Quantum turbulence in two dimensional Bose-Einstein condensates

We examine the energy cascades and quantum vortex structures in two-dimensional quantum turbulence through a special unitary time evolution algorithm. An early attempt at using the Lattice Boltzmann Method proved successful in correctly representing some features of the Nonlinear Schrodinger System (NLS), such as the phase shift following the one-dimensional soliton-soliton collision, as well as the two-dimentional modulation instability. However, to accurately evaluate NLS, the implicit Euler method is required to resolve the time evolution, which is computationally expensive. A more accurate and efficient method, the Quantum Lattice Gas model is employed to simulate the quantum turbulence governed by the Gross-Pitaevskii equation, an equaiton that describes the evolution of the ground state wave function for a Bose-Einstein condensate (BEC). It is discovered that when the ratio of the internal energy to the kinetic energy is below 0.05, an unexpected short Poincare recurrence occurs independent of the initial profile of the wave function. It is demonstrated that this short recurrence is destroyed as the internal energy is strengthened. to compare the two-dimensional quantum turbulence with its classical counterpart, the incompressible energy spectra of quantum turbulence is analyzed. However, the result reveals no sign of dual cascades which is a hallmark of the classical incompressible two-dimensional fluid (inverse energy cascade to large scales with a direct cascade of enstrophy to small scales). It is the spectra of the compressible energy that can exhibits multiple cascades, but this is strongly dependent on the initial condition

Translating 3D Gel Dosimetry Research into Clinical Routine Use in Radiotherapy

PhDRadiotherapy involves the treatment of tumours with ionising radiation. Technological advances have improved the ability to conform dose distributions to tumours in three dimensions (3D) and thereby reduce morbidity. However, sophisticated measurement devices are required to verify these complex distributions and ensure their accuracy. Radiation-sensitive gels, including polymer and Fricke gels, are a potential solution to this 3D dosimetry problem. Scanning these detectors using imaging methods such as magnetic resonance imaging (MRI) provides quantifiable images of dose distribution. Despite research efforts, 3D gel dosimetry has not yet been implemented as a routine dosimetry tool in clinical radiotherapy. This thesis aims to investigate the implementation of Fricke gel detectors within a clinical radiotherapy department. The existing literature was reviewed to establish what evidence already existed on the dosimetric accuracy of Fricke gel detectors. This review highlighted gaps for many important dosimetric characteristics and a lack of a systematic approach to the testing of these detectors. Basic dosimetric characteristics were then investigated using test tube Fricke gel samples and an MR spectrometer. These experiments showed an excellent basic precision over a dose range of 3 to 20Gy. However, detectors need to be scanned within a certain time of irradiation to avoid signal drift. There was no evidence of any dependence of response on dose rate, energy or fractionation. Larger volume detector samples were analysed using a 3T MRI scanner. Detector response was homogeneous and did not vary with volume. Post-irradiation blurring of the measured distribution due to ferric ion diffusion was within acceptable limits if detectors were scanned within 2 hours following irradiation for typical clinical dose gradients. Finally, large volume Fricke gel detectors were used to measure complex VMAT stereotactic plans, describing the integrated dose distribution with sufficient accuracy and demonstrating clear potential to be applied to our clinical practice.Barts Charity grant reference 691-1003; Translating Polymer Gel Dosimetry Research into Clinical Routine Use in Radiotherap

Development of Many-Body Potential for Deformation Study in Al-Tin Nanolayered Composites

A novel interatomic potential of ternary Al-Ti-N has been developed to study the deformation behavior of Al-TiN nanolaminates. The ternary nanolayered Al-TiN composite has attracted a lot of interest due to its combination of strength and ductility. The current analysis on the system has been primarily concentrated on continuum models which are inadequate to explain the key deformation events such as nucleation and interaction of dislocations. Progress in the preferred atomistic approach has been hampered however by the lack of available interatomic potential optimized for the ternary system. I developed a many-body potential based on embedded atomic model (EAM) by employing the force-fitting code Potfit to sample the energy and force data generated from the ab-initio molecular dynamics simulations of the ternary system using VASP code. The potential\u27s analytical EAM function was subsequently optimized and utilized to simulate structures of bulk Al & TiN and Al-TiN nanolaminates. I then focused on modeling the deformation behavior of Al-TiN multilayers under compression through classical molecular dynamics simulations. I found that the total bilayer thickness as well as volume ratio between TiN and Al nanolayers play a major role in controlling the dislocation nucleation and mobility and the stress accumulation at the layer interface and thus determine the deformation behavior and failure mechanisms of the nanolayered composites

Proceedings of the Salford Postgraduate Annual Research Conference (SPARC) 2011

These proceedings bring together a selection of papers from the 2011 Salford Postgraduate Annual Research Conference(SPARC). It includes papers from PhD students in the arts and social sciences, business, computing, science and engineering, education, environment, built environment and health sciences. Contributions from Salford researchers are published here alongside papers from students at the Universities of Anglia Ruskin, Birmingham City, Chester,De Montfort, Exeter, Leeds, Liverpool, Liverpool John Moores and Manchester