• Journal of Biomedical Engineering Research
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• v.22 no.5
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• pp.403-412
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• 2001

The Present study analyzed the pressure-flow characteristics of a Korean shunt valve. Changes in the characteristic currie depending on the design parameters were also investigated. The Korean shunt valve used in the present study was constant pressure type and our analyses were validated through experiments. We applied fluid-structure interaction to solve the flow dynamic Problem because the small diaphragm in the valve was made from flexible silicone elastomers. Considering the material nonlinearity of the hyper-elastic material. the Mooney-Rivlin approximation was employed. The results of the numerical analyses were close to the experimental results The major Pressure drop was observed to happen in the small diaphragm. The slope of the pressure-flow characteristic curve was computed to be 0.37mm$H_2O$.hr/cc, which was similar to the average value of commercial shunt valves. 0.40mm$H_2O$.hr/cc. Therefore. our valves analyzed in the Present study showed a Proper Pressure control characteristics of the constant pressure type shunt valves. The opening pressure could be controlled by adjusting the amount of predeflection of the valve diaphragm. In order to obtain opening pressures of 25mm$H_2O$ and 80mm$H_2O$, respectively, and the required predeflection was found to be 10.2$\mu$m and 35.3$\mu$m. The flow orifice size was found to be within 10$\mu$m during valve operation Therefore, Precision design and manufacturing techniques are necessary for successful operations of the shunt valve. The study indicated the amount of predeflection as well as the magnitude of corner rounding of the diaphragm edge are important design parameters to influence the slope of the pressure-flow characteristic curve.

• Journal of Biomedical Engineering Research
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• v.24 no.2
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• pp.77-82
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• 2003

Virtual colonoscopy is a non-invasive computerized procedure to detect polyps by examining the colon from a CT data set. To fly through the inside of colons. the extraction of a suitable flight-path is necessary to Provide the viewpoint and view direction of a virtual camera. However. manual path extraction by Picking Points is a very time-consuming and difficult task due 1,c, the long and complex shape of colon. Also, existing automatic methods are computationally complex. and tend to generate an improper and/or discontinuous path for complicated regions. In this paper, we propose a fast flight-path generation algorithm using the distance and order maps. The order map Provides all Possible directions of a path. The distance map assigns the Euclidean distance value from each inside voxel to the nearest background voxel. By jointly using these two maps. we can obtain a proper centerline regardless of thickness and curvature of an object. Also, we Propose a simple smoothing technique that guarantees not to collide with the surface of an object. The phantom and real colon data are used for experiments. Experimental results show that for a set of human colon data, the proposed algorithm can provide a smoothened and connected flight-path within a minute on an 800MHz PC. And it is proved that the obtained flight-Path provides successive volume-rendered images satisfactory for virtual navigation.

• Journal of Global Scholars of Marketing Science
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• v.15 no.2
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• pp.27-48
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• 2005

This study analyzed the structural elements of transformational leadership on hotel employees job satisfaction and organizational identification, and inquired into how moderating variables such as demographical characteristics and the features of hotels affect transformational leadership. The ultimate purpose of this study was to provide managerial implications to hotel business operators and hotel employees. The main results of this study are as follows; According to the result of factor analysis on transformational leadership and hotel employees job satisfaction, 18 variables were derived as two factors 'obliging leadership' & 'vision leadership' factor in the area of transformational leadership, and 31 variables were derived as four factors 'welfare and work environment', 'ability display and job stability', 'colleague relationship and job performance' and 'company policy' factor. Second, stepwise regression analysis on whether the type of transformational leadership at hotels has a significant effect on employees job satisfaction & organizational identification, 'vision leadership' and job satisfaction and the both 'vision leadership' & 'obliging leadership' among the types of transformational leadership appeared to have a significant effect on hotel employees organizational identification. Third, One-Way ANOVA and t-test in order to examine significant difference in the type of transformational leadership according to demographical characteristics and general characteristics, statistically significant difference was found according to income level, the current position, work experience, the type of hotel operation and the experience of job change.

• The Korean Journal of Financial Management
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• v.20 no.2
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• pp.181-200
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• 2003

Comovement of international stock market prices has been lately a major controversy in the global stock market. This paper explores whether the common trend has really existed among the US, Japan and Korea's stock markets using the econometric techniques such as VAR, VECM as applied. Pair of indices from the exchange market and the over-the-counter market in each country has been tested, and the exchange market only has been turned out that the common trend existed. The dynamic analyses using the Granger causality test, impulse response function, and the forecast error decomposition have followed to show that the US stock market has played some important role in the Korea and Japan's market in the exchange as well as in the OTC market. The results of the paper imply that the more careful investigation with respect to the co-integration may be necessary in the global market integration studies.

• Journal of Korean Association for Spatial Structures
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• v.11 no.3
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• pp.95-103
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• 2011

Among structural systems for complex-shaped tall buildings, diagrid system is widely used because of its structural efficiency and beauty of form. Recently, mega frame is favorably employed as a suitable structural system for skyscrapers because this structural system has sufficient stiffness against the lateral forces by combination of mega members which consist of many columns and girders. Diagrid mega frame system is expected to be promising structural system for future super tall buildings. However, it takes tremendous analysis times and engineer's efforts to predict the structural behavior of tall buildings applied with diagrid mega frame system because the diagrid mega frame structure has significant numbers of elements and nodes. Therefore, efficient analytical method for all buildings applied with diagrid mega frame system has been proposed in this study to reduce the efforts and time required for the analysis and design of diagrid mega frame structure. To this end, an efficient modelling technique using the characteristics of diagrid mega frame structures and an efficient analytical model using minimal DOFs by the matrix condensation method were proposed in this study. Based on the analysis of an example structure, the effectiveness and accuracy of the proposed method have been verified by the comparison between the results of the proposed method and the conventional method.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.24 no.12
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• pp.1181-1189
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• 2013

