair, 16 sections in 3 traffic modes (travel by car, bus, and metro), and 6 nodes. Three representative strategies of Pareto solutions were selected, including optimise service provider benefits (OP-S), optimise network travel time (OP-T), and optimise transportation carbon emissions (OP-C). Furthermore, the original (OR) state was also presented as the background. The result showed that the travel price significantly increased in OP-S, which was unfriendly to travellers. In contrast, OP-T and OP-C were respectively metro-friendly and public transport-friendly strategies. Compared with the OR state, service benefits and carbon emissions were optimised, which means that the service provider could achieve emission reductions in multi-modal transport networks while ensuring their own profitability through rationalised regulation of service pricing. The traffic volume analysis also proved that the service provider could optimise the network travel mode structure, thereby reducing road congestion and increasing the share of public transport. By comparing the results of the optimisation strategies under different demands, we found that with the travel demand increased, the service provider benefits continued to grow (especially in OP-S). Although traffic carbon emissions increased, the optimisations could always reduce the traffic carbon emissions of the system. [Conclusions] This paper validates the feasibility of travel service pricing strategies in multi-modal network traffic optimisation and low-carbon transport development. Service providers should not only seek to maximise their own revenue but also take into account the cost of travel and its impact on the transport environment and take responsibility for the coordination and reduction of transport system emissions. This paper identifies the profitability and responsibilities of travel service providers in the green and low-carbon development of transport and provides a basis for service pricing strategies.
  • MECHANICAL ENGINEERING
    YAO Ming, DUAN Jinhao, SHAO Zhufeng, YUAN Shaolun, SU Yunzhou
    Journal of Tsinghua University(Science and Technology). 2024, 64(1): 117-129. https://doi.org/10.16511/j.cnki.qhdxxb.2023.21.022
    Abstract (1398) PDF (548) HTML (23)   Knowledge map   Save CSCD(1)
    [Objective] automated guided vehicle (AGV) forklift is an important material transportation equipment in the industrial field. Its positioning and path-tracking accuracy is an important basis for improving material transportation efficiency, factory automation, and intelligence. Thus, this paper uses a single steering wheel AGV forklift in an indoor structured environment of the pharmaceutical industry as an object, realizing the lidar positioning based on the reflector using the density-based spatial clustering of applications with noise (DBSCAN) and the fast iterative closest point (FICP) algorithms, and designing a proportional-integral (PI) controller to address the path-tracking problem of the AGV forklift.[Methods] First, the kinematics characteristics of the single steering wheel AGV forklift are analyzed, and its kinematics equations and state space equations are established. Subsequently, the DBSCAN and FICP algorithms were used to implement a reflector-based lidar positioning method for an accurate positioning problem. Moreover, a distance-based outlier elimination rule is proposed to address the problem of outliers interfering with the positioning process, which ensures the stability of the positioning results and the robustness of the algorithm. The Kalman filter algorithm is used to fuse the measurement data of the inertial measurement unit (IMU) and the angle sensor to improve the accuracy of the lidar positioning algorithm of the AGV forklift. This study establishes the position error and attitude error in the two core paths of straight lines and arcs based on the geometric relationship for the path-tracking problem. Following that, a PI controller is designed to realize the path tracking of the AGV forklift. Considering curvature discontinuity when the arc of equal curvature is connected with the straight-line path, the arc path based on the third-order Bézier curve was designed in this study. Furthermore, according to the limitation of the AGV forklift in the arc movement process, the parameters of the Bézier curve are analyzed and optimized to avoid the decrease of the path-tracking accuracy caused by the abrupt change of the path curvature.[Results] The experimental verification showed that the lidar positioning algorithm based on DBSCAN and FICP algorithms could achieve ±3 mm positioning accuracy. Stable AGV forklift positioning could be achieved when combined with the outlier elimination rules. Furthermore, the Kalman filter-based fusion of IMU and angle sensor data resulted in accurate AGV forklift positioning. The improved arc path based on the Bézier curve reduced the arc path tracking error by about 72% compared with the equal-curvature arc path. The AGV's position and attitude errors were controlled based on the PI controller, which could control the dynamic tracking accuracy to within 25 mm. Furthermore, the repeated positioning accuracy of the work site reached ±12 mm, meeting the expected design requirements.[Conclusions] This paper studies the lidar positioning and path-tracking technology of a single steering wheel AGV forklift in an indoor structured environment. An accurate and stable lidar positioning algorithm based on DBSCAN and FICP algorithms is realized by introducing outlier elimination rules and the Kalman filter. The AGV forklift's path tracking is realized using the PI controller, and the tracking accuracy of the arc path is improved using the Bézier curve. Finally, the positioning accuracy, path-tracking accuracy, and repeated positioning accuracy of the work site all met the expected design requirements.
  • HYDRAULIC ENGINEERING
    GUO Shiyuan, MA Weizhi, LU Ruilin, LIU Jinlong, YANG Zhigang, WANG Zhongjing, ZHANG Min
    Journal of Tsinghua University(Science and Technology). 2023, 63(12): 1924-1934. https://doi.org/10.16511/j.cnki.qhdxxb.2023.21.005
    Abstract (1390) PDF (444) HTML (36)   Knowledge map   Save CSCD(1)
    [Objective] Water discharge prediction in canals under complex conditions is a fundamental problem with prominent practical significance in improving farmland irrigation water efficiency, conserving water resources, and reducing involved costs. The state-of-art solution of prediction is establishing nonlinear partial differential equations with numerical calculation methods, with time cost being exponential to the fineness of the spatiotemporal division. Moreover, the current time step calculation depends on the result of the last time step, i.e., the calculation cannot be parallelized, which results in a tradeoff between accuracy and efficiency. In actual irrigation areas, the control of gate openings in canals primarily relies on human experience, which has an extremely long feedback process. Therefore, it is challenging to employ human experience and numerical calculation methods when multiple gate changes are required. The rapid development of artificial intelligence-related technologies has yielded more opportunities for modernizing conventional industries. In this study, the input and output were definite for the water discharge prediction task, which corresponds to the "regression" problem-one of the two types of fundamental problems that neural networks are good at solving. This study presents new insights to leverage the neural network to solve the water discharge prediction problem end-to-end. The neural network only needs to be trained once, and further, multiple results can be obtained with high efficiency during testing. Therefore, the proposed approach overcomes the shortcomings of the conventional methods, which involve extremely high time costs.[Methods] Based on the Internet-of-Water theory of "real-time perception, water-information interconnection, process tracking, and intelligent processing", this study introduced a novel approach for water discharge prediction. First, we investigated the sequence features of the upstream and downstream canal water discharge gate control and introduced the static features of the gates and canal. Second, we proposed a novel predicting method for canal discharge based on a long short-term memory (LSTM) neural network, in which the gating mechanism allows better modeling and prediction of problems with sequential information. Feature discretization and normalization were applied to the static features to improve the generalization ability of the model to predict unseen data. Layer normalization was performed on the output of the LSTM network to adjust the distribution of the output to the unsaturated region of the activation function, making the neural network more sensitive to the input and output, as well as accelerating its convergence.[Results] The following comparative experimental results were obtained:1) The proposed model can complete the prediction task with an accuracy rate exceeding 97% in every canal segment, which is significantly better than all baselines, indicating the effectiveness of using the hidden sequence features inside the canal and the gating mechanism of the LSTM neural network. 2) Under normal circumstances, introducing static features as part of the model's input improves the prediction performance. 3) The proposed model demonstrates good robustness. It successfully learns and shows good prediction performance without too much data fed into it. Hence, it is extremely useful in situations of data shortage and when requiring model migration to other canals. 4) Compared to the conventional numerical calculation method, the proposed model demonstrates 308 times higher prediction efficiency, reducing the prediction time from 950 h to about 3 h on 100,000 pieces of data.[Conclusions] This study verifies the feasibility of artificial intelligence-based methods in improving the conventional canal discharge prediction problem, achieves a win-win situation between accuracy and efficiency through a reasonably designed deep learning model, and provides a new idea for applying artificial intelligence-based methods in solving hydraulic problems.
  • Special Section: Construction Management
    Hong ZHANG, Zhijun BI
    Journal of Tsinghua University(Science and Technology). 2025, 65(1): 1-11. https://doi.org/10.16511/j.cnki.qhdxxb.2024.22.038
    Abstract (1388) PDF (958) HTML (627)   Knowledge map   Save

    Objective: The β coefficient is a critical indicator for stock sector investment, and its stability is essential for making informed future investment decisions based on historical data. The real estate sector, known for its high investment risks and stock fluctuations, plays a crucial role in many investors' portfolios. Although there is a growing body of literature on the β coefficient of the real estate sector, research on its systematic calculation and stability remains limited. This paper analyzes the changes and stability of the β coefficient in the real estate sector, providing valuable insights for investors. Methods: Through method screening, this paper uses the single index equation to calculate the monthly and annual β coefficients of the Chinese A-share real estate sector from 2013 to 2022. After confirming data stationarity, daily data are processed through least squares regression analysis to obtain accurate and reliable monthly and annual β coefficients. The stability of the β coefficient is assessed using the Chow test for adjacent calendar months and years, and statistical analysis is conducted on the results. Ultimately, the study includes a comparative analysis between the real estate, financial, and construction sectors to provide a comprehensive understanding of the β coefficient characteristics. Results: The research results reveal the followings: (1) The monthly and annual mean β coefficients of the real estate sector are close to but less than 1. Monthly β coefficients show significant variability, while the annual β coefficient initially increases and then decreases. (2) The monthly β coefficient demonstrates stronger stability compared to the annual β coefficient. (3) The trajectories of the β coefficient in both the real estate and construction sectors are highly similar, with the stability of the β coefficient in the real estate sector being lower than that of the construction sector but higher than that of the financial sector. Conclusions: There are clear differences in the stability characteristics of the monthly and annual β coefficients in the real estate sector, and these differences vary across different sectors. This paper suggests that the followings: (1) Short-term investors should monitor changes in monthly β coefficients to predict market volatility. (2) For long-term investment decisions based on the real estate sector's β coefficients, timely adjustments should be made according to macroeconomic factors and other variables. (3) When investing across different stock sectors, investors should focus on the volatility relationship among the construction, financial, and the real estate sectors, and adopt appropriate risk hedging strategies to reasonably diversify investment risks.

  • Special Section: Construction Management
    Xinxiang JIN, Xiao LIN, Xinru YU, Hongling GUO
    Journal of Tsinghua University(Science and Technology). 2025, 65(1): 35-44. https://doi.org/10.16511/j.cnki.qhdxxb.2025.22.006
    Abstract (1369) PDF (338) HTML (793)   Knowledge map   Save CSCD(1)

    Objective: Progress management is an important part of construction management, which helps effectively reduce the risk of project delay. Its main objective is to monitor the actual construction progress and compare it with the construction plan. The traditional method of progress updating relies on manual checking and recording, which not only lags behind but also is prone to recording errors. Following the development of building information modeling (BIM), technologies such as the internet of things (IoT), point clouds, and visual images have been gradually applied to construction progress identification and plan comparison. However, these methods require the introduction of additional acquisition equipment, and point cloud acquisition equipment is costly. In addition, image processing is easily affected by factors such as occlusion, light, and weather. Therefore, the present study proposes a construction progress updating method based on BIM and large language models (LLMs). This approach enables construction personnel to verbally report progress information to the LLM, allowing a three-dimensional (3-D) building model to be accordingly updated. Methods: This research develops a system that automatically extracts relevant information from natural language, which identifies the corresponding component using the planned construction time in the component database and visualizes the progress status of the 3-D building model in Blender. The system does not require detailed information such as precise component IDs but completes the progress update by recognizing fuzzy information (e.g., construction section, floor, and other relevant information). Specifically, this study first parses the industry foundation classes (IFC) format BIM file and construction schedule to extract and correlate the component IDs, location information, and scheduled construction time. It then constructs a database of building components. Subsequently, the LLM is enhanced through prompt engineering so that it can generate accurate information query instructions based on natural language inputs, retrieve component information from the database, assess the progress status, and generate corresponding model update instructions to achieve dynamic updates in Blender. Results: This study tested the accuracy and consistency of the proposed method using a BIM model with 716 components and a dataset of 200 progress reports in various natural language formats. The testing results showed that after prompt fine-tuning, the LLM-based method achieved an average accuracy of 96% in progress assessment and model updating and 62.5% improvement over the non-fine-tuned model. The consistency reached 87% or an increase of 68% over the non-fine-tuned model, demonstrating the effectiveness and feasibility of this method for construction progress updating. Conclusions: This study has successfully combined BIM and LLMs to develop a construction progress updating method, including the construction of component retrieval database and schedule updating process based on LLMs. The case studies show that the method effectively improves the accuracy and consistency of the LLM in generating progress update instructions without providing additional equipment and significant computing costs. The method allows construction personnel to describe progress information in natural language and achieves accurate progress updating of the 3-D model of a building, which meets the demand for visualizing and updating progress information on construction sites. However, this study suffers from certain limitations. Due to the use of prompt fine-tuning for the LLM, consistency remains a challenge. Future work is expected to improve the model's accuracy and consistency by training a local model.

