II/VI metastable sulphides : fundamental studies of MBE growth, characterization and nanostructure formation

This thesis presents a fundamental study of II-VI metastable sulfides. Details of the growth by Molecular Beam Epitaxy (MBE) and characterization of CrS,ZnS,MgS, and ZnMgSSe structures on GaP and GaAs substrates are presented. Multilayer structures of ZnS/CrS and ZnMgS/CrS were grown on GaP substrates and characterized using X-ray interference. Asymmetric X-ray spectra indicated the presence of mosaic structure in the layers. A discussion on solutions to the disordered surface is presented. Superlattice structures were designed to contain 100Å of CrS. These samples were sent to the Polish academy of science for further analysis of magnetic properties. The surface morphology of zinc blende MgS layers grown on ZnSe buffer layers has been investigated by AFM. Nanowire formation is studied as a function of flux ratio and MgS layer thickness. Typical wire dimensions were found to be 0.6μm (length), 900Å (width), and 20Å (height). The method of wire formation is consistent with an anisotropic relaxation of the MgS layer by mismatch dislocations leading to a surface instability by the Asaro-Tiller-Grinfield mechanism. RHEED patterns from zincblende MgS (100) surfaces have been observed during growth, annealing and both during and after irradiation of the surface with an Mg flux. The results are compatible with the c(2x2) surface being formed from a ZnMgS alloy which converts to a pure MgS 4x1 reconstruction on Mg irradiation. Samples containing ZnMgSSe alloy were grown and analyzed by X-ray Interference. The alloy composition was found to be Zn0.20Mg0.80S0.64Se0.36. Samples with this composition are shown to be single phase using transmission electron microscopy. Structures with Zn0.20Mg0.80S0.64Se0.36 barriers were grown with ZnSe quantum wells and CdSe quantum dots, and showed good quantum confinement. The incorporation of Zn0.20Mg0.80S0.64Se0.36 in an epitaxial lift off technology has also been demonstrated

Cyclic Porewater Pressure Generation in Intact Silty Soils

The results of cyclic strain-controlled, constant volume direct simple shear (CDSS) tests and field shaking tests have been evaluated for intact, natural, low-plastic silts from six different fine-grained soils with 54%–100% fines content, 47%–83% silt content, and plasticity indices (PI) ranging from nonplastic to 16. These tests constitute a subset of a larger archive of CDSS tests performed on silt deposits from the Pacific Northwest, British Columbia, and Alaska collected and analyzed by the co-authors. The cyclic data are presented in this paper for two objectives: (a) to characterize cyclically-induced excess pore pressure generation in intermediate soils with various soil index properties and stress histories, and (b) to provide calibrated Vucetic and Dobry model parameters for simulating excess pore pressure generation in the silt soils based on the data and trends presented in the first objective. The CDSS test results showed that excess pore pressure ratios decrease with PI over the narrow range of PI evaluated and decrease with overconsolidation ratio. The cyclic threshold shear strain amplitude for pore pressure generation extracted from field shaking tests on silts were within the range proposed in the literature, confirming that the cyclic threshold shear strain amplitude is a fundamental soil property. Calibrated Vucetic and Dobry model parameters for these intermediate, fine-grained silts were significantly different than those reported for sands in the literature and were heavily influenced by the overconsolidation ratio. The calibrated parameters obtained in this study can be used as a benchmark in selecting model parameters for silts

Understanding Democratic Engagement at the Micro-Level: Communication, Participation and Representation

Theoretical and ‘real world’ research into democratic engagment concentrates on larger-scale contexts. There is an accompanying tendency to focus on participation, neglecting other aspects of engagement. The thesis rethinks the notion of democratic engagement by dividing it into three analytically distinct, but interwoven, aspects namely communication, participation and representation, and drawing attention to small-scale or micro-level contexts. Understanding the communicative, participative and representative aspects of engagment in micro-level settings favours a case study approach and a research strategy designed to capture the minutiae of experiences of engagement. ‘Mossbank’, a neighbourhood in a small-to-medium sized Scottish town, has been chosen as an appropriate case. Mossbank is undergoing a physical and social regeneration initiative that has created new sites of democratic activity centred on Mossbank-related issues. It is also a setting where democratic engagement is likely to be constrained. A flexible mixed methods approach to data collection has been adopted using questionnaires, interviews, documentary analysis and non-participative observation, enabling the generation of ‘rich’ and ‘thick’ data. A theoretically informed analytical framework is used to explore the different aspects of democratic engagement in Mossbank. Here, Iris Marion Young’s theorising on communication in deliberative settings has been particularly influential. Democratic engagement in Mossbank is dominated and constrained by formal, familiar and broadly conventional institutions, processes and roles ‘imported’ from established larger-scale democratic settings. Less visible, context-specific factors also have an influence. ‘Messy’ practices and asymmetry affect the ‘quality’ of communication. Participation in democratic processes has its own particular constraining characteristics related to individual motivations and abilities to ‘fit in’ and ‘succeed’ within pre-existing processes. Representation in Mossbank is distant and sporadic, culminating in the evolution of an increasingly brokered approach to the relationship, administered by an intermediary. The thesis contributes to ‘empirical’ debates relating to the scope and nature of democratic engagement. This is especially relevant given the continued growth and development of micro-level democratic institutions and processes in developed democracies. The thesis also contributes to debates concerning the nature and extent of the ‘dialogue’ between normative ideals of democracy and engagement, and research into ‘real world’ democratic engagement

