Browsing by Author "Cao, Nan"

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Open Access
Approach to determine and evaluate the homogeneity of operating programs in railway operation based on infrastructure occupancy
(2017) Cao, Nan; Martin, Ullrich (Prof. Dr.-Ing.)
Contemporary railway traffic requires different train services share the same infrastructure. Capacity consumption together with the homogeneous level of train traffic gives a picture of the efficient use of infrastructure. Previous research suggests that the utilization is more efficient with a homogeneous operating program. During last decades, many researchers tried to describe and/or define the homogeneity of operating programs in rail service; however, no definition considered the infrastructure occupation. In addition, several methods were developed to evaluate the homogeneity in railway operation considering variations in speed, running time and headway. But, the occupancy of infrastructure has not been discussed in the existing methods. An extension of existing definitions is presented from the perspective of the infrastructure, which can be characterized by variations in blocking time, buffer time and running direction. The blocking time, buffer time and running direction describe the occupancy of train path on track sections based on the blocking time model. Accordingly, the homogeneity of operating programs is evaluated through three parameters, namely the homogeneity of blocking time (HBL), the homogeneity of buffer time (HBU) and the homogeneity of running direction (HRD). The overall homogeneity (OH) combined HBL; HBU and HRD to realize an integrity evaluation of homogeneity of operating programs. The results show that this new methodology can quantify the homogeneity of railway operations, not only for track sections but for an entire network, which contributes significantly to the efficient utilization of infrastructure. With the method developed in this thesis, the interrelationship between homogeneity of operating programs and operation quality were investigated quantitatively. Firstly, both the influence of each parameter of homogeneity and the overall homogeneity were analyzed. The operation quality (delay-coefficient) is evaluated for timetables with different train types, arrangements of buffer times and sequences of train runs. The results show that the operation quality deteriorates with less homogeneous timetables, in which the variation in buffer time has a more significant influence. Finally, the influence of homogeneity of operating programs is studied for different traffic flows. The low traffic flow is more sensitive to the homogeneity of buffer time and the homogeneity of blocking time is more significant for high traffic flow.
Open Access
Datamator : an authoring tool for creating datamations via data query decomposition
(2023) Guo, Yi; Cao, Nan; Cai, Ligan; Wu, Yanqiu; Weiskopf, Daniel; Shi, Danqing; Chen, Qing
Datamation is designed to animate an analysis pipeline step by step, serving as an intuitive and efficient method for interpreting data analysis outcomes and facilitating easy sharing with others. However, the creation of a datamation is a difficult task that demands expertise in diverse skills. To simplify this task, we introduce Datamator, a language-oriented authoring tool developed to support datamation generation. In this system, we develop a data query analyzer that enables users to generate an initial datamation effortlessly by inputting a data question in natural language. Then, the datamation is displayed in an interactive editor that affords users the ability to both edit the analysis progression and delve into the specifics of each step undertaken. Notably, the Datamator incorporates a novel calibration network that is able to optimize the outputs of the query decomposition network using a small amount of user feedback. To demonstrate the effectiveness of Datamator, we conduct a series of evaluations including performance validation, a controlled user study, and expert interviews.