In one aspect, the invention provides a system that predicts the location of an entity, such as a friend of a user of a mobile device, and displays to the user this prediction information on a display screen of the mobile device. A portion of projected streaks on the friction joining steel plate is designed to have a Vickers hardness at least 3 times greater than the surface of the steel products, which allows the projected streaks to more easily enter the steel products thereby increasing the friction coefficient between the steel products. The mounting apparatus is arranged to support the sterile camera unit relative to a subject to be photographed such that the camera quickly obtains in-focus close-up photographs of subjects of interest. This system realizes high-speed retrieving of intended unit record areas when writingreading a file tofrom the recording medium.