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No description available.

No description available.

No description available.

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No description available.

The flow of wood fiber suspensions plays an important role during the pulp and paper manufacture process. Considerable research has been carried out in the past 50 years to characterize the fiber suspension flow behavior and to monitor the fiber suspension flow during paper manufacture. However, the above research has been hampered by the lack of techniques to directly characterize fiber suspension flow fields because fibers and fiber flocs tend to interfere with instruments inserted into the flow. The fundamental studies in this thesis concentrated on three parts: (1) examine the feasibility of measuring wood fiber suspension flow by Pulsed Ultrasonic Doppler Velocimetry (PUDV), (2) apply PUDV to characterize fiber suspension flow behavior in a rectangular channel, (3) apply PUDV to measure the forming jet velocity profile along the jet thickness direction (ZD). In the first part, it is demonstrated that PUDV is an accurate technique for the velocity profile measurement of fiber suspension flow. The measurement has high repeatability and sensitivity. Suitable parameters should be selected in order to obtain the optimum measuring results.

Arterial endothelial cells (ECs) are subjected to pulsatile strain due to pressure changes in the cardiac cycle and this may play a significant role in vascular function in health and disease. Further, ECs differentially respond to different patterns of strain. There is much evidence that cyclic uniaxial strain results in a perpendicular orientation of ECs and their stress fibers, while no such alignment occurs in response to cyclic equaibiaxial stretch. It is unclear how cells and their stress fibers determine their specific response to particular spatiotemporal changes in the matrix, however. Given that ECs located at regions in the arterial tree prone to atherogenesis are non-aglined, while ECs in relatively healthy regions are oriented perpendicular to the principal direction of cyclic stretch, it is important to understand the mechanisms which regulate stretch-induced stress fiber alignment. The focus of this thesis was to develop realistic models to describe the dynamic changes in the organization of stress fibers in response to diverse spatiotemporal patterns of stretch. The model is based on the premise that stress fibers are pre-stressed at a ?homeostatic? level so that stress fibers are extended beyond their unloaded lengths, and that perturbation in stress fiber length from the homeostatic level destabilizes the stress fibers. A deterministic model described experimentally measured time courses of stress fiber reorientation perpendicular to the direction of cyclic uniaxial stretch, as well as the lack of alignment in response to equibiaxial stretch. In the case of cyclic simple elongation with transverse matrix contraction, stress fibers oriented in the direction of least perturbation in stretch. Model analysis indicated the need for a time-dependent stress fiber mechanical property, however. Thus, a stochastic model was developed that incorporated the concept that stress fibers tend to self-adjust to an equilibrium level of extension when they are perturbed from their unload lengths with the turnover of stress fibers. The stochastic model successfully described experimentally measured time courses of stress fiber reorganization over a range of frequencies. At a frequency of 1 Hz, stress fibers predominantly oriented perpendicular to stretch, while at 0.1 Hz the extent of stress fiber alignment was markedly reduced and at 0.01 Hz there was no alignment at all. Both the deterministic and stochastic models accurately described the relationship between stretch magnitude and the extent of stress fiber alignment in endothelial cells subjected to cyclic uniaxial stretch. Parameter sensitivity analyses for each model were used to demonstrate the effects of each parameter on the characteristics of the system response. In summary, the mathematical models were capable of describing stress fiber reorganization in response to diverse temporal and spatial patterns of stretch. These models provide a theoretical framework to elucidate the mechanisms by which adherent cells sense the characteristics of matrix deformation and describe a mechanism by which the cells can then adapt to such deformations to maintain mechanical homeostasis.