Critical Path Method (CPM) Scheduling has proven to be an effective project management tool. However, teaching the topic has proven difficult to include all elements of CPM yet keep it simple enough for students to un...Critical Path Method (CPM) Scheduling has proven to be an effective project management tool. However, teaching the topic has proven difficult to include all elements of CPM yet keep it simple enough for students to understand. In an effort to simplify the teaching of critical path method scheduling, the issue of two total floats in an activity does not get the attention necessary to address its occurrence. The objective of this paper is to present a mathematical method to show multiple total floats are possible for an activity. Also presented are suggestions for schedule crashing when multiple total floats are found. Two totals floats can be found if constraints (Lag or Lead) or non-Finish-to-Start (FS) relationships, or both are used in a network diagram. Situations are possible where an activity may have a start total float (STF) of zero but have a finish total float (FTF) greater than zero, or vice versa. Because the critical path generally follows the zero total float, these situations, where either the STF or the FTF is critical while the other is not, determines how the critical path activity must be controlled and crashed. This paper will present approaches of how to crash the schedule when a portion of the activity, either start or finish, is critical. Also presented will be methods to teach the subject matter with or without the use of scheduling software. Critical Path Method was revisited to see what the minimal conditions are needed to have activities with two total float. Generalized crashing methods were studied to see if the methods can be used when two total floats exist.展开更多
This study investigates the inward flux events following sawtooth crashes in the edge of HL-2A neutral beam heated plasmas.We identified three distinct types of inward fluxes with varying magnitudes and durations,each...This study investigates the inward flux events following sawtooth crashes in the edge of HL-2A neutral beam heated plasmas.We identified three distinct types of inward fluxes with varying magnitudes and durations,each associated with unique plasma parameter fluctuations.Magnetic fluctuations,particularly the disruption of magnetic surface structures caused by sawtooth crashes,may play a significant role in modulating plasma dynamics.Moreover,the crossphase term and coherence between density and velocity fluctuations were found to be key factors in these flux events,with high coherence correlating with peak inward flux.These findings enhance the understanding of fluctuation-induced transport after sawtooth crashes and have implications for plasma confinement in fusion devices.展开更多
EXCERPTS FROM MAJOR CHINESE MAGAZINES SMART DRIVING SAFETY DEBATE China Newsweek 14 April A fatal Xiaomi SU7 crash on 29 March involving NOA(navigation on autopilot)-assisted driving mode has ignited debates about sma...EXCERPTS FROM MAJOR CHINESE MAGAZINES SMART DRIVING SAFETY DEBATE China Newsweek 14 April A fatal Xiaomi SU7 crash on 29 March involving NOA(navigation on autopilot)-assisted driving mode has ignited debates about smart driving safety in China.Preliminary data shows the car was in NOA mode before colliding with highway barriers,killing three people.展开更多
BACKGROUND Traumatic hemothorax is a common complication of chest trauma;however,the timeline for its resolution,even with chest tube thoracostomy,remains unclear.AIM To determine the time to resolution of the hemotho...BACKGROUND Traumatic hemothorax is a common complication of chest trauma;however,the timeline for its resolution,even with chest tube thoracostomy,remains unclear.AIM To determine the time to resolution of the hemothorax to ensure safe discharge based on chest radiography(CXR)findings.METHODS A retrospective observational study was conducted at Hamad General Hospital,Qatar,from June 2014 to October 2019,including all patients with hemothorax diagnosed via computed tomography(CT)following chest trauma.Based on the initial imaging study,the hemothorax was divided into right,left,and bilateral.RESULTS The study included 422 patients.Of the total,57.82%(n=244/422)resolved their hemothorax within three days of admission.Among these,44 patients required chest tube insertion(CTI)and 200 were cleared without it.Between days 3 and 7,an additional 16.83%(n=71/422)of cases were resolved,of which 28 required chest tubes.By days 8 to 14,another 11.37%(n=48/422)were cleared,with 15 patients requiring chest tubes.After 14 days,13.98%(n=59/422)of patients still had hemothorax,14 of whom required CTI.CONCLUSION This study showed that a subset of patients continued to experience retained hemothorax despite early tube thoracostomy.Patients with a larger hemothorax,particularly on the left side,showed prolonged resolution times.Regular imaging such as CXR or CT is recommended for up to 14 days post-intervention.After this period,outpatient follow-up is generally safe,although some patients may still have a persistent hemothorax beyond two weeks.展开更多
