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Egg masses of Epitheca cynosura were collected from Bays Mountain Park, Tennessee, USA, in June, 1999. Newly hatched individuals were placed into enclosures and sampled at scheduled time intervals throughout the summer. Enclosures were exposed to combinations of high and low densities and presence/absence of a second-year class E. cynosura predator. Survivorship, mean head widths, and mean dry masses were compared across treatments. Due to poor recovery of early-instar larvae, survivorship showed no significant differences in mortality among treatments. The predator present treatment caused significantly smaller head widths and dry masses only on days 42 and 55. The density treatment had a significant effect on larval growth from day 28 through day 86 (end of the experiment). Larvae from low density treatments had larger head widths and dry masses. The effects observed within the density treatments were likely to have resulted in a cohort split. Those individuals in the low density treatment followed a univoltine life history, and high density individuals followed a semivoltine life history. Density is probably a very important factor influencing the voltinism of E. cynosura at Bays Mounain Lake.

Traditional methods for the investigation of sound fields generally rely on a microphone to convert sound pressure into an electrical signal which can be recorded, displayed, and so forth. The squared sound pressure is directly related to potential energy density. Consequently, the measurement of sound pressure alone does not inherently provide insight into the total energy density of the sound field. Specifically, no information about the kinetic energy density of the sound field is available from this measurement alone. However, it is possible to use two microphones to estimate particle velocity. The squared particle velocity magnitude is directly related to kinetic energy density. The two energy quantities combine to yield total acoustic energy density. The purpose of this work is to investigate and compare three probes designed to measure acoustic energy density. It is also to determine which probe may be most practically implemented in real-world applications. All three designs are based on a rigid spherical housing and are referred to as follows: the six microphone probe, the tetrahedron probe, and the orthogonal probe. The six microphone probe is so named because it is made up of six microphones, with one pair of microphones oriented along each Cartesian axis. The tetrahedron probe is so named because it has four microphones, one at each of the vertices of a regular tetrahedron. The orthogonal probe has four microphones positioned in such a way that the lines drawn from an origin microphone to the other microphones form an orthogonal set. The majority of the work presented in this thesis uses Matlab to numerically predict the behavior of the probes. Four numeric models are used to predict the behavior of the three different probes. The models match the geometric arrangement of the various probes. A simple experiment also shows how the probes respond to a source in an anechoic environment. The results of the numeric modeling indicate that the orthogonal probe has the greatest useable frequency range. Both the tetrahedron and the orthogonal probes have a greater frequency range than the six microphone probe. However, in the simple experiment, the orthogonal probe did not measure energy density as accurately as the tetrahedron probe when the orthogonal probe was rotated, such that no Cartesian axis was parallel to the radial axis of the source. The data indicate that more work must be done before a decision can be made between the tetrahedron probe and the orthogonal probe. It is clear that it is possible to measure acoustic energy density in 3-dimensions using only four microphones, instead of six.

Nowadays, studying materials for renewable energy applications are highly de- manded. Hybrid halide perovskites have proven to be promising materials for such technology since their first application in solar cells in 2008, with a power conversion efficiency of 2.7%. Since then, hybrid halide perovskites have proven their superior properties for light-absorbing devices. In this scope, studying the optical properties is ultimately essential. This work investigates the tempera- ture dependence of the optical spectra for formamidinium lead iodide/bromide perovskites (FAPb[IxBr1-x]3 (0 ≤ x ≤ 1) using spectroscopic ellipsometry mea- surements, empirical optical modeling, density functional theory, and molecular dynamics. Five FAPb[IxBr1-x]3 perovskite samples were fabricated by a hybrid processing technique. External Quantum Efficiency measurements reported an energy bandgap range between 1.58 eV and 1.77 eV for the resulted samples. Next, multi-angle spectroscopic ellipsometry measurements were applied with a temperature-controlled stage, allowing the variance of temperature from 25 ◦C to 75 ◦C. The results show a blue shift in the optical spectra at elevated tempera- tures. We then conducted a temperature-dependent empirical model that predicts the optical spectra for the sample of study at higher temperatures using input data of the spectra at room temperature. The model reports low mean squared errors which are less than ≈ 2 around the bandgap, and further development can be applied for better utilization. First-principles investigations were conducted on four FAPb[IxBr1-x]3 per- ovskite unit cells. Structural optimization was applied with assuming fixed angles of the lattice. Atomic configuration was chosen to achieve minimal ground state energies. Ab initio molecular dynamics simulations were applied to each opti- mized structures at target temperatures of 300 K and 350 K using Berendsen thermostat. The simulation time was 4ps with 1fs time step, and the electronic energy bandgap was calculated at each step using PBE functional. The simula- tions reported a rotational motion for the FA molecule that showed to be faster at 350 K, along with higher mean energy bandgap compared to the reported value at 300 K. The optical spectra were extracted using a snapshot from the resulted structures. Similar to the spectroscopic ellipsometry measurements, a temperature induced blue shift was reported. Overall, this work detects and predicts the temperature-dependent optical spectra and confirms the role of the atomic thermal motion. With further devel- opment, higher accuracy can be achieved along with broadening the materials of study for photovoltaic and optoelectronic applications.

