Thesis advisor: Douglas A. Edmonds / Delta morphology is traditionally explained by differences in fluvial energy and wave and tidal energy. However, deltas influenced by similar ratios of river to marine energy can display strikingly different morphologies. Other variables, such as grain size of the sediment load delivered to the delta, influence delta morphology, but these models are largely qualitative leaving many questions unanswered. To better understand how grain size modifies deltaic processes and morphologies I conducted 33 numerical modeling experiments and quantified the effects produced by different grain sizes. In these 33 runs I change the median (0.01 - 1 mm), standard deviation (0.1 - 3 φ), and skewness (-0.7 - 0.7) of the incoming grain-size distribution. The model setup includes a river carrying constant discharge entering a standing body of water devoid of tides, waves, and sea-level change. The results show that delta morphology undergoes a transition as median grain size and standard deviation increase while changing skewness has little effect. At small median grain size and standard deviation, deltas have elongate planform morphologies with sinuous shorelines characterized by shallow topset gradients ranging from 1 x 10<super>-4</super> to 3 x 10<super>-4</super>, and by 1 - 8 stable active channels. At large median grain size and standard deviation, deltas transition to semi-circular planform morphologies with smooth shorelines characterized by steeper topset gradients ranging from 1 x 10<super>-3</super> to 2 x 10<super>-3</super>, and by 14 - 16 mobile channels. The change in delta morphology can be morphodynamically linked to changes in grain size. As grain size increases delta morphology transitions from elongate to semi-circular because the average topset gradient increases. For a given set of flow conditions, larger grain sizes require a steeper topset gradient to mobilize and transport. The average topset gradient reaches a dynamic equilibrium through time. This requires that, per unit length of seaward progradation, deltas with steeper gradients have higher vertical sedimentation rates. Higher sedimentation rates, in turn, perch the channel above the surrounding floodplain (so-called `super-elevation'), resulting in unstable channels that frequently avulse and create periods of overbank flow. The overbank flow is more erosive because the steeper gradient causes higher shear stresses on the floodplain, which creates more channels. More channels reduce the average water and sediment discharge at a given channel mouth, which creates time scales for mouth bar formation in coarse-grained deltas that are longer than the avulsion time scale. This effectively suppresses the process of bifurcation around river mouth bars in coarse-grained deltas, which in turn creates semi-circular morphologies with smooth shorelines as channels avulse across the topset. On the other hand, the finest-grained (i.e. mud) deltas have low topset gradients and fewer channels. The high water and sediment discharge per channel, coupled with the slow settling velocity of mud, advects the sediment far from channel mouths, which in turn creates mouth bar growth and avulsion time scales that are longer than the delta life. This creates an elongate delta as stable channels prograde basinward. Deltas with intermediate grain sizes have nearly equal avulsion and bifurcation time scales, creating roughly semi-circular shapes but with significant shoreline roughness where mouth bars form. / Thesis (MS) — Boston College, 2013. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Earth and Environmental Sciences.

"The phase content and grain size of titanium dioxide often have a strong influence on properties for a variety of applications. In many cases it would be desirable to produce the stable rutile phase with an ultra-fine particle size (<10nm), but most low temperature synthesis methods produce predominantly the metastable anatase phase. The anatase-rutile transformation in TiO2 is known to be affected by dopant type and concentration, as well as the titanium precursor used in solution chemical synthesis. Recently, use of cavitation in the synthesis process has been shown to yield smaller grain size for a variety of oxides. However, the relative importance of these synthesis variables on the grain size and phase content of TiO2 is not well understood. In this study, Taguchi analysis was used to determine the relative effects of dopants (Sn), titanium precursor (butoxide, sulfate, chloride), and cavitation power on grain size and phase content. Precursor residuals were also measured by analytical chemistry. Grain size and phase content results were analyzed statistically to determine whether there is a size dependence of the anatase-rutile transformation. Results show that grain size is strongly dependent on the concentration of chlorine. Absent chlorine, a definite grain size-phase content correlation exists; rutile content increases as grain size decreases. An L-4 orthogonal Taguchi analysis shows chlorine content and tin content as the major influences on the final product. With minimum grain size and maximum rutile content being considered optimal, our best result was 100% rutile and an average grain size of 5nm, which was achieved by acoustic synthesis with 3% tin dopant and low residual chlorine. "