Understanding crash contributing factors is essential in safety management and improvement. These factors drive investment decisions, policies, regulations, and other safety-related initiatives. This paper analyzes fa...Understanding crash contributing factors is essential in safety management and improvement. These factors drive investment decisions, policies, regulations, and other safety-related initiatives. This paper analyzes factors that contribute to crash occurrence based on two national datasets in the United States (CISS and NASS-CDS) for the years 2017-2022 and 2010-2015, respectively. Three taxonomies were applied to enhance understanding of the various crash contributing factors. These taxonomies were developed based on previous research and practice and involved different groupings of human factors, vehicle factors, and roadway and environmental factors. Statistics for grouping the different types of factors and statistics for specific factors are provided. The results indicate that human factors are present in over 95% of crashes, roadway and environmental factors are present in over 45% of crashes, and vehicle factors are present in less than 2% of crashes. Regarding factors related to human error and vehicle maintenance, speeding is involved in over 25% of crashes, distraction is involved in over 20% of crashes, alcohol and drugs are involved in over 9% of crashes, and vehicle maintenance is involved in approximately 0.45% of crashes. Approximately 4.4% of crashes involve a driver who “looked but did not see.” Weather is involved in over 13% of crashes. Conclusions: The findings indicate that, consistent with previous research, human factors or human error are present in around 95% of crashes. Infrastructure and environmental factors contribute to about 45% of crashes. Vehicle factors contribute to only 1.67% - 1.71% of crashes. The results from this study could potentially be used to inform future safety management and improvement activities, including policy-making, regulation development, safe systems and systemic safety approaches to safety management, and other engineering, education, emergency response, enforcement, evaluation, and encouragement activities. The findings could also be used in the development of future Driver Assistance Technologies (DAT) systems and in enhancing existing technologies.展开更多
Electron cyclotron emission imaging(ECEI)is a critical diagnostic tool for measuring two-dimensional electron temperature fluctuations.The optical system,a key component of the ECEI diagnostic,determines the spatial r...Electron cyclotron emission imaging(ECEI)is a critical diagnostic tool for measuring two-dimensional electron temperature fluctuations.The optical system,a key component of the ECEI diagnostic,determines the spatial resolution,field of view,and imaging performance of electron temperature fluctuations.In this study,comprehensive laboratory tests and characterizations of the optical system,including the local oscillator(LO)coupling optics and the radio frequency(RF)receiving optics,were conducted to ensure optimal performance during plasma discharge experiments.Laboratory testing of the LO optics revealed that the light intensity at the edge channels reaches 36%of that at the central channels;however,both are sufficient to effectively drive the down-converted mixers.The RF optics focus covers the entire non-harmonic overlap region,corresponding to a normalized plasma minor radius range of ρ=−0.2 to 0.9,and offers three zoom modes:narrow,medium,and wide,with poloidal resolutions of 1.5 cm,1.8 cm,and 2.1 cm,respectively.The characterizations for these zoom modes align well with the optical design specifications.It was observed that the imaging surfaces of all zoom modes are exceptionally flat,indicating high-quality ECEI measurements with excellent spatial resolution.The LO lens,focusing lens,and zoom adjustment lens are capable of remote independent control,which enhances the operational flexibility of the system.Preliminary analyses conducted with the ECEI system successfully captured the two-dimensional structure and spatiotemporal evolution of phenomena such as sawtooth crashes,demonstrating the robust capability of the system to provide valuable insights into plasma dynamics.展开更多
