• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.308-309
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• 2012

One of the critical issues in the growth of multijunction solar cell is the formation of a highly doped Esaki interband tunnel diode which interconnects unit cells of different energy band gap. Small electrical and optical losses are the requirements of such tunnel diodes [1]. To satisfy these requirements, tens of nanometer thick gallium arsenide (GaAs) can be a proper candidate due to its high carrier concentration in low energy band gap. To obtain highly doped GaAs in molecular beam epitaxy, the temperatures of Si Knudsen cell (K-cell) for n-type GaAs and Be K-cell for p-type GaAs were controlled during GaAs epitaxial growth, and the growth rate is set to 1.75 A/s. As a result, the doping concentration of p-type and n-type GaAs increased up to $4.7{\times}10^{19}cm^{-3}$ and $6.2{\times}10^{18}cm^{-3}$, respectively. However, the obtained n-type doping concentration is not sufficient to form a properly operating tunnel diode which requires a doping concentration close to $1.0{\times}10^{19}cm^{-3}$ [2]. To enhance the n-type doping concentration, n-doped GaAs samples were grown with a lower growth rate ranging from 0.318 to 1.123 A/s at a Si K-cell temperature of $1,180^{\circ}C$. As shown in Fig. 1, the n-type doping concentration was increased to $7.7{\times}10^{18}cm^{-3}$ when the growth rate was decreased to 0.318 A/s. The p-type doping concentration also increased to $4.1{\times}10^{19}cm^{-3}$ with the decrease of growth rate to 0.318 A/s. Additionally, bulk resistance was also decreased in both the grown samples. However, a transmission line measurement performed on the n-type GaAs sample grown at the rate of 0.318 A/s showed an increased specific contact resistance of $6.62{\times}10^{-4}{\Omega}{\cdot}cm^{-2}$. This high value of contact resistance is not suitable for forming contacts and interfaces. The increased resistance is attributed to the excessively incorporated dopant during low growth rate. Further studies need to be carried out to evaluate the effect of excess dopants on the operation of tunnel diode.

• Journal of Korean Tunnelling and Underground Space Association
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• v.26 no.1
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• pp.59-78
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• 2024

In tunnel construction, the stability is evaluated by the settlement of adjacent structures and ground, but the shear strain of the ground is the main factor that determines the failure mechanism of the ground due to the tunnel excavation and the change of the operating load, and can be used to review the stability of the tunnel excavation and to calculate the reinforcement area. In this study, a twin tunnel excavation was simulated on a soft ground in an urban area through a laboratory model test to analyze the behavior of the twin tunnel excavation on the adjacent pile grouped foundation and adjacent ground. Both the displacement and the shear strain of ground were obtained using a close-range photogrammetry during laboratory model test. In addition, two-dimensional finite element numerical analysis was performed based on the model test. The results of a back-analysis showed that the maximum shear strain rate tends to decrease as the horizontal distance between the pillars of the twin tunnel and the vertical distance between the toe of the pile group and the crown of the tunnel were decreased. The impact of the second tunnel on the first tunnel and pile group was decreased as the horizontal distance between the pillars of the twin tunnel was increased. In addition, the vertical distance between the toe of the pile group and the crown of the tunnel had a relatively greater impact on the shear strain results than the horizontal distance of the pillars between the twin tunnels. According to the results of the close-range photogrammetry and numerical analysis, the settlement of adjacent pile group and adjacent ground was measured within the design criteria, but the shear strain of the ground was judged to be outside the range of small strain in all cases and required reinforcement.

• Proceedings of the KSME Conference
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• 2008.11a
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• pp.1527-1532
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• 2008

45% of the sports accidents is the knee damage and the representative case is the damage of an Anterior Cruciate Ligament (ACL) and the Posterior Cruciate Ligament(PCL). Although the past different views of ACL reconstruction comes to an agreement, the disputes of PCL is remained yet. The most important engineering approach for these various surgery techniques is accurately to understand and to evaluate the fatigue behavior depending on the stress flow and the stress distribution under the allotted load and the cyclic load, which are caused by the graft fixing device, the proximal tibia of the PCL reconstructing structure. Therefore, this study is the basic research of these above facts. The current transtibial tunnel surgery using the cadaveric Achilles tendon grafts is chosen for the various PCL reconstruction. The relationships between the slippage, the extension ratio, and the slippage ratio by the heel bone fixing method and the soft tissue fixing method of the Achilles tendon were also defined. This research will be the essential data to help the resonable operating techniques for the next PCL reconstruction.