  • SPECIAL SECTION: BIG DATA
    WU Houyue, LI Xianwei, ZHANG Shunxiang, ZHU Honghao, WANG Ting
    Journal of Tsinghua University(Science and Technology). 2024, 64(12): 1997-2006. https://doi.org/10.16511/j.cnki.qhdxxb.2024.21.027
    Abstract (1356) PDF (481) HTML (28)   Knowledge map   Save
    [Objective] The generation of adversarial samples in text represents a significant area of research in natural language processing. The process is employed to test the robustness of machine learning models and has gained widespread attention from scholars. Owing to the complex nature of Chinese semantics, generating Chinese adversarial samples remains a major challenge. Traditional methods for generating Chinese adversarial samples mainly involve word replacement, deletion/insertion, and word order adjustment. These methods often produce samples that are easily detectable and have low attack success rates, and thus, the methods struggle to balance attack effectiveness and semantic coherence. To address these limitations, this study introduces DiffuAdv, a novel method for generating Chinese adversarial samples. This approach enhances the generation process by simulating the data distribution during the adversarial attack phase. The gradient changes between adversarial and original samples are used as guiding conditions during the model's reverse diffusion phase in pre-training, resulting in the generation of more natural and effective adversarial samples. [Methods] DiffuAdv entails the introduction of diffusion models into the generation of adversarial samples to improve attack success rates while ensuring the naturalness of the generated text. This method utilizes a gradient-guided diffusion process, leveraging gradient information between original and adversarial samples as guiding conditions. It consists of two stages: forward diffusion and reverse diffusion. In the forward diffusion stage, noise is progressively added to the original data until a noise-dominated state is achieved. The reverse diffusion stage involves the reconstruction of samples, in which the gradient changes between adversarial and original samples are leveraged to maximize the adversarial objective. During the pre-training phase, data capture and feature learning occur under gradient guidance, with the aim of learning the data distribution of original samples and analyzing the deviations from adversarial samples. In the reverse diffusion generation phase, adversarial perturbations are constructed using gradients and integrated into the reverse diffusion process, ensuring that at each step of reverse diffusion, samples evolve toward greater adversarial effectiveness. To validate the effectiveness of the proposed method, extensive experiments are conducted across multiple datasets and various natural language processing tasks, and the performance of the method is compared with those of seven existing state-of-the-art methods. [Results] Compared with existing methods for generating Chinese adversarial samples, DiffuAdv demonstrates higher attack success rates across three tasks: text sentiment classification, causal relation extraction, and sentiment cause extraction. Ablation experiments confirm the effectiveness of using gradient changes between original and adversarial samples to guide the generation of adversarial samples and improve their quality. Perplexity (PPL) measurements indicate that the adversarial samples generated by DiffuAdv have an average PPL value of only 0.518, demonstrating that these samples are superior in rationality and readability compared with the samples generated by other methods. [Conclusions] DiffuAdv effectively generates high-quality adversarial samples that closely resemble real text in terms of fluency and naturalness. The adversarial samples produced by this method not only achieve high attack success rates but also exhibit strong robustness. The introduction of DiffuAdv enhances the research perspective on generating adversarial text samples and broadens the approaches for tasks such as text sentiment classification, causal relationship extraction, and emotion-cause pair extraction.
  • SPECIAL SECTION: ROBOTICS
    JIANG Xiao, WANG Song, WU Dan
    Journal of Tsinghua University(Science and Technology). 2024, 64(10): 1677-1685. https://doi.org/10.16511/j.cnki.qhdxxb.2024.27.023
    Abstract (1318) PDF (475) HTML (32)   Knowledge map   Save CSCD(2)
    [Objective] Oblong holes are commonly used across various industries to improve fault tolerance and adjustment capabilities. However, their complex geometric characteristics pose significant challenges for vision detection and location algorithms in industrial applications, impacting their utilization in automatic assembly processes. [Methods] This research investigates a high-precision and robust vision segmentation and location algorithm tailored for oblong holes. First, the geometric features of oblong holes, which are symmetric but lack a simple analytical description, are analyzed. This complexity renders traditional imaging methods ineffective for accurate localization. The detection and segmentation of oblong hole features are conducted using a novel vision location algorithm that integrates deep learning with conventional image processing techniques. Specifically, the algorithm employs a sequential connection framework of YOLO and fully convolutional networks to achieve accurate localization. This framework first identifies the region of interest and then performs semantic segmentation. YOLO networks rapidly detect the region of interest, prioritizing areas where the oblong hole is prominently featured. Semantic segmentation is subsequently performed using fully convolutional networks. Afterward, a skeleton feature extraction method based on medial axis transformation is applied to precisely locate the oblong hole. This method effectively reduces the impact of shape errors from semantic segmentation, achieving subpixel accuracy. However, medial axis transformation may produce redundant lines owing to the presence of image artifacts, potentially leading to inaccuracies. To address this issue, principal component analysis is employed to approximate the center of the oblong hole, thereby minimizing errors. For further precision, a Hough transformation ellipse detection method is utilized to identify the central skeleton of the oblong hole, which is interpreted both as a line segment and a special ellipse. The center of this skeleton represents the center of the oblong hole. [Results] Experimental validation conducted in a specific robotics automatic assembly system confirms the effectiveness of the proposed algorithm. The robustness of the algorithm is further demonstrated through image sampling using camera hardware distinct from that used in the training dataset. Additionally, the impact of surface features and oblong hole shapes on the detection performance is analyzed. The experimental outcomes indicate the optimal performance of the algorithm on objects with nonreflective surfaces, with minimal effect from the shape of the oblong hole on accuracy. Despite potential deformations in segmentation output due to hardware variations, the oblong hole region degenerating location algorithm, based on medial axis transformation, accurately locates the center. The final location error is recorded at 1.05 pixels, which surpasses the accuracy achieved through the direct calculation of the center of gravity of the segmented region. These results underscore the substantial benefits of the algorithm in scenarios with varying hardware and object conditions, demonstrating its high accuracy and exceptional robustness. [Conclusions] By merging deep learning techniques with traditional image processing methods, the location tasks for diverse objects are effectively resolved. The extraction of highly nonlinear features through deep learning, followed by processing with traditional image methods incorporating prior geometric knowledge, enhances the robustness and accuracy of the algorithm, making it suitable for practical production applications.
  • Public Safety
    Jiamei ZHOU, Wei LÜ, Jinghui WANG
    Journal of Tsinghua University(Science and Technology). 2025, 65(6): 1050-1059. https://doi.org/10.16511/j.cnki.qhdxxb.2025.22.015
    Abstract (1307) PDF (151) HTML (1033)   Knowledge map   Save

    Objective: With increased globalization, multiple countries are involved in supply chains, forming complex supply networks. Frequent occurrences of natural disasters, geopolitical instability, and global health crises pose unprecedented challenges to traditional supply chain management methods. Local disruptions in the supply chain can spread internally, causing a series of chain reactions. Enhancing supply chain risk resilience and robustness has become a research focus for many scholars. The widespread use of the Internet has led to rapid information exchange between enterprises; an increasing number of scholars have recognized the importance of early warning information in preventing supply chain disruptions. Therefore, understanding how information affects the propagation of risks within the supply chain and maximizing the early warning function of information have significant practical implications. Moreover, the heterogeneity in the responses of enterprises to early warning information also needs attention. Methods: To capture the propagation of early warning information and disruption risks, a two-layer propagation model that couples risk and information is constructed. In this model, the upper layer represents the information layer and the lower layer represents the risk layer. The information of a disruption in a lower-layer enterprise is transmitted to upstream and downstream enterprises with a certain probability. After receiving the early warning information, an enterprise transitions into a conscious node and this transition is reflected in the upper layer network. In this model, there are five possible states for the nodes in the network. A microscopic Markov chain (MMC) method is used to analyze the state transition process between nodes and calculate the risk propagation threshold of the system. Furthermore, the key factors influencing the propagation of disruption risk are analyzed. An agent-based approach is used for case simulation to validate the model's effectiveness. Numerical analysis of the model reveals that the network structure, network size, extent of risk information propagation in the information layer, and the probability of disruption risk propagation are the key factors influencing the propagation of the risk. Financial data from Tesla's supply chain in China are also collected. In case simulation, an agent-based method is used to study the effects of the information layer network structure, information propagation rate, and risk propagation rate on the supply chain resilience. Results: The results show that for a low information propagation rate, the scale-free network structure accelerates information dissemination, allowing more enterprises to quickly obtain early warning information, thereby helping the supply chain resist risks and improve resilience. When the information propagation rate exceeds 0.4, the small-world network structures can propagate risks more efficiently because of their shorter average paths. Additionally, three disruption schemes are used to analyze system resilience, revealing that prioritizing the disruption of nodes with higher degrees has the greatest impact on the network, while deliberately attacking nodes with smaller degrees allows the supply chain to maintain higher operational efficiency. This finding suggests that maintaining the robustness of the key nodes in the supply chain is critical for enhancing the overall network resilience. Conclusions: Adjusting the supply chain network structure can help improve the risk resilience and robustness of the system. Enhancing risk awareness of enterprises and their response strategies can effectively improve supply chain resilience and suppress risk diffusion. Deliberate attacks on hub nodes with high degrees cause the greatest damage to the network system. Thus, this study provides theoretical support for supply chain management and can serve as a basis for decision-making to improve supply chain risk resilience and optimize management strategies.

  • Advanced Ocean Energy Technology
    Libing ZOU, Mingjun ZHOU, Chao WANG, Xiangyuan ZHENG, Zouduan SU, Junwei LI
    Journal of Tsinghua University(Science and Technology). 2025, 65(8): 1377-1386. https://doi.org/10.16511/j.cnki.qhdxxb.2025.27.039
    Abstract (1304) PDF (378) HTML (861)   Knowledge map   Save CSCD(4)

    Significance: Floating wind turbines (FWTs), as a revolutionary breakthrough in offshore renewable energy technology, are redefining the boundaries of human development of ocean energy with innovative technological solutions. With the collaborative innovation of floating foundations and dynamic anchoring systems, this technology has successfully broken through the limitations of traditional fixed wind turbines on water depth, expanding the scope of wind power development to deep-sea and high wind speed resource rich areas. Compared to offshore fixed wind turbines, FWTs not only significantly reduce marine ecological disturbances, but also provide a dual solution for global energy transformation that combines environmental friendliness and production efficiency through the potential for large-scale cluster deployment. This article systematically reviews the current development status of floating wind power technology and deeply analyzes the core pain points that constrain its commercialization process, including key technical challenges such as dynamic response control, mooring system durability, and life cycle cost optimization. Of particular note is the milestone breakthrough achieved by China's innovation forces in this field-the "Mingyang-Tiancheng" floating platform, as the world's largest single unit capacity floating wind turbine system, has opened up a new paradigm for the development of far-reaching offshore wind power and provided important technical references for the global iteration of floating wind power technology. Progress: Globally, floating wind power projects represented by Hywind (Spar) and WindFloat (semi-submersible) have completed the transition from experimental prototypes to small-scale commercial applications, and their technological level and industrial chain layout are in a world leading position. In contrast, China's floating wind power is still in the demonstration and verification stage, represented by the 5.5 MW (2021) and 7.25 MW (2023) units of the "Yinlinghao" and "Guanlanhao". Although key technological breakthroughs have been achieved, the maturity of technology and the construction of supporting industrial chains still need to be improved. Currently facing three development bottlenecks: at the economic level, floating wind power technology is not yet mature, research and application costs are high, and it is still far from achieving the goal of grid parity; In terms of environmental constraints, the special working conditions in typhoon prone areas require higher adaptability of the units; At the level of industrial synergy, an industrial cluster effect covering design, manufacturing, and operation and maintenance has not yet been formed. Therefore, it is urgent to promote technological innovation to drive the development of related industrial chains, gradually reduce development costs, and achieve large-scale commercial applications. At the same time, it is necessary to promote the coordinated upgrading of offshore wind power equipment manufacturing and marine engineering industry, build a full life cycle cost control system, and lay a technical and economic foundation for large-scale commercial applications. Conclusions and Prospects: In order to address these challenges, the "Mingyang-Tiancheng" floating wind power platform has made innovative breakthroughs in areas such as prestressed high-strength concrete technology, composite lightweight buoy design and construction technology, intelligent perception collaborative control technology, single point mooring technology, dual wind turbine technology, and typhoon resistance technology, reflecting China's emerging leadership position in floating wind technology. It combines material science breakthroughs, intelligent control systems, and ecological design principles. Future progress will require sustained interdisciplinary collaboration and accelerated global deployment through industrialization to reduce costs. The "Mingyang-Tiancheng" provides valuable practical experience and technical reference for the future development of floating wind power.

