Thesis advisor: Gail C. Kineke / An observational study was conducted from 2013 to 2016 to investigate suspended-sediment transport processes in the stratified Connecticut River estuary. Time-series measurements of velocity and suspended-sediment concentration from the upper estuary were analyzed to determine the relative importance of different processes driving sediment flux under highly-variable river discharge. Results indicate that under high discharge the salt intrusion is forced towards the mouth causing large seaward sediment fluxes throughout the water column. Seaward fluxes are dominated by mean advection, with some contribution due to tidal pumping. Under low discharge the salt intrusion extends to the upper estuary, advancing as a bottom salinity front during each flood tide. Stratification and strong velocity shear during the ebb tide cause the upper and lower water column to become dynamically decoupled. Sediment flux near the bed is landward throughout the tidal cycle despite the net seaward depth-integrated flux, and is almost fully attributed to the mean estuarine circulation. River discharge is the primary factor affecting the magnitude and direction of sediment flux because of its high variability and direct connection to the salt-wedge dynamics. A generalized three-phase conceptual model describes suspended-sediment transport in shallow, stratified estuaries with low trapping efficiencies. First, fine sediment bypasses the estuary during high river flows and exports to the coastal ocean where a portion of this sediment is temporarily deposited outside the mouth. Second, during low discharge offshore mud deposits are reworked by wave- and tidally-driven currents and some sediment is advected back into the estuary with the advancing salt intrusion that transports sediment landward. Third, spatial salinity gradients facilitate sediment transport from the main channel to channel margins, marshes and off-river coves where it is retained and deposited long-term, as demonstrated in prior studies. This re-introduction and trapping of recycled sediment under low-discharge conditions can have important implications for pollutant transport, shoaling of navigation channels and harbors, and salt marsh accretion in the face of rising sea levels. / Thesis (MS) — Boston College, 2018. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Earth and Environmental Sciences.

Polygonal terrain underlain by ice wedges (IWs) are a widespread feature in continuous permafrost and make up 20-35%vol of the ground ice in the upper few meters of permafrost. Despite the numerous contemporary studies examining factors that control ice wedge cracking, development and degradation, relatively few have explored ice wedge activity in relation with past climate and vegetation conditions. In the Eureka Sound region, ice wedge polygons dominate the permafrost terrain. Their degradation has started to occur, leading to growth of thaw slumps. The objective of this study is twofold, the principal objective is to investigate the timing of ice wedge activity in the Eureka Sound region using the ¹⁴CDOC dates. The second objective is to evaluate the use of ice wedges as paleotemperature proxies. In July 2018, four ice wedges were sampled at 3-4 depths with each core sample being ~1m in length. In the following summer, eight ice wedges were sampled from the surface, 3-5 core samples were extracted per wedge. Active layer and snow samples were also recovered. Laboratory analyses on the ice wedge samples includes dissolved organic carbon content (DOC) and δ¹³CDOC, radiocarbon dating of DOC, geochemical concentration, and stable water isotopes. The DOC and geochemical results show that snowmelt is the main moisture source for ice wedges in the Eureka Sound region with a minor contribution of leached surface organics. The age (¹⁴CDOC) and size of the studied ice wedges were compared against a cracking occurrence model developed by Mackay (1974), these ice wedges align well with this model and suggest that ice wedge growth is non-linear. Ice wedges in the Eureka Sound region were active during the early to late Holocene (9-2.5 ka). The majority of the activity occurred in the later stage of the early Holocene following regional deglaciation and marine regression. ¹⁴CDOC, high resolution δ¹⁸O and D-excess suggests the occurrence of peripheral cracking in both large and small ice wedges. Rayleigh-type isotopic fractionation was found to occur with depth. As well, post depositional isotopic modification of snow and snowmelt accounts for up to a 4‰ difference of δ18O in surface ice wedge samples. δ¹³CDOC of surface ice wedge samples suggest a habitat transition during the late Holocene from dry meadows to polygonal terrain and the geochemical composition of ice wedges closely reflects that of glacial ice core records.

