The wheel-rail contact problems, such as the number, location and the track of contact patches, are very important for optimizing the spatial structure of the rails and lowering the vehicle-turnout system dynamics. Ho...The wheel-rail contact problems, such as the number, location and the track of contact patches, are very important for optimizing the spatial structure of the rails and lowering the vehicle-turnout system dynamics. However, the above problems are not well solved currently because of having the difficulties in how to determine the multi-contact, to preciously present the changeable profiles of the rails and to establish an accurate spatial turnout system dynamics model. Based on a high-speed vehicle-turnout coupled model in which the track is modeled as flexible with rails and sleepers represented by beams, the line tracing extreme point method is introduced to investigate the wheel-rail multiple contact conditions and the key sections of the blade rail, longer nose rail, shorter rail in the switch and nose rail area are discretized to represent the varying profiles of rails in the turnout. The dynamic interaction between the vehicle and turnout is simulated for cases of the vehicle divergently passing the turnout and the multi-point contact is obtained. The tracks of the contact patches on the top of the rails are presented and the wheel-rail impact forces are offered in comparison with the contact patches transference on the rails. The numerical simulation results indicate that the length of two-point contact occurrence of a worn wheel profile and rails is longer than that of the new wheel profile and rails; The two-point contact definitely occurs in the switch and crossing area. Generally, three-point contact doesn’t occur for the new rail profile, which is testified by the wheel-rails interpolation distance and the first order derivative function of the tracing line extreme points. The presented research is not only helpful to optimize the structure of the turnout, but also useful to lower the dynamics of the high speed vehicle-turnout system.展开更多
A rapid and accurate method for two-point ray tracing in horizontally layered velocity model is presented in this paper. Numerical experiments show that this method provides stable and rapid convergence with high accu...A rapid and accurate method for two-point ray tracing in horizontally layered velocity model is presented in this paper. Numerical experiments show that this method provides stable and rapid convergence with high accuracies, regardless of various 1-D velocity structures, takeoff angles and epicentral distances. This two-point ray tracing method is compared with the pseudobending technique and the method advanced by Kim and Baag (2002). It turns out that the method in this paper is much more efficient and accurate than the pseudobending technique, but is only applicable to 1-D velocity model. Kim's method is equivalent to ours for cases without large takeoff angles, but it fails to work when the takeoff angle is close to 90°. On the other hand, the method presented in this paper is applicable to cases with any takeoff angles with rapid and accurate convergence. Therefore, this method is a good choice for two-point ray tracing problems in horizontally layered velocity model and is efficient enough to be applied to a wide range of seismic problems.展开更多
Conifer needles bioaccumulate atmospheric pollutants, including trace metals, and may be used to monitor variations in atmospheric concentration. Needles were analyzed to determine whether a correlation exists between...Conifer needles bioaccumulate atmospheric pollutants, including trace metals, and may be used to monitor variations in atmospheric concentration. Needles were analyzed to determine whether a correlation exists between elevations and trace metal concentrations in proximity to roadways and other non-point sources. Composite samples of white spruce (Picea glauca) and balsam fir (Abies balsamea) needles were collected along hillsides in eastern and western Calgary, respectively. A combined total of 11 sites was sampled along two transects of increasing elevation. Qualitative and quantitative analysis of trace metal concentrations was completed using inductively coupled plasma-mass spectrometry (ICP-MS) and synthesized using regression analysis. The concentrations of cobalt, nickel, and calcium in the samples were found to exhibit a significant (P < 0.05) relationship with respect to elevation and proximity to roadways.展开更多
文摘知识追踪任务旨在通过对学生历史学习数据实时准确地追踪学生知识状态,并预测学生未来的答题表现.针对当前研究忽略了题目涵盖知识点中复杂的高阶关系的问题,提出一种融合知识点关系的深度记忆网络知识追踪模型(deep memory network knowledge tracing model incorporating knowledge point relationships,HRGKT).首先,HRGKT使用知识点关系图定义图中节点之间的关系信息,表示知识点之间的丰富信息.使用GAT获取两者之间的高阶关系.然后,学习过程中存在着遗忘,HRGKT综合考虑4个影响知识遗忘的因素来更准确地追踪学生知识状态.最后,根据真实在线教育数据集上的实验比较结果,与当前知识追踪模型相比,HRGKT在追踪学生知识掌握状态方面表现更加准确,并且具备更好的预测性能.
基金supported by National Natural Science Foundation of China (Grant Nos. 51175032, U1134201)National Basic Research Program of China (973 Program, Grant No. 2011CD711104)
文摘The wheel-rail contact problems, such as the number, location and the track of contact patches, are very important for optimizing the spatial structure of the rails and lowering the vehicle-turnout system dynamics. However, the above problems are not well solved currently because of having the difficulties in how to determine the multi-contact, to preciously present the changeable profiles of the rails and to establish an accurate spatial turnout system dynamics model. Based on a high-speed vehicle-turnout coupled model in which the track is modeled as flexible with rails and sleepers represented by beams, the line tracing extreme point method is introduced to investigate the wheel-rail multiple contact conditions and the key sections of the blade rail, longer nose rail, shorter rail in the switch and nose rail area are discretized to represent the varying profiles of rails in the turnout. The dynamic interaction between the vehicle and turnout is simulated for cases of the vehicle divergently passing the turnout and the multi-point contact is obtained. The tracks of the contact patches on the top of the rails are presented and the wheel-rail impact forces are offered in comparison with the contact patches transference on the rails. The numerical simulation results indicate that the length of two-point contact occurrence of a worn wheel profile and rails is longer than that of the new wheel profile and rails; The two-point contact definitely occurs in the switch and crossing area. Generally, three-point contact doesn’t occur for the new rail profile, which is testified by the wheel-rails interpolation distance and the first order derivative function of the tracing line extreme points. The presented research is not only helpful to optimize the structure of the turnout, but also useful to lower the dynamics of the high speed vehicle-turnout system.
基金National Natural Science Foundation of China (40074008 and 40134010).
文摘A rapid and accurate method for two-point ray tracing in horizontally layered velocity model is presented in this paper. Numerical experiments show that this method provides stable and rapid convergence with high accuracies, regardless of various 1-D velocity structures, takeoff angles and epicentral distances. This two-point ray tracing method is compared with the pseudobending technique and the method advanced by Kim and Baag (2002). It turns out that the method in this paper is much more efficient and accurate than the pseudobending technique, but is only applicable to 1-D velocity model. Kim's method is equivalent to ours for cases without large takeoff angles, but it fails to work when the takeoff angle is close to 90°. On the other hand, the method presented in this paper is applicable to cases with any takeoff angles with rapid and accurate convergence. Therefore, this method is a good choice for two-point ray tracing problems in horizontally layered velocity model and is efficient enough to be applied to a wide range of seismic problems.
文摘Conifer needles bioaccumulate atmospheric pollutants, including trace metals, and may be used to monitor variations in atmospheric concentration. Needles were analyzed to determine whether a correlation exists between elevations and trace metal concentrations in proximity to roadways and other non-point sources. Composite samples of white spruce (Picea glauca) and balsam fir (Abies balsamea) needles were collected along hillsides in eastern and western Calgary, respectively. A combined total of 11 sites was sampled along two transects of increasing elevation. Qualitative and quantitative analysis of trace metal concentrations was completed using inductively coupled plasma-mass spectrometry (ICP-MS) and synthesized using regression analysis. The concentrations of cobalt, nickel, and calcium in the samples were found to exhibit a significant (P < 0.05) relationship with respect to elevation and proximity to roadways.
