Foamed concrete is widely employed in highway transition sections,due to its lightweight,high-strength,and effective settlement control.It is crucial to investigate its dynamic response linked to the traffic-loading i...Foamed concrete is widely employed in highway transition sections,due to its lightweight,high-strength,and effective settlement control.It is crucial to investigate its dynamic response linked to the traffic-loading influence zone of embankment and transition section smoothness.In this study,in-situ truck tests were conducted in the road-culvert-bridge transition section to obtain the spatio-temporal response patterns.Based on the vertical response,the influence zone was ascertained.Depending on the longitudinal response,the smoothness was evaluated by equivalent dynamic stiffness(EDS)and acceleration variation rate(AVR).Furthermore,the response discrepancies of embankments with different fillings were compared.Findings reveal exponential attenuation of dynamic stress and acceleration with increasing depth.The acceleration and dynamic displacement exhibit U-shaped patterns in the culvert subsection and abrupt changes in the bridgehead subsection.The influence zone determined by the acceleration attenuation coefficient method,dynamic stress attenuation method,and stress diffusion angle method was 1.55 m,2.05 m,and 2.89 m,respectively.The maximum disparity in EDS occurs at the culvert subsection and bridge abutment,and the AVR ranges from 0 to 0.52 s^(-2).Moreover,94.1%attenuation of the dynamic stress occurred within the 1.5-meter foamed concrete embankment under the setting of 100 kN-60 km/h.展开更多
BACKGROUND Transition is a critical period for adolescents as they begin to assume responsibility for their own health.Similarly,the shift from pediatric to adult healthcare represents a vulnerable phase,marked by uni...BACKGROUND Transition is a critical period for adolescents as they begin to assume responsibility for their own health.Similarly,the shift from pediatric to adult healthcare represents a vulnerable phase,marked by unique challenges in adolescent health care.Despite its importance,only a few studies have explored healthcare transition among adolescents in Uganda.AIM To identify factors associated with the transition to adult human immunodeficiency virus(HIV)-centered care among adolescents attending HIV/AIDS clinics in Uganda.METHODS A cross-sectional mixed-methods study was conducted among 265 adolescents,randomly selected from three antiretroviral therapy(ART)clinics,using a structured questionnaire.Focus group discussions and key informant interviews were conducted.Individuals aged 10-20 years who were actively enrolled in the ART program between January 4,2022 and January 30,2023 were recruited.The primary outcome of interest was the transition to adult care.Bivariate and multivariate analyses were performed for quantitative data,while content analysis was used to analyze qualitative data.RESULTS The prevalence of transition to adult care was 40.6%.Most participants were male(53.6%)and fell within the 13-15 age group(35.6%).Multivariate logistic regression analysis identified several factors significantly associated with transition to adult care:Age group 10-12 years[prevalence ratio(PR)=2.525,95%CI:2.121-2.944,P=0.002],Age group 13-15 years(PR=1.900,95%CI:1.196-3.416,P=0.001),successful viral load suppression(PR=1.534,95%CI:1.173-1.648,P=0.016),disclosure of HIV status to relatives(PR=5.001,95%CI:3.411-3.611,P=0.000),being prepared for transitioning(PR=5.417,95%CI:3.468-7.135,P=0.041)and having skilled pediatric caregivers(PR=3.724,95%CI:2.084-4.105,P=0.005).CONCLUSION Transition to adult care among adolescents was low.Improving transition outcomes may require strengthening individual support within the family context and integrating transition-focused care into existing specialized clinical settings to enhance the delivery of adolescent-friendly services.展开更多
Firstly, sample square-circular transition tube along straight central route was modeled on CATIA software. The parameters are as follows： let the tube length is L, and the constant cross section area is S, and S = ...Firstly, sample square-circular transition tube along straight central route was modeled on CATIA software. The parameters are as follows： let the tube length is L, and the constant cross section area is S, and S = πR^2 = a2, in which R stands for the circle radius on one end, and a the square side length on the other end; set up the coordinate system with OX axis on the central route in which the origin O is on centroid of the square end and assume the cross section size at x as the square shaped with all four comers filleted in radius r which is proportional to x, that is, the linear slope of r is R/L, thus, both values r and square side length ax can be attained on the constant cross section area assumption. Secondly, some sample polygonal-circular transition tubes along straight, circular and helical central route were implemented similarly. Thirdly, numerical analysis of stress and displacement of these tubes were carried out on MSC/PATRAN software which are important to the distribution of turbulent flow and the layout of these transitional tube structures.展开更多
