The Experts below are selected from a list of 258 Experts worldwide ranked by ideXlab platform
Felix W Wehrli - One of the best experts on this subject based on the ideXlab platform.
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quantification of the roles of trabecular microarchitecture and trabecular type in determining the elastic modulus of human trabecular bone
Journal of Bone and Mineral Research, 2006Co-Authors: Paul Sajda, Punam K Saha, Felix W WehrliAbstract:The roles of microarchitecture and types of trabeculae in determining elastic modulus of trabecular bone have been studied in μCT images of 29 trabecular bone samples by comparing their Young's moduli calculated by finite element analysis (FEA) with different trabecular type-specific reconstructions. The results suggest that trabecular plates play an essential role in determining elastic properties of trabecular bone. Introduction: Osteoporosis is an age-related disease characterized by low bone mass and architectural deterioration. Other than bone volume fraction (BV/TV), microarchitecture of bone is also believed to be important in governing mechanical properties of trabecular bone. We quantitatively examined the role of microarchitecture and relative contribution of trabecular types of individual trabecula in determining the elastic property of trabecular bone. Materials and Methods: Twenty-nine human cadaveric trabecular bone samples were scanned at 21-μm resolution using a μCT system. Digital topological analysis (DTA) consisting of skeletonization and classification was combined with a trabecular type-specific reconstruction technique to extract the skeleton and identify topological type of trabeculae of the original trabecular bone image. Four different μCT-based finite element (FE) models were constructed for each specimen: (1) original full voxel; (2) skeletal voxel; (3) rod-reconstructed, preserving rod volume and plate skeleton; and (4) plate-reconstructed, preserving plate volume and rod skeleton. For each model, the elastic moduli were calculated under compression along each of three image-Coordinate Axis directions. Plate and rod tissue fractions directly measured from DTA-based topological classification were correlated with the elastic moduli computed from full voxel model. Results: The elastic moduli of skeleton models were significantly correlated with those of full voxel models along all three Coordinate axes (r2 = 0.38−0.53). The rod-reconstructed model contained 21.3% of original bone mass and restored 1.5% of elastic moduli, whereas the plate-reconstructed model contained 90.3% of bone mass and restored 53.2% of elastic moduli. Plate tissue fraction showed a significantly positive correlation (r2 = 0.49) with elastic modulus by a power law, whereas rod tissue fraction showed a significantly negative correlation (r2 = 0.42). Conclusions: These results quantitatively show that the microarchitecture alone affects elastic moduli of trabecular bone and trabecular plates make a far greater contribution than rods to the bone's elastic behavior.
Mujde Guzelkaya - One of the best experts on this subject based on the ideXlab platform.
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sliding mode control of high order systems using a constant nonlinear sliding surface on a transformed Coordinate Axis
Journal of Vibration and Control, 2008Co-Authors: Sezai Tokat, Ibrahim Eksin, Mujde GuzelkayaAbstract:Sliding mode control allows insensitivity to bounded parameter variations, and rejection of disturbances. However, this property is valid only in the sliding phase. Therefore, various studies have been performed with the aim of improving system performance by minimizing, or even removing, the time needed to reach the sliding phase. Sliding surface design is one method of achieving this aim. In this study, a new approach to the design of nonlinear sliding surface for high order systems, which relies on defining a new Coordinate Axis, is proposed. A constant and nonlinear sliding surface is presented in this newly defined Coordinate Axis. Next, the control law for the proposed method is derived, and it is seen that the equivalent control term is composed of the equivalent control term of the conventional sliding mode controller and an additive signal, which is a nonlinear function of the system state error vector and conventional sliding surface design parameters. In order to set these design parameters, va...
Alok Kumar Samanta - One of the best experts on this subject based on the ideXlab platform.
