Design and Validation of a Prototype Collimation System with Reduced Applicator Weights for Elekta Electron Therapy Beams

The objective of this study was to design an electron collimation system for Elekta Infinity accelerators with significantly reduced applicator weights, while maintaining acceptable in-field beam flatness and out-of-field leakage dose. The design was restricted to 6-20 MeV beams for 6x6 to 25x25 cm2 applicators at 100 cm SSD with the MLCi2 treatment head. In Aim1, measured off-axis profiles showed that the current Elekta collimation system met dose flatness (4%) and IEC leakage dose specifications in the patient plane for custom 7, 13, and 20 MeV beams at MBPCC. Also, Monte Carlo (MC) calculations based on MBPCC beam models sufficiently agreed with measured doses to be useful for collimation design. In Aim 2, fast, analytical models for the electron and photon dose components were developed for calculating dose inside the field and its penumbra during trimmer weight optimization. In Aim 3, 1% electron ranges and out-of-field leakage doses were both computed using MC for copper, lead, and tungsten. At 20 MeV tungsten and lead had comparable ranges (g cm-2), both lower than copper. However, tungsten had lower out-of-field dose, making it the preferred trimmer material. In Aim 4, MC calculations evaluated the effect of diverging the trimmer inner edges on out-of-field dose. Results showed that edges diverging from the virtual source for the upper and middle trimmers gave the least out-of-field dose; the divergence of the lower trimmers edges made little difference. In Aim 5, off-axis positions of the inner and outer trimmer edges computed by a simple model resulted in initial 10x10 and 20x20 cm2 applicator designs having excessive trimmer weights of 7.06 and 10.87 kg, respectively. Trimmer modifications (beveling outer edges, optimizing z-positions, optimizing edge positions, reducing photon jaw positions, and adjusting trimmer thicknesses and bevel shapes) reduced trimmer weights to 3.73 and 5.09 kg, well below the objectives (5.00 and 7.10 kg, respectively). In Aim 6, dose measurements with fabricated 10x10 and 20x20 cm2 prototype applicators confirmed acceptable in-field flatness and out-of-field leakage dose at 7, 13, and 20 MeV, achieving the objective. Also, photon jaw inner edges should be within 1 cm of the optimized locations

In silico modelling of in-host tuberculosis dynamics : towards building the virtual patient

Tuberculosis (TB) accounts for over 1 million deaths each year, despite effective treatment regimens being available. Improving the treatment of TB will require new regimens, each of which will need to be put through expensive and lengthy clinical trials, with no guarantee of success. The ability to predict which of many novel regimens to progress through the clinical trial stages would be an important tool to TB research. as current models are constrained in their ability to reflect the whole spectrum of pathophysiology, particularly as there remains uncertainty around the events that occur. This thesis explores the use of computational techniques to model a pulmonary human TB infection. We introduce the first in silico model of TB occurring over the whole lung that incorporates both the environmental heterogeneity that is exhibited within different spatial regions of the organ, and the different bacterial dissemination routes, in order to understand how bacteria move during infection and why post-primary disease is typically localised towards the apices of the lung. Our results show that including environmental heterogeneity within the lung can have profound effects on the results of an infection, by creating a region towards the apex which is preferential for bacterial proliferation. We also present a further iteration of the model, whereby the environment is made more granular to better understand the regions which are afflicted during infection, and show how sensitivity analysis can determine the factors that contribute most to disease outcomes. We show that in order to simulate TB disease within a human lung with sufficient accuracy, better understanding of the dynamics is required. The model presented in this thesis is intended to provide insight into these complicated dynamics, and thus make progress towards an end goal of a virtual clinical trial, consisting of a heterogeneous population of synthetic virtual patients."“This work was supported by the PreDiCT TB consortium (IMI Joint undertaking grant agreement number 115337, resources of which are composed of financial contribution from the European Union’s Seventh Framework Programme (FP7/2007-2013) and EF-PIA companies’ in kind contribution.)” -- Acknowledgement

Control via electron count of the competition between magnetism and superconductivity in cobalt and nickel doped NaFeAs

Using a combination of neutron, muon and synchrotron techniques we show how the magnetic state in NaFeAs can be tuned into superconductivity by replacing Fe by either Co or Ni. Electron count is the dominant factor, since Ni-doping has double the effect of Co-doping for the same doping level. We follow the structural, magnetic and superconducting properties as a function of doping to show how the superconducting state evolves, concluding that the addition of 0.1 electrons per Fe atom is sufficient to traverse the superconducting domain, and that magnetic order coexists with superconductivity at doping levels less than 0.025 electrons per Fe atom.Comment: 4 pages, 6 figure

Tilt engineering of spontaneous polarization and magnetization above 300 K in a bulk layered perovskite

Crystalline materials that combine electrical polarization and magnetization could be advantageous in applications such as information storage, but these properties are usually considered to have incompatible chemical bonding and electronic requirements. Recent theoretical work on perovskite materials suggested a route for combining both properties. We used crystal chemistry to engineer specific atomic displacements in a layered perovskite, (CaySr1–y)1.15Tb1.85Fe2O7, that change its symmetry and simultaneously generate electrical polarization and magnetization above room temperature. The two resulting properties are magnetoelectrically coupled as they arise from the same displacements

A new 111 type iron pnictide superconductor LiFeP

A new iron pnictide LiFeP superconductor was found. The compound crystallizes into a Cu2Sb structure containing an FeP layer showing superconductivity with maximum Tc of 6K. This is the first 111 type iron pnictide superconductor containing no arsenic. The new superconductor is featured with itinerant behavior at normal state that could helpful to understand the novel superconducting mechanism of iron pnictide compounds.Comment: 3 figures + 1 tabl