Wind-sand flow generates erosion and deposition around obstacles such as bridges and roadbeds, resulting in sand damage and endangering railway systems in sandy regions. Previous studies have mainly focused on the flo...Wind-sand flow generates erosion and deposition around obstacles such as bridges and roadbeds, resulting in sand damage and endangering railway systems in sandy regions. Previous studies have mainly focused on the flow field around roadbeds, overlooking detailed examinations of sand particle erosion and deposition patterns near bridges and roadbeds. This study employs numerical simulations to analyze the influence of varying heights and wind speeds on sand deposition and erosion characteristics at different locations: the bridge-road transition section(side piers), middle piers, and roadbeds. The results show that the side piers, experience greater accumulation than the middle piers. Similarly, the leeward side of the roadbed witnesses more deposition compared to the windward side. Another finding reveals a reduced sand deposition length as the vertical profile, in alignment with the wind direction, moves further from the bridge abutments at the same clearance height. As wind speeds rise, there’s a decline in sand deposition and a marked increase in erosion around the side piers, middle piers and roadbeds. In conclusion, a bridge clearance that’s too low can cause intense sand damage near the side piers, while an extremely high roadbed may lead to extensive surface sand deposition. Hence, railway bridges in areas prone to sandy winds should strike a balance in clearance height. This research provides valuable guidelines for determining the most suitable bridge and roadbed heights in regions affected by wind and sand.展开更多
In order to decrease relative settlement, foundation treatment plays an extremely important role in bridgehead transition section, especially, the situation of building the bridge piles firstly, and then processing pi...In order to decrease relative settlement, foundation treatment plays an extremely important role in bridgehead transition section, especially, the situation of building the bridge piles firstly, and then processing piles. On the basis of engineering practice, the authors analyzed the influence of foundation treatment on bridge piles in bridgehead transition section by finite-element method (FEM). This research has positive significance in predicting displacement of bridge pile, directing construction of foundation treatment, and improving quality of engineering and so forth.展开更多
As the lifeline of social development,road and bridge projects are the main channel to realize resource transportation and economic circulation.Ensuring the quality of road and bridge project construction is crucial f...As the lifeline of social development,road and bridge projects are the main channel to realize resource transportation and economic circulation.Ensuring the quality of road and bridge project construction is crucial for the development of society,the economy,and people’s livelihoods.This paper studies the design of roadbed pavement structures in road and bridge transition sections.It aims to provide technical references and significance for China’s road and bridge engineering design and construction units,promoting scientific and standardized design in these actions.This will contribute to the safety and stable operation of road and bridge projects,offering effective technical support.Furthermore,it seeks to foster the sustainable and healthy development of China’s road and bridge engineering on a macro level.展开更多
In this paper,combined with the relevant speed theory and characteristics of the law,the current highway speed transition design problems are studied and analyzed.In the process of specific analysis,mainly combined wi...In this paper,combined with the relevant speed theory and characteristics of the law,the current highway speed transition design problems are studied and analyzed.In the process of specific analysis,mainly combined with the characteristics of different types of highway speed changes and road section design requirements,this paper studies and analyzes the design methods of different types of highway speed transition section.And on this basis,according to the design principles and requirements of highway operation speed transition section,the paper summarizes the matters needing attention in the design of highway operation speed transition section,in order to provide certain reference value for relevant personnel.展开更多
The road surface at the transition section of the highway bridge can connect the two ends of the bridge, which is the basis for the normal operation of highway traffic and the guarantee for the safe driving of vehicle...The road surface at the transition section of the highway bridge can connect the two ends of the bridge, which is the basis for the normal operation of highway traffic and the guarantee for the safe driving of vehicles. In the process of construction, if its quality is not too high, it will inevitably reduce the safety of vehicles after the completion of the bridge. Therefore, it is necessary to apply effective construction technology in order to ensure the normal use of the bridge. However, with the continuous progress of China's entire transportation industry, many problems in the process of bridge construction have gradually emerged, such as cracks at the bridge and road junctions and road damage, which in turn hinder the normal use of bridges. In this paper, the author analyzes the technical problems and difficulties in the construction process in detail, and gives constructive solutions, which can be used as a reference for future bridge construction projects.展开更多
