The use of cosmogenic beryllium-7 (7Be) as a soil and sediment tracer relies upon a number of important assumptions which to date have not been fully underpinned by supporting data. As a catchment management tool 7Be offers unique potential to assess the effects of recent land use or climate change but further research is required to provide confidence in key data and elucidate sources of uncertainty. Through a range of laboratory and field studies, this thesis aims to explore knowledge gaps relating to i) the temporal and spatial dynamics of 7Be activity in rainfall which has importance in the context of estimating fallout input during erosion studies ii) adsorption behaviour in soils which is of critical importance when considering tracer stability at the field and catchment-scale and iii) the reliability of erosion estimates using 7Be inventories at the slope-scale to address the current lack of model validation. Findings showed temporal and spatial variability of 7Be fallout emphasising the need for regular site-specific sampling to determine fallout flux during erosion studies. Data supported the assumption of rapid tracer adsorption upon fallout although highlighted the potential for 7Be mobility under changing environmental parameters, thus, raising questions with regard to tracer stability at the catchment-scale. Field investigations demonstrated the potential for current models to overestimate erosion rates by failing to accurately represent key model components, namely, 7Be depth distributions, particle size enrichment and fallout input dynamics. Where these factors cannot be determined directly, a range of erosion estimates should be given based upon realistic sensitivity analysis of model components. In this manner, reported uncertainties will reflect field processes rather than propagated analytical uncertainty alone.

In RF communications with a rotorcraft such as a helicopter, the rotor blades can impart a modulation onto the received signal called Rotor Blade Modulation (RBM). This modulation is caused by the reflection of a signal off the rotating blades. The reflected signal is Doppler shifted based on where the signal is reflected along the length of the blade as well as the angle between the axis of rotation and the emitter. RBM is known to degrade the performance of RF communications on rotorcraft and can be used in radar applications to detect and classify aircraft, but there is little on its usefulness in other areas. This thesis looks at the ability to utilize the RBM phenomenon on the rotorcraft itself to geo-locate and track a signal emitter on the ground. To do this a 3D RF ray tracing program was developed in C++ to produce simulations of RBM signals. The developed program is based on optical ray tracing algorithms with modified physical propagation effects for RF signals, and swapping lights and cameras for RF transmitters and receivers respectively. The ray tracer was then run over a realistic set of physical parameters to determine their effects on the received signal; this includes transmitter azimuth and elevation angle, receiver position, blade pitch, etc. along with their combinations. The simulations of the azimuth and elevation angle produce predictable modulations on the received signal. Based on the trends in the signal's modulation, a DSP algorithm was distilled down that accurately determines the azimuth and elevation angle of the transmitter from simulated signal data.