Background: Cubitus varus is a cosmetically unacceptable complication of supracondylar fractures of the elbow in children. We have performed the lateral closing wedge (French) osteotomy to correct the varus for 27 years. More complex osteotomies have been described to correct the associated hyperextension and internal rotation deformities and to prevent a prominent lateral condyle. Methods: We retrospectively reviewed 90 consecutive patients (1986-2012). The mean age of the patients at surgery was 8.2 years (3 to14 years). The varus angle (mean 21.4°, range 8°- 40°) was assessed pre-operatively with the humero-elbow-wrist (HEW) angle. The postoperative carrying angle (mean 10.4) and the pre- and postoperative range of movement were assessed clinically. The lateral condylar prominence index (LCPI) was retrospectively measured at union. Results: Seventy five (93.3%) of the patients had a good or excellent result. Six (6.7%) had a poor result (residual varus, loss of >20°of pre-operative range of flexion or extension or a complication necessitating repeat surgery). There were no neuro-vascular complications. The mean LCPI was +0.14. Conclusions: The results of the French osteotomy are comparable to the more technically demanding dome, step-cut translation and multi-planar osteotomies, with a lower complication rate. The literature reports adequate remodelling of the hyperextension deformity ( ≤ 10 years) patient. Level of evidence: Level IV: Case series

Rock wedge stability is a common concern in underground excavations. Since the wedge stability influences the support design, it is important to use a wedge stability analysis method that can capture factors like excavation geometry, joint parameters and properties, rock mass properties, rock cover, and stress field as accurately as possible. This thesis compared the Limit Equilibrium Method (LEM) and the Discrete Element Method (DEM) using the software UnWedge (LEM) and 3DEC (DEM). The objectives included studying how factors like excavation and joint geometry, stress field, rock cover, and rock mass properties could be considered by the methods and how that affected the wedge stability and support design. Nine different analysis cases were defined with the aim of capturing wedge stability analysis parameters representable for both the civil engineering and mining sector. The study found that 3DEC allows for more accurate modelling of excavation and joint geometry, considering joint density and full 3D geometries, while UnWedge has limitations in creating intersecting tunnels and does not consider joint density. Only 3DEC, with stress redistribution and a plastic material model, captures rock mass failure mechanisms other than wedge failure. Based on the study, it is recommended to use DEM for situations where the excavation geometry cannot be assumed as two-dimensional with constant cross-section, and, when stress-induced rock mass failure is expected, use DEM with stress redistribution. It is also recommended to use information about joint lengths if available and apply engineering judgement when studying results of wedge volume and support force.

In recent years, the study of fluid flow with nanoparticles in base fluids has attracted the attention of several researchers due to its various applications to science and engineering problems. Recent investigations on convective heat transfer in nanofluids indicate that the suspended nanoparticles markedly change the transport properties and thereby the heat transfer characteristics. Convection in saturated porous media with nanofluids is also an area of growing interest. In this thesis, we study the effects of radiation on the heat and mass transfer characteristics of nanofluid flows over solid surfaces. In Chapter 2, an investigation is made into the effects of radiation on mixed convection over a wedge embedded in a saturated porous medium with nanofluids, while in Chapter 3 results are presented for the effects of radiation on convection heat transfer about a cone embedded in a saturated porous medium with nanofluids. The resulting governing equations are non-dimensionalized and transformed into a non-similar form and then solved by Keller box method. A comparison is made with the available results in the literature, and the results are found to be in very good agreement. The numerical results for the velocity, temperature, volume fraction, the local Nusselt number and the Sherwood number are presented graphically. The salient features of the results are analyzed and discussed for several sets of values of the pertinent parameters. Also, the effects of the Rosseland diffusion and the Brownian motion are discussed.

No description available.