In recent years, due to the influence of various factors, the road surface in the process of practical application of uneven, subsidence, collapse and other problems become more and more serious. Traffic accidents cau...In recent years, due to the influence of various factors, the road surface in the process of practical application of uneven, subsidence, collapse and other problems become more and more serious. Traffic accidents caused by these conditions have caused serious doubts on the quality of the road surface among the masses. As an important part of the safety guarantee, the transition section of road and bridge, if the flatness is not up to the standard in the actual construction, will bury a huge hidden danger for the subsequent safety. Therefore, in order to ensure people's travel safety effectively, it is of great significance for the development of China's economy to take certain methods to improve the current existing construction technology. This paper will also study the construction technology of subgrade and pavement in the transition section of road and bridge construction.展开更多
Road and bridge engineering as one of an important part of urban transportation infrastructure, its because itself has the characteristics of high complexity, so the designer in developing road and bridge transition s...Road and bridge engineering as one of an important part of urban transportation infrastructure, its because itself has the characteristics of high complexity, so the designer in developing road and bridge transition section roadbed design work, must strictly according to the bridge, the main points of transition section roadbed design to improve the scientific nature and rationality of subgrade pavement design, at the same time do a good job in road and bridge transition section roadbed settlement deal with related work, can effectively reduce the transition section roadbed uneven settlement problem of risk at the same time, promote the safety of the bridge engineering operation and stability. This paper mainly analyzes and discusses the design points and settlement treatment measures of roadbed and pavement in the transition section of road and bridge.展开更多
With the increase of axle load and the train speed, dynamic interaction of train-track system becomes so exacerbated that the deformation and dynamic response of subgrade are more aggravated. The differential settleme...With the increase of axle load and the train speed, dynamic interaction of train-track system becomes so exacerbated that the deformation and dynamic response of subgrade are more aggravated. The differential settlement will be created in bridge-embankment transition section under such dynamic action, and an adverse effect on the train operation safety can be caused. Meanwhile, differential settlement will produce additional dynamic effect when high-speed trains go through the transition between bridge-embankment. Such dynamic action will aggravate the differential settlement and subgrade damage. This paper applies the methods of field test and finite-element to systematically study the dynamic response characteristics of subgrade in bridge-embankment transition section of heavy haul railway under dynamic load for the first time. This research is focused on the analysis of influence of the different axle load, train speed, filled soil modulus, etc.. At last, the dynamic response rules are systematically summarized.展开更多
This paper studies the short-term prediction methods of sectional passenger flow, and selects BP neural network combined with the characteristics of sectional passenger flow itself. With a case study, we design three ...This paper studies the short-term prediction methods of sectional passenger flow, and selects BP neural network combined with the characteristics of sectional passenger flow itself. With a case study, we design three different schemes. We use Matlab to realize the prediction of the sectional passenger flow of the Beijing subway Line 2 and make comparative analysis. The empirical research shows that combining data characteristics of sectional passenger flow with the BP neural network have good prediction accuracy.展开更多