  • MECHANICAL ENGINEERING
    FENG Xiaobing, WANG Jianjun, WANG Yongke, CHEN Suyun, LIU Aiping
    Journal of Tsinghua University(Science and Technology). 2023, 63(10): 1608-1625. https://doi.org/10.16511/j.cnki.qhdxxb.2022.26.057
    Abstract (1300) PDF (361) HTML (19)   Knowledge map   Save CSCD(2)
    [Significance] Welding has reached a very important position in large structural workpieces. The welding of large structural members also has been covered many fields, including high-end manufacturing fields such as shipbuilding, oil and gas chemical industry, nuclear power engineering, energy and power, building steel structure, and rail transit. The problems of traditional manual welding are instability and low efficiency. Even semi-automatic welding such as gantry welding and rail robot welding, which has not yet to meet the requirements of more efficient and high-quality automation industry. The welding development trend of large structural parts is more intelligent and automatic welding. In this case, the welding robot that has no track and can crawl in all positions has become the representative of intelligent welding equipment, and gradually has promote and solve the automatic intelligent welding of large structural parts. [Progress] In this paper, the research status of intelligent robots for welding large structural parts at home and abroad was systematically introduced, and the welding robots were classified according to the welding robots with and without rails. The application scenarios, advantages and disadvantages of these two types of welding robots were compared. Through these comparisons, it was concluded that the welding robot without rail was more suitable for welding large structural parts because of its better flexibility, adaptability and convenience. There were many problems in the welding process of large structural parts, especially when multi-layer and multi pass thick plates were welded. At the same time, these problems caused low welding process accuracy and low welding quality. Problems included low machining accuracy, inaccurate assembly, metal thermal deformation, many weld passes, weld beads stacked together and many other reasons. In the welding of large structural parts, there were still many difficulties that need to be solved urgently. Automatic backing welding technology and multi-layer and multi-channel automatic routing technology were two very critical and difficult problems that hindered the progress of the welding industry. Until now, the backing welding of large structural parts has mainly depends on manual work, because backing welding was the first weld connecting two welding workpieces, which was very critical in the whole welding process. In the process of automatic backing welding, there were strict requirements on the assembly clearance, unfitness, blunt edge, curling and welding heat input. If these factors were not well controlled, a large number of welding defects such as missing welding and incomplete welding would occur in the process of backing welding. Multi layer and multi pass welding also depended on manual arrangement to cause unstable welding quality. Therefore, it was more and more important to automatically plan the number of welding passes and layers, arrange the welding sequence, determine the position coordinates of each weld pass and adjust the welding parameters. [Conclusions and Prospects] Based on this situation, this paper summarizes the exploration of related technologies from the aspects of automatic backing welding technology, seam tracking technology, multi-layer and multi-channel automatic lane arrangement technology, etc. Multi-modal deep learning and multi-sensor fusion technology are widely used in many fields, and have become a concern in military, industrial and high-tech development. Thus, these two technologies will be the key to developing welding robots and provide guidance for the intelligent welding of large structural parts. In the future, artificial intelligence technology will lead the welding robot to achieve better welding quality.
  • MECHANICAL ENGINEERING
    LIU Tao, YANG Kaiming, ZHU Yu
    Journal of Tsinghua University(Science and Technology). 2023, 63(10): 1640-1649. https://doi.org/10.16511/j.cnki.qhdxxb.2023.26.002
    Abstract (1291) PDF (436) HTML (10)   Knowledge map   Save
    [Objective] The feedforward controller is crucial to achieving nano-level motion accuracy for the lithography wafer stage under high acceleration and deceleration conditions. Traditional 4-order feedforward is widely used to control precision motion systems because of its intuitive physical meaning and simple parameter tuning. However, its capacity to fit the inverse model is inadequate, and it is difficult to eliminate the repetitive error caused by the input trajectory. Therefore, a feedforward control architecture using the 4-order feedforward and an extra rational fraction compensator is proposed. [Methods] In this study,the input signal of the compensator is the higher-order derivative of the reference trajectory, and the numerator and denominator of the compensator use the delay unit as the basis function. Therefore, obtaining the unknown parameters of the basis function is crucial to the design. This paper proposes a data-driven iterative parameter tuning strategy for the compensation controller. The difficulty is that the tuning problem is a nonconvex optimization problem, making global parameter optimization challenging. This paper uses the relevant rules of system identification to address the issue at hand. The purpose of adding compensatory feedforward is to eliminate the residual error after using the 4-order feedforward, which is equivalent to achieving a zero-generalized error. Since the generalized error has a linear connection with the compensator parameters, the original nonconvex optimization problem is successfully transformed into a convex problem by minimizing the 2-norm of the generalized error. Through the above transformation, the global optimal point is obtained by the Gauss—Newton method, and the step size condition for ensuring iterative convergence is provided. In addition, the gradient and Hessian matrix of the objective function need to be incorporated into the parameter updating law, even though their exact values are difficult to obtain. This paper derives their unbiased estimates using two impulse response experiments and 2 trajectory tracking experiments. [Results] The proposed method was applied to the wafer stage of the lithography machine, and the experiment showed the following results: (1) Using the proposed method to tune three compensation controllers with different orders, their error 2-norm almost converged after five iterations. (2) After adding compensation feedforward, the acceleration and deceleration phase errors were reduced from ±35 nm to ±10 nm; the constant velocity phase error was almost equal to the positioning error, and its trajectory tracking effect was very close to that of iterative learning control (ILC) compensation. (3) Compared with the existing compensation controller parameter tuning method, the maximum moving average and moving standard deviation at velocity phase of the proposed method were smaller, and the lower the compensator order, the more obvious the advantage. (4) After changing trajectory, the proposed compensator could still achieve a better control effect than ILC compensation. [Conclusions] The above experiments verify the convergence performance of the proposed parameter tuning algorithm. It is shown that the proposed feedforward compensation architecture can effectively eliminate the residual repetition error of the 4-order feedforward; simultaneously, it can adapt to variable trajectories. In addition, compared to the current compensator tuning result, this method can achieve a superior trajectory tracking control effect while using a low-order compensation controller.
  • Hydraulic Engineering
    Jiahong LIU, Mengxue ZHANG, Jia WANG, Chao MEI
    Journal of Tsinghua University(Science and Technology). 2025, 65(10): 1853-1867. https://doi.org/10.16511/j.cnki.qhdxxb.2025.21.038
    Abstract (1288) PDF (264) HTML (912)   Knowledge map   Save CSCD(1)

    Objective: The frequency and intensity of global flood events are increasing, which is deeply driven by climate change and human activities. The key risk factors of hazard, exposure, and vulnerability are interconnected and collectively influence the occurrence and progression of flood disasters. Therefore, the relationships between these three factors need to be understood, and a comprehensive indicator system for the integrated assessment of flood risk needs to be developed. This study aims to analyze the spatiotemporal trends of global flood events from 1965 to 2023. Moreover, based on the key risk factors of hazard, exposure, and vulnerability, the spatiotemporal characteristics of the flood risk were revealed, which could provide a scientific basis for flood prevention and disaster mitigation decision-making. Methods: This study uses the Emergency Events Database, which includes global flood data, to analyze flood events from 1965 to 2023. This study conducts a trend analysis of the global flood occurrence, affected population, and mortality per unit area from 1965 to 2023. Based on the affected population and mortality per unit area, floods in six continents are classified into light, moderate, and severe categories using the percentage method. Spatial analysis of the flood occurrence, affected population, and mortality per unit area was performed for each country. The results showed the spatial distribution and impact intensity of flood disasters in different regions. In addition, key risk indicators, such as geographic elevation, precipitation, population density, and urbanization rate, are selected to analyze the characteristics of flood risk. Elevation and precipitation represent hazards. Population density indicates exposure, and urbanization rate reflects vulnerability. Trend analysis of these indicators was performed for three distinct periods, i.e., 1965-1984, 1985-2004, and 2005-2023. To examine the spatial trends of these indicators across countries over the entire study period, the Theil-Sen slope estimation method was employed. The entropy weight method was applied to calculate the weight of each risk indicator, and the flood risk values of six continents from 1965 to 2023 were calculated. Results: The main results are as follows: (1) From 1965 to 2023, global flood events show a fluctuating upward trend, although the affected population and number of deaths have shown a downward trend since the 1990s. At the continental level, floods occur most frequently in Asia, Africa, and South America, with a total of 2 322, 1 266, and 1 084 events, respectively. At the national level, Haiti experiences the highest frequency of flood events per unit area, with 23 events per 104 km2. Bangladesh has the highest total number of flood-affected people per unit area, with 27.1 million people per 104 km2, and the highest record of cumulative deaths, with 3 313 deaths per 104 km2. (2) Flood hazard, exposure, and vulnerability vary significantly across six continents. Among the indicators, population density and precipitation show the greatest influence on flood risk, with weights of 0.33 and 0.30, respectively. From 1965 to 2023, an obvious regional variation in flood risk across six continents is detected. The flood risk in Asia is significantly higher than that in other continents, with the flood risk values of both Asia and Africa showing a significant increase. By contrast, the flood risk value of South America decreased after 2010. Europe and North America show relatively low and stable flood risk values. Oceania exhibits the lowest flood risk values with significant fluctuations. Conclusions: This study conducts not only a systematic analysis of global flood events over a long time series but also an analysis of the changes in risk indicators, such as precipitation, geographic elevation, population density, and urbanization rate, from 1965 to 2023. Moreover, the relative impact of different indicators is quantified, which clarifies their respective contributions to flood risk. The results further revealed the comprehensively changing characteristics of flood risk. The findings provide guidance and evidence to inform flood prevention planning and disaster response strategies. In the future, exposure change based on population mobility and integrated adaptive capacity should be considered to reveal the dynamic characteristics of flood risk.

