The effect of flow control devices（FCDs） on the uniformity of flow characteristics in a seven-strand symmetrical trapezoidal tundish was studied using both an experimental 1：2.5 hydraulic model and a numerical simu...The effect of flow control devices（FCDs） on the uniformity of flow characteristics in a seven-strand symmetrical trapezoidal tundish was studied using both an experimental 1：2.5 hydraulic model and a numerical simulation of a 1：1 geometric model.The variation coefficient（CV） was defined to evaluate the flow uniformity of the seven-strand tundish.An optimized FCD configuration was proposed on the basis of the evaluation of experimental results.It is concluded that a turbulence inhibitor（TI） and U-type dam are essential to improve the uniformity of fluid flow in the seven-strand tundish.In addition,the configuration of inclination T-type dams with a height of 200 mm between the second and third strands and with a height of 300 mm between the third and fourth strands can minimize the proportion of dead zone.After optimizing the configuration of FCDs,the variation coefficient reduces below 20%of the mean value,and the average proportion of dead zone is just 14.6%;in addition,the temperature fluctuation between the strands could be controlled within 0.6 K.In summary,the uniformity of flow and temperature in the seven-strand tundish is greatly improved.展开更多
High-speed maglev trains represent a key direction for the future development of rail transportation.As operating speeds increase,they face increasingly severe aerodynamic challenges.The streamlined aerodynamic shape ...High-speed maglev trains represent a key direction for the future development of rail transportation.As operating speeds increase,they face increasingly severe aerodynamic challenges.The streamlined aerodynamic shape of a maglev train is a critical factor influencing its aerodynamic performance,and optimizing its length plays a significant role in improving the overall aerodynamic characteristics of the train.In this study,a numerical simulation model of a high-speed maglev train was established based on computational fluid dynamics(CFD)to investigate the effects of streamline length on the aerodynamic performance of the train operating on an open track.The results show that the length of the streamlined section has a pronounced impact on aerodynamic performance.When the streamline length increases from 8.3 to 14.3 m,the aerodynamic drag of the head and tail cars decreases by 16.2%and 32.1%,respectively,with reductions observed in both frictions drag and pressure drag-the latter showing the most significant decrease in the tail car.Moreover,the extended streamline length effectively suppresses flow separation on the train body surface.The intensity of the positive pressure region on the upper surface of the head car streamlined section is reduced,directly leading to a 38.2%reduction in lift.This research provides a theoretical basis for the parametric design of aerodynamic shapes for high-speed maglev trains and offers guidance and recommendations for drag and lift reduction optimization.展开更多
Seven types of activated carbon were used to investigate the effect of their structure on separation of CO2 from（H2 ＋ CO2） gas mixture by the adsorption method at ambient temperature and higher pressures. The resul...Seven types of activated carbon were used to investigate the effect of their structure on separation of CO2 from（H2 ＋ CO2） gas mixture by the adsorption method at ambient temperature and higher pressures. The results showed that the limiting factors for separation of CO2 from 53.6 mol% H2 ＋ 46.4 mol% CO2 mixture and from 85.1 mol% H2 ＋ 14.9 mol% CO2 mixture were different at 20 °C and about 2 MPa. The best separation result could be achieved when the pore diameter of the activated carbon ranged from 0.77 to 1.20 nm, and the median particle size was about2.07 lm for 53.6 mol% H2 ＋ 46.4 mol% CO2 mixture and 1.41 lm for 85.1 mol% H2 ＋ 14.9 mol% CO2 mixture. The effect of specific area and pore diameter of activated carbon on separation CO2 from 53.6 mol% H2 ＋ 46.4 mol% CO2 mixture was more significant than that from 85.1 mol% H2 ＋ 14.9 mol% CO2 mixture. CO2 in the gas phase can be decreased from 46.4 mol% to 2.3 mol%–4.3 mol% with a two-stage separation process.展开更多
