Ignition and Extinction Behavior of Fuels in a Microcombustor
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Combustion in microscale heat-recirculating burners
In order to optimize the design of microscale combustors, macroscale spiral counterflow heat-recirculating "Swiss Roll" burners were constructed and tested using hydrocarbon fuels at the Reynolds and Damkhler numbers typical of desired microscale values. Both Ò2DÓ Swiss Roll burners (basically a linearly extruded spiral shape) and fully Ò3DÓ Swiss Roll burners (in which the spiral is extruded in a circular pattern to create a toroidal geometry) were built using a ceramic "rapid prototyping" technique. It was found that combustion could be sustained in a low-temperature "flameless" mode in which no visible flame occurs. Mixtures well below the conventional lean flammability limit could be burned even at mean flow velocities 30 times the stoichiometric laminar burning velocity. The addition of catalytic materials in the combustion region was found to either increase or decrease the range of flammable mixtures, by substantial amounts in both cases, depending on the Reynolds number. The possibility of using fuels that are selfstarting (i.e. require no external ignition source) on catalytic surfaces was also explored. Preliminary numerical simulations compared rather poorly with the experimental results, most likely due to inaccurate heat loss and chemical reaction rate (both gasphase and surface) sub-models. It is concluded that combustion in microscale burners is feasible, however, heat recirculation, catalysis and careful management of heat losses are essential to the success of such designs.
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.