Soils with a history of 2,4-dichlorophenoxyacetic acid (2,4-D) treatment at field application rates and control soils with no prior exposure to 2,4-D were amended with 2,4-D in the laboratory. Before and during these treatments, the populations of 2,4-D-degrading bacteria were monitored by most-probable-number (MPN) enumeration and hybridization analyses, using probes for the fd genes of plasmid pJP4, which encode enzymes for 2,4-D degradation. Data obtained by these alternate methods were compared. Several months after the most recent field application of 2,4-D (-1 ppm), soils with a 42-year history of 2,4-D treatment did not have significantly higher numbers of 2,4-D-degrading organisms than did control soils with no prior history of treatment. In response to laboratory amendments with 2,4-D, both the previously treated soils and those with no prior history of exposure exhibited a dramatic increase in the number of 2,4-D-metabolizing organisms. The MPN data indicate a 4to 5-log population increase after one amendment with 250 ppm of 2,4-D and ultimately a 6to 7-log increase after four additional amendments, each with 400 ppm of 2,4-D. Similarly, when total bacterial DNA from the soil microbial community of these samples was analyzed by using a probe for the efd4 gene (2,4-D monooxygenase) or the fdB gene (2,4-dichlorophenol hydroxylase) a dramatic increase in the level of hybridization was observed in both soils. Probes to the fdC,-D,-E, and-F genes did not hybridize to the bacterial community DNA to any significant extent before or after 2,4-D treatment, indicating that pathways different from the canonical pJP4-encoded pathway at the DNA sequence level, and possibly at the functional level, account for the degradative activity in these soils. Quantitative hybridization data and MPN values were in agreement, indicating that most of the 2,4-D-degrading populations were detected by the (fdA and #dB gene

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High resolution experimental characterization of material stretch and rotation fields in relatively fine-grained polycrystals has been limited, inhibiting direct comparison with predictions of crystal plasticity theory. In this study, micron scale grids used more commonly in etching of substrates for microelectronic circuits were deposited on specimens of Oxygen Free High Conductivity Copper (OFHC Cu) subsequently subjected to uniaxial compressive deformations to effective strain levels up to unity. Material stretch and rotation fields were assessed for fields of view encompassing on the order of 20 grains. Some rather striking features emerge, including the apparent relative lack of deformation in regions sized on the order of large grains, and the apparent concentration of stretch and rotation in bands surrounding these relatively undeformed areas. Comparisons are drawn with results of 3D crystal plasticity calculations performed on digitized grain structures that conform to representative microstructures in terms of initial grain size and shape distributions. The crystal plasticity simulations predict regions of relatively large rotation and relatively localized stretch traversing multiple grains. The numerical solutions also exhibit slightly higher local stresses in the vicinity of grain boundaries and triple points than in grain interiors, a phenomenon attributed to local lattice misorientation among neighboring grains. However, the crystal plasticity calculations do not, in an average sense, predict larger-than-average maximum stretch or rotation in the grain boundary regions. The numerical solutions are also quite sensitive to initial lattice orientations assigned to the grains. Comments are made regarding the segmentation of slip within the grains and its implications for modeling, based upon direct comparison of results from experiments and simulations.

Finite element simulations of ball and cone indentation tests were performed with systematic variations in the input constitutive laws. The ball indentation simulations were used to evaluate the assumptions and applicability of proposed analytical methods to extract the constitutive laws from instrumented load-penetration data. These methods were found to provide good approximations for a small, but useful, range of strain-hardening rates. However, significant differences were found for low (elastic-perfectly plastic) and high (hardening exponents > 0.2) strain-hardening laws and when significant hardening occurs at small plastic strains (< 0.02). The cone indentation simulations were used to investigate the corresponding effects of constitutive behavior on the pile-up geometry around the indentation. In agreement with previous work, the height-to-width aspect ratio of the pile-up increases with a decreasing strain-hardening exponent. However, the pile-up aspect ratio method is sensitive only to the average strain-hardening exponent, and not to details of the constitutive behavior at very high and low strains.

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