Improving and predicting the accuracy of positioning estimates derived from the global positioning system (GPS) continues to be a problem of great interest. Dependable and accurate positioning is especially important for navigation applications such as the landing of commercial aircraft. This subject gives rise to many interesting and challenging mathematical problems. This dissertation investigates two such problems. The first problem involves the study of the relationship between positioning accuracy and satellite geometry configurations relative to a user's position. In this work, accuracy is measured by so-called dilution of precision (DOP) terms. The DOP terms arise from the linear regression model used to estimate user position from GPS observables, and are directly related to user position errors. An analysis of the statistical properties explaining the behavior of the DOP terms is presented. The most accurate satellite geometries and worst configurations are given for some cases. The second problem involves finding methods for detecting and repairing cycle-slips in range delay data between a satellite and a receiver. The distance between a satellite and a receiver can be estimated by measuring the difference in the carrier frequency phase shift experienced between the satellite and receiver oscillators. Cycle-slips are discontinuities in the integer number of complete cycles in these data, and are caused by interruptions or degradations in the signal such as low signal to noise ratio, software failures, or physical obstruction of the signals. These slips propagate to errors in user positioning. Cycle-slip detection and repair are crucial to maintaining accurate positioning. Linear regression models and sequential hypothesis testing are used to model, detect, and repair cycle-slips. The effectiveness of these methods is studied using data obtained from ground-station receivers.

The skin of the palm of the hand has no friction. It is only when in contact with other objects that frictional forces appear. This friction does not, however, conform to the classic laws of friction. The thesis shows that static skin friction is lower than dynamic friction, and that increased velocity increases the coefficient of friction, but increasing load reduces it. Consequently, references to coefficient of friction where palm skin is one of the friction partners require velocity, surface pressure and skin conditions to be specified in addition to contaminants in the friction interface, before reliable conclusions can be drawn. Eleven textured and one non-textured samples all made from the same material were investigated using eighteen male subjects. They were exposed to five contaminants, three skin conditions, three levels ofload and velocities in the range 2-128 mm/so It was concluded that velocity in the friction interface is the most dominant factor contributing to palm friction. Only small, non-significant, differences in friction were found between different types of textures under non-contaminated conditions, but major, and significant differences were observed under contaminated conditions. Coarse textures increased discomfort. For static- and dynamic friction the type of texture, coarse or fine, will affect friction in different ways depending on the skin conditions being "clean" or "contaminated." Experiments show that coarse textures generate less friction than fine under the clean conditions. Under contaminated conditions however coarse textures generate more friction than fine. The highest coefficient offriction 1-1=2.22 (SO=1.12) was recorded under dynamic conditions for a clean hand on a non-textured surface when the surface pressure was low - 6.3 kPa (SO 2.1). The lowest coefficient offriction 1-1=0.05 (SO=0.03) was found under static conditions, with lard present on a non-textured surface when the surface pressure was high - 81.4 kPa (SO=31.0). Two regression models were developed. Regression coefficients are presented for surface topography variables as well as skin condition and contamination, velocity surface pressure and discomfort. Two new surface topography representations explain the generation of friction forces. The uppermost 5% of the volume of texture peaks provided significant information for transfer offriction forces.

The work presented in this thesis is devoted to the study of mechanism of tyre force generation and its influence on handling dynamics of ground vehicles. The main part of the work involves the development of tyre models for use under steady-state and transient operating conditions. The general capability of these models is assessedin a full vehicle simulation environment. The interaction between tyre and vehicle dynamics is critically evaluated and the observed vehicle behaviour is related to the inherent characteristics of different tyre models. In the field of steady-state tyre modelling, two versions of a numerical tyre model are developed. The modelling procedure is carried out in accordance with the viscoelastic properties of rubber, which influence the mechanical properties of the tyre structure and play a significant role in the determination of friction in the tyre contact patch. Whilst the initial simple version of the tyre model assumes a parabolic pressure distribution along the contact, a later more elaborate model employs a numerical method for the calculation of the actual normal pressure distribution. The changes in the pressure distribution as a result of variations in the rolling velocity and normal load influence mainly the levels of self-aligning moment, whilst the force characteristics remain practically unaffected. The adoption of a velocity dependent friction law explains the force generating behaviour of tyres at high sliding velocities. The analysis is extended to the area of transient tyre behaviour with the development of a tyre model appropriate for the study of transient friction force generation within the contact patch. The model incorporates viscoelasticity and inertial contributions, and incorporates a numerical stick-slip law. These characteristics are combined together for the successful simulation of transient friction force generation. The methodologies developed for the modelling of transient friction and steady-state tyre force generation are combined and further extended in order to create a generic transient tyre model. This final model incorporates a discretised flexible viscoelastic belt with inertia and a separate fully-dynamic discretised tread, also with inertia and damping, for the simulation of actual prevailing conditions in the contact patch. The generic tyre model appears to be capable of performing under a variety of operating conditions, including periodic excitations and transient inputs which extend to the non-linear range of tyre behaviour. For the evaluation of the influence of the aforementioned tyre models on the handling responses of a vehicle, a comprehensive vehicle model is developed, appropriate for use in handling simulations. The two versions of the steady-state models and the generic transient model are interfaced with the vehicle model, and the response of the vehicle to a step-steer manoeuvre is compared with that obtained using the Magic Formula tyre model. The comparison between the responses is facilitated by the definition of a new measure, defined as the non-dimensional yaw impulse. It is found that the transience involved in tyre behaviour may largely affect the response of a vehicle to a prescribed input.

