Intercepting high-maneuverability hypersonic targets in near-space environments poses significant challenges due to their extreme speeds and evasive capabilities.To address these challenges,this study presents an inte...Intercepting high-maneuverability hypersonic targets in near-space environments poses significant challenges due to their extreme speeds and evasive capabilities.To address these challenges,this study presents an integrated approach that combines a Three-Dimensional Finite-Time Optimal Cooperative Guidance Law(FTOC)with an Information Fusion Anti-saturation Predefined-time Observer(IFAPO).The proposed FTOC guidance law employs a nonlinear,non-quadratic finite-time optimal control strategy designed for rapid convergence within the limited timeframes of near-space interceptions,avoiding the need for remaining flight time estimation or linear decoupling inherent in traditional methods.To complement the guidance strategy,the IFAPO leverages multi-source information fusion theory and incorporates anti-saturation mechanisms to enhance target maneuver estimation.This method ensures accurate and real-time prediction of target acceleration while maintaining predefined convergence performance,even under complex interception conditions.By integrating the FTOC guidance law and IFAPO,the approach optimizes cooperative missile positioning,improves interception success rates,and minimizes fuel consumption,addressing practical constraints in military applications.Simulation results and comparative analyses confirm the effectiveness of the integrated approach,demonstrating its capability to achieve cooperative interception of highly maneuvering targets with enhanced efficiency and reduced economic costs,aligning with realistic combat scenarios.展开更多
Research has been carried out on a hybrid discharge ion thruster,aiming to combine the advantages of Direct Current(DC)discharge ion thrusters(known for their high thrust density and high power supply efficiency)with ...Research has been carried out on a hybrid discharge ion thruster,aiming to combine the advantages of Direct Current(DC)discharge ion thrusters(known for their high thrust density and high power supply efficiency)with microwave discharge ion thrusters(which do not require a hollow cathode and are capable of efficient ionization at low pressures).Comparative experiments with different anode structures and single-probe diagnostics revealed that applying a DC bias voltage created a new ionization zone based on microwave discharge.This DC bias increased the sheath potential of the screen grid and led to an elevation in electron temperature and plasma density.It is speculated that the reduced loss of high-energy electrons generated by microwave discharge at the screen grid is the primary reason for the enhanced discharge.By adding a DC bias of approximately 50 V to the microwave discharge,the screen grid current was doubled without a significant increase in discharge power consumption.Under appropriate bias voltages that consider minimizing ion sputtering,DC bias holds promise as a design approach to increase the extracted beam current in microwave ion thrusters.展开更多
Ground subsidence caused by extraction of longwall panels has always been a great concern all over the world.Conventional longwall mining system(CLMS)gives rise to wavy subsidence causing great damage to surface struc...Ground subsidence caused by extraction of longwall panels has always been a great concern all over the world.Conventional longwall mining system(CLMS)gives rise to wavy subsidence causing great damage to surface structures.A coal mine in Shanxi,China,utilizes a split-level longwall layout(SLL)for a sub-horizontal No.8 coal seam to improve the cavability of mudstone interlayer and top coal.This layout,however,also produced unexpectedly favorable surface subsidence.Subsidence of No.6 and No.8 longwall panels was monitored while mining was conducted.Field instrumentation and numerical simulation were carried out.It is demonstrated that an asymmetric subsidence profile with stepped subsidence and cracks occurred on the tailgate side but relatively mild and smooth deformation on the other.Due to elimination of conventional parallelepiped gate pillar,No.6 and No.8 gobs were connected.Extraction of two SLL panels acted as one supercritical panel.The maximum possible subsidence was reached which lowers the likelihood of potential future secondary subsidence as underground gob fractures and voids have closed.Therefore,SLL is more favorable for postmining land reuse as gobs are more consolidated underground.展开更多
Based on three-dimensional cellular automata （CA）, a new stochastic simulation model to simulate the microstructures and particle flow of talus deposit is proposed. Ill addition, an auto-modeling program CARS is dev...Based on three-dimensional cellular automata （CA）, a new stochastic simulation model to simulate the microstructures and particle flow of talus deposit is proposed. Ill addition, an auto-modeling program CARS is developed, with which nunaerical simulations can be conducted conveniently. For the problem of simulating mechanical behaviors of talus deposit, spatial anangement or sphere shapes should be considered. In the new modeling method, four sphere anangement models are developed for the particle flow simulation of talus deposit. Numerical results show that the talus deposit has the mechanical characteristics of typical stress-strain curves, as other rock-like materials. The cohesion of talus deposit decreases with increasing rock content, while the internal friction angle increases with increasing rock contents. Finally, numerical simulation is verified with the results of field test.展开更多
