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Woo D.G.,Yonsei University | Kim C.H.,Yonsei University | Lim D.,Korea Institute of Industry Technology | Kim H.S.,Yonsei University
Current Applied Physics | Year: 2010

Osteoporotic vertebral fractures present a major health care burden worldwide, thereby prompting vigorous investigation of the mechanical properties of vertebral bone. Because most vertebral fractures occur gradually and asymptomatically, they are thought to result from loading in daily activities rather than traumatic events. Hence, with respect to stress resistance, the elastic properties of osteoporotic vertebral trabecular bone have generated many studies. A large part of this data describes the linear elastic properties of the bone, with relatively less focus on the plastic mechanical characteristics which may be closely associated with load-induced fracture. We performed experimental and simulated studies of the plastic mechanical characteristics of osteoporotic trabecular bone using non-destructive technologies, rapid-prototyping (RP), and finite element (FE) analysis to build models based on high-resolution micro-computed tomography (micro-CT) data. Two-dimensional geometries for RP and FE models were derived from micro-CT scans of specimens from the central part of the lumbar vertebrae of aged female donors. A cubic specimen (6.5 mm) and a cylindrical specimen (7 mm in diameter and 5 mm long) were generated for the RP and FE models and analysed in place of real bone specimens. We performed simulated compression tests with the FE models to indirectly validate results of the experimental compression tests. To a remarkable degree, results obtained from experimental and simulated compression tests with the RP and FE models concurred. The results of this study support the use of RP technology and FE analysis in the non-destructive evaluation of the plastic mechanical characteristics of osteoporotic bone. © 2009 Elsevier B.V. All rights reserved. Source


Park M.Y.,Seoul National University | Kim B.J.,Korea Institute of Industry Technology | Kim E.S.,Seoul National University
Annals of Nuclear Energy | Year: 2014

Prediction and mitigation of tritium permeation is an important safety issue in high temperature gas-cooled reactors (HTGRs) especially for industrial applications such as hydrogen production and process heat. This study investigated the effect of non-uniform temperature distribution on the tritium permeation rate through the heat exchanger wall and improved the prediction capability of the existing models by reflecting it. To be more explicit, the effective diffusivity (Dm) and the effective temperature (Tm) was newly defined for the heat exchanger wall, and the effective weight (xeff) was derived from one-dimensional diffusion equation. Based on the data collected by numerical methods, an empirical correlation for xeffwas developed by a linear regression method and it was validated by comparisons with randomly generated separate numerical solutions. As a result, the new permeation model based on the effective temperature (Teff) showed very good agreement with the numerical results within an error of 1.28% on average while the existing model based on the average wall temperature (Tm) showed large discrepancies exceeding 200% in the maximum error. This study concludes that the newly developed tritium permeation model significantly improves the prediction capability on the tritium permeation rate through the heat exchangers. Which is the main tritium transport path in the high temperature reactor and the integrated industrial process systems. © 2014 Elsevier B.V. All rights reserved. Source


Kim J.S.,Seoul National University | Hwang J.-S.,Seoul National University | Kim E.S.,Seoul National University | Kim B.J.,Korea Institute of Industry Technology | Oh C.H.,Idaho National Laboratory
Annals of Nuclear Energy | Year: 2016

This study experimentally investigates fundamental phenomena in the HTGR small break air-ingress accident. Several important parameters including density ratio, break angle, break size, and main flow velocity are considered in the measurement and the analysis. The test-section is made of a circular pipe with small holes drilled around the surface and it is installed in the helium/air flow circulation loop. Oxygen concentrations and flow rates are recorded during the tests with fixed break angles, break sizes, and flow velocities for measurement of the air-ingress rates. According to the experimental results, the higher density difference leads to the higher rates of air-ingress with large sensitivity of the break angles. It is also found that the break angle significantly affects the air-ingress rates, which is gradually increased from 0° to 120° and suddenly decreased to 180°. The minimum air ingress rate is found at 0° and the maximum, at 110°. The air-ingress rate increases with the break size due to the increased flow-exchange area. However, it is not directly proportional to the break area due to the complexity of the phenomena. The increased flow velocity in the channel inside enhances the air-ingress process. However, among all the parameters, the main flow velocity exhibits the lowest effect on this process. In this study, the Froude Number relevant to the small break air-ingress conditions are newly defined considering both heavy and light fluids, and break angles. Based on this definition, the experimental data can be well re-arranged and collected. Finally, this study develops and proposes a non-dimensional parameter and a criteria for determination of the small break air-ingress flow regimes. As a result, the non-dimensional parameter higher than 0.49 indicates that the air-ingress is mainly controlled by density gradient effect. On the other hand, that lower than 0.47 indicates that the other effects such as inertia or diffusion are dominant air-ingress mechanisms. © 2015 Elsevier Ltd. All rights reserved. Source


Park S.,Yonsei University | Jeon O.,Yonsei University | Kim C.H.,Yonsei University | Kim H.-S.,Yonsei University | And 2 more authors.
Tissue Engineering and Regenerative Medicine | Year: 2010

Bone is one of the most favored sites of tumor metastasis. However, the existent animal models developed to understand mechanism of occurrence and progress of metastatic bone tumor generally showed difficulties of reproducibility and performance of longitudinal study, and inaccuracy of validation. The aim of this study was, therefore, to newly develop and accurately validate an animal model for study of metastatic bone tumor with overcome of the limitations shown in the existent animal models. Eighteen female Sprague-Dawley rats (12 weeks old, 250+7 g) were randomly allocated in Sham and Tumor groups. W256 breast cancer cell was inoculated in the right femur of the rat for Tumor group, while 0.9% NaCl was injected for Sham group. Urine was collected by metabolic cages for DPD (deoxypyridinoline) test in order to evaluate bone resorption at 0, 4, 8, 12 weeks after surgery. At the same time, the right hind limbs of all rats were scanned by in-vivo micro-computered tomography (CT) to identify tumor-mediated bone destruction driven from metastatic bone tumor. Finally, positron emission tomography was examined to directly identify existence of tumor cells inoculated in the bone. DPD test showed that bone resorption markedly increased in the bone of Tumor group compared to that of Sham group (p<0.05). In-vivo micro-computed tomography showed that there were significant bone losses and X-ray attenuation values in the bone of Tumor group compared to that of Sham group after surgery. In addition, tumor cells were directly identified in the bone of Tumor group by positron emission tomography, not in the bone of Sham group. The results indicated that the developed animal model might be confidential and reasonable to performances of studies related to metastatic bone tumor, with easy reproducibility, accuracy of validation, and suitability to performance of longitudinal study. To our knowledge, this study may prove valuable as the first development of the animal model overcoming the limitations shown in the existent animal models. The animal model developed in the present study may be useful for further metastatic bone tumor studies as mentioned. Source

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