Look before planting: using smokewater as an inventory tool to predict the soil seed bank and inform ecological management and restoration

This study tested the efficacy of smokewater to determine the potential germination from soil seed bank in three management sites of the same National Park: a forest site prior to restoration, an ex-pine plantation site and an ex-mine site. This will provide further information to land managers so that more accurate planning can occur. Results showed that smokewater significantly increased the germination from the soil seed bank, and significant differences in the level of germination of weed species from the soil seed bank were seen between the three management sites. This use of smokewater may be a useful tool to help predict differences in the soil seed bank compared with predicting soil seed bank based on land-use history and recent condition

Temperature and inoculation method influence disease phenotypes and mortality of Eucalyptus marginata clonal lines inoculated with Phytophthora cinnamomi

Survival of 1-year-old plants of three clonal lines of Eucalyptus marginata (jarrah), two ranked as resistant (RR1 and RR2) and one as susceptible (SS1) to Phytophthora cinnamomi, was assessed after pathogen inoculation with either mycelial mats underbark or zoospores on the stem. Plants were grown at 15, 20, 25 and 30°C. Method of inoculation did not produce comparable mortalities of the clonal lines, particularly at 25 and 30°C. At these temperatures, all three clonal lines had 100% mortality when inoculated underbark, but when inoculated with zoospores, RR1 had 60% survival and lines SS1 and RR2 had 100% mortality. Generally, the level of resistance of all clonal lines declined with increasing temperature. RR2 had consistently higher mortality than SS1, and is therefore not considered resistant. Lesion development was also measured in detached stems of RR1 and a susceptible clonal line (SS2) each inoculated underbark with four different P. cinnamomi isolates. Stems were assessed for lesion development at 20, 25 and 30°C for 4 days. For all four isolates, detached stems of RR1 generally had smaller lesions than those of SS2, particularly at 30°C. The increase in lesion length with increasing temperature was greatest for SS2. Detached stems may have potential in screening for jarrah resistant toP. cinnamomi and allow identification of susceptible clonal lines at 30°C

Prediction of crack growth in a nickel-based superalloy under fatigue-oxidation conditions

Prediction of oxidation-assisted crack growth has been carried out for a nickel-based superalloy at elevated temperature based on finite element analyses of oxygen diffusion, coupled with viscoplastic deformation, near a fatigue crack tip. The material constitutive behaviour, implemented in the finite element code ABAQUS via a user-defined material subroutine (UMAT), was described by a unified viscoplastic model with non-linear kinematic and isotropic hardening rules. Diffusion of oxygen was assumed to be controlled by two parameters, the oxygen diffusivity and deformation-assisted oxygen mobility. Low frequencies and superimposed hold periods at peak loads significantly enhanced oxygen concentration near the crack tip. Evaluations of near-tip deformation and oxygen concentration were performed, which led to the construction of a failure envelop for crack growth based on the consideration of both oxygen concentration and accumulated inelastic strain near the crack tip. The failure envelop was then utilised to predict crack growth rates in a compact tension (CT) specimen under fatigue-oxidation conditions for selected loading ranges, frequencies and dwell periods. The predictions from the fatigue-oxidation failure envelop compared well with the experimental results for triangular and dwell loading waveforms, with marked improvements achieved over those predicted from the viscoplastic model alone. The fatigue-oxidation predictions also agree well with the experimental results for slow-fast loading waveforms, but not for fast-slow waveforms where the effect of oxidation is much reduced

High temperature fatigue behaviour in an advanced nickel based superalloy: The effects of oxidation and stress relaxation at notches

The low cycle fatigue performance of the nickel based superalloy RR1000 was investigated under a variety of load waveforms at high temperature, employing a double edge notch geometry under load control. Experiments on a plain cylindrical specimen design under strain control were later performed to simulate the constrained conditions at the root of the notch in order to characterise the interaction between surface constituents and the environment. A significant fatigue debit was demonstrated under both load/strain scenarios when superimposing a dwell period at the minimum point of the cycle. This debit was attributed to a reduction in fatigue crack initiation life resulting from oxidation damage which subsequently cracks under cyclic tension together with a modification to the mean stress through cyclic stabilisation. The same dwell period superimposed at the peak of the cycle was essentially benign for excursions under strain control loading

MC decomposition and boride formation in a next generation polycrystalline Ni based superalloy during isothermal exposure at 900 °C

