Research was conducted to formulate a temperature-dependent population level model for johnsongrass seed germination and rhizome bud break. A nonlinear poikilotherm rate equation was used to describe development rate as a function of temperature, and a temperature-independent Weibull function was used to distribute development times for the population. Seed germination and initiation of rhizome bud break of johnsongrass were collected under constant temperature conditions to parameterize the model. Seed germination rate increased with temperature up to 36 C, then declined at 40 C. Rate of rhizome bud break increased with temperature up to 32 C, then rapidly decreased with further temperature increases. Rate of rhizome bud break was higher than for seed germination at temperatures of 32 C or below, but lower at higher temperatures. Time to first germination or bud break event was longer for seed than for rhizomes, but subsequent progression of development was higher for seed. A population level temperature-dependent model was developed by coupling the poikilotherm equation with the Weibull function. The model was validated against two independent seed germination and three independent rhizome bud germination data sets.

Research was conducted to determine the utility of a single, temperature-independent Weibull function for describing cumulative seed germination under several temperature regimes with 14 sets of weed and crop seed germination data. A modified cumulative Weibull function was derived to distribute germination times for individuals within the population and distributed the occurrence of germination given ample sample size and appropriate sample interval. The descriptive and predictive attributes of the stochastic model component are well suited for incorporation into seed germination models and are likely applicable to models to predict distribution of times for other developmental processes of plants.

Research was conducted to determine the suitability of the Fermi-Dirac distribution function for modeling the seedling emergence of downy brome, johnsongrass, and round-leaved mallow, as influenced by burial depth. Six sets of previously published emergence data were used to formulate the model and test its adequacy. Two independent johnsongrass emergence data sets were used to validate the model. Constant temperature growth chamber studies were conducted to evaluate the effects of temperature and moisture on the model parameters. The Fermi-Dirac distribution function was found to adequately describe the seedling emergence of downy brome, johnsongrass, and round-leaved mallow as indicated by a good visual data fit, narrow confidence intervals for the model parameters, and regression analysis of observed vs. modeled data. Although this function is a model used in physical science, its parameters can be related to abiotic factors such as soil texture, temperature, and moisture.

Research was conducted to formulate a temperature-dependent population-level model to predict rhizome johnsongrass development to the four-leaf stage. A nonlinear poikilotherm rate equation was used to describe development rates as a function of temperature. Development rate was highest at 36 C and declined at higher temperatures. A temperature-independent Weibull function adequately distributed development times for the population. Coupling the poikilotherm rate equation and the Weibull distribution function yielded a model suitable for characterizing rhizome johnsongrass development to the four-leaf growth stage. The model was tested and validated against independent data sets. Model predictions of 80% of rhizome johnsongrass population at the four-leaf stage were used as the central point of a 4-d application window for using reduced rates of herbicides in johnsongrass management programs. This application window included an average interval of 85 to 99% of johnsongrass population at the desired growth stage in field validation experiments.

This paper presents the mechanical characterization of the elastic modulus, hardness and fracture toughness of silicon oxynitride films (SiON) with different oxygen and nitrogen content, subjected to thermal annealing processed at 400 °C and 800 °C. The Fourier-transform infrared (FT-IR) spectroscopy was employed to characterize the SiON films with respect to the absorbance peak in the infrared spectrum. The nanoindentation testing showed that both the elastic modulus and hardness slightly increased after thermal annealing. Finally, the fracture toughness of the SiON films were estimated using Vickers micro-indentation tests and the result revealed that the fracture toughness decreased with increasing rapid thermal annealing (RTA) temperature and nitrogen content. We believe these results benefit microelectromechanical systems (MEMS) in regards to maintaining the structural integrity and improving reliability performance.

In this work, thin ALD alumina films were fabricated for evaluating their capabilities as a barrier material for corrosive environments. The fracture toughness and the corrosion-resisting properties after fatigue cycle of these thin ALD alumina films have been characterized. Indentation tests indicate that the ALD alumina/Al structures could enhance both the yield strength of the metal and the effective fracture toughness of the coated ALD alumina films and this result could be useful for designing nanocomposite structures. However, the test results also indicate that the interfacial strength of the ALD/Al structures was prone to degrade under fatigue loading under corrosive environment. This could potentially be a problem for the long term reliability of related devices operated under a harsh environment. In addition, the strong correlation between indentation behavior and fatigue loading for the structure indicate that nanoindentation response could be possibly used to indicate the damage level of microstructures for future reliability evaluations.