Based on the load model of a uniform isotropic semi-infinite elastic medium,we deduced a calculation of vertical displacement and tilt and proposed a method of calculation of vertical displacements and tilts caused by...Based on the load model of a uniform isotropic semi-infinite elastic medium,we deduced a calculation of vertical displacement and tilt and proposed a method of calculation of vertical displacements and tilts caused by irregular load on the ground or underground at a certain point with two-dimensional and three-dimensional shapes. We compared the difference between the simplified model and the irregular model. Finally,the vertical displacements near the irregular load and the distribution of horizontal tilt are presented.The results show that,compared with the point simplified model,the irregular load model has certain advantages for describing the near field. The establishment of a twodimensional irregular load model can help with the calculation of the modal vector superposition after load scattering. The three-dimensional irregular load model can redistribute load through different weights given to the scattered points after the load scattering,and then obtain displacement with the vector calculation method. The results of vector superposition calculation from the scattered irregular load both in two-dimensions and three-dimensions are all convergent obviously as grids become denser,and it is shown that the calculation method is correct and feasible.展开更多
The proportions of older drivers continue to increase since baby boom generation is becoming old. The level of mobility of older drivers is also increasing. Older drivers begin to noticeably be over-involved in fatal ...The proportions of older drivers continue to increase since baby boom generation is becoming old. The level of mobility of older drivers is also increasing. Older drivers begin to noticeably be over-involved in fatal crashes. Intersections appear to be hazardous to older drivers, particularly left turn due to one or more of. sensory, perceptual, cognitive, physical and general driving knowledge deficiencies. The safety concern of older drivers is also becoming significant. Ten years of crash data has been extracted from Kansas accident report system. It has been analyzed using SAS （statistical analysis system） software. Five different age groups have been considered. Comparison has been made between different age groups of the same gender, and the same age group for different gender. Effects of light condition, weather condition, surface type, surface condition, road character and construction/maintenance zone on older drivers＇ safety have also been considered in this study. It has been found out that proportion of older drivers in through movement involved in accident decreases as age increases whereas the proportion of left turn accidents increases with age, left turn is harder for females in all age groups, and proportion of right turn accidents has no specific trend. Most of the accidents have taken place during daylight when there are no adverse weather conditions on dry surface, straight and level road, and blacktop surface type.展开更多
A new probabilistic seismic hazard analysis was performed for the city of Bridgetown, Barbados, West Indies. Hazard computations have been performed using the standard Cornell-McGuire approach based on the definition ...A new probabilistic seismic hazard analysis was performed for the city of Bridgetown, Barbados, West Indies. Hazard computations have been performed using the standard Cornell-McGuire approach based on the definition of appropriate seismogenic sources and expected maximum magnitudes, the authors take into consideration the possibility of large subduction interface earthquakes of magnitude 8.0-9.0 beneath the Barbados accretionary prism via application of a characteristic model and slip rates. The analysis has been conducted using a standard logic-tree approach. Uniform hazard spectra have been calculated for the 5% of critical damping and the horizontal component of ground motion for rock site conditions setting 5 return periods （95, 475, 975, 2,475 and 4,975 years） and spectral accelerations for 34 structural periods ranging from 0 to 3 s. The disaggregation results suggest that the magnitude-distance pair that dominates the hazard yields M 7.4 and 8.6 and a distance of 42.5 km in the Interface Subduction Zone beneath Barbados for the 475 and 975 years RP （return period）, respectively. An event with an M 8.0 at a distance of 107.5 km in the Intraplate Subduction Zone is the second scenario that dominates the hazard for both 475 and 975 years RP.展开更多
Models for the gravitational field of Mars moon Phobos were developed using the latest shape model and assuming homogeneous density distribution.Three methods were applied in our study.Comparisons were made between th...Models for the gravitational field of Mars moon Phobos were developed using the latest shape model and assuming homogeneous density distribution.Three methods were applied in our study.Comparisons were made between these methods and all were shown to yield consistent results.Notably,the most accurate shape model of Phobos to date,complete up to degree and order 17 was used for the first time in our analysis.A set of spherical harmonic coefficients up to degree and order 17 were derived for the gravitational field of Phobos.Also considered was the gravitational field on the surface of Phobos.Typical characteristics as well as some pronounced surface features of this irregular-shaped small body could be conveniently identified.The results are readily applicable for such purposes as spacecraft orbit analysis and assessing the dynamical environment of Phobos.展开更多
