Investigation of the quality of umbilical artery Doppler waveforms

In Doppler systems which automatically calculate the maximum frequency envelope and pulsatility index (PI) of umbilical artery Doppler waveforms there is the possibility of error in these parameters when the technical quality of the acquired waveform is low. Low quality waveforms may arise when there is an inappropriate set of physical parameters or when there are other sources of noise such as overlying vessels signals. In this thesis the effect of physical parameters on the envelope and on PI are investigated, and also methods for the detection of low quality waveforms are described and tested. A flow phantom which is able to produce realistic looking umbilical artery Doppler waveforms is described. This is based upon microcompruter control of a stepping motor / gear pump combination. The statistics of the Doppler spectra produced using artificial blood and human blood in the phantom are found to be identical. The effect of a number of physical parameters on the simulated umbilical artery waveforms produced using the phantom is investigated. The accuracy of estimation of the envelope and the PI is similar over a wide range of physical conditions. A suitable image processing algorithm for speckle reduction of Doppler waveforms is developed and tested using simulated waveforms from the phantom. Using the flow device it was found that both filtering of the envelope and also speckle suppression of the spectrum improved the accuracy of estimation of the envelope and of the PI. A number of quality indices based upon the degree of noise of the envelope are described. Using the flow device there is found to be a high correlation between the quality index values, and the errors in PI and errors in envelope estimation respectively. In a clinical trial the quality index values from umbilical arteries were compared with the waveform quality as assessed by a skilled observer. The clinical results show that quality indices are able to separate high and low quality waveforms when the indices are calculated from the unprocessed envelope, but not when calculated from the filtered envelop

Spatial and temporal characteristics of benthic invertebrate communities at Culbin Sands lagoon, Moray Firth, NE Scotland, and impacts of the disturbance of cockle harvesting

In the present study, Culbin Sands lagoon, a protected site in NE Scotland, was surveyed every 2 to 4 weeks during a three-year period (1994-1996) to study benthic invertebrate communities. Beds of Mytilus edulis covered 18000 m(2). 53 macroinfaunal species were identified outside these areas. The most conspicuous were: the lugworm Arenicola marina (mean up to 55 casts m(-2)); and bivalves Cerastoderma edule (mean up to 158 ind. m(-2)) and Macoma balthica (mean up to 79 ind. m(-2)) after settlement. The standing stock ranged from 20 to 32 g AFDW m(-2) yr(-1) respectively from more exposed to more sheltered areas. Most species showed a clear recruitment peak in autumn, but others (e.g. Capitella capitata, and Spionidae) displayed several peaks in a year. Communities were also compared between the Sampling sites before and after an incidental disturbance caused by cockle Cerastoderma edule harvesting, which took place in June 1995. One site showed -0.7% variation in the total standing stock, but +22% for smaller-cockles, as larger filter-feeding cockles were removed therefore enhancing their own larval settlement. Polychaete Spionidae Populations also increased after larger cockles were removed. The polychaete Arenicola marina population returned to its normal activities just after the dramatic disturbance of the sediment.info:eu-repo/semantics/publishedVersio

Nonlinear Harmonic Distortion of Complementary Golay Codes

Recent advances in electronics miniaturization have led to the development of low-power, low-cost, point-of-care ultrasound scanners. Low-cost systems employing simple bi-level pulse generation devices need only utilize binary phase modulated coded excitations to significantly improve sensitivity; however the performance of complementary codes in the presence of nonlinear harmonic distortion has not been thoroughly investigated. Through simulation, it was found that nonlinear propagation media with little attenuative properties can significantly deteriorate the Peak Sidelobe Level (PSL) performance of complementary Golay coded pulse compression, resulting in PSL levels of -62 dB using nonlinear acoustics theory contrasted with -198 dB in the linear case. Simulations of 96 complementary pairs revealed that some pairs are more robust to sidelobe degradation from nonlinear harmonic distortion than others, up to a maximum PSL difference of 17 dB between the best and worst performing codes. It is recommended that users consider the effects of nonlinear harmonic distortion when implementing binary phase modulated complementary Golay coded excitations.</p

Modulated extrusion for textured 3D printing

This research utilises a Fused Deposition Modelling 3D Printer to investigate the aesthetics of 3D printing and it's broader applications. The presented research re-evaluates the 3D printer as a tool to manipulate materials, as opposed to a machine that discretely reproduces digital models at a fine resolution. The research questions the utility of automation, and attempts to find a level that permits materially expressive modes of fabrication. The exploration of aesthetics has uncovered a variety of unexpected textures and interesting material properties that may have wider use. For instance, rigid plastic has been extruded and manipulated finer than the extrusion nozzle diameter, which confers flexibility and fabric like qualities to the printed object. The discovered techniques for 3D printed aesthetics are reproducibly reliable and can be incorporated back into orthodox digital-model driven fabrication