The geological conditions and processes of fine-grained gravity flow sedimentation in continental lacustrine basins in China are analyzed to construct the model of fine-grained gravity flow sedimentation in lacustrine...The geological conditions and processes of fine-grained gravity flow sedimentation in continental lacustrine basins in China are analyzed to construct the model of fine-grained gravity flow sedimentation in lacustrine basin,reveal the development laws of fine-grained deposits and source-reservoir,and identify the sweet sections of shale oil.The results show that fine-grained gravity flow is one of the important sedimentary processes in deep lake environment,and it can transport fine-grained clasts and organic matter in shallow water to deep lake,forming sweet sections and high-quality source rocks of shale oil.Fine-grained gravity flow deposits in deep waters of lacustrine basins in China are mainly fine-grained high-density flow,fine-grained turbidity flow(including surge-like turbidity flow and fine-grained hyperpycnal flow),fine-grained viscous flow(including fine-grained debris flow and mud flow),and fine-grained transitional flow deposits.The distribution of fine-grained gravity flow deposits in the warm and humid unbalanced lacustrine basins are controlled by lake-level fluctuation,flooding events,and lakebed paleogeomorphology.During the lake-level rise,fine-grained hyperpycnal flow caused by flooding formed fine-grained channel–levee–lobe system in the flat area of the deep lake.During the lake-level fall,the sublacustrine fan system represented by unconfined channel was developed in the flexural slope breaks and sedimentary slopes of depressed lacustrine basins,and in the steep slopes of faulted lacustrine basins;the sublacustrine fan system with confined or unconfined channel was developed on the gentle slopes and in axial direction of faulted lacustrine basins,with fine-grained gravity flow deposits possibly existing in the lower fan.Within the fourth-order sequences,transgression might lead to organic-rich shale and fine-grained hyperpycnal flow deposits,while regression might cause fine-grained high-density flow,surge-like turbidity flow,fine-grained debris flow,mud flow,and fine-grained transitional flow deposits.Since the Permian,in the shale strata of lacustrine basins in China,multiple transgression-regression cycles of fourth-order sequences have formed multiple source-reservoir assemblages.Diverse fine-grained gravity flow sedimentation processes have created sweet sections of thin siltstone consisting of fine-grained high-density flow,fine-grained hyperpycnal flow and surge-like turbidity flow deposits,sweet sections with interbeds of mudstone and siltstone formed by fine-grained transitional flows,and sweet sections of shale containing silty and muddy clasts and with horizontal bedding formed by fine-grained debris flow and mud flow.The model of fine-grained gravity flow sedimentation in lacustrine basin is significant for the scientific evaluation of sweet shale oil reservoir and organic-rich source rock.展开更多
One of the great difficulties in understanding nitrogen plasma elementary processes is the lack of an available database of the cross-sections of electron-impact excitations and radiations. Ab initio calculations of v...One of the great difficulties in understanding nitrogen plasma elementary processes is the lack of an available database of the cross-sections of electron-impact excitations and radiations. Ab initio calculations of vibrational excitation cross sections for electron collisions with nitrogen molecules in low-lying states using similarity function approach, such as a-a＇, a-w, B-B＇ and B-W transition systems, are reported here for the first time. In the meantime, the average excitation energies of neighboring levels of these systems have been calculated. In order to obtain the cross sections, accurate spectroscopic constants and transition dipole moments have been investigated. Potential energy curves and other electronic transition dipole moments for the low-lying states of N2 have been re-evaluated using complete active space self-consistent field （CASSCF） approach with aug-cc-pVqZ basis set. The calculated cross-sections could provide a database for studying the elementary processes and the properties in N2 plasma.展开更多
基金National Natural Science Foundation of China under Grant Nos.52078205 and 42172322Joint Fund for High-Speed Railway Basic Research under Grant No.U2268213the Postgraduate Scientific Research Innovation Project of Hunan Province under Grant Nos.QL20230104 and CX20240431。
文摘Foamed concrete is widely employed in highway transition sections,due to its lightweight,high-strength,and effective settlement control.It is crucial to investigate its dynamic response linked to the traffic-loading influence zone of embankment and transition section smoothness.In this study,in-situ truck tests were conducted in the road-culvert-bridge transition section to obtain the spatio-temporal response patterns.Based on the vertical response,the influence zone was ascertained.Depending on the longitudinal response,the smoothness was evaluated by equivalent dynamic stiffness(EDS)and acceleration variation rate(AVR).Furthermore,the response discrepancies of embankments with different fillings were compared.Findings reveal exponential attenuation of dynamic stress and acceleration with increasing depth.The acceleration and dynamic displacement exhibit U-shaped patterns in the culvert subsection and abrupt changes in the bridgehead subsection.The influence zone determined by the acceleration attenuation coefficient method,dynamic stress attenuation method,and stress diffusion angle method was 1.55 m,2.05 m,and 2.89 m,respectively.The maximum disparity in EDS occurs at the culvert subsection and bridge abutment,and the AVR ranges from 0 to 0.52 s^(-2).Moreover,94.1%attenuation of the dynamic stress occurred within the 1.5-meter foamed concrete embankment under the setting of 100 kN-60 km/h.