<p> Neutron radiography has the ability to differentiate between gas and liquid in twophase flow due both to the density difference and the high neutron scattering probability of hydrogen. Previous studies have used dynamic neutron radiography - in both real-time and high-speed - for air-water, steam-water and gas-liquid metal two-phase flow measurements. Radiography with thermal neutrons is straightforward and efficient as thermal neutrons are easier to detect with relatively higher efficiency and can be easily extracted from nuclear reactor beam ports.</p> <p> The quality of images obtained using neutron radiography and the imaging speed depend on the neutron beam intensity at the imaging plane. A high quality neutron beam, with thermal neutron intensity greater than 3.0xl06 n/cm2-s and a collimation ratio greater than 100 at the imaging plane, is required for effective dynamic neutron radiography up to 2000 frames per second.</p> <p> The primary objectives of this work are: (1) tu optimize a neutron radiography facility for dynamic neutron radiography applications and (2) to investigate a new technique for three-dimensional neutron radiography using information obtained from neutron scattering. </p> <p> In this work, neutron transport analysis and experimental validation of a dynamic neutron radiography facility is studied with consideration of real-time and high-speed neutron radiography requirements. A beam port based dynamic neutron radiography facility, for a target thermal neutron flux of l.Oxl07 n/cm2-s, has been analyzed, constructed and experimentally verified at the McMaster Nuclear Reactor.</p> <p> The neutron source strength at the beam tube entrance is evaluated experimentally by measuring the thermal and fast neutron fluxes using copper activation flux-mapping technique. The development of different facility components, such as beam tube liner, gamma ray filter, beam shutter and biological shield, is achieved analytically using neutron attenuation and divergence theories. Monte-Carlo simulations (using MCNP-4B code) are conducted to confirm the neutron parameters along the beam path and at the imaging plane. Good agreement between the analytical and the numerical values for the thermal neutron flux at the imaging plane to within 5% has been achieved. The MCNP simulations show that neutron back scattering, due to the presence of the back-wall biological shielding and the beam catcher, have an insignificant effect on the thermal neutron flux at the imaging plane, however, the epithermal and fast neutron fluxes have increased by 4-11 %.</p> <p> Experimental results show that the thermal neutron flux is nearly uniform over an imaging area of 20.0-cm diameter. The thermal neutron fl11x ranges from 1.0x 107 - 1.26x10 7 n/ cm2 -s at a reactor operating power of 3. 0 MW. The measured value for the neutron-to-gamma ratio is 6.0x 105 n/cm2-μSv and the Cadmium-ratio is observed to be 1.22. These values promote real-time neutron radiography with relatively high neutron attenuating materials such as light water and high-speed neutron radiography with relatively low neutron attenuating materials such as heavy water and Freon type fluids with a minimal contrast degradation resulting from non-thermal neutron content of the beam.</p> <p> A dynamic neutron radiography system has been developed and modified to obtain less neutron damage to the low-light level video camera. The system is used to visualize air-water two-phase flow in a natural-circulation loop to examine the dynamic capabilities of the radiography facility. Measurements of bubble velocity, void fraction, and phase distribution are successfully made. Single frames (-33 ms) of neutron images were captured using the dynamic neutron radiography system for air-water two-phase flow. The system was able to resolve single bubbles interfaces with an image spatial resolution of approximately 0.44 mm.</p> <p> Thermal neutron detectors are placed at the periphery of the neutron beam to detect neutrons scattered by a non-flowing two-phase object placed on a turntable to simulate motion of the gas phase. The results show the potential ability to use neutron scattering technique to provide two-dimension neutron radiography with additional information to the third dimension.</p> / Thesis / Doctor of Philosophy (PhD)