We investigate high-frequency traders’behavior in the context of the fastest and most extreme price movements(EPMs)that can be observed in the market,specifically ultrafast flash events,challenging the methodologies ...We investigate high-frequency traders’behavior in the context of the fastest and most extreme price movements(EPMs)that can be observed in the market,specifically ultrafast flash events,challenging the methodologies employed in the academic and practitioner literature for identifying sudden liquidity black holes.To refine the price-shock identification methodology,we introduce a new approach called sequence-based flash events(SFEs),which relies on tick sequences instead of predetermined fixed-time intervals within which all flash events in the sample are assumed to occur.This alternative methodology offers the advantage of pinpointing the exact time and duration of a crash,which,in turn,provides a way to more accurately define the observation windows around it.We compare our sample of SFEs with both the so-called“mini flash crashes”,as identified by the Nanex detection algorithm,and the so-called EPMs,as identified by Brogaard et al.(2018).We use close and open prices,as well as high and low prices.Based on our sample of SFEs,we find no evidence that HFTs trigger extreme price shocks.However,we find that HFTs exacerbate SFEs by increasing the net imbalance in the direction of these shocks as they occur.Finally,we show that the choice of the price-shock identification methodology is critical.Thus,we urge regulators to exercise caution and avoid hasty conclusions regarding HFTs’contribution to price stability in stressful market conditions.展开更多
Within-Visual-Range(WVR)air combat is a highly dynamic and uncertain domain where effective strategies require intelligent and adaptive decision-making.Traditional approaches,including rule-based methods and conventio...Within-Visual-Range(WVR)air combat is a highly dynamic and uncertain domain where effective strategies require intelligent and adaptive decision-making.Traditional approaches,including rule-based methods and conventional Reinforcement Learning(RL)algorithms,often focus on maximizing engagement outcomes through direct combat superiority.However,these methods overlook alternative tactics,such as inducing adversaries to crash,which can achieve decisive victories with lower risk and cost.This study proposes Alpha Crash,a novel distributional-rein forcement-learning-based agent specifically designed to defeat opponents by leveraging crash induction strategies.The approach integrates an improved QR-DQN framework to address uncertainties and adversarial tactics,incorporating advanced pilot experience into its reward functions.Extensive simulations reveal Alpha Crash's robust performance,achieving a 91.2%win rate across diverse scenarios by effectively guiding opponents into critical errors.Visualization and altitude analyses illustrate the agent's three-stage crash induction strategies that exploit adversaries'vulnerabilities.These findings underscore Alpha Crash's potential to enhance autonomous decision-making and strategic innovation in real-world air combat applications.展开更多
This paper selects the Corporate Social Responsibility(CSR)index from Hexun.com(2010–2020)and the stock price crash index of China’s Shanghai and Shenzhen A-share listed companies from the China Stock Market&Acc...This paper selects the Corporate Social Responsibility(CSR)index from Hexun.com(2010–2020)and the stock price crash index of China’s Shanghai and Shenzhen A-share listed companies from the China Stock Market&Accounting Research Database(CSMAR)for empirical analysis.By examining the impact of CSR performance on stock price crash risk,this study identifies key relationships and further investigates the moderating role of media promotion and communication as an intermediary to explore the transmission mechanisms and influence between the two.The empirical results indicate that CSR performance is significantly negatively correlated with stock price crash risk,suggesting that strong CSR performance can effectively reduce the likelihood of a stock price crash.Furthermore,additional analysis reveals that media plays a moderating role in the relationship between CSR performance and stock price crash risk.This study aims to contribute to the understanding of the formation mechanisms and analytical paradigms of factors influencing stock price crash risk while providing theoretical support and reference value for risk prevention strategies.展开更多
针对某典型前缘结构,研究了使用纤维金属层板(Fibre Metal Laminates,FMLs)蒙皮进行抗鸟撞设计的可行性。以显式动态冲击分析程序PAM-CRASH为平台,结合由鸟撞平板试验结果验证的鸟体本构模型参数,建立了鸟撞前缘结构数值模型。通过计算...针对某典型前缘结构,研究了使用纤维金属层板(Fibre Metal Laminates,FMLs)蒙皮进行抗鸟撞设计的可行性。以显式动态冲击分析程序PAM-CRASH为平台,结合由鸟撞平板试验结果验证的鸟体本构模型参数,建立了鸟撞前缘结构数值模型。通过计算研究了使用不同蒙皮(铝合金、FMLs)的前缘结构在鸟撞作用下的变形破坏模式及吸能效果。结果表明:采用适当铺层的FMLs蒙皮可以有效地提高前缘结构的抗鸟撞性能。研究结论对飞机结构的抗鸟撞研究具有一定的参考价值。展开更多
