For many animals, rapid movements place high power demands on underlying muscles. Storage of muscle energy in elastic structures and the subsequent rapid release of that energy can effectively amplify muscle power. Elastic recoil can also confer thermal robustness to performance in behaviors occurring at variable temperatures. Muscle contractile performance tends to decrease at lower temperatures, but elastic recoil is less affected by temperature. Here I examine the impacts of temperature and scale in systems using elastic recoil and I explore possible interactive effects on movement performance. I explored the role that muscle contractile properties play in the differences in performance and thermal robustness between elastic and non-elastic systems by examining muscles from two species of plethodontid salamanders with elastically powered tongue projection and one with non-elastic tongue projection. These salamanders use tongue projection to capture prey and in species with elastic mechanisms, tongue projection is characterized by higher mechanical power output and thermal robustness compared to tongue projection of closely-related genera with non-elastic mechanisms. In vitro and in situ muscle experiments reveal that species differ in their muscle contractile properties, but these patterns do not predict the performance differences between elastic and non-elastic tongue projection. Overall, salamander tongue muscles are like other vertebrate muscles in contractile performance and thermal sensitivity. I conclude that changes in the tongue-projection mechanism, specifically the elaboration of elastic structures, are responsible for high performance and thermal robustness in species with elastic tongue projection. This suggests that the evolution of high-performance and thermally robust elastic-recoil mechanisms can occur via relatively simple changes to morphology, while muscle contractile properties remain relatively unchanged. The efficacy of elastic recoil in the face of changing temperature depends on the mechanical work done by muscle contraction being unaffected by temperature. In vitro stimulation of Cuban tree frog (Osteopilus septentrionalis) plantaris muscles reveals that interactions between force and temperature affect the mechanical work of muscle. At low temperatures (9 – 17°C), muscle work depends on temperature when shortening at any force, and temperature effects are greater at higher forces. At warmer temperatures (13 – 21°C), muscle work depends on temperature when shortening with intermediate and high forces (≥ 30% peak isometric tetanic force). Shortening velocity is most strongly affected by temperature at low temperatures and high forces. Power is also most strongly affected at low temperature intervals but this effect is minimized at intermediate forces. Effects of temperature on muscle force explain these interactions; force production decreases at lower temperatures, increasing the challenge of moving a constant force relative to the muscle’s capacity. These results suggest that animal performance that requires muscles to do work with low forces relative to a muscle’s maximum force production will be robust to temperature changes, and this effect should be true whether muscle acts directly or through elastic-recoil mechanisms and whether force is prescribed (i.e. internal) or variable (i.e. external). Conversely, performance requiring muscles to shorten with relatively large forces is expected to be more sensitive to temperature changes. How muscle work and power scale determines, in part, the scaling of movement performance. Muscle-mass-specific work is predicted to remain constant across a range of scales, assuming geometric similarity, while muscle-mass-specific power is expected to decrease with increasing scale. I tested these predictions by examining muscle morphology and contractile properties of plantaris muscles from frogs ranging in mass from 1.28 to 20.60 g. Scaling of muscle work and power was examined using both linear regression on log10-transformed data (LR) and non-linear regressions on untransformed data (NLR). In LR, muscle-mass-specific work decreased with increasing scale, but this is counteracted by a positive allometry of muscle mass to predict constant movement performance at all scales. These relationships were non-significant in NLR, though scaling with geometric similarity also predicts constant jump performance across scales. Both intrinsic shortening velocity and muscle-mass-specific power were positively allometric in both types of analysis. However, these differences between methods are caused not by large changes in scaling slopes, but by changing levels of statistical significance using corrections for multiple tests. The dependence of these conclusions on the method of regression, largely because of the setting and adjusting of an arbitrary alpha, demonstrates the importance of careful consideration of statistical methods when analyzing patterns of scaling. Nonetheless, scale accounts for little variation in contractile properties over the range of scales examined, indicating that other sources of intraspecific variation may be more important in determining muscle performance and its effects on movement. Elastic recoil used for power amplification is most often found in smaller animals, suggesting that performance in larger animals using less elastic recoil would be affected more by changing temperatures. To examine the interaction between scale and temperature on performance, I recorded jumps from 1-34 g Cuban tree frogs (Osteopilus septentrionalis) at 10, 20, and 30°C and compared jump performance to predictions based on the effects of temperature and scaling on muscle properties. High muscle-mass-specific power requirements from measured jumps indicate that frogs use elastic recoil at all scales to achieve performance that would be impossible using only muscle, and elastic recoil allows small frogs to achieve the same level of performance as large frogs. Performance that is greater at all temperatures than predictions from models using only muscle power could result from some combination of elastic recoil and power directly from muscle. The relative contributions of muscle power and elastic recoil cannot be discerned by examining temperature effects on performance because these effects are predicted to be so similar. Predicted performance from models of elastic recoil is significantly affected by changing temperature at all scales with temperature coefficient (Q10) values similar to predictions for muscle-powered jumping. Measured Q10 values are similar to those from both predictive models and there is no interaction between temperature and scale. Therefore, elastic recoil allows for jump performance that could not be achieved by muscle power alone at all temperatures and scales, but performance predictions from elastic recoil are not more thermally robust than predictions for muscle-powered jumping.