  • SPECIAL SECTION: BIG DATA ANALYTICS
    LI Mingzhu, TIAN Rongrong, LI Ran, ZHANG Jing, WANG Shujuan, LIU Jia, XU Lizhen, LI Yan, ZHAO Yonggan
    Journal of Tsinghua University(Science and Technology). 2024, 64(10): 1759-1770. https://doi.org/10.16511/j.cnki.qhdxxb.2024.21.020
    Abstract (1280) PDF (1170) HTML (30)   Knowledge map   Save CSCD(7)
    [Objective] Saline-alkali soil is an important reserve resource of cultivated land and potential granary in China, and its management and utilization are related to national food security. Therefore, innovative techniques and amendments should be developed to address these challenges in saline-alkali regions. Among these, calcium supplementation is recognized as one of the most effective methods for ameliorating saline-alkali soil. In the past two decades, gypsum from the desulfurization of flue gas (FGDG) in coal-fired power plants has become a preferred calcium source for ameliorating saline-alkali soil because of its high calcium content and economic feasibility. Given that FGDG has developed into a soil amendment and has been widely used, a profound understanding of the progress of its patents can provide technical guidance for the large-scale amelioration of saline-alkali soil. [Methods] Based on the incoPat global patent database, a bibliometric analysis was conducted on 520 invention patents in the field of using FGDG to ameliorate saline-alkali soil from 2003 to 2022. The application and authorization trends, high-yield mechanisms, operational status, substance composition, and their correlation with patents in this field were systematically analyzed. In addition, a comparative analysis was conducted on the effectiveness of 52 patents with application cases. [Results] The results showed that the annual number of patent applications for using FGDG amendments to ameliorate saline-alkali soil has a trend of first increasing and then decreasing, with a peak period of 115 patents in 2016. Most patents take 20-30 months from publication to authorization. However, the overall proportion of authorization has shown a decreasing trend. The number of patents granted by universities and research institutes is higher than that granted by enterprises, whereas the number of patents jointly granted by universities and enterprises accounts for 15.6% of the total. A total of 37 patents were converted, 7 of which were pledged, accounting for 33.3% of the total number of grants, all of which were transferred by universities to enterprises and pledged by enterprises for financing. More than 70% of patents comprised three or more substances, primarily including organic and inorganic minerals, microbial agents, and nutrient supplements. Organic materials can directly provide nutrients for the soil to make up for the shortage of FGDG in terms of nutrients, with the frequency of application as high as 95.7%, followed by inorganic minerals, which account for 44.5%; microbial agents, which account for 41.3%; and nutrient supplements, which account for 21.3%. Compared with soils with or without other types of amendments, the application of FGDG amendments significantly decreased soil pH, exchangeable sodium percentage, and salt ions that are toxic to crop growth and increased soil Ca2+, SO42-, and total/available nitrogen and phosphorus contents, which provided a better soil environment, thereby increasing crop yield. [Conclusions] Generally, research and development on FGDG amendments for saline-alkali soil amelioration have matured, and some innovative achievements have been transformed into real productivity; thus, the value of related patents has been increasingly highlighted. However, problems such as the relatively simple composition of current patents, unclear technical requirements for the amount of application and method, and serious homogeneity of patents have been encountered. In the future, we should strengthen the cooperation among schools, enterprises, universities, and research institutes, intensify research on the FGDG formula used in saline-alkali soil, and enhance the application benefits of FGDG amendments.
  • BUILDING SCIENCE
    JIE Yuxin, FU Zhibin, WANG Yangqiang, YIN Changyun
    Journal of Tsinghua University(Science and Technology). 2023, 63(11): 1897-1908. https://doi.org/10.16511/j.cnki.qhdxxb.2023.25.033
    Abstract (1277) PDF (627) HTML (26)   Knowledge map   Save CSCD(1)
    [Objective] The determination of bearing capacity of foundation soil is one of the classical research fields of soil mechanics. For large area artificial fill projects, the current specifications of China do not consider the correction factor of foundation width in the calculation of bearing capacity. This paper discusses this problem, and investigates the definition and measurement methods of the foundation bearing capacity, related theoretical principles, and the method of determining allowable bearing capacity. We also discuss and speculate the possible basis for the selection of correction factors of the bearing capacity of foundation soil made of artificial fill and soft underlying stratum. It may provides theoretical guidance for width and depth correction of bearing capacity of foundation soil in large area artificial fill under current technical conditions. [Methods] In this paper, two main approaches for calculating bearing capacity of foundation soil are studied. One is to determine the bearing capacity of the foundation soil according to the extension range of the plastic zone; the other is to use the ultimate load as the ultimate bearing capacity, and then divide it by the safety factor to obtain the bearing capacity. The width and depth correction of bearing capacity is also based on these theories. We reviews the sources of the calculation method of bearing capacity together with the width and depth correction factors in the current specifications of China. On the basis of deriving the calculation formula and analyzing the principle of bearing capacity of foundation soil, two cases are investigated in this paper: one is a homogeneous foundation soil, and the other is that the shear strength of the soil outside the foundation boundaries is lower than the foundation soil. The possible essence for the correction factors of the bearing capacity is then discussed in order to guide the determination of the width and depth correction factors for large area artificial fill. [Results] For large area artificial fill projects, the correction factor of width is not considered in current specifications of China. The main reasons may be as follows: 1) The compaction quality of the foundation soil is not be able to guarantee easily. 2) The quality control standard of the soil under the foundation is stricter than that outside the foundation boundaries. 3) Post-construction settlement may occur for artificial fill. Since that the existing construction technology and quality control level has made great progress compared to the past, it is theoretically feasible to increase the correction factors of width and depth for large area artificial fill such as in island and reef. However, the following items are needed: 1) The degree of compaction should meet the requirement in the fill site. 2) The engineering quality of the fill outside the foundation boundaries should also be guaranteed not to be lower than the foundation soil. 3) Settlement calculation of the buildings are necessary. [Conclusions] Based on the theories of determining the bearing capacity of the foundation soil, this paper investigates the method of selecting the values of correction factors of width and depth. It is thought that the correction factors of width and depth can be appropriately increased under certain conditions for large area artificial fill. This will have good economic benefits, especially for offshore islands and reefs.
  • PUBLIC SAFETY
    WANG Hongping, HU Yanzhu, ZHANG Yufeng, WANG Song
    Journal of Tsinghua University(Science and Technology). 2023, 63(10): 1584-1597. https://doi.org/10.16511/j.cnki.qhdxxb.2023.22.036
    Abstract (1205) PDF (391) HTML (17)   Knowledge map   Save CSCD(1)
    [Objective] The rapid proliferation of electric vehicles (EVs) and the large-scale deployment of charging facilities have considerably increased the electrification of transportation road networks. However, road networks exhibit vulnerability to failure at several critical sections, which in turn may trigger a cascade of failures, ultimately leading to widespread road network disruptions. In the context of mixed electric and nonelectric vehicular flows, such adverse impacts may further spread and cascade due to EV-specific characteristics, such as limited EV range and required charging time. Protective measures for vulnerable road sections of electrified road networks against hazards could mitigate the risk of cascading failures and the further spread of disruptive events. Therefore, assessing the vulnerability of electrified transportation road networks and identifying critical road sections have become paramount. Given that the vulnerability of electrified transportation road networks has been scarcely explored in existing literature, this paper proposes a two-layered attacker-defender model to study the vulnerability of electrified transportation road networks. [Methods] The outer layer model aims to minimize system performance by targeting roads within the system for disruption, i.e., maximizing the total system travel time. The inner layer model serves as a defender, minimizing the total system travel time by dynamically and optimally distributing traffic flows containing both electric and nonelectric vehicles. The inner layer model is formulated based on an enhanced link transmission model, taking into consideration the critical characteristics of the electrified transportation road networks. This two-layered model can describe the temporal and spatial evolution of the mixed electric and nonelectric vehicular flows. Additionally, this paper provides a detailed solution method and theoretical analysis of this model. A mixed-integer quadratic programming problem is obtained by considering the dual of the inner problem and combining the inner problem with the outer problem. This problem is subsequently converted into a mixed-integer linear programming problem using the big M method. [Results] The proposed model is applied to a segment of the highway network in North Carolina, U.S. The experimental results reveal that (1) critical road sections as determined with and without EVs differ considerably. Therefore, it is necessary to incorporate EVs when analyzing the vulnerability of an electrified transportation road network. (2) The set of critical road sections varies depending on the level of attack resources. In particular, the set of critical road sections in the low attack resource level scenarios is not necessarily a subset of the critical road sections in the high attack resource level scenarios. (3) The experimental results confirm the existence of a critical point in the attack resource level. When this critical point is reached, the system performance displays a phase change phenomenon, marked by a notable decline. [Conclusions] The results verify that the proposed model can identify the set of critical road sections in the system and provide theoretical support to improve the vulnerability of the electrified transportation road networks.
  • CONSTRUCTION MANAGEMENT
    CHEN Zixiao, LIANG Yao, LIU Hongyu
    Journal of Tsinghua University(Science and Technology). 2024, 64(2): 181-188. https://doi.org/10.16511/j.cnki.qhdxxb.2023.22.053
    Abstract (1194) PDF (348) HTML (5)   Knowledge map   Save
    [Objective] High-quality development and exploration of a new development model for the real estate industry has recently attracted considerable attention. Scale expansion and relevant land-buying are essential components of the development model. Much of the literature investigating land-buying behaviors of real estate firms has focused on the number of lands bought rather than the number of cities entered, which is also an important aspect. Besides buying lands, listed real estate firms must concern the market value management related to financing and investors' valuation. Therefore, this paper investigates the relationship between the land-buying behaviors of listed real estate firms and their capital market performance. Investors can build more efficient stock portfolios and real estate firms can improve land-buying strategies based on the results. [Methods] We employed regression analysis to estimate the influence of land-buying behaviors on the capital market performance of A-listed real estate firms. The data was primarily obtained from the CREIS and CSMAR databases, spanning from 2009 to 2021 and involving 87 firms. The model included the number of lands bought, cities entered, and other aspects of land-buying behaviors. Capital market performance was divided into two aspects:firm investment value and firm risk, which are represented using Tobin's Q and Beta coefficients, respectively. The model also controlled firm and manager characteristics, financial ratios, and market environment and employed the two-way fixed effect ordinary least squares (OLS) method. The heterogeneity effect on ownership, firm scale, and year of listing was explored using a regression on the subsample, while robustness testing was conducted by handling extreme values. Finally, we discussed a potential channel through which land-buying behaviors affected the capital market performance. [Results] The results show an inverted U-shaped relation between the firm investment value and number of cities entered; furthermore, the investment value increases when more cities are entered within a certain range throughout the study period. In the market downturn period, i.e., since 2017, the lifting effect due to entering more cities on the firm investment value has decreased, while that on firm risk has increased. Comparatively, the effect of the number of lands bought on capital market performance is not as important as that of the number of cities entered. The capital market performance of non-state-owned, smaller, or shorter-listed real estate firms is more affected by their land-buying behaviors. The impact of land-buying behaviors on capital market performance passes through the land-buying expense and sale revenue ratio channel. [Conclusions] The findings indicate a change in the reaction of the capital market to the regional expansion of land-buying. We recommend that real estate firms respond to feedback from the capital market and adjust their land-buying strategies in time, especially when selecting and entering more cities. Furthermore, investors should pay attention to region-focused real estate firms. The findings also suggest that the government should be cautious about structural changes in the real estate market, and a shift from focusing on the investment demand of real estate firms to focusing on the end-use demand of space is required to coordinate and guide the further improvement of the development model.
  • HYDRAULIC ENGINEERING
    XING Yue, LIU Jiahui, NI Guangheng
    Journal of Tsinghua University(Science and Technology). 2023, 63(12): 1909-1923. https://doi.org/10.16511/j.cnki.qhdxxb.2023.21.004
    Abstract (1175) PDF (321) HTML (4)   Knowledge map   Save
    [Objective] Anthropogenic heat is a crucial feature of urbanization and human activities. Large amounts of anthropogenic heat emissions can affect the regional land-atmosphere process and exacerbate the local climate change in cities. In winter, the anthropogenic heat emissions caused by central heating increase significantly in the North China, thereby enhancing the urban heat effect. The urban heat effect may have a substantial impact on winter snowfall. Therefore, studying the impact of anthropogenic heat on urban winter precipitation can help improve our understanding of the impact of urbanization and human activities on urban precipitation.[Methods] Here, the weather research and forecasting (WRF) model was used to analyze the impact of anthropogenic heat on urban winter precipitation by simulating a winter precipitation event in Beijing. To study the impact mechanism of anthropogenic heat on the urban water and thermal environment in winter and the possible threshold, sensitivity experiments were conducted using the default anthropogenic heat built in the WRF, which is an ideal experiment to explore the possible threshold of anthropogenic heat magnitude. By setting built-in anthropogenic heat values of different intensities, the impact mechanism and intensity threshold of different anthropogenic heat intensities on urban water and thermal environment in winter were compared and analyzed. Based on the conclusion of the sensitivity experiment, anthropogenic heat with high spatiotemporal resolution calculated using the large-scale urban consumption of energy (LUCY) model in Beijing was used as the input data for WRF. The WRF-LUCY coupling model was applied to investigate the impact of anthropogenic heat on winter precipitation in Beijing. By setting up simulated scenarios with and without anthropogenic heat, the impact of anthropogenic heat on winter precipitation was compared and analyzed. Furthermore, the results of the WRF-LUCY coupling model were compared with the existing effects of anthropogenic heat on summer precipitation, and the differences between summer and winter precipitation are summarized.[Results] The following results were obtained:1) Anthropogenic heat primarily affects the phase state of mixed precipitation and has little effect on single-phase precipitation. With the increase in anthropogenic heat, snowfall and rainfall gradually decrease and increase, respectively. 2) No evident threshold exists for the impact of anthropogenic heat increase on air temperature; however, a threshold for the impact height, with a maximum impact height of about 1.3 km, is noted. 3) The increase in anthropogenic heat intensifies the vertical wind shear and water vapor convergence, thereby increasing the water vapor content in the boundary layer and providing favorable developmental conditions for the convective system. 4) For summer precipitation, the effect of anthropogenic heat demonstrates large scope and magnitude, and the impact mechanism is relatively complex; in contrast, the impact on winter precipitation is primarily concentrated in the urban interior, mainly affecting the precipitation phase.[Conclusions] A threshold for the impact height of anthropogenic heat is found, while no evident threshold for the anthropogenic heat magnitude is observed. Compared with the complex mechanism of summer precipitation, the impact of anthropogenic heat on winter precipitation is more concentrated. This study analyzes the impact of anthropogenic heat on urban winter precipitation, which has a crucial scientific application for exploring the urban land-atmosphere process and improving the urban environment.
  • AEROSPACE ENGINEERING
    HUANG Hao, MA Wenhui, LI Jiacheng, FANG Yangwang
    Journal of Tsinghua University(Science and Technology). 2024, 64(2): 358-369. https://doi.org/10.16511/j.cnki.qhdxxb.2023.27.001
    Abstract (1164) PDF (385) HTML (14)   Knowledge map   Save CSCD(6)
    [Objective] Formations of fixed-wing unmanned aerial vehicles (UAVs), which are commonly used in military, rescue, and other missions, often do not have the ability to hover and have a large turning radius. Thus, when operating in an unknown environment, it is easy for the formations to collide in the presence of obstacles, which will gravely affect flight safety if not guarded against. It is difficult to avoid unknown environmental obstacles using traditional modeling methods. However, artificial potential field methods can address deadlock problems such as target infeasibility and cluster congestion. [Methods] To achieve the cooperation of UAV formations without collision, a deep deterministic policy gradient (DDPG)-based centralized UAV formation control method is proposed in this study, which is designed by combining the centralized communication architecture, reinforcement learning, and artificial potential field method. First, a greedy-DDPG flight control method is studied for leader UAVs, which improves collision avoidance effectiveness. Considering maneuver constraints, reward functions, action spaces, and state spaces are improved. Additionally, to shorten the training duration, the exploration strategy of DDPG is improved using the greedy scheme. This improvement mainly uses the critic network to evaluate the value of random action groups and improves greedy selection to make actions more inclined, thus achieving rapid updates regarding the critic network and accelerating the update of the overall network. Based on this, incorporated with the artificial potential field method and leader-follower consensus, a collision-free control method is designed for followers, which can ensure collision-free following cooperation. [Results] The numerical simulation experimental results show that the improved DDPG algorithm has a 5.9% shorter training time than the original algorithm. In the same scenario, the method that we proposed perceives the same number of obstacles as the artificial potential field method. The artificial potential field method has significant fluctuations in heading angle, while the proposed method has relatively small fluctuations. The DDPG algorithm has a smoother heading angle due to a smaller number of perceived obstacles; however, the minimum distance from the obstacles is only 9.1 m. The method that we proposed here is above 17 m from the obstacles. Furthermore, Monte Carlo experimental data under different scenarios of the long aircraft show that the ability of obstacle avoidance generalization of the proposed method is improved. Moreover, experiments were applied to the proposed formation control method. Under the same scenario and control parameters, the UAV formation control method based on the proposed architecture has lower formation errors during flight, with a maximum error of no more than 10 m. However, the artificial potential field-based formation control method has a maximum formation error of over 25 m. When encountering narrow gaps, our proposed method can quickly pass through without congestion, while the artificial potential field-based formation control method appears to hover in front of obstacles, which is not conducive to flight safety. During the entire flight, this method has a greater distance from obstacles and higher safety. [Conclusions] Compared with the original DDPG algorithm, the improved DDPG algorithm has faster training speed and better training effect. The formation control method can realize the formation flight of unmanned aerial vehicles under unknown obstacles. Compared with the formation control method based on artificial potential field, the formation control method avoids the hovering in place before obstacles, which is of great significance to the formation flight safety of unmanned aerial vehicles.
  • LOW-CARBON TRANSPORTATION & GREEN DEVELOPMENT
    BI Jun, DU Yujia, WANG Yongxing, ZUO Xiaolong
    Journal of Tsinghua University(Science and Technology). 2023, 63(11): 1750-1759. https://doi.org/10.16511/j.cnki.qhdxxb.2023.26.038
    Abstract (1158) PDF (345) HTML (9)   Knowledge map   Save CSCD(6)
    [Objective] With the increasing prevalence of electric vehicles (EVs) in urban transportation systems, charging guidance service has become an effective means to solve the charging problem in the context of insufficient charging infrastructure. However, for optimizing the charging station selection decision-making plan of users, most existing research studies aim to minimize travel costs, which rarely considers the charging experience of users during travel and ignores the interaction of charging station selection decision-making between multiple users. To enhance the charging experience of users, based on the analysis of charging satisfaction of EV users, an EV charging guidance optimization model that integrates user satisfaction with detour distance, queuing time, and charging cost is proposed in this study. The model aims to maximize the average comprehensive satisfaction of multiple users. [Methods] To quantify the comprehensive satisfaction of users with charging stations during charging processes, evaluation indicators of detour distance, queuing time, and charging cost are constructed. To accurately deduce the queuing time of users at charging stations, this study fully considers the interaction influence of charging station selection decision-making between multiple EV users. Prediction models of the charging station operation state are established by considering several charging scenarios based on the arrival patterns of two successive users. According to the characteristics of the proposed model, an immune algorithm and the Floyd shortest path algorithm are applied to optimize the decision-making plan of charging station selections and the travel paths of multiple users, respectively. A numerical example with multiple charging requests is designed to confirm the feasibility and effectiveness of the proposed model and the algorithms. [Results] The experimental results indicated that optimal charging station selections and driving paths of multiple EVs to maximize average comprehensive satisfaction could be obtained by solving the optimization model. Compared with models with single optimization objectives, namely, minimum detour distance, shortest queuing time, and least charging cost, the average comprehensive satisfaction of EV users was increased by 15.0%, 17.8%, and 11.4%, respectively. The results also showed that average driving speed was a critical factor affecting optimal charging station selection and average comprehensive satisfaction of EV users. By analyzing the arrival patterns of two successive users at the same charging station under different charging scenarios, their queuing time after arriving at the charging station could be accurately obtained. Subsequently, optimal charging station selections by multiple users could be determined by considering the interaction that influences their selections. [Conclusions] The proposed optimization model provides multiple EV users with decision-making support for selecting charging stations by considering their interaction influences. Provided that the threshold values of each satisfaction indicator remain unchanged, the comprehensive average satisfaction obtained by the proposed model is considerably higher than that obtained by models with single objectives: minimum detour distance, shortest queuing time, and least charging cost. Thus, the proposed method can enhance the charging experience of EV users during travel.
  • Lithium-Ion Battery
    Yuanhua HE, Xingchen SU, Liang ZHAO
    Journal of Tsinghua University(Science and Technology). 2025, 65(9): 1805-1820. https://doi.org/10.16511/j.cnki.qhdxxb.2025.22.046
    Abstract (1148) PDF (246) HTML (920)   Knowledge map   Save