<p> Bayesian filtering refers to the process of sequentially estimating the current state of a complex dynamic system from noisy partial measurements using Bayes' rule. This thesis considers Bayesian filtering as applied to an important class of state estimation problems, which is describable by a discrete-time nonlinear state-space model with additive Gaussian noise. It is known that the conditional probability density of the state given the measurement history or simply the posterior density contains all information about the state. For nonlinear systems, the posterior density cannot be described by a finite number of sufficient statistics, and an approximation must be made instead.</p> <p> The approximation of the posterior density is a challenging problem that has engaged many researchers for over four decades. Their work has resulted in a variety of approximate Bayesian filters. Unfortunately, the existing filters suffer from possible divergence, or the curse of dimensionality, or both, and it is doubtful that a single filter exists that would be considered effective for applications ranging from low to high dimensions. The challenge ahead of us therefore is to derive an approximate nonlinear Bayesian filter, which is theoretically motivated, reasonably accurate, and easily extendable to a wide range of applications at a minimal computational cost.</p> <p> In this thesis, a new approximate Bayesian filter is derived for discrete-time nonlinear filtering problems, which is named the cubature Kalman filter. To develop this filter, it is assumed that the predictive density of the joint state-measurement random variable is Gaussian. In this way, the optimal Bayesian filter reduces to the problem of how to compute various multi-dimensional Gaussian-weighted moment integrals. To numerically compute these integrals, a third-degree spherical-radial cubature rule is proposed. This cubature rule entails a set of cubature points scaling linearly with the state-vector dimension. The cubature Kalman filter therefore provides an efficient solution even for high-dimensional nonlinear filtering problems. More remarkably, the cubature Kalman filter is the closest known approximate filter in the sense of completely preserving second-order information due to the maximum entropy principle. For the purpose of mitigating divergence, and improving numerical accuracy in systems where there are apparent computer roundoff difficulties, the cubature Kalman filter is reformulated to propagate the square roots of the error-covariance matrices. The formulation of the (square-root) cubature Kalman filter is validated through three different numerical experiments, namely, tracking a maneuvering ship, supervised training of recurrent neural networks, and model-based signal detection and enhancement. All three experiments clearly indicate that this powerful new filter is superior to other existing nonlinear filters. </p> / Thesis / Doctor of Philosophy (PhD)

<p> This thesis presents the results of an attempt to study the chemical bond in terms of the three-dimensional electronic charge distribution and the force which this charge distribution exerts on the nuclei. The homonuclear diatomic molecules Li2, B2, C2, N2, O2, and F2 are discussed in terms of covalent binding while the heteronuclear diatomic molecules LiF and LiH are discussed in terms of ionic binding.</p> / Thesis / Doctor of Philosophy (PhD)

We consider the construction of multivariate histogram estimators for any density f seeking to minimize its L1 distance to the true underlying density using arbitrarily large sample sizes. Theory for such estimators exist and the early stages of distributed implementations are available. Our main contributions are new algorithms which seek to optimise out unnecessary network communication taking place in the distributed stages of the construction of such estimators using sparse binary tree arithmetics.

