Cleaved surface of i-AlPdMn quasicrystals: Influence of the local temperature elevation at the crack tip on the fracture surface roughness

Roughness of i-AlPdMn cleaved surfaces are presently analysed. From the atomic scale to 2-3 nm, they are shown to exhibit scaling properties hiding the cluster (0.45 nm) aperiodic structure. These properties are quantitatively similar to those observed on various disordered materials, albeit on other ranges of length scales. These properties are interpreted as the signature of damage mechanisms occurring within a 2-3 nm wide zone at the crack tip. The size of this process zone finds its origin in the local temperature elevation at the crack tip. For the very first time, this effect is reported to be responsible for a transition from a perfectly brittle behavior to a nanoductile one.Comment: 8 page

Effect of Disorder and Notches on Crack Roughness

We analyze the effect of disorder and notches on crack roughness in two dimensions. Our simulation results based on large system sizes and extensive statistical sampling indicate that the crack surface exhibits a universal local roughness of $\zeta_{loc} = 0.71$ and is independent of the initial notch size and disorder in breaking thresholds. The global roughness exponent scales as $\zeta = 0.87$ and is also independent of material disorder. Furthermore, we note that the statistical distribution of crack profile height fluctuations is also independent of material disorder and is described by a Gaussian distribution, albeit deviations are observed in the tails.Comment: 6 pages, 6 figure

Origin of the Universal Roughness Exponent of Brittle Fracture Surfaces: Correlated Percolation in the Damage Zone

We suggest that the observed large-scale universal roughness of brittle fracture surfaces is due to the fracture process being a correlated percolation process in a self-generated quadratic damage gradient. We use the quasi-static two-dimensional fuse model as a paradigm of a fracture model. We measure for this model, that exhibits a correlated percolation process, the correlation length exponent nu approximately equal to 1.35 and conjecture it to be equal to that of uncorrelated percolation, 4/3. We then show that the roughness exponent in the fuse model is zeta = 2 nu/(1+2 nu)= 8/11. This is in accordance with the numerical value zeta=0.75. As for three-dimensional brittle fractures, a mean-field theory gives nu=2, leading to zeta=4/5 in full accordance with the universally observed value zeta =0.80.Comment: 4 pages RevTeX

A longitudinal study of influences on alcohol consumption and related harm in Central Australia: with a particular emphasis on the role of price.

Made available by the Northern Territory Library via the Publications (Legal Deposit) Act 2004 (NT).Northern Territory, Department of Health, Central Australian Aboriginal Congres

COVID-19 and tuberculosis in South Africa: A dangerous combination

There has been much speculation during the past week about the catastrophe that awaits once coronavirus disease 2019 (COVID-19) establishes itself in the poorest communities of South Africa (SA) and, importantly, in informal settlements. Evidence to date suggests that COVID-19 is efficiently passed from infected individuals via large droplets and hard-surface fomites

Permeability of self-affine rough fractures

The permeability of two-dimensional fractures with self-affine fractal roughness is studied via analytic arguments and numerical simulations. The limit where the roughness amplitude is small compared with average fracture aperture is analyzed by a perturbation method, while in the opposite case of narrow aperture, we use heuristic arguments based on lubrication theory. Numerical simulations, using the lattice Boltzmann method, are used to examine the complete range of aperture sizes, and confirm the analytic arguments.Comment: 11 pages, 9 figure

Management of tree diversity in agricultural landscapes around Mabira Forest

Abstract As natural forests contract, farming systems become increasingly important to landscape biodiversity conservation, yet assets and limits of their contribution are insufficiently documented. A sound understanding of farmer strategies in the management of on-farm tree biodiversity is also critical to landscape approaches for biodiversity conservation and livelihood improvement. Diversity and management of woody species were surveyed in 105 farms around Mabira Forest in South-Central Uganda. Farms were selected according to distance to forest, landscape axis, gender, wealth, and specialized forest use of household heads. Farmer management has a strong influence on tree diversity in the coffee-banana systems around Mabira Forest. This is reflected in the relatively high number of planted and exotic species at the levels of farm niche, farm and landscape. Both the number of years under cultivation and farmer involvement in specialized forest use were conducive to higher species diversity. Gender, wealth and tenure status did not influence tree diversity. Variation in on-farm species richness was noted between landscape axes radiating out of the forest rather than concentric distance categories. Farming systems around Mabira Forest Reserve provide a key complementary rather than substitute tree diversity refuge and can be managed to enhance overall landscape biodiversity