Studies of long range order and excitations in the iron arsenide superconductors

The study of iron based superconductors began in 2006 when the compound LaOFeP was found to have a superconducting transition at a modest temperature Tc of 3.2 K. Because elemental iron is a strong ferromagnet, this discovery was a great surprise due to the fact that magnetic moments are generally associated with magnetic pair breaking. Soon after this discovery, variations of these superconductors were made through chemical substitutions and the Tc rose to 55 K two years later. The explosion of research that has followed these discoveries has led to the synthesis of several families of iron based superconductors whose high values of Tc are second only to the cuprates and which bringing them into the field of high temperature superconductivity (SC). This thesis focuses on how pressure and electron doping effect the crystallographic and magnetic properties of the iron based superconductors (Ca,Ba)Fe2 As2 which are part of a group of compounds known as 122s. Upon cooling, these compounds undergo a dual structural-magnetic transition from a tetragonal paramagnetic state to an orthorhombic and antiferromagnetic state. By tuning the pressure or dopant concentration knob, we have been able to show clearly that this has the effect of suppressing the magnetism and associated structural transition observed in un-doped or ambient pressure compounds. Neutron scattering measurements on CaFe2 As2 under pressure have demonstrated that the onset of superconductivity is observed after the stabilization of the room-temperature tetragonal phase at low temperatures under non-hydrostatic pressure. For the case of electron doping BaFe2 As2, it is clear that a sufficient suppression of structural and magnetic ordering transitions is necessary for the appearance and optimization of superconductivity. These studies have provided key information about the static magnetic ordering and the associated magnetic excitations, and have allowed for the attempt to address questions about the nature of magnetism in these materials and what role magnetism plays in the appearance of superconductivity

Boundary Integral Equation Method for Electrostatic Field Prediction in Piecewise-Homogeneous Electrolytes

This thesis presents a method to predict electrostatic fields, potentials, and currents in regions containing piecewise-homogeneous electrolytes. Additionally, an efficient electric field calculation is presented. A boundary integral equation is formulated for the boundary potentials and currents and is discretized using the Locally Corrected Nyström method. Solution convergence with respect to the mesh discretization and basis order is investigated. The techniques are validated through analysis of problems with either analytic solutions, with published data, or with other solution methods

An appropriate level of risk: Balancing the need for safe livestock products with fair market access for the poor

This paper examines the role of livestock products as commodities of trade, responding to the demand and higher prices that many external markets offer, and at the same time providing important contributions to the development process in poorer countries. It highlights that this opportunity is not without its threats: much of the Western world has, over the last half century in particular, invested substantial amounts of money in controlling and eradicating many infectious diseases of livestock, and in building up healthy and highly productive animals, the products derived from which earn them very large sums of money on world markets. Such countries are not willing to take risks that could threaten their livestock industries, and their domestic and export markets that maintain high animal health and food safety standards. The study builds on a number of 'success stories', examples where developing countries have succeeded in exporting livestock or livestock products to external markets. An analysis of the factors governing their success revealed some commonalities: all were driven by strong private sector partners who contributed capital, management expertise and entrepreneurial flair; most concerned livestock products, rather than live animals, which matched the market's requirements; many had developed strong brand identities which had become synonymous with quality, safety and dependability; and many were vertically integrated systems, incorporating small and medium scale out-grower producers. Often these successes have been achieved despite the absence of effective support from the public sector, such as national veterinary authorities. One of the key findings of this study is the disparity between the push for global harmonisation of animal health standards for trade, and the lack of capacity of developing countries, particularly LDCs, to meet these standards. The study considers how this might be rectified and concludes that building capacity of regional bodies to create regional centres of excellence with regard to SPS matters may be the most practical way forward.Livestock Production/Industries,

