ABSTRACT Doubtful Sound, in SW New Zealand, exposes an exhumed section of lower crust that represents the root of an Early Cretaceous magmatic arc. Here, the lower crust underwent a change from contraction to extension and these tectonic cycles are fundamental to the growth of continental crust. Mafic-intermediate granulite gneisses occur below the extensional Doubtful Sound shear zone (DSSZ) which records the retrogression and transposition of granulite fabrics at the upper amphibolite facies. I compared 3D rock fabrics, microstructures and textures within and below the DSSZ to determine the processes involved in the shift from contraction to extension and to infer the sequential processes of transforming L>S granulites to L=S amphibolites. Below the DSSZ, dehydration zones around felsic veins and leucosome in migmatitic orthogneiss record granulite facies metamorphism. Aggregates of clinopyroxene (cpx) and orthopyroxene (opx) that are rimmed by garnet (grt) and interstitial melt are set in a plagioclase (pl) matrix. Peritectic grt, pl-grt symplectites, beads of pl along grain boundaries, and elongate, inclusion-free pl reflect the anatexis. Pl exhibits a crystal preferred orientation (CPO) and evidence of subgrain rotational recrystallization and grain boundary migration, indicating subsolidus deformation outlasted melting. Mafic aggregates are boudinaged and opx developed subgrains. During peak metamorphism high strain was partitioned to locations enriched in melt, producing L>S fabrics and an upward trajectory in the strain path. A comparison of mineral grain shapes indicates that pl accommodated most of the strain. Granulite-amphibolite transitional rocks inside the DSSZ record a heterogeneous retrogression of the granulites to a polyphase metamorphic assemblage of hornblende (hbl), biotite (bt), and fine pl. Also preserved is the resetting of high strain L>S granulite to low strain, L=S amphibolite. Folia of porphyroblastic hbl + bt progressively penetrate the pl matrix via solution mass transfer. Porphyroblastic pl in the rock matrix becomes increasingly transposed to gneissic layering. A path of decreasing gradient from high strain L>S granulite to low strain L=S amphibolite reflects the development of the DSSZ fabric, growth of new minerals and onset to deformation at the amphibolite facies. Inside the DSSZ, amphibolites show an increasing strain gradient from low strain L=S amphibolite to high strain L=S amphibolite. Pl aggregates lack a CPO and are mostly annealed but preserve grain boundary migration microstructures. Hbl is recrystallized and forms asymmetric fish. Evidence of high fluid activity and reaction softening within the DSSZ include increased hbl + bt and bt beards on pl relative to rocks outside the DSSZ. My observations suggest that magma, heat, and melting initially weakened the lower crust, facilitating the development of high strain zones with L>S fabrics. Partially molten regions deformed by suprasolidus flow and solid portions deformed mostly by dislocation creep in pl and boudinage of cpx + opx. Later, the lower crust was weakened and high strain fabrics were reset from overprinting and transposition as retrogression progressed and low strain L=S fabrics formed. During extension there was an upward trajectory in the strain path to high strain L=S fabrics within the DSSZ, where hbl and bt accommodated more strain. My results illustrate the importance of 1) melting, cooling, and hydration in controlling strain partitioning and the rheological evolution of lower crustal shear zones, and 2) the importance of integrating microstructural and fabric analysis to determine strain paths.

