Over-Improved Stout-Link Smearing

A new over-improved stout-link smearing algorithm, designed to stabilise instanton-like objects, is presented. A method for quantifying the selection of the over-improvement parameter, $\epsilon$, is demonstrated. The new smearing algorithm is compared with the original stout-link smearing, and Symanzik improved smearing through calculations of the topological charge and visualisations of the topological charge density.Comment: 9 pages, 18 figures, submitted to Physical Review

Impact of Dynamical Fermions on QCD Vacuum Structure

We examine how dynamical fermions affect both the UV and infrared structure of the QCD vacuum. We consider large $28^3 \times 96$ lattices from the MILC collaboration, using a gluonic definition of the topological charge density, founded on a new over-improved stout-link smearing algorithm. The algorithm reproduces established results from the overlap formalism and is designed to preserve nontrivial topological objects including instantons. At short distances we focus on the topological charge correlator, , where negative values at small $x$ reveal a sign-alternating layered structure to the topological-charge density of the QCD vacuum. We find that the magnitudes of the negative dip in the correlator and the positive $$ contact term are both increased with the introduction of dynamical fermion degrees of freedom. This is in accord with expectations based on charge renormalization and the vanishing of the topological susceptibility in the chiral limit. At large distances we examine the extent to which instanton-like objects are found on the lattice, and how their distributions vary between quenched and dynamical gauge fields. We show that dynamical gauge fields contain more instanton-like objects with an average size greater than in the quenched vacuum. Finally, we directly visualize the topological charge density in order to investigate the effects of dynamical sea-quark degrees of freedom on topology.Comment: 9 pages, 8 figure

The residential school; some aspects of the physical and social environment

This thesis considers the environment of mainstream residential schools largely from the viewpoint of the pupils' perception. The nature of the physical environment and in particular the evolution of the built environment is discussed in detail. The temporal element is not forgotten in this context, as major influences, be they personalities or trends are assessed for their impact. The second major element of the environment is then considered, being the social climate. A whole range of factors are assessed for the level of impact in terms of their influence on the atmosphere of a residential school. The role of Government, and in particular the impact of the Children Act.(1989), is covered in detail. The range of areas where the legislation impinges on the form of the physical environment is discussed. Behaviorialism as an approach to the study of the perception of the environment is developed as a concept. The major trends in developing an approach to perceptual studies are traced and individual contributors are given due recognition. From this a field programme is created, drawing upon ideas employed in the past for the assessment of the environment. The field programme is applied to a variety of residential schools, which declare themselves to have a distinctive ethos. The field programme is completed by the pupils in the schools in order to assess their perception of the effectiveness of the school environment in their educational experience. Fifteen case studies are detailed to illustrate specific points of contrast between schools. The mean school for comparative purposes is calculated and recommendations for the improvement and development of the whole residential school environment are made

Low-lying Odd-parity States of the Nucleon in Lattice QCD

The world's first examination of the odd-parity nucleon spectrum at light quark masses in 2+1 flavor lattice QCD is presented. Configurations generated by the PACS-CS collaboration and made available through the ILDG are used, with the lightest pion mass at 156 MeV. A novel method for tracking the individual energy eigenstates as the quark mass changes is introduced. The success of this approach reveals the flow of the states towards the physical masses. Using the correlation matrix method, the two lowest-energy states revealed are found to be in accord with the physical spectrum of Nature.Comment: 5 page