    Significance: Amid the rapid development of new productivity tools, the active thermal management system of power lithium-ion batteries is facing significant challenges, such as improving charge and discharge ratios and adapting to harsh application scenarios. To maintain stable operations of the power system in the best state, the technical bottleneck of efficient and long-term heat dissipation needs to be overcome. At the same time, in the consumer market, the cost factors of engineering products, including design, materials, space volume, cooling refrigerants, and plumbing systems, need to be carefully considered. Therefore, the active thermal management system of power lithium-ion batteries, which is widely used and has great potential, needs to be systematically summarized. Progress: This paper comprehensively reviews research progress on the active thermal management of power lithium-ion batteries in recent years. First, we summarize the research status of single-phase thermal management methods, including forced air cooling, natural air cooling, immersion liquid cooling, and microchannel liquid cooling. In the context of low charge and discharge ratios and lightweight engineering, air cooling still plays an important role. The main factors affecting battery temperature include air flow rate, air flow velocity, battery layout, and flow channel design. The air cooling system has unique engineering advantages because of its low cost. With an increase in charge and discharge ratios, the effect of microchannel and immersion liquid cooling is significantly enhanced, which is beneficial in controlling the battery's temperature and temperature uniformity. Several factors, such as liquid flow rate and channel design, have notable effects on the battery's heat dissipation; however, corresponding costs also increase. Second, we discuss advanced cooling techniques based on gas/liquid two-phase flow, such as submerged boiling cooling and spray-integrated cooling. In the context of increasing demand for batteries with high charge and discharge ratios, these technologies provide efficient, flexible, and adaptable solutions to thermal management challenges. The cooling medium, the flow rate, and the nozzle arrangement all have different effects on the temperature of the battery, along with the size of the droplets. The feasibility of the comprehensive and market recovery costs to maintain profits and long-term development of the enterprise also needs to be considered. Conclusions and Prospects: Based on the literature review, this paper forecasts the progress trend of active thermal management technology from multiple application scenarios to meet the development needs of lithium electric power in sea, land, and air. We believe that the development of the active thermal management technology of the new generation of power lithium-ion batteries should fully consider practical engineering requirements, such as charge and discharge ratios and harsh application scenarios. Future research and development should focus on improving heat transfer efficiency, system integration, and intelligent control capabilities while overcoming the challenges of reliability, cost, adaptability to extreme operating conditions, and energy consumption optimization.

