ZHANG YUELIN

In baseball, frequent ball head collisions are high-speed collisions with low-mass objects, a characteristic concussion injury situation compared to other sports, suggesting that the mechanism and threshold for concussion onset may be different. In this study, we investigated the mechanical response of the brain during ball impact using finite element analysis. The peak values of all mechanical parameters of the brain increased in dependence on the translational velocity of the ball. As the rotational velocity of the ball was increased, the rotational acceleration and the maximum principal strain increased, but the translational acceleration did not change. The increase in peak values when the translational velocity of the ball was changed was greater than the increase in peak values when the rotational velocity of the ball was changed for all the brain mechanical parameters. This is thought to be due to the increase in impact force, suggesting that translational velocity of the ball has a greater effect on the brain dynamic response than rotational velocity of the ball.

Recent years the number of patients that has articular cartilage disease is increasing. So it needs to make noncontact diagnostic method of articular cartilage for early diagnosis. By making clear mechanical properties of articular cartilage, diagnosing osteoarthritis can be expected before articular cartilage is worn away by rubbing. This paper describes the development of a new method for measuring viscoelastic properties of articular cartilage by acoustic excitation in low frequency range. Low frequency of 1～100Hz load is applied to the articular cartilage when human is walking or running. To evaluate articular cartilage’s mechanical function by using non-contact method is socially demanded for minimally invasive diagnosis. In this study articular cartilage’s complex shear modulus is obtained by measuring phase velocity and damping coefficient of surface wave on articular cartilage that is excited by acoustic vibration. In the acoustic excitation system, the vibration is generated by a wide range speaker and the surface wave displacements in two points are measured by two laser displacement sensors simultaneously. The system is constructed and the measurement experiment of articular cartilage is performed. Frequency of input acoustic vibration is 40~90Hz. The result shows steady-state vibration is excited at surface of articular cartilage. Therefore acoustic excitation is able to produce surface wave at arbitrarily frequency of articular cartilage.

In this study, to evaluate the strain distribution of the articular cartilage in three-dimension, digital volume correlation method is used. Digital volume correlation program is constructed and used to measure the displacement and strain of the porcine knee joint under compressive load. The deformation of the porcine knee joint is obtained from MR image under non-compressive and compressive load. The result of the analysis of the compression experiment shows that the strains are observed at the compressive area at three-dimensions. It is possible to obtain displacement and strain distribution of the articular cartilage by using MRI.

This paper discusses the coefficient of restitution about oblique collision. There are two kinds as a definition of restitution coefficient called as Newton's impact low and Poisson's impact low. The former one is based on the normal velocity change that measured before and after impact. The latter one is based on the impulse change during impact. To observe and compare these coefficients of restitution, use numerical analysis. We formulated the model of rigid body in rigid v-block by using unilateral contact method which contains no approximation but can exactly express a rigid body's transformation on collision. Consider the differences of two kinds of coefficients and find better way of measuring coefficient of restitution.

This paper proposes a health monitoring system for detecting a blockage in a pipe using the acoustic vibration excitation with high power laser. Non-contact acoustic impulse excitation can be applied to acoustic fields by using a shock wave generated by laser-induced breakdown in air. A high-power Nd:YAG pulse laser is used in the present vibration testing system for generating the laser-induced breakdown in acoustic fields. The laser excitation makes a precise measurement of the acoustic resonant frequency in wide frequency range possible with high reproducibility. The acoustic resonant frequency changes by the blockage and its position in the pipe. In this study, the detection of the blockage in the pipe is focused. The acoustic resonant frequencies in the pipe with/without the blockage are measured by a microphone. Then the position of the blockage is identified by evaluating the cross section ratio between the pipe and the blockage analyzed from the measured data.

This study proposes a tuning method of model-based controller with adaptive parameters in the controller, that is effective to maintain the control performance and stability for characteristic variation of the structures. The main idea of this tuning method is tuning the poles of the controller that have great effect on the control performance and stability. Simultaneous perturbation stochastic approximation (SPSA) is used as tuning algorithm. The vibration control simulation by using the proposed tuning method is carried out. The perturbations are given to the model of the controlled object to change its physical characteristics, and the controller is tuned for adapting to these changes. This study shows the effectiveness of the proposed tuning method by conducting the simulations.

In this study, in order to measure the softness of cultured tissue, ball indentation tests were performed. As first step, the principle of ball indentation test was applied to the thin silicone rubber sheet (t=0.1mm), which achieved results confirm the validation of the measurement result. Next step, Young's modulus of monolayer cultured nerve cell (PCI2) was measured, and the validation of the measured results was confirmed by comparing with previous studies. The Young's modulus of the cell body is 36.5kPa, and distal, middle and proximal of neuritis are 50.2kPa, 21.8kPa and 51.5kPa, respectively. In addition, Young's modulus of three-dimensional gel-culture system consisting of primary human gingival fibroblasts (GF) and gingival epithelial (GE) cells in collagen gels were measured. The Young's modulus of whole gel and gingival epithelial cells are 3.46kPa and 81.9kPa, respectively. The results were shown the possibility of measuring the Young's modulus of each layer of cultured tissue in the case of laminate structure.

Degradation of extra-cellular matrices is an integral pathophysiological part in periodontitis. Previously, we have isolated "aggressive fibroblasts" derived from severe periodontitis regions from human patients and established an in vitro periodontitis model using a three dimensional (3D) culture system. We have been screened candidate drugs for periodontitis by evaluating inhibition of collagen degradation employing this model. Although several drugs effectively inhibited collagen gel degradation, some of them have resulted fragile collagen gel. Therefore, we tried to evaluate collagen gel "softness" using ball indentation tests together with residual amount of collagen. Evaluation of candidate drugs by the Young's modulus of in vitro periodontitis model was useful, and one of the drugs (herbal medicines) successfully improved "softness" of the gel. These results suggested that the measurement of the Young's modulus of in vitro periodontitis model may be a useful tool for screening of candidate drugs for periodontitis.

In this study, the resistance of PC 12 cells against strain is investigated by the impact test. The resistance of cell body is evaluated by the cell mortality and the citotoxicity. The axonal injury is evaluated by the morphological observation. The cell mortality and the citotoxicity increase according to the increase of strain rate. PC 12 cells with axons show larger cell mortality and citotoxicity than without axons, and the axons of injured/dead cells show the morphological features of axonal injury. This result shows the difference between the impact resistance of neuronal cells with axons and without axons quantitatively.

The finite element analyses of the cerebral contusion based on judicial autopsy reports were performed in order to show the relationship between the input force duration and occurrence of the coup contusion, contrecoup contusion. In finite element analysis the skull fracture was taken into consideration. The result showed that coup contusion would occur when impacted by light weight impactor with high velocity which yielded short force duration, and contrecoup contusion would occur when impacted by heavy weight impactor with low velocity which yielded long force duration. When force duration was less than 5ms, coup contusion tended to occur, and contrecoup contusion tended to occur when force duration was more than 5ms.