Toshiyuki Shimooka

Artificial Immune System for Personal Identification with Finger Vein Pattern

The partial template method using the concept of an immune system was developed for finger vein pattern identification. The partial templates, that is, anti-bodies were made by cutting out standard images. The template anti-bodies were selected based on the rules similar to the clonal selection. Two procedures for the identification were proposed and their performances were evaluated using the samples of transilluminated finger vein image. With a preliminary test system, we could distinguish the self out of several tens of nonself images. It was verified that the artificial immune system based on the partial template method is effective for the personal identification with finger vein patterns.

Surface pitting of heart valve disks tested in an accelerated fatigue tester

There are various reports on the fracture of mechanical heart valves implanted in humans or animals and it has been pointed out that fractures are induced by erosion of the disk surface due to cavitation bubbles. Cavitation erosion on mechanical heart valves was studied using our originally designed accelerated fatigue tester. Several valve housings with different compliance values were used. The number and position of pits on the valve disk were measured using an optical microscope. Disk-closing velocity was measured and cavitation bubbles were monitored by a high-speed video camera. It was found that disk-closing velocity increased and cavitation erosion was enhanced with an increase in compliance of the valve holder. Therefore, careful attention should be paid to the compliance of an accelerated fatigue tester.

Idiotypic Network Model for Feature Extraction in Pattern Recognition – Effect of Diffusion of Antibody

An idiotypic network model using antibodies as partial templates was applied to a pattern recognition problem. A novel network model that contains diffusion of antibodies was proposed. The proposed technique was applied to classification of 33 samples of Chinese characters that have a common sub-structure in the character. With partial template matching they were classified into 12 groups. Using the dynamics of the proposed network, the samples were classified into 18 groups. Through this study, the applicability of the idiotypic network with antibody diffusion to pattern recognition was verified.

Examination of cavitation-induced surface erosion pitting of a mechanical heart valve using closing velocities

Abstract Recently, cavitation on the surface of mechanical heart valves has been studied as a cause of fractures that occur in implanted mechanical heart valves. Several factors, including peak dp/dt of the ventricular pressure, maximum closing velocity of the leaflet, and squeeze flow, have been studied as indices of the cavitation threshold. In the present study, cavitation erosion on the surface of a mechanical valve was examined by focusing on squeeze flow and the water-hammer phenomenon during the closing period of the valve. A simple solenoid-actuated test device that can directly control the valve closing velocity was developed, and opening–closing tests of 3000 and 40 000 cycles were performed at various closing velocities. The results showed that there was a closing velocity threshold above which erosion pitting was induced and that the threshold was about 0.4 m/s in the valves used in this study. Cavitation-induced erosion pits were observed only in regions where squeeze flow occurred immediately before valve closure. On the other hand, the number of the pits was found to be closely related to the area of the water hammer-induced pressure were below the critical pressure defined by water vapor pressure. Therefore, it was concluded that cavitation is initiated and augmented by the two pressure drops due to squeeze flow and the water-hammer phenomenon, respectively.

Study on the Idiotypic Network Model for Feature Extraction of Patterns

The dynamics of an idiotypic network was studied for the purpose of the feature extraction of patterns. When observed patterns are considered antigens, the immune network is the pattern-matching system using antibodies as partial templates. Antigens are represented by steady solutions as internal images via the interaction of antibodies. Farmer’s mathematical model and modified model with antibody-antibody complex were adopted, and the dynamics of simple cyclic networks were simulated. Orbits in the phase plots or steady states could represent differences in the network structures. The periodic orbits of the dynamics of the network will be useful for feature extraction of patterns.

Numerical study of flow dynamics through prosthetic heart valves in a steady state flow model.

In this paper a numerical technique and simulation models are described to analyze flow patterns around prosthetic heart valves under steady flow conditions. The finite difference method was employed to solve the time-dependent and non-linear Navier-Stokes equations (NS eq.) for an incompressible viscous fluid. Chorins scheme was used to solve the governing equations, NS eq. and equation of continuity. In this method the discretized algebraic equations approximating the governing differential equations were obtained from the analytic solutions of the governing equations ; this method was shown capable for providing a stable numerical solution and a proper simulation of the flow dynamics. The flow geometry, including a flow chamber and a prosthetic heart valve, was overlaid with a rectangular grid. The several types of clinical valves and the trial model valves developed in our laboratory were chosen as subjects of this study.

The effect of left ventricular assist device (LVAD) on cardiac reserve in dogs.

The effect of LVAD on the preservation of cardiac reserve against ischemic damage was studied using Sarnoffs ventricular function curve. An LVAD was implanted between the canine left atrium and the aorta. Left ventricular function was measured by changing the height of the reservoir connected to the left atrium. The left ventricular function curve (LVFC) was drawn by plotting left ventricular stroke work (LVSW) against left atrial pressure (LAP). The coronary artery was occluded under a pump-on (ON group) or pump-off (OFF group). After reperfusion, measurements were repeated and changes in the LVFC caused by ischemia were compared in both groups. The gradient of the LVFC was significantly reduced by ischemia (107± 15ml/beat 80± 14, n= 13) but not in the ON group. LVSW under normal preload did not significantly change in either group. This suggests that the LVAD preserved cardiac reserve against ischemic damage.