Irreversible cooperative processes on lattices

Kinetic models for irreversible cooperative processes on lattices are developed. Hierarchial rate equations for the probabilities of configurations of empty sites are discussed in detail and the concept of shielding is introduced. Several, exactly soluble, one-dimensional processes are treated including (1) those incorporating a cooperative range of influence of one lattice vector beyond a fixed number of blocking sites, (2) filling in stages for highly repulsive interactions, (3) correlation functions, (4) configurational entropy of ring lattices, (5) processes with competing events, (6) periodic lattices and (7) limited mobility. Approximate solution techniques for analyzing other one-dimensional processes are also discussed;A special irreversible kinetic process on a two-dimensional square lattice is also treated and a computer program is described which has been developed to generate the appropriate two-dimensional kinetic equations. The resultant equations are treated using various factorization/truncation schemes;A method is given to determine rate constants for irreversible polymer reactions from experimental measurements of the fraction of converted sites with time. Other aspects of irreversible polymer reactions are also treated;The chemisorption of nitrogen onto the (100) face of tungsten is discussed as an example of how irreversibility influences surface processes;A short discussion of irreversible three-dimensional processesin crystalline solids concludes the work;*DOE Report IS-T-1035. This work was performed under ContractW-7405-eng-82 with the Department of Energy

Movement of pathogens between horticultural crops and endemic trees in the Kimberleys

Recently a survey of endophytes associated with boabs (Adansonia gregorrii) and associated tree species in the Kimberleys, Western Australia has resulted in the description of seven new species in the Botryosphaeriaceae (Pavlic et al. 2008). Additionally several common species of Lasiodiplodia, (L. theobromae, L. pseudoptheobromae and L. parva) were also isolated as endophytes of endemic tree species. Concurrently, surveys in the Ord River Irrigation Area (ORIA) have revealed Mangiferum indica trees showing symptoms of dieback and cankers. In this project we isolated, identified and determined the pathogenicity of fungi associated with these cankers

Nitrogen Isotopic Composition and Density of the Archean Atmosphere

Understanding the atmosphere's composition during the Archean eon is a fundamental issue to unravel ancient environmental conditions. We show from the analysis of nitrogen and argon isotopes in fluid inclusions trapped in 3.0-3.5 Ga hydrothermal quartz that the PN2 of the Archean atmosphere was lower than 1.1 bar, possibly as low as 0.5 bar, and had a nitrogen isotopic composition comparable to the present-day one. These results imply that dinitrogen did not play a significant role in the thermal budget of the ancient Earth and that the Archean PCO2 was probably lower than 0.7 bar

A Microscopic Derivation of the SO(5)-Symmetric Landau-Ginzburg Potential

We construct a microscopic model of electron interactions which gives rise to both superconductivity and antiferromagnetism, and which admits an approximate SO(5) symmetry that relates these two phases. The symmetry can be exact, or it may exist only in the long-wavelength limit, depending on the detailed form of the interactions. We compute the macroscopic Landau-Ginzburg free energy for this model as a function of temperature and doping, by explicitly integrating out the fermions. We find that the resulting phase diagram can resemble that observed for the cuprates, with the antiferromagnetism realized as a spin density wave, whose wavelength might be incommensurate with the lattice spacing away from half filling.Comment: 29 pp., plain TeX, 7 figures, uses macros.tex (included) and epsf.tex; added subject clas

The origin and degassing history of the Earth's atmosphere revealed by Archean xenon

Xenon (Xe) is an exceptional tracer for investigating the origin and fate of volatile elements on Earth. The initial isotopic composition of atmospheric Xe remains unknown, as do the mechanisms involved in its depletion and isotopic fractionation compared with other reservoirs in the solar system. Here we present high precision analyses of noble gases trapped in fluid inclusions of Archean quartz (Barberton, South Africa) that reveal the isotopic composition of the paleo-atmosphere at ≈3.3 Ga. The Archean atmospheric Xe is mass-dependently fractionated by 12.9±2.4 ‰ u^(−1) (± 2σ, s.d.) relative to the modern atmosphere. The lower than today ^(129)Xe excess requires a degassing rate of radiogenic Xe from the mantle higher than at present. The primordial Xe component delivered to the Earth's atmosphere is distinct from Solar or Chondritic Xe but similar to a theoretical component called U-Xe. Comets may have brought this component to the Earth's atmosphere during the last stages of terrestrial accretion

Evaluating the provision of school performance information for school choice

We develop and implement a framework for determining the optimal performance metrics to help parents choose a school. This approach combines the three major critiques of the usefulness of performance tables into a natural metric. We implement this for 500,000 students in England for a range of performance measures. Using performance tables is strongly better than choosing at random: a child who attends the highest ex ante performing school within their choice set will ex post do better than the average outcome in their choice set twice as often as they will do worse

Canonical BF-type Topological Field Theory and Fractional Statistics of Strings

We consider BF-type topological field theory coupled to non-dynamical particle and string sources on spacetime manifolds of the form \IR^1\times\MT, where \MT is a 3-manifold without boundary. Canonical quantization of the theory is carried out in the Hamiltonian formalism and explicit solutions of the Schr\"odinger equation are obtained. We show that the Hilbert space is finite dimensional and the physical states carry a one-dimensional projective representation of the local gauge symmetries. When \MT is homologically non-trivial the wavefunctions in addition carry a multi-dimensional projective representation, in terms of the linking matrix of the homology cycles of \MT, of the discrete group of large gauge transformations. The wavefunctions also carry a one-dimensional representation of the non-trivial linking of the particle trajectories and string surfaces in \MT. This topological field theory therefore provides a phenomenological generalization of anyons to (3 + 1) dimensions where the holonomies representing fractional statistics arise from the adiabatic transport of particles around strings. We also discuss a duality between large gauge transformations and these linking operations around the homology cycles of \MT, and show that this canonical quantum field theory provides novel quantum representations of the cohomology of \MT and its associated motion group.Comment: 30 pages, plain TeX; MITCTP#2326, UBCTP-94-00

Codimension Two Branes and Distributional Curvature

In general relativity, there is a well-developed formalism for working with the approximation that a gravitational source is concentrated on a shell, or codimension one surface. By contrast, there are obstacles to concentrating sources on surfaces that have a higher codimension, for example, a string in a spacetime with dimension greater than or equal to four. Here it is shown that, by giving up some of the generality of the codimension one case, curvature can be concentrated on submanifolds that have codimension two. A class of metrics is identified such that (1) the scalar curvature and Ricci densities exist as distributions with support on a co-dimension two submanifold, and (2) using the Einstein equation, the distributional curvature corresponds to a concentrated stress-energy with equation of state p equals minus the energy density, where p is the isotropic pressure tangent to the submanifold. This is the appropriate stress-energy to describe a self-gravitating brane that is governed by an area action, or a brane world deSitter cosmology. The possibility of having a different equation of state arise from a wider class of metrics is discussed.Comment: 18 pages; v2 references added; typos corrected, references added; additional references adde