文摘BACKGROUND Transition is a critical period for adolescents as they begin to assume responsibility for their own health.Similarly,the shift from pediatric to adult healthcare represents a vulnerable phase,marked by unique challenges in adolescent health care.Despite its importance,only a few studies have explored healthcare transition among adolescents in Uganda.AIM To identify factors associated with the transition to adult human immunodeficiency virus(HIV)-centered care among adolescents attending HIV/AIDS clinics in Uganda.METHODS A cross-sectional mixed-methods study was conducted among 265 adolescents,randomly selected from three antiretroviral therapy(ART)clinics,using a structured questionnaire.Focus group discussions and key informant interviews were conducted.Individuals aged 10-20 years who were actively enrolled in the ART program between January 4,2022 and January 30,2023 were recruited.The primary outcome of interest was the transition to adult care.Bivariate and multivariate analyses were performed for quantitative data,while content analysis was used to analyze qualitative data.RESULTS The prevalence of transition to adult care was 40.6%.Most participants were male(53.6%)and fell within the 13-15 age group(35.6%).Multivariate logistic regression analysis identified several factors significantly associated with transition to adult care:Age group 10-12 years[prevalence ratio(PR)=2.525,95%CI:2.121-2.944,P=0.002],Age group 13-15 years(PR=1.900,95%CI:1.196-3.416,P=0.001),successful viral load suppression(PR=1.534,95%CI:1.173-1.648,P=0.016),disclosure of HIV status to relatives(PR=5.001,95%CI:3.411-3.611,P=0.000),being prepared for transitioning(PR=5.417,95%CI:3.468-7.135,P=0.041)and having skilled pediatric caregivers(PR=3.724,95%CI:2.084-4.105,P=0.005).CONCLUSION Transition to adult care among adolescents was low.Improving transition outcomes may require strengthening individual support within the family context and integrating transition-focused care into existing specialized clinical settings to enhance the delivery of adolescent-friendly services.
文摘Firstly, sample square-circular transition tube along straight central route was modeled on CATIA software. The parameters are as follows： let the tube length is L, and the constant cross section area is S, and S = πR^2 = a2, in which R stands for the circle radius on one end, and a the square side length on the other end; set up the coordinate system with OX axis on the central route in which the origin O is on centroid of the square end and assume the cross section size at x as the square shaped with all four comers filleted in radius r which is proportional to x, that is, the linear slope of r is R/L, thus, both values r and square side length ax can be attained on the constant cross section area assumption. Secondly, some sample polygonal-circular transition tubes along straight, circular and helical central route were implemented similarly. Thirdly, numerical analysis of stress and displacement of these tubes were carried out on MSC/PATRAN software which are important to the distribution of turbulent flow and the layout of these transitional tube structures.
基金financially supported by the fellowship of the China Postdoctoral Science Foundation (2021M703466)the Natural Science Foundation of Gansu Province, China (20JR10RA231)the Natural Science Foundation of Gansu Province, China (22JR5RA050)。
文摘Wind-sand flow generates erosion and deposition around obstacles such as bridges and roadbeds, resulting in sand damage and endangering railway systems in sandy regions. Previous studies have mainly focused on the flow field around roadbeds, overlooking detailed examinations of sand particle erosion and deposition patterns near bridges and roadbeds. This study employs numerical simulations to analyze the influence of varying heights and wind speeds on sand deposition and erosion characteristics at different locations: the bridge-road transition section(side piers), middle piers, and roadbeds. The results show that the side piers, experience greater accumulation than the middle piers. Similarly, the leeward side of the roadbed witnesses more deposition compared to the windward side. Another finding reveals a reduced sand deposition length as the vertical profile, in alignment with the wind direction, moves further from the bridge abutments at the same clearance height. As wind speeds rise, there’s a decline in sand deposition and a marked increase in erosion around the side piers, middle piers and roadbeds. In conclusion, a bridge clearance that’s too low can cause intense sand damage near the side piers, while an extremely high roadbed may lead to extensive surface sand deposition. Hence, railway bridges in areas prone to sandy winds should strike a balance in clearance height. This research provides valuable guidelines for determining the most suitable bridge and roadbed heights in regions affected by wind and sand.
