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Passive Structures (passive + structure)
Selected AbstractsSeptation of the anorectal and genitourinary tracts in the human embryo: Crucial role of the catenoidal shape of the urorectal sulcusBIRTH DEFECTS RESEARCH, Issue 4 2002Daniel S. Rogers Background Previous studies of the tracheoesophageal sulcus and the sulci of the developing heart have suggested that the catenoidal or saddle-shaped configuration of the sulcus had mechanical properties that were important to developmental processes by causing regional growth limitation. We examined the development of the human perineal region to determine if a similar configuration exists in relation to the urorectal septum. We wished to re-examine the controversial issue of the role of the urorectal sulcus in the partitioning of the cloaca. Methods Digitally scanned photomicrographs of serial histologic sections of embryos from Carnegie stages 13, 15, 18, and 22, obtained from the Carnegie Embryological Collection were used. Each image was digitally stacked, aligned, and isolated using image-editing software. Images were compiled using 3-D image-visualization software (T-Vox), into full 3-D voxel-based volume renderings. Similarly, digital models were made of the urogenital sinus, anorectum, cloaca, allantois, mesonephric ducts, ureters, and kidneys by isolating their associated epithelium in each histologic section and compiling the data in T-Vox. Methods were developed to create registration models for determining the exact position and orientation of outlined structures within the embryos. Results Models were oriented and resectioned to determine the configuration of the urorectal sulcus. The results show that the urorectal sulcus maintains a catenoidal configuration during the developmental period studied and, thus, would be expected to limit caudal growth of the urorectal septum. Conclusion The observations support the concept that the urorectal septum is a passive structure that does not actively divide the cloaca into urogenital and anorectal components. Teratology 66:144,152, 2002. © 2002 Wiley-Liss, Inc. [source] The intertarsal joint of the ostrich (Struthio camelus): Anatomical examination and function of passive structures in locomotionJOURNAL OF ANATOMY, Issue 6 2009Nina U. Schaller Abstract The ostrich (Struthio camelus) is the largest extant biped. Being flightless, it exhibits advanced cursorial abilities primarily evident in its characteristic speed and endurance. In addition to the active musculoskeletal complex, its powerful pelvic limbs incorporate passive structures wherein ligaments interact with joint surfaces, cartilage and other connective tissue in their course of motion. This arrangement may enable energy conservation by providing joint stabilisation, optimised limb segment orientation and automated positioning of ground contact elements independently of direct muscle control. The intertarsal joint is of particular interest considering its position near the mid-point of the extended limb and its exposure to high load during stance with significant inertial forces during swing phase. Functional-anatomical analysis of the dissected isolated joint describes the interaction of ligaments with intertarsal joint contours through the full motion cycle. Manual manipulation identified a passive engage-disengage mechanism (EDM) that establishes joint extension, provides bi-directional resistance prior to a transition point located at 115° and contributes to rapid intertarsal flexion at toe off and full extension prior to touch down. This effect was subsequently quantified by measurement of intertarsal joint moments in prepared anatomical specimens in a neutral horizontal position and axially-loaded vertical position. Correlation with kinematic analyses of walking and running ostriches confirms the contribution of the EDM in vivo. We hypothesise that the passive EDM operates in tandem with a stringently coupled multi-jointed muscle-tendon system to conserve the metabolic cost of locomotion in the ostrich, suggesting that a complete understanding of terrestrial locomotion across extinct and extant taxa must include functional consideration of the ligamentous system. [source] Electrically adjustable thermotropic windows based on polymer gelsPOLYMERS FOR ADVANCED TECHNOLOGIES, Issue 11-12 2003Tamás Gyenes Abstract Several attempts have been made recently in order to develop "Smart" windows, which can moderate light and heat intensities. Based upon the phase transitions of polymer gels, a novel electrically adjustable window, which includes a gel layer, has been developed in our laboratory. Unlike other electrically controlled structures, the optical properties of the gel layer are abruptly modified by the Joule heat of audio frequency AC current. The so-called "gel-glass" becomes opaque when the temperature exceeds a critical value and changes back to its original transparent state when it is cooled down again. This method results in fast control and relatively low operational cost. Two types of gel-glasses,active and passive structures,have been developed and investigated. In this paper, we demonstrate the structural build-up and working of these novel electrically adjustable thermotropic windows. Experimental studies have been made at different frequencies and voltages. The optical properties, as well as the energy balance of the systems, have been reported. Copyright © 2003 John Wiley & Sons, Ltd. 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