  • PUBLIC SAFETY SCIENCE AND TECHNOLOGY
    HE Sheng, SHU Xueming, HU Jun, ZHANG Lei, ZHANG Jia, ZHANG Jiale, ZHOU Yang
    Journal of Tsinghua University(Science and Technology). 2024, 64(3): 478-491. https://doi.org/10.16511/j.cnki.qhdxxb.2024.26.002
    Abstract (1137) PDF (375) HTML (10)   Knowledge map   Save CSCD(4)
    [Objective] Risk quantification is crucial in risk assessment of accidents or disasters. This study aims to investigate the risk quantification method utilized in over-temperature faults in electrical circuits. The existing technologies of the abovementioned method are summarized in electrical and fire signals of disaster early warning. Thus, a new method based on the fire big data is proposed. [Methods] Different frequency electrical parameters are collected by the detector arranged at the front end and transmitted in real time to the fire big data to mine the influencing factors and changing patterns of electrical circuit temperature based on the deep-learning method. Subsequently, the probability distribution of temperature is determined statically, and risk is described by comparison of prediction temperature in different cumulative probabilities with actual temperature. To predict the electrical circuit temperature, a recurrent neural network (RNN) is utilized to model temperature prediction. The input parameters are voltage, current, temperature, and residual current. Among the parameters, there are two data sources for the model: one is real electrical fire data, 6 min-1, used to learn the periodic law of temperature increase in electrical circuits of RNN for low-frequency data (LF-RNN), and the other is experimental data based on simulated fault of the temperature increase in electrical circuits. This experiment is implemented in three-phase resistive electrical circuits. Exceeding rated current is utilized to produce temperature rising. Meanwhile, electrical parameters are collected to study the law of temperature oscillation of RNN for high-frequency data (HF-RNN). Among these electrical parameters, the sampling frequency of voltage, current, and residual current is 50 kHz, but 1 Hz for temperature exceptionally. The optimization method, hyperparameter traversal, aims to minimize the loss function and root mean square error; thus, temperature prediction in electrical circuits is preliminarily applied. To increase the accuracy of the prediction model and elucidate the relationship between fire risk and prediction result, a temperature probability prediction model is established based on its second-order residual normal distribution. The error and its reducing methods are analyzed, and the relationship between prediction error and temperature mutation is determined. [Results] The results demonstrated that temperature mutation within three window lengths had a remarkable linear correction effect with temperature prediction error; moreover, the second-order residual approximately followed a normal distribution. The upper and lower limited of temperature prediction confidence intervals with different significant levels (α=0.02, 0.04, 0.06,…, 0.98) can be computed by interval estimation, which had a one-to-one correspondence with temperature prediction accumulate probability (1-α/2) and (α/2). The results revealed that the cumulative distribution probability 1% prediction curve and 99% prediction curve appeared to have a fine coverage effect on the actual temperature. With the aim of measuring temperature prediction probability distribution with electrical fire risk, the concept of “early-warning quantile” similar to cumulative distribution probability, was proposed. The ability to predict temperature was established using different “early-warning quantile curves” and confirmed through 2 943 sets of real electrical fire scene data. The results demonstrated that early-warning quantiles in the range of 10%-30% could overlap the majority of the actual temperature data, and the higher the quantile of the curve was, the higher the frequency of overestimating the temperature was. [Conclusions] To summarize, when the temperature in electrical circuits suddenly increases, there is a substantial upward trend in the early-warning quantile of the actual temperature. Thus, the use of LF-RNN and HF-RNN can timely and accurately predict the temperature probability distribution to characterize fire risks in electrical circuits so that early dynamic perception of fire risk is realized.
  • Jingjing CHEN, Xin HU, Xinke SHEN, Dan ZHANG
    Journal of Tsinghua University(Science and Technology). 2025, 65(12): 2341-2350. https://doi.org/10.16511/j.cnki.qhdxxb.2025.21.049
    Abstract (1122) PDF (375) HTML (1014)   Knowledge map   Save

    Significance: Empowering machines to understand human emotions remains one of the primary challenges in developing artificial intelligence (AI). The affective brain-computer interface (BCI), which decodes emotional states based on brain signals, is an emerging field combining psychology, neuroscience, and AI. Brain signals are inherently uncontrollable, contain rich emotion-specific information, and provide a promising physiological basis for developing computing systems that support continual emotion monitoring. Since its inception, affective BCI research has required close collaboration across various disciplines: it depends on the use of information science for feature engineering and algorithm development, psychology for theoretical frameworks of emotion, and neuroscience for revealing the neural mechanisms underlying emotional processes. Such a demand for multidisciplinary co-operation forms the core focus of this review. Specifically, this paper focuses on the methods by which psychology-and neuroscience-based insights can inspire and advance affective BCI research. Progress: We summarize the current progress at three levels: theoretical, technical, and applied. In the first one, recent advances in affective science offer new perspectives for shaping affective BCI paradigms. The traditional discrete and dimensional frameworks have laid the groundwork for emotion decoding but often overlook positive emotions and the dynamic intensity of affective experiences. Recent emotion theories emphasizing refined positive emotions, mixed emotions, and context-dependent emotions provide valuable directions for improving emotion representation. Affective computing should align with these developments, integrating them into computational models to enhance ecological validity. In turn, affective BCI research may also contribute to psychology by offering evidence to test and refine emotion theories, fostering reciprocal progress across disciplines. At the technical level, neuroscience provides crucial insights for building more robust affective BCIs. Findings on emotional valence lateralization and distributed emotion-associated brain representations can inform the design of models that better capture emotional processing complexity. Moreover, inter-subject brain synchronization research has revealed mechanisms that enhance model generalizability across users, suggesting that incorporating neuroscientific findings can substantially improve the performance and reliability of affective BCIs. At the application level, affective BCIs are expanding beyond emotion recognition toward understanding emotion-related individual differences. Variability between individuals—often treated as noise—may instead offer meaningful information about personality traits or mental health conditions. In the long term, the goal of affective BCI systems may evolve from accurately identifying emotions to comprehensively understanding each individual's psychological tendencies and dynamic affective patterns across multimodal neural and behavioral data. We advocate for stronger integration between affective BCI technologies and practical domains. Such integration allows practical demands to drive technological development, ensuring that affective BCI remains human-centered. Conclusions and Prospects: Finally, we discuss the technical challenges of affective BCI, including extending algorithms from controlled laboratory settings to real-world scenarios, advancing sensor technology for more convenient and reliable brain-signal acquisition, and leveraging large models to enhance performance for affective BCI. Specifically, we emphasize the vital role of ethical considerations: as affective BCIs move from passive emotion detection toward active emotional support or intervention, the responsibility of humans as rational moral agents in a future era of man-computer symbiosis must be considered, ensuring the autonomy of human emotions.

  • LOW-CARBON TRANSPORTATION & GREEN DEVELOPMENT
    YANG Zimu, JIANG Hongsheng, ZHUGE Weilin, QIAN Yuping, ZHANG Yangjun
    Journal of Tsinghua University(Science and Technology). 2023, 63(11): 1791-1807. https://doi.org/10.16511/j.cnki.qhdxxb.2023.26.023
    Abstract (1112) PDF (395) HTML (10)   Knowledge map   Save CSCD(2)
    [Significance] The supercritical carbon dioxide (S-CO2) Brayton cycle is a power cycle at intermediate temperature and high pressure. This cycle is considered an important solution to improving the efficiency of traffic power systems such as gas turbines and internal combustion engines by recycling exhaust energy at high temperatures. The compressor is considered one of the most important components of this cycle. Its efficient and stable operation plays an important role in cycle performance. [Progress] In this paper, the research progress on S-CO2 centrifugal compressor flow characteristics was reviewed from four aspects: experiment, one-dimensional flow analysis, three-dimensional flow characteristics, and flow control. Researchers learned from the experimental studies of the S-CO2 centrifugal compressor that the special thermophysical properties of S-CO2, particularly their dramatic change near the critical point, brought great challenges to the design and stable operation of this compressor. Therefore, the problems of compressor flow caused by the drastic physical properties change near the critical point of the working medium, and the related research contents were emphatically expounded. The current research on one-dimensional flow analysis of the S-CO2 centrifugal compressor is mainly conducted by the one-dimensional mean streamline method considering the special thermophysical properties of S-CO2 fluid. The preliminary aerodynamic design of the S-CO2 centrifugal compressor was conducted using one-dimensional flow analysis. This method is limited by its prediction accuracy under off-design conditions. In addition, the flow details inside the compressor could not be obtained by this method. To reveal the flow mechanism of the S-CO2 centrifugal compressor, its three-dimensional flow characteristics must be deeply understood, and its internal flow field information must be obtained. The research on the three-dimensional flow characteristics of the S-CO2 centrifugal compressor was mostly conducted by the computational fluid dynamics (CFD) numerical simulation method, which can be used to obtain the flow field of the centrifugal compressor and present the relevant flow phenomenon. Because of the drastic variations in the thermophysical properties of S-CO2 fluid near the critical point, special consideration was taken in the process of the CFD simulation of the flow inside the centrifugal compressor. By applying CFD to S-CO2 centrifugal compressor three-dimensional flow characteristics, researchers found that this special thermal physical property also brought special flow phenomena inside the flow domain of the S-CO2 centrifugal compressor. The research on S-CO2 centrifugal compressor three-dimensional flow characteristics mainly focused on its steady flow and needs to further reveal deeply and comprehensively the flow mechanism of the S-CO2 centrifugal compressor under various unsteady working conditions. The flow control of the S-CO2 centrifugal compressor was mainly by the passive flow control method using the relevant control method of the air compressor for reference, and its effect was remarkable. As for the active flow control method, few studies have heeded its effect on the S-CO2 centrifugal compressor. [Conclusions and Prospects] In this paper, the flow characteristics of the S-CO2 centrifugal compressor are summarized, and their research prospects are proposed. These flow characteristics are considerably different from those of centrifugal compressors with conventional fluids, mainly because of the special physical properties of S-CO2 fluid. In the future, more advanced research methods are expected to be used, such as visual flow experiments, one-dimensional flow analysis incorporating machine learning algorithms, and active flow control, to conduct more in-depth and comprehensive studies of S-CO2 compressor flow characteristics.
  • BIG DATA
    XING Yujie, WANG Xiao, SHI Chuan, HUANG Hai, CUI Peng
    Journal of Tsinghua University(Science and Technology). 2024, 64(1): 13-24. https://doi.org/10.16511/j.cnki.qhdxxb.2024.21.002
    Abstract (1092) PDF (482) HTML (15)   Knowledge map   Save CSCD(1)
    [Objective] Many recent studies have indicated that graph neural networks exhibit a lack of robustness when facing adversarial attacks involving perturbations in both graph structures and node features, and the subsequent predictions of these networks may become unreliable under such circumstances. This issue affects graph contrastive learning methods similarly. However, the existing evaluation of robustness methods is often entangled with attack algorithms, data labels, and downstream tasks, which are best avoided, especially within the self-supervised setup of graph contrastive learning. Therefore, this paper introduces a robustness verification algorithm for graph contrastive learning to assess the robustness of graph convolutional networks against node feature adversarial attacks.[Methods] To begin with, considering the nature of positive and negative pairs found in graph contrastive learning models, this paper defines the robustness verification problem of graph contrastive learning as a similarity comparison between adversarial samples and the target node along with its negative samples. This problem is then expressed as a dynamic programming problem, which avoids dependency on attack algorithms, data labels, and downstream tasks. To address this dynamic programming problem, a series of novel and effective methods are proposed in this paper. For the binary attributes commonly used in graph data, corresponding perturbation spaces are therefore constructed here. Considering the challenge posed by a large negative sample space in graph contrastive learning, a negative sample sampling strategy is designed to improve the efficiency of problem-solving. In cases where binary discrete attributes and nonlinear activation functions render the dynamic programming problem difficult to address, this paper employs relaxation techniques and uses dual problem optimization methods to further improve the solution's efficiency.[Results] To assess the effectiveness of the proposed graph contrastive learning robustness verification algorithm, we conducted experiments using the classic GRACE model on the Cora and CiteSeer datasets. Employing the robustness verification algorithm introduced for graph contrastive learning, we evaluated its robustness. As the perturbation intensity increased, the proportion of nodes that were verified as robust decreased rapidly, and the proportion of nodes that were verified as non-robust increased significantly. Simultaneously, the proportion of unverifiable nodes remained at a lower level. These observations show the effectiveness of the proposed framework for verifying the robustness of graph contrastive learning. Additionally, the experiments revealed that the robustness of the contrastive learning model ARIEL, designed against specific attack algorithms, lacks generalizability and exhibits poor verifiable robustness performance, suggesting its vulnerability to other attack algorithms. Besides, ablation experiments identified the adversarial attack components of ARIEL as the main reason for its diminished verifiable robustness. Lastly, parameter experiments demonstrated the reasonability of the proposed negative sample sampling strategy. The results showed that sampling 20 negative samples is sufficient to achieve a favorable performance of our robustness verification algorithm with high efficiency.[Conclusions] Through the analysis of our methods and experimental results, the graph contrastive learning robustness verification algorithm proposed in this study not only eliminates dependency on attack algorithms, data labels, and downstream tasks but also presents a more comprehensive measurement compared to traditional robustness metrics. It can verify robustness in multiple directions, thereby boosting the development of comprehensively robust graph contrastive learning algorithms.
  • AEROSPACE ENGINEERING
    YAN Huihui, LI Haoyu, ZHOU Bohao, ZHANG Yuzhou, LAN Xudong
    Journal of Tsinghua University(Science and Technology). 2023, 63(10): 1672-1685. https://doi.org/10.16511/j.cnki.qhdxxb.2022.25.023
    Abstract (1083) PDF (258) HTML (4)   Knowledge map   Save CSCD(4)
    [Objective] As the core component of an aeroengine, a compressor significantly affects the flow and power of the engine. Compared with the axial compressor, the centrifugal compressor is characterized by structural simplicity, manufacturing convenience, and high single-stage pressure ratio. Therefore, the compressor is highly suitable for turboshaft engines with low flow rates and low total pressure ratios. However, the piston engine plays a more important role in the market. Accelerating the research on centrifugal compressors used in small turboshaft engines is essential.[Methods] The design methods currently used in this project include experimentation, theoretical analysis, and numerical simulation. The numerical simulation method can eliminate the requirements of experimentation, overcome measurement difficulties, and eliminate the costs associated with the experiment process. Therefore, it is a relatively accurate and efficient method for flow and transfer analysis. In this paper, according to the theory of numerical simulation, the impeller and diffuser of the centrifugal compressor are designed under specified working conditions. A three-dimensional numerical simulation of the centrifugal compressor is conducted. The influence of typical parameters on the centrifugal compressors is studied, and the parameters of the preliminary design model are optimized to obtain the ideal model of the centrifugal compressor under the design conditions.[Results] The results of this study were obtained according to the static pressure distribution cloud map and the total pressure distribution cloud map of the meridional channel surface at the highest efficiency of the centrifugal compressor and design speed conditions. The efficiency of the optimized centrifugal compressor was 0.831; the corresponding pressure ratios was 8.771, which was 3.68% higher than that of the preliminary design; and the working margin was 18.44%, which was 4.79% higher than that of the preliminary design centrifugal compressor.[Conclusions] Through the numerical simulation results of an Eckardt impeller and comparison of the simulation with reference experimentation results, the reliability of the numerical simulation of a centrifugal compressor by FINE/Turbo is proved. The results demonstrate that the kinetic energy of the gas at the impeller outlet of the centrifugal compressor is basically transformed into pressure energy and that the supercharging effect is relatively good. The entropy increase mainly occurs at the tip clearance, where the leakage flow is relatively critical. The static pressure distribution of the B2B (blade to blade) section is compared with that of the meridional flow channel. The meridional section is a contraction channel along the flow direction caused by the large turning angle of the hub. Owing to the effect of centrifugal force, a low-speed zone is developed in the flow channel to form a separation zone and result in energy loss. The separation area can be reduced through the reduction of the inlet flow angle to improve the overall performance of the compressor. The research shows that properly reducing the inlet hub ratio and the inlet angle of the impeller blade root and reasonably selecting the blade tip clearance value and the relative width of the impeller outlet are beneficial to improving the efficiency and pressure ratio of the compressor.
  • Safety Science
    Siyuan MU, Quanyi LIU, Ruxuan YANG, Yi LIU, Rui YANG
    Journal of Tsinghua University(Science and Technology). 2025, 65(7): 1368-1376. https://doi.org/10.16511/j.cnki.qhdxxb.2025.22.001
    Abstract (1083) PDF (451) HTML (715)   Knowledge map   Save CSCD(2)

