Calcium carbonate growth and dissolution to the nanoscale

This thesis describes three examples of how the functionality of a growth surface affects the crystallisation of CaC03; investigates the dissolution of calcium carbonates and phosphates on the microscale; and describes a new atomic force microscopy (AFM) method which has been used to investigate the reactivity of the (104) surface of single calcite microcrystals. Growth surfaces bearing carboxylic acid- functionalised nanoparticles were prepared by deposition onto glass using a layer-by-layer method with poly(allylamine) hydrochloride as the cross linker. These surfaces were found to influence the extent of CaC03 crystallisation, which increased with nanoparticle surface coverage. For these nucleation experiments, two crystal growth techniques were used: the Kitano method, in which the supersaturation of the growth solution slowly increased with time; and a jet crystallisation method, incorporating the mixing of two undersaturated solutions to create a supersaturated solution which was jetted onto the surface of interest via a specially designed cell. Calcite was the predominant CaCC>3 polymorph formed on these surfaces, with a high proportion of the crystals nucleating on the (015) plane rather than on tire stable (104) plane, thus showing that nanoparticles have an orientational effect on CaCOj crystallisation. Functionalisation of gold surfaces was achieved via the deposition of self-assembled monolayers (SAMs) and the effect of an applied potential on CaCC>3 nucleation was investigated. Application of a potential more negative than the potential of zero charge to any of the functionalised SAM surfaces resulted in the inhibition of CaC(>3 nucleation, whereas at more positive potentials, extensive vaterite growth was evident These studies showed that the extent of CaCC>3 nucleation could be tuned readily via the applied potential. K coli bacterial biofilms served as substrates for experiments with direct implications on household care. The biofilms dramatically affected the crystallisation of CaCC>3, first by acting as nucleation centres for growth, and, secondly, causing significant surface and structural damage to the crystals formed. Stabilisation of crystals from unusual nucleating planes, (012) and (015), was also evident. As a new approach for investigating proton-promoted dissolution, an ultramicroelectrode was used to direct a flux of protons towards a calcite surface, by the oxidation of water. Etch pit analysis revealed that the pit volumes increased with increasing proton flux, in a linear fashion. Modelling this process using the finite element method allowed the rate constant for dissolution to be calculated. Dissolution of more complex calcium carbonate and phosphate simulated limescale pellets was also addressed using this technique, allowing the reactivity of a range of materials to be ranked. AFM, combined with an inverted optical microscope, was used to study the growth of individual surfaces of calcite (104) microcrystals, which were shown to exhibit a single spiral growth hillock. Growth rates of the individual spirals were found to be dependent on solution supersaturation and controlled by diffusion of species to the crystal from bulk solution. The step patterns formed were shown to depend strongly on the supersaturation. This methodology also allowed the effects of maleic acid, as a crystal growth inhibitor, to be monitored

Experiences of social welfare policy in the context of caring and bereavement in Western Sydney

University of Technology Sydney. Faculty of Health.: Caring and bereavement in the context of life-limiting illness has been associated with a myriad of challenges for informal carers that may precipitate social welfare needs, including those related to income support and housing. Structural determinants such as interactions with government agencies and social welfare policy possess potential to contribute to inequity, yet their impact upon carers pre- and post-death is under-explored. : This study aimed to inform approaches that might improve the caring and bereavement experience of informal carers of people with life-limiting illnesses, who interact with welfare policy and public organisations during and following informal care provision in Western Sydney; a region associated with recognised socio-economic disadvantage. The objectives included undertaking in-depth exploration of the experiences of former carers, alongside specialist palliative care workers and welfare workers engaged in related support provision or policy administration; and the identification of approaches that may increase structural and community capacity. : Phase one involved a scoping review which highlighted limited scholarship on social and structural inequity post-caring, and informed the adopted conceptual framework. Guided by an interpretive descriptive approach, phase two involved in-depth interviews with specialist palliative care workers (n=7), welfare sector workers (n=14) and former carers of people with life-limiting illnesses (n=12). Data were analysed using framework analysis. In phase three, features of Intersectionality-Based Policy Analysis were applied to findings to illuminate issues pertaining to inequity, and policy implications. : Welfare policy and process-related burdens were identified that related to low rates of income support payments, complex requirements, increasingly virtualised support and transactional agency cultures. These structural burdens contributed to the work of system navigation for carers. Individual social locations, resources and coping approaches differentially subjected carers to this work of system navigation and varying degrees of advantage or disadvantage. Vulnerably positioned carers encountered inequities in the form of financial, housing and employment insecurity and uncertainty and heightened psychological distress, related to diminishing, difficult to access or invalidated resources. : Recognition of the potential for the creation and perpetuation of inequity for vulnerably positioned carers during end-of-life and in bereavement is essential. Strategic and coordinated upstream investment is integral to advance necessary changes to policy and processes. Alongside this, downstream attention within the clinical or practice encounter to individualised assessment and support, the development of grief and policy literacy, the application of discretion and advocacy, and consideration of the impact of structural forces, is vital

Bureaucracy and burden: An Intersectionality-Based Policy Analysis of social welfare policy with consequences for carers of people with life-limiting illness

