A probabilistic approach to segmentation and classification of neoplasia in uterine cervix images using color and geometric features

In one embodiment, a first air flow meter includes a pair of ultrasonic transducers mounted on one wall of a conduit, and an opposite reflective wall is shaped to focus acoustic signals from one transducer to the other. In a second embodiment, the opposite wall is separated into a stepped series of cylindrical reflective surfaces spaced from the transducers by different distances, each surface being one-half wavelength from its adjoining surfaces so that constructive combination of the acoustic signals occurs. For noise of the same wavelength emitted at sources axially spaced from the transducers, the reflective surfaces appear to be spaced by approximately 3/4-wavelength steps so that reflected noise signals tend to cancel.