A two-dimensional model of a metal-semiconductor-metal （MSM） ZnO-based photodetector （PD） is developed. The PD is based on a drift diffusion model of a semiconductor that allows the calculation of potential distri...A two-dimensional model of a metal-semiconductor-metal （MSM） ZnO-based photodetector （PD） is developed. The PD is based on a drift diffusion model of a semiconductor that allows the calculation of potential distribution inside the structure, the transversal and longitudinal distributions of the electric field, and the distribution of carrier concentration. The ohmicity of the contact has been confirmed. The dark current of MSM PD based ZnO for different structural dimensions are likewise calculated. The calculations are comparable with the experimental results. Therefore, the influence with respect to parameters s （finger spacing） and w （finger width） is studied, which results in the optimization of these parameters. The best optimization found to concur with the experimental results is s = 16 μm, w = 16 μm, l = 250 μm, L = 350 μm, where l is the finger length and L is the length of the structure. This optimization provides a simulated dark current eaual to 24.5 nA at the polarization of 3 V.展开更多
With the increasing integration of intermittent power sources (IPSs) into the power system, the uncertainty of IPSs requires solution and current dispatch system needs improvement. This paper aims to generate the opti...With the increasing integration of intermittent power sources (IPSs) into the power system, the uncertainty of IPSs requires solution and current dispatch system needs improvement. This paper aims to generate the optimal dispatch plan for day-ahead scheduling and real-time dispatch using the proposed model of characteristic optimal power flow (COPF). The integral time period represented by the median load point and the heavy and light load point with simplicity and accuracy. Simulation case studies on a 30-bus system </span><span style="font-family:Verdana;">are </span><span style="font-family:Verdana;">presented, which shows that COPF is an effective model to generate the optimal dispatch plan for power systems with high penetration of IPSs.展开更多
Vertical-cavity surface-emitting lasers(VCSELs)are essential in modern optoelectronic systems,driving applications in high-speed optical communications,3D sensing,and LiDAR.While significant progress has been made in ...Vertical-cavity surface-emitting lasers(VCSELs)are essential in modern optoelectronic systems,driving applications in high-speed optical communications,3D sensing,and LiDAR.While significant progress has been made in improving VCSEL performance,the role of cavity geometry in optimizing key optical characteristics remains insufficiently explored.This study systematically examines how distinct cavity geometries—circular,square,D-shaped,mushroom-shaped,and pentagonal—affect both the static and dynamic properties of broad-area VCSELs.We analyze their effects on optical power,multimode behavior,beam profile,spatial coherence,and polarization dynamics.Our results show that breaking the continuous rotational symmetry of the cavity effectively increases gain utilization and power,changes the multimode lasing characteristics,shapes the beam,and modifies the polarization.Notably,the pentagonal VCSEL exhibits more than twice the optical power density of its circular counterpart.It also supports the highest number of modes and the fastest mode dynamics,driven by strong mode interaction.These properties make it a strong candidate for high-speed entropy generation.Mushroom-shaped VCSELs demonstrate high power and low spatial coherence,making them ideal for speckle-free imaging and illumination applications.Meanwhile,D-shaped VCSELs provide the most stable polarization and controllable multimode behavior with high power,showcasing their potential for applications that require stable and low-coherence light sources.This study offers a comprehensive analysis of the impact of cavity geometry on VCSEL performance,which provides insights for optimizing VCSEL designs tailored to diverse applications that require distinct properties with broad applicability to advanced imaging,sensing,optical coherence tomography,high-speed communication,and other photonic technologies.展开更多
This paper deals with the optimal transportation for generalized Lagrangian L = L（x, u, t）, and considers the following cost function： c（x, y） = inf x（0）=x x（1）=y u∈U∫0^1 L（x（s）, u（x（s）, s）, s）ds, w...This paper deals with the optimal transportation for generalized Lagrangian L = L（x, u, t）, and considers the following cost function： c（x, y） = inf x（0）=x x（1）=y u∈U∫0^1 L（x（s）, u（x（s）, s）, s）ds, where U is a control set, and x satisfies the ordinary equation x（s） = f（x（s）, u（x（s）, s））.It is proved that under the condition that the initial measure μ0 is absolutely continuous w.r.t. the Lebesgue measure, the Monge problem has a solution, and the optimal transport map just walks along the characteristic curves of the corresponding Hamilton-Jacobi equation：Vt（t, x） ＋ sup u∈U = 0,V（0, x） = Φ0（x）.展开更多
