This study focused on the effect of fines (minus 75 microns) content and type (plasticity) on the strength of granular base materials. Four different sources of crushed rock Granular A materials were selected by the MTO for testing. Routine laboratory tests were carried out on the four Granular A materials including sieve analysis, standard Proctor compaction, Atterberg limits, California bearing ratio, resilient modulus and permeability tests. Fines from an additional source, to be plastic, were selected and used as substitute fines for the Granular A natural fines but were found to have a similar index of plasticity (PI). The influence of fines content on CBR varied for each Granular A source as some increased with increasing fines content and others decreased as the fines content increased. With the similarities in the PI of the two fines no clear trend in CBR values between samples with natural and substitute fines was observed. The resilient modulus (MR) values were by and large similar when the natural fines were replaced with substitute fines. The MR decreased as the fines content increased when the water content was below 5 percent but at 7 percent water content some of the tests failed (could not be tested) at higher confining pressures. Energy dissipation was calculated from the resilient modulus tests and it was observed that the energy dissipation decreased as the confining pressure increased, with lower dissipated energies corresponding to higher MR values. Given that definitive trends could not be identified with respect to the influence of fines and plasticity, the influence of the percent paste (sum of moisture and fines content at the time of compaction) was examined. As the paste increased the resilient modulus decreased and the damping ratio increased. Results from permeability tests showed that for specimens with no fines present the permeability was much higher than those with fines. There was no significant change observed in permeability for specimens in which natural fines were replaced by substitute fines or as the hydraulic gradient was varied. / Thesis / Master of Applied Science (MASc)

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Numerous experiments have demonstrated that the activity of neurons can alter the strength of excitatory synapses. This synaptic plasticity is bidirectional and synapses can be strengthened (potentiation) or weakened (depression). Synaptic plasticity offers a mechanism that links the ongoing activity of the brain with persistent physical changes to its structure. For this reason it is widely believed that synaptic plasticity mediates learning and memory. The hypothesis that synapses store memories by modifying their strengths raises an important issue. There should be a balance between the necessity that synapses change frequently, allowing new memories to be stored with high fidelity, and the necessity that synapses retain previously stored information. This is the plasticity stability dilemma. In this thesis the plasticity stability dilemma is studied in the context of the two dominant paradigms of activity dependent synaptic plasticity: Spike timing dependent plasticity (STDP) and long term potentiation and depression (LTP/D). Models of biological synapses are analysed and processes that might ameliorate the plasticity stability dilemma are identified. Two popular existing models of STDP are compared. Through this comparison it is demonstrated that the synaptic weight dynamics of STDP has a large impact upon the retention time of correlation between the weights of a single neuron and a memory. In networks it is shown that lateral inhibition stabilises the synaptic weights and receptive fields. To analyse LTP a novel model of LTP/D is proposed. The model centres on the distinction between early LTP/D, when synaptic modifications are persistent on a short timescale, and late LTP/D when synaptic modifications are persistent on a long timescale. In the context of the hippocampus it is proposed that early LTP/D allows the rapid and continuous storage of short lasting memory traces over a long lasting trace established with late LTP/D. It is shown that this might confer a longer memory retention time than in a system with only one phase of LTP/D. Experimental predictions about the dynamics of amnesia based upon this model are proposed. Synaptic tagging is a phenomenon whereby early LTP can be converted into late LTP, by subsequent induction of late LTP in a separate but nearby input. Synaptic tagging is incorporated into the LTP/D framework. Using this model it is demonstrated that synaptic tagging could lead to the conversion of a short lasting memory trace into a longer lasting trace. It is proposed that this allows the rescue of memory traces that were initially destined for complete decay. When combined with early and late LTP/D iii synaptic tagging might allow the management of hippocampal memory traces, such that not all memories must be stored on the longest, most stable late phase timescale. This lessens the plasticity stability dilemma in the hippocampus, where it has been hypothesised that memory traces must be frequently and vividly formed, but that not all traces demand eventual consolidation at the systems level.