The location of U-turn bays is an important consideration in indirect driveway left-turn treatments.In order to improve the performance of right-turns followed by U-turns（RTUTs）,this study evaluates the impacts of t...The location of U-turn bays is an important consideration in indirect driveway left-turn treatments.In order to improve the performance of right-turns followed by U-turns（RTUTs）,this study evaluates the impacts of the separation distances between driveway exits and downstream U-turn locations on the safety and operational performance of vehicles making RTUTs.Crash data are investigated at 179 selected roadway segments,and travel time data are measured using video cameras at 29 locations in the state of Florida,USA.Crash rate models and travel time models are developed based on data collected in the field.It is found that the separation distance between driveway exits and downstream U-turn locations significantly impacts the safety and operational performance of vehicles making right turns followed by U-turns.Based on the research results,the minimum and optimal separation distances between driveways and U-turn locations under different roadway conditions are determined to facilitate driver use of RTUTs.The results of this study can be used for future intersection improvement projects in China.展开更多
In order to improve crash occurrence models to account for the influence of various contributing factors, a conditional autoregressive negative binomial （CAR-NB） model is employed to allow for overdispersion （tackl...In order to improve crash occurrence models to account for the influence of various contributing factors, a conditional autoregressive negative binomial （CAR-NB） model is employed to allow for overdispersion （tackled by the NB component）, unobserved heterogeneity and spatial autocorrelation （captured by the CAR process）, using Markov chain Monte Carlo methods and the Gibbs sampler. Statistical tests suggest that the CAR-NB model is preferred over the CAR-Poisson, NB, zero-inflated Poisson, zero-inflated NB models, due to its lower prediction errors and more robust parameter inference. The study results show that crash frequency and fatalities are positively associated with the number of lanes, curve length, annual average daily traffic （AADT） per lane, as well as rainfall. Speed limit and the distances to the nearest hospitals have negative associations with segment-based crash counts but positive associations with fatality counts, presumably as a result of worsened collision impacts at higher speed and time loss during transporting crash victims.展开更多
文摘Critical Path Method (CPM) Scheduling has proven to be an effective project management tool. However, teaching the topic has proven difficult to include all elements of CPM yet keep it simple enough for students to understand. In an effort to simplify the teaching of critical path method scheduling, the issue of two total floats in an activity does not get the attention necessary to address its occurrence. The objective of this paper is to present a mathematical method to show multiple total floats are possible for an activity. Also presented are suggestions for schedule crashing when multiple total floats are found. Two totals floats can be found if constraints (Lag or Lead) or non-Finish-to-Start (FS) relationships, or both are used in a network diagram. Situations are possible where an activity may have a start total float (STF) of zero but have a finish total float (FTF) greater than zero, or vice versa. Because the critical path generally follows the zero total float, these situations, where either the STF or the FTF is critical while the other is not, determines how the critical path activity must be controlled and crashed. This paper will present approaches of how to crash the schedule when a portion of the activity, either start or finish, is critical. Also presented will be methods to teach the subject matter with or without the use of scheduling software. Critical Path Method was revisited to see what the minimal conditions are needed to have activities with two total float. Generalized crashing methods were studied to see if the methods can be used when two total floats exist.
基金support of these experiments.This work was supported by the National Natural Science Foundation of China(12405268,12175227,11875255,12375226,and 11975231)the National Magnetic Confinement Fusion Science Program of China(2022YFE03060003,2022YFE03100004)+1 种基金the Fundamental Research Funds for the Central Universities(WK2140000016)the China Postdoctoral Science Foundation(2022M723066).