Background: For informal carers of people with life-limiting illness, social welfare policy related to income support and housing has been associated with varied psychosocial issues, yet remains relatively under-explored. An intersectional approach offers potential to illuminate diverse experiences and implications. Aim: To explore the way in which caring in the context of life-limiting illness is framed within welfare policy, to articulate inequities encountered by carers, and to identify policy and practice recommendations. Design: The Intersectionality-Based Policy Analysis (IBPA) Framework was used to situate findings of a broader qualitative study. Setting/participants: Data were collected via semi-structured interviews with participants who were bereaved carers (n = 12), welfare workers (n = 14) and palliative care workers (n = 7), between November 2018 and April 2020, in an Australian region associated with socioeconomic disadvantage. Five elements of IBPA were applied to the products of analysis of this data. Results: Use of the IBPA Framework revealed that representations of carers and causes of their welfare needs in policy were underpinned by several assumptions; including that caring and grieving periods are temporary or brief, and that carers have adequate capacity to navigate complex systems. Policy and processes had differentiated consequences for carers, with those occupying certain social locations prone to accumulating disadvantage. Conclusions: This intersectional analysis establishes critical exploration of the framing and consequences of welfare policy for carers of people with life-limiting illness, presented in a novel conceptual model. Implications relate to intersectoral development of structural competency, responsiveness to structurally vulnerable carers in clinical practice, and needed policy changes

Quantitative localized proton-promoted dissolution kinetics of calcite using scanning electrochemical microscopy (SECM)

Scanning electrochemical microscopy (SECM) has been used to determine quantitatively the kinetics of proton-promoted dissolution of the calcite (101̅4) cleavage surface (from natural “Iceland Spar”) at the microscopic scale. By working under conditions where the probe size is much less than the characteristic dislocation spacing (as revealed from etching), it has been possible to measure kinetics mainly in regions of the surface which are free from dislocations, for the first time. To clearly reveal the locations of measurements, studies focused on cleaved “mirror” surfaces, where one of the two faces produced by cleavage was etched freely to reveal defects intersecting the surface, while the other (mirror) face was etched locally (and quantitatively) using SECM to generate high proton fluxes with a 25 μm diameter Pt disk ultramicroelectrode (UME) positioned at a defined (known) distance from a crystal surface. The etch pits formed at various etch times were measured using white light interferometry to ascertain pit dimensions. To determine quantitative dissolution kinetics, a moving boundary finite element model was formulated in which experimental time-dependent pit expansion data formed the input for simulations, from which solution and interfacial concentrations of key chemical species, and interfacial fluxes, could then be determined and visualized. This novel analysis allowed the rate constant for proton attack on calcite, and the order of the reaction with respect to the interfacial proton concentration, to be determined unambiguously. The process was found to be first order in terms of interfacial proton concentration with a rate constant k = 6.3 (± 1.3) × 10–4 m s–1. Significantly, this value is similar to previous macroscopic rate measurements of calcite dissolution which averaged over large areas and many dislocation sites, and where such sites provided a continuous source of steps for dissolution. Since the local measurements reported herein are mainly made in regions without dislocations, this study demonstrates that dislocations and steps that arise from such sites are not needed for fast proton-promoted calcite dissolution. Other sites, such as point defects, which are naturally abundant in calcite, are likely to be key reaction sites

Fundamental Curie temperature limit in ferromagnetic GaMnAs

We provide experimental evidence that the upper limit of ~110 K commonly observed for the Curie temperature T_C of Ga(1-x)Mn(x)As is caused by the Fermi-level-induced hole saturation. Ion channeling, electrical and magnetization measurements on a series of Ga(1-x-y)Mn(x)Be(y)As layers show a dramatic increase of the concentration of Mn interstitials accompanied by a reduction of T_C with increasing Be concentration, while the free hole concentration remains relatively constant at ~5x10^20 cm^-3. These results indicate that the concentrations of free holes and ferromagnetically active Mn spins are governed by the position of the Fermi level, which controls the formation energy of compensating interstitial Mn donors.Comment: 14 pages, 3 figure

China and the GATT: a study of political and economic implications

published_or_final_versionBusiness AdministrationMasterMaster of Business Administratio

The effect of modelling rating severity on candidates' measurement in an English language essay examination

Rater effects are of concern when different raters score candidates' responses. This study demonstrates how models can be used to evaluate the scores assigned by raters on a freeresponse English essay question from a high stakes Examinations Board in the Caribbean Region. In addition, it seeks to use these models to assess the validity of the grades based on these scores. A new Classical test theory (CIT) model was created and compared with the many-faceted Rasch measurement (MFRM) models of rater severity in this investigation, comparing the effects of modelling individual raters and Table group severity, and the additional influence of the Table Leaders (considered by policy as 'standard bearers'). Models for the whole marking period were also compared with those for seven individual days of marking within the period. The. models used exposed quite substantial differences in person measurement. In particular, the study shows how variations in severity within and across moderated (standardised) tables groups of raters can be significantly sustained and variable over time. The knock-on effect of adjusting for rater severity is to change the scores on average by only 0.5 marks but the subsequent effect on the grades showed that about 6% of the candidates' grades would change by at least 1 grade level. The statistical modelling of the Table group rather than the individual raters is also new to the literature and is used for an empirical investigation of the Table group and so by implication its Table Leader. The individual raters and Table groups significantly affect candidate scores and grades but the variation between the Table groups is smaller than between individual raters. Accounting for Table Leaders' severity has shown that the Table Leaders' input in general led to a depression of scores and grades, implying that the Table Leaders on average were more severe in their allocation of marks than the Table group and the individual raters they supervised.EThOS - Electronic Theses Online ServiceGBUnited Kingdo