In this study,a packed bed reactor was developed to investigate the gasification process of coal particles.The effects of coal particle size and heater temperature of reactor were examined to identify the thermochemic...In this study,a packed bed reactor was developed to investigate the gasification process of coal particles.The effects of coal particle size and heater temperature of reactor were examined to identify the thermochemical processes through the packed bed.Three different coal samples with varying size,named as A,B,and C,are used,and the experimental results show that the packed bed with smaller coal size has higher temperature,reaching 624°C,582°C,and 569°C for coal A,B,and C,respectively.In the case of CO formation,the smaller particle size has greater products in the unit of mole fraction over the area of generation.However,the variation in the porosity of the packed bed due to different coal particle sizes affects the reactions through the oxygen access.Consequently,the CO formation is least from the coal packed bed formed by the smallest particle size A.A second test with the temperature variations shows that the higher heater temperature promotes the chemical reactions,resulting in the increased gas products.The findings indicate the important role of coal seam porosity in underground coal gasification application,as well as temperature to promote the syngas productions.展开更多
Background:Epidemic models of sexually transmitted infections(STIs)are often used to characterize the contribution of risk groups to overall transmission by projecting the transmission population attributable fraction...Background:Epidemic models of sexually transmitted infections(STIs)are often used to characterize the contribution of risk groups to overall transmission by projecting the transmission population attributable fraction(tPAF)of unmet prevention and treatment needs within risk groups.However,evidence suggests that STI risk is dynamic over an individual’s sexual life course,which manifests as turnover between risk groups.We sought to examine the mechanisms by which turnover influences modelled projections of the tPAF of high risk groups.Methods:We developed a unifying,data-guided framework to simulate risk group turnover in deterministic,compartmental transmission models.We applied the framework to an illustrative model of an STI and examined the mechanisms by which risk group turnover influenced equilibrium prevalence across risk groups.We then fit a model with and without turnover to the same risk-stratified STI prevalence targets and compared the inferred level of risk heterogeneity and tPAF of the highest risk group projected by the two models.Results:The influence of turnover on group-specific prevalence was mediated by three main phenomena:movement of previously high risk individuals with the infection into lower risk groups;changes to herd effect in the highest risk group;and changes in the number of partnerships where transmission can occur.Faster turnover led to a smaller ratio of STI prevalence between the highest and lowest risk groups.Compared to the fitted model without turnover,the fitted model with turnover inferred greater risk heterogeneity and consistently projected a larger tPAF of the highest risk group over time.Implications:If turnover is not captured in epidemic models,the projected contribution of high risk groups,and thus,the potential impact of prioritizing interventions to address their needs,could be underestimated.To aid the next generation of tPAF models,data collection efforts to parameterize risk group turnover should be prioritized.展开更多
基金supported by the National Natural Science Foundation of China(Grant No.61773142).
文摘Intercepting high-maneuverability hypersonic targets in near-space environments poses significant challenges due to their extreme speeds and evasive capabilities.To address these challenges,this study presents an integrated approach that combines a Three-Dimensional Finite-Time Optimal Cooperative Guidance Law(FTOC)with an Information Fusion Anti-saturation Predefined-time Observer(IFAPO).The proposed FTOC guidance law employs a nonlinear,non-quadratic finite-time optimal control strategy designed for rapid convergence within the limited timeframes of near-space interceptions,avoiding the need for remaining flight time estimation or linear decoupling inherent in traditional methods.To complement the guidance strategy,the IFAPO leverages multi-source information fusion theory and incorporates anti-saturation mechanisms to enhance target maneuver estimation.This method ensures accurate and real-time prediction of target acceleration while maintaining predefined convergence performance,even under complex interception conditions.By integrating the FTOC guidance law and IFAPO,the approach optimizes cooperative missile positioning,improves interception success rates,and minimizes fuel consumption,addressing practical constraints in military applications.Simulation results and comparative analyses confirm the effectiveness of the integrated approach,demonstrating its capability to achieve cooperative interception of highly maneuvering targets with enhanced efficiency and reduced economic costs,aligning with realistic combat scenarios.
基金National Key R&D Program of China(No.2020YFC2201000).
文摘Research has been carried out on a hybrid discharge ion thruster,aiming to combine the advantages of Direct Current(DC)discharge ion thrusters(known for their high thrust density and high power supply efficiency)with microwave discharge ion thrusters(which do not require a hollow cathode and are capable of efficient ionization at low pressures).Comparative experiments with different anode structures and single-probe diagnostics revealed that applying a DC bias voltage created a new ionization zone based on microwave discharge.This DC bias increased the sheath potential of the screen grid and led to an elevation in electron temperature and plasma density.It is speculated that the reduced loss of high-energy electrons generated by microwave discharge at the screen grid is the primary reason for the enhanced discharge.By adding a DC bias of approximately 50 V to the microwave discharge,the screen grid current was doubled without a significant increase in discharge power consumption.Under appropriate bias voltages that consider minimizing ion sputtering,DC bias holds promise as a design approach to increase the extracted beam current in microwave ion thrusters.
