The invention relates to a method and system for measuring the internal refractive index of an optical fiber preform with high precision. The annular ring has at least four transition sections extending transversely across the annular ring, dividing the annular ring into at least a first, second, third and fourth segment. The adapter may include the combination of a reservoir and transition, or simply a transition. The present invention is particularly applicable with MIG and CSC welding systems. The activation module may generate a set of entries in a resource mapping table, the set of entries corresponding to the allocated resources and defining the virtual PCIe device. The bearing inner periphery and bearing outer periphery are linked by a pressure gradient descending slowly, and therefore bubbles present in the bearing inner periphery can be guided to the bearing outer periphery through the auxiliary grooves, and discharged outside of the bearing from the air-liquid interface, so that lubricating oil leakage due to bubbles can be prevented.