Understanding the phase behaviour of colloidal systems is relevant to designing new colloid-based nanostructured materials. One common platform for studying the colloidal system is the model of hard spheres. Over the last few decades, different hard-sphere models have been developed. We study the phase behaviour of three hard-sphere models: the lattice gas model, the local density approximation model, and the white bear version of the fundamental measure theory, with short-range attractive and long-range repulsive (SALR) interactions. The competition between the attraction and repulsion results in the formation of clusters composed of many particles, whereas the spatial arrangement of these clusters leads to the formation of long-range ordered phases. Phase diagrams containing the commonly observed body-center-cubic (BCC) and hexagonally close-packed (HCP) phases, as well as the novel Frank-Kasper $\sigma$ and A15 phases, have been constructed using the density functional theory applied to hard spheres with SALR interactions. Similar phase transition sequences have been predicted for the three hard-sphere models, implying a universality of the observed phase behaviour for hard spheres interacting with SALR potentials. However, the details of the phase diagrams could vary significantly. The results obtained from our study shed light on understanding the emergence of complex phases from simple systems. / Thesis / Master of Science (MSc) / Soft condensed matter physics, a sub-field of condensed matter physics, primarily concerns the investigation of physical properties of pliable, deformable materials such as plastics, gels, and colloidal suspensions. One particularly intriguing feature of these soft materials is their ability to self-assembly, leading to the spontaneous formation of ordered structures, including but not limited to body-centered cubic and face-centered cubic phases. In particular, a group of complex spherical phases, known as the Frank-Kasper phases, has been identified in various soft matter systems, encompassing polymeric blends, colloidal suspensions, and more. Notably, in colloidal systems, when nanoparticles are grafted with polymer chains, the Frank-Kasper phases could become stable. However, the emergence of these complex phases from the diverse soft matter systems have not been fully understood. In this thesis, we employ the classical density functional theory based on three different hard-sphere models to probe the formation of the Frank-Kasper phases in colloidal systems. Our results provide insights into the formation mechanism of the Frank-Kasper phases in a simple system and demonstrate the universality of different hard-sphere models.

When a body vibrates in a fluid, some of the fluid is carried with it and the mass loading lowers its resonant frequency. Similarly, when compression of the fluid occurs, there is an added stiffness which by design can be made to predominate. In addition, there is an energy dissipation arising from viscous losses and acoustic radiation. The starting point of this research was a tuning fork with flat rectangular tines, designed to trap a narrow laminar of gas which is forced to pump in and out as the tines vibrate. The increase in kinetic energy, contributed by this high velocity' gas, gives the device a relatively large sensi ti vi ty as a gas density transducer. The change in frequency between vacuum and atmospheric pressure is typically a few percent, during which period the mechanical "Q" remains high enough to keep the fork sharply resonant. A high stability oscillator incorporating the transducer as the frequency controlling element was built. Small piezoelectric Cp2t) elements were used to drive the transducer and pick up the vibrations. A typical stability, equivalent to a pressure change of 0. 05 mBar was achieved. The supporting equipment re qui red for the work centred around a vacuum system with facilities for introducing a range of gases at precise rates. Computer control enabled the transducer's temperature, frequency, and "Q" factor to be measured and stored as the gas pressure was increased from vacuum. Extensive experiments were carried out on a range of tuning fork transducers, including a circular one in which a pair of disks clamped at the center acted as the tines and gave a simple radial gas displacement. Common to all these transducers is, the linearity of 1/f 2 with gas density for pressures above about 50 mBar; a departure from. linearity below this pressure; and below 10 mBar an overriding stiffness effect, where from vacuum to a few mBar the frequency paradoxically increases. The resultant calibration to this non-linear response, while exhibiting high stablility, is unattractive for general use. It has however applications over limited ranges as for example, those of a barometer or altimeter. Insight gained from experience with the double disk resonator, led to a new geometry which has resulted in an extremely viable transducer, without calibration anomalies, and capable of operating in a pressure or dehsity mode. Here, the gas is confined in two cylindrical cavities above and below a thin circular diaphragm, clamped at the periphery and again made to vibrate using p2t elements. In the fundamental mode, the alternating change in cavity volume due to compression and rarefaction of the gas, adds stiffness to the diaphragm. In the next mode, there is no net volume change, but the gas is pumped across the cavities adding inertial loading. No anomalies were experienced in the empirical calibrations obtained for each mode- the fundamental being linear with pressure Cf 2 proportional to Pl, and the first overtone linear with density (1/f 2 proportional to pl. A simple theory, which is sufficiently accurate for general design purposes, has been developed. Future work, which is of a straightforward development nature, is proposed. The high degree of stability achieved for these vibrating structures was later realised in a different geometry. In this, a long rod was excited into a torsional mode so as to produce two nodes a quarter wavelength from. either end. By securing the rod at these points and immersing the lower length in a liquid, a sensitive, robust, viscometer was produced. Driving the rod with a burst of oscillations, shears the liquid in contact with it. By removing this drive and measuring the rate of vibrational decay under the action of viscous dissipatiop, an indication of the viscosity can be obtained. The features of a pure shearing force, and the real-time, on-line nature of the device, makes it attractive for the characterisation of both thick and thin liquids and automatic process control.