16 research outputs found
Ultrasonic study of the gelation of gelatin: phase diagram, hysteresis and kinetics
We map the ultrasonic (8 MHz) speed and attenuation of edible-grade gelatin
in water, exploring the key dependencies on temperature, concentration and
time. The ultrasonic signatures of the sol-gel transition, confirmed by
rheological measurements, and incomplete gel formation at low concentrations,
enable a phase diagram of the system to be constructed. Sensitivity is also
demonstrated to the kinetics of gel formation and melting, and associated
hysteresis effects upon cyclic temperature sweeps. Furthermore, simple acoustic
models of the sol and gel state enable estimation of the speed of sound and
compressibility of gelatin. Our results demonstrate the potential of ultrasonic
measurements to characterise the structure and visco-elasticity of gelatin
hydrogels.Comment: 15 pages, 8 figure
Reductions in grassland species evenness increase dicot seedling invasion and spittle bug infestation
Previous experiments that tested whether diverse plant communities have lower invasibility have all varied species richness. We experimentally varied evenness of four grassland species (three grasses and one forb) by planting a field experiment in Texas, and monitored the number of unplanted dicot and monocot species that invaded plots for two growing seasons. By varying evenness, we eliminated any sampling effect in our diversity treatment, because all plots contained the same plant species. Experimentally reducing evenness led to a greater number of dicot invaders, which emerged in plots throughout the growing season, but had less of an effect on monocot invaders, which emerged in flushes when experimental plants were semi-dormant. Frequency of Solidago canadensis (altissima) stems with spittle bugs significantly increased with reductions in evenness during the first year, apparently because the greater number of Solidago stems in high evenness plots diluted the spittle-bug effect. These results support the view that higher diversity plant communities are more resistant to dicot invaders and insect herbivores