文摘In order to decrease relative settlement, foundation treatment plays an extremely important role in bridgehead transition section, especially, the situation of building the bridge piles firstly, and then processing piles. On the basis of engineering practice, the authors analyzed the influence of foundation treatment on bridge piles in bridgehead transition section by finite-element method (FEM). This research has positive significance in predicting displacement of bridge pile, directing construction of foundation treatment, and improving quality of engineering and so forth.
文摘As the lifeline of social development,road and bridge projects are the main channel to realize resource transportation and economic circulation.Ensuring the quality of road and bridge project construction is crucial for the development of society,the economy,and people’s livelihoods.This paper studies the design of roadbed pavement structures in road and bridge transition sections.It aims to provide technical references and significance for China’s road and bridge engineering design and construction units,promoting scientific and standardized design in these actions.This will contribute to the safety and stable operation of road and bridge projects,offering effective technical support.Furthermore,it seeks to foster the sustainable and healthy development of China’s road and bridge engineering on a macro level.
文摘In this paper,combined with the relevant speed theory and characteristics of the law,the current highway speed transition design problems are studied and analyzed.In the process of specific analysis,mainly combined with the characteristics of different types of highway speed changes and road section design requirements,this paper studies and analyzes the design methods of different types of highway speed transition section.And on this basis,according to the design principles and requirements of highway operation speed transition section,the paper summarizes the matters needing attention in the design of highway operation speed transition section,in order to provide certain reference value for relevant personnel.
文摘The road surface at the transition section of the highway bridge can connect the two ends of the bridge, which is the basis for the normal operation of highway traffic and the guarantee for the safe driving of vehicles. In the process of construction, if its quality is not too high, it will inevitably reduce the safety of vehicles after the completion of the bridge. Therefore, it is necessary to apply effective construction technology in order to ensure the normal use of the bridge. However, with the continuous progress of China's entire transportation industry, many problems in the process of bridge construction have gradually emerged, such as cracks at the bridge and road junctions and road damage, which in turn hinder the normal use of bridges. In this paper, the author analyzes the technical problems and difficulties in the construction process in detail, and gives constructive solutions, which can be used as a reference for future bridge construction projects.
文摘In recent years, due to the influence of various factors, the road surface in the process of practical application of uneven, subsidence, collapse and other problems become more and more serious. Traffic accidents caused by these conditions have caused serious doubts on the quality of the road surface among the masses. As an important part of the safety guarantee, the transition section of road and bridge, if the flatness is not up to the standard in the actual construction, will bury a huge hidden danger for the subsequent safety. Therefore, in order to ensure people's travel safety effectively, it is of great significance for the development of China's economy to take certain methods to improve the current existing construction technology. This paper will also study the construction technology of subgrade and pavement in the transition section of road and bridge construction.
文摘Road and bridge engineering as one of an important part of urban transportation infrastructure, its because itself has the characteristics of high complexity, so the designer in developing road and bridge transition section roadbed design work, must strictly according to the bridge, the main points of transition section roadbed design to improve the scientific nature and rationality of subgrade pavement design, at the same time do a good job in road and bridge transition section roadbed settlement deal with related work, can effectively reduce the transition section roadbed uneven settlement problem of risk at the same time, promote the safety of the bridge engineering operation and stability. This paper mainly analyzes and discusses the design points and settlement treatment measures of roadbed and pavement in the transition section of road and bridge.
文摘With the increase of axle load and the train speed, dynamic interaction of train-track system becomes so exacerbated that the deformation and dynamic response of subgrade are more aggravated. The differential settlement will be created in bridge-embankment transition section under such dynamic action, and an adverse effect on the train operation safety can be caused. Meanwhile, differential settlement will produce additional dynamic effect when high-speed trains go through the transition between bridge-embankment. Such dynamic action will aggravate the differential settlement and subgrade damage. This paper applies the methods of field test and finite-element to systematically study the dynamic response characteristics of subgrade in bridge-embankment transition section of heavy haul railway under dynamic load for the first time. This research is focused on the analysis of influence of the different axle load, train speed, filled soil modulus, etc.. At last, the dynamic response rules are systematically summarized.