基金This study was funded by the General Program of the National Natural Science Foundation of China(52274092)Hu-Bao-E National Independent Innovation Demonstration Zone Construction Science and Technology Support Project(2023XM08)Funds for Talents Supported by the China Association for Science and Technol-0gy(YESS20200211).
文摘Ground subsidence caused by extraction of longwall panels has always been a great concern all over the world.Conventional longwall mining system(CLMS)gives rise to wavy subsidence causing great damage to surface structures.A coal mine in Shanxi,China,utilizes a split-level longwall layout(SLL)for a sub-horizontal No.8 coal seam to improve the cavability of mudstone interlayer and top coal.This layout,however,also produced unexpectedly favorable surface subsidence.Subsidence of No.6 and No.8 longwall panels was monitored while mining was conducted.Field instrumentation and numerical simulation were carried out.It is demonstrated that an asymmetric subsidence profile with stepped subsidence and cracks occurred on the tailgate side but relatively mild and smooth deformation on the other.Due to elimination of conventional parallelepiped gate pillar,No.6 and No.8 gobs were connected.Extraction of two SLL panels acted as one supercritical panel.The maximum possible subsidence was reached which lowers the likelihood of potential future secondary subsidence as underground gob fractures and voids have closed.Therefore,SLL is more favorable for postmining land reuse as gobs are more consolidated underground.
基金Supported by the National Natural Science Foundation of China(50979030 and 50911130366)
文摘Based on three-dimensional cellular automata （CA）, a new stochastic simulation model to simulate the microstructures and particle flow of talus deposit is proposed. Ill addition, an auto-modeling program CARS is developed, with which nunaerical simulations can be conducted conveniently. For the problem of simulating mechanical behaviors of talus deposit, spatial anangement or sphere shapes should be considered. In the new modeling method, four sphere anangement models are developed for the particle flow simulation of talus deposit. Numerical results show that the talus deposit has the mechanical characteristics of typical stress-strain curves, as other rock-like materials. The cohesion of talus deposit decreases with increasing rock content, while the internal friction angle increases with increasing rock contents. Finally, numerical simulation is verified with the results of field test.
基金The first author gratefully acknowledges the Ministry of Research,Technology,and Higher Education(KEMENRISTEKDIKTI)of Republic Indonesia for the scholarship funding through the Research and Innovation in Science and Technology Project(RISET-Pro)program and also the University of Glasgow for supporting this research.
文摘In this study,a packed bed reactor was developed to investigate the gasification process of coal particles.The effects of coal particle size and heater temperature of reactor were examined to identify the thermochemical processes through the packed bed.Three different coal samples with varying size,named as A,B,and C,are used,and the experimental results show that the packed bed with smaller coal size has higher temperature,reaching 624°C,582°C,and 569°C for coal A,B,and C,respectively.In the case of CO formation,the smaller particle size has greater products in the unit of mole fraction over the area of generation.However,the variation in the porosity of the packed bed due to different coal particle sizes affects the reactions through the oxygen access.Consequently,the CO formation is least from the coal packed bed formed by the smallest particle size A.A second test with the temperature variations shows that the higher heater temperature promotes the chemical reactions,resulting in the increased gas products.The findings indicate the important role of coal seam porosity in underground coal gasification application,as well as temperature to promote the syngas productions.
基金The study was supported by the National Institutes of Health,Grant number:NR016650the Center for AIDS Research,Johns Hopkins University through the National Institutes of Health,Grant number:P30AI094189.
文摘Background:Epidemic models of sexually transmitted infections(STIs)are often used to characterize the contribution of risk groups to overall transmission by projecting the transmission population attributable fraction(tPAF)of unmet prevention and treatment needs within risk groups.However,evidence suggests that STI risk is dynamic over an individual’s sexual life course,which manifests as turnover between risk groups.We sought to examine the mechanisms by which turnover influences modelled projections of the tPAF of high risk groups.Methods:We developed a unifying,data-guided framework to simulate risk group turnover in deterministic,compartmental transmission models.We applied the framework to an illustrative model of an STI and examined the mechanisms by which risk group turnover influenced equilibrium prevalence across risk groups.We then fit a model with and without turnover to the same risk-stratified STI prevalence targets and compared the inferred level of risk heterogeneity and tPAF of the highest risk group projected by the two models.Results:The influence of turnover on group-specific prevalence was mediated by three main phenomena:movement of previously high risk individuals with the infection into lower risk groups;changes to herd effect in the highest risk group;and changes in the number of partnerships where transmission can occur.Faster turnover led to a smaller ratio of STI prevalence between the highest and lowest risk groups.Compared to the fitted model without turnover,the fitted model with turnover inferred greater risk heterogeneity and consistently projected a larger tPAF of the highest risk group over time.Implications:If turnover is not captured in epidemic models,the projected contribution of high risk groups,and thus,the potential impact of prioritizing interventions to address their needs,could be underestimated.To aid the next generation of tPAF models,data collection efforts to parameterize risk group turnover should be prioritized.