基金supported by the National Natural Science Foundation of China (No.51404018)the Fundamental Research Funds for the Central Universities of China (No.FRF-TP-15-008A3)
文摘The effect of flow control devices（FCDs） on the uniformity of flow characteristics in a seven-strand symmetrical trapezoidal tundish was studied using both an experimental 1：2.5 hydraulic model and a numerical simulation of a 1：1 geometric model.The variation coefficient（CV） was defined to evaluate the flow uniformity of the seven-strand tundish.An optimized FCD configuration was proposed on the basis of the evaluation of experimental results.It is concluded that a turbulence inhibitor（TI） and U-type dam are essential to improve the uniformity of fluid flow in the seven-strand tundish.In addition,the configuration of inclination T-type dams with a height of 200 mm between the second and third strands and with a height of 300 mm between the third and fourth strands can minimize the proportion of dead zone.After optimizing the configuration of FCDs,the variation coefficient reduces below 20%of the mean value,and the average proportion of dead zone is just 14.6%;in addition,the temperature fluctuation between the strands could be controlled within 0.6 K.In summary,the uniformity of flow and temperature in the seven-strand tundish is greatly improved.
基金funded by Research and Development Project of JDD For HTS Maglev Transportation System(NO.JDDKYCF2024002)ChinaNational Railway Group Science and Technology Program grant(K2024T005).
文摘High-speed maglev trains represent a key direction for the future development of rail transportation.As operating speeds increase,they face increasingly severe aerodynamic challenges.The streamlined aerodynamic shape of a maglev train is a critical factor influencing its aerodynamic performance,and optimizing its length plays a significant role in improving the overall aerodynamic characteristics of the train.In this study,a numerical simulation model of a high-speed maglev train was established based on computational fluid dynamics(CFD)to investigate the effects of streamline length on the aerodynamic performance of the train operating on an open track.The results show that the length of the streamlined section has a pronounced impact on aerodynamic performance.When the streamline length increases from 8.3 to 14.3 m,the aerodynamic drag of the head and tail cars decreases by 16.2%and 32.1%,respectively,with reductions observed in both frictions drag and pressure drag-the latter showing the most significant decrease in the tail car.Moreover,the extended streamline length effectively suppresses flow separation on the train body surface.The intensity of the positive pressure region on the upper surface of the head car streamlined section is reduced,directly leading to a 38.2%reduction in lift.This research provides a theoretical basis for the parametric design of aerodynamic shapes for high-speed maglev trains and offers guidance and recommendations for drag and lift reduction optimization.
基金the Talent Scientific Research Fund of LSHU (No. 2016XJJ-015)the fund of the Liaoning Provincial Department of Education (No. L2017LQN005)the National Natural Science Foundation of China (No. 21606120)
文摘Seven types of activated carbon were used to investigate the effect of their structure on separation of CO2 from（H2 ＋ CO2） gas mixture by the adsorption method at ambient temperature and higher pressures. The results showed that the limiting factors for separation of CO2 from 53.6 mol% H2 ＋ 46.4 mol% CO2 mixture and from 85.1 mol% H2 ＋ 14.9 mol% CO2 mixture were different at 20 °C and about 2 MPa. The best separation result could be achieved when the pore diameter of the activated carbon ranged from 0.77 to 1.20 nm, and the median particle size was about2.07 lm for 53.6 mol% H2 ＋ 46.4 mol% CO2 mixture and 1.41 lm for 85.1 mol% H2 ＋ 14.9 mol% CO2 mixture. The effect of specific area and pore diameter of activated carbon on separation CO2 from 53.6 mol% H2 ＋ 46.4 mol% CO2 mixture was more significant than that from 85.1 mol% H2 ＋ 14.9 mol% CO2 mixture. CO2 in the gas phase can be decreased from 46.4 mol% to 2.3 mol%–4.3 mol% with a two-stage separation process.