• The Proceeding of the Korean Institute of Electromagnetic Engineering and Science
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• v.11 no.4
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• pp.39-52
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• 2000

A design of 2 stage S-DLVA(successive detector log video amplifier) was studied to detect wide dynamic radar pulse ranging from -70 ㏈m to 0㏈m. A basic design idea was focused on the linear detection in logarithmic scale of wide dynamic range radar pulses from nosie-like weak power of -70 ㏈m to relatively high power 0 ㏈m. It is highly formidable, since it requires high speed detection less than 10 nsec over the operating frequency ranges from 6 to 18 ㎓. A limiter diode, a tunnel diode and an L17-C were used as a protecting device, a detector diode and a log video amplifier in companion as a single stage detector to give voltage output proportional to the input power of about 35 ㏈ dynamic range. A protype of 2-stage DLVA having one more single stage detector was fabricated with a 32 ㏈ low noise amplifier and a 3 ㏈ hybrid coupler to provide total 70 ㏈ dynamic range detection. The logging characteristics were measured to have log slope of 25m.V/㏈ against 70 ㏈ logging range from -55 ㏈m to +15 ㏈m, the log linearity of within +/- 1.5 ㏈, and tangential sensitivity was at -63 ㏈m. The pulse dynamics of rise time and recovery time were measured as 50 nsec and 1.2 $\mu$sec, respectively. The reason might be due to the parasitic capacitances of packaged limiter, tunnel diode, and L17-C.

• Proceedings of the KSR Conference
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• 2008.06a
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• pp.1166-1171
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• 2008

Through Korean high speed train development project "G7 Leading Technology Development Project" from 1996 to 2002, HSR-350X has been developed. It can run the maximum operating speed of 350 km/h. Based on this technology, KTX-2 which will be served commercially has been developed till 2007. This paper introduces the aerodynamic analysis of the High-Speed EMU and shows the results of optimized aerodynamic nose shape design techniques and clean pantograph panhead original techniques study. These are the important parts of developments for high speed train which maximum speed is 400 km/h. Especially for decrease of tunnel micro pressure waves, the optimized nose area distributions were derived and the characteristics of micro pressure wave were analyzed. The robust optimized pantograph panhead shapes investigated to improve the performance and decrease the vortex flow which is thought to be its noise source. These shapes are clean and robust to external disturbances like unsteady accelerated flow or side wind was derived. Finally aerodynamic performances was verified with PIV and smog visualization by wind tunnel test.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.03a
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• pp.460-468
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• 2008

Recent activities on the scramjet and rocket-ramjet combined-cycle engine of Japan Aerospace Exploration Agency(JAXA) are herein presented. The scramjet engines and combined-cycle engines have been studied in the world and JAXA has also studied such the engines experimentally, numerically and conceptually. Based on the studies, 2 to 3 m long, hydrogen-fueled engine models were designed and tested at the Ramjet Engine Test Facility(RJTF) and the High Enthalpy Shock Tunnel(HIEST). A scramjet engine model was tested in Mach 10 to 14 flight condition at HIEST. A 3 m long scramjet engine model was designed to reduce a dissociation energy loss in a high temperature condition. Drag reduction by a tangential injection and two ways of a transverse fuel injection were examined. Combustor model tests at three operating modes of the combined-cycle engine were conducted, demonstrating the combustor operation and producing data for the engine design at each mode. Aerodynamic engine model tests were conducted in a transonic wind tunnel, demonstrating the engine operation in the ejector-jet mode. A 3 m long combined-cycle engine model has been tested in the ejector-jet mode and the ramjet mode since March 2007. Carbon composite material was examined for application to the engines. Production of the cooling channel on a nickel alloy plate succeeded by the electro-chemical etching.

• Journal of the Korean Society of Systems Engineering
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• v.20 no.spc1
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• pp.65-75
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• 2024

As the demand for logistics services increases rapidly in modern society, the existing freight delivery system through road transportation is caused various problems such as traffic congestion and greenhouse gas emissions. To solve that, the development of an 'underground logistics tunnel-based cargo transportation system' is currently being considered in Korea. In order to build a new concept stable and safe logistics system, derive system design requirements and functional specifications, and reflect them at the development of target system. In this study, to make foundation for development of an "underