Ayaka Sato

Formation of a submillimeter bubble from an orifice using pulsed acoustic pressure waves in gas phase

The mechanism of a bubble production method using pulsed acoustic pressure waves in gas phase is investigated using high-speed photography. The acoustic characteristics of the present bubble generator are also investigated. We found out the optimal acoustic waveform for producing only one bubble per one action; the bubble detachment radius is accurately controlled by first applying the positive onset-assistance acoustic pressure wave and then the negative detachment-assistance acoustic pressure wave with an accurately controlled time lapse. From an orifice with a radius of 0.09mm submerged in water, bubbles with radii in the range of 0.28–0.78mm with an extremely small standard deviation of less than 1μm are obtained. The shrinking and pinch-off motions of a capillary bridge connecting the bubble and orifice at the time of bubble detachment are observed in detail. The balancing force on a growing bubble, which is based on a spherical bubble formation model is also estimated. As a result, we reveal that wh...

A 3D Kinematic Measurement of Knee Prosthesis Using X-ray Projection Images (Countermeasure to the Overlap between Tibio-femoral Component Silhouettes)

We have developed a technique for estimating 3D motion of knee prosthesis from its 2D perspective projections. As Fourier descriptors were used for compact representation of library templates and contours extracted from the prosthetic X-ray images, the entire silhouette contour of each prosthetic component was required. This caused such a problem as our algorithm did not function when the silhouettes of tibio and femoral components overlapped with each other. Here we planned a novel method to overcome it ; which was processed in two steps. First, the missing part of silhouette contour due to overlap was interpolated using a free-formed curvature such as Bezier. Then the first step position/orientation estimation was performed. In the next step, a clipping window was set in the projective coordinate so as to separate the overlapped silhouette drawn using the first step estimates. After that the localized library whose templates were clipped in shape was prepared and the second step estimation was performed. Computer model simulation demonstrated sufficient accuracies of position/orientation estimation even for overlapped silhouettes ; equivalent to those without overlap.