The finite difference time domain (FDTD) method is commonly used for numerical simulations of the electromagnetic wave propagation in time domain. The FDTD method is easy to implement and the computational results are highly relevant to the analytical solution, so that the FDTD method is applied to variety application problems. However, the computational efficiency of the FDTD method is constrained by the upper limit of the temporal discretisation. The Courant Friedrich Lewy (CFL) stability condition limits the time step for the computation of the FDTD method, so that if the spatial discretisation of the computation is set to be small in order to obtain high accurate results, the size of the temporal discretisation need to be satisfy the CFL stability condition. The locally one dimensional FDTD (LOD-FDTD) method is unconditionally stable. The time step and the spatial step can be independently chosen for the computation of the LOD-FDTD method. The arithmetic operations of the LOD-FDTD method is fewer than that of the other implicit FDTD method, such as the Crank Nicolson FDTD (CN-FDTD) method and the alternating direction implicit FDTD (ADI-FDTD) method. Although the implementation of the LOD-FDTD method is simpler than that of the ADI-FDTD method,the numerical error in the computational results of the LOD-FDTD method is equivalent to that in the computational results of the ADI-FDTD method. In this thesis, a new three dimensional (3D) frequency dependent (FD) LOD-FDTD method is proposed. The one pole Debye model is incorporated into the 3D-FD-LOD-FDTD method in order to deal with practical applications. The proposed method is implemented in Fortran 90 and parallelised with OpenMP. A simulation model of the human phantom is developed in the 3D-FD-LOD-FDTD method with fine structures and frequency dependent dielectric properties of the human tissues, and numerical simulation of electromagnetic wave propagation inside the human head is shown.

To assist in the development of mechanical structures which are subjected to dynamic loads, structural dynamic testing, using a test rig loaded by servo-hydraulic actuators to reproduce operational measured responses in the laboratory, may form an essential element of the development process. The input loads acting on the structure under operational conditions can in most cases not be measured directly, and instead the structural dynamic responses to these loads are recorded. The input forcing functions then need to be determined to effect a simulation of the operational conditions. With this work, a time domain based testing system has been developed to enable the reproduction of service-acquired dynamic responses on any actual full scale structure in the laboratory, taking into account the full multiple axis dynamics of the system. The system is able to determine the input forcing functions in such a way that, when applied to the teststructure, an accurate reproduction of the in-service measured responses are reproduced on the computer controlled laboratory test rig. The test structure is instrumented with suitable transducers which are used to record the structural dynamic response under operational conditions. The test structure is thereafter installed in a servo-hydraulic actuator test rig in the laboratory. The test rig is excited with synthetic random inputs while simultaneously recording the responses to these inputs. Using the experimental input-output data, a dynamic model of the test system is found by using parametric dynamic system identification techniques. By using the service aquired vibration responses together with the dynamic model, the system inputs may be determined. A series of iterations around this first approximation finally provides a high degree of accuracy in the simulation. To prove the integrity of the developed system, it has been applied to a number of case studies using a variety of different engineering structures, and very accurate results were achieved. / Thesis (PhD)--University of Pretoria, 1993. / tm2015 / Mechanical and Aeronautical Engineering / PhD / Unrestricted

The Global Positioning System (GPS) and other satellite-based positioning systems are often a key component in applications requiring localization. However, accurate positioning in areas with poor GPS coverage, such as inside buildings and in dense cities, is in increasing demand for many modern applications. Fortunately, recent developments in ultra-wideband (UWB) radio technology have enabled precise positioning in places where it was not previously possible by utilizing multipath-resistant wide band pulses. Although ultra-wideband signals are less prone to multipath interference, it is still a bottleneck as increasingly ambitious projects continue to demand higher precision. Some UWB radios include on-board detection of multipath conditions, however the implementations are usually limited to basic condition checks. In order to address these shortcomings, We propose an application of machine learning to reliably detect non-line-of-sight conditions when the on-board radio classifier fails to recognize these conditions. Our solution includes a neural network classifier that is 99.98% accurate in a variety of environments.

This thesis is about measuring charger and discharger properties of dielectrics materials in time domain and transformation of acquired characteristics to the frequency domain. For transformation between time and frequency domain are used Fourier transform and Haman approximation. The result is frequency dependent on loss number. Part of this work is about comparison of these methods in theoretical and practical applications on the basis of accuracy, speed and performance.

This masters thesis is focusing on the issue of passive optic access networks. It is dealing with the limiting factors for broadband connections, especially attenuation of fibre optics and dispersion. It is also dealing with most commonly used standards of passive optic networks. It clarifies the issue of wavelength-division multiplexing, its advantages and disadvantages, used standards, various types of components for the WDM-networks, their characteristics, application etc. In the practical part of the work you can find the measuring and diagnostics of the passive optic network EPON. It contains measuring by the direct method OLTS, measuring by the Pon Power Meter and optic reflectometer OTDR. At the end I am dealing with the measuring of splitter in the rate of 1:16.

This work is focused on fractal dimension utilization for heart rate variability analysis. Both the theory of heart rate variability and the methods of HRV analysis in time domain and using the fractal dimesion are summarized. Short comparsion of time domain and fractal dimension method is presented.

