Abstract: The invention provides a method for preparing pyrrolidone, and the invention provides a method for catalytically preparing pyrrolidone with ?-aminobutyric acid in the presence of carnitine-CoA ligase CaiC. The carnitine-CoA ligase CaiC has an amino acid sequence as shown in SEQ ID NO:1. The ligase has catalytic activity in the cyclization of ?-aminobutyric acid to produce pyrrolidone. The carnitine-CoA ligase provided in the present invention affords a yield of pyrrolidone of 3.26 g/L and a molar yield of 39.53% in 24 h when ?-aminobutyric acid is used as a substrate, thus reducing the production period, improving the production of pyrrolidone, and accelerating the industrialization process of producing pyrrolidone by enzymatic conversion method.

Abstract: A rail train is provided in the embodiment of the present disclosure, comprising: a semi-enclosed air duct, the semi-enclosed air duct comprises an air duct top and an air duct side; the air duct top is fixed with an inner top of a rail train body, the air duct side is connected on both sides of the air duct top and extends downward; a large side top, and the the large side top is fixed to the rail train body as a part of a rail train roof, and the large side top is top-sealed at a bottom of the air duct side to form an air passage with the air duct. The rail train solves the technical problem that the roof and the air duct of the rail train are not conducive to overall weight reduction of the rail train.