Considering both the high complexity of urban traffic flow systems and the bounded rationality of travelers,providing traffic information to all travelers is an effective method to induce each individual to make a mor...Considering both the high complexity of urban traffic flow systems and the bounded rationality of travelers,providing traffic information to all travelers is an effective method to induce each individual to make a more rational route-choice decision.Within Advanced Traveler Information System(ATIS)working environment,temporal and spatial evolution processes of traffic flow in urban road networks are closely related to strategies of providing traffic information and contents of information.In view of the day-to-day route-choice situations,this study constructs original updating models of the cognitive travel time of travelers under four conditions,including not providing any route travel time,only providing the most rapid route travel time,only providing the most congested route travel time,and providing all the routes travel times.The disaggregate route-choice approach is adopted for simulation to reveal the relationship between the evolution process of network traffic flow and the strategy of providing traffic information.The simulation shows that providing traffic information to all travelers cannot improve the operational efficiency of road networks.It is noteworthy that an inappropriate information feedback strategy would lead to intense variation in various routes traffic flow.Compared with incomplete information feedback strategies,it is inefficient and superfluous to provide complete traffic information to all travelers.展开更多
The Wenchuan earthquake that occurred on 12 May 2008 induced numerous landslides.Loose landslide materials were deposited on hillslopes,and deep channels were easily remobilized and transformed into debris flows by ex...The Wenchuan earthquake that occurred on 12 May 2008 induced numerous landslides.Loose landslide materials were deposited on hillslopes,and deep channels were easily remobilized and transformed into debris flows by extreme rainstorms.Twelve years after the Wenchuan earthquake,debris flows were still active in the Qipangou Ravine in the quake-hit area.In this paper,we continuously tracked the spatiotemporal evolution of the landslides and vegetation restoration and evaluated the evolution of debris flow activity in the Qipan catchment with the aid of a GIS platform and field investigations from 2008 to 2019.We observed that the area with active landslides increased sharply immediately following the earthquake,and then decreased with time;however,the total area of landslides continued to increase from 6.93 km^(2)in 2008 to 10.55 km^(2)in 2019.The active landslides shifted towards lower angles and higher elevations after 2013.Since 2009,the vegetation coverage has been gradually increasing and approaching the coverage present before the earthquake as of 2019.The landslide activity was high and the vegetation recovery rates were rapidly rising during the first five years after the earthquake;the recovery rates then slowed over time.Therefore,we divided the evolution that occurred during the post landslide period into an active period(2008-2013),a self-adjustment period(2013-2026)and a stable period(after 2026).We then proposed a quantitative model to determine the trends of landslide activity rates and NDVI values in the catchment,which indicated that the landslide activities and postseismic vegetation restoration rates in this catchment will return to preseismic levels within approximately two decades.We also analysed the runout volumes of the debris flows after the earthquakes(Diexi and Wenchuan)and the standard deviation of the vegetation coverage and predicted that the debris flow activities will last for an additional 50 years or more.展开更多
