Nondestructive Electromagnetic Characterization of Uniaxial Materials

In this dissertation, a method for the simultaneous non-destructive extraction of the permittivity and permeability of a dielectric magnetic uniaxial anisotropic media is developed and several key contributions are demonstrated. The method utilizes a single fixture in which the MUT is clamped between two rectangular waveguides with 6 x 6 PEC flanges. The transmission and reflection coefficients are measured, then compared with theoretically calculated coefficients to find a least squares solution to the minimization problem. One of the key contributions of this work is the development of the total parallel plate spectral-domain Green\u27s function by two independent methods. The Green\u27s function is thereby shown to be correct in form and in physical meaning. A second significant contribution of this work to the scientific community is the evaluation of one of the inverse Fourier transform integrals in the complex plane. This significantly enhances the efficiency of the extraction code. A third significant contribution is the measurement of a number of uniaxial anisotropic materials, many of which were envisioned, designed and constructed in-house using 3D printing technology. The results are shown to be good in the transverse dimension, but mildly unstable in the longitudinal dimension. A secondary contribution of this work that warrants mention is the inclusion of a flexible, complete, working code for the extraction process. Although such codes have been written before, they have not been published in the literature for broader use

Electron Multipactor: Theory Review, Comparison and Modeling of Mitigation Techniques in ICEPIC

Mitigation approaches for single surface multipactor at dielectric windows are investigated using Particle-In-Cell (PIC) simulations. Initially baseline susceptibility diagrams are constructed analytically and compared with self-consistent, dynamic system trajectories. The power deposited on the surface of a dielectric window in an HPM system is considered using three different methods and the results of PIC simulations. Geometric mitigation is then considered by varying the window orientation with respect to the HPM electric held. Small angular deviations, less than 20 degrees, from the nominal case of normal incidence show dramatic changes in the susceptibility diagram. A materials approach to mitigation is then considered. Titanium Nitride, TiN, coatings applied to the dielectric surface can substantially reduce the secondary emission yield. Representative modifications of the secondary emission yield are simulated and the resulting susceptibility diagrams are discussed

Assimilation of real-time riometer measurements into models of 30 MHz polar cap absorption

Space weather events may adversely affect high frequency (HF) radio propagation, hence the ability to provide now-casting and forecasting of HF radio absorption is key for industries that rely on HF communications. This paper presents methods of assimilating 30 MHz radio absorption measurements into two types of ionospheric polar cap absorption (PCA) model to improve their performance as nowcasting tools. Type 1 models calculate absorption as m times the square root of the flux of solar protons above an energy threshold, Et. Measurements from 14 riometers during 94 solar proton events (1995-2010) are assimilated by optimising the day and night values of m by linear regression. Further non-linear optimisations are demonstrated in which parameters such as  Et are also optimised and additional terms characterise local time and seasonal variations. These optimisations reduce RMS errors by up to 36%. Type 2 models incorporate altitude profiles of electron and neutral densities and electron temperatures. Here the scale height of the effective recombination coefficient profile in the D-region is optimised by regression. Furthermore, two published models of the rigidity cut-off latitude (CL) are assessed by comparison with riometer measurements. A small improvement in performance is observed by introducing a three-hour lag in the geomagnetic index Kp in the CL models. Assimilating data from a single riometer in the polar cap reduces RMS errors below 1 dB with less than 0.2 dB bias. However, many high-latitude riometers now provide absorption measurements in near real time and we demonstrate how these data may be assimilated by fitting a low-order spherical harmonic function to both the measurements and a PCA model with optimised parameters

Dynamic Institutionalization of the Terms of Presentation in Information Technology Management

This report of research in progress describes a study of how senior executives incorporate statements concerning information technology innovation into their public representations of firm performance, activities, and direction. Drawing on institutional theory and using longitudinal content analysis, we consider how discourse in the wider business milieu potentially shapes and constrains executives\u27 representations

Predicting the response of coastal wetlands of Southeastern Australia to sea-level rise

Coastal saltmarsh is an endangered ecological community in New South Wales and sea-level rise has been listed as a key threatening process. Over the previous five decades moderate rates of sea-level rise have coincided with the invasion of saltmarsh by mangrove. Surface elevation tables (SETs) were installed in 12 coastal wetlands in Southeastern Australia to establish elevation and accretion trajectories for comparisons with mangrove encroachment of saltmarsh and sea-level rise. SETs confirmed that the elevational response of wetlands is more complex than accretion alone and elevation changes may also be attributed to below-ground processes that alter the soil volume such as subsidence/compaction, groundwater volume fluctuations, and below-ground biomass changes. A simple modelling approach was employed to establish a relationship between the observed rate of mangrove encroachment of saltmarsh and relative sea-level rise, which incorporates the eustatic component of sea-level rise and changes in the marsh elevation. Increasing access to high resolution digital elevation models will enhance our capacity to predict the response of coastal wetlands to sea-level rise. Long-term datasets of elevation dynamics and improved understanding of the feedback mechanisms influencing marsh elevations will further enhance our modelling capacity

Coastal saltmarsh vulnerability to climate change in SE Australia

Coastal saltmarsh has been listed as an Endangered Ecological Community in New South Wales. Recent research has highlighted the importance of coastal saltmarsh as a source of nutrition for fish, a nocturnal feeding habitat for microbats, and a roosting habitat for several species of migratory shorebirds. Since European colonisation, coastal saltmarsh has been reclaimed for agricultural, residential and industrial use, and the past five decades has seen a consistent replacement of saltmarsh by mangrove throughout SE Australia. Analysis of data from the network of Surface Elevation Tables in NSW and Victoria has demonstrated a link between the replacement of saltmarsh by mangrove and relative sea-level rise. However, this is not the only potential climate change impact, given the strong inverse relationship between saltmarsh diversity and temperature in Australia. Saltmarsh species diversity increases with latitude, with temperature explaining more than 80 percent of variability in saltmarsh species numbers between bioregions. A southward translation of climatic zones in Australia would pose significant challenges to the preservation of saltmarsh diversity at a continental scale

Evaluating the mobile web accessibility of electronic text for print impaired people in higher education

The aim of this extended abstract is to demonstrate a framework that provides a novel solution for evaluating the mobile web accessibility of electronic text for print impaired people in Higher Education (HE). The current framework explores over 500 device settings. Furthermore, the scope of this research is outlined alongside two research questions. The paper then concludes by suggesting the potential impact this research could have on existing standards, the public availability of metadata and guidelines, and the automatic generation of personalised eTexts as per user need