In this dissertation, charge transport through organic field effect transistors is explored. In particular, small molecule-based devices consisting of Pentacene semiconducting thin films are investigated. The relationship between electric field and carrier velocity is explored over a wide range of electric fields. These velocities are then compared to directly measured velocities measured from transient measurements. New device structures are fabricated in order to provide low voltage operation, along with a method to stabilize the output response and reduce bias stress effects. A novel method is proposed to investigate the dynamics of trap response rate in highly localized systems through the characterization of the large signal frequency response of a vii device. This method is then used to gain greater insight into bias stress effects and the ability of a transistor to respond to a rapidly changing input. A greater understanding of the transport of charge through a channel is obtained, leading to a more realistic picture in which a single mobility value is an insufficient description of carrier transport through a material. / text

This three part study attempted to enhance our understanding of vegetation change and its potential effects on ecohydrology in drylands. The first study developed a method to measure the velocity of shallow overland flow. Under rainfall simulation, dye tracers were applied to runoff and photographed to calculate mean surface velocity. Results showed this approach was a significant improvement explaining 13% more of the variation in mean velocity compared to traditional methods. Results from the first study were used to compare hydraulic parameters on shrub- and grass-dominated plots in the second study. Previous research has suggested microtopography in shrublands acts to concentrate flow, leading to increased runoff velocity compared to grasslands. However, present findings showed that flow velocities were similar on many grass and shrub plots; only plots with ground cover > 90% exhibited significantly lower flow velocities, and some shrub-dominated plots had lower flow velocities than grass-dominated plots implying that horizontal water flux is reduced under certain states of woody plant encroachment. In terms of ground cover characteristics, velocity increased rapidly with increases in the fraction of bare soil, up to a value of ~20% bare soil. Above ~20% bare soil, basal gap became a dominant factor suggesting a possible threshold where spatial metrics related to the distance between plants become important indicator of shallow flow velocity. The third study tested an approach to quantify woody plant canopy metrics over large areas. Radar has been used to map biomass in forests but few studies have examined open canopy ecosystems. Field measurements of shrublands were compared to satellite images to identify the relationship between radar signal and height and cover of woody vegetation. Results indicated that radar signal increased positively with shrub height or shrub volume explaining 74% and 90% of the variation, respectively. The effect of surface roughness and sub-canopy species on radar signal appears reduced when images are collected at large incidence angles.

Properties of coherent media in the regime of electromagnetically induced transparency (EIT) are studied. A study of the shape and width of the EIT resonance is presented for coherent media with buffer gas. Observation of an absorption-like resonance for large one-photon detunings in a medium with buffer gas and its properties are shown. The regime of ``slow'' and ``fast'' group velocities are studied. Observation of narrow resonances with a phase broadened probe field is presented, and possible application of this regime are outlined.

No description available.

Using a specially constructed Gas Hydrate Resonant Column (GHRC), the University of Southampton explored different methods of hydrate synthesis and measured the properties of the resulting sediments, such as shear wave velocity (Vs), compressional wave velocity (Vp) and their respective attenuation measurements (Qs -1 and Qp -1). Two approaches were considered. The first utilises an excess gas technique, where known water volume in the pore space dictates the quantity of hydrate. The second approach uses a known quantity of methane gas within the water saturated pore space to constrain the volume of hydrate. Results from the two techniques show that hydrates formed in excess gas environments cause stiffening of the sediment structure at low concentrations (3%), whereas, even at high concentrations of hydrate (40%) in excess water environments, only moderate increase in stiffness was observed. Additionally, attenuation results show a peak in damping at approximately 5% hydrate in excess gas tests, whereas in excess water tests, damping continues to increase with increasing hydrate content in the pore space. By considering the results from the two approaches, it becomes apparent that formation method has an influence on the properties of the hydrate bearing sand, and must therefore influence the morphology of the hydrate in the pore space.

The study of haptics, or the sense of touch in virtual reality environments, is constantly looking for improvements in modeling with a high fidelity. Highly detailed models are desirable, but they often lead to slow processing times, which can mean a loss of fidelity in the force feedback sensations. Model compression techniques are critical to balancing model detail and processing time. One of the proposed compression techniques is to create multiple models of the same object but with different levels of detail (LOD) for each model. The technique hypothesizes that the human arm loses sensitivity to forces with the increase of its movement speed. This the compression technique determines which model to use based on the user's movement speed. This dissertation examines studies how the movement speed of the user affects the user's ability to sense changes in details of haptic models. Experiments are conducted using different haptic surfaces. Their levels of detail are changed while the subject interacts with them to mimic the effects of a multiresolution compression implementation. The tests focus on the subjects' ability to differentiate changes of the surfaces at each speed. The first experiment uses curved surfaces with multiple resolutions. This test observes the sensitivity of the user when the details on the surface are small. The results show that the subjects are more sensitive to changes of small details at a lower speed than higher speed. The second experiment measures sensitivity to larger features by using trapezoidal surfaces with different angles. The trapezoidal surfaces can be seen as a low-resolution haptic model with only two vertices, and changing the angles of the trapezoids is seen as changing the radii of curvature. With the same speed settings from the first experiment applied to the subjects, the sensitivity for changes in curvature is predicted to decrease with the increase of speed. However, the results of this experiment proved otherwise. The conclusions suggest that multiresolution designs are not a straightforward reduction of LOD, even though the movement speed does affect haptic sensitivity. The model's geometry should be taken into account when designing the parameters for haptic model compression. The results from the experiments provide insights to future haptic multiresolution compression designs.

