The strength of polycrystalline materials increases with decreasing grain size. The increase of strength is usually associated with deterioration of ductility, especially for materials having sub-micrometer or nanometer in grain size. It has bee suggested that the ductility of submicro- or nano- grained materials can be improved significantly by introducing a bimodal distribution of grain sizes. The purpose of the present study aims at clarifying the microstructural parameters of the bimodal distribution, such as area ratio and size difference, on the strength and ductility of pure nickel and nickel-cobalt specimens produced by electrodeposition. The microstructural parameters were determined from orientation imaging mapping technique using electron backscatter diffraction. Results indicated that the yield strength is mainly determined by the average size of the fine grains, whereas the tensile strength has a good relation with the average grain size in total. Moreover, it was showed that samples having a area ratio of the fine grains lower than 30% or higher than 70% possess a better ductility. The possible mechanism is discussed in detail.

This study used the sediment samples collected in May (dry season) and September (wet season) 2010 in a river delta and tidal flat complex around Jhoushuei River mouth in Central Taiwan to examine seasonal sediment transport pathways and sources. Four different approaches were used in the analysis of grain-size distribution pattern. They include (1) the McLaren-Bowles method, and (2) the transport vector technique (Gao-Collins method), and (3) a combination of `filtering' and the empirical orthogonal (eigen) function (EOF) analysis technique, and (4) C/N elemental ratios of organic sediments. The results of surface grain size distributions of sediment range from clay to medium sand towards the sea, and very fine sand deposited in the river delta. On the upper tidal flat, mud content of the wet season is higher than dry season due to higher river output of organic sediment and low-energy sediment transport. In wet season, according to the fine-grained sediment from the Jhoushuei River is therefore mainly discharged to the offshore area and little remain around the tidal flat, the influence of river on the grain-size distribution is the least. The results based on McLaren-Bowles method indicate that there were two type sediment transport pathways, (1) the river carried sediment to the coast, then alone the northeast-southwest direction by the longshore current, and (2) during the flood tide, the riverine sediment move to northeast and east through the river delta and tidal creek to the upper tidal flat, respectively. The results based on Gao-Collins method indicate that there was possible seasonal variation of sediment transport pathways on the river delta front, where the significant transport was seaward in the wet season whereas the transport was the opposite in the dry season. On the tidal flat, the model results indicate that seaward transport seems to be controlled by ebb tidal current perhaps due to the sampling at low-tide.

The strength of the ultrafine-grained materials is increased with grain refinement, but it will also reduce the ductility. In the previous study, there are higher strength and better ductility for the copper with bimodal distribution of grain size. In this study, Ni with lamellar structure is fabricated by electrodeposition in order to explore the mechanical properties of the materials with bimodal distribution of grain size, which is obtained by controlling the grain size. From the result of EBSD analysis, it shows that the area ratio of coarse grains and fine grains is from 0.3 to 3 by changing the plating parameters. The average grain size of fine grains is about 0.5 £gm, and the maximum average grain size of coarse grains is up to 6.0 £gm. From the result of tensile test, the materials with 35% of micro-grains embedded regularly inside a matrix of ultrafine grains have better strength and ductility. When the area ratio of micro-grains is up to 62.5%, there is no difference in mechanical properties between the general electrodeposited materials and ones with bimodal distribution of grain size. For pure Ni, the enhancement of ductility for bimodal distribution of grain size is only in post uniform elongation. Otherwise, it is found that the strength and ductility of the material with lamellar structure are increased through the heat treatmeant under the appropriate temperature.

A series of deposits, located along the southern flanks of Grand Mesa, Colorado, and extending to the south, are problematic, and the processes related to emplacement are not understood. The overall area is dominated by two landform systems, Grand Mesa, which supported a Pleistocene ice cap, and the North Fork Gunnison River drainage. Thus, one has to ask: Are these deposits the result of the melting of the ice cap or are they fluvial terraces associated with the evolution of the ancestral Gunnison River? The goal of this research was to map the areal extent of the deposits and to interpret the formation and climatic significance in understanding the evolution of the Pleistocene landscape in the region. An extensive exposure, parallel to State Highway 65 near Cory Grade, was used for detailed description and sampling. Three additional exposures, ~10 to 20 km (~6 to 12 mi) were used to extend the areal extent of sampling. The study area was mapped using aerial photography and traditional field mapping aided by GPS. From the field work, a detailed stratigraphic column, including lithology and erodability, was constructed. Vertical exposures of the deposits were described, mapped, and recorded in the field and using detailed photo mosaics. Samples were collected from each stratum of the deposits for grain-size, shape, and sorting analyses. Five distinct depositional facies were identified. Sieve analysis on collected samples shows that four distinct grain-sizes occur in the outcrops; coarse sand, very-coarse sand, granule, and pebble and boulder. Mean grain-sizes range from 0.0722 to 0.9617, -0.0948 to -0.9456, -1.0566 to -1.9053, and -2.0050 to -3.4643, respectively. Glacio-fluvial depositional environments were identified and supported with observations of sedimentary structures and clast composition. Two major environments of deposition are recorded in the deposits; fluvial deposits from glacial outburst floods, and debris flow deposits. Imbrication of clasts in the strata suggests the flow came from the direction of Grand Mesa to the north. Facies and subsequent sequences were constructed to portray evidence that supports the glacio-fluvial mode of deposition.

