Abstract: A panoramic imaging apparatus is provided, which is able to freely display a focus-optimized internal structural image of the tooth row depending on a position using image data acquired by only one-time X-ray panoramic imaging from an arbitrary section along a patient's tooth row. The panoramic imaging apparatus comprise an X-ray source (31) and a detector (32) outputting a digital electrical signal depending on an incident X-ray at a constant frame rate.

Abstract: A marine contra-rotating propeller system comprises a large gear driven by an engine, and a plurality of small gears disposed so as to respectively mesh with the large gear at a plurality of fixed positions along the circumference of the large gear. Planet gears are respectively mounted to the gear shafts of the small gears. A sun gear and an inner-toothed gear are respectively meshed with the planet gears. A rear propeller is mounted to an inner shaft serving as a gear shaft of the sun gear. A front propeller is mounted to a tubular outer shaft serving as a gear shaft of the inner-toothed gear. The present invention can eliminate, with the simple construction, the inconvenience caused by a differential planetary gear operations in the prior art, can derive a propeller efficiency to the maximum extent.