Prior to achieving high precision navigation of a spacecraft using X-ray observations,a pulsar rotation model must be built and analysis of the precise position of the Earth should be performed using ground pulsar tim...Prior to achieving high precision navigation of a spacecraft using X-ray observations,a pulsar rotation model must be built and analysis of the precise position of the Earth should be performed using ground pulsar timing observations.We can simulate time-of-arrival ground observation data close to actual observed values before using pulsar timing observation data.Considering the correlation between the Earth's position and its short arc section of an orbit,we use polynomial regression to build the correlation.Regression coefficients can be calculated using the least square method,and a coordinate component series can also be obtained;that is,we can calculate Earth's position in the Barycentric Celestial Reference System according to pulse arrival time data and a precise pulsar rotation model.In order to set appropriate parameters before the actual timing observations for Earth positioning,we can calculate the influence of the spatial distribution of pulsars on errors in the positioning result and the influence of error source variation on positioning by simulation.It is significant that the threshold values of the observation and systematic errors can be established before an actual observation occurs;namely,we can determine the observation mode with small errors and reject the observed data with big errors,thus improving the positioning result.展开更多
Objective To explore the efficacy of logistic regression modeling based on plasma amino acid profile and patient age,for diagnosing hepatic fibrosis in patients with chronic hepatitis B (CHB) .Methods One-hundredand-f...Objective To explore the efficacy of logistic regression modeling based on plasma amino acid profile and patient age,for diagnosing hepatic fibrosis in patients with chronic hepatitis B (CHB) .Methods One-hundredand-forty-eight patients (108 males;mean age:38.1±11.9 years,range:16—72 years)展开更多
针对城市轨道交通OD客流量短时预测问题,提出基于向量自回归(Vector Auto Regression,VAR)和动态模式分解(Dynamic Mode Decomposition,DMD)的VAR-DMD组合预测模型.首先,以北京市范围内的地铁站点为例,基于自动售检票系统数据(Auto Fare...针对城市轨道交通OD客流量短时预测问题,提出基于向量自回归(Vector Auto Regression,VAR)和动态模式分解(Dynamic Mode Decomposition,DMD)的VAR-DMD组合预测模型.首先,以北京市范围内的地铁站点为例,基于自动售检票系统数据(Auto Fare Collection,AFC),对地铁OD客流进行时空特征分析;其次,构建高阶加权向量自回归模型捕获OD客流数据的时空关联性,利用动态模式分解算法估算模型的参数,提取OD客流数据动态特征,实现数据的降维和降噪,利用实时更新算法更新模型的参数,实现长期连续预测;最后,以北京地铁AFC数据为算例,对模型进行验证.研究结果表明:相较于基准模型,VAR-DMD模型的运行时间减少96.67%,预测误差减少2.6%,具有较高的预测速度和预测精度,为城市轨道交通运营管理部门提供了可靠又及时的决策依据.展开更多
基金supported by the National Natural Science Foundation of China (Grant Nos. 10973030,10973032,11003039,10903032 and 10973049)the National Science Foundation of Shanghai,China (Grant No. 10ZR1435700)
文摘Prior to achieving high precision navigation of a spacecraft using X-ray observations,a pulsar rotation model must be built and analysis of the precise position of the Earth should be performed using ground pulsar timing observations.We can simulate time-of-arrival ground observation data close to actual observed values before using pulsar timing observation data.Considering the correlation between the Earth's position and its short arc section of an orbit,we use polynomial regression to build the correlation.Regression coefficients can be calculated using the least square method,and a coordinate component series can also be obtained;that is,we can calculate Earth's position in the Barycentric Celestial Reference System according to pulse arrival time data and a precise pulsar rotation model.In order to set appropriate parameters before the actual timing observations for Earth positioning,we can calculate the influence of the spatial distribution of pulsars on errors in the positioning result and the influence of error source variation on positioning by simulation.It is significant that the threshold values of the observation and systematic errors can be established before an actual observation occurs;namely,we can determine the observation mode with small errors and reject the observed data with big errors,thus improving the positioning result.
文摘Objective To explore the efficacy of logistic regression modeling based on plasma amino acid profile and patient age,for diagnosing hepatic fibrosis in patients with chronic hepatitis B (CHB) .Methods One-hundredand-forty-eight patients (108 males;mean age:38.1±11.9 years,range:16—72 years)
文摘针对城市轨道交通OD客流量短时预测问题,提出基于向量自回归(Vector Auto Regression,VAR)和动态模式分解(Dynamic Mode Decomposition,DMD)的VAR-DMD组合预测模型.首先,以北京市范围内的地铁站点为例,基于自动售检票系统数据(Auto Fare Collection,AFC),对地铁OD客流进行时空特征分析;其次,构建高阶加权向量自回归模型捕获OD客流数据的时空关联性,利用动态模式分解算法估算模型的参数,提取OD客流数据动态特征,实现数据的降维和降噪,利用实时更新算法更新模型的参数,实现长期连续预测;最后,以北京地铁AFC数据为算例,对模型进行验证.研究结果表明:相较于基准模型,VAR-DMD模型的运行时间减少96.67%,预测误差减少2.6%,具有较高的预测速度和预测精度,为城市轨道交通运营管理部门提供了可靠又及时的决策依据.
