This licentiate thesis reports analytical results for the electrostatic response to a test charge moving through dusty plasma. Two particular cases for a slowly moving test charge, namely, grain size distribution and grain charging dynamics are considered. Analytical results for the delayed shielding of a test charge due to dynamical grain charging in dusty plasma are also reported. In the first case, a dusty plasma in thermal equilibrium and with a distribution of grain sizes is considered. A size distribution is assumed which decreases exponentially with the grain mass for large sizes and gives a simple smooth reduction for small sizes. The electrostatic response to a slowly moving test charge, using a second order approximation is found and the effects of collisions are also investigated. It turns out that for this particular size distribution, there is a remarkably simple result that the resulting effective distribution for the electrostatic response is a kappa (generalized Lorentzian) distribution. In the second case, we present an analytical model for the shielding of a slowly moving test charge in a dusty plasma with dynamical grain charging for cases both with and without the collision effects. The response potential is treated as a power series in test charge velocity. Analytical expressions for the response potential are found up to second order in test charge velocity. The first-order dynamical charging term is shown to be the consequence of the delay in the shielding due to the dynamics of the charging process. It is concluded that the dynamical charging of the grains in a dusty plasma enhances the shielding of a test charge. To clarify the physics, a separate study is made where the charging is approximated by using a time delay. The resulting potential shows the delayed shielding effect explicitly. The terms in the potential that depend on the charging dynamics involve a spatial shift given by the test charge velocity and the charging time. This kind of work has relevance both in space and astrophysical plasmas. / QC 20101220

<p> A microscopic study of two samples of the Gowganda Formation, both having undergone pure shear deformation at greenschist f acies metamorphism has shown: Sample A -Reduction in quartz grain size, and pressure solution shadows were evidence for strong pressure solution activity. Pre-lithification fractures provided channelways for the removal of quartz and water out of the system. Matrix quartz was not recrystallized. Sample B -Extensive local recrystallization of quartz due to pressure solution activity caused metamorphic segregation and the formation of a cleavage. Cleavage behaviour differs in the matrix from that observed in an area of contact strain, as produced by a buckled quartz vein. There is no evidence for removal of quartz from the system. </p> <p> A comparison between the two samples suggests that (a) water, in this case at least, is necessary to produce metamorphic segregation, (b) the system has to be closed to reach metamorphic segregation and (c) original features may be preserved through limited metamorphism if the rock is dried out early in its history. </p> / Thesis / Bachelor of Science (BSc)

OBJECTIVES: This study examined mechanical, chemical and microstructural properties of multilayer zirconia materials that are composed of layers of different forms of zirconia with varying translucency. Their resistance to low temperature degradation and their properties were compared to each other, and to monolithic zirconia. METHODOLOGY: “ZirCAD Prime” from Ivoclar Vivadent, “AxZir XT Multilayer Dental Zirconia” from Axsys Dental Solutions, and “inCoris ZI” from Dentsply Sirona, were examined. Twenty specimens were created from each material, half of which were aged. Specimens were examined for the following: Three point bending flexural strength, grain size, microhardness, indentation fracture toughness, warp and elemental composition. RESULTS: inCoris ZI had significantly higher flexural strength than ZirCAD Prime, which in turn had significantly higher strength than AxZir XT. The flexural strength values were 1113.55MPa, 857.21MPa and 625.77MPa, respectively. Grain size patterns were noted in multilayer specimens; more translucent layers had significantly larger grain sizes. AxZir XT’s incisal most layer average grain size was 0.988μm, whereas ZirCAD Prime’s was 1.172μm. The dentin most layer of AxZir XT average grain size was 0.529μm whereas ZirCAD Prime’s was 0.470μm. Microhardness results showed few significant differences between layers. The highest microhardness was found in AxZir XT’s incisal most layer, after aging, with a value of 13.502 GPa. The lowest was found in the aged inCoris ZI specimen, with a value of 10.775 GPa. In the ZirCAD Prime, fracture toughness was highest in the dentin most layer with a value of 8.88 MPa m¹/², compared to its incisal most layer that had a value of 4.92 MPa m¹/². This pattern was not seen in AxZir XT, where the dentin most layer had a value of 8.36 MPa m¹/², and the incisal most layer had a value of 6.40 MPa m¹/². Hydrothermal aging had detrimental and significant impacts on fracture toughness of all materials. Elemental composition analysis revealed predictable levels of elements or molecules in ZirCAD Prime. and inCoris ZI, but not within the AxZir XT. 5Y levels were seen in ZirCAD Prime’s incisal layer, and 2.5-3Y in the dentin most layer. inCoris ZI had constant levels of 3Y, but AxZir XT had no distinct level of Yttria in its layers. CONCLUSIONS: 1. Flexural Strength of multilayer materials was significantly lower than monolithic zirconia. 2. Grain sizes appeared largest in translucent incisal-most layers, with significant differences between them and the opaque dentin-most layers. 3. The elemental composition analysis showed an expected level of 3 mol% Yttria in the inCoris ZI with varying amounts by layer in the ZirCAD Prime from 3Y (cervical) to 5Y (incisal), but there was no clear gradation in the AxZir XT. 4. Some significant differences were seen between the materials and their layers in the microhardness tests. inCoris ZI had significantly lower values than both ZirCAD Prime and AxZir XT. The highest values were found within AxZir Xt. 5. Fracture toughness was significantly higher in the dentin-most layer compared to the incisal most-layer of ZirCAD Prime but not in AxZir XT. 6. LTD significantly decreased some fracture toughness test values. inCoris ZI, AxZir XT’s 1st incisal layer and ZirCAD Prime’s 2nd transition layer had significant decreases in fracture toughness after aging. 7. LTD had no impact on flexural strength or microhardness values. 8. LTD significantly decreased grain size of inCoris ZI.

