Bus demand fluctuation at different time periods is one of the most intangible problems for bus operators, which seriously affects operational efficiency. A good knowledge of performance variation at different periods is helpful in developing an effective transit schedule. The aim of this study is to evaluate the efficiency of an urban bus operation at different periods using a mixed frontier model and to explore a better operating strategy which is adaptive to bus demand fluctuation. A mixed data envelopment analysis–stochastic frontier analysis (DEA–SFA) model is proposed, in which multiple outputs are aggregated by the DEA model, and then the technical efficiency is calculated by SFA. The model deals with multiple outputs while considering the stochastic factor simultaneously, so as to ensure model practicability. Using field data from Shanghai Transit Route 55, this study evaluates efficiency at different periods by analysing various aspects. The results indicate that the model effectively describes the characteristics of the bus line efficiency with time period changes, which provides an innovative perspective to solve the operational problem of the urban transit system.
Nowadays, researches concerned magnetic abrasive finishing (MAF) are becoming increasingly popular. Polishing head is one of the most important factors in the whole polishing system in which magnetic abrasive act directly on the workpiece. In this paper, two kinds of polishing heads applied in the polishing of free form surface are proposed. They are hard polishing head and soft polishing head, respectively. And some important factors are contrasted such as selfsharpening capacity, morphology distribution, and removal uniformity. Moreover, the finishing force is the key factor which is different between the two polishing heads having a great influence on polishing effect. Through comparison and analysis, the soft polishing head is better to finish free form surface. And the experimental results reflect its superiority in polishing free form surface.
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