Influence of processing conditions on dielectric properties of CaCu3Ti 4O12 thin films
CaCu3Ti4O12 possesses one of the largest values of the effecti ve dielectric permittivity in a large frequency and temperature range ever reported for a ce amic material, and is thus a very promising materi l for various electronic and electromechanical applic ations. The origin of such high permittivity has be en attributed to ‘electrical’ heterogeneities in the m icrostructure [1-3]. By Chemical Solution Depositio n, we have prepared CaCu 3Ti4O12 ceramic thin films under different conditions, try ing to establish the influence of microstructure on their dielectric properties.
Characterization of grain boundary impedances in fine- and coarse-grained Ca Cu 3 Ti 4 O 12 ceramics
The influence of electrode material, dc bias, and pellet thickness on the electrical properties of fine- and coarse-grained $\mathrm{Ca}{\mathrm{Cu}}_{3}{\mathrm{Ti}}_{4}{\mathrm{O}}_{12}$ (CCTO) ceramics has been investigated using impedance spectroscopy. The low frequency arc observed in ${\mathrm{Z}}^{*}$ plots near room temperature is independent of the electron work function of the metal electrode. It shows significant variation with dc bias and pellet thickness for coarse-grained ceramics, but no such variations for fine-grained ceramics. The results demonstrate the importance of ceramic microstructure in controlling the electrical properties of CCTO ceramics and support the internal barrier layer capacitor (IBLC) model of Schottky barriers at the grain boundaries between semiconducting grains. The IBLC model explains the high permittivity and nonlinear current-voltage characteristics commonly reported for CCTO ceramics.
The infection process, sporulation and survival of Alternaria helianthi on sunflower
SUMMARY 
 
Electron microscopy was used to study the infection of sunflower leaves by Alternaria helianthi. Conidia germinated by producing one to many germ tubes which grew across the leaf surface before forming appressoria. The fungus directly penetrated its host through the cuticle and epidermis. Entry into the host through wounds and stomates was also observed. Extracellular sheaths were found to be associated with germ tubes and intercellular hyphae of A. helianthi. Conidiophores developed through collapsed stomates, from leaf veins, trichomes and also from mycelium growing across the host leaf surface. Microcylic conidia were produced directly from parent conidia under certain conditions. Studies using a volumetric spore trap showed that the airborne spore concentration followed a distinct periodicity with peaks occurring between 0900 and 1100 h each day. Laboratory studies showed that safflower, noogoora burr and bathurst burr could serve as alternative hosts for A. helianthi. The pathogen was readily isolated from sunflower crop debris from a diseased crop that had been harvested 1 yr earlier.