The combined finite-discrete element method (FEM/DEM) has been used to simulate processes of brittle fracturing and associated seismicity. With the newly extended FEM/DEM algorithm, two topics involving rock mechanics and geophysics are investigated. In the first topic, a velocity-weakening law is implemented to investigate the initiation of frictional slip, and an innovative method that incorporates surface roughness with varying friction coefficients is introduced to examine the influences of surface roughness. Simulated results revealed detailed responses of stresses to the propagation of the slip front. In the second topic, acoustic activities induced in confined compression tests are simulated and quantitatively studied using the internal monitoring algorithm in FEM/DEM. It is shown that with increasing confinement, AE events are spatially more concentrated and temporally more separated, accompanied by a decreasing b-value. Moreover, interesting correlation between orientations of cracks and the mechanical behavior of the rock was observed.

The combined finite-discrete element method (FEM/DEM) has been used to simulate processes of brittle fracturing and associated seismicity. With the newly extended FEM/DEM algorithm, two topics involving rock mechanics and geophysics are investigated. In the first topic, a velocity-weakening law is implemented to investigate the initiation of frictional slip, and an innovative method that incorporates surface roughness with varying friction coefficients is introduced to examine the influences of surface roughness. Simulated results revealed detailed responses of stresses to the propagation of the slip front. In the second topic, acoustic activities induced in confined compression tests are simulated and quantitatively studied using the internal monitoring algorithm in FEM/DEM. It is shown that with increasing confinement, AE events are spatially more concentrated and temporally more separated, accompanied by a decreasing b-value. Moreover, interesting correlation between orientations of cracks and the mechanical behavior of the rock was observed.

Deterioration of reinforced concrete structures due to reinforcement corrosion is a serious problem that faces concrete infrastructure worldwide. Effect of the rebar corrosion in the shear span on the structural behaviour is not fully addressed in the published literature. This study examined the effects of corrosion of the longitudinal reinforcement in the shear span on the structural behaviour of RC beams and the effectiveness of three rehabilitation schemes on the structural performance of such beams. The experimental program consisted of testing fifteen medium-scale reinforced concrete beams (150mm wide x 350mm deep x 2400mm long) under static load. Test variables included: span to depth ratio, the degree of corrosion and the anchorage end condition and repair schemes. Two span to depth (a/d) ratios were considered: a/d=3.4 with one-point loading and a/d=2.4 with two-point loading. Two anchorage end-conditions were used: bonded or un-bonded reinforcement in the an-chorage zone. Four degrees of corrosion were chosen to simulate minor (2.5% to 5% mass loss), medium (7.5% mass loss), and severe (15% mass loss) degrees of corrosion. Corrosion was induced in the longitudinal reinforcement in the shear-span using accelerated corrosion techniques based on Faradays’ law. Three different repair scenarios were applied. The first scenario included removing the deteriorated concrete, cleaning the corroded steel and patching with a new self-compacting concrete. The second scenario included U-wrapping the beams cross-section using Glass fiber reinforced cement-based composite (GFRCM), and Carbon fiber reinforced cement-based composite (CFRCM) without removing the deteriorated concrete. The third scenario included patch repair and confinement by wrapping with GFRCM or CFRCM. Following corrosion and repair, all specimens were loaded statically to failure. Test results showed no major effect of shear-span corrosion on the flexural behaviour for the beams with end anchorage whereas a noticeable effect on the flexural behaviour was observed for beams with no end anchorage regions. The corrosion degree and the shear span to depth ratio affected the mode of failure for the specimens with no end anchorages. The type of repair significantly affected the overall behaviour of the corroded specimens. An analytical model was proposed and used to predict the load-deflection response of the tested specimens. The program calculated the mid-span deflection for a given load as an integration of the deflection of a series of elements, with the deflection being based on the elongation of the steel reinforcement in each element. A modified bond stress-slip model was incorporated into the calculations to account for the change in bond strength caused by the corrosion and/or confinement that are provided by repairs. The predicted results were in reasonable agreement with the experimental results.

