Degree of polarization of light diffracted from resting striated muscle

A laser light diffractometer has been developed to measure directly the total degree of polarization of ({ie145-1}) of light diffracted and randomly scattered from striated muscle fibers. From {ie145-2} the degree of polarization ({ie145-3}) of light diffracted from the periodically arranged contractile filaments is determined. Measurements on single muscle fibers and small fiber bundles indicate that both {ie145-4} and {ie145-5} of the firstorder diffraction decrease monotonically with sarcomere length. For the second-order diffraction, {ie145-6} and {ie145-7} exhibit a peak at sarcomere length of about 3.0 μm. A proposed theory based on the anisotropic light scattering efficiencies of the thick and thin filaments can account for the measurements. The comparison between the theory and measurements indicates that the A-band, as well as the I-band, are optically anisotropic.     

Experimental stress analysis of topographic diversity in early hominid gnathic morphology

Reconstructing the biomechanics of early hominid mastication is a key element in most models of hominid differentiation. Traditionally, ostelogical features marking muscle attachment surfaces have served as a reference system from which the vector geometry of the masticatory force system and resultant force distributions could be predicted. To augment traditional morphological and computational approaches, we developed a simulation system capable of replicating human and non-human primate chewing motions. The forces of occlusion are recorded as photoelastic fringes in a urethane alveolar process. Simulation experiments evaluating the functional correlates of topographic diversity in zygomatic root position and mandibular ramus height in early hominids indicated that the mandibles and dentitions of robust australopithecines are well adapted to sustain high magnitude, low gradient load distributions.     

Polarization changes in light diffracted from contracting muscle fibers

Single fibers were isolated from the semitendinosus muscle of frog and illuminated with an He-Ne laser. The polarization of the laser beam was varied by a photoelastic modulator. The time course of the degree of polarization of light diffracted from the muscle fiber during an isometric contraction was measured directly with a time resolution of 1 ms. Tension, sarcomere length, and diffraction intensity were also measured. During the contraction cycle, the degree of polarization of the active fiber exhibited a biphasic variation relative to that of the resting fiber. Analysis identifies the movement of heavy meromyosin toward actin and the rise in myoplasmic calcium ion concentration as the main contributors to the polarization transient of active fibers. A quantitative theory describing the polarized diffraction from muscle fibers is formulated. There is good agreement between the theory and measurements.     

Finite element and photoelastic modelling of an abdominal aortic aneurysm: a comparative study

Rupture prediction of abdominal aortic aneurysms (AAAs) remains a clinical challenge. Finite element analysis (FEA) may allow for improved identification for intervention timing, but the method needs further substantiation. In this study, experimental photoelastic method and finite element techniques were compared using an idealised AAA geometry. There was good agreement between the numerical and experimental results. At the proximal and distal end of the AAA model, the maximum differences in principle strain for an internal pressure of 120 mmHg had differences ranging from 0.03 to 10.01%. The maximum difference in principle strain for the photoelastic and the finite element model at a pressure of 120 mmHg was 0.167 and 0.158, respectively. The current research strengthens the case for using FEA as an adjunct to the current clinical practice of utilising diameter measurement for intervention timing.