Thesis (Ph.D. 1981) - The Department of Physical and Inorganic Chemistry, University of Adelaide.

Thesis--University of Wisconsin--Madison. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 197-200).

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Cord-forming fungi form extensive networks that continuously adapt to maintain an efficient transport system, and we can photograph their growth, digitize the network structure, and measure the movement of radio-tracers. Mycelial networks are more accessible than the transport networks of other multicellular organisms, but there are many open questions concerning the coordination of growth and transport within fungal networks. As osmotically driven water uptake is often distal from the growing margin, and aqueous fluids are effectively incompressible, we propose that growth induces mass flows across the mycelium, towards the growing regions. We imaged the temporal evolution of networks formed by Phanerochaete velutina, and at each stage calculated the unique set of currents that account for the observed changes in cord volume, while minimizing the work required to overcome viscous drag. Predicted speeds were in reasonable agreement with experimental data, and cords that were predicted to carry large currents were significantly more likely to increase in size than cords with small currents. We have also developed an efficient method for calculating the exact quantity of resource in each part of an arbitrary network, where the resource is lost or delivered out of the network at a given rate, while being subject to advection and diffusion. This method enabled us to model the spatial distribution of resource that emerges as a fungal network grows over time, and we found good empirical agreement between our model and experimental data gathered using radio-labelled tracers. Our results suggest that in well insulated fungal networks, growth-induced mass flow is sufficient to account for long distance transport. We conclude that active transport mechanisms may only be required at the very end of the transport pathway, near the growing tips. We also developed a simple model of glucose delivery through vascular networks, which indicates that increasing the number of blood vessels in a region can actually decrease the total rate of glucose delivery.

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Combined PFG and T1 methods for rapid acquisition of multiple scans of an NMR pulse sequence are presented. The methods apply initially two RF-pulses in combination with two magnetic field gradient pulses of opposite polarity, different strengths and different durations. The basic idea is to spoil any magnetization in any direction before letting the system recover to some degree of restoration of the thermal equilibrium magnetization. Thereafter any pulse sequence can be applied, and the next scan may be run immediately after the end of this spoiler pulse sequence. Thus one avoids the 5 times T1 delay between each scan. The method has been verified at 11.7 Tesla correlating spectral information with T1 or diffusion.

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Extraction of accurate quantitative parameters to characterize water diffusion in complex porous media like brain tissue in neuroimaging is a challenging inverse problem, that depends on medium\''s structural and geometrical factors [1,3]. If the role of membranes is generally invoked, probe collisions with the insoluble cytoskeleton network and water hydrodynamic interactions with dissolved macromolecules and cytoskeleton occur as well [2]. The latter two interactions have been shown to determine the phenomenological “anomalous diffusion” of probes in the cytoplasm [4,5,6,7,8]. Additionally, the diffusion of small solutes in cytoplasm could be slowed by the local micro-viscosity of the aqueous phase, a phenomenon generally not taken into account in simulations. We suggest that the Grey and White Matter contrast in Diffusion Decay Imaging (DDI) could be caused by differences in cytoskeleton structures, composed respectively of actin and tubulin that could act by the elimination of one possible water diffusion pathlength by the volume occupied by the network phase. This could explain why anomalous DDI signal has been shown to be independent of membrane integrity [9]. Cytoplasm is able to rapidly shift from a sol (aqueous solutions embedded with insolubles particles) to a gel state (a colloidal solutions with a structured semi-solid and an aqueous fluid phase) or to a viscous solution when the insoluble particles become soluble. Does water have the ability of being a sensor of its local “self-viscosity” ? What is the length of the water diffusion\''s path compared to cells size ? Compared to this path length, how many cellular structures should be probed by water\''s translational diffusion ? We try to respond to these questions by investigating Diffusion Decay Imaging models and their effects on the hypothese-free q-space diffusion propagator shape [3], containing all informations concerning viscosity-slowed gaussian diffusion, structural informations [3] and restricted diffusion [1].

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