文摘This study investigates the inward flux events following sawtooth crashes in the edge of HL-2A neutral beam heated plasmas.We identified three distinct types of inward fluxes with varying magnitudes and durations,each associated with unique plasma parameter fluctuations.Magnetic fluctuations,particularly the disruption of magnetic surface structures caused by sawtooth crashes,may play a significant role in modulating plasma dynamics.Moreover,the crossphase term and coherence between density and velocity fluctuations were found to be key factors in these flux events,with high coherence correlating with peak inward flux.These findings enhance the understanding of fluctuation-induced transport after sawtooth crashes and have implications for plasma confinement in fusion devices.
文摘EXCERPTS FROM MAJOR CHINESE MAGAZINES SMART DRIVING SAFETY DEBATE China Newsweek 14 April A fatal Xiaomi SU7 crash on 29 March involving NOA(navigation on autopilot)-assisted driving mode has ignited debates about smart driving safety in China.Preliminary data shows the car was in NOA mode before colliding with highway barriers,killing three people.
文摘BACKGROUND Traumatic hemothorax is a common complication of chest trauma;however,the timeline for its resolution,even with chest tube thoracostomy,remains unclear.AIM To determine the time to resolution of the hemothorax to ensure safe discharge based on chest radiography(CXR)findings.METHODS A retrospective observational study was conducted at Hamad General Hospital,Qatar,from June 2014 to October 2019,including all patients with hemothorax diagnosed via computed tomography(CT)following chest trauma.Based on the initial imaging study,the hemothorax was divided into right,left,and bilateral.RESULTS The study included 422 patients.Of the total,57.82%(n=244/422)resolved their hemothorax within three days of admission.Among these,44 patients required chest tube insertion(CTI)and 200 were cleared without it.Between days 3 and 7,an additional 16.83%(n=71/422)of cases were resolved,of which 28 required chest tubes.By days 8 to 14,another 11.37%(n=48/422)were cleared,with 15 patients requiring chest tubes.After 14 days,13.98%(n=59/422)of patients still had hemothorax,14 of whom required CTI.CONCLUSION This study showed that a subset of patients continued to experience retained hemothorax despite early tube thoracostomy.Patients with a larger hemothorax,particularly on the left side,showed prolonged resolution times.Regular imaging such as CXR or CT is recommended for up to 14 days post-intervention.After this period,outpatient follow-up is generally safe,although some patients may still have a persistent hemothorax beyond two weeks.
文摘Understanding crash contributing factors is essential in safety management and improvement. These factors drive investment decisions, policies, regulations, and other safety-related initiatives. This paper analyzes factors that contribute to crash occurrence based on two national datasets in the United States (CISS and NASS-CDS) for the years 2017-2022 and 2010-2015, respectively. Three taxonomies were applied to enhance understanding of the various crash contributing factors. These taxonomies were developed based on previous research and practice and involved different groupings of human factors, vehicle factors, and roadway and environmental factors. Statistics for grouping the different types of factors and statistics for specific factors are provided. The results indicate that human factors are present in over 95% of crashes, roadway and environmental factors are present in over 45% of crashes, and vehicle factors are present in less than 2% of crashes. Regarding factors related to human error and vehicle maintenance, speeding is involved in over 25% of crashes, distraction is involved in over 20% of crashes, alcohol and drugs are involved in over 9% of crashes, and vehicle maintenance is involved in approximately 0.45% of crashes. Approximately 4.4% of crashes involve a driver who “looked but did not see.” Weather is involved in over 13% of crashes. Conclusions: The findings indicate that, consistent with previous research, human factors or human error are present in around 95% of crashes. Infrastructure and environmental factors contribute to about 45% of crashes. Vehicle factors contribute to only 1.67% - 1.71% of crashes. The results from this study could potentially be used to inform future safety management and improvement activities, including policy-making, regulation development, safe systems and systemic safety approaches to safety management, and other engineering, education, emergency response, enforcement, evaluation, and encouragement activities. The findings could also be used in the development of future Driver Assistance Technologies (DAT) systems and in enhancing existing technologies.