    Objective: Due to the high flammability of nonflame-retardant pure acrylonitrile-butadiene-styrene (ABS), a material often used for passenger luggage, it is easily ignited by open flames, posing risks to aviation operations. Therefore, in-depth research on the pyrolytic combustion characteristics of ABS at high temperatures and high radiation intensities is crucial for the safe operation of aircraft. Methods: This study evaluated the thermal stability and combustion characteristics of ABS under different heating rates and radiation intensity conditions using thermogravimetric analysis and cone calorimeter systems. This study also analyzed the variations in the characteristic parameters of ABS. Results: The results show that the pyrolysis process of ABS can be divided into an initial volatilization stage, a rapid decomposition stage, a residual combustion stage, and a pyrolysis termination stage. In the rapid decomposition stage, when ABS reaches temperatures of approximately 310 ℃ to 343 ℃, the main polymer chains of ABS undergo cleavage, breaking down into different components, such as acrylonitrile and polyethylene monomers, leading to the decomposition of polymer molecules. When heated, the main chain of ABS ruptures. The molecular structure of ABS contains different components, such as styrene and butadiene, which are prone to decomposition and cross-linking reactions upon heating, resulting in the occurrence of the pyrolysis process. An increase in heating rate significantly shortens the pyrolysis time and enhances the maximum thermal decomposition rate. As the radiation intensity increases, the combustion process of ABS accelerates, with the heat release rate increasing and the peak heat release rate increasing by 53%. The combustion and ignition times decrease by 32% and 78%, respectively, because of the increase in material temperature and the exacerbation of heat conduction and convection phenomena leading to an increase in heat release rate. Under low radiation intensities, ABS cannot rapidly absorb energy to reach combustion conditions. However, as the radiation intensity increases, ABS can rapidly absorb sufficient energy for faster decomposition, thus shortening the combustion time. The generation time of carbon monoxide (CO) and carbon dioxide (CO2) is enhanced, and the maximum generation amounts of CO2 and CO increase by 49% and 74%, respectively. The oxygen consumption increases and the oxygen consumption rate accelerates due to the intensified molecular motion caused by thermal radiation, leading to a faster reaction with oxygen in the air. The mass loss time is enhanced, the remaining sample mass decreases, and the maximum mass loss rate increases by 53.8%. Based on the thermal penetration model, 2 mm thick ABS material is classified as a thermally thin material, and verification is conducted. Based on the ignition time model, a critical radiative heat flux formula is established, and the critical radiative heat flux is calculated to be 16.255 kW/m2. Finally, according to the fire performance indicators, as the radiation intensity increases, the material combustion rate increases, releasing higher amounts of heat, leading to faster fire growth and development, thereby increasing fire risk. The fire risk of ABS is positively correlated with the radiation intensity. Conclusions: This study concludes that ABS exhibits a high fire risk. This research provides crucial data and practical references on the fire risks associated with ABS material for safe aviation operations.

  • SPECIAL SECTION: BIG DATA
    LI Jiayi, HUANG Ruizhang, CHEN Yanping, LIN Chuan, QIN Yongbin
    Journal of Tsinghua University(Science and Technology). 2024, 64(12): 2007-2018. https://doi.org/10.16511/j.cnki.qhdxxb.2024.21.028
    Abstract (1073) PDF (348) HTML (8)   Knowledge map   Save CSCD(4)
    [Objective] The increasing maturity of large language model technology has facilitated its widespread application in downstream tasks across various vertical fields. Large language models have exhibited beneficial performance in text summarization tasks in general fields, such as news and art. However, the highly specific language style in the judicial field and the unique complexity of judicial documents in terms of structure and logic make it difficult for large language models to generate judicial document summaries. This study aims to combine prompt learning with large language models to explore their performance in summarizing judicial documents. Prompt templates containing structural information and judicial documents are used as inputs for fine-tuning large language models. As a result, large language models can generate judicial document summaries that adhere to judicial language styles and the structural and logical complexities of judicial documents. [Methods] This study proposes a judicial document summary method that combines prompt learning and the Qwen large language model. Judicial document data are used as the input for fine-tuning a large language model using supervised fine-tuning technology to enhance its applicability in the judicial field. Simultaneously, prompt templates that incorporate structural information and role instructions are designed to optimize summary generation to more accurately reflect the structural characteristics and logical relationships of documents. According to the characteristics of the pretraining data format of the large language model, the fine-tuning data were constructed in the form of question-answer pairs. [Results] The experimental results show that the proposed method improves the F1 of the baseline model by 21.44%, 28.50%, and 28.97% in ROUGE-1, ROUGE-2, and ROUGE-L, respectively, and exceeds all of the comparison models. The ablation experiment demonstrated that the summary generation method using prompt learning was superior to the method without prompt learning for all indicators, and the performance of summarization generated by the large language model utilizing prompt learning was significantly enhanced. The case demonstration reveals that after prompt learning is used to enhance the perception of structural information in the judgment document by the large language model, the judgment document summary generated by this model can better capture and retain key information in the judgment document. Moreover, the language style of this model is closer to that of a real judgment document summary, which further illustrates the effectiveness of the proposed method. [Conclusions] This study integrates the structural information of a judgment document into the task of generating a judgment document summary using a large language model in the form of prompt templates. Prompt templates containing structural information are used to assist the large language model in summarization generation. Therefore, the model can focus on the key information in the judgment document and capture deeper semantic logical relationships. The results demonstrate that after fine-tuning the large language model with judicial document data and introducing structural information, the model demonstrated excellent performance and great application potential in the judicial document summary task. The proposed method can effectively enhance the capability of a large language model in the field of judicial document summaries.
  • HYDRAULIC ENGINEERING
    WANG Zhongjing, YU Suyue, XU Xing
    Journal of Tsinghua University(Science and Technology). 2024, 64(2): 303-317. https://doi.org/10.16511/j.cnki.qhdxxb.2023.21.021
    Abstract (1057) PDF (228) HTML (6)   Knowledge map   Save CSCD(6)
    [Objective] The research on soil salinization is complicated, and the traditional literature review method struggles to grasp the development trend systematically due to its subjective nature. Hence, it becomes important and necessary to seek alternative methods to objectively summarize and analyze the existing research papers and reasonably guide the future development of this field. [Methods] Based on the quantitative analysis of the Web of Science and China's national knowledge network databases related to soil salinization and saline-alkali land management and its utilization in the past 30 years, this paper proposes a quantitative review method for obtaining the research trend in this subject. This paper uses various software tools, including VOSviewer, Citespace, and SPSS, to analyze the number of publications, cooperation networks, and keywords within this field. [Results] The results show a continuous increase in the research on soil salinization at home and abroad. The number of scholars participating in the study of soil salinization has also increased significantly. The primary stage of development was before 1999, the stage of stable development was from 2000 to 2011, and the stage of rapid development was from 2012 to the present. Despite significant progress, according to Kuhn's model, the field remains in the primary science stage, indicating ample room for development. English journals such as Agricultural Water Management and Science of the Total Environment and Chinese journals such as Soil Bulletin and Soil can be regarded as core journals in the field of soil salinization, with the highest number of publications and higher journal impact factors. China, the United States, India, Australia, and other countries (in order of the number of papers published by them) have made outstanding contributions to soil salinization research, with Chinese scholars leading in terms of the highest number of published papers and are the main force in the study of soil salinization. The cooperation network analysis shows the importance of research institutions and direct government agencies in promoting institutional cooperation. However, at present, most cooperations are limited to intra-institutional cooperation, but future efforts should focus on the positive impact of cross-context, cross-institutional, transnational, and interdisciplinary cooperations on leapfrog and diversified development of soil salinization research. Keyword burst detection shows that "biochar", "yield", "salt stress", "quality", "freeze-thaw cycle" and "water and salt transport" are the recent hot spots of concern. Additionally, keyword co-occurrence and trend analyses show the shift in research focus from irrigation and drainage and saline-alkali land improvement in the 1990s to soil-plant salt interaction mechanism, salt-tolerant plant cultivation, soil water and salt regulation mechanism, optimization control technology, research and development technology of saline-alkali soil amendment, large-scale applications, remote sensing monitoring of saline-alkali land, and salinization impact assessment. It represents the developmental trend of research on soil salinization and saline-alkali land management and its utilization from drainage improvement to comprehensive utilization. [Conclusions] The research results of this paper quantitatively highlight the research hotspot and developmental trend of soil salinization and provide a reference for relevant researchers to grasp the developmental trends of the field and explore valuable new research directions.
  • ELECTRONIC ENGINEERING
    CHEN Tianyuan, ZHOU Yuying, GAO An
    Journal of Tsinghua University(Science and Technology). 2023, 63(12): 2057-2075. https://doi.org/10.16511/j.cnki.qhdxxb.2023.25.034
    Abstract (1036) PDF (337) HTML (1)   Knowledge map   Save CSCD(1)
    [Objective] Overlay targets with a small range and requiring extremely high measurement accuracy are used in the lithography system's alignment, exposure, and measurement processes. They are inevitably affected by many errors when performing specialized functions, e.g., line width and design difference, line edge roughness, and target edge effect. This paper conducts a simulation study on the micro diffraction-based overlay target (μDBO) in the condition of wafer stage overlay (WSO), which is commonly used in lithography, based on the design of overlay alignment targets in the field of measurement. Litho-target design simulation software is known to be more advanced than lithographic imaging simulation software, but its license is usually rarer and more expensive. We propose a novel method for simulating lithography target metrology results using lithography imaging simulation software. The method predicts the detected light intensity distribution in the experiment qualitatively and can calculate target performance in metrology.[Methods] This paper compares the similarities between metrology process imaging in the optical method and lithography imaging. In the metrology process imaging simulation, the target, lens, and imaging sensor modules have analogs in the lithography simulation, which are the mask, lens, and aerial image modules. Thus, metrology target patterns can be represented as mask patterns, and the output of an aerial image from lithography simulation software can be analyzed to obtain metrology information. We use WSO-μDBO targets, which have two different critical dimensions and suffer from a heavy marginal effect in experiments. The self-made DrM software in Matlab code with the rigorous couple wave analysis (RCWA) algorithm and the commercial program HyperLith with the finite-difference time-domain algorithm are used as tools to restore the phenomenon in the experiment. Both programs import the illumination patterns of the experimental instruments as well as the structures of WSO-μDBO targets. The Abbe imaging principle in DrM and the Hopkins approximation in HyperLith are used in the simulations. The pupil imaging simulation is applied to analyze the marginal effect on the original targets. In this simulation study, four key performance indicators (KPI) of WSO-μDBO performance are selected as evaluation indices.[Results] The simulation of WSO-μDBO targets showed that:(1) The special phenomenon of bright and dark lines in the experiment can be reproduced in simulation using both tools and algorithms. (2) In the simulation, this method can provide calculated KPI of μDBO targets in simulation. (3) The aerial image generated by this method was closed between both tools but with a relative error of 1% to 5%, resulting in a discrepancy of around 1 nm between the simulated overlay values. (4) This work presented a novel design of WSO-μDBO targets (Edge, Windmill, and Hybrid) with a relative improvement in simulated stack sensitivity(SS) of 202.6% over the original design. As a result, the simulated metrology error of the target was reduced by 50.9% to 1.3%.[Conclusions] The feasibility of our simulation method is verified by comparing simulated and experimental WSO-μDBO images, which can serve as a new simulation research platform for studying metrology targets. This method is also simple and easy to implement, and it has the potential to reduce the software cost investment in marking design during the production process.
  • CONSTRUCTION MANAGEMENT
    ZHANG Zhitian, WANG Yuanyuan, LUO Zhub, GUO Ziyang, GUO Hongling
    Journal of Tsinghua University(Science and Technology). 2024, 64(2): 198-204. https://doi.org/10.16511/j.cnki.qhdxxb.2023.22.047
    Abstract (1018) PDF (376) HTML (2)   Knowledge map   Save CSCD(2)
    [Objective] Tower crane operations are characterized by long durations, extensive moving scopes, heavy loads, and complex spatial interactions with workers. These factors often contribute to construction accidents. Furthermore, construction workers standing under crane hooks and their lifting objects during the lifting process pose high safety risks, often encountering accidents such as collisions and object falling. Information technology plays a crucial role in enhancing tower crane monitoring and reducing workers' safety risks. Although existing studies on tower crane monitoring have made considerable advancements, they primarily focus on the operating state of cranes and overlook safety issues arising from interactions between cranes and workers. This study aims to employ the schedule information extracted from building information modeling (BIM) and computer vision and sensing technologies to propose an automatic hazard detection method for detecting dangerous scenarios during the lifting process in tower cranes. [Methods] This study develops an automatic detection framework for identifying hazardous scenarios involving spatial interaction between tower cranes and workers. This framework comprises four components. (1) Equipment installation and network environment establishment:cameras are installed at elevated positions to monitor the spatial locations of workers under the operating plane of a tower crane in real time. Furthermore, various sensors and cameras are fixed beneath the crane's trolley and cab to collect data regarding its operating status. A local area network is set up on the site to facilitate instantaneous data transmission. (2) Collection of tower crane operating data:the exact spatial location of the crane's hook is calculated using arm tracking and spatial trigonometric relations to determine its operating status. (3) Collection of workers' operational status data:advanced image recognition techniques are used to identify workers' positions, which are then converted into three-dimensional spatial coordinates through coordinate transformation. (4) Spatial relationship analysis and identification:precise spatial mapping of the tower crane's operating status and workers' positions is obtained using a unified BIM, followed by automatic detection according to predefined hazard assessment rules. [Results] The effectiveness and feasibility of the proposed method are validated by implanting it during a one-month real construction project. The analysis of data collected for 15 days reveals that the number of hazardous scenarios fluctuates considerably, peaking 523 times and plunging 35 times. These fluctuations correlate strongly with the number of workers on site, verifying the reliability of the proposed method and highlighting the need for intelligent hazardous scenario detection. Moreover, the results show that construction workers generally lack adequate awareness of the safety implications of tower crane trajectories. [Conclusions] This study successfully integrates BIM, sensing, and computer vision technologies to develop an automatic hazard detection method that focuses on the spatial interaction between tower cranes and workers. The proposed method enhances the timeliness and accuracy of hazard detection and provides innovative perspectives and technical support for construction site safety management. However, this study has certain limitations, such as data interferences caused by minor vibrations during tower crane operations to be further mitigated using noise reduction techniques in future research.
  • Liang JIANG, Yuan WU, Yongshun ZHANG, Jiaxin ZHENG, Yushan CHEN, Xia ZHONG, Liao ZHOU, Yuting WEI, Lei CHEN, Linmao QIAN
    Journal of Tsinghua University(Science and Technology). 2025, 65(2): 215-232. https://doi.org/10.16511/j.cnki.qhdxxb.2025.21.010
    Abstract (1017) PDF (250) HTML (602)   Knowledge map   Save CSCD(1)

