Telomeres comprise the physical ends of chromosomes. In the absence of telomerase, the enzyme responsible for replenishing telomeric DNA, telomeres progressively shorten due to the end replication problem. Eventually telomeres reach a length where they are recruited into end-to-end chromosome fusions. Through the use of novel PCR strategies, I followed the fate of telomeres in plants lacking telomerase as they progressed into dysfunction. I uncovered two distinct structural/functional length transitions. The first transition (~1 kb) marks the onset of telomere dysfunction, where telomeres are transiently uncapped and a subset of them engage in end-to-end fusions. The second transition (~300 bp) defines complete telomere dysfunction as telomeres below this length lack G-overhangs and the vast majority of the chromosome ends fuse. Thus, these two telomere lengths define architectural transitions that link structure and function. In addition, I uncovered a hierarchy of end-joining pathways that join dysfunctional telomeres in which the non-homologous end-joining (NHEJ) protein, KU predominates. In the absence of KU, telomeres are joined by a microhomologymediated end-joining pathway (MMEJ) that is dependent on Mre11. I also show that DNA ligase IV (LIG4) is the predominant enzyme that ligates dysfunctional telomeres as fusions are reduced in its absence. These studies highlight the importance of repairing DSBs and demonstrate that Arabidopsis possesses highly redundant means for processing dysfunctional telomeres. The G-overhang is an essential feature of the telomere that is required for proper telomere function. I employed methods to examine G-overhang status in various mutants known to contribute to telomere maintenance in Arabidopsis. My analysis revealed that the putative G-overhang binding proteins POT1a, POT1b and POT1c, make modest, but distinct contributions to the G-overhangs. Additionally, I uncovered a major role for the putative telomere capping protein, CIT1 in maintenance of the Goverhang. G-overhang signals obtained from cit1 mutants were grossly increased indicating that CIT1 is involved in either protecting the C-rich strand of the telomere from nuclease attack, or in controlling telomerase extension of the G-strand. Together, these data have provided new insight into factors that contribute to telomere integrity and have further developed Arabidopsis as a model for telomere biology.

The first part of the thesis addresses the fatigue performance of concrete bridge decks with GFRP stay-in-place structural forms replacing the bottom layer of rebar. The forms were either flat plate with T-up ribs joined using lap splices, or corrugated forms joined through pin-and-eye connections. The decks were supported by simulated Type III precast AASHTO girders spaced at 1775mm (6ft.). Two surface preparations were examined for each GFRP form, either using adhesive coating that bonds to freshly cast concrete, or simply cleaning the surface before casting. For the bonded deck with flat-ribbed forms, adhesive bond and mechanical fasteners were used at the lap splice, whereas the lap splice of the unbonded deck had no adhesive or fasteners. All the decks survived 3M cycles at 123kN service load of CL625 CHBDC design truck. The bonded flat-ribbed-form deck survived an additional 2M cycles at a higher load simulating a larger girder spacing of 8ft. Stiffness degradations were 9-33% with more reduction in the unbonded specimens. Nonetheless, live load deflections of all specimens remained below span/1600. The residual ultimate strengths after fatigue were reduced by 5% and 27% for the flat-ribbed and corrugated forms, respectively, but remained 7 and 3 times higher than service load. The second part of the thesis investigates the performance of bridge deck overhangs reinforced by GFRP rebar. Overhangs of full composite slab-on-girder bridge decks at 1:2.75 scale were tested monotonically under an AASHTO tire pad. Five tests were conducted on overhangs of two lengths: 260mm and 516mm, representing scaled overhangs of 6ft. and 8ft. girder spacing, respectively. The 260mm overhang was completely reinforced with GFRP rebar while the 516mm overhang consisted of a GFRP-reinforced section and a steel-reinforced section. The peak loads were approximately 2 to 3 times the established equivalent service load of 24.3kN, even though the overhangs were not designed for flexure according to the CHBDC but rather with lighter minimum reinforcement in anticipation of shear failure. The failure mode Abstract ii of each overhang section was punching shear. The steel-reinforced overhang section exhibited a greater peak load capacity (13.5%) and greater deformability (35%) when compared to the GFRP-reinforced overhang section. / Thesis (Master, Civil Engineering) -- Queen's University, 2013-09-17 18:54:18.131

Additive manufacturing (AM) shows great promise for the manufacturing of next-generation engineering structures by enabling the production of engineered cellular structures, overhangs, and reducing waste. Melt-pool geometry prediction and control is critical for widespread implementation of laser powder bed processes due to speed and accuracy requirements. The process mapping approach used in previous work for different alloys and additive manufacturing processes is applied to the selective laser powder bed process for IN625 and 17-4 stainless steel alloys. The ability to predict the resulting steady state melt-pool geometry in terms of process parameters, specifically power and velocity, is explored in detail numerically and experimentally verified. A finite element model was created that simulates powder at the macro scale. This model correlates well with current experiments in showing that small amounts of powder relative to melt-pool depth have negligible effects on resulting geometry. Results indicate that the effect of powder may be negligible when comparing steady state widths of the no powder and one layer of powder cases. The work in this thesis investigates the effect of powder on the resulting steady-state melt-pool geometries for IN625 and 17-4 alloys. This analysis has been extended to the production of overhanging and cellular structures. The successful analysis will allow for better predictions and possible correction for cellular structure production issues as well as overhanging features.

<p>Synthesis of terrains with complex features has been a challenging problem in computer graphics since most of the existing methods are based on the height field representation. Complex features in terrains adds to the overall realism of the terrain. Hence, there is a need to synthesize terrains in real-time with complex features that adhere to user input. The methodology described in this thesis describes a novel way to synthesize terrains with complex features based on user drawn sketches. Layered stack data structure is used to ensure that the resulting terrain has complex features. Since, Neural Networks are used to generate the terrains, the process is real-time.</p>