An investigation of the detection and treatment of colorectal liver metastases

In the United Kingdom, colorectal cancer creates a significant health burden, with over 34 000 new cases diagnosed each year and over 16 000 deaths per year. Almost 50% of patients with colorectal cancer will develop liver metastases: up to 25% will have liver metastases at time of initial presentation with the remaining 25% developing liver metastases during the course of their disease. Death from hepatic metastases accounts for a large percentage of colorectal cancer mortalities and if left untreated the prognosis is poor, with median survival from 5 to 21 months with almost none alive at 5 years. Surgical resection offers the only potential curative treatment for colorectal liver metastases with the five year survival rate varying in the literature from 25% to 51%. Hepatic surgery was associated with high morbidity and mortality and it is only since the 1990s that an evidence base has been published showing improved long term outcomes. Radiological imaging plays an essential role in the detection and characterisation of colorectal liver metastases. Accurate staging of the disease allows patient selection for hepatic surgery. Despite recent and significant technological advances in radiological imaging, up to 50% of patients that have undergone curative partial hepatectomy will develop hepatic recurrence in the first two years after surgery. Evidence from growth rate studies has shown that colorectal liver metastases are slow growing and that these recurrences were present at the time of initial staging. Therefore, the problem of occult liver metastases remains. This thesis has assessed the potential clinical role of a new imaging modality in the detection of colorectal liver metastases: contrast enhanced ultrasound (CE-US). Initially a prospective trial using percutaneous CE-US with intravenous administration of an ultrasound contrast agent that has been used primarily in cardiac imaging was performed. The results of this study found that CE-US enhanced late phase vascular imaging. This is an important finding as the persistence of a hypoechoic liver lesion in to the late phase of CE-US imaging is typical of a colorectal liver metastasis and an agent that optimises the late phase would allow improved characterisation of colorectal liver metastases. As a result, CE-US was then compared to percutaneous unenhanced ultrasound and found to have improved sensitivity and accuracy in the detection of colorectal liver metastases (sensitivity 100%, accuracy 90.8% versus 64.4% and 64.4% respectively). Furthermore, the optimal late phase imaging was achieved by the lowest dose of agent (0.4mL) that would allow repeated injections if incorporated into routine clinical practice. These findings support the growing evidence base for percutaneous CE-US and it is likely that CE-US will replace unenhanced ultrasound in routine clinical practice. (Abstract shortened by ProQuest.)

The relationship between sarcopenia and survival at 1 year in patients undergoing elective colorectal cancer surgery

Background: Colorectal cancer remains a common cause of cancer death in the UK, with surgery being the mainstay of treatment. An objective measurement of the suitability of each patient for surgery, and their risk–benefit calculation, would be of great utility. We postulate that sarcopenia (low muscle mass) could fulfil this role as a prognostic indicator. The aim of this study was to determine the relationship between sarcopenia and long-term outcomes in patients undergoing elective bowel resection for colorectal cancer. Methods: One hundred and sixty-three consecutive patients who had elective curative colorectal resection for cancer were eligible for inclusion in the study. Psoas muscle mass was assessed on preoperative computed tomography scan at the level of the L3 vertebra and standardised for patient height (total psoas index, TPI). Sarcopenia (low muscle mass) was defined as < 524 mm2/m2 in males and 385 mm2/m2 in females. In addition to clinical–pathological parameters, postoperative complications were recorded and patients were followed up for mortality for 1 year after surgery. Results: Sarcopenia was present in 19.6% of the study participants and was significantly related to body mass index (p = 0.007), 30-day mortality (p = 0.042) and 1-year mortality (p = 0.046). In univariate analysis, American Society of Anesthesiologists grade (p = 0.016), tumour stage (p = 0.018) and sarcopenia (p = 0.043) were found to be significant independent predictors of 1-year mortality. Conclusions: This study has found sarcopenia to be prevalent in patients with colorectal cancer having elective surgery. Independent of age, sarcopenia was associated with poorer 30-day mortality and survival at 1 year. Measurement of muscle mass preoperatively could be used to stratify a patient’s risk, allowing targeted strategies such as prehabilitation, to be implemented to modify sarcopenia and improve long-term outcomes for patients