Detailed microstructural characterisation of phases present in a next generation polycrystalline Ni based superalloy after thermal exposure at 900 °C was carried out, focusing on carbides and borides. Metastable M5B3 precipitated after 32 h had a stoichiometry of (Cr0.7Mo0.2W0.1)5B3 with substitutions with Ni, Co, Nb and Ta. Fine M23C6 (a = 10.62 Å) was overgrown by metastable M5B3, as shown by rigorous TEM-SAD pattern investigation. The borides were eventually dominated by Mo rich M3B2, at the apparent expense of MC. Decomposition of MC was confirmed; it transformed sequentially to γ and then γ΄. The primary driving force for the MC decomposition was attributed to γ΄ precipitation, increasing its fraction to the thermodynamic equilibrium at 900 °C

Oxygen diffusion and crack growth for a nickel-based superalloy under fatigue-oxidation conditions

Advanced microscopy characterisation and numerical modelling have been carried out to investigate oxygen diffusion and crack growth in a nickel-based superalloy under fatigue-oxidation conditions. Penetration of oxygen into the material and the associated internal oxidation, which leads to material embrittlement and failure, have been found from Focused Ion Beam (FIB) examinations. Applied fatigue loading tends to enhance the extent of internal oxidation for temperatures at 750°C and above. Using a submodelling technique, finite element analyses of oxygen penetration at grain level have been carried out to quantify the fatigue-oxidation damage and calibrate the diffusion parameters based on the measurements of maximum depth of internal oxidation. The grain microstructure was considered explicitly in the finite element model, where the grain boundary was taken as the primary path for oxygen diffusion. A sequentially coupled mechanical-diffusion analysis was adopted to account for the effects of deformation on diffusion during fatigue loading, for which the material constitutive behaviour was described by a crystal plasticity model at grain level. Prediction of oxidation-assisted crack growth has also been carried out at elevated temperature from the finite 2 element analyses of oxygen diffusion near a fatigue crack tip. A failure curve for crack growth has been constructed based on the consideration of both oxygen concentration and accumulated inelastic strain near the crack tip. The predictions from the fatigue-oxidation failure curve compared well with the experimental results for triangular and dwell loading waveforms, with significant improvement achieved over those predicted from the viscoplastic model alone

Distribution of Eigenvalues for the Modular Group

The two-point correlation function of energy levels for free motion on the modular domain, both with periodic and Dirichlet boundary conditions, are explicitly computed using a generalization of the Hardy-Littlewood method. It is shown that ion the limit of small separations they show an uncorrelated behaviour and agree with the Poisson distribution but they have prominent number-theoretical oscillations at larger scale. The results agree well with numerical simulations.Comment: 72 pages, Latex, the fiogures mentioned in the text are not vital, but can be obtained upon request from the first Autho

Interactions, Distribution of Pinning Energies, and Transport in the Bose Glass Phase of Vortices in Superconductors

We study the ground state and low energy excitations of vortices pinned to columnar defects in superconductors, taking into account the long--range interaction between the fluxons. We consider the ``underfilled'' situation in the Bose glass phase, where each flux line is attached to one of the defects, while some pins remain unoccupied. By exploiting an analogy with disordered semiconductors, we calculate the spatial configurations in the ground state, as well as the distribution of pinning energies, using a zero--temperature Monte Carlo algorithm minimizing the total energy with respect to all possible one--vortex transfers. Intervortex repulsion leads to strong correlations whenever the London penetration depth exceeds the fluxon spacing. A pronounced peak appears in the static structure factor $S(q)$ for low filling fractions $f \leq 0.3$. Interactions lead to a broad Coulomb gap in the distribution of pinning energies $g(\epsilon)$ near the chemical potential $\mu$, separating the occupied and empty pins. The vanishing of $g(\epsilon)$ at $\mu$ leads to a considerable reduction of variable--range hopping vortex transport by correlated flux line pinning.Comment: 16 pages (twocolumn), revtex, 16 figures not appended, please contact [email protected]

Antihydrogen formation dynamics in a multipolar neutral anti-atom trap

Antihydrogen production in a neutral atom trap formed by an octupole-based magnetic field minimum is demonstrated using field-ionization of weakly bound anti-atoms. Using our unique annihilation imaging detector, we correlate antihydrogen detection by imaging and by field-ionization for the first time. We further establish how field-ionization causes radial redistribution of the antiprotons during antihydrogen formation and use this effect for the first simultaneous measurements of strongly and weakly bound antihydrogen atoms. Distinguishing between these provides critical information needed in the process of optimizing for trappable antihydrogen. These observations are of crucial importance to the ultimate goal of performing CPT tests involving antihydrogen, which likely depends upon trapping the anti-atom