SynopsisThe tensile and dynamic mechanical properties of poly(norbornene), prepared through ring-opening polymerization, were studied. Tensile strength and extensibility increased, while Young's modulus decreased with increasing molecular weight and with increasing content of trans relative to cis unsaturation. The damping factor A was dependent on molecular weight only for the lower molecular weight samples. The out-of-phase modulus E" and the damping factor decreased as the translcis ratio increased.
The images etched in a positive photoresist layer by means of polychromatic exposures and all-reflective projection printing methods can be described by a model presented elsewhere.For that model, the lateral intensity distributions of the optical image need be computed only at a single effective exposure wavelength that is compatible with a properly focused resist image profile. Although the illumination in the optical system we used was partially coherent, we successfully used the effective enhanced numerical aperture for the system, and calculated the lateral intensity distribution in the optical image on the assumption of incoherent illumination.In this study, we deposited a layer of Al over a Si substrate wafer which we then coated with a layer of quartz and a layer of positive photoresist.We calculated the dynamic exposure response of the photoresist film by using the modulation transfer function of a defocused perfect lens in order to simulate the resist images from zero to a few Rayleigh units of defocus.Simulated and experimentally determined resist image profiles and linewidths were compared and shown to be in good agreement. The results of this comparison lead us to believe that defocusing at the time of our study was caused by a tilt of the wafer along the scan axis.
Background Modern computational modeling could provide the key to obtaining new insights into the mechanisms of maize stalk failure as well as suggesting new ways to improve stalk strength. However, a complete set of mechanical properties of maize tissues is required to enable computational modeling of maize stems. This study developed two compression test methods for obtaining the longitudinal modulus of elasticity of both rind and pith tissues, assessed the influence of water content on tissue properties, and investigated the relationship between rind modulus and pith modulus. These methods involved uniform 5–7 cm segments of maize stems which were scanned using a flatbed scanner then tested in compression using a universal testing machine in both intact and dissected (rind-only and pith-only) states. Results The modulus of elasticity of pith tissues was highest for fully turgid specimens and decreased as water was removed from the specimens. Water content was negatively correlated with the modulus of elasticity of the rind. Rind and pith tissues were found to be weakly correlated. The median ratio of rind modulus to pith modulus was found to be 17. Of the two methods investigated, the pith-only specimen preparation was found to be simple reliable while the rind-only method was found to be adversely affected by lateral bowing of the specimen. Conclusions Researchers can use the information in this paper to improve computational models of maize stems in three ways: (1) by incorporating realistic values of the longitudinal modulus of elasticity of pith and rind tissues; (2) by selecting pith and rind properties that match empirically observed ratios; and (3) by incorporating appropriate dependencies between these material properties and water content. From an experimental perspective, the intact/pith-only experimental method outlined in this paper is simpler than previously reported methods and provides reliable estimates of both pith and rind modulus of elasticity values. Further research using this measurement method is recommended to more clearly understand the influence of water content and turgor pressure on tissue properties.
Maize stalk lodging is the structural failure of the stalk prior to harvest and is a major problem for maize (corn) producers and plant breeders. To address this problem, it is critical to understand precisely how geometric and material parameters of the maize stalk influence stalk strength. Computational models could be a powerful tool in such investigations, but current methods of creating computational models are costly, time-consuming, and most importantly, do not provide parameterized control of the maize stalk parameters. The purpose of this study was to develop and validate a parameterized three-dimensional model of the maize stalk. The parameterized model provides independent control over all aspects of the maize stalk geometry and material properties. The model accurately captures the shape of actual maize stalks and is predictive of maize stalk stiffness and strength. The model was validated using stochastic sampling of material properties to account for uncertainty in the values and influence of mechanical tissue properties. Results indicated that buckling is influenced by material properties to a greater extent that flexural stiffness. Finally, we demonstrate that this model can be used to create an unlimited number of synthetic stalks from within the parameter space. This model will enable the future implementation of parameter sweep studies, sensitivity analysis and optimization studies, and can be used to create computational models of maize stalks with any desired combination of geometric and material properties.
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