Plastic deformation processes transform material fromas-received state to products meeting certain requirements inproperties, microstructure and shape. To achieve thistransformation, the relationship between material response andprocess conditions should be understood. This is usuallycomplicated by the complex conditions describing the actualprocess. Numerous techniques including empirical, physical,analytical and numerical can be employed. In this thesis, numerical technique supported by lab- andfull-scale experiments has been employed to analyse the formingparameters. The first part of the thesis is focused on the useof such parameters to predict occurrence of material poresduring manufacturing of bearing rings. The second part dealswith the influence of forming parameters on the grain sizeduring fabrication of large copper canisters for encapsulationof nuclear waste. The primary task has been to study with thehelp of commercial FE-codes the magnitude and distribution offorming parameters such as accumulated effective strain,temperature, instantaneous hydrostatic pressure and materialflow at different stages of the forming process. In the firstpart, two types of ring manufacturing routes, which result inpore free and pore loaded rings are studied and compared.Material elements located in different areas of the workpiecehave been traced throughout the process. Results of theaccumulated strain and instant hydrostatic pressure have beenanalysed and presented in pressure-strain space. It’sassumed that high hydrostatic pressures together with higheffective strains are favourable for pore closure. Area of theworkpiece with unfavourable parameters have been identified andcompared with ultrasonic test results. Good agreement has beenobtained. Based on the results of this analysis, a new conceptfor avoiding pores in manufacturing of yet heavier rings hasbeen presented. The concept proposes a lighter upsetting in theinitial stage of the process and a more efficient piercingwhich results in higher hydrostatic pressure and bigger andbetter distributed effective strain. In the second part of the thesis, the influence of formingparameters such as effective strain and temperature on thefinal grain size of the product has been studied in laboratoryscale. As-cast billets of cylindrical shape were extruded atdifferent temperatures and reductions. It has been shown thatthe grain size in the final product should be small in order toenable ultrasonic tests and to guarantee resistance towardscreep and corrosion. Simulations for different materialelements located at different distances from the axis ofsymmetry of the initial cylindrical workpiece have been carriedout. In this way, the parameters describing the deformationhistory of the elements have been determined as functions oftime. Experimentally obtained pre- and post deformation grainsize in the corresponding locations of the material weredetermined. It’s concluded that low temperature coupledwith high effective strain are conducive for obtaining a smallgrain size. Based on the beneficial conditions for extrusion ofcopper, a more detailed FE-analysis of a full-scale industrialprocess is carried out. A coarse-grained cast ingot of purecopper is heated and by upset forging formed into a cylinder,which is then punched into a hollow blank for subsequentextrusion. The blank is extruded over a mandrel through a45-degree semi-angle die. Accumulated effective strain andtemperatureas functions of the tubular wall thickness havebeen studied at five different locations along the tubularaxis. Forming load requirement as function of tool displacementfor each stage of the process has been determined. Strain andtemperature levels obtained have been related to the grain sizeinterval obtained in the earlier work. It has been concludedthat the levels reached are within the interval that ensures asmall grain size. A similar analysis has been carried out forforging of large copper lids and bottoms. Die designmodifications to improve the grain size in the lid and tooptimise the forging process with respect to forging load andmaterial yield have been proposed. A method requiring a smallforging load for fabrication of the lids has been analysed <b>Keywords:</b>Pores; grain size; low forging load; effective strain;temperature; hydrostatic pressure; extrusion; forging;canister; lid; rings

The Gaoping Slope, off the south west coast of Taiwan, is a tectonically active sedimentation environment attaining most of its sediment from the Gaoping River. This study examines sediment cores from two localities at 375 m and 495 m water depth by using X-radiography, Grain size- and 210Pb analysis, with the purpose of comparing the sedimentation environment at the two sites and examine how they were both affected by high sediment delivery during typhoon Morakot.The shallow site has coarse bioturbated sediment, whereas the deeper site had laminated fine sediment containing high amounts of organic material. Both localities display a 13-20 cm thick recently deposited layer in the cores taken after typhoon Morakot. The layers are characterized by coarsening-fining sequences. All cores show cyclicity in the grain size data.We suggest that the shallow station has a more energetic environment, affected by wave reworking, tides, and alongshore currents supplying riverine material from the Gaoping river. The deep site has a calmer sedimentation environment dominated by hemipelagic settling of suspended material. The recent accumulated deposits are most likely hyperpycnites from density driven hyperpycnal flows, originally caused by canyon overflows in the Gaoping- and the Kaohsiung canyon during the typhoon. The strata found at the Gaoping slope is a result of submarine mass transport of sediment, and reflect the interaction between annual seasons and extreme events triggered by typhoons and earthquakes - eroding, transporting, and depositing sediment in the area.