    Significance: This review highlights the progress and challenges in chip atomic layer polishing. Chips are fundamental to the modern information society. According to Moore's Law, the chip feature size is shrinking and approaching the physical limit. At the same time, advanced packaging technologies such as hybrid bonding continuously evolve. These create pressing needs to develop atomic layer polishing, a technique that enables extremely precise material removal at the atomic layer level, to achieve surfaces with atomic-level precision for demanding processes such as photolithography and bonding. Currently, chemical mechanical polishing (CMP) is the only key technology in chip manufacturing capable of simultaneously achieving local and global planarization of the wafer surface, with the potential to realize atomic layer polishing. This review provides a systematic summary of the mechanisms and processes of CMP for chip substrate surfaces and interconnect heterogeneous surfaces. Progress: Significant progress has been made in the controlled removal with a single atomic layer precision at the microscopic level and in the CMP with surface roughness close to the theoretical limit at the macroscopic level for the monocrystalline silicon substrate. These advances highlight the extreme precision processing capability of CMP for the wafer surface. Furthermore, ongoing developments in multi-field assisted CMP and energy particle beam polishing hold promise for enabling atomic layer polishing for new substrates like GaN, SiC and diamond. In the case of interconnect heterogeneous surfaces, two material removal modes in CMP are summarized from a tribological perspective based on the interactions between the abrasive and material surfaces: mechanical plowing and chemical bonding. Copper, cobalt, and nickel are mainly removed through the mechanical plowing mode, while tantalum, ruthenium, and titanium are mainly removed through chemical bonding. According to this foundation, control principles and methods for achieving equivalent removal of heterogeneous surfaces are proposed based on different material removal modes. In the mechanical plowing material removal mode, corrosion and its impact on the mechanical strength of the material surface can be adjusted through the modulation of the effects of oxidation, complexation, and corrosion inhibition, as well as their synergistic effects. This approach allows for controlling the material removal rate (MRR). In the chemical bonding material removal mode, the number of reactive sites and their influence on interfacial chemical bonds can be regulated through the adjustment of pH, oxidation, and ionic strength, along with their synergistic effects, thus controlling the MRR. According to these control principles, a systematic summary of the planarization processes for interconnect heterogeneous surfaces, such as copper/tantalum, copper/cobalt, and copper/ruthenium, is provided. Finally, based on existing research progress, it is proposed to leverage the synergistic effects of mechanical, chemical, and electrical/optical/plasma/energy beams to confine chemical reactions and mechanical-chemical reactions to the surface atomic layer, to achieve atomic layer polishing. Specifically, for the mechanical plowing material removal mode, the focus is on designing the molecular structures of chemical additives to precisely modulate the effects of oxidation, complexation, and corrosion inhibition. This approach confines the corrosion behavior to the outermost atomic layer while controlling the mechanical action of the abrasive to enable precise, controllable atomic layer removal. For the chemical bonding material removal mode, the investigation focuses on confining chemical bonding reactions to the outermost atomic layer, weakening back bonds, and simultaneously controlling the mechanical action of the abrasive to disrupt chemical bonds between the outermost and sub-surface atoms, thus achieving controlled atomic layer removal. Conclusions and Prospects: This review highlights the growing demand for atomic-level manufacturing of high-end chips and the development of atomic layer polishing. It provides a systematic summary of the mechanisms, progress, and challenges in atomic layer polishing, with the aim of offering critical theoretical and technical support for the atomic-level manufacturing of advanced chips. The findings from this research have potential applications in key areas such as high-end optical components and superlubricity devices.

  • ENVIRONMENTAL SCIENCE AND ENGINEERING
    LI Xinyang, ZHU Xiaoshan, TAO Yi
    Journal of Tsinghua University(Science and Technology). 2023, 63(12): 2042-2056. https://doi.org/10.16511/j.cnki.qhdxxb.2023.21.006
    Abstract (1002) PDF (304) HTML (0)   Knowledge map   Save
    [Significance] Marine environmental pollution has become a globally concerning environmental issue, which has attracted the great attention of governments and scientists in coastal countries. The release of large quantities of pollutants into the oceans has inevitable lasting effects and harm to marine life and can even bring about irreversible changes leading to the degradation or deterioration of the ecosystem. However, marine organisms under pollution stress do not always await their doom. Considerable evidence suggests that marine organisms could respond to pollution stress at the individual, population, and community levels, leading to molecular-level to ecosystem-scale effects and eventually reaching either adaptation/coexistence or degradation/death, with dynamic processes of interactions and changeable evolutionary outcomes between the two.[Progress] In general, organisms can adapt to complex environments in three mechanisms, namely, behavioral change, phenotypic alteration, and genetic evolution. The initial response to environmental stress from pollution is generally behavioral (such as escape or migration to favorable habitats or vigilance). However, the continuous degradation of the environment makes migration more difficult, and some sedentary organisms (e.g., corals) can hardly move once immobilized, forcing the organisms to immediately react in situ. Altering the phenotype appears to be the best solution. This rapid nongenetic mechanism is based on the ability of individual genotypes to produce different phenotypes in response to the environment, which allows marine organisms to adapt and survive in the polluted marine environment. However, such phenotypic adjustments can be highly variable in the life cycle within a generation or even across generations. Phenotypic plasticity within a generation may play an important role in survival through rapid environmental change. In marine pollution, organisms may alter their macro or micromorphology and sex specificity or adjust the transcriptome characteristics and metabolic pathway expression of different organs, which play a detoxification-oriented role, within a generation for self-preservation. Although plasticity is usually shown under environmental conditions experienced by the parental generation, these conditions can also affect their offspring from one to multiple generations. That is, populations can adjust their phenotypes within several generations, which is called transgenerational phenotypic plasticity. Environmental pollution persists across generations for most species, and these organisms may evolve through transgenerational phenotypic plasticity to fight against environmental pollution. This may help in understanding the effects of pollution on marine organisms. Accordingly, supposing that plasticity works for the adaptation of organisms, its primary role is likely to buffer the cost of evolutionary mismatches and facilitate genetic evolution by "gaining time". Consequently, the phenotypes could be more adaptive to the current conditions, and these genetically based adaptations would continue to evolve until completion.[Conclusions and Prospects] This review has done comprehensive literature research, collected various scenarios, and summarized the laws of the short-term response and long-term adaptation of marine organisms under pollution stress based on the viewpoint of evolutionary ecology and relevant principles in pollution ecology. From the perspective of behavior, adaptation, and evolution, this review preliminarily discussed the significance of marine pollution evolutionary ecology and attempted to summarize and explore the interactions and connections between pollution and organisms in the marine environment, providing new insights for the protection of the marine environment and the development of marine sciences.