Coherent injection, detection and manipulation of spins in semiconductor nansotructures can herald a new genre of information processing devices that are extremely energy-efficient and non-volatile. For them to work reliably, spin coherence must be maintained across the device by suppressing spin relaxation. Suppression can be accomplished by structural engineering, such as by confining spin carriers to the lowest subband in a semiconductor quantum wire. Accordingly, we have fabricated 50-nm diameter InSb nanowire spin valves capped with Co and Ni nanocontacts in which a single conduction subband is occupied by electrons at room temperature. This extreme quantum confinement has led to a 10-fold increase in the spin relaxation time due to dramatic suppression of the D’yakonov -Perel’ (DP) spin relaxation mechanism. We have observed the spin-valve and Hanle effects at room temperature in these systems. Observing both effects allowed us to estimate the carrier mobility and the spin relaxation length/time and we found that the latter is ~10 times larger than the value reported in bulk InSb despite a four orders of magnitude decrease in the carrier mobility due to surface roughness scattering. We ascribe this dramatic increase in spin relaxation time to the suppression of the DP relaxation mode due to single subband occupancy. Modulation of spin relaxation rate by an external agent can open new possibilities for spintronic devices. Any agent that can excite electrons from the lowest subband to higher subbands will dramatically increase the DP spin relaxation rate. We have shown that the spin relaxation rate in InSb nanowires can be modulated with infrared light. In the dark, almost all the electrons in the nanowires are in the lowest conduction subband, resulting in near-complete absence of DP relaxation and long spin coherence length. This results in a high resistance state in a spin valve whose ferromagnetic contacts have anti-parallel spin polarizations. Under infrared illumination, higher subbands get populated and the DP spin relaxation mechanism is revived, leading to a three-fold decrease in the spin relaxation length. As a result, injected spins flip in the spacer layer of the spin valve and this causes the spin valve resistance to drop. Therefore, this effect can be exploited to implement an infrared detector. We also studied the transport behavior of a single nanowire (~50 nm diameter) captured between two non-magnetic contact pads. The wire was attached between the pads using dielectrophoresis. A giant (∼10,000,000%) negative magnetoresistance at 39 mT field was observed at room temperature in Cu nanowires contacted with Au contact pads. In these nanowires, potential barriers form at the two Cu/Au interfaces because of Cu oxidation that results in an ultrathin copper oxide layer forming between Cu and Au. Current flows when electrons tunnel through, and/or thermionically emit over these barriers. A magnetic field applied transverse to the direction of current flow along the wire deflects electrons toward one edge of the wire because of the Lorentz force, causing electron accumulation at that edge and depletion at the other. This makes the potential barrier at the accumulated edge shorter and at the depleted edge taller. The modulation of the potential barrier height with a magnetic field dramatically alters the tunneling and/or thermionic emission rate causing a giant magnetoresistance. Currently, effort is underway to demonstrate strain sensitive anisotropic magnetoresistance (AMR) in a single Co-Cu-Co nanowire spin valve. AMR is caused by spin-orbit coupling effects which makes the resistance of a ferromagnet depend on the angle between the direction of current flow and the magnetization. The resistance maximizes when the angle is 00 or 1800 and minimizes when the angle is 900. When an external magnetic field is applied in a direction opposite to a ferromagnet’s magnetization, the latter begins to rotate in the direction of the field and hence its resistance continuously changes. This results in a trough in the magnetoresistance of a spin valve structure between the two fields when the magnetization starts to rotate and when the magnetization completes the rotation. We have observed a magnetoresistance peak (instead of trough) in the Co-Cu-Co spin valve, which is due to the normal spin valve effect that overshadows AMR. However, when an intense infrared light source is brought close to the sample, the peak gets overshadowed by a trough, showing that the AMR effect becomes dominant. We attribute this intriguing feature to the fact that the AMR effect is strongly influenced by strain. Heating by the light source generates strain in the Co contacts owing to unequal thermal expansion of Co and the underlying substrate. We also observed that the AMR effect becomes more pronounced as the light source is brought closer to the sample, resulting in increased heating and hence increased strain generation.

This report deals with reconstruction of strain fields within deformed materials. The method relies upon data generated from Bragg edge measurements, in which information is gained from neutron beams that are sent through the sample. The reconstruction has been made by modelling the strain field as a Gaussian process, assigned a covariance structure customized by incorporation of the so-called equilibrium constraints. By making use of an approximation scheme well suited for the problem, the complexity of the computations has been significantly reduced. The results from numerical simulations indicates a better performance as compared to previous work in this area.

