The current research of autonomous vehicle motion control mainly focuses on trajectory tracking and velocity tracking. However, numerous studies deal with trajectory tracking and velocity tracking separately, and the ...The current research of autonomous vehicle motion control mainly focuses on trajectory tracking and velocity tracking. However, numerous studies deal with trajectory tracking and velocity tracking separately, and the yaw stability is seldom considered during trajectory tracking. In this research, a combination of the longitudinal–lateral control method with the yaw stability in the trajectory tracking for autonomous vehicles is studied. Based on the vehicle dynamics, considering the longitudinal and lateral motion of the vehicle, the velocity tracking and trajectory tracking problems can be attributed to the longitudinal and lateral control. A sliding mode variable structure control method is used in the longitudinal control. The total driving force is obtained from the velocity error in order to carry out velocity tracking. A linear time-varying model predictive control method is used in the lateral control to predict the required front wheel angle for trajectory tracking. Furthermore, a combined control framework is established to control the longitudinal and lateral motions and improve the reliability of the longitudinal and lateral direction control. On this basis, the driving force of a tire is allocated reasonably by using the direct yaw moment control, which ensures good yaw stability of the vehicle when tracking the trajectory. Simulation results indicate that the proposed control strategy is good in tracking the reference velocity and trajectory and improves the performance of the stability of the vehicle.展开更多
Survival of HIV/AIDS patients is crucially dependent on comprehensive and targeted medical interventions such as supply of antiretroviral therapy and monitoring disease progression with CD4 T-cell counts. Statistical ...Survival of HIV/AIDS patients is crucially dependent on comprehensive and targeted medical interventions such as supply of antiretroviral therapy and monitoring disease progression with CD4 T-cell counts. Statistical modelling approaches are helpful towards this goal. This study aims at developing Bayesian joint models with assumed generalized error distribution (GED) for the longitudinal CD4 data and two accelerated failure time distributions, Lognormal and loglogistic, for the survival time of HIV/AIDS patients. Data are obtained from patients under antiretroviral therapy follow-up at Shashemene referral hospital during January 2006-January 2012 and at Bale Robe general hospital during January 2008-March 2015. The Bayesian joint models are defined through latent variables and association parameters and with specified non-informative prior distributions for the model parameters. Simulations are conducted using Gibbs sampler algorithm implemented in the WinBUGS software. The results of the analyses of the two different data sets show that distributions of measurement errors of the longitudinal CD4 variable follow the generalized error distribution with fatter tails than the normal distribution. The Bayesian joint GED loglogistic models fit better to the data sets compared to the lognormal cases. Findings reveal that patients’ health can be improved over time. Compared to the males, female patients gain more CD4 counts. Survival time of a patient is negatively affected by TB infection. Moreover, increase in number of opportunistic infection implies decline of CD4 counts. Patients’ age negatively affects the disease marker with no effects on survival time. Improving weight may improve survival time of patients. Bayesian joint models with GED and AFT distributions are found to be useful in modelling the longitudinal and survival processes. Thus we recommend the generalized error distributions for measurement errors of the longitudinal data under the Bayesian joint modelling. Further studies may investigate the models with various types of shared random effects and more covariates with predictions.展开更多
This paper introduces a new kind of train impact detecting system that detect the train impact through detecting the train running acceleration,proposes that uniting the train running acceleration and the change rate ...This paper introduces a new kind of train impact detecting system that detect the train impact through detecting the train running acceleration,proposes that uniting the train running acceleration and the change rate of acceleration to token the train impact. The detector takes the portable computer as platform of data processing,utilizes the database technology to process data,making instrument Pc true,and improving the data processing ability of the instrument. The detector can show the train running acceleration on-line and real-timely,indicating the train impact situation directly,and uses the method that the software and hardware unifies to strengthen the system anti-jamming ability. At present,this detector has been tryout in some locomotive depots,each design function and the performance index conforms to request of the scene; the anti-jamming ability is strong,the monitor precision is reasonable,the detector can carry out the on-line examination to the train impact and monitoring the train running condition.展开更多
Longitudinal vibration of wheelset with respect to bogie frame often exists with a high acceleration magnitude and relative high frequency. First, a simplified model with a single wheelset moving at a constant speed o...Longitudinal vibration of wheelset with respect to bogie frame often exists with a high acceleration magnitude and relative high frequency. First, a simplified model with a single wheelset moving at a constant speed on a tangential track with irregularity is used to investigate the longitudinal vibration dynamics. Computional results indicate that the longitudinal vibration frequency of the wheelset is most sensitive to the primary longitudinal stiffness and the mass of the wheelset. As to the locomotive model, the longitudinal vibration is concerned with cross-level irregularity and vertical profile irregularity. Meanwhile, a method to estimate the resonance speed is presented. Finally, a possible solution is brought forward to extend wheel-rail service life by eliminating longitudinal vibration of the wheelset. The solution is simply to arrang the primary vertical damper with a forward angle, so that its damping component can be applied to longimdinal direction.展开更多
In the novel approach to the diagnostic tests of continuous welded rail （CWR） track by the use of the tamping machine, the fundamental statement related to the recording of the curvature with a definite value of the...In the novel approach to the diagnostic tests of continuous welded rail （CWR） track by the use of the tamping machine, the fundamental statement related to the recording of the curvature with a definite value of the lateral displacement being subjected to verification, can provide a basis for the determination of the longitudinal axial force in the rail. An attempt has also been made to define an alternative factor which by means of the measured signals, could be used for the determination of the axial forces in the rail sections. A power engineering approach has been adopted to this concept. Within the framework of the experimental investigations, measurements were carried out in the track test section. The investigations were based on stretching the rail sections by stretchers and on lateral displacements of the track by the tamping machine. The operation of the measuring apparatus was also tested in the experimental railway track section while carrying out the geometrical adjustments by the tamping machine. As a result of next series of the investigation carried out in 2006-2007, the authors worked out a procedure of estimating the longitudinal forces in rails of CWR track.展开更多
