The structural transition of carbon films including unstable linear chain components upon rare-gas exposure has been investigated by using molecular dynamics simulations. The carbon film with about 33.5%sp/sp^2 ratio was exposed to helium or argon gas atmosphere at pressures of 1, 5, 20, 50atm for up to nanoseconds timescale at room temperature, and the simulation revealed that the helium gas induced more sp-sp^2 transitions than argon gas. The residence time analysis showed that the frequent collisions with a small momentum exchange were more critical for the unstable linear chain.

抄録全体を表示

Large-scale molecular dynamics simulations of high acceleration energy single impacts on diamond and amorphous carbon surfaces were performed using the molecular dynamics method in order to investigate the cluster surface interaction. A transient crater is formed on the diamond surface while a permanent one is formed on the amorphous surface. The cluster size and velocity dependence on the transient crater's structure, volume, depth and radius were also clarified. Furthermore, multiple impacts on amorphous surface were also performed to investigate the possibility of surface hardening of amorphous carbon.

抄録全体を表示

The jet of linear shaped charges (LSC) has been utilized separation of space rocket's components or cutting of large steel constructions. The behavior of the jet still remains unexplained. We experimented with visualization of the jet using the flash X-ray shooting system. We also conducted numerical simulation using the AUTODYN, applied the multi-material Euler solver. Some X-ray photos indicate that the velocity of the jet is approximately 3,000m/s at the tip of the jet. Although the number of meshes on the calculation model was not enough to get an accurate result, we decided that the multi-material Euler solver is useful for evaluating the performance of the LSC jet.

抄録全体を表示

We formulate a mathematical model to describe the stress-strain relationship of the porcine thoracic aorta under uniaxial tensile loadings. We assume that the vascular wall consists of elastic fibers and collagen fibers, both orienting in three rectangular directions, and a fluid phase which has static pressure. It is also assumed that the distribution of the natural length of these fibers is expressed by a Gaussian function and that the elastic fibers show a linear stress-strain relationship while the collagen fibers show a nonlinear one under tension and no resistance under compression. The model is applied to simulate the stress-strain relationship of the aortic specimens with and without freezing and thawing. The numerical simulation results describe a hardening of the aorta by shortening the natural length of collagen fibers, which may reflect the micro-structural change in the collagen fiber networks.

抄録全体を表示

When a large scaled structure, typically represented by bridge structures in civil engineering area, is designed, the effect of dynamic wind load cannot be neglected. As the counter measure to the load, Tuned Mass Damper is applied in some case. The author investigated the damping effect of a friction force, which is acted to the surface between a trolley wheel and the rail, through the simulation. As a result, the damping effect is turned out to be sensitive to the position of the trolley, with regard to the whole length of the main girder. In this paper, a possible optimization of the damping effect of a friction force is reported here in after.

抄録全体を表示

Image-guided surgery has been becoming a standard technique in the field of neurosurgery. However, brain shift throughout the surgical procedure has been a major issue affecting the spatial accuracy of conventional neuronavigation system. This study aims at developing the anatomically detailed three-dimensional finite element brain model and demonstrating the importance of the anatomical constraint of the falx cerebri with tentorium for prediction capability of gravity-induced brain shift. The model of brain parenchyma consisted of 253,278 tetrahedral elements whose material property was hyper-viscoelastic model presented in the literature. The computation of the gravity-induced brain shift by assuming that the patient was positioned lateral (left fronto-temporal craniotomy) was conducted using ABAQUS/Explicit. Deformation of the brain surface due to gravity after dura opening was demonstrated in 3D view under the anatomical constraint of the brain substructures. The illustrative results successfully demonstrated the prediction capability of brain shift using the developed model with the brain substructures.

抄録全体を表示