文摘A two-dimensional model of a metal-semiconductor-metal （MSM） ZnO-based photodetector （PD） is developed. The PD is based on a drift diffusion model of a semiconductor that allows the calculation of potential distribution inside the structure, the transversal and longitudinal distributions of the electric field, and the distribution of carrier concentration. The ohmicity of the contact has been confirmed. The dark current of MSM PD based ZnO for different structural dimensions are likewise calculated. The calculations are comparable with the experimental results. Therefore, the influence with respect to parameters s （finger spacing） and w （finger width） is studied, which results in the optimization of these parameters. The best optimization found to concur with the experimental results is s = 16 μm, w = 16 μm, l = 250 μm, L = 350 μm, where l is the finger length and L is the length of the structure. This optimization provides a simulated dark current eaual to 24.5 nA at the polarization of 3 V.
文摘With the increasing integration of intermittent power sources (IPSs) into the power system, the uncertainty of IPSs requires solution and current dispatch system needs improvement. This paper aims to generate the optimal dispatch plan for day-ahead scheduling and real-time dispatch using the proposed model of characteristic optimal power flow (COPF). The integral time period represented by the median load point and the heavy and light load point with simplicity and accuracy. Simulation case studies on a 30-bus system </span><span style="font-family:Verdana;">are </span><span style="font-family:Verdana;">presented, which shows that COPF is an effective model to generate the optimal dispatch plan for power systems with high penetration of IPSs.
基金supported by the King Abdullah University of Science and Technology(KAUST)under the Grant of Transition Award in Semiconductors:Grant No.FCC/1/5939,the KAUST Center of Excellence for Renewable Energy and Storage Technologies(CREST):Grant No.FCC/1/5937,and the KAUST Grant Nos.RFS-OFP2023-5534,BAS/1/1614-01-01,ORA-2022-5313,and ORFS-2022-CRG11-5079.The authors acknowledge the use of the KAUST Nanofabrication Core Lab and the KAUST Imaging and Characterization Core Lab facilities.
文摘Vertical-cavity surface-emitting lasers(VCSELs)are essential in modern optoelectronic systems,driving applications in high-speed optical communications,3D sensing,and LiDAR.While significant progress has been made in improving VCSEL performance,the role of cavity geometry in optimizing key optical characteristics remains insufficiently explored.This study systematically examines how distinct cavity geometries—circular,square,D-shaped,mushroom-shaped,and pentagonal—affect both the static and dynamic properties of broad-area VCSELs.We analyze their effects on optical power,multimode behavior,beam profile,spatial coherence,and polarization dynamics.Our results show that breaking the continuous rotational symmetry of the cavity effectively increases gain utilization and power,changes the multimode lasing characteristics,shapes the beam,and modifies the polarization.Notably,the pentagonal VCSEL exhibits more than twice the optical power density of its circular counterpart.It also supports the highest number of modes and the fastest mode dynamics,driven by strong mode interaction.These properties make it a strong candidate for high-speed entropy generation.Mushroom-shaped VCSELs demonstrate high power and low spatial coherence,making them ideal for speckle-free imaging and illumination applications.Meanwhile,D-shaped VCSELs provide the most stable polarization and controllable multimode behavior with high power,showcasing their potential for applications that require stable and low-coherence light sources.This study offers a comprehensive analysis of the impact of cavity geometry on VCSEL performance,which provides insights for optimizing VCSEL designs tailored to diverse applications that require distinct properties with broad applicability to advanced imaging,sensing,optical coherence tomography,high-speed communication,and other photonic technologies.
文摘This paper deals with the optimal transportation for generalized Lagrangian L = L（x, u, t）, and considers the following cost function： c（x, y） = inf x（0）=x x（1）=y u∈U∫0^1 L（x（s）, u（x（s）, s）, s）ds, where U is a control set, and x satisfies the ordinary equation x（s） = f（x（s）, u（x（s）, s））.It is proved that under the condition that the initial measure μ0 is absolutely continuous w.r.t. the Lebesgue measure, the Monge problem has a solution, and the optimal transport map just walks along the characteristic curves of the corresponding Hamilton-Jacobi equation：Vt（t, x） ＋ sup u∈U = 0,V（0, x） = Φ0（x）.
