Provided, among other things, is a compound of the formula: . The method can include receiving over a computer network a user request to access a remote course, providing course material for the requested, and providing a virtual picture frame wherein the frame surrounds the course material and includes one or more links to executable applications relevant to the requested course. The negative feedback loop further includes a correction signal generator for generating a correction signal and supplying it to the negative feedback loop as a disturbance of the loop so that the parallel light beam is focused onto the object.