A display apparatus includes a light source, and a partition wall which divides an inside of the display apparatus into an enclosing space which includes a plurality of optical elements and an outer space with respect to the enclosing space. Queries directed towards summarizing and reporting on event records may be received at a search head. The clock used for the phase modulation is obtained by injecting a continuous wavelength into the intensity modulator. The system includes at least one source of radiation having wavelength in the range of 400 to 2200 nanometers and at least one detector responsive to such incident radiation. With respect to the subscriber data being put as the inactive holding state, it is deleted if no location registration is made within a predetermined period of time. Curved surfaces having a radius of curvature of 0.