FORMATION OF METASTABLE VATERITE CRYSTALS IN A POLYMER MATRIX BY GASEOUS DIFFUSION

A composite consisting of a polymer and calcium carbonate has been synthesized by allowing carbon dioxide to diffuse into a poly(ethylene oxide) film containing a Source of calcium ions. The X-ray pattern of the synthetic composite material shows that the least thermodynamically stable polymorph of calcium carbonate, vaterite is the mineral phase which is formed, rather than the most thermodynamically stable calcite phase. This effect has been seen in other reports of crystallization of inorganic phases which have been mediated by a polymer matrix and/or other organic moieties. In this paper, some possible explanations are presented which may help explain this phenomenon.Publisher's Versio

Synthesizing 35 years of seagrass spatial data from the Great Barrier Reef World Heritage Area, Queensland, Australia

The Great Barrier Reef World Heritage Area in Queensland, Australia contains globally significant seagrasses supporting key ecosystem services, including habitat and food for threatened populations of dugong and turtle. We compiled 35 years of data in a spatial database, including 81,387 data points with georeferenced seagrass and species presence/absence, depth, dominant sediment type, and collection date. We include data collected under commercial contract that have not been publicly available. Twelve seagrass species were recorded. The deepest seagrass was found at 76 m. Seagrass meadows are at risk from anthropogenic, climate and weather processes. Our database is a valuable resource that provides coastal managers and the global marine community with a long-term spatial resource describing seagrass populations from the mid-1980s against which to benchmark change. We address the data issues involved in hindcasting over 30 years to ensure confidence in the accuracy and reliability of data included

Environmentally-induced changes to brain morphology predict cognitive performance

The relationship between the size and structure of a species’ brain and its cognitive capacity has long interested scientists. Generally this work relates interspecific variation in brain anatomy with performance on a variety of cognitive tasks. However, brains are known to show considerable short-term plasticity in response to a range of social, ecological and environmental factors. Despite this, we have a remarkably poor understanding of how this impacts on an animal’s cognitive performance. Here, we non-invasively manipulated the relative size of brain regions associated with processing visual and chemical information in fish (the optic tectum and olfactory bulbs, respectively). We then tested performance in a cognitive task in which information from the two sensory modalities was in conflict. Although the fish could effectively utilise both visual and chemical information if presented in isolation, when they received cues from both modalities simultaneously, those with relatively better developed optic tecta showed a greater reliance on visual information, while individuals with relatively better developed olfactory bulbs showed a greater reliance on chemical information. These results suggest that short-term changes in brain structure, possibly resulting from an attempt to minimise the costs of developing unnecessary but energetically expensive brain regions, may have marked effects on cognitive performance

Case Series on Veno - venous extracorporeal membrane oxygenation (VV-ECMO) as a bridge to complete recovery in influenza type A related refractory ARDS

Introduction: Influenza A sequelae range from mild symptoms to acute respiratory distress syndrome (ARDS), which can be refractory to conventional ventilator therapy. We present a case series of three non-H1N1 Influenza patients with ARDS, who completely recovered after VV-ECMO. Case Presentation: In January and February 2013, we experienced three cases of Influenza A induced ARDS that failed conventional ARDS ventilator therapy. All three patients presented with typical flu-like symptoms, which deteriorated over several days, requiring intubation. They were all treated with oseltamivir. They had bilateral chest infiltrates on chest x-rays. After a few days of failing conventional treatment these patients were placed on VV-ECMO using Avalon Dual Lumen catheters. Presented 24th Annual ELSO Conference

Temporal variations in river water surface elevation and slope captured by AirSWOT

The Surface Water and Ocean Topography (SWOT) satellite mission aims to improve the frequency and accuracy of global observations of river water surface elevations (WSEs) and slopes. As part of the SWOT mission, an airborne analog, AirSWOT, provides spatially-distributed measurements of WSEs for river reaches tens to hundreds of kilometers in length. For the first time, we demonstrate the ability of AirSWOT to consistently measure temporal dynamics in river WSE and slope. We evaluate data from six AirSWOT flights conducted between June 7–22, 2015 along a ~90 km reach of the Tanana River, AK. To validate AirSWOT measurements, we compare AirSWOT WSEs and slopes against an in situ network of 12 pressure transducers (PTs). Assuming error-free in situ data, AirSWOT measurements of river WSEs have an overall root mean square difference (RMSD) of 11.8 cm when averaged over 1 km2 areas while measurements of river surface slope have an RMSD of 1.6 cm/km for reach lengths >5 km. AirSWOT is also capable of recording accurate river WSE changes between flight dates, with an RMSD of 9.8 cm. Regrettably, observed in situ slope changes that transpired between the six flights are well below AirSWOT's accuracy, limiting the evaluation of AirSWOT's ability to capture temporal changes in slope. In addition to validating the direct AirSWOT measurements, we compare discharge values calculated via Manning's equation using AirSWOT WSEs and slopes to discharge values calculated using PT WSEs and slopes. We define or calibrate the remaining discharge parameters using a combination of in situ and remotely sensed observations, and we hold these remaining parameters constant between the two types of calculations to evaluate the impact of using AirSWOT versus the PT observations of WSE and slope. Results indicate that AirSWOT-derived discharge estimates are similar to the PT-derived discharge estimates, with an RMSD of 13.8%. Additionally, 42% of the AirSWOT-based discharge estimates fall within the PT discharge estimates' uncertainty bounds. We conclude that AirSWOT can measure multitemporal variations in river WSE and spatial variations in slope with both high accuracy and spatial sampling, providing a compelling alternative to in situ measurements of regional-scale, spatiotemporal fluvial dynamics