The design of the freight train truck has gone relatively unchanged over the past 150 years. There has been relatively little change to the fundamental railway truck design because of the challenges of implementing a cost effective and reliable modification to designs that have proven effective in decades of operation. A common U. S. railway truck consists of two sideframes, a bolster, two spring nests, and four friction wedges. The two sideframes sit on the axels. The bolster rides on springs on top of the sideframes. The friction wedges also ride on springs on top of the sideframe, and are positioned between the bolster and sideframe, acting as a damping mechanism. Better understanding the dynamic behavior and forces on the bodies are critical in reducing unnecessary wear on the components, along with potential negative behavior such as loss of productivity and increase in operating costs. This thesis will investigate the dynamic behavior of the truck under warping conditions using a stand-alone model created in Virtual.Lab. This research covers two main areas. First, the full-truck model will be developed and its simulation results will be compared to test data from the Transportation Technology Center, Inc. (TTCI). Data was provided from warp testing performed at the TTCI facilities in the spring of 2008. Once validated, the model will be used to gain a better understanding of the forces and moments that are propagated through the system, and of the dynamics of all bodies. Due to costs and physical constraints, not every bogie component can be instrumented during test, so the computer model will be able to provide valuable information not easily obtained otherwise. Second, full-truck models using different contact geometry between the wedges, sideframes, and bolster will be compared. A model with extremely worn sideframes will allow for investigation into the effects of wear on the damping abilities and warp stiffness of the truck. Another model using split wedges will be compared with the previous model to investigate into the behavior differences in the truck using different types of wedges. By understanding the impact of different geometries on the overall performance of the truck, better decisions on design and maintenance can be made in the future. After creating the models, we found that the full-truck model created in LMS® Virtual.Lab compared well with the test data collected by TTCI. In the comparison with NUCARS® we determined that the stand-alone model, which incorporates the wedges as bodies, captures the warp dynamics of the truck better than NUCARS®, which models the wedges as connections. By creating a model with severely worn sideframes, we were able to determine that the truck loses its abilities to damp bounce in the system as well as to prevent warping when the components become sufficiently worn. The split-wedge model behaved similarly to the standard full-truck model for bounce inputs, but had a significantly different behavior in warp. Further development will be needed on the split-wedge model to be confident that it behaved as expected. / Master of Science

When bonds between copper and printed circuit board laminates are subjected to impulsive forces, the need arises to characterize fracture energies corresponding to related, high-speed failure events. Work (or energy) is required to create new surface area—with associated dissipation events—during fracture, and this energy (for a given material system) is dependent on the speed of crack propagation, the locus of failure, and the temperature of the bond when it is broken. Since the 90° peel test has been widely employed in quasi-static fracture testing of film adhesion for printed circuit board applications, this test was first used as a basis to which other test results could be compared. A test fixture was designed and built for quasi-static peel testing that accommodated peeling at different angles and temperatures. A similar test was then desirable for the direct comparison of dynamic fracture events to those quasi-static results. The “loop peel test” was thus developed to mimic the common 90° peel test and to quantify the time- and temperature-dependent fracture energies of peel specimens during low-velocity impact. This test has been successfully used to determine the apparent critical strain energy release rate of copper/epoxy bonds for low-velocity impact conditions (1-10 m/s), for a case of near-interfacial failure. The falling wedge test has also been adapted to estimate the apparent critical strain energy release rate at similar fracture conditions. Four types of printed circuit boards have been analyzed with the above impact test methods as well as with their corresponding quasi-static tests, and the fracture energies measured with the impact tests have been compared to those obtained using quasi-static tests. Fracture energies of the material systems considered were dependent on time (speed of fracture), temperature, and the amount of moisture migration, as determined via humidity conditioning parameters. / Master of Science

Thesis advisor: Robert Ross / Great powers use alliances to amass capabilities. As such, alliance balancing strategies are important part of a balance-of-power system. In order to seek security, great powers frequently employ alliance balancing strategies, which can take two forms: to divide hostile alliances or prevent those from forming (i.e. wedge strategies), and to bind their own allies (i.e. binding strategies). When choosing these strategies, great powers face two options: accommodation and coercion. This dissertation explores the question of how great powers choose between these two options. I argue that a great power chooses its wedge strategies based on two factors: its leverage over its target and the degree of security cooperation between its target and its adversary. When the great power’s leverage is strong, it will opt for accommodative wedge strategies, despite the degree of security cooperation between its target and its adversary. Meanwhile the great power is likely to use coercive wedge strategies as its complementary strategy. When the great power’s leverage is weak, it will evaluate the degree of security cooperation between its target and its adversary. When such cooperation is at a high level, the great power will choose coercive wedge strategies as its primary strategy and accommodative ones as its complementary strategy. In contrast, a great power’s choice of its binding strategies is determined by its leverage over its target and its fear of being abandoned by its target. When its leverage is strong, the great power will choose coercive binding strategies as its primary strategy and accommodative ones as its complementary strategy, despite the fear of abandonment. When its leverage is low, the great power will assess its fear of abandonment. Strong fear of abandonment will lead the great power to choose accommodative binding strategies as its primary strategy and coercive ones as its complementary strategy. I test this theory using qualitative cases studies of China’s choices of its alliance balancing strategies. These cases include variation in China’s strategic choices that allows me to test the explanatory power of my theory. I examine these cases drawing on archives, government documents, newspapers, and secondary materials from China and the United States. I conclude this dissertation with a summary of my findings and a discussion on implications and future research avenues. / Thesis (PhD) — Boston College, 2022. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Political Science.