The Thesis deals with Strain-Space Plasticity and its implementation in Nonlinear Finite Element frame-work coupled with damage. Conventional Stress-Space Plasticity, though very popular amongst commercial nonlinear FEM software package, has severe limitations especially in dealing with perfect-plasticity situations and also for softening behaviour. Strain-Space Plasticity, when fully evolved, has the potential to replace the Stress-space Plasticity. The thesis is a welcome addition in furthering the understanding of Strain-Space Plasticity and its illustration to analyze practical engineering problems. Continuum Damage Mechanics (CDM) is an evolving area of Solid Mechanics with great potential for application in failure and integrity analyses. Research activities have been initiated by several research groups world-wide, thus demonstrating its acceptance as an area of mechanics in its own right .This thesis further demonstrates coupling of Continuum Damage Mechanics with Strain-Space Plasticity. The thesis has been organized into 11 chapters with a good review of Plasticity (Stress-Space as well as Strain-Space), CDM, Stainless-steel Plasticity as well as Adhesive Plasticity. Main research contributions include: Formulation, FEM implementation and benchmarking of Strain Space Plasticity for Plane-Stress, Plane Strain, Axi-symmetric as well as 3-D case. Both isotropic and kinematic hardening models have been implemented. Further, these implementations have been extended by coupling with Damage. Special illustrations have been made to practical situations involving constitutive modeling of Stainless-steel and structural-adhesive.

As opposed to earlier beliefs, the brain is altering itself throughout an individual’s life. The process of functional or structural alterations is referred to as plasticity, and can be induced by several factors such as experience or physical exercise. In this thesis, the research area of experience-dependent plasticity, with focus on exercise-induced plasticity is examined critically. Evidence from a vast array of studies are reviewed and compared in order to find whether physical exercise can induce neural plasticity in the human brain, how it may be beneficial, and what some of the plausible mediators of exercise-induced plasticity are. The findings demonstrated in this thesis suggest that although there are knowledge gaps and limitations in the literature, physical exercise can indeed result in exhibited plasticity as well as being beneficial for the human brain in several ways.

The construction of road works in the world has always been a challenge for engineering, especially in areas where the conditions and types of soil are not adequate for the execution of this type of projects. The present investigation has as main objective to determine the influence that has the rice husk ash (RHA) to stabilize the subgrade layer of a pavement, composed of a low resistance clayey soil. RHA is a waste and pollutant material for the environment; therefore that its use can be considered as an economic and ecological alternative. Thus, several tests were carried out where it proved the value of CBR increased from 4.30% to 20.70%, by adding a 20% RHA dosage, achieving its optimum value to be considered a very good subgrade. In this way, it is possible to affirm that the addition of RHA improves the geotechnical properties of the soil.

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During high speed cutting processes, metals are subject to high strains and strain rates. The dynamic nature of the deformation during high speed cutting makes it difficult to detect atomic scale deformation mechanisms experimentally. Atomic scale plasticity behaviour is often studied using various micromachining techniques such as micropillar compression testing, nanoindentation, and nanoscratching. However, strain rates in micromachining experiments are far lower than those seen during high speed cutting. Atomistic simulations can be used to study high strain rate plasticity at nanometre length scales. In this thesis, we present results from molecular dynamics simulations of plasticity in nanostructures. Results from simulations of uniaxial strain of both bcc and fcc nanopillars are presented. We find that the outcomes of these uniaxial strain simulations depend sensitively on the initial configurations of the systems. In particular, the choice of crystallographic surfaces on the faces of the pillars and the means by which strain is implemented in the simulations can affect the simulation results. We find that the twinning anti-twinning asymmetry in bcc materials causes nanopillars to deform by dislocation glide in compression and by twinning in tension. This explains the compression tension asymmetry reported experimentally in bcc micropillars. We find that deformation is mediated by glide of shockley partials in fcc pillars for compressive and tensile strains. Simulations of pure shear of nanocrystalline Fe are also presented. We find a change in deformation mechanisms for this system when at high temperatures. At low temperatures, plasticity is mediated in part by dislocation glide and twinning. However, at temperatures above 1200K the deformation is dominated by grain boundary sliding, recrystallization, and amorphization.

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