To estimate the near-fault inelastic response spectra, the accuracy of six existing strength reduction factors （R） proposed by different investigators were evaluated by using a suite of near-fault earthquake records...To estimate the near-fault inelastic response spectra, the accuracy of six existing strength reduction factors （R） proposed by different investigators were evaluated by using a suite of near-fault earthquake records with directivity-induced pulses. In the evaluation, the force-deformation relationship is modelled by elastic-perfectly plastic, bilinear and stiffness degrading models, and two site conditions, rock and soil, are considered. The R-value ratio （ratio of the R value obtained from the existing R-expressions （or the R-p-T relationships） to that from inelastic analyses） is used as a measurement parameter. Results show that the R-expressions proposed by Ordaz ＆ Perez-Rocha are the most suitable for near-fault ground motions, followed by the Newmark ＆ Hall and the Berrill et al. relationships. Based on an analysis using the near-fault ground motion dataset, new expressions of R that consider the effects of site conditions are presented and verified.展开更多
Endothelium is the interior layer of an artery made up of tremendous number of endothelial cells which are located side by side. Finding the effective parameters that cause the cells to obtain mechanical strength in d...Endothelium is the interior layer of an artery made up of tremendous number of endothelial cells which are located side by side. Finding the effective parameters that cause the cells to obtain mechanical strength in different morphologies is an important issue in cell biomechanics. In this work a numerical model for a single endothelial cell is developed. This model includes cell’s plasma membrane and nucleus using the traingular network of spectrin level approach. Cy-toskeleton main components such as intermediate and actin filaments as well as microtubules are the other important subsets of the simulated model. Mass and spring theory is utilized in cytoskeleton components simulation. A spreading model is applied on the cell in order to simulate the adhesion on a substrate and test the model’s qualitative performance and the result is verified by the experiment. Also deformation of the cell caused by an external compressive force is another quantitative test which is predicted by the model and the results are validated with an experimental AFM test. The two most popular morphologies of the cells resulted from this work are the cell suspension morphology which is the result of no external forces and the cell adherent morphology which is the result of cell adhesion to the extracellular matrix. The mechanical stiffness of the endothelial cell is obtained in this simulation.展开更多
Cell poking is an experimental technique that is widely used to study the mechanical properties of plant cells. A full understanding of the mechanical responses of plant cells to poking force Is helpful for experiment...Cell poking is an experimental technique that is widely used to study the mechanical properties of plant cells. A full understanding of the mechanical responses of plant cells to poking force Is helpful for experimental work. The aim of this study was to numerically investigate the stress distribution of the cell wall, cell turgor, and deformation of plant cells in response to applied poking force. Furthermore, the locations damaged during poking were analyzed. The model simulates cell poking, with the cell treated as a spherical, homogeneous, isotropic elastic membrane, filled with incompressible, highly viscous liquid. Equilibrium equations for the contact region and the non-contact regions were determined by using membrane theory. The boundary conditions and continuity conditions for the solution of the problem were found. The forcedeformation curve, turgor pressure and tension of the cell wall under cell poking conditions were obtained. The tension of the cell wall circumference was larger than that of the meridian. In general, maximal stress occurred at the equator around. When cell deformation increased to a certain level, the tension at the poker tip exceeded that of the equator. Breakage of the cell wall may start from the equator or the poker tip, depending on the deformation. A nonlinear model is suitable for estimating turgor, stress, and stiffness, and numerical simulation is a powerful method for determining plant cell mechanical properties.展开更多
基金Foundation for Research and Science and Technology of New Zealand, Contract Number: C05X0208 and C05X0301the Foundation for Western Transportation Science and Technology Research, Contract No. 200831800098
文摘To estimate the near-fault inelastic response spectra, the accuracy of six existing strength reduction factors （R） proposed by different investigators were evaluated by using a suite of near-fault earthquake records with directivity-induced pulses. In the evaluation, the force-deformation relationship is modelled by elastic-perfectly plastic, bilinear and stiffness degrading models, and two site conditions, rock and soil, are considered. The R-value ratio （ratio of the R value obtained from the existing R-expressions （or the R-p-T relationships） to that from inelastic analyses） is used as a measurement parameter. Results show that the R-expressions proposed by Ordaz ＆ Perez-Rocha are the most suitable for near-fault ground motions, followed by the Newmark ＆ Hall and the Berrill et al. relationships. Based on an analysis using the near-fault ground motion dataset, new expressions of R that consider the effects of site conditions are presented and verified.
文摘Endothelium is the interior layer of an artery made up of tremendous number of endothelial cells which are located side by side. Finding the effective parameters that cause the cells to obtain mechanical strength in different morphologies is an important issue in cell biomechanics. In this work a numerical model for a single endothelial cell is developed. This model includes cell’s plasma membrane and nucleus using the traingular network of spectrin level approach. Cy-toskeleton main components such as intermediate and actin filaments as well as microtubules are the other important subsets of the simulated model. Mass and spring theory is utilized in cytoskeleton components simulation. A spreading model is applied on the cell in order to simulate the adhesion on a substrate and test the model’s qualitative performance and the result is verified by the experiment. Also deformation of the cell caused by an external compressive force is another quantitative test which is predicted by the model and the results are validated with an experimental AFM test. The two most popular morphologies of the cells resulted from this work are the cell suspension morphology which is the result of no external forces and the cell adherent morphology which is the result of cell adhesion to the extracellular matrix. The mechanical stiffness of the endothelial cell is obtained in this simulation.
基金Supported by the National Natural Science Foundation of China(10472132)
文摘Cell poking is an experimental technique that is widely used to study the mechanical properties of plant cells. A full understanding of the mechanical responses of plant cells to poking force Is helpful for experimental work. The aim of this study was to numerically investigate the stress distribution of the cell wall, cell turgor, and deformation of plant cells in response to applied poking force. Furthermore, the locations damaged during poking were analyzed. The model simulates cell poking, with the cell treated as a spherical, homogeneous, isotropic elastic membrane, filled with incompressible, highly viscous liquid. Equilibrium equations for the contact region and the non-contact regions were determined by using membrane theory. The boundary conditions and continuity conditions for the solution of the problem were found. The forcedeformation curve, turgor pressure and tension of the cell wall under cell poking conditions were obtained. The tension of the cell wall circumference was larger than that of the meridian. In general, maximal stress occurred at the equator around. When cell deformation increased to a certain level, the tension at the poker tip exceeded that of the equator. Breakage of the cell wall may start from the equator or the poker tip, depending on the deformation. A nonlinear model is suitable for estimating turgor, stress, and stiffness, and numerical simulation is a powerful method for determining plant cell mechanical properties.