The Liwan Sag, with an area of 4 000 km-2, is one of the deepwater sags in the Zhujiang River（Pearl River） Mouth Basin, northern South China Sea. Inspired by the exploration success in oil and gas resources in the d...The Liwan Sag, with an area of 4 000 km-2, is one of the deepwater sags in the Zhujiang River（Pearl River） Mouth Basin, northern South China Sea. Inspired by the exploration success in oil and gas resources in the deepwater sags worldwide, we conducted the thermal modeling to investigate the tectono-thermal history of the Liwan Sag,which has been widely thought to be important to understand tectonic activities as well as hydrocarbon potential of a basin. Using the multi-stage finite stretching model, the tectonic subsidence history and the thermal history have been obtained for 12 artificial wells, which were constructed on basis of one seismic profile newly acquired in the study area. Two stages of rifting during the time periods of 49–33.9 Ma and 33.9–23 Ma can be recognized from the tectonic subsidence pattern, and there are two phases of heating processes corresponding to the rifting.The reconstructed average basal paleo-heat flow values at the end of the rifting events are -70.5 and -94.2 mW/m^2 respectively. Following the heating periods, the study area has undergone a persistent thermal attenuation phase since 23 Ma and the basal heat flow cooled down to -71.8–82.5 mW/m^2 at present.展开更多
Current transient analysis predominantly relies on zero-dimensional/one-dimensional tools,proficient at capturing aerothermodynamic variations across critical engine stations but insufficient for analyzing the interna...Current transient analysis predominantly relies on zero-dimensional/one-dimensional tools,proficient at capturing aerothermodynamic variations across critical engine stations but insufficient for analyzing the internal flow field evolution during transients.Addressing this gap,the study presents an enhanced quasi-three dimensional(quasi-3D)transient simulation technique that integrates component volume effects,offering a significant leap from the preceding quasi-3D transient simulation method based on quasi-steady assumption.By embedding the component volume effects on density,momentum,and energy within the physical temporal dimension of the Navier-Stokes equations,the refined quasi-3D transient model achieves a closer representation of physical phenomena.Validation against a single-shaft turbofan engine’s experimental data confirms the model’s accuracy.Average errors for key performance indicators,including shaft speed,thrust,mass flow rate,and critical component exit temperature and pressure,remain below 0.41%,5.69%,2.55%,3.18%and 0.67%,respectively.Crucially,the model exposes a discernible temporal lag in the compressor outlet pressure and temperature response due to volume effects—previously unquantified in quasi-3D transient simulations.And further exploration of the meridional flow field emphasizes the consequential role of volumes in transient flow field evolution.Incorporating volume effects within quasi-3D transient simulations enhances engine modeling and is pivotal for precise transient analysis in engine design and optimization.展开更多
Using Time History of Events and Macroscale Interactions during Substorms （THEMIS） observations from 2007 to 2011 tail seasons, we study the plasma properties of high speed flows （HSFs） and background plasma sheet...Using Time History of Events and Macroscale Interactions during Substorms （THEMIS） observations from 2007 to 2011 tail seasons, we study the plasma properties of high speed flows （HSFs） and background plasma sheet events （BPSs） in Earth＇s magnetotail （｜YGsM｜〈13RE, ｜ZGsM｜〈5RE, -30RE〈XrsM〈-6RE）, and their correlations with solar wind parameters. Statistical results show that the closer the HSFs and BPSs are to the Earth, the hotter they become, and the temperature increase of HSFs is larger than that of BPSs. The density and temperature ratios between HSFs and BPSs are also larger when events are closer to Earth. We also find that the best correlations between the HSFs （BPSs） density and the solar wind density occur when the solar wind density is averaged 2 （3.5） hours prior to the onset of HSFs （BPSs）. The normalized densities of both HSFs and BPSs are correlated with the interplanetary magnetic field （IMF） 0 angles （ 0 = arctan（Bz √Bx^2＋y^2 ） which are averaged 3 hours before the observation time. Further analysis indicates that both HSFs and BPSs become denser during the northward IMF period.展开更多
