Two methods of modelling electric current systems by analysis of magnetic field data, with particular reference to the quasi-dc magnetic field of the human leg

This thesis deals with two approaches to the problem of obtaining information about electric current distributions by analysing the associated magnetic field. Both methods have been developed within the context of a particular biomagnetic study, the analysis of the quasi dc magnetic field of the human leg. The techniques have been designed to deal with data sensed by a gradiometer in a series of horizontal scans above the current—carrying region and take full account of the gradiometer configuration. Method 1, the line-dipole technique, analyses each scan individually and calculates the dipole term of a multipole expansion which best characterises the current distribution cross-section immediately below the line of scan. Method 2, the line current loop iterative-perturbative algorithm, uses data from all the scans to compute the coordinates of the best fit line current loop for the whole data map. Both methods have been extensively tested with computer simulated data and with real data from current-carrying wire loops and the results show that both methods are capable of producing an accurate replication of the target system provided it satisfies the initial model assumptions. The dc magnetic field of the human leg has been investigated for a number of normal subjects. The line- dipole technique provides a useful method of characterising the data and indicates regions of high current density which allow inferences to be drawn about the physiological nature of the current generators. Analysis of the field from a leg with a fibula fracture shows significant differences from the normal pattern, although a direct, causal connection with the fracture is not necessarily implied. The line current loop technique has been less successful in achieving a high quality fit to the leg data but this lack of success is consistent with a physiologically reasonable model of the source currents. Although both methods have been designed for this rather specialised biomagnetic inverse problem, they are of more general applicability and may be useful in other fields such as geophysics or non-destructive testing

Defining Areas: Linking Geographic Data in New Zealand

This paper develops a match quality statistic to quantify the trade-off between 'specificity' and 'completeness' when aggregating one regional aggregation to another. We apply this statistic to calculate the degree of mismatch between various regional aggregations for New Zealand using 1991 and 2001 Census Data. A program to calculate mismatch statistics is included as an appendix, as a Stata(r) ado file.Match quality; Geographic Aggregation

Molecular dynamics study of oxygen diffusion in Pr₂NiO_4+δ

Oxygen transport in tetragonal Pr2NiO4+δ has been investigated using molecular dynamics simulations in conjunction with a set of Born model potentials. Oxygen diffusion in Pr2NiO4+δ is highly anisotropic, occurring almost entirely via an interstitialcy mechanism in the a-b plane. The calculated oxygen diffusivity has a weak dependence upon the concentration of oxygen interstitials, in agreement with experimental observations. In the temperature range 800-1500 K, the activation energy for migration varied between 0.49 and 0.64 eV depending upon the degree of hyperstoichiometry. The present results are compared to previous work on oxygen self-diffusion in related K2NiF4 structure materials

Vitello-lipid and vitello-protein deposition in environmentally stressed and non-stressed populations of Morone saxatilis (striped bass)

Summer somatic indices of three and four year old striped bass (Morone saxatilis) from Lake Anna (LA), Virginia, a cooling water reservoir, indicated prey ingestion was not sufficient to maintain growth during summer months when striped bass metabolism was elevated by thermal and hypoxic stress. Vitello-lipid and vitello-protein concentrations of stressed LA striped bass were compared to those of non-stressed striped bass from Smith Mountain Lake (SML) , Virginia, a hydroelectric reservoir. Seasonal comparisons of LA and SML striped bass vitello-lipid concentrations and vitello-protein concentrations showed no significant differences between sites (P [less than or equal to] 0.05). Vitello nutrients were not utilized as metabolic substrates by stressed LA striped bass, indicating striped bass vitello-nutrient deposition is not significantly affected by thermal, hypoxic, and starvation stresses of eight to ten weeks duration

Anisotropic oxygen diffusion in tetragonal La₂NiO_4+δ: molecular dynamics calculations

Molecular dynamics simulations, used in conjunction with a set of Born model potentials, have been employed to study oxygen transport in tetragonal La2NiO4+δ. We predict an interstitialcy mechanism with an activation energy of migration of 0.51 eV in the temperature range 800-1100 K. The simulations are consistent with the most recent experiments. The prevalence of oxygen diffusion in the a-b plane accounts for the anisotropy observed in measurements of diffusivity in tetragonal La2NiO4+δ

Development of a radiation computation dose model for use in ultraviolet phototherapy

The ultimate motivation for this research is to investigate and quantify the nature of ultraviolet radiation for medical application over a variety of skin diseases. While application of both narrow-band and broad-band ultraviolet light have demonstrated great success in the treatment of a multitude of dermatological conditions, over-exposure to this section of the electromagnetic spectrum can be detrimental to human health, and the crux of the issue is striking a balance between maintaining a biologically effective dose while minimizing the impact on the overall health of the patient. Treatment cabins typically consist of a series of ultraviolet emitting lamps surrounded by an array of anodized aluminium reflectors positioned around the lamp to increase the incident dose on the patient in the treatment cabin. Many different factors are important in estimating the patient dose, including the nature of lamp emission, the properties and placement of the reflectors and the position and self-shielding from the patient as well as cabin geometry. Lamp failure can also occur, complicating matters. A dose model that estimates all these factors and quantifies them could be of use in a variety of clinical applications. This research focuses on methods of quantifying these various elements contributing to patient dose, and the creation of a dose model for patients undergoing ultraviolet phototherapy

Interstitialcy diffusion of oxygen in tetragonal La₂CoO_4+δ

We report on the mechanism and energy barrier for oxygen diffusion in tetragonal La2CoO4+δ. The first principles-based calculations in the Density Functional Theory (DFT) formalism were performed to precisely describe the dominant migration paths for the interstitial oxygen atom in La2CoO4+δ. Atomistic simulations using molecular dynamics (MD) were performed to quantify the temperature dependent collective diffusivity, and to enable a comparison of the diffusion barriers found from the force field-based simulations to those obtained from the first principles-based calculations. Both techniques consistently predict that oxygen migrates dominantly via an interstitialcy mechanism. The single interstitialcy migration path involves the removal of an apical lattice oxygen atom out from the LaO-plane and placing it into the nearest available interstitial site, whilst the original interstitial replaces the displaced apical oxygen on the LaO-plane. The facile migration of the interstitial oxygen in this path is enabled by the cooperative titling-untilting of the CoO6 octahedron. DFT calculations indicate that this process has an activation energy significantly lower than that of the direct interstitial site exchange mechanism. For 800-1000 K, the MD diffusivities are consistent with the available experimental data within one order of magnitude. The DFT- and the MD-predictions suggest that the diffusion barrier for the interstitialcy mechanism is within 0.31-0.80 eV. The identified migration path, activation energies and diffusivities, and the associated uncertainties are discussed in the context of the previous experimental and theoretical results from the related Ruddlesden-Popper structures

Advances in the stochastic modelling of satellite-derived rainfall estimates using a sparse calibration dataset

As satellite technology develops, satellite rainfall estimates are likely to become ever more important in the world of food security. It is therefore vital to be able to identify the uncertainty of such estimates and for end users to be able to use this information in a meaningful way. This paper presents new developments in the methodology of simulating satellite rainfall ensembles from thermal infrared satellite data. Although the basic sequential simulation methodology has been developed in previous studies, it was not suitable for use in regions with more complex terrain and limited calibration data. Developments in this work include the creation of a multithreshold, multizone calibration procedure, plus investigations into the causes of an overestimation of low rainfall amounts and the best way to take into account clustered calibration data. A case study of the Ethiopian highlands has been used as an illustration