基金Supported by National Natural Science Foundation of China(Grant Nos.51575103,11672127,U1664258)Fundamental Research Funds for the Central Universities of China(Grant No.NT2018002)+1 种基金China Postdoctoral Science Foundation(Grant Nos.2017T100365,2016M601799)the Fundation of Graduate Innovation Center in NUAA(Grant No.k j20180207)
文摘The current research of autonomous vehicle motion control mainly focuses on trajectory tracking and velocity tracking. However, numerous studies deal with trajectory tracking and velocity tracking separately, and the yaw stability is seldom considered during trajectory tracking. In this research, a combination of the longitudinal–lateral control method with the yaw stability in the trajectory tracking for autonomous vehicles is studied. Based on the vehicle dynamics, considering the longitudinal and lateral motion of the vehicle, the velocity tracking and trajectory tracking problems can be attributed to the longitudinal and lateral control. A sliding mode variable structure control method is used in the longitudinal control. The total driving force is obtained from the velocity error in order to carry out velocity tracking. A linear time-varying model predictive control method is used in the lateral control to predict the required front wheel angle for trajectory tracking. Furthermore, a combined control framework is established to control the longitudinal and lateral motions and improve the reliability of the longitudinal and lateral direction control. On this basis, the driving force of a tire is allocated reasonably by using the direct yaw moment control, which ensures good yaw stability of the vehicle when tracking the trajectory. Simulation results indicate that the proposed control strategy is good in tracking the reference velocity and trajectory and improves the performance of the stability of the vehicle.
文摘Survival of HIV/AIDS patients is crucially dependent on comprehensive and targeted medical interventions such as supply of antiretroviral therapy and monitoring disease progression with CD4 T-cell counts. Statistical modelling approaches are helpful towards this goal. This study aims at developing Bayesian joint models with assumed generalized error distribution (GED) for the longitudinal CD4 data and two accelerated failure time distributions, Lognormal and loglogistic, for the survival time of HIV/AIDS patients. Data are obtained from patients under antiretroviral therapy follow-up at Shashemene referral hospital during January 2006-January 2012 and at Bale Robe general hospital during January 2008-March 2015. The Bayesian joint models are defined through latent variables and association parameters and with specified non-informative prior distributions for the model parameters. Simulations are conducted using Gibbs sampler algorithm implemented in the WinBUGS software. The results of the analyses of the two different data sets show that distributions of measurement errors of the longitudinal CD4 variable follow the generalized error distribution with fatter tails than the normal distribution. The Bayesian joint GED loglogistic models fit better to the data sets compared to the lognormal cases. Findings reveal that patients’ health can be improved over time. Compared to the males, female patients gain more CD4 counts. Survival time of a patient is negatively affected by TB infection. Moreover, increase in number of opportunistic infection implies decline of CD4 counts. Patients’ age negatively affects the disease marker with no effects on survival time. Improving weight may improve survival time of patients. Bayesian joint models with GED and AFT distributions are found to be useful in modelling the longitudinal and survival processes. Thus we recommend the generalized error distributions for measurement errors of the longitudinal data under the Bayesian joint modelling. Further studies may investigate the models with various types of shared random effects and more covariates with predictions.
文摘This paper introduces a new kind of train impact detecting system that detect the train impact through detecting the train running acceleration,proposes that uniting the train running acceleration and the change rate of acceleration to token the train impact. The detector takes the portable computer as platform of data processing,utilizes the database technology to process data,making instrument Pc true,and improving the data processing ability of the instrument. The detector can show the train running acceleration on-line and real-timely,indicating the train impact situation directly,and uses the method that the software and hardware unifies to strengthen the system anti-jamming ability. At present,this detector has been tryout in some locomotive depots,each design function and the performance index conforms to request of the scene; the anti-jamming ability is strong,the monitor precision is reasonable,the detector can carry out the on-line examination to the train impact and monitoring the train running condition.
文摘Longitudinal vibration of wheelset with respect to bogie frame often exists with a high acceleration magnitude and relative high frequency. First, a simplified model with a single wheelset moving at a constant speed on a tangential track with irregularity is used to investigate the longitudinal vibration dynamics. Computional results indicate that the longitudinal vibration frequency of the wheelset is most sensitive to the primary longitudinal stiffness and the mass of the wheelset. As to the locomotive model, the longitudinal vibration is concerned with cross-level irregularity and vertical profile irregularity. Meanwhile, a method to estimate the resonance speed is presented. Finally, a possible solution is brought forward to extend wheel-rail service life by eliminating longitudinal vibration of the wheelset. The solution is simply to arrang the primary vertical damper with a forward angle, so that its damping component can be applied to longimdinal direction.
文摘In the novel approach to the diagnostic tests of continuous welded rail （CWR） track by the use of the tamping machine, the fundamental statement related to the recording of the curvature with a definite value of the lateral displacement being subjected to verification, can provide a basis for the determination of the longitudinal axial force in the rail. An attempt has also been made to define an alternative factor which by means of the measured signals, could be used for the determination of the axial forces in the rail sections. A power engineering approach has been adopted to this concept. Within the framework of the experimental investigations, measurements were carried out in the track test section. The investigations were based on stretching the rail sections by stretchers and on lateral displacements of the track by the tamping machine. The operation of the measuring apparatus was also tested in the experimental railway track section while carrying out the geometrical adjustments by the tamping machine. As a result of next series of the investigation carried out in 2006-2007, the authors worked out a procedure of estimating the longitudinal forces in rails of CWR track.
