A method for preparing a polyimide includes introducing a mixture of an oligomer and a solvent to an extruder, removing solvent via at least one extruder vent, and melt kneading the oligomer to form a polyimide. An access node can determine a scheduling scheme based on an indication of data addressed to wireless devices. The electronic device attached to pet uses the electrical energy of the integrated battery to perform a predetermined operation. Each of the swivels includes a thrust bearing. A focusing value of the second digital image is calculated by a focusing detection module. The carrier injection efficiency into the active layer 6 can be improved by making the total film thickness of the first and second undoped InGaN layers 20 nm or less.