The upward lightning(UL) initiated from the top of tall buildings(at least above 100 m) is a type of atmospheric discharge. Currently, we understand the nature of the UL from ground observations, but the corresponding...The upward lightning(UL) initiated from the top of tall buildings(at least above 100 m) is a type of atmospheric discharge. Currently, we understand the nature of the UL from ground observations, but the corresponding theoretical research is lacking. Based on an existing bidirectional leader stochastic model, a stochastic parameterization scheme for the UL has been built and embedded in an existing two-dimensional thundercloud charge/discharge model. The ULs simulated from the experiments with two-dimensional high resolution agree generally with the observation results. By analyzing the charge structure of thunderstorm clouds, we determined the in-cloud environmental characteristics that favor the initiation of conventional cloud-to-ground(CG) flashes and analyzed the differences and similarities of some characteristics of the positive and the negative UL. Simulation results indicate that the positive ULs are typically other-lightning-triggered ULs(OLTUL) and are usually a discharge phenomenon between the ground and the lower positive charge region appearing below the main middle negative charge region. The effect of the previous in-cloud lightning(IC) process of space electrical field provides favorable conditions for the initiation of a positive UL. Its entire discharge process is limited, and the branches of the leader are fewer in number as its discharge is not sufficient. A negative UL is generally a discharge phenomenon of the dipole charge structure between the ground and the main negative charge region. The lower temperature stratification and the sinking of the hydrometeors typically initiate a negative UL. Negative ULs develop strongly and have more branches. The OLTUL is initiated mainly during the development stage of a thunderstorm, while the self-triggered UL(STUL) is initiated mainly during the dissipation stage of a thunderstorm.展开更多
基金funded by the Earthquake Tracing Oriented Task of Monitoring and Forecasting Department of China Earthquake Administration in 2015(2015020201):the 12th“Five-year Plan”Science and Technology Support Plan of China(2012BAK19B02)
文摘Based on the load model of a uniform isotropic semi-infinite elastic medium,we deduced a calculation of vertical displacement and tilt and proposed a method of calculation of vertical displacements and tilts caused by irregular load on the ground or underground at a certain point with two-dimensional and three-dimensional shapes. We compared the difference between the simplified model and the irregular model. Finally,the vertical displacements near the irregular load and the distribution of horizontal tilt are presented.The results show that,compared with the point simplified model,the irregular load model has certain advantages for describing the near field. The establishment of a twodimensional irregular load model can help with the calculation of the modal vector superposition after load scattering. The three-dimensional irregular load model can redistribute load through different weights given to the scattered points after the load scattering,and then obtain displacement with the vector calculation method. The results of vector superposition calculation from the scattered irregular load both in two-dimensions and three-dimensions are all convergent obviously as grids become denser,and it is shown that the calculation method is correct and feasible.
文摘The proportions of older drivers continue to increase since baby boom generation is becoming old. The level of mobility of older drivers is also increasing. Older drivers begin to noticeably be over-involved in fatal crashes. Intersections appear to be hazardous to older drivers, particularly left turn due to one or more of. sensory, perceptual, cognitive, physical and general driving knowledge deficiencies. The safety concern of older drivers is also becoming significant. Ten years of crash data has been extracted from Kansas accident report system. It has been analyzed using SAS （statistical analysis system） software. Five different age groups have been considered. Comparison has been made between different age groups of the same gender, and the same age group for different gender. Effects of light condition, weather condition, surface type, surface condition, road character and construction/maintenance zone on older drivers＇ safety have also been considered in this study. It has been found out that proportion of older drivers in through movement involved in accident decreases as age increases whereas the proportion of left turn accidents increases with age, left turn is harder for females in all age groups, and proportion of right turn accidents has no specific trend. Most of the accidents have taken place during daylight when there are no adverse weather conditions on dry surface, straight and level road, and blacktop surface type.