Large-head variable-amplitude pump turbines(PTs) encounter serious transient hydraulic instability issues. To explore the evolution mechanisms of pressure fluctuations(PFs) and flow patterns inside large-head variable...Large-head variable-amplitude pump turbines(PTs) encounter serious transient hydraulic instability issues. To explore the evolution mechanisms of pressure fluctuations(PFs) and flow patterns inside large-head variable-amplitude PTs, the load rejection process(LRP) was investigated using a one-and three-dimensional coupled flow simulation approach. The temporal,spatial, and frequency characteristics of the fluctuating pressures were analyzed for four monitoring points using a combined time-frequency analysis approach. The results indicated that PFs during the LRP of large-head variable-amplitude PTs had a new fluctuation frequency component related to Dean vortices(DVs) in the volute, in addition to the common fluctuation frequency components related to rotor-stator interaction phenomena and local backflow vortices near the impeller inlet. The PF frequency component existed throughout the LRP and had a significant influence on the transient maximum pressure at the volute end. This study provides a useful theoretical guide for the design and optimization of large-head variable-amplitude PTs.展开更多
Crustal deformation shows different patterns at different depths due to changes in the physical properties of rock.Tectonic levels can be defined based on the geometry and deformation mechanisms of crustal deformation...Crustal deformation shows different patterns at different depths due to changes in the physical properties of rock.Tectonic levels can be defined based on the geometry and deformation mechanisms of crustal deformation patterns. Nujiang Gorge, with a high riverbed drop, great erosion depth, and strong deformation, has rock exposures at different tectonic levels and thus provides an ideal lab for deformation study. This paper takes the Nujiang Gorge from Chawalong to Fugong as the object to identify structural deformation patterns at different depths through field study and deformation analysis. At depth, the primary form of deformation is flow deformation, as shown on the outcrops at Maji. Ductile shear deformation can be found in many outcrops within the study region, e.g., the Gaoligong dextral shear zone and Puladi-Songta sinistral shear zone that lie to the south and north of Maji, respectively. Further to the north of Puladi, the dominated deformation pattern is similar fold and dense sub-vertical foliation. In addition, brittle faults, as evidence of shallow deformation, can be seen overprinting on the deeper deformation features all over the region. Based on those observations, this paper identifies four tectonic levels from depth to the surface: flow deformation, ductile shear deformation, similar fold, and brittle fault deformation, all of which result from the NEE-SWW compressive stress field. Further evidence from studies on the region′s thermal evolution and regional tectonics suggests that the development of different tectonic levels is closely linked to the discrepant uplift or denudation since the Miocene(~21 Ma).展开更多
基金the National Social Science Foundation of China(Grant No.14XGL011)the Humanity and Social Science Youth Foundation of Ministry of Education in China(Grant No.12YJC630200)+1 种基金the Natural Science Foundation of Gansu Province in China(Grant No.145RJZA190)the Social Science Planning Project of Gansu Province in China(Grant No.13YD066).
文摘Considering both the high complexity of urban traffic flow systems and the bounded rationality of travelers,providing traffic information to all travelers is an effective method to induce each individual to make a more rational route-choice decision.Within Advanced Traveler Information System(ATIS)working environment,temporal and spatial evolution processes of traffic flow in urban road networks are closely related to strategies of providing traffic information and contents of information.In view of the day-to-day route-choice situations,this study constructs original updating models of the cognitive travel time of travelers under four conditions,including not providing any route travel time,only providing the most rapid route travel time,only providing the most congested route travel time,and providing all the routes travel times.The disaggregate route-choice approach is adopted for simulation to reveal the relationship between the evolution process of network traffic flow and the strategy of providing traffic information.The simulation shows that providing traffic information to all travelers cannot improve the operational efficiency of road networks.It is noteworthy that an inappropriate information feedback strategy would lead to intense variation in various routes traffic flow.Compared with incomplete information feedback strategies,it is inefficient and superfluous to provide complete traffic information to all travelers.