M.Ing. (Mechanical Engineering) / Please refer to full text to view abstract

<p>Vertically aligned nanocomposite (VAN) configuration has been recognized as the state-of-the-art architecture in the complex oxide epitaxial thin films, which are constructed by two immiscible phases simultaneously and vertically growing on a given substrate and forming various columnar microstructures, such as nanopillars embedded in matrix, nanomaze, and nanocheckboard. Due to its architectural features, VAN structure enables a powerful control on the multifunctionalities via vertical strain engineering, microstructural variations, and interfacial coupling. It provides flexibility in complex oxide designs with various functionalities (e.g., electrical, magnetic, optical, etc.), as well as a platform to explore the correlations between strain, microstructure, and multifunctionalities of the nanocomposite thin films.</p> <p>In this dissertation, integrated VAN systems with multilayer configuration have been constructed as a new three-dimensional (3D) framework, e.g., inserting 1-3 layers of CeO₂ (or LSMO) interlayers into the La_0.7Sr_0.3MnO₃ (LSMO)-CeO₂ VAN system and forming 3D interconnected CeO₂ (or LSMO) skeleton embedded in LSMO matrix. This new VAN 3D framework enables both lateral and vertical strain engineering simultaneously within the films and obtains highly enhanced magnetotransport properties, such as the record high magnetoresistance (MR) value of ~51-66%, compared with its VAN single layer counterpart. In order to demonstrate the flexibility of this design, other systems such as 3D ZnO framework embedded in LSMO matrix have been constructed to explore the thickness effects of the ZnO interlayers on the magnetotransport properties of the LSMO-ZnO system. The maximum MR value is obtained at the ZnO interlayer thickness of ~2 nm, which enables the optimal magnetoresistance tunneling effect. Meanwhile, the significance of the interlayer selection in the microstructure and magnetoresistance properties of the LSMO-ZnO system has been investigated by varying the interlayer materials yttria-stabilized zirconia (YSZ), CeO₂, SrTiO₃, BaTiO₃, and MgO. The formed 3D heterogeneous framework provides a new dimension to tailor the microstructure, strain and functionalities within the films.</p> <p>Moreover, a new strain engineering approach with engineered tilted interfaces has been demonstrated by multilayering different VAN layers with various two phase ratio and creating a hybrid nanodumbbell structure within the LSMO-CeO₂ VAN thin films. The nanodumbbell structure accomplishes a more efficient strain engineering and exhibits highly enhanced magnetic and magnetoresistance properties, compared with its VAN single layer and interlayer counterparts. </p> <p>These examples presented in the thesis demonstrate the flexibility and potential of 3D strain engineering in complex VAN systems and a higher level of property control, coupled with unique microstructures and interfaces. Beyond perovskites, these 3D designs can be extended to other material systems for a broader range of applications, such as energy conversion and storage related applications.</p>

MSc (Occupational Therapy), Faculty of Health Sciences, University of the Witwatersrand / Ergonomic interventions, addressing work and lifestyle factors, seem more effective in reducing computer related upper limb repetitive strain injury (RSI).This study considered the efficacy of such a programme on the resolution of RSI symptoms. A cross sectional survey, of 325 computer workers in a medical aid company call centres, in Gauteng, South Africa was used to establish a point prevalence of 30.23% for RSI symptoms, which correlates with those found elsewhere. An occupational therapy ergonomic intervention was then designed and piloted for efficacy. A randomised control trial conducted on 37 participants with RSI used the programme and computer generated “Break Software”. The six week intervention included the assessment of: three physical outcome measures and lifestyle factors for, the experimental and control groups. Results indicated positive effects on pain, grip strength, and lifestyle factors including feelings of inefficiency, pressure at the end of the day, depression and work capacity, but little extrapolation of ergonomic knowledge to the workplace.

Thesis advisor: Yvette D. Kuiper / Crystallographic Preferred Orientations (CPO) are common in deformed rocks, and usually result from crystal plastic deformation by dislocation creep. Whether deformation mechanisms that occur at lower differential stress and lower temperature than dislocation creep, such as Dissolution-Precipitation Creep (DPC), may result in the development of a CPO is less certain. DPC, a process also known as pressure-solution creep or dissolution creep, has caused substantial removal and reprecipitation of quartz within the Purgatory Conglomerate of Rhode Island. The conglomerate is exposed within the southeastern region of the Pennsylvanian Narragansett basin and experienced folding during the Alleghanian orogeny. Strain within the southeastern portion of the Narragansett basin increases from west to east and is associated with a metamorphic gradient from very low grade greenschist facies in the west to the lower biotite zone in the east. Within the Pugatory Conglomerate DPC has led to the dissolution of quartz along cobble surfaces perpendicular to the shortening direction, and to be precipitated as overgrowths at the ends of the cobbles (strain shadows), parallel to the maximum extension direction. This offers a unique opportunity to study the effects of dissolution and precipitation separately, because the quartz grains within the cobbles experienced dissolution only, while precipitation occurred in the strain shadows. Cathodoluminescence (CL) analysis was conducted on regions within the strain shadow in order to determine what amount of the quartz was formed authigenically. The results suggest that quartz-rich areas of the strain shadow were comprised primarily of authigenic quartz and formed channels or wedges. Electron Backscatter Diffraction (EBSD) analysis was used to test whether quartz dissolution processes within the cobbles and/or quartz precipitation within the strain shadows resulted in CPO development. Quartz grain c-axis orientations of various domains within the cobbles and strain shadows indicate that CPO patterns are absent in both domains of dissolution and of precipitation irrespective of the degree of strain or metamorphic grade. The existence of discrete mica selvages along the cobble margins suggests that quartz dissolution only occurred along the cobble surface and did not affect the grains, or result in a CPO, within the cobble's interior. Quartz precipitation within the strain shadows did not result in a CPO, probably because the strain shadows are truly localized regions of low strain with little to no differential stress, allowing quartz grain growth in random orientations. / Thesis (MS) — Boston College, 2010. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Geology and Geophysics.

