Jean-Pierre Brincat

Anomalous elastic properties in stishovite

Auxetics are materials which have a negative Poissons ratio, that is, upon uniaxial tensile loading, they also expand in a direction perpendicular to the applied force. Here, we analyze the elastic constants of stishovite, a high pressure silica polymorph which is known to be a significant constituent of the earths mantle, and show that it exhibits a negative Poissons ratio when stressed in a range of directions in the (100), (010) and (001) planes under specific ambient pressure ranges. We explain this behaviour through mechanisms involving rotations and distortions of the constituent octahedra. These findings have important practical implications since stishovite is one of the hardest known oxides, and has proven to be important to various fields ranging from seismology to materials science.

A Comprehensive Review of the Pear Fungal Diseases

ABSTRACT In this article a detailed review of the fungal diseases that can affect pear fruit is provided. Each section comprises a complete description of the fungi responsible for the diseases and the symptoms they produce on the pears. The majority of pear fungal diseases, including blue mold, grey mold, bitter rot, black spot, brown rot, bull’s eye rot, Phytophthora rot, pink mold rot, powdery mildew, Rhizopus rot, scab, side rot, sooty blotch, and flyspeck, are presented. Sources of infection are comprehensively described in relation to harvesting or post-harvesting handling and intervention practices, respectively. As these diseases are dependent on a number of environmental parameters, the optimal temperature ranges for disease development are described and the causal agents are identified. Previous studies on the diagnostic indications are reviewed while information about the optimal environmental parameters of temperature, pressure, pH, water activity, and oxygen level for the fungal growth is comprehensively summarized.

Assessing the anti-fungal efficiency of filters coated with zinc oxide nanoparticles

Air filters support fungal growth, leading to generation of conidia and volatile organic compounds, causing allergies, infections and food spoilage. Filters that inhibit fungi are therefore necessary. Zinc oxide (ZnO) nanoparticles have anti-fungal properties and therefore are good candidates for inhibiting growth. Two concentrations (0.012 M and 0.12 M) were used to coat two types of filters (melt-blown and needle-punched) for three different periods (0.5, 5 and 50 min). Rhizopus stolonifer and Penicillium expansum isolated from spoiled pears were used as test organisms. Conidial suspensions of 105 to 103 spores ml−1 were prepared in Sabouraud dextrose agar at 50°C, and a modified slide-culture technique was used to test the anti-fungal properties of the filters. Penicillium expansum was the more sensitive organism, with inhibition at 0.012 M at only 0.5 min coating time on the needle-punched filter. The longer the coating time, the more effective inhibition was for both organisms. Furthermore, it was also determined that the coating process had only a slight effect on the Youngs Moduli of the needle-punched filters, while the Youngs Moduli of the melt-blown filters is more susceptible to the coating method. This work contributes to the assessment of the efficacy of filter coating with ZnO nanopaticles aimed at inhibiting fungal growth.