基金supported by the National Key Research and Development Program of China(No.2017YFC1501004)the National Natural Science Foundation of China(No.41672299)。
文摘The Wenchuan earthquake that occurred on 12 May 2008 induced numerous landslides.Loose landslide materials were deposited on hillslopes,and deep channels were easily remobilized and transformed into debris flows by extreme rainstorms.Twelve years after the Wenchuan earthquake,debris flows were still active in the Qipangou Ravine in the quake-hit area.In this paper,we continuously tracked the spatiotemporal evolution of the landslides and vegetation restoration and evaluated the evolution of debris flow activity in the Qipan catchment with the aid of a GIS platform and field investigations from 2008 to 2019.We observed that the area with active landslides increased sharply immediately following the earthquake,and then decreased with time;however,the total area of landslides continued to increase from 6.93 km^(2)in 2008 to 10.55 km^(2)in 2019.The active landslides shifted towards lower angles and higher elevations after 2013.Since 2009,the vegetation coverage has been gradually increasing and approaching the coverage present before the earthquake as of 2019.The landslide activity was high and the vegetation recovery rates were rapidly rising during the first five years after the earthquake;the recovery rates then slowed over time.Therefore,we divided the evolution that occurred during the post landslide period into an active period(2008-2013),a self-adjustment period(2013-2026)and a stable period(after 2026).We then proposed a quantitative model to determine the trends of landslide activity rates and NDVI values in the catchment,which indicated that the landslide activities and postseismic vegetation restoration rates in this catchment will return to preseismic levels within approximately two decades.We also analysed the runout volumes of the debris flows after the earthquakes(Diexi and Wenchuan)and the standard deviation of the vegetation coverage and predicted that the debris flow activities will last for an additional 50 years or more.
基金The Program of the Key Technologies for Petroleum Exploration in Deep Oceanic Areas under contract No.2011ZX05025-006-05the Chinese Postdoc Fund,No.58 General Fund,2015 under contract No.2015M582636the National Natural Science Foundation of China under contract No.41602251
文摘The Liwan Sag, with an area of 4 000 km-2, is one of the deepwater sags in the Zhujiang River（Pearl River） Mouth Basin, northern South China Sea. Inspired by the exploration success in oil and gas resources in the deepwater sags worldwide, we conducted the thermal modeling to investigate the tectono-thermal history of the Liwan Sag,which has been widely thought to be important to understand tectonic activities as well as hydrocarbon potential of a basin. Using the multi-stage finite stretching model, the tectonic subsidence history and the thermal history have been obtained for 12 artificial wells, which were constructed on basis of one seismic profile newly acquired in the study area. Two stages of rifting during the time periods of 49–33.9 Ma and 33.9–23 Ma can be recognized from the tectonic subsidence pattern, and there are two phases of heating processes corresponding to the rifting.The reconstructed average basal paleo-heat flow values at the end of the rifting events are -70.5 and -94.2 mW/m^2 respectively. Following the heating periods, the study area has undergone a persistent thermal attenuation phase since 23 Ma and the basal heat flow cooled down to -71.8–82.5 mW/m^2 at present.
基金supported by the National Natural Science Foundation of China(No.52376021).
文摘Current transient analysis predominantly relies on zero-dimensional/one-dimensional tools,proficient at capturing aerothermodynamic variations across critical engine stations but insufficient for analyzing the internal flow field evolution during transients.Addressing this gap,the study presents an enhanced quasi-three dimensional(quasi-3D)transient simulation technique that integrates component volume effects,offering a significant leap from the preceding quasi-3D transient simulation method based on quasi-steady assumption.By embedding the component volume effects on density,momentum,and energy within the physical temporal dimension of the Navier-Stokes equations,the refined quasi-3D transient model achieves a closer representation of physical phenomena.Validation against a single-shaft turbofan engine’s experimental data confirms the model’s accuracy.Average errors for key performance indicators,including shaft speed,thrust,mass flow rate,and critical component exit temperature and pressure,remain below 0.41%,5.69%,2.55%,3.18%and 0.67%,respectively.Crucially,the model exposes a discernible temporal lag in the compressor outlet pressure and temperature response due to volume effects—previously unquantified in quasi-3D transient simulations.And further exploration of the meridional flow field emphasizes the consequential role of volumes in transient flow field evolution.Incorporating volume effects within quasi-3D transient simulations enhances engine modeling and is pivotal for precise transient analysis in engine design and optimization.