This aim of this thesis is to examine the possibility of using Magnetic Barkhausen Noise (MBN) technique in characterizing the microstructures of quenched and tempered low alloy steels as well as annealed low carbon steels. To determine the average grain size by MBN, SAE 1010 steel consisting of dominantly ferrite was used. The specimens were slowly cooled in the furnace after austenitizing at different time and temperature variations. By metallographic examination the average ferrite grain size of specimens was determined. The magnetic parameters were measured by a commercial MBN system. With increasing ferrite grain size, the magnetic Barkhausen jumps caused by the microstructure were decreased due to the reduction in grain boundary density per unit volume. A clear relationship has been observed between average grain size and the magnetic Barkhausen noise signals. SAE 4140, 5140 and 1040 steels were used to characterize the microstructures of quenched and tempered specimens. After austenitizing and quenching identically, the specimens were tempered at various temperatures between 200oC and 600oC. Formation of the desired microstructures was ensured by metallographic examinations and hardness measurements. The results show that as tempering temperature increases the Barkhausen activity increases due to the enhancement of domain wall displacement with softening of the martensite. It has been shown that MBN is a powerful tool for evaluating the microstructures of martensitic and annealed steels.

Along with advancement of human industrialization, pollution in the ocean is getting worse. Moreover, the overfishing through the years has caused catastrophic damage to the ocean eco-system. In order to avoid exhaustion of fishery resource, many concepts of planned administrative fishery has become popular, and thereamong, ocean ranch draws the most attention. Artificial reef plays a key role in an ocean ranch, which starts with incubating brood fish in the laboratory. Often, the brood fish will grow in the cage near coast till proper size, then be released to the artificial reef. If fish groups do not disperse and multiply, the artificial reef can be considered successful. The success of the artificial reef relies on the stable foundation. Consequently, the composition of seabed sediment under the planned site should be investigated thoroughly before hand. This research introduced a remote investigation method, which an active sonar, depth sounder, was used to emit and collect acoustic signals. By using the signals reflected from the seabed, the sediment composition can be analyzed. However, all acoustic signals are subjected to noise through propagation, and distorted somehow. Therefore, certain signal pre-processing should be applied to the received signal, and representative characteristics can be extracted from it. In this research, the recognition platform was built on artificial neural network (ANN) in this research. Among many network algorithm modes, this research chose the widely used backpropagation learning algorithm to be the main structure in ANN. The goal of this research was to discriminate among three seabed sediments: fine sand, medium sand, and rock. During the signal processing, characteristics were extracted by using peak value selection method. Selected major frequency peaks were fed into the network to train and learn. According to partial error relation between recognition and practical result, weights of the network were adjusted for improving successful ratio. Finally, a reliable acoustic wave signal recognition system was constructed.