Compression tests along the rolling and normal direction of AZ31B plate materials under 10 s strain rate were performed at room temperature to understand the effect of grain size on the formation of deformation twins. When compressed along the rolling direction, tension twins were formed in bands. Within the twin bands, nearly all grains contained tension twins, irrespective of grain size. And outside the bands, no twin was found. Under this deformation condition, grain size has no effect on the formation of tension twins. The reason for this is due to the fact that the formation of a tension twin can trigger the formation of tension twin in the neighboring grain, irrespective of the neighboring grain size. When compressed along the normal direction, no twin band was formed, and compression twins were formed evenly in the specimens. Under this deformation condition, it was found that the larger the grain size, the higher the fraction of grains which contained compression twins. This result indicates that compression twins are easier to be formed in the large grains.

Abstract The South China is the largest marginal sea in the western Pacific. It¡¦s unique geographic settings and high sedimentation rates preserve the paleo- climatic signals with larger amplitude than those from the open ocean. In this study, grain size and elemental compositions of the fine fractions (<63 mm) from the sediments collected by the ODP Leg 184 Sites 1143 and 1146 were analyzed to reconstruct the depositional settings for the last 8 My. Particle size and elements analyses, in conjunction with the carbonate contents and sedimentation rates from core sediments, reflect the possible increase in precipitation, which was caused by the strengthened summer monsoon between 5 and 3 Ma. In addition to the grain sizes change from silt-domain to clay-domain, Ti/Al ratio of sediments increase while the Si/Al, Zr/Al, and K/Al ratios decrease, which could be related to the enhanced sediments input through rivers. These environmental changes could be attributed to the uplift of Tibet plateau and the formation of Western Pacific Warm Pool. On the contrary, the impact of climate changes is not evident in the loess plateau in the northwestern China. It is likely that the climate in the South China Sea became warm and humid from 5 to 3 Ma were regional changes. Key words: Grain size, element analyses, South China Sea, summer monsoon

<p>Plastic deformation processes transform material fromas-received state to products meeting certain requirements inproperties, microstructure and shape. To achieve thistransformation, the relationship between material response andprocess conditions should be understood. This is usuallycomplicated by the complex conditions describing the actualprocess. Numerous techniques including empirical, physical,analytical and numerical can be employed.</p><p>In this thesis, numerical technique supported by lab- andfull-scale experiments has been employed to analyse the formingparameters. The first part of the thesis is focused on the useof such parameters to predict occurrence of material poresduring manufacturing of bearing rings. The second part dealswith the influence of forming parameters on the grain sizeduring fabrication of large copper canisters for encapsulationof nuclear waste. The primary task has been to study with thehelp of commercial FE-codes the magnitude and distribution offorming parameters such as accumulated effective strain,temperature, instantaneous hydrostatic pressure and materialflow at different stages of the forming process. In the firstpart, two types of ring manufacturing routes, which result inpore free and pore loaded rings are studied and compared.Material elements located in different areas of the workpiecehave been traced throughout the process. Results of theaccumulated strain and instant hydrostatic pressure have beenanalysed and presented in pressure-strain space. It’sassumed that high hydrostatic pressures together with higheffective strains are favourable for pore closure. Area of theworkpiece with unfavourable parameters have been identified andcompared with ultrasonic test results. Good agreement has beenobtained. Based on the results of this analysis, a new conceptfor avoiding pores in manufacturing of yet heavier rings hasbeen presented. The concept proposes a lighter upsetting in theinitial stage of the process and a more efficient piercingwhich results in higher hydrostatic pressure and bigger andbetter distributed effective strain.</p><p>In the second part of the thesis, the influence of formingparameters such as effective strain and temperature on thefinal grain size of the product has been studied in laboratoryscale. As-cast billets of cylindrical shape were extruded atdifferent temperatures and reductions. It has been shown thatthe grain size in the final product should be small in order toenable ultrasonic tests and to guarantee resistance towardscreep and corrosion. Simulations for different materialelements located at different distances from the axis ofsymmetry of the initial cylindrical workpiece have been carriedout. In this way, the parameters describing the deformationhistory of the elements have been determined as functions oftime. Experimentally obtained pre- and post deformation grainsize in the corresponding locations of the material weredetermined. It’s concluded that low temperature coupledwith high effective strain are conducive for obtaining a smallgrain size. Based on the beneficial conditions for extrusion ofcopper, a more detailed FE-analysis of a full-scale industrialprocess is carried out. A coarse-grained cast ingot of purecopper is heated and by upset forging formed into a cylinder,which is then punched into a hollow blank for subsequentextrusion. The blank is extruded over a mandrel through a45-degree semi-angle die. Accumulated effective strain andtemperatureas functions of the tubular wall thickness havebeen studied at five different locations along the tubularaxis. Forming load requirement as function of tool displacementfor each stage of the process has been determined. Strain andtemperature levels obtained have been related to the grain sizeinterval obtained in the earlier work. It has been concludedthat the levels reached are within the interval that ensures asmall grain size. A similar analysis has been carried out forforging of large copper lids and bottoms. Die designmodifications to improve the grain size in the lid and tooptimise the forging process with respect to forging load andmaterial yield have been proposed. A method requiring a smallforging load for fabrication of the lids has been analysed</p><p><b>Keywords:</b><i>Pores; grain size; low forging load; effective strain;temperature; hydrostatic pressure; extrusion; forging;canister; lid; rings</i></p>

