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No description available.

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The physical state of the seedbed is of importance to the plant environment as it influences some important processes in the soil such as seedling emergence, water and solute transport, and ease of root penetration. This is affected to a large extent by tillage process, the tillage implement type and the geometry of the implement used. / A field experiment was carried out on a clay soil to determine the effect of the geometry of bladed tillage implements on some soil physical properties after tillage. The soil properties evaluated were bulk density, mean clod size distribution and total pore space after tillage and the extent of loosening achieved. / Implement parameters considered were blade width, rake angle and depth of operation of the implement. Two blade widths of 75 and 150 mm were evaluated in combination with three rake angles of 30, 60 and 90 degrees. Each tillage implement was drawn through the soil at four operating depths of 100, 150, 200 and 250 mm. / Larger rake angles were observed to result in larger mean aggregate sizes and greater bulk density reductions when compared to smaller rake angles. Greater reduction in bulk density was observed with the wider of the two blade widths evaluated. Mean clod size after tillage was also observed to be large for the wider of the two widths evaluated. Irrespective of width and rake angle, greater operating depths resulted in larger mean clod sizes and greater reductions in bulk density as compared to shallower operating depths. Fractal analysis showed the extent of fragmentation to be greater at shallower operating depths, hence the small mean clod sizes obtained.

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The primary objective of this thesis is to develop a framework to compare the performance of fixed-wing aircraft, airships, and the rotary-wing aircraft in the Martian environment and through that framework, determine which of these platforms is best suited to conduct a series of scientific investigations on Mars. Three Mars mission scenarios provide the context within which the performance of the platforms is evaluated. The mission scenarios are used to derive the performance requirements including the range and flight path to be covered, the altitude at which the platforms fly, and the scientific investigations to be performed along with the associated scientific instrumentation to be carried as payload. Existing platform designs are used for the purpose of this comparative study and are modified depending on specific mission requirements. A set of weighted performance metrics, including the gross takeoff mass, power required, manoeuvrability, and complexity, serves as a common basis for comparing the performance of the three aerial platforms. The results of this comparative study indicate that the airship is best suited for all mission scenarios considered due to its simplicity and high degree of manoeuvrability. However, it is important to note that a series of subjective design choices with respect to platform speed and available power were made that significantly impact the overall performance of the platforms. Altering these design choices as well as the mission requirements could result in a different platform being best suited for each Mars mission. For instance, increasing the cruising velocity of the fixed-wing aircraft may allow its dimensions to be scaled down thereby reducing the complexity and making it a more competitive platform for long-range missions. In addition, for short-range missions that do not require a high degree of manoeuvrability but where the gross takeoff mass and complexity are more important factors, the rotary-wing aircraft becomes the best option.

Chronic knee injury accounts for nearly half of the injuries from which runners suffer. Impact and propulsive forces are believed to contribute to the development of overuse injuries, so one method of protecting runners might be to reduce those forces. The purpose of this study was to examine the biomechanical role of running poles by comparing normal running to pole running. Ground reaction forces, tibial acceleration, and video data were collected on ten middle-age male recreational runners with a history of knee pain. Subjects ran across a force plate at a constant velocity of 3.5-3.7m/s with an accelerometer attached to the anteromedial aspect of the tibia. Hip, knee, and ankle joint range of motion and torque were calculated. Results indicated significant decreases in the average peak propulsive force and impulse, and a significant increase in peak hip joint torque. It was concluded that by providing an outside source of propulsion, running poles may be useful in reducing the risk of injury to runners. / School of Physical Education

Elastic bands are becoming more popular in strength and power training. Although increases in strength and power have been anecdotally reported with high loads of elastic resistance, there is no research on large band tensions and their effects on force and power variables. The purpose of this study was to quantify peak concentric force, peak concentric power and peak eccentric velocity produced by the subject when using differing levels of elastic resistance (0%, 20%, 50% and 75% of the total load being elastic resistance) in the bench press. Seven experienced male powerlifters and body builders participated in this study. Prior to subject testing all elastic bands were calibrated for force output throughout the bench press range of motion. Each subject performed a single repetition maximum press to determine the total correct testing load (85% of maximum press). The subjects then performed four presses with various elastic band resistances, each having the total equivalent weight of 85% of the subject’s maximal press weight at lockout. Dependent variables were peak concentric force, peak concentric power, and peak eccentric velocity as produced by the subject. A one-way ANOVA was used to determine the differences among the four levels of elastic resistance (ER) used in the study (α = 0.05). Compared to the baseline condition (2123.6 ± 499.9N), significantly lower average peak concentric force was observed with ER of 75% (1451.2 ± 151.0N, 31.9% decrease) (p = .010) and with an ER of 50% (1781.1 ± 174.3N, 16.4% decrease) (p = .052). When compared with baseline peak concentric power (702.6 ± 274.6W), higher peak power was observed in all band trials: 20% (895.2 ± 187.7W, 27.4% increase), 50% (972.5 ± 189.8W, 38.4% increase) and 75% (979.6 ± 171.0W, 39.4% increase) (p = .009; p = .007; p = .033, respectively). There was no significant difference in peak concentric power in any ER trials. No significant differences (p = .080) were seen in peak eccentric velocity. Therefore ER loads of 20, 50 and 75% provide greater stimuli for producing peak concentric power than no ER, with only a 20% load of ER maintaining the same peak concentric force production as baseline. ER loads of 50 and 75% may not be as effective a stimuli as free weights when the training objective is to increase force production. / School of Physical Education, Sport, and Exercise Science

Previous studies have suggested that if exercise intensity is established by perceived effort, the metabolic demand varies among exercise machines and the treadmill optimizes energy expenditure (EE). However, these studies have been completed utilizing young people with normal body fat percentages. Therefore, the purpose of this study was to assess whether there was a difference in acute energy expenditure when obese people used different exercise modes at a self-selected intensity (RPE 11-12) commonly recommended for overweight individuals. Twelve obese subjects (7 male; 5 female; BMI >29 kg/m2), aged 37-71 years completed two familiarization trials on four machines: treadmill (TM), stationary cycle (C), Body Trec elliptical arm/leg (BT), and Airdyne (AD). On separate days, subjects then completed a 15 minute trial on each machine at a self-selected intensity corresponding to a target RPE of I 1-12 on the Borg 15 point scale. Machine order was randomly assigned, and subjects were blinded to the workload throughout each trial. Workload was self-adjusted during the first 5 minutes and then remained stable for the rest of the trial. Physiological data were obtained during the last five minutes of each trial via HR telemetry and the Aerosport TEEM 100. The group means were compared across modes using a one-way repeated measures ANOVA. Significant differences (p <0.05) were observed across exercise modes for energy expenditure. The BT produced the highest rate of energy expenditure among exercise machines and C the lowest (8.0±2.0, 6.6±2.1, 6.3±2.0, 5.3±2.1 Kcal/min, for BT, TM, AD, and C, respectively). These results suggest that perceptually-based exercise prescriptions are not reliable across modes typically found in a fitness center environment, and that weight-bearing arm/leg exercise optimizes EE during self-selected exercise of moderate intensity in obese subjects. / School of Physical Education