<p>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.</p>

<p>The understanding of the strengthening mechanisms is crucialboth in the development of new materials with improvedmechanical properties and in the development of better materialmodels in the simulation of industrial processes. The aim ofthis work has been to study different strengthening mechanismsfrom a fundamental point of view that enables the developmentof a general model for the flow stress. Two differentmechanisms namely, solid solution strengthening and grain sizestrengthening have been examined in detail. Analytical modelsproposed in the literature have been critically evaluated withrespect to experimental data from the literature. Two differentexperimental surface techniques, atomic force microscopy (AFM)and electron backscattered diffraction (EBSD) were used tocharacterize the evolving deformation structure at grainboundaries, in an ultra low-carbon (ULC) steel. A numericalmodel was also developed to describe experimental featuresobserved locally at grain boundaries.</p><p>For the case of solid solution strengthening, it is shownthat existing models for solid solution strengthening cannotexplain the observed experimental features in a satisfactoryway. In the case of grain size strengthening it is shown that asimple model seems to give a relatively good description of theexperimental data. Further, the strain hardening in materialsshowing a homogenous yielding, is controlled by grainboundaries at relatively small strains. The experimentalresults from AFM and EBSD, indicate more inhomogenousdeformation behaviour, when the grain size is larger. Bothtechniques, AFM and EBSD, correlate well with each other andcan be used to describe the deformation behaviour both on alocal and global scale. The results from the numerical modelshowed a good qualitative agreement with experimentalresults.</p><p>Another part of this project was directed towards thedevelopment of continuum models that include relevantmicrostructural features. One of the results was the inclusionof the pearlite lamellae spacing in a micromechanically basedFEM-model for the flow stress of ferriticperlitic steels.Moreover a good agreement was achieved between experimentalresults from AFM and FEM calculations using a non-local crystalplasticity theory that incorporates strain gradients in thehardening moduli.</p><p>The main philosophy behind this research has been to combinean evaluation of existing strengthening models, with newexperiments focused on studying the fundamental behaviour ofthe evolving dislocation structure. This combination can thenbe used to draw general conclusions on modelling thestrengthening mechanisms in metals.</p><p><b>Keywords:</b>strengthening mechanisms, flow stress, solidsolution strengthening, grain size strengthening,micromechanical modelling, AFM, EBSD</p>

Bottom sediment is an archive of the historical changes in a lake and its catchment. This thesis is apalaeoenvironmental reconstruction of catchment processes in Bolgoda Lake situated in western SriLanka. We studied a sediment core retrieved from this lake. In our study, we focus on multiplephysical and chemical proxies: grain-size, loss-on-ignition, total organic carbon content, C:N ratio,and δ13C stored in the organic matter. The aim of this study is to contribute to a better understandingof the palaeoenvironmental conditions in the region and allow a comparison between this site andothers.In the deepest part of the core, we see an overall high sand content, which indicates a period ofhigher discharge into the lake compared to what the other core parts indicate. This is probably aresult of higher precipitation. This is followed by a decline in C:N and a rise in TOC in the second partwhich indicates an increase of primary production in the lake. In the third part we again see a shift inthe C:N indicating a source change back to more terrestrial runoff. The increase in TOC and LOIvalues together with decrease in C:N ratio and a steady increase in δ13C indicate an increase inlacustrine productivity in the upper part of the core.By reconstructing the palaeoenvironmental history in Bolgoda Lake we can conclude that it isprobable that some other factor than diagenetic change affects the lake. Our results indicate thatthese changes most likely are due to more wet periods and anthropogenic activity, mainly throughland use changes.

A wetland in west-central Florida was studied to characterize the local hydrostratigraphic configuration of surficial deposits overlying more-permeable limestones and conceptualize groundwater recharge. Eight continuous cores were drilled through the surficial deposits and partially into the underlying limestone. A total of 111 samples were extracted from the cores for laboratory sediment analyses and testing. The surficial deposits are roughly eight meters thick and made up of upper and lower clean-sand hydrostratigraphic layers (S1 and S3, respectively) separated by a low-permeability layer of clayey sand (S2). Also, a discontinuous low-permeability layer of clayey sand (S4) lies between S3 and the top of limestone. Equivalent hydraulic conductivity values for the S2 and S4 clayey layers (0.01 and 0.1 m/day respectively) are significantly less than those of the S1 and S3 sand layers (2 and 1 m/day respectively).Significant confinement between the surficial and Upper Floridan aquifers by means of a laterally extensive dense-clay unit immediately above the limestone is consistently reported elsewhere in the region, but was not encountered within the wetland. Partial confinement is apparently the result of low-permeability layers within the surficial deposits alone. Results of ground-penetrating radar and vertical head difference measurements suggest the presence of buried sinkhole features which perforate the low-permeability S2 layer and create preferred pathways for flow or karst drains. Comparison of results between laboratory sediment testing and a site-scale aquifer performance test (APT) suggest that the primary mechanism for drainage during the APT was by vertical percolation through the S2 layer while flow through karst drains was minimized. In this case, calculated leakances based on laboratory sediment testing are most accurate in approximation of effective leakance.It is predicted that as water table stages rise within the wetland, effective leakance will increase as flow toward karst drains becomes the more dominant mechanism for drainage. As a result, calculated leakances based on direct laboratory sediment testing are a decreasingly accurate approximation of effective leakance.