Thesis advisor: Chia-Kuang F. Tsung / Thesis advisor: Dunwei Wang / In order to understand the lattice strain effect and its relationship to size, shape, composition, and catalytic performance, novel well-defined nanocrystal archetypes were designed and synthesized by taking advantage of wet chemical, seed-mediated (mild) reduction routes developed by our lab. First, the current synthesis challenges are addressed in creating smaller monometallic shape-controlled metal nanocrystals, and novel cuboctopods via a hybrid nanoparticle stabilizer. A look at the relationship between lattice strain and morphology is then shown in a single-component system, where still new features have been observed for the first time by the traditional technique of powder x-ray diffraction. Synthesis methods for differently strained Pd surfaces are described and catalysis by these surfaces is discussed. Finally, studies of the synthesis, characterization, electrocatalytic activity, and restructuring of novel and more sophisticated strained architectures are presented: core-island-shell nanocrystals, phase-segregated nanoboxes, island nanoframeworks, and core-sandwich-shell nanoparticles. Lattice strain and composition effects were studied in carbon monoxide, small alcohol, and formic acid electrocatalytic oxidations as well as in oxygen reduction, the latter of which, governs the commercial viability of automotive fuel cells, a sustainable energy and zero-emission technology. Here it is demonstrated how a tunable thickness of Ni sandwich layers can be used to improve catalytic performance by increasing lattice strain on the Pt surface. The sandwich archetype offers a new platform for the investigation of lattice strain and could be a promising, industrially relevant, catalyst design concept, to help address the need for a more sustainable energy future. The results help paint a new picture of catalysis by metal nanocrystals; one which brings lattice strain to the forefront of the discussion, as an important parameter for further study and for use in developing higher-performing catalysts. / Thesis (PhD) — Boston College, 2015. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.