Study area, the Eskipazar Basin, is located in the western part of the North Anatolian Fault System. It is a 3-5 km wide, 10 km long and NWSE trending depression, bounded by a complex array of oblique-slip normal faults and strike-slip faults. The Eskipazar Basin is interpreted to be a superimposed basin. The basin fill is composed of two different units deposited under the control of different tectonic regimes, namely the paleotectonic and the neotectonic regimes. The latest paleotectonic fill of the basin is the fluvio-lacustrine deposits of the paleotectonic Eskipazar formation. This formation is unconformably overlain by a group of neotectonic units namely, the Budaklar, the Karkin and the imanlar formations. The unconformity in between these paleotectonic and neotectonic units represents the time interval during which the paleotectonic period comes to end and the neotectonic period started. Thus, onset age of the strike-slip neotectonic regime in the study area is Late Pliocene (&amp / #8764 / 2.6 My). Common basin margin-bounding faults of the Eskipazar Basin are the Kadilar fault set, the Beytarla Fault Zone, the Budaklar fault set, the Arslanlar fault set, the Dibek fault, the Karkin fault, the Boztepe fault and the Acisu fault. These faults display well preserved fault scarps, in places. Morphological expressions of these faults and their geometrical relationships to regional stress system indicate that these faults are mostlystrike-slip faults with normal component. However the Kadilar fault set displays a different characteristic, being the major fault controlling the basin to the west and it is indeed an oblique slip normal fault. Long term seismicity and their epicentral distribution in and very close to the study area suggest that the Eskipazar basin is located in an area of seismic quiescence, nevertheless the morphotectonic expressions of the faults exposing in the basin suggest that these faults are active. Since the most of settlements are located on different lithologies of poorly consolidated deposits of the Eskipazar formation susceptible to landslides, the area is open to future earthquake hazard. Therefore, structures and settlements have to be constructed on strong ground away from active faults.

The influence of drying parameters namely residence time before drying, drying temperature, drying time, relative humidity, and slip recipe on the drying rate of slip cast sanitary wares, predominantly lavatories and toilet closets, was studied. The drying temperatures were changed from 80 oC to 110 oC with an increment of 10 oC. The drying time was changed from 10 to 7 h with a decrease of 1 hour. Relative humidity of the environment was changed from 60 to 75 %. The percent weight loss, percent residual moisture and the percent shrinkage of the samples were determined by weighing and measuring the samples before and after the tests. The percent weight loss was within the range of 6.5 to 6.6 % after holding the as cast samples for 6 hours at ambient casting shop conditions while it was within the range of 17.96 to 18.10 % when subsequently dried for 10 hours at 110 oC in the dryer. The percent shrinkage was within the range of 2.9 - 3.0 % after holding the as cast samples 6 h at ambient laboratory conditions. No shrinkage was observed in the sample when it was subsequently dried for 10 hours at 110 oC in the dryer. Optimum moisture content of dried wares was obtained after drying for 8 hours at 100 oC in the dryer. It has been seen that the relative humidity of the dryer at the beginning of the drying should be lower than 75 %. As the non-plastic content in the recipe of the sanitary ware slip increased, drying shrinkage and residual moisture content decreased. The results of this study showed that through increasing the residence time up to 6h with a casting shop environment of approximately 30 oC and 60 % relative humidity, the drying time could be safely reduced from 10 h to 8 h with a drying temperature of 100 oC for the test plates. The same approach can be used for more complex shapes, e.g., WC closets, basins, tanks etc. in EczacibaSi Vitra plant. Once the drying time was reduced, the amount of natural gas per ware would be reduced to a certain extent. Aside from that the reduction in the drying time would increase the quantity of the drying cycles per week so that more wares could be dried. When all these observations were taken into account, this thesis study could also be utilized by other sanitary ware producing companies whose processes require slip cast drying.

Wheel slip is a common problem in planetary rover exploration tasks. During the current Mars Exploration Rover (MER) mission, the Spirit rover almost became trapped on a dune because of wheel slip. As rover missions on harsh terrains expand in scope, mission success will depend not only on rover safety, but also alacrity in task completion. Speed combined with exploration of varied and difficult terrains, the risk of slip increases dramatically. We first characterize slip performance of a rover on harsh terrains by implementing a novel High Fidelity Traversability Analysis (HFTA) algorithm in order to provide slip prediction and detection capabilities to a planetary rover. The algorithm, utilizing path and energy cost functions in conjunction with simulated navigation, allows a rover to select the best path through any given terrain by predicting high slip paths. Integrated software allows the rover to then accurately follow a designated path while compensating for slippage, and reach intended goals independent of the terrain over which it is traversing. The algorithm was verified using ROAMS, a high fidelity simulation package, at 3.5x real time speed. We propose an adaptive path following algorithm as well as a human-trained neural network to traverse multiple harsh terrains using slip as an advantage. On a near-real-time system, and at rover speeds 15 times the current average speed of the Mars Exploration Rovers, we show that the adaptive algorithm traverses paths in less time than a standard path follower. We also train a standard back-propagation neural network, using human and path following data from a near-real-time system. The neural network demonstrates it ability to traverse new paths on multiple terrains and utilize slip to minimize time and path error.

Thesis (M.S.)--University of Nevada, Reno, 2007. / "May, 2007." Includes bibliographical references (leaves 155-165). Online version available on the World Wide Web.