Doctor of Philosophy / Department of Physics / Bruce M. Law / We have studied two critical binary liquid mixtures in the mixed phase regime with x-ray and neutron reflectometry to verify universal critical scaling at a non-critical interface. We compared our results with previous results obtained with ellipsometry. At a solid-liquid or liquid-vapor interface of an AB binary liquid mixture the component with the lower surface tension will dominate that interface. If the surface tension differential between the components of the mixture is large enough the composition of the surface layer will loose its dependence on. This case is referred to as strong adsorption. We study the case of strong adsorption for a binary liquid mixture at the critical composition with respect to the demixing phase transition. Sufficiently close to the critical temperature Tc the influence of bulk critical behavior is expected to dominate the way the surface adsorption layer decays with depth z from the surface composition to the bulk composition. The length scale of the decay profile is expected to be proportional to the composition correlation length, and is expected to scale with a universal composition scaling function. In a neutron reflectometry study of a critical mixture of D2O and 3-methylpyridine against a quartz substrate we verify universal critical scaling using a scaling function previously used to describe ellipsometry data. In an x-ray reflectometry study of the liquid-vapor interface of a critical mixture of n-dodecane and 1,1,2,2 tetrabromoethane, which had previously been studied with ellipsometry, we find that we are able to describe all data by using the same scaling function provided that we account for non-critical, system dependent surface structure as well. We are also able to simulate ellipsometry with our mathematical profile model and compare the simulation to the previous ellipsometry data.

This thesis investigates multiple-input-multiple-output (MIMO) channel modelling for a wideband indoor environment. Initially the theoretical basis of geometric modelling for a typical indoor environment is looked at, and a space-time model is formulated. The transmit and receive antenna correlation is then separated and is expressed in terms of antenna element spacing, the scattering parameter, mean angle of arrival and number of antenna elements employed. These parameters are used to analyze their effect on the capacity for this environment. Then the wideband indoor channel operating at center frequencies of 2.4 GHz and 5.2 GHz is investigated. The concept of MIMO frequency scaling is introduced and applied to the data obtained in the measurement campaign undertaken at the University of Pretoria. Issues of frequency scaling of capacity, spatial correlation and the joint RX/TX double direction channel response for this indoor environment are investigated. The maximum entropy (ME) approach to MIMO channel modelling is investigated and a new basis is developed for the determination of the covariance matrix when only the RX/TX covariance is known. Finally, results comparing this model with the established Kronecker model and its application for the joint RX/TX spatial power spectra, using a beamformer, are evaluated. Conclusions are then drawn and future research opportunities are highlighted. / Thesis (PhD)--University of Pretoria, 2008. / Electrical, Electronic and Computer Engineering / unrestricted