Low back pain in junior Australian Rules football: a cross-sectional survey of elite juniors, non-elite juniors and non-football playing controls

<p>Abstract</p> <p>Background</p> <p>Low back pain in junior Australian Rules footballers has not been investigated despite findings that back pain is more prevalent, severe and frequent in senior footballers than non-athletic controls and findings that adolescent back pain is a strong predictor for adult back pain. The aim of this study was to determine the prevalence, intensity, quality and frequency of low back pain in junior Australian Rules footballers and a control group and to compare this data between groups.</p> <p>Methods</p> <p>A cross-sectional survey of male non-elite junior (n = 60) and elite junior players (n = 102) was conducted along with a convenience sample of non-footballers (school children) (n = 100). Subjects completed a self-reported questionnaire on low back pain incorporating the Quadruple Visual Analogue Scale and McGill Pain Questionnaire (short form), along with additional questions adapted from an Australian epidemiological study. Linear Mixed Model (Residual Maximum Likelihood) methods were used to compare differences between groups. Log-linear models were used in the analysis of contingency tables.</p> <p>Results</p> <p>For current, average and best low back pain levels, elite junior players had higher pain levels (p < 0.001), with no difference noted between non-elite juniors and controls for average and best low back pain. For low back pain at worst, there were significant differences in the mean pain scores. The difference between elite juniors and non-elite juniors (p = 0.040) and between elite juniors and controls (p < 0.001) was significant, but not between non-elite juniors and controls. The chance of suffering low back pain increases from 45% for controls, through 55% for non-elite juniors to 66.7% for elite juniors. The chance that a pain sufferer experiences chronic pain is 16% for controls and 41% for non-elite junior and elite junior players. Elite junior players experienced low back pain more frequently (p = 0.002), with no difference in frequency noted between non-elite juniors and controls. Over 25% of elite junior and non-elite junior players reported that back pain impacted their performance some of the time or greater.</p> <p>Conclusions</p> <p>This study demonstrated that when compared with non-elite junior players and non-footballers of a similar age, elite junior players experience back pain more severely and frequently and have higher prevalence and chronicity rates.</p

Wall shear stress measurement in carotid artery phantoms with variation in degree of stenosis using plane wave vector doppler

Wall shear stress (WSS) plays an important role in the formation, growth, and rupture of atherosclerotic plaques in arteries. This study measured WSS in diseased carotid artery phantoms with degrees of stenosis varying from 0 to 60% with both steady and pulsatile flow. Experiments were performed using in silico and real flow phantoms. Blood velocities were estimated using plane wave (PW) vector Doppler. Wall shear stress was then estimated from the velocity gradient near the wall multiplied by the viscosity of a blood-mimicking fluid. The estimated WSS using the in silico phantom agreed within 10% of the ground-truth values (root-mean-square error). The phantom experiment showed that the mean WSS and maximum WSS increased with the increasing degree of stenosis. The simulation and experiment results provide the necessary validation data to give confidence in WSS measurements in patients using the PW vector Doppler technique

The impact of the mixing properties within the Antarctic stratospheric vortex on ozone loss in spring

Calculations of equivalent length from an artificial advected tracer provide new insight into the isentropic transport processes occurring within the Antarctic stratospheric vortex. These calculations show two distinct regions of approximately equal area: a strongly mixed vortex core and a broad ring of weakly mixed air extending out to the vortex boundary. This broad ring of vortex air remains isolated from the core between late winter and midspring. Satellite measurements of stratospheric H2O confirm that the isolation lasts until at least mid-October. A three-dimensional chemical transport model simulation of the Antarctic ozone hole quantifies the ozone loss within this ring and demonstrates its isolation. In contrast to the vortex core, ozone loss in the weakly mixed broad ring is not complete. The reasons are twofold. First, warmer temperatures in the broad ring prevent continuous polar stratospheric cloud (PSC) formation and the associated chemical processing (i.e., the conversion of unreactive chlorine into reactive forms). Second, the isolation prevents ozone-rich air from the broad ring mixing with chemically processed air from the vortex core. If the stratosphere continues to cool, this will lead to increased PSC formation and more complete chemical processing in the broad ring. Despite the expected decline in halocarbons, sensitivity studies suggest that this mechanism will lead to enhanced ozone loss in the weakly mixed region, delaying the future recovery of the ozone hole