A fluorene-based pyrimidine-containing conjugated oligomer applied in six different layers in an OLED, respectively, used as an electron-transport emitting layer, an emitting layer, a host in the emitting layer, the ETL, a host in the electron-transport emitting layer, and a hole-blocking layer to upgrade light-emitting efficiency and regulate emitting color of the OLED. 5%, and wherein at least one of a compound having an organopolysiloxane structure and a compound having a ring siloxane structure is detected when the external additive is analyzed by a pyrolysis gas chromatography mass spectroscopy method after the external additive is washed with chloroform. If the distance between the trailing vehicle and lead vehicle is deemed below a minimum threshold at a given vehicle speed, the rear brake lights are illuminated. A client may also request a write lease which allows an application on the client to modify the directory metadata, such as by creating or deleting new files in the directory, or changing their attributes, and cache those changes.