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Engineering analysis is applied to two problems: (1) an experimental study of time-dependent blood flow and (2) a theoretical study of oxygen (O(,2)) transport in a red blood cell (RBC). Since in vivo blood flow is time-dependent, the ability to predict unsteady blood flow from steady-flow rheological data for blood is of interest. Oscillatory and pulsatile flow of blood and related suspensions was studied in 400 (mu)m and 218 (mu)m glass tubes at 37(DEGREES)C. The flow was sinusoidally driven with a frequency of 0.5 Hz to 3.0 Hz, and the resulting pressure gradient in the tube was measured. The pressure and flow data were compared to a predicted relation obtained from solving the momentum equation subject to rheological data; these data were acquired from steady-flow viscometers at a hematocrit (RBC concentration) value equal to the average tube hematocrit. For a given pressure-gradient amplitude for oscillatory flow, the predicted flowrate amplitude is smaller than that found by experiment. The discrepancy is attributable to a residual Fahraeus-Lindqvist effect not compensated for by using the average tube hematocrit in the predictions. In addition, the discrepancy depends on the RBC suspending medium and the hematocrit, and is less than about 10 percent for RBC in plasma. Pulsatile flow was more predictable than oscillatory flow, indicating possible differences in the Fahraeus-Lindqvist effect for the two cases. Viscoelastic fluid effects were negligible. The second problem deals with O(,2) transport in a red cell. A significant fraction of intracapillary resistance to O(,2) transport occurs in the red cell and is not well understood. A simple model is used to study the interaction of diffusion, facilitated diffusion, and reaction kinetics during the O(,2) unloading of a red cell. The nonequilibrium region adjacent to the RBC membrane is elucidated using boundary layer analysis, and the O(,2) transport equations are solved numerically using double orthogonal collocation. The minimum time required to unload O(,2) from a red cell is calculated and depends strongly on the plasma surrounding the cell. The minimum release time is comparable to some estimates of capillary transit time in working skeletal muscle. The present model is compared to the standard Krogh model for O(,2) transport.

This dissertation describes a model of the visual cortex of the cat. The model has been applied to some of the problems faced by contemporary computer vision systems. The model goes beyond previous models of visual cortex in that it models both the anatomy of visual cortex and the ability of individual cells in visual cortex to learn. The model is based on the hypothesis that image processing in the cat's visual system consists of three levels: the retinothalamic, the primary and secondary cortical (Area 17, 18, and 19), and the associative. The retinothalamic system is modeled by using operators modeling different types of retinal ganglion cells (X, Y, and W). Cells in Areas 17, 18, and 19 are modeled using CAMs, which are models of cortical cells having associative and plastic properties. CAMs modeling Areas 17, 18 and 19 use unsupervised learning to form primitives for segmenting preprocessed images on the basis of edges, moving edges, and texture. Only one associative area, Area 21, is modeled. The model of Area 21 receives input from the models of Areas 17 and 19 via the model of the Lateral Pulvinar, which transforms the segmentations into geometrical features on the basis of the two-dimensional regions. The model of Area 21 uses supervised learning to form pattern classes which are specific and hence useful to a particular domain (environment). The domains used to test the model are Roman text, Japanese text, digitized photographs of house scenes, and examples of various textures. Experiments demonstrate that the model is relevant to computer vision research because it presents a method of solving the problem of domain-specific knowledge in computer vision systems. The model also demonstrates that many techniques for computer vision systems are suggested by the anatomy and physiology of the cat's visual system.

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