In this work I study the advanced geophysical method - the time domain electromagnetics. In the theoretical part I summarize principles of the method, describe several measuring systems and guide the reader through the software for data processing. I further prove reliability of the applied methodology by forward and inverse computations for a simplified model of supposed target structures. The results show that for the selected configuration of field measurements with a depth range of 100-200 m the influence of 3D structures is significant when placed in a distance smaller than approximately 100 m. In the practical part I test the method in the sedimentary environment and find that results of the method are in accordance with the vertical electrical sounding method. Subsequently, I show that the artificial highly conductive object placed inside the current loop significantly affects the outcomes of the method. Artificial conductive object has only minute effect if placed in a close distance but outside of the current circuit. Besides the theoretical and experimental findings about the reliability of the method I have applied the method for research of maar volcanoes. I have confirmed with high probability the presence of maar volcano near the Jablonná village. The results measured close to the...

This project focuses on wavelength division multiplexing passive optical network (WDM-PON) supervision using optical time domain reflectometer (OTDR) for detection and localization of any fault occurred in optical distribution network. The objective is to investigate the impact of OTDR monitoring signal on the data transmission in the WDM-PON based on wavelength re-use system, where the same wavelength is assigned for both upstream and downstream to each end user. Experimental validation has been carried out to measure three different schemes, i.e. back-to-back, WDM-PON with and without OTDR connection by using 1xN and NxN arrayed waveguide gratings. Furthermore, a comprehensive comparison has been made to trace out the effect of the monitoring signal which is transmitted together with the data through the implemented setup. Finally, the result has confirmed that the OTDR supervision signal does not affect the data transmission. The experiment has been carried out at Ericsson AB, Kista.

Many modern technologies are enabled by the use of thin films and/or nanostructured composite materials. For example, many thermoelectric devices, solar cells, power electronics, thermal barrier coatings, and hard disk drives contain nanostructured materials where the thermal conductivity of the material is a critical parameter for the device performance. At the nanoscale, the mean free path and wavelength of heat carriers may become comparable to or smaller than the size of a nanostructured material and/or device. For nanostructured materials made from semiconductors and insulators, the additional phonon scattering mechanisms associated with the high density of interfaces and boundaries introduces additional resistances that can significantly change the thermal conductivity of the material as compared to a macroscale counterpart. Thus, better understanding and control of nanoscale heat conduction in solids is important scientifically and for the engineering applications mentioned above. In this dissertation, I discuss my work in two areas dealing with nanoscale thermal transport: (1) I describe my development and advancement of important thermal characterization tools for measurements of thermal and thermoelectric properties of a variety of materials from thin films to nanostructured bulk systems, and (2) I discuss my measurements on several materials systems done with these characterization tools. First, I describe the development, assembly, and modification of a time-domain thermoreflectance (TDTR) system that we use to measure the thermal conductivity and the interface thermal conductance of a variety of samples including nanocrystalline alloys of Ni-Fe and Co-P, bulk metallic glasses, and other thin films. Next, a unique thermoelectric measurement system was designed and assembled for measurements of electrical resistivity and thermopower of thermoelectric materials in the temperature range of 20 to 350 °C. Finally, a commercial Anter Flashline 3000 thermal diffusivity measurement system is used to measure the thermal diffusivitiy and heat capacity of bulk materials at high temperatures. With regards to the specific experiments, I examine the thermal conductivity and interface thermal conductance of two different types of nanocrystalline metallic alloys of nickel-iron and cobalt-phosphorus. I find that the thermal conductivity of the nanocrystalline alloys is reduced by a factor of approximately two from the thermal conductivity measured on metallic alloys with larger grain sizes. With subsequent molecular dynamics simulations performed by a collaborator, and my own electrical conductivity measurements, we determine that this strong reduction in thermal conductivity is the result of increased electron scattering at the grain boundaries, and that the phonon component of the thermal conductivity is largely unchanged by the grain boundaries. We also examine four complex bulk metallic glass (BMG) materials with compositions of Zr₅₀Cu₄₀Al₁₀, Cu_46.25Zr_44.25Al_7.5Er₂, Fe₄₈Cr₁₅Mo₁₄C₁₅B₆Er₂, and Ti_41.5Zr_2.5Hf₅Cu_42.5Ni_7.5Si₁. From these measurements, I find that the addition of even a small percentage of heavy atoms (i.e. Hf and Er) into complex disordered BMG structures can create a significant reduction in the phonon thermal conductivity of these materials. This work also indicates that the addition of these heavy atoms does not disrupt electron transport to the degree with which thermal transport is reduced. / Ph. D.

abstract: Several key, open questions in astrophysics can be tackled by searching for and mining large datasets for transient phenomena. The evolution of massive stars and compact objects can be studied over cosmic time by identifying supernovae (SNe) and gamma-ray bursts (GRBs) in other galaxies and determining their redshifts. Modeling GRBs and their afterglows to probe the jets of GRBs can shed light on the emission mechanism, rate, and energetics of these events. In Chapter 1, I discuss the current state of astronomical transient study, including sources of interest, instrumentation, and data reduction techniques, with a focus on work in the infrared. In Chapter 2, I present original work published in the Proceedings of the Astronomical Society of the Pacific, testing InGaAs infrared detectors for astronomical use (Strausbaugh, Jackson, and Butler 2018); highlights of this work include observing the exoplanet transit of HD189773B, and detecting the nearby supernova SN2016adj with an InGaAs detector mounted on a small telescope at ASU. In Chapter 3, I discuss my work on GRB jets published in the Astrophysical Journal Letters, highlighting the interesting case of GRB 160625B (Strausbaugh et al. 2019), where I interpret a late-time bump in the GRB afterglow lightcurve as evidence for a bright-edged jet. In Chapter 4, I present a look back at previous years of RATIR (Re-ionization And Transient Infra-Red Camera) data, with an emphasis on the efficiency of following up GRBs detected by the Fermi Space Telescope, before some final remarks and brief discussion of future work in Chapter 5. / Dissertation/Thesis / Doctoral Dissertation Physics 2019