We investigate evolution of mountain channel morphology and riverbed surface roughness by conducting laboratory experiments. The experimental flume is 4m long by 0.1m wide with a working length of 2.5m. We control initial sediment size distribution, flume slope, water discharge, and sediment feed rate. Measurements include topographic profiles, flow depth, surficial grain-size distribution, sediment transport rate, and sediment size distribution. Experiments begin with a gravel bed of a broad sediment size distribution, at two initial flume slopes: 8.2% and 12.4%. Discharge is held constant until transport rates and topographic changes indicate the system is at near steady state. Coarse sand is then fed into the channel at 1,000 g/min as a means to perturb the system. Sediment feed is held constant until the perturbed bed reach steady-state conditions. The feed is subsequently ceased and measurements continue until sediment transport rates and topography stabilize. These laboratory experiments provide first-hand observations of channel systems evolving after perturbations. Transport rates decay exponentially following perturbations and remain very low when the channel bed is stabilized. The introduction of coarse sand acts to smooth the channel bed by filling in topographic lows in the 8.2% sloped channel. At a 12.4% slope, increased mobility of sand allows steady state conditions to be met with little smoothing of the bed. The sand also increases the mobility of coarser sediment that was previously stable, likely due to local surface smoothing at grain scale. The increased fraction of surface sand cover maintains increased scouring and mobilization of coarser grains. These post-perturbation mechanisms are interpreted to be responsible for topographic adjustments as the system readjusts towards new steady-state conditions. Surface sorting and transporting distributions reflect high sand fractions well after perturbations have ceased. This suggests that brief pulses of fine sediment can increase coarse sediment mobility for prolonged periods. / text

In this study a new method is introduced to produce bimodal grain structures in low carbon steels. This method is based on cold rolling of dual phase structures and appropriate annealing treatments. The difference in the recrystallization behaviour of ferrite and martensite yields a heterogeneous microstructure with a distribution of coarse and fine grains. These types of microstructures are of interest for optimizing the balance of strength and uniform elongation in ultra-fine grained low carbon steels.

The goal of this study was to investigate the effects of intertidal mudflat biofilms on sediment erosion in the Minas Basin of the Bay of Fundy, Canada. From April through November 2012, sediment cores were collected biweekly and eroded using a Gust micro- cosm. Half of the cores were eroded without undergoing prior treatment, while the other half were treated with bleach prior to erosion to destroy biofilms. Size-specific sediment retention by biofilms was evaluated by comparing the disaggregated inorganic grain size (DIGS) distributions of sediment resuspended from untreated and treated cores, while seasonal variation in natural sediment erodibility was assessed by focusing on the mass eroded from untreated cores only. Results show that biofilms preferentially retained clays and very fine silts (< 10 μm), and that overall sediment erodibility decreased from spring to fall. Results also indicate that abundance of the infaunal amphipod Corophium volutator and rainfall increased sediment erodibility.