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projection of the dynamics of electron transfer reaction in dual space onto the one dimensional slower reaction Coordinate Axis
Journal of Physical Chemistry B, 2015Co-Authors: Aniket Patra, Kanagala Ajay Acharya, Alok Kumar SamantaAbstract:We have derived here for the first time an exact dynamical equation within the domain of classical mechanics for the time dependent density distribution function of one-dimensional reaction Coordinate (RC) in the condensed phase for electron transfer reaction by projecting the dynamics of slower modes in multidimensional Liouville space starting with a given set of Coordinates of the faster modes. After the faster modes were ensemble averaged, the dynamics of the whole system solely depends on the slower RC. To simplify the complicated equation into a tractable form, benchmark approximations are employed to reduce the formally exact equation into an equation similar to the Smoluchowski equation with a delocalized sink term. As a test case, a Hamiltonian for the solute–solvent system modeled by quadratic functions for fast-relaxing vibrational and slow-relaxing polarization modes, respectively, has been considered. Interestingly, our simplified kinetic equation corresponding to this model Hamiltonian is tr...
Jussi Valtonen - One of the best experts on this subject based on the ideXlab platform.
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cognitive representation of orientation a case study
Cortex, 2008Co-Authors: Jussi Valtonen, Daniel D Dilks, Michael MccloskeyAbstract:Abstract Although object orientation in the human brain has been discussed extensively in the literature, the nature of the underlying cognitive representation(s) remains uncertain. We investigated orientation perception in BC, a patient with bilateral occipital and parietal damage from a herpes encephalitis infection. Our results show that in addition to general inaccuracy in discriminating and reproducing line orientations, her errors take the form of left–right mirror reflections across a vertical Coordinate Axis. We propose that in BC, the cognitive impairment is in failing to represent the direction of tilt for line orientations. Our results suggest that there exists a level of representation in the human brain at which line orientations are represented compositionally, such that the direction of a line orientation's tilt from a vertical mental reference meridian is coded independently of the magnitude of its angular displacement. Reflection errors across a vertical Axis were observed both in visual and tactile line orientation tasks, demonstrating that these errors arise at a supra-modal level of representation not restricted to vision, or, alternatively, that visual-like representations are being constructed from the tactile input.
Paul Sajda - One of the best experts on this subject based on the ideXlab platform.
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quantification of the roles of trabecular microarchitecture and trabecular type in determining the elastic modulus of human trabecular bone
Journal of Bone and Mineral Research, 2006Co-Authors: Paul Sajda, Punam K Saha, Felix W WehrliAbstract:The roles of microarchitecture and types of trabeculae in determining elastic modulus of trabecular bone have been studied in μCT images of 29 trabecular bone samples by comparing their Young's moduli calculated by finite element analysis (FEA) with different trabecular type-specific reconstructions. The results suggest that trabecular plates play an essential role in determining elastic properties of trabecular bone. Introduction: Osteoporosis is an age-related disease characterized by low bone mass and architectural deterioration. Other than bone volume fraction (BV/TV), microarchitecture of bone is also believed to be important in governing mechanical properties of trabecular bone. We quantitatively examined the role of microarchitecture and relative contribution of trabecular types of individual trabecula in determining the elastic property of trabecular bone. Materials and Methods: Twenty-nine human cadaveric trabecular bone samples were scanned at 21-μm resolution using a μCT system. Digital topological analysis (DTA) consisting of skeletonization and classification was combined with a trabecular type-specific reconstruction technique to extract the skeleton and identify topological type of trabeculae of the original trabecular bone image. Four different μCT-based finite element (FE) models were constructed for each specimen: (1) original full voxel; (2) skeletal voxel; (3) rod-reconstructed, preserving rod volume and plate skeleton; and (4) plate-reconstructed, preserving plate volume and rod skeleton. For each model, the elastic moduli were calculated under compression along each of three image-Coordinate Axis directions. Plate and rod tissue fractions directly measured from DTA-based topological classification were correlated with the elastic moduli computed from full voxel model. Results: The elastic moduli of skeleton models were significantly correlated with those of full voxel models along all three Coordinate axes (r2 = 0.38−0.53). The rod-reconstructed model contained 21.3% of original bone mass and restored 1.5% of elastic moduli, whereas the plate-reconstructed model contained 90.3% of bone mass and restored 53.2% of elastic moduli. Plate tissue fraction showed a significantly positive correlation (r2 = 0.49) with elastic modulus by a power law, whereas rod tissue fraction showed a significantly negative correlation (r2 = 0.42). Conclusions: These results quantitatively show that the microarchitecture alone affects elastic moduli of trabecular bone and trabecular plates make a far greater contribution than rods to the bone's elastic behavior.