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This thesis focuses on the development of a health monitoring system for gearbox transmissions. This was accomplished by developing and understanding a two-stage gearbox computer model that emulates an actual gearbox test rig. The computer model contains actual gearbox geometry, flexible shafts, bearings, gear contact forces, input motor torque, output brake torque, and realistic gearbox imbalance. The gear contact force of each gear stage and the input bearing translational acceleration were the main outputs compared between a healthy gearbox and damaged gearbox computer model. The damage of focus was a fatigue crack on the input pinion gear. A sideband energy ratio comparison yielded the computer simulation accurately modeled the difference between a healthy and damaged gearbox. The next step in this study involved the development of a repeatable procedure to initiate and propagate a fatigue crack at the tooth root in an actual spur gear. A damaged spur gear allows for a future comparison of an actual healthy and damaged gearbox system in the lab. A custom fatigue fixture was designed and manufactured for a Martin S1224BS 1 spur gear. The fatigue crack was initiated by position control fatigue testing which deflects the gear tooth a set amplitude for a number of cycles. Over the length of the test, the load that the tooth can withstand in bending decreases as damage begins to occur. Once the max load on the gear has dropped by a significant percentage (5-15%) a crack has initiated and begun to propagate across the tooth face. The use of a scanning electron microscope confirmed the presence a fatigue crack.

There is considerable evidence that pollinator shifts can explain many differences in flower morphology between closely related plant species, but the extent to which pollinator shifts can explain the maintenance of among-population variation in floral traits within species is poorly known. In this thesis, I combined comparative and experimental approaches to examine the evolution of floral traits in the moth-pollinated orchid Platanthera bifolia. More specifically, I investigated (1) the relationship between flower and pollinator morphology, (2) phenotypic selection on morphology and phenology in populations in contrasting environments, (3) components of prezygotic reproductive isolation among divergent populations, and (4) the adaptive and functional significance of two correlated floral traits. A study of Scandinavian of P. bifolia populations revealed that spur length was positively correlated with proboscis length of local pollinators, which suggests that variation in spur length reflects adaptive evolution in response to geographically variable pollinator-mediated selection. A phenotypic selection study on Öland, SE Sweden, suggested that disruptive selection on spur length contributes to the maintenance of a bimodal distribution of spur length in mixed habitats, but provided very limited evidence of divergent selection on plant morphology and flowering phenology in grassland and woodland habitats. Field experiments revealed strong reproductive isolation between divergent populations on Öland, due to differences in spatial distribution, flowering phenology, and pollinators, and among-population incompatibility. The results suggest that prezygotic reproductive isolation contributes to the maintenance of population differentiation in floral traits in P. bifolia. A field manipulation experiment demonstrated that spur length but not perianth size affects pollination success and seed production. This suggests that among-population differentiation in perianth size may be the result of a genetic correlation with spur length. Taken together, the results of this thesis suggest that pollinator-mediated selection can shape the evolution of intraspecific floral variation.

With the advances in wireless communication technology over last two decades, the use of fractional-N frequency synthesizers has increased widely in modern wireless communication applications due to their high frequency resolution and fast settling time. The performance of a fractional-N frequency synthesizer is degraded due to the presence of unwanted spurious tones (spurs) in the output spectrum. The Digital Delta-Sigma Modulator can be directly responsible for the generation of spur because of its inherent nonlinearity and periodicity. Many deterministic and stochastic techniques associated with the architecture of the DDSM have been developed to remove the principal causes responsible for production of spurs. The nonlinearities in a frequency synthesizer are another source for the generation of spurs. In this thesis we have predicted that specific nonlinearities in a fractional-N frequency synthesizer produce spurs at well-defined frequencies even if the output of the DDSM is spur-free. Different spur free DDSM architectures have been investigated for the analysis of spurious tones in the output spectrum of fractional-N frequencysynthesizers. The thesis presents simulation and experimental investigation of mechanisms for spur generation in a fractional-N frequency synthesizer. Simulations are carried out using the CppSim system simulator, MATLAB and Simulink while the experiments are performed on an Analog Devices ADF7021, a high performance narrow-band transceiver IC.

There is a strong need in forging industry to reduce waste of material, improve quality, and reduce cost of forgings. About 30% of the material is wasted during conventional closed-die forging. Therefore, in order to reduce the cost of forged products and to obtain near-net or net shape parts, new forging methods should be applied. Precision forging concept is a cost-effective way to produce net-shape or near-net shape components. In recent years, there has been an increased interest in the production of gears by the net-shape forging technique. This has specific advantages over the traditional manufacturing processes of cutting gears such as hobbing, turning, and grinding including savings on cost and raw material, increased productivity, and gears with higher dynamic properties than conventionally cut ones. In this study, precision forging of a particular spur gear has been investigated. The precision forging die set has been conceptually designed and modeled in a computer aided design environment. The forging process of particular spur gear has been simulated by using a commercially available finite volume program. After the successful simulation results, the prototype die set and the tube-shaped billets were manufactured. The real-life experiments have been realized by using 1000 tons mechanical forging press available in METUBILTIR Research and Application Center Forging Laboratory. The results have been compared with the computer simulations. After the real-life experiments, it has been observed that the conceptual die design is appropriate and near-net shape spur gears are successfully obtained by the proposed precision forging die set.

Frequency synthesizer is a key building block of fully-integrated wireless communication systems. Design of a frequency synthesizer requires the understanding of not only the circuit-level but also of the transceiver system-level considerations. This dissertation presents a full cycle of the synthesizer design procedure starting from the interpretation of standards to the testing and measurement results. A new methodology of interpreting communication standards into low level circuit specifications is developed to clarify how the requirements are calculated. A detailed procedure to determine important design variables is presented incorporating the fundamental theory and non-ideal effects such as phase noise and reference spurs. The design procedure can be easily adopted for different applications. A BiCMOS frequency synthesizer compliant for both wireless local area network (WLAN) 802.11a and 802.11b standards is presented as a design example. The two standards are carefully studied according to the proposed standard interpretation method. In order to satisfy stringent requirements due to the multi-standard architecture, an improved adaptive dual-loop phase-locked loop (PLL) architecture is proposed. The proposed improvements include a new loop filter topology with an active capacitance multiplier and a tunable dead zone circuit. These improvements are crucial for monolithic integration of the synthesizer with no off-chip components. The proposed architecture extends the operation limit of conventional integerN type synthesizers by providing better reference spur rejection and settling time performance while making it more suitable for monolithic integration. It opens a new possibility of using an integer-N architecture for various other communication standards, while maintaining the benefit of the integer-N architecture; an optimal performance in area and power consumption.

Zugl.: München, Univ., Magisterarbeit, 2004 u.d.T.: Niggl, Selima: Pinot Gallizio in München