The use of shared common water points (WPs) and grazing points (GPs) at two different levels of administrative aggregation (village and kebelle) in a region of the Highlands of Ethiopia was explored by means of a questionnaire survey and social network analysis. Despite GPs being more abundant than WPs (208 and 154, respectively), individual GPs provide more contact opportunities for animals. There was great variability in the contact structure of the selected villages within kebelles for both networks, with this variability being higher in the GP networks for each kebelle. Contrary to the commonly held view that WPs are critical for the potential transmission of infectious diseases, intervention at GPs in the Ethiopian Highlands may have greater impact on contacts and thereby opportunities for transmission of infectious diseases between flocks. Some villages appear naturally at much lower risk of introducing disease. These findings could help the design of surveillance and control activities for directly transmitted infectious diseases.

Extended abstract of a paper presented at Microscopy and Microanalysis 2007 in Ft. Lauderdale, Florida, USA, August 5 – August 9, 2007

The self-affine character of the fracture surfaces of metals, polymers and ceramics has been well documented over the past two decades. It has been established that these surfaces are selfaffine objects characterized by so called ‘universal’ roughness exponents independent of the microstructure and the loading conditions. Here we show that the self-affine correlation length is closely associated with the microstructure heterogeneities. We also explore the possibility of the existence of attractor values that govern the fracture process, as opposed to universal exponents. The possible origin of this behavior is also briefly discussed.

The investigation of the morphology of crystalline solids surfaces is of practical and general interest because many processes such as the growth of epitaxial films, catalytic reactions and others, are intimately connected with surface conditions. In this work we study the surface morphology and structure of the spinel as produced in the system MgO- Al2O3-Fe2O3 at 1400°C for 15 h in a conventional furnace and in a microwave oven for 30 min. The spinel was analyzed by X-ray diffraction, scanning electron microscopy (SEM), X-ray spectrometry (EDX), and atomic force microscopy (AFM). The AFM images were recorded in the contact mode. Images scanned at different magnifications show steps and flat terraces. Experimental observations were made on the nature and distribution of the observed polygonal morphology.

In this work we report the self-affinity analysis of the fracture surfaces of a polymeric semicrystalline material and an opal glass. In the case of the plastic material, samples of isotactic polypropylene (i-PP) were prepared by varying the cooling rate from the melt; this resulted in different spherulite sizes. Samples were then broken in bend test after being immersed in liquid nitrogen. In the case of the opal glass, samples with different sizes of the opacifying particles, obtained by different thermal treatments, were broken in a punch test. In both cases the fracture surfaces were analyzed by both Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM) in the contact mode. Self-affinity analysis was performed by the variable bandwidth method, covering a range of length scales spanning from a few nanometers up to ten micrometers. The roughness exponents are found to be of similar values close to ζ = 0.8 with the correlation length corresponding to the size of the spherulites in the plastic material and to the size of the opacifying particles in the opal glass. These results should be taken into account in the development of multiscale models and simulations of the fracture process of real heterogeneous materials.

The influence of Fe on the microstructure of Al2O3-MgO-Fe2O3 spinel is described in this work. Heating a mixture of initial oxides in an electric furnace at 1400°C for 15 hrs produced the spinel. A ternary diagram for concentration ranges: Al2O3 (5-75 mol%), MgO (10-80 mol%), and Fe2O3 (3-70 mol%) summarize the constitution of this spinel. Amount, composition and weight ratios of each phase were determined by X-rays powder diffraction.

Microstructure of specimens was characterized by scanning electronic microscopy and Xray spectrometry. Distribution, size, shape of phases and pores were examined. Hardness measurements of spinel completed this study.

The present work reports the results of fractal analysis of the grain boundaries of AISI 304 stainless steel. Microstructure in the non deformed condition is compared against microstructure with 50% tensile strain. Observations were made by optical microscopy, magnifications used were 50, 100, 200, 400, and 1000x. Measurements were made over digitized images using image analysis. Fractal dimension of the grain boundaries were obtained using Richardson plots of perimeter against yardstick length. Our results agree well with reported values for different natural fractal curves. We found that, in general, grains exhibit two different fractal dimensions: one structure dimension that gives information about the morfology of the grain and one texture dimension which accounts for the fine details of the grain boundary.

Fractal dimension of the microstructure of AISI 316L steel (17 Cr, 12.7 Ni, 2.1 Mo, 1. 5 Mn, 0.01 C) with different degrees of strain were obtained from Richardson plots of grain boundary perimeter against magnification. Grain boundaries were revealed using conventional metallographic techniques and measurements were taken with the aid of an automatic image analizer (Quantimet 520) attached to an optical microscope. The magnifications used were 50, 100, 200, 400, and 1000X. The samples were obtained from a 4” diameter tubing, machined according to ASTM A370 standard test method and deformed to 5, 10, 15, and 20 % tensile strain. The results show that the fractal dimension of the grain boundaries changes as deformation is imparted to the material.

These results suggest that fractal dimension may be used to describe microstructural evolution of metals during deformation processes.