文摘A new probabilistic seismic hazard analysis was performed for the city of Bridgetown, Barbados, West Indies. Hazard computations have been performed using the standard Cornell-McGuire approach based on the definition of appropriate seismogenic sources and expected maximum magnitudes, the authors take into consideration the possibility of large subduction interface earthquakes of magnitude 8.0-9.0 beneath the Barbados accretionary prism via application of a characteristic model and slip rates. The analysis has been conducted using a standard logic-tree approach. Uniform hazard spectra have been calculated for the 5% of critical damping and the horizontal component of ground motion for rock site conditions setting 5 return periods （95, 475, 975, 2,475 and 4,975 years） and spectral accelerations for 34 structural periods ranging from 0 to 3 s. The disaggregation results suggest that the magnitude-distance pair that dominates the hazard yields M 7.4 and 8.6 and a distance of 42.5 km in the Interface Subduction Zone beneath Barbados for the 475 and 975 years RP （return period）, respectively. An event with an M 8.0 at a distance of 107.5 km in the Intraplate Subduction Zone is the second scenario that dominates the hazard for both 475 and 975 years RP.
基金supported by the CAS-DAAD joint scholarship,the National Natural Science Foundation of China (Grant No.10973031)the National High Technology Research and Development Program of China (Grant No.2010AA122206)the Ministry of Education and Science of the Russian Federation (Grant NO.11.G34.31.0021)
文摘Models for the gravitational field of Mars moon Phobos were developed using the latest shape model and assuming homogeneous density distribution.Three methods were applied in our study.Comparisons were made between these methods and all were shown to yield consistent results.Notably,the most accurate shape model of Phobos to date,complete up to degree and order 17 was used for the first time in our analysis.A set of spherical harmonic coefficients up to degree and order 17 were derived for the gravitational field of Phobos.Also considered was the gravitational field on the surface of Phobos.Typical characteristics as well as some pronounced surface features of this irregular-shaped small body could be conveniently identified.The results are readily applicable for such purposes as spacecraft orbit analysis and assessing the dynamical environment of Phobos.
基金supported by the National Key Basic Research Development Program of China (Grant No. 2014CB441403)the National Natural Science Foundation of China (Grant Nos. 41175003 & 41475003)
文摘The upward lightning(UL) initiated from the top of tall buildings(at least above 100 m) is a type of atmospheric discharge. Currently, we understand the nature of the UL from ground observations, but the corresponding theoretical research is lacking. Based on an existing bidirectional leader stochastic model, a stochastic parameterization scheme for the UL has been built and embedded in an existing two-dimensional thundercloud charge/discharge model. The ULs simulated from the experiments with two-dimensional high resolution agree generally with the observation results. By analyzing the charge structure of thunderstorm clouds, we determined the in-cloud environmental characteristics that favor the initiation of conventional cloud-to-ground(CG) flashes and analyzed the differences and similarities of some characteristics of the positive and the negative UL. Simulation results indicate that the positive ULs are typically other-lightning-triggered ULs(OLTUL) and are usually a discharge phenomenon between the ground and the lower positive charge region appearing below the main middle negative charge region. The effect of the previous in-cloud lightning(IC) process of space electrical field provides favorable conditions for the initiation of a positive UL. Its entire discharge process is limited, and the branches of the leader are fewer in number as its discharge is not sufficient. A negative UL is generally a discharge phenomenon of the dipole charge structure between the ground and the main negative charge region. The lower temperature stratification and the sinking of the hydrometeors typically initiate a negative UL. Negative ULs develop strongly and have more branches. The OLTUL is initiated mainly during the development stage of a thunderstorm, while the self-triggered UL(STUL) is initiated mainly during the dissipation stage of a thunderstorm.