In this paper, a retrodirective anatenna array system is proposed and the possibility of actively cancelling electromagnetic waves based on this system is investigated. When a rectrodirective array system receives an electromagnetic wave, it can send waves in the direction of the incoming signal without prior knowledge of the direction. In applications to cancellation of radar signals, the system can generate and send signals to the radar so that it cancels the radar signals that are reflected back to the radar. In such a system, isolation between the input and output ports is a key factor that determines the effectiveness of cancellation. In this work, a dual-conversion mixer system is proposed to maximize the isolation. Since this minimizes the difference between the direction of reflection of radar signals and the transmission of cancellation signals, the effectiveness of cancellation is maximized. Experimental results for a metallic plate and metallic cylinder shows as much as 29-dB reduction in reflection for a $2{\times}2$ retrodirective array based on proposed dual-conversion mixer system, which verifies the proposed method of active cancellation.

• Journal of Environmental Policy
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• v.12 no.4
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• pp.119-132
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• 2013

Hosta longipes is one of the most popular ornamental perennials in use in Korea today, and is mainly used as a groundcover plant in urban shaded places. In this study, the pytoremediation effect of Hosta longipes was tested using four concentrations (Control, 100, 250 and $500mg{\cdot}kg^{-1}$) of Cd, Pb and Zn in soil. The plants were planted in $300mm{\times}200mm{\times}250mm$ drainless-containers, which were filled with a artificial amended soil for 7 months. The results showed that the contents of heavy metals cadmium and lead in the shoot of Hosta longipes increased with increasing heavy metal concentration levels exception of zinc. The amount of zinc, cadmium, and lead accumulated in roots were increased with heavy metal concentration levels up in soil. The shoot/root ratios(TF; translocation factor) values were found to be more than 80% of total Zn, Cd, and Pb take up by Hosta longipes. These results indicated that root is the major part for accumulation of heavy metal. The removal contents of zinc, cadmium, and lead increased significantly with the increasing heavy metal concentration in the soil, which was planted with Hosta longipes. The heavy metal concentration accumulation in plant/soil ratios (BF; bioaccumulation factor) values for three metals were found to be more than 30% in cadmium and lead, but lower in zinc treatments. The different responses of Hosta longipes suggest that in heavy metal contaminated soils the plant adsorbs available metals depending on the concentration soils in which they are present. Therefore, this species can be an efficient phytoremediator for soils contaminated with cadmium and lead in urban shaded places.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.33 no.5
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• pp.1797-1807
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• 2013

Dams always have the possibility of failure due to unexpected natural phenomena. In particular, dam failure can cause huge damage including damage for humans and properties when dam downstream regions are densely populated or have important national facilities. Although many studies have been conducted on the analysis of flood waves about single dam failure thus far, studies on the analysis of flood waves about the sequential failure of dams are lacking. Therefore, the purpose of this study was to calculate the peak discharge of sequential failure of dams through flood wave analysis of sequential failure of dams and this analysis techniques to predict flood wave propagation situation in downstream regions. To this end, failure flood wave analysis were conducted for Lawn Lake Dam which is a case of sequential failure of dams among actual failure cases using DAMBRK to test the suitability of the dam failure flood wave analysis model. Based on the results, flood wave analysis of sequential failure of dams were conducted for A dam in Korea assuming a virtual extreme flood to predict flood wave propagation situations and 2-dimensional flood wave analysis were conducted for major flooding points. Then, the 1, 2-dimensional flood wave analysis were compared and analyzed. The results showed goodness-of-fit values exceeding 90% and thus the accuracy of the 1-dimensional sequential failure of dams simulation could be identified. The results of this study are considered to be able to contribute to the provision of basic data for the establishment of disaster prevention measures for rivers related to sequential failure of dams.

• Progress in Medical Physics
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• v.14 no.1
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• pp.8-14
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• 2003

The spinal cord dose is the one of the limiting factor for the radiation treatment of the head ＆ neck or the thorax region. It is not an easy task to maintain the spinal cord dose below tolerance and to keep the clinically acceptable dose to the PTV in this region. To overcome this problem, the spinal cord partial block technique (PBT) with the dynamic Multi-Leaf Collimator (dMLC) has been developed. This technique is an extension of the conventional treatment planning. In the beginning the beam directions are selected as same as the conventional treatment planning to encompass the PTV, then the partial block are designed to shield the spinal cord. The plan comparisons between the conventional therapy plan and the PTB plan were performed to evaluate the validity of this technique. The mean dose and the dose volume histogram (DVH) were used as the plan comparison indices. A series of quality assurance (QA) was performed to guarantee the reliable treatment. The QA consisted of the film dosimetry for the verification of the dose distribution and the point measurements. The PBT plan generated better results than the conventional treatment plan and it was proved to be useful for the H＆N region.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.1
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• pp.111-116
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• 2010

To improve occupants' safety in an emergency, crashworthy design is necessary to rotorcraft design and development. Especially, landing gear has the important role for crashworthy design because landing gear absorbs relatively large energy for the crash landing. In addition, military specifications require failure of landing gear shall not increase danger to any occupants by penetration of the airframe. To meet the specification requirements, crashworthiness device like failure mechanism should be prepared so that landing gear is collapsed safely and doesn't penetrate the airframe. In this study, design and design development test of the failure mechanism which is necessary for the rotorcraft landing gear was performed. First, collapse scenario was determined for the landing gear not to penetrate the airframe. Then, the failure pin which is the most important part of the failure mechanism was designed with 2 strength range in order to meet design criteria. Finally, design of the failure mechanism was verified successfully by design development test.