Habitat loss is among the biggest threats to conservation worldwide, so habitat restoration plays an increasing role in endangered species management. This is especially true for species with high site fidelity, such as nesting marine turtles. Sand replenishment is commonly used to restore coastal beaches after severe erosion events, and may affect marine turtles and other species that live or reproduce in that habitat. I investigated how abiotic characteristics of sand used in a dune restoration project at Archie Carr National Wildlife Refuge, Florida, affected reproduction of the federally-endangered green turtle (Chelonia mydas). Sand structure and composition can affect egg development and hatching success by altering nest conditions, with nests in fine-grain or very coarse sand suffering decreased hatching success. I determined that calcium carbonate content (27.0% ± 1.4 SE vs. 15.1% ± 3.8 SE), moisture content (3.29% ± 0.26 SE vs. 4.59% ± 0.25 SE), and grain size (427.53 µm ± 14.1 SE vs. 274.66 µm ± 29.1 SE) differed significantly between natural and restored dunes. Hatching success of green turtles (44.7% ± 6.2 SE vs. 65.8% ± 5.3 SE) was significantly lower on restored dunes compared to natural dunes with an estimated loss of 22,646 hatched eggs. Hatching success also decreased as the nesting season progressed. These results demonstrate the importance of regulating fill material used in beach restoration projects; substrate characteristics are easily evaluated and can significantly influence marine turtle hatching success.

This dissertation presents a numerical model constructed to investigate the dynamics and structures of the Earth’s mantle. Deformation of the Earth’s mantle, which is composed of solid silicate minerals, is strongly governed by the constitutive relation-ship among multiple length-scale structures and properties. To explain the realistic consti-tutive behavior of the silicate mantle, an Internal State Variable (ISV) theory that is an advanced and novel constitutive approach for history-dependent elastoviscoplasticity was applied. The ISV constitutive model was, in turn, implemented into a three-dimensional geodynamic code, TERRA3D, which uses the Finite Element method developed for the mantle convection problem. The sequential studies performed in this dissertation are presented in the follow-ing order: i) a comprehensive summary of the mantle material structures (compositions and microstructural features) and its mechanical properties (elasticity and rheology), ii) a development of a recrystallization and grain size dependent ISV constitutive model for the polycrystalline materials such as minerals and metals, which explains comprehensive mineral physics occurring under the conditions of pressure, temperature, and strain rate within the mantle and their history dependence, and iii) an application of the recrystalli-zation and grain size dependent ISV model to the Earth’s mantle convection problem us-ing the TERRA3D for an investigation of the grain size and dynamic recrystallization efect on the mantle dynamics. The applied ISV constitutive model within the TERRA3D Finite Element frame-work captures the subscale dynamics (dislocation density evolution, dynamic and static recrystallization, grain growth, and grain refinement) and their effect on the large-scale rheology and dynamics of the Earth’s mantle. The numerical investigations reveal that the potential for the mechanical instability and weakening within the mantle arises from the kinetics of grain size and recrystallization and their rheological effect. This mechanical instability leads to the mantle convection entering the episodic overturn regime. The TERRA3D-ISV mantle convection model herein also provides some insightful discover-ies regarding the dynamics and structures within the mantle, explaining its complex rhe-ology caused by the kinetics of recrystallization, grain size, hardening, dislocation recov-ery, and diffusion in the geological settings.

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