Cause and Amelioration of MRI-Induced Heating Through Medical Implant Lead Wires

The RF fields present in magnetic resonance imaging (MRI) scanners can induce hazardous heating in patients wearing medical implants. The inherent design and locale of deep brain stimulators (DBS) and spinal cord stimulators (SCS) make them particularly susceptible. We apply antenna concepts and use electromagnetic (EM) simulation to explain the phenomenon and anticipate its sensitivity to lead wire length. We anticipate that a DC resistance of less than 50 Ω/m and an RF impedance of more than 1:23kΩ/m would be required for a safe electrode for SCS use. We investigate the possibility of manipulating wire conductivity and diameter in order to use the skin depth effect to achieve a safe electrode. The effect of the thickness and permittivity of insulation surrounding the wires is explored

Impulse TDR and its application to measurement of antennas

The traditional stimulus signal used in a time-domain reflectometer (TDR) is a voltage step. We propose an alternative technique, whereby an impulse generator is employed in place of the step generator in a TDR. The advantage conferred by “impulse TDR” is that more energy is available at higher frequencies than with conventional step TDR, and so a higher bandwidth and signal-to-noise ratio (SNR) is achieved. The theoretical result is compared with measurement

Measurement of antennas and microwave components using time-domain reflectometry of a voltage impulse

Band-pass microwave systems such as ultra-wideband antennas are traditionally characterized in the frequency-domain through a vector network analyzer in an anechoic chamber. A recent study proved antennas could be accurately measured in the time-domain using a step-function time-domain reflectometer (TDR), without the need for an anechoic chamber. We propose a new advance in the TDR characterization method. An impulse generator is employed in place of the step generator in a TDR set-up. The advantage conferred by this change is that more energy is available beyond a given frequency than with a step, and so a higher signal-to-noise ratio is achieved. The theoretical result is compared with measurement

A coevolutionary framework for engaging trading partners in interorganisational e-commerce

University of Technology, Sydney. Faculty of Information Technology.The objective of this research was to produce a better understanding of the way trading partners engage in interorganisational e-commerce systems in order to help practitioners. An interpretive philosophical approach was taken via an empirical study of ten e- commerce interorganisational systems, spanning a variety of technological approaches, trading scenarios and industry settings. Using semi-structured interviews, qualitative data were collected and a thematic analysis undertaken. The results suggested coevolutionary theory as a useful perspective for understanding the context. An in-depth case study was then used to build a detailed coevolutionary interpretation for the history of change, technological development and engagement in a single system. The resulting framework incorporates social and technological components in a three level coevolutionary hierarchy. The e-commerce system is reconceptualised as a socio- technical trading system, and the move to Internet based trading operations as part of the ongoing evolution of that system. Under this interpretation interdependencies and coevolutionary effects, both between components and between levels, lie at the heart of understanding why trading partners are successfully or unsuccessfully engaged in e- commerce. Successful engagement is characterised by positive feedback loops, and failure is characterised by negative feedback loops and whole-part coevolutionary competition

Water deficit responses of non-nodulated and nodulated Vicia faba (broad bean) when supplied with various forms on concentrations of medium nitrogen nutrition

A Thesis submitted to the Faculty of Science, Technology & Design, University of Luton, in partial fulfilment of the requirements for the Degree of Doctor of PhilosophyV. faba fixes nitrogen effectively (Richards & Soper, 1979), however nitrogen fixation is reportedly energetically expensive and water deficit sensitive. Research was designed to determine whether medium nitrogen applications would result in increased productivities in V. faba, particularly during water deficits. Non-nodulated and nodulated V. faba were subjected to gradual water deficit imposition, and were supplied with a variety of medium nitrogen nutrition. Nitrogen fixing V. faba exhibited greater productivities than V. faba which were supplied with low medium nitrate concentrations (0.8 roM N), even during water deficits. Plant performance parameters (growth; net photosynthesis; nitrogen assimilatory enzyme activities; osmotic adjustment) were greater in nodulated than in non-nodulated 'no nitrate' supplied V. faba throughout water deficits, inferring water deficit tolerance for nitrogen fixation. However significantly greater plant performance paramaters were exhibited in V. faba when supplied with increasingly concentrated medium nitrogen nutrition (> 0.8 roM N) than when reliant on nitrogen fixation. In contrast to the bulk of previous literature, NR activities were maintained in V. faba until water deficits became severe, inferring a role for nitrate assimilation in nitrogenous osmotica production. Medium ammonia additions resulted in the exhibition of significantly increased root biomasses; cumulative leaf areas (important for a green manure crop); heights; and nitrogen assimilation in V. faba throughout water deficits, and accordingly in increased osmotic adjustment (including compatible solute accumulation), protein concentrations and vegetative yields. Greater plant productivities in v. faba when supplied with medium ammonia additions were attributed in part to lower associated assimilatory costs for ammonia than nitrate nutrition (Raven, 1992). Results indicated increased metabolism as opposed to storage of medium ammonia, and therefore potentially alleviated 'sink size' feedback inhibition of photosynthesis and nitrogen metabolism in V. faba when supplied with medium ammonia additions. Furthermore ammonia supplied V. faba may have been predisposed towards water deficit tolerance. In summary V. faba exhibited significantly greater nitrogen assimilation; osmotic adjustment; net photosynthesis; and growth when supplied with increasingly concentrated medium nitrogen nutrition (and particularly with medium ammonia additions) than when reliant on nitrogen fixation, both during periods of adequate irrigation and during water deficits

SPRINT AND DISTANCE SWIMMERS: THE SAME ANIMAL?

In this talk the techniques of sprint and distance swimmers are discussed with a view to informing coaches of the similarities and differences between these groups. In the past it has been reported that sprint and distance swimmers are different in several aspects of technique. However, previous comparisons were at the respective race pace and sprint and distance specialists have not been compared when swimming at the same pace. Therefore it is difficult for coaches to know whether to teach the swimmers the same way when developing good technique. This talk presents new information based on recent scientific research conducted at the Centre for Aquatics Research and Education (CARE). The variables of interest were: average swim speed, stroke length, stroke frequency, stroke index, hand stroke pattern, foot range of motion, elbow angle, shoulder and hip roll angle and stroke phase durations. Interesting and unexpected findings emerged that have implications for the way specialist sprint and distance swimmers should be coached