Functional morphologists have extensively used measurements of performance to investigate the relationship among form, function and ecology through ontogeny. Among different measurements of performance bite force play a crucial role influencing fitness. Although, bite force has been thoroughly investigated among vertebrates, the majority of the studies on fishes have been concentrated only in small species. Consequently, this is the first study that compares the bite force performance in two large marine predators, the great barracuda (Sphyraena barracuda) and bull shark (Carcharhinus leucas). Values of posterior bite force in S. barracuda varied from 3 - 258 N for an ontogenetic series of 27 individuals (23 - 130 cm, TL). Bite force as well as the majority of the biomechanical variables that contribute to it scaled with isometry in S. barracuda. Values of posterior bite force in C. leucas varied from 170 - 5,914 N for and ontogenetic series of 16 individuals (73 - 285 cm, TL). Bite force at the most anterior bite point scaled with positive allometry as well as the majority of the subdivisions of the adductive musculature that greatly contribute to bite force. Bite force performance in this two species showed strong differences, where S. barracuda has one of the lowest relative values of bite force among fishes and C. leucas has one of the largest ones. Additionally, the scaling patterns for bite force and most of the biomechanical variables investigated in this study differed among these two species. These results suggest that predatory success may be acquired by different strategies, and that the same ecological role in a marine ecosystem may be reached by having different bite force performance.

Modern smartphones are being designed with increasing processing power, memory capacity, network communication, and graphics performance. Although all of these features are enriching and expanding the experience of a smartphone user, they are significantly adding an overhead on the limited energy of the battery. This thesis aims at enhancing the energy efficiency of modern smartphones and increasing their battery life by minimizing the energy consumption of smartphones Graphical Processing Unit (GPU). Smartphone operating systems are becoming fully hardware-accelerated, which implies relying on the GPU power for rendering all application graphics. In addition, the GPUs installed in smartphones are becoming more and more powerful by the day. This raises an energy consumption concern. We present a novel implementation of GPU Scaling Governors, a Dynamic Voltage and Frequency Scaling (DVFS) scheme implemented in the Android kernel to dynamically scale the GPU. The scheme includes four main governors: Performance, Powersave, Ondmand, and Conservative. Unlike previous studies which looked into the power efficiency of mobile GPUs only through simulation and power estimations, we have implemented our approach on a real modern smartphone GPU, and acquired actual energy measurements using an external power monitor. Our results show that the energy consumption of smartphones can be reduced up to 15% using the Conservative governor in 2D rendering mode, and up to 9% in 3D rendering mode, with minimal effect on the performance.

Magister Scientiae (Medical Bioscience) - MSc(MBS) / Introduction: Nosocomial infections are infections that occur 48 hours after receiving care for an unrelated condition in a clinic or a hospital environment, many of which are resistant to at least one of the drugs most commonly used to treat them. The dental clinical settings are reservoirs for the transmission of microbes through aerosols produced by routine dental procedures.

Polymer gels undergo a volume phase transition in solvent in response to an infinitesimal environmental change. This remarkable phenomenon has resulted in many potential applications of polymer gels. The understanding of its mechanical properties has both scientific and technological importance. For this purpose, we have developed a novel method for measuring Poisson's ratio, which is one of the most important parameters determining the mechanical property of gels. Using this method, Poisson's ratio in N-isopropyacrylamide (NIPA) and polyacrylamide (PAAM) gels has been studied.

Principal surfaces are smooth two-dimensional surfaces that pass through the middle of a p-dimensional data set. They minimise the distance from the data points, and provide a nonlinear summary of the data. The surfaces are nonparametric and their shape is suggested by the data. The formation of a surface is found using an iterative procedure which starts with a linear summary, typically with a principal component plane. Each successive iteration is a local average of the p-dimensional points, where an average is based on a projection of a point onto the nonlinear surface of the previous iteration. Biplots are considered as extensions of the ordinary scatterplot by providing for more than three variables. When the difference between data points are measured using a Euclidean embeddable dissimilarity function, observations and the associated variables can be displayed on a nonlinear biplot. A nonlinear biplot is predictive if information on variables is added in such a way that it allows the values of the variables to be estimated for points in the biplot. Prediction trajectories, which tend to be nonlinear are created on the biplot to allow information about variables to be estimated. The goal is to extend the idea of nonlinear biplot methodology onto principal surfaces. The ultimate emphasis is on high dimensional data where the nonlinear biplot based on a principal surface allows for visualisation of samples, variable trajectories and predictive sets of contour lines. The proposed biplot provides more accurate predictions, with an additional feature of visualising the extent of nonlinearity that exists in the data.

The purpose for this study was to develop guidelines for the implementation of Goal Attainment Sealing (a mental health measurement technique) in the medical care setting. As a graduate student of social work, I have become involved in the delivery of medical care and am interested in the dynamics of psycho-social variables as they affect the structure, delivery, and outcome of medical services.

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