基金National Natural Science Foundation of China (Grant Nos. 41322031, 41031065 & 41574157)the Shandong Province Outstanding Young Scientist Award (Grant No. 2013BSE27132)+2 种基金the Research Fund for the Doctoral Program of Higher Education (Grant No. 20130131120073)the program for New Century Excellent Talents in University (Grant No. NCET-12-0332)State Key Laboratories of Space Weather
文摘Using Time History of Events and Macroscale Interactions during Substorms （THEMIS） observations from 2007 to 2011 tail seasons, we study the plasma properties of high speed flows （HSFs） and background plasma sheet events （BPSs） in Earth＇s magnetotail （｜YGsM｜〈13RE, ｜ZGsM｜〈5RE, -30RE〈XrsM〈-6RE）, and their correlations with solar wind parameters. Statistical results show that the closer the HSFs and BPSs are to the Earth, the hotter they become, and the temperature increase of HSFs is larger than that of BPSs. The density and temperature ratios between HSFs and BPSs are also larger when events are closer to Earth. We also find that the best correlations between the HSFs （BPSs） density and the solar wind density occur when the solar wind density is averaged 2 （3.5） hours prior to the onset of HSFs （BPSs）. The normalized densities of both HSFs and BPSs are correlated with the interplanetary magnetic field （IMF） 0 angles （ 0 = arctan（Bz √Bx^2＋y^2 ） which are averaged 3 hours before the observation time. Further analysis indicates that both HSFs and BPSs become denser during the northward IMF period.
基金supported by the National Natural Science Foundation of China(Grant Nos.52209108 and 52079034)Sichuan Science and Technology Program(Grant No.2023YFQ0021)+1 种基金the Natural Science Foundation of Heilongjiang Province,China(Grant No.LH2023E058)China Postdoctoral Science Foundation(Grant No.2022M720948)。
文摘Large-head variable-amplitude pump turbines(PTs) encounter serious transient hydraulic instability issues. To explore the evolution mechanisms of pressure fluctuations(PFs) and flow patterns inside large-head variable-amplitude PTs, the load rejection process(LRP) was investigated using a one-and three-dimensional coupled flow simulation approach. The temporal,spatial, and frequency characteristics of the fluctuating pressures were analyzed for four monitoring points using a combined time-frequency analysis approach. The results indicated that PFs during the LRP of large-head variable-amplitude PTs had a new fluctuation frequency component related to Dean vortices(DVs) in the volute, in addition to the common fluctuation frequency components related to rotor-stator interaction phenomena and local backflow vortices near the impeller inlet. The PF frequency component existed throughout the LRP and had a significant influence on the transient maximum pressure at the volute end. This study provides a useful theoretical guide for the design and optimization of large-head variable-amplitude PTs.
基金supported by the Project of the China Geological Survey (Grant No. 12120113013700)the Director Fund project of China Earthquake Disaster Prevention Center (Grant No. 201604)
文摘Crustal deformation shows different patterns at different depths due to changes in the physical properties of rock.Tectonic levels can be defined based on the geometry and deformation mechanisms of crustal deformation patterns. Nujiang Gorge, with a high riverbed drop, great erosion depth, and strong deformation, has rock exposures at different tectonic levels and thus provides an ideal lab for deformation study. This paper takes the Nujiang Gorge from Chawalong to Fugong as the object to identify structural deformation patterns at different depths through field study and deformation analysis. At depth, the primary form of deformation is flow deformation, as shown on the outcrops at Maji. Ductile shear deformation can be found in many outcrops within the study region, e.g., the Gaoligong dextral shear zone and Puladi-Songta sinistral shear zone that lie to the south and north of Maji, respectively. Further to the north of Puladi, the dominated deformation pattern is similar fold and dense sub-vertical foliation. In addition, brittle faults, as evidence of shallow deformation, can be seen overprinting on the deeper deformation features all over the region. Based on those observations, this paper identifies four tectonic levels from depth to the surface: flow deformation, ductile shear deformation, similar fold, and brittle fault deformation, all of which result from the NEE-SWW compressive stress field. Further evidence from studies on the region′s thermal evolution and regional tectonics suggests that the development of different tectonic levels is closely linked to the discrepant uplift or denudation since the Miocene(~21 Ma).
