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Field experiments were conducted at the Elora Research Station, Elora, Ontario, in 1988 and 1989 to quantify the inherent competitive ability of three white bean cultivars: OAC Gryphon, OAC Sprint, and OAC Laser growing with a naturally occurring population of annual weeds. An attempt was made to increase the competitive ability of these cultivars by altering row spacing and seeding density. Uncontrolled populations of weeds reduced white bean yields by 70%. OAC Gryphon and OAC Laser reduced weed biomass by 10 to 35% compared to OAC Sprint. The ability of cultivars to reduce weed biomass was further enhanced in medium and narrow rows compared to traditional wide rows. Cultivar, row spacing, and seeding density combinations which maximized leaf area index when grown under weedy conditions also had significantly less weed biomass. However, cultivar selection, row spacing, and seeding density did not reduce weed density. A significant negative correlation was observed between weed biomass accumulation and final yield of white bean. For each kg ha−1increase in weed biomass the corresponding white bean yield loss averaged 0.380 kg ha−1. Season-long weed competition significantly reduced total number of pods per plant, number of seeds per pod, and 100-seed weight.

Attached ultrasonic sensors can detect changes caused by crack initiation and growth if the wave path is directed through the area of critical crack formation. Dynamics of cracks opening and closing under load cause nonlinear modulation of received ultrasonic signals, enabling small cracks to be detected by stationary sensors. A methodology is presented based upon the behavior of ultrasonic signals versus applied load to detect and monitor formation and growth of cracks originating from fastener holes. Shear wave angle beam transducers operating in through transmission mode are mounted on either side of the hole such that the transmitted wave travels through the area of expected cracking. Time shift is linear with respect to load, and is well explained by path changes due to strain combined with wave speed changes due to acoustoelasticity. During subsequent in situ monitoring with unknown loads, the measured time of flight is used to estimate the load, and behavior of the received energy as a function of load is the basis for crack detection. Results are presented from low cycle fatigue tests of several aluminum specimens and illustrate the efficacy of the method in both determining the applied load and monitoring crack initiation and growth.

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Field studies were conducted in 1986 and 1987 to determine the critical period for weed control in white bean grown in Ontario. The treatments consisted of either allowing weeds to infest the crop for increasing durations after planting or maintaining plots weed free for increasing durations after planting. The beginning of the critical period was defined as the crop stage by which weed interference reduced yields by 3%. Similarly, the end of the critical period was defined as the crop stage to which the crop had to be weed free to prevent a 3% yield loss. The critical period of weed control occurred between the second-trifoliolate and first-flower stages of growth for all cultivars and years, with the exception of the cultivar ‘OAC Seaforth’ in 1986. The average number of pods per plant for both cultivars was reduced by increasing durations of weed interference after planting in both years. However, pod number of the cultivar OAC Seaforth was reduced at a greater rate in 1986 than ‘Ex Rico 23’. The beginning of the critical period corresponded with the beginning of a rapid increase in total weed biomass.

Rate-dependent constitutive relations for single crystals are derived in terms of dislocation dynamics. Contributions from slip on the individual glide planes are assumed to superpose linearly to give the total plastic strain. As an application of the theory, equations describing elastic precursor decay are developed for longitudinal plane-wave propagation in fcc, bcc, and rocksalt structures with wave propagation in the [100], [110], and [111] directions. In addition, expressions for precursor decay in zinc (hcp structure) are derived for wave propagation both parallel and perpendicular to the c-axis. Calculated theoretical results are compared with experimental data on precursor amplitudes for single-crystal copper (fcc), tungsten (bcc), NaCl (rocksalt), and LiF (rocksalt). Dislocation mobilities determined from direct observation of dislocations are used in these calculations. In general the theory predicts the proper relative order of the precursor amplitudes for different propagation directions. The comparisons show that in order for theoretically determined amplitudes to agree with experimental data, initial mobile dislocation densities must be two or three orders-of-magnitude greater than initial total densities which are measured in the material prior to shock loading. Possible explanations for this discrepancy are discussed.