基金partly supported by the National MCF Energy R&D Program of China(No.2022YFE03060003)partly by the Chinese National Fusion Project for ITER(No.2024YFE03190000)+2 种基金partly by National Natural Science Foundation of China(No.12405254)partly by the Innovation Program of Southwestern Institute of Physics(No.202301XWCX001-02)partly by Sichuan Science and Technology Program(No.2023ZYD0014).
文摘Electron cyclotron emission imaging(ECEI)is a critical diagnostic tool for measuring two-dimensional electron temperature fluctuations.The optical system,a key component of the ECEI diagnostic,determines the spatial resolution,field of view,and imaging performance of electron temperature fluctuations.In this study,comprehensive laboratory tests and characterizations of the optical system,including the local oscillator(LO)coupling optics and the radio frequency(RF)receiving optics,were conducted to ensure optimal performance during plasma discharge experiments.Laboratory testing of the LO optics revealed that the light intensity at the edge channels reaches 36%of that at the central channels;however,both are sufficient to effectively drive the down-converted mixers.The RF optics focus covers the entire non-harmonic overlap region,corresponding to a normalized plasma minor radius range of ρ=−0.2 to 0.9,and offers three zoom modes:narrow,medium,and wide,with poloidal resolutions of 1.5 cm,1.8 cm,and 2.1 cm,respectively.The characterizations for these zoom modes align well with the optical design specifications.It was observed that the imaging surfaces of all zoom modes are exceptionally flat,indicating high-quality ECEI measurements with excellent spatial resolution.The LO lens,focusing lens,and zoom adjustment lens are capable of remote independent control,which enhances the operational flexibility of the system.Preliminary analyses conducted with the ECEI system successfully captured the two-dimensional structure and spatiotemporal evolution of phenomena such as sawtooth crashes,demonstrating the robust capability of the system to provide valuable insights into plasma dynamics.
文摘We investigate high-frequency traders’behavior in the context of the fastest and most extreme price movements(EPMs)that can be observed in the market,specifically ultrafast flash events,challenging the methodologies employed in the academic and practitioner literature for identifying sudden liquidity black holes.To refine the price-shock identification methodology,we introduce a new approach called sequence-based flash events(SFEs),which relies on tick sequences instead of predetermined fixed-time intervals within which all flash events in the sample are assumed to occur.This alternative methodology offers the advantage of pinpointing the exact time and duration of a crash,which,in turn,provides a way to more accurately define the observation windows around it.We compare our sample of SFEs with both the so-called“mini flash crashes”,as identified by the Nanex detection algorithm,and the so-called EPMs,as identified by Brogaard et al.(2018).We use close and open prices,as well as high and low prices.Based on our sample of SFEs,we find no evidence that HFTs trigger extreme price shocks.However,we find that HFTs exacerbate SFEs by increasing the net imbalance in the direction of these shocks as they occur.Finally,we show that the choice of the price-shock identification methodology is critical.Thus,we urge regulators to exercise caution and avoid hasty conclusions regarding HFTs’contribution to price stability in stressful market conditions.
基金supported by the National Key R&D Program of China(No.2021YFB3300602)。
文摘Within-Visual-Range(WVR)air combat is a highly dynamic and uncertain domain where effective strategies require intelligent and adaptive decision-making.Traditional approaches,including rule-based methods and conventional Reinforcement Learning(RL)algorithms,often focus on maximizing engagement outcomes through direct combat superiority.However,these methods overlook alternative tactics,such as inducing adversaries to crash,which can achieve decisive victories with lower risk and cost.This study proposes Alpha Crash,a novel distributional-rein forcement-learning-based agent specifically designed to defeat opponents by leveraging crash induction strategies.The approach integrates an improved QR-DQN framework to address uncertainties and adversarial tactics,incorporating advanced pilot experience into its reward functions.Extensive simulations reveal Alpha Crash's robust performance,achieving a 91.2%win rate across diverse scenarios by effectively guiding opponents into critical errors.Visualization and altitude analyses illustrate the agent's three-stage crash induction strategies that exploit adversaries'vulnerabilities.These findings underscore Alpha Crash's potential to enhance autonomous decision-making and strategic innovation in real-world air combat applications.