A Ilha de São Sebastião, localizada no Embaiamento de São Paulo, representa a fronteira entre a plataforma ao sul, coberta predominantemente por sedimentos lamosos derivados da pluma de água do Rio da Prata, e a plataforma ao norte, onde a distribuição de sedimentos provém de múltiplas fontes e com granulometria variável. O ressurgimento gerado pelas dinâmicas de massas de água, através do avanço e retração da Água Central do Atlântico Sul, aporta quantidade considerável de sedimentos para a plataforma interna, que então são transportados devido aos regimes oceanográficos atuantes, com correntes que alternam sazonalmente e que fluem em resposta à direção dominante dos ventos. A interação entre estes sedimentos e a complexa fisiografia da costa da Ilha de São Sebastião possibilita a deposição de um depósito sedimentar em forma de cunha de escala quilométrica, identificado pela primeira vez durante o cruzeiro oceanográfico NAP-Geosedex, em 2013, a bordo do NOc. Alpha Crucis. A análise de dados sísmicos coletados com quatro tipos de fontes diferentes ao longo de três cruzeiros oceanográficos, aliada a resultados ainda não publicados de datação e taxa de sedimentação de um testemunho sedimentar de 4 m de comprimento, permitiram a proposição de um modelo genético e evolutivo para a cunha sedimentar. Ademais, propõe-se a inserção da cunha no contexto global de depósitos progradantes de sedimentos fluviais da plataforma interna, segundo as nomenclaturas Cunha Progradante Infralitoral (Infralitoral Prograding Wedge - IPW) e Depocentros Lamosos (Mud Depocenters- MDCs). O depósito é formado por uma unidade inferior transgressiva (TST- Unidade U1) subjacente a um depósito característico de nível de mar alto (TSNA), formado, por sua vez, por três unidades (U2, U3 e U4), que exibem padrões progradantes e agradacionais. De acordo com a análise do testemunho, as idades da base das unidades superiores U3 e U4 datam de 1484 e 422 anos, respectivamente, sendo estimada uma idade de 6520 anos para o início da deposição do TSNA, o que ocorreu ao final da subida do nível do mar após o Último Máximo Glacial. As características de idade e de estrutura interna da cunha sedimentar possibilitam concluir que se trata de um depósito misto, com características tanto de IPWs como de MDCs. / The Sao Sebastião Island, located in the Bight of São Paulo, is the boundary between the continental shelf to the south, covered by muddy sediments mainly derived from the La Plata River\'s water plume, and the shelf to the north, where the sediment distribution comes from multiple sources and is variable in grain size. The upwelling generated by the water masses dynamics through the advance and retreat of the South Atlantic Central Water, carries considerable amount of sediment to the inner shelf, which are then transported due to active oceanographic regimes, with seasonally alternating current that flows in response to the prevailing wind direction. The interaction between these sediments and the complex physiography of the coast of São Sebastião Island enables the deposition of a sedimentary deposit in the form of a kilometric scale wedge, first identified during the oceanographic cruise NAP-Geosedex in 2013, aboard the R/V Alpha Crucis. The analysis of seismic data collected from four different sources over three oceanographic cruises, combined with results of dating and sedimentation rate of a 4 m long core, allowed the proposition of a genetic and evolutionary model for the sedimentary wedge. Furthermore, it is proposed the wedge insertion in the global context of progradational deposits of river sediments in the inner shelf, according to the terms Infralittoral Prograding Wedge (IPW) and Mud Depocenters (MDCs). The deposit is composed by a lower transgressive unit (TST - Unit U1) underlying a characteristic deposit of highstand sea level (HST), which comprises three units (U2, U3 and U4). These HST units exhibit a progradational and agradational patterns. According to the sediment core analysis, the ages of the base of the two topmost units U3 and U4 dating from 1484 and 422 years B.P., respectively. The estimated age of the onset of deposition of the HST is 6520 years B.P., which occurred at the end of the sea level rise after the Last Glacial Maximum transgression. The age and the internal structure of the sedimentary wedge allow the conclusion that it is a mixed deposit, which has characteristics of both IPWs and MDCs.