文摘This paper studies the short-term prediction methods of sectional passenger flow, and selects BP neural network combined with the characteristics of sectional passenger flow itself. With a case study, we design three different schemes. We use Matlab to realize the prediction of the sectional passenger flow of the Beijing subway Line 2 and make comparative analysis. The empirical research shows that combining data characteristics of sectional passenger flow with the BP neural network have good prediction accuracy.
基金Supported by the Petrochina Science and Technology Project(2021DJ18).
文摘The geological conditions and processes of fine-grained gravity flow sedimentation in continental lacustrine basins in China are analyzed to construct the model of fine-grained gravity flow sedimentation in lacustrine basin,reveal the development laws of fine-grained deposits and source-reservoir,and identify the sweet sections of shale oil.The results show that fine-grained gravity flow is one of the important sedimentary processes in deep lake environment,and it can transport fine-grained clasts and organic matter in shallow water to deep lake,forming sweet sections and high-quality source rocks of shale oil.Fine-grained gravity flow deposits in deep waters of lacustrine basins in China are mainly fine-grained high-density flow,fine-grained turbidity flow(including surge-like turbidity flow and fine-grained hyperpycnal flow),fine-grained viscous flow(including fine-grained debris flow and mud flow),and fine-grained transitional flow deposits.The distribution of fine-grained gravity flow deposits in the warm and humid unbalanced lacustrine basins are controlled by lake-level fluctuation,flooding events,and lakebed paleogeomorphology.During the lake-level rise,fine-grained hyperpycnal flow caused by flooding formed fine-grained channel–levee–lobe system in the flat area of the deep lake.During the lake-level fall,the sublacustrine fan system represented by unconfined channel was developed in the flexural slope breaks and sedimentary slopes of depressed lacustrine basins,and in the steep slopes of faulted lacustrine basins;the sublacustrine fan system with confined or unconfined channel was developed on the gentle slopes and in axial direction of faulted lacustrine basins,with fine-grained gravity flow deposits possibly existing in the lower fan.Within the fourth-order sequences,transgression might lead to organic-rich shale and fine-grained hyperpycnal flow deposits,while regression might cause fine-grained high-density flow,surge-like turbidity flow,fine-grained debris flow,mud flow,and fine-grained transitional flow deposits.Since the Permian,in the shale strata of lacustrine basins in China,multiple transgression-regression cycles of fourth-order sequences have formed multiple source-reservoir assemblages.Diverse fine-grained gravity flow sedimentation processes have created sweet sections of thin siltstone consisting of fine-grained high-density flow,fine-grained hyperpycnal flow and surge-like turbidity flow deposits,sweet sections with interbeds of mudstone and siltstone formed by fine-grained transitional flows,and sweet sections of shale containing silty and muddy clasts and with horizontal bedding formed by fine-grained debris flow and mud flow.The model of fine-grained gravity flow sedimentation in lacustrine basin is significant for the scientific evaluation of sweet shale oil reservoir and organic-rich source rock.
基金supported by National Natural Science Foundation of China(Nos.11175035,10875023)the National Magnetic Confinement Fusion Science Program of China(No.2013GB109005)+1 种基金Chinesisch-Deutsches Forschungsprojekt(GZ768)the Fundamental Research Fundsfor the Central Universities of China(No.DUT12ZD(G)01)
文摘One of the great difficulties in understanding nitrogen plasma elementary processes is the lack of an available database of the cross-sections of electron-impact excitations and radiations. Ab initio calculations of vibrational excitation cross sections for electron collisions with nitrogen molecules in low-lying states using similarity function approach, such as a-a＇, a-w, B-B＇ and B-W transition systems, are reported here for the first time. In the meantime, the average excitation energies of neighboring levels of these systems have been calculated. In order to obtain the cross sections, accurate spectroscopic constants and transition dipole moments have been investigated. Potential energy curves and other electronic transition dipole moments for the low-lying states of N2 have been re-evaluated using complete active space self-consistent field （CASSCF） approach with aug-cc-pVqZ basis set. The calculated cross-sections could provide a database for studying the elementary processes and the properties in N2 plasma.