This work does not limit itself to its title and touches on a number of related topics beyond it. Starting with the title, Polarization Aberrations of Optical Coatings, the immediate question that comes to mind is: what coatings? All coatings? Not all coatings, but just enough that a third person could take this information and apply it anywhere: to all coatings. The computational work-flow required to break-down the aberrations caused by polarizing events (3D vector forms of reflection and refraction) in dielectric and absorbing materials and for thick and thin films is presented. Therefore, it is completely general and of interest to the wide optics community. The example system is a Ritchey-Chrétien telescope. It looks very similar to a Cassegrain, but it is not. It has hyperbolic surfaces, which allows for more optical aberration corrections. A few modern systems that use this configuration are the Hubble Space Telescope and the Keck telescopes. This particular system is a follow-up on this publication, where an example Cassegrain with aluminum coatings is characterized, and I was asked to simply evaluate it at another wavelength. To my surprise, I found a number of issues which lead me to write a completely new, one-of-its-kind 3D polarization ray-tracing code. It can do purely geometrical ray-tracing with add-on the polarization analysis capability, and more importantly: it keeps your data at your fingertips while offering all the outstanding facilities of Mathematica. The ray-tracing code and its extensive library, which can do several advanced computations, is documented in the appendix. The coatings of the Ritchey-Chrétien induce a number of aberrations, primarily, but not limited to: tilt, defocus, astigmatism, and coma. I found those forms to exist in both aluminum and with a reflectance-enhancing dielectric quarter-wave multilayer coating over aluminum. The thickness of the film stack varies as function of position to present a quarter-wave of optical thickness to oblique rays. Most commercial optical software that I know cannot compute this. And the results are impressive: the scalar transmission, which is a measure of ray efficiency, was raised from 78% to 95%. This means that only 5% of the incident light is lost, assuming ideal coating interfaces. This is very advantageous, considering the application: coronagraphs for exoplanet detection. Exoplanets are very far away, and therefore efficient use of light is essential. I also created a ray! I call it Huygens' twin ray. It is credited to Christiaan Huygens, who postulated that points on a wavefront can be considered as a sources of secondary spherical wavelets. This concept normally belongs to physical optics. The twin ray is emitted from the exact same object point but traced in a slightly different direction, which can be assumed by invoking Huygens's principle, and defined in a special way that consistently prevents vignetting. This requires high-precision ray-tracing, which is introduced along with this thesis work as part of the appendix. The application of this concept is exemplified in finding the exit pupil of the Ritchey-Chrétien telescope. It can be modified to work in a plurality of cases and find the precise image location in three-dimensions, making it completely general and useful. Mastering the ray-tracing documented here depends on how much optics the user knows, but tracing a single ray is something that can be learned in minutes. I welcome you to freely use it and make it your own. If your goal is to learn to ray-trace in Mathematica, the reader is directed to the appendix, especially to the four-port polarimeter example, as it is a 3D system that contains both reflection and refraction through thin films, thick films, retarders, and a single surface is traced at a time!

No description available.

Student Number : 0006329K - MSc(Eng) Dissertation - School of Electrical and Information Engineering - Faculty of Engineering and the Built Environment / Geometric optimisations are presented for the UTD in SuperNEC which is a commercial electromagnetic software package. Path finding optimisations rapidly find propagation paths of electromagnetic waves by using back face culling to determine the visible plates of polyhedral structures and by using reflection and diffraction zones which use image theory and the law of diffraction to determine illuminated spatial regions. An octree reduces the number of intersections during the shadow tests. Numerical results show that overall the optimisations halve the run time of the software for models which consist of plates and cylinders. The path finding optimisations do not scale with model size, are limited to plates and introduce errors. The mean absolute error due to the path finding optimisations is on average 0:02 dB for first order rays and 0:17 dB for second order rays. The octree optimisation scales with model size, can be used with any geometry and any type of ray and does not cause errors.

The desire to follow student learning within intelligent tutoring systems in near real time has led to the development of several models anticipating the correctness of the next item as students work through an assignment. Such models have in- cluded Bayesian Knowledge Tracing (BKT), Performance Factors Analysis (PFA), and more recently with developments in Deep Learning, Deep Knowledge Tracing (DKT). The DKT model, based on the use of a recurrent neural network, exhibited promising results in paper [PBH+15]. Thus far, however, the model has only considered the knowledge components of the problems and correctness as input, neglecting the breadth of other features col- lected by computer-based learning platforms. This work seeks to improve upon the DKT model by incorporating more features at the problem-level and student-level. With this higher dimensional input, an adaption to the original DKT model struc- ture is also proposed, incorporating an Autoencoder network layer to convert the input into a low dimensional feature vector to reduce both the resource requirement and time needed to train. Experimental results show that our adapted DKT model, which includes more combinations of features, can effectively improve accuracy.