Introduction and Purpose: In chronic heart failure (CHF), exercise rehabilitation results in a reduced risk of mortality, decreased disease severity, and increased functional ability. Resistance training is an important component of cardiac rehabilitation; however, an optimal training velocity that produces physiological and functional benefits at minimal perceived exertion and cardiovascular stress has yet to be identified. CHF patients need to be very efficient and perform the exercise that will give them the greatest benefits because of their poor exercise tolerance and increased risk of cardiovascular complications during exercise. In older populations, high velocity resistance training results in greater improvements in functional ability than low velocity resistance training. The use of high velocity resistance training in patients with CHF has yet to be examined; however it may enhance higher velocity activities of daily living while using a lower training load. The lower load associated with high velocity training may be less strenuous and result in lower cardiovascular stress, whilst maintaining a relatively similar power output compared to traditional low-velocity training. The purpose of this study was to compare the acute cardiovascular responses and perceived exertion of high and low velocity resistance exercises. Methods and Measures: 6 male and 1 female patients with systolic heart failure (CHF NYHA Class I-III) were recruited to perform two separate, randomly assigned exercise sessions. These sessions consisted of 5 exercises (hack squat, chest press, knee flexion, lat pull down and knee extension); one with a low velocity of contraction (3 second concentric phase: 3 second eccentric phase at 50% of the slow velocity 1-RM) and one with a high velocity (1 second concentric phase: 3 second eccentric phase at 50% of the high velocity 1-RM). During both sessions, heart rate, blood pressure, and a rating of perceived exertion (RPE) were obtained after the completion of each exercise. Results: Despite a similar relative mechanical load, the high velocity workout produced significantly lower systolic blood pressure (121.2 vs. 132.8 mmHg), mean arterial pressure (87.8 vs. 93.5), and RPE (3.7 vs.4.8) than the low velocity workout (p<0.05). The high velocity workout was not significantly different from the low velocity workout for heart rate, rate pressure product and diastolic blood pressure. Conclusion: We conclude that the high velocity workout produces more favourable blood pressure responses to resistance training in patients with CHF than the low velocity workout and may be used to enhance functional outcomes in cardiac rehabilitation programs.

Impact induced dynamic cracks are produced with a Split Hopkinson Pressure Bar (SHPB) apparatus in two rocks (Kuru granite and Flamboro limestone) with impact velocities ranging from 8 to 12 m/s. Impact bit (tungsten carbide) diameters range from 8mm to 15mm. Dye impregnation combined with UV imaging, CAT scans and Optical scans were employed to study the resulting crack patterns. The resulting damage is quantified in terms of radial crack density on impact surface, crater, crushed zone and crack density with depth. In both rocks &lsquo;total&rsquo; damage obtained is directly proportional (exponential) with bit diameter and impact velocity. The &lsquo;total&rsquo; damage in Kuru granite is found to be greater than Flamboro limestone at all impact velocities; however, the crushed zone in the latter is found to consistently greater than the former. 2D simulations of dynamic fractures with AUTODYN have also been carried out showing good qualitative agreement with experimental results.

No description available.

This report details a physical modeling study to investigate the flow characteristics of circular corrugated structural plate (CSP) culverts with 10% embedment and projecting end inlets using a 0.62 m diameter corrugated metal pipe under a range of flows (0.064 m3/s to 0.254 m3/s) and slopes (0%, 0.5% and 1.0%). An automated sampling system was used to record detailed velocity measurements at cross-sections along the length of the model. The velocity data was then used to develop isovel plots and observations were made regarding the effect of water depth, average velocity, boundary roughness and inlet configuration on the velocity structure. Other key aspects examined include the distribution of shear velocity and equivalent sand roughness, Manning’s roughness, an evaluation of composite roughness calculation methods, secondary currents, area-velocity relationships, the effect of embedment on maximum discharge and a simulation of model results using HECRAS. Recommendations are presented to focus future research.