PubMed · 10518298
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M T Cibulka. 1999. Classifying sacroiliac dysfunction.. https://doi.org/10.2519/jospt.1999.29.9.556
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The objective of this study was to quantify the effect of specific physical and biological factors on the relative likelihood of biomechanical failure in wheat. Wind-related crop damage is a major obstacle to wheat production that costs several billion dollars per year. The four factors varied in this study were breeding line, dwarfing gene dose, soil type, and fertilization. A theoretical model describing the dynamic structural response of living plants was used to define margins of safety against global buckling, anchorage rotation, and tissue rupture. These relative safety factors were defined for each treatment in comparison with a tall wheat variety selected from a breeding line called Seri and grown in sandy soil with low fertilization. Compared to this reference, the relative safety factor against global buckling was increased (+39%, p<0.01), and the relative safety factor against anchorage rotation was decreased (-11%, p<0.025), by one allele of the dwarfing gene. The relative safety factor against tissue rupture was unaffected by the dwarfing gene but was consistently lower (-26%, p<0.01) in a second breeding line called Kauz. Soil type and fertility did not affect the relative safety factors and this negative finding was significant at p<0.05. The key finding was that the strength of wheat was affected more by genetic rather than by environmental factors, which suggests that some varieties are intrinsically more robust than others. Also, the relative safety factor against anchorage rotation was inversely proportional to the relative safety factor against buckling, which suggests that there are competing constraints on the dynamic structural behavior of wheat.
The stability of shape fluctuations of a flat charged membrane immersed in a fluid is analyzed using a linear stability analysis. A displacement of the membrane surface causes a fluctuation in the conterion density at the surface. This in turn causes an additional contribution to the force density in the momentum equation for the fluid, which results in a normal stress at the surface which is opposite in direction to the stress caused by surface tension. This electrohydrodynamic effect destabilizes fluctuations when the surface potential exceeds a critical value.
BACKGROUND: Despite widespread acknowledgement that strain injuries do occur to surgeons, ergonomic assessments in minimally invasive surgery are comparatively rare. Current assessment techniques rely on labor-intensive manual recording techniques, so there is a need for an automated system. METHODS: We used an optoelectronic measurement system to make postural measurements at frequencies of ~5 Hz and then converted these measurements to ergonomic stress scores using a modified Rapid Upper Limb Assessment (RULA) method. RESULTS: We successfully recorded postures at least once per second during 96% of the time the surgeon was performing tissue manipulation tasks. We found that the ergonomic stress scores were comparatively high throughout the procedure, particularly for the wrist. CONCLUSION: An automated high-frequency postural measurement system is feasible for making ergonomic assessments in an intraoperative setting. Such a system will also be a critical component in validating surgical simulations for use in training and credentialing surgeons and in designing and evaluating equipment.