In Time-of-Arrival (TOA) based indoor human tracking system, the human body mounted with the target sensor can cause non-line-of-sight (NLOS) scenario and result in significant ranging error. In this thesis, we measured the TOA ranging error in a typical indoor environment and analyzed sources of inaccuracy in TOAbased indoor localization system. To quantitatively describe the TOA ranging error caused by human body, we introduce a statistical TOA ranging error model for body mounted sensors based on the measurement results. This model separates the ranging error into multipath error and NLOS error caused by the on-body creeping wave phenomenon. Both multipath error and NLOS error are modeled as a Gaussian variable. The distribution of multipath error is only relative to the bandwidth of the system while the distribution of NLOS error is relative to the angle between human facing direction and the direction of Transmitter-Receiver, signal to noise ratio (SNR) and bandwidth of the system, which clearly shows the effects of human body on TOA ranging. An efficient way to fight against the TOA ranging error caused by human body is to employ site-specific channel models by using ray-tracing technology. However, existing ray-tracing softwares lack the propagation model that takes the effects of human body into account. To address that issue, this thesis presents a empirical model for near human body ultra-wideband (UWB) propagation channel that is valid for the frequency range from 3GHz to 8GHz. It is based on measurements conducted in a anechoic chamber which can be regarded as free space. The empirical model shows the joint propagation characteristics of the on body channel and the channel between body surface and external access point. It includes the loss of the first path, arrival time of the first path and the total pathloss. Models for all three aspects have been partitioned into two sections by a break point due to the geometrical property of human body and the creeping wave phenomenon. The investigation on first path behavior can be regarded as a theoretical basis of raytracing technique that takes the effects of human body into consideration.

This thesis evaluates a method for extracting architectural dependencies and performance measures from an evolving distributed software system. The research goal was to establish methods of determining potential scalability issues in a distributed software system as it is being iteratively developed. The research evaluated the use of industry available distributed tracing methods to extract performance measures and queuing network model parameters for common user activities. Additionally, a method was developed to trace and collect system operations the correspond to these user activities utilizing automated acceptance testing. Performance measure extraction was tested across several historical releases of a real-world distributed software system with this method. The trends in performance measures across releases correspond to several scalability issues identified in the production software system. / Graduate

<p>Image rendering is the process of creating realistic computer images from  geometric models and physical laws of light and reflection. This master thesis deals mainly with the numerical intricacies of implementing an image renderer using spherical harmonics. It investigates how to calculate the reflection of light in a surface using the Phong model, and employs ray tracing to create a realistic image of a geometric model. Further, it investigates different ways of calculating the spherical harmonic representation of a function defined on the sphere. The thesis also deals with the implementation of self-shadowing, and the effects of adding this component to the rendering equation.</p>

During magnetically disturbed periods, the spatially and temporally structured electron precipitation in the auroral zone creates a significant population of thermal secondary ions. Acceleration mechanisms exist that are capable of energizing the thermal population to suprathermal energies (1 eV to 1 keV). Suprathermal ions escape into the magnetosphere and undergo "bounce" motion along magnetic field lines. These ions are bound to the magnetic flux tubes, which undergo ExB convective drift within the magnetosphere. Magnetospheric convection transports flux tubes of bouncing suprathermal ions through the auroral zone and the subauroral polarization stream (SAPS) regions. Precipitating suprathermal ions enhance ionospheric plasma density structure and constitute a possible source for the enhanced echo occurrence observed by ground-based radars in the SAPS region. Satellite energy spectrometer data often show multiple bands of suprathermal particles with enhanced number and energy flux, and with an energy increase with increasing latitude. The present work examines the hypothesis that these signatures are the result of thermal secondary ions that have been accelerated out of the auroral ionosphere over the short time scales characterizing bursts of intense auroral electron precipitation. The analysis of three events of energy-dispersed ion signatures was facilitated by three-dimensional ion tracing software developed for this thesis. The short-lived acceleration hypothesis can account for the energy-dispersed ion signatures if there exist inter-hemispheric field aligned potentials of the order of 100 V. If the source of the ions is within the auroral zone, the suprathermal ions observed in the SAPS region are most likely to be O+ ions. The long bounce period of O+ (compared to H+) allows convection to transport O+ auroral ions equatorward through a convection reversal, into the SAPS region during a single half-bounce.