Senior Recital

List of performers and performances

Parameterization Effects in the analysis of AMI Sunyaev-Zel'dovich Observations

Most Sunyaev--Zel'dovich (SZ) and X-ray analyses of galaxy clusters try to constrain the cluster total mass and/or gas mass using parameterised models and assumptions of spherical symmetry and hydrostatic equilibrium. By numerically exploring the probability distributions of the cluster parameters given the simulated interferometric SZ data in the context of Bayesian methods, and assuming a beta-model for the electron number density we investigate the capability of this model and analysis to return the simulated cluster input quantities via three rameterisations. In parameterisation I we assume that the T is an input parameter. We find that parameterisation I can hardly constrain the cluster parameters. We then investigate parameterisations II and III in which fg(r200) replaces temperature as a main variable. In parameterisation II we relate M_T(r200) and T assuming hydrostatic equilibrium. We find that parameterisation II can constrain the cluster physical parameters but the temperature estimate is biased low. In parameterisation III, the virial theorem replaces the hydrostatic equilibrium assumption. We find that parameterisation III results in unbiased estimates of the cluster properties. We generate a second simulated cluster using a generalised NFW (GNFW) pressure profile and analyse it with an entropy based model to take into account the temperature gradient in our analysis and improve the cluster gas density distribution. This model also constrains the cluster physical parameters and the results show a radial decline in the gas temperature as expected. The mean cluster total mass estimates are also within 1 sigma from the simulated cluster true values. However, we find that for at least interferometric SZ analysis in practice at the present time, there is no differences in the AMI visibilities between the two models. This may of course change as the instruments improve.Comment: 19 pages, 13 tables, 24 figure

Unsettling the role of culture as panacea: The politics of culture-led urban regeneration in Buenos Aires

In recent years the rise of culture as a universal cure to a myriad of urban, social and economic ‘diseases’ has been celebrated without precedent, both in policy and academic accounts. Unlike these celebratory discourses, this paper provides a critique of the politics underpinning culture-led urban regeneration in order to unsettle the role of culture as panacea. Drawing on a case study – the on-going redevelopment of the post office palace into a commemorative cultural centre in Buenos Aires, Argentina – the analysis offers an in-depth account of the policy process by which industrial heritage is redeveloped through a cultural rhetoric. The analysis reveals how the recycling of the post office building enabled multiple meanings of culture to emerge and circulate within a range of policy, architectural, urban regeneration, real estate and media discourses. These, in turn, express existing disputes over the making of cultural policies, the uses of heritage, the image of the capital city and the value of the post office. In the redevelopment of the postal building, the paper argues, policy invocations of culture were aimed at de-politicising cultural activities in post-2001/2002 crisis Argentina, when politics had become a synonym of corruption and mismanagement. The paper concludes by drawing attention to the urgent need to adopt a critical perspective to the study of culture-led urban regeneration in Latin America, one which situates the analysis in historical and political terms and acknowledges the contending circumstances out of which these urban strategies often emerge

Research for the future: Investments for efficiency, sustainability, and equity

Source Publication: 2022 Global Food Policy Report: Climate Change and Food Systems. Chapter 4, Pp. 38-47Food systems everywhere are facing major new challenges. Shocks caused by COVID-19 have currently seized our attention, but the pandemic has also accentuated persistent problems of poverty, hunger and malnutrition, population growth, and pressure on natural resources, notably land, water, and biodiversity. Adding to these challenges, climate change poses a serious threat to food security and livelihoods as greenhouse gas (GHG) emissions continue to rise. Changing temperatures, highly variable precipitation, shifting growing seasons, and extreme weather events are already making agricultural yields and prices more volatile, with rural areas across the world feeling the effects most profoundly. Yet, as the world’s population moves toward 9 or 10 billion by 2050, unprecedented increases in global food production — of at least 60 percent over 2005–2007 levels — will be needed to meet growing demand

A simple parametric model for spherical galaxy clusters

We present an analytic parametric model to describe the baryonic and dark matter distributions in clusters of galaxies with spherical symmetry. It is assumed that the dark matter density follows a Navarro, Frenk and White (NFW) profile and that the gas pressure is described by a generalised NFW (GNFW) profile. By further demanding hydrostatic equilibrium and that the gas fraction is small throughout the cluster, one obtains unique functional forms, dependent on basic cluster parameters, for the radial profiles of all the properties of interest in the cluster. We show these profiles are consistent both with numerical simulations and multi-wavelength observations of clusters. We also use our model to analyse six simulated SZ clusters as well as A611 SZ data from the Arcminute Microkelvin Imager (AMI). In each case, we derive the radial profile of the enclosed total mass and the gas pressure and show that the results are in good agreement with our model prediction.Comment: 10 pages, 3 table, 17 figure