Nonlocal spectral properties of disordered alloys

A general method is proposed for calculating a fully k-dependent, continuous, and causal spectral function A(k,E) within the recently introduced nonlocal version of the coherent-potential approximation (NLCPA). The method involves the combination of both periodic and anti-periodic solutions to the associated cluster problem and also leads to correct bulk quantities for small cluster sizes. We illustrate the method by investigating the Fermi surface of a two-dimensional alloy. Dramatically, we find a smeared electronic topological transition not predicted by the conventional CPA.Comment: 17 pages, 5 figures, Submitted to: J. Phys.: Condens. Matter Editorial receipt 25 May 200

Adjacencies and distances: sculptural site intervention

Within the urban landscape, the tempo of destruction and redevelopment of our built environment reveals a palimpsest of change. The abandonment of these sites could go unnoticed, often a fleeting moment before destruction, with the next structure then re-cloaking the land. This research project locates itself spatially and conceptually within this pause or transitional state of select sites. It utilises this brief period of time to consider how these sites can offer poetic information and new readings as creative practice, despite their impending obsolescence. Through my work, I engaged physically with sites through various material intervention processes. Cutting, slicing, reconfiguring the surfaces and the structural integrity of these sites becomes a visceral engagement, bringing with it an urgency, an intensity, and a consequentiality. They are emphatic gestures that stand in contrast to the obsolescence of the space, but at the same time reveal the layered nature of not just the physical but also the metaphorical and memorial constructions of these built structures. Adjacencies and distances, prompts us to re-evaluate our proximity and understanding of everything around us. Drawing attention to what may go unnoticed, the research within these sites highlights how these spaces can hold a degree of separation from their previous function; an autonomy within the context of our built landscape. The human presence in these sites becomes one aspect of many, rather than the sole reason for their existence. My investigations and subsequent interventions into sites reflect prominently on my own sense of how I read the environment. Reflecting on what is known within these sites and finding some distance here with an aim to create some sense of ambiguity; to un-know and/or to re-know what may have been hidden. The fluctuation between these two states, knowing and unknowing becomes a rich area of research opening up greater ways for me to challenge my perceptions within site and then to spatially respond to these in the form of sculptural interventions. Through the exploration of further material process and techniques, such as photography, film and sound, this practice-led research project has allowed me to expand my capacity to capture and extend my observations and sculptural interventions. This documentation, in light of the loss of the physical sites and work, is then to become a crucial path back to the experience of a site. Whilst this does not reproduce the full liveness of the experience, I see it as a step towards understanding my thinking at the time. Each photograph, film or sound document, then, is like a word that can return you to a sentence, a memory, a moment. This final document is written foremost from the perspective of being in site, and the reflections derived from these experiences. From here, I explore current thinking and artist practices that broaden the reflective writing, deriving a statement of research outcomes that balances an analytical understanding of my journey with the poetic

Investigation of the nonlocal coherent-potential approximation

Recently the nonlocal coherent-potential approximation (NLCPA) has been introduced by Jarrell and Krishnamurthy for describing the electronic structure of substitutionally disordered systems. The NLCPA provides systematic corrections to the widely used coherent-potential approximation (CPA) whilst preserving the full symmetry of the underlying lattice. Here an analytical and systematic numerical study of the NLCPA is presented for a one-dimensional tight-binding model Hamiltonian, and comparisons with the embedded cluster method (ECM) and molecular coherent potential approximation (MCPA) are made.Comment: 18 pages, 5 figure

Evidence of Variable Zn/Fe in Zinc-Ferrites Produced From Roasting of Zinc Sulphide Concentrate

Zn-Fe-O phases formed during roasting of concentrates from zinc sulfide ores produce soluble zinc oxide, oxy-sulfates and insoluble ferrite compounds. The ferrites have a general formula ZnOFe2O3. However, these ferrites have a range of magnetic properties, suggesting variable stoichiometry. Scanning electron microscopy has been used to obtain the general relationship between the Zn/Fe ratio of the ferrites and their magnetic susceptibility

Macroscopic control parameter for avalanche models for bursty transport

Similarity analysis is used to identify the control parameter RA for the subset of avalanching systems that can exhibit self-organized criticality (SOC). This parameter expresses the ratio of driving to dissipation. The transition to SOC, when the number of excited degrees of freedom is maximal, is found to occur when RA-->0. This is in the opposite sense to (Kolmogorov) turbulence, thus identifying a deep distinction between turbulence and SOC and suggesting an observable property that could distinguish them. A corollary of this similarity analysis is that SOC phenomenology, that is, power law scaling of avalanches, can persist for finite RA with the same RA-->0 exponent if the system supports a sufficiently large range of lengthscales, necessary for SOC to be a candidate for physical (RA finite) systems