Evaluation of technical vs economic decisions in rail grinding
Rail is a significant capital asset for railway companies. It contributes more than half of the capital assets of railway infrastructure. Recent rail inspection data using Ultrasonic rail testing has shown increasing number of rail defects, failures and causing disruptions to rail services. This cost can be further increased when the track quality is poor. In recent years, railroads have been purchasing over 500,000 tons of rails per year at an estimated total cost of US $1.25 billion for replacement of worn out and degraded rails. Rail grinding is considered as viable means in reducing the impacts of rail defects and failures. Rail grinding can result in improved curving performance (wheel/rail interaction) and prevents crack initiation and propagation of surface cracks due to RCF. This paper focuses on analysis of rail degradation process and development of mathematical model considering technical and economic decisions in rail grinding to rail infrastructure owners.
Failure of a low rail in a curved railway track subject to long term rail-wheel interactive wear
This paper investigated the failure of a rail that had been in service for approximately 25 years in Tasmania, Australia. A segment of the rail was taken from the site on a curved railway track. From its service history, it was found that the maximum train speed over that period was around 35km/h. However, approximately one third of the movements were at a speed less than 20km/h due to the fact that the rail was located on the steepest section of the line. Visual examination on the rail sample revealed that the rail had experienced mixed traffic conditions during the service history. Mushrooming shaped plastic flow occurred in the railhead. The chemical composition of the rail was analysed using the optical emission spectroscopy method. Metallurgical observation on the rail sample and a hardness test were conducted, aiming to investigate the root cause of the failure. The aim of this study was to conduct the failure analysis of the rail and to provide knowledge regarding the selection of a sustainable type of rail for this application.
Overproduction of a truncated poly (vinyl alcohol) dehydrogenase in recombinant Pichia pastoris by low-temperature induction strategy and related mechanism analysis
Based on the N-terminal sequencing of poly (vinyl alcohol) dehydrogenase (PVADH), a 1,644-bp gene encoding a truncated PVADH (tPVADH) was amplified using the synthetic gene (GenBank accession No. JQ235753) as a template, and was further transformed into Pichia pastoris GS115 with the vector pPIC9K. The maximal tPVADH activity reached 546 U/mL in shake flask. The influence of methanol concentration and induction temperature on tPVADH production was further investigated in 3-L bioreactor. When the methanol concentration and induction temperature were controlled at 15 g/L and 22 °C, respectively, the maximal tPVADH activity reached 8,464 U/mL, which was nearly 10 times that of mature PVADH expressed under the same condition and was the highest level ever reported. The reason responsible for the significant improvement of tPVADH production at low induction temperature was explored in terms of cell viability, extracellular proteases activity, and alcohol oxidase activity.