The transformations occurring in the sub-stoichiometric Ti(C,N) – W - Al system processed by high energy ball mill were investigated. The milling parameters included the milling time and the temperature comprising milling at subzero temperature and above 25°C. Two sub-stoichiometric Ti(C,N) stocks were selected, the Ti(C0.5N0.05) containing more interstitial elements than the Ti(C0.5N0.5)0.6.The transformation stages and mechanisms of alloying are discussed with respect to the changes in crystal structures of the powder constituents. The milling atmosphere had an effect on the lattice strain of milled products, and hence on the kinetics of solid state dissolution between the powder constituents, but it did not affect the fracturing process. The release of the stored crystallite lattice strain energy was the major determinant in mechanical alloying, with particle size reduction playing a necessary, but less significant role. The strain energy and the fine particle size contributed to the increased chemical reactivity with oxygen of the powders milled for shorter times. The affinity of the powders with oxygen decreased after W dissolution in Ti(C,N), and the subsequent decrease in lattice strains. The annealing behaviour of Ti(C0.5N0.05) - 40wt% W and Ti(C0.5N0.5)0.6 - 40wt% W mechanically alloyed powders were investigated using XRD, TEM, SEM and DTA techniques. It was observed that the reaction start and finish temperatures between constituents were lower in the system that had higher residual lattice strains after milling. The compositions of the intermetallic compounds and the solid solutions formed were dependent on the milling conditions and the annealing temperature. Thermal alloying was observed during annealing of Ti(C0.5N0.05) - 40wt% W mechanically alloyed products, whereas de-mixing of W-rich phases from the metastable solid solution occurred during annealing of the Ti(C0.5N0.5)0.6 - 40wt% W milled powders. The effects of Al addition and milling at subzero temperatures on the transformation of Ti(C0.5N0.05)-W powder mixtures were investigated. Addition of Al powder improved the kinetics of solid solution between powder constituents. The effect of Al was ascribed to the increase of lattice strain during short milling time followed of relaxation at longer time, and to the fast diffusion of atoms. Also, it was noticed that the high viscosity of the process control agent could inhibit the alloying process. Multiple three-component compounds could be formed. Aluminium preferably reacted with tungsten. The W(Al,C) and W(Al,Ti) formed were stable, thus solubility of W in Ti(C0.5N0.05) in the presence of Al was limited. The evolution of the morphologies of Ti(C,N)-W mixtures show that fracturing of hard particles dominated in the early stage of milling in the absence of Al, whereas with Al, plastic deformation of particles and cold welding of Ti(C,N) and W particles by the softer Al prevailed at the same time. Longer milling time improved the homogeneity and the formation of nanostructured binder pools in the sintered products. Lower oxygen contents in sintered PcBN were achieved by mechanically alloying Ti(C,N), W and Al in the high energy ball milling stage. Low level of Co in the infiltration layer was also achieved when sintering PcBN with this type of binder. A link was established between the addition of Al at the attrition milling stage and high oxygen content in the sintered PcBN, thus should be avoided. The pressure and temperature applied during sintering or annealing had a strong effect on the compositions and the crystal structures of the phases formed in the mechanically alloyed binder. The lattice strains of the binder and the PcBN were higher in the sintered materials prepared with the Ti(C0.5N0.5)0.6-W binder than in those made using the Ti(C0.5N0.05)-W alloys.

Introduction: Unicompartmental knee replacements (UKRs) are an alternative to total knee replacements (TKRs) for treating isolated medial compartment knee osteoarthritis. However, revision rates are consistently higher than for TKR and UKRs are commonly revised for “unexplained” pain, a possible cause of which is elevated proximal tibial bone strain. The influence of implant design on this strain has not been previously investigated. Aims: The aims of this thesis are to determine the effect of medial UKR tibial component design on proximal tibial strain and ongoing pain. Methods: A retrospective clinical cohort study was performed comparing patient reported outcome and implant survival of a metal backed mobile bearing UKR implant (n=289) and an all-polyethylene (AP) fixed bearing UKR implant (n=111) with minimum 5 year follow up. A method of digital radiological densitometry, the greyscale ratio b (GSRb), was developed, validated and applied to plain radiographs to measure changes in bone density over 5 years in both the metal backed (n=173) and all-polyethylene (n=72) UKR patients. A finite element model (FEM) was validated against previous mechanical testing data and was used to analyse the effect of metal backing and implant thickness on proximal tibial cancellous bone strain in fixed bearing UKR implants. Results: There were no significant differences in patient reported outcomes between implants throughout follow up. Ten year all cause survival was 90.2 (95%CI 86-94) for the metal backed implant and 79.9 (60.7 to 99) for the all-polyethylene. Revision for unexplained pain was significantly greater in the AP implant where revisions were performed significantly earlier. Overall, the mean GSRb reduced following medial UKR with no difference between implants. In those patients where GSRb increased, patient reported outcomes were worse with an association with ongoing pain. A finite element model was successfully validated using acoustic emission and digital image correlation data. This model confirmed that the volume of cancellous bone exposed to compressive and tensile strains in excess of 3000 (pathological overloading) and 7000 (fracture) microstrain were higher in the AP implants, as were peak tensile and compressive strains. Varying polyethylene insert thickness did not affect these strain parameters in the metal backed implant, but varying polyethylene thickness in the AP implants had significant effects at all loads with elevated strains in thinner implants. Increasing the AP thickness to 10mm did not reduce strains to the levels found under metal backed implants, and imminent cancellous bone failure was implied when AP thickness was reduced to 6mm. Conclusion: UKRs with all-polyethylene tibial components are associated with greater proximal tibial strains than metal backed implants and this is exacerbated in thinner implants. The clinical consequences of this are uncertain. Medial UKR implantation does alter proximal tibial GSRb, though this is not uniform and is independent of implant type. When GSRb increases it is associated with ongoing pain.