基金R&D Program of Beijing Municipal Education Commission(Grant No.SM202210005007)。
文摘This paper selects the Corporate Social Responsibility(CSR)index from Hexun.com(2010–2020)and the stock price crash index of China’s Shanghai and Shenzhen A-share listed companies from the China Stock Market&Accounting Research Database(CSMAR)for empirical analysis.By examining the impact of CSR performance on stock price crash risk,this study identifies key relationships and further investigates the moderating role of media promotion and communication as an intermediary to explore the transmission mechanisms and influence between the two.The empirical results indicate that CSR performance is significantly negatively correlated with stock price crash risk,suggesting that strong CSR performance can effectively reduce the likelihood of a stock price crash.Furthermore,additional analysis reveals that media plays a moderating role in the relationship between CSR performance and stock price crash risk.This study aims to contribute to the understanding of the formation mechanisms and analytical paradigms of factors influencing stock price crash risk while providing theoretical support and reference value for risk prevention strategies.
文摘针对某典型前缘结构,研究了使用纤维金属层板(Fibre Metal Laminates,FMLs)蒙皮进行抗鸟撞设计的可行性。以显式动态冲击分析程序PAM-CRASH为平台,结合由鸟撞平板试验结果验证的鸟体本构模型参数,建立了鸟撞前缘结构数值模型。通过计算研究了使用不同蒙皮(铝合金、FMLs)的前缘结构在鸟撞作用下的变形破坏模式及吸能效果。结果表明:采用适当铺层的FMLs蒙皮可以有效地提高前缘结构的抗鸟撞性能。研究结论对飞机结构的抗鸟撞研究具有一定的参考价值。
文摘The location of U-turn bays is an important consideration in indirect driveway left-turn treatments.In order to improve the performance of right-turns followed by U-turns（RTUTs）,this study evaluates the impacts of the separation distances between driveway exits and downstream U-turn locations on the safety and operational performance of vehicles making RTUTs.Crash data are investigated at 179 selected roadway segments,and travel time data are measured using video cameras at 29 locations in the state of Florida,USA.Crash rate models and travel time models are developed based on data collected in the field.It is found that the separation distance between driveway exits and downstream U-turn locations significantly impacts the safety and operational performance of vehicles making right turns followed by U-turns.Based on the research results,the minimum and optimal separation distances between driveways and U-turn locations under different roadway conditions are determined to facilitate driver use of RTUTs.The results of this study can be used for future intersection improvement projects in China.
基金The National Science Foundation by Changjiang Scholarship of Ministry of Education of China(No.BCS-0527508)the Joint Research Fund for Overseas Natural Science of China(No.51250110075)+1 种基金the Natural Science Foundation of Jiangsu Province(No.SBK200910046)the Postdoctoral Science Foundation of Jiangsu Province(No.0901005C)
文摘In order to improve crash occurrence models to account for the influence of various contributing factors, a conditional autoregressive negative binomial （CAR-NB） model is employed to allow for overdispersion （tackled by the NB component）, unobserved heterogeneity and spatial autocorrelation （captured by the CAR process）, using Markov chain Monte Carlo methods and the Gibbs sampler. Statistical tests suggest that the CAR-NB model is preferred over the CAR-Poisson, NB, zero-inflated Poisson, zero-inflated NB models, due to its lower prediction errors and more robust parameter inference. The study results show that crash frequency and fatalities are positively associated with the number of lanes, curve length, annual average daily traffic （AADT） per lane, as well as rainfall. Speed limit and the distances to the nearest hospitals have negative associations with segment-based crash counts but positive associations with fatality counts, presumably as a result of worsened collision impacts at higher speed and time loss during transporting crash victims.
