A new method of process control for fusion welding maintains a controlled weld pool size or volume, for example in some applications a substantially constant weld pool size or volume. The apparatus includes a housing member for positioning the ignition assembly on a lid of the drum. These constituent features are provided in a layer configuration to realize high portability and ease of development. Other aspects relate to enhanced position determination, adaptive coverage enhancement, local mobile networks, open access femtocells without a backhaul, and local broadcast of media though utilization of femto enabled devices. The movement of the specimen under the beam of incident electrons may be continuous, and data for multiple image pixels may be acquired in parallel using a time delay integrating detector. The invention includes, for example, prosthetic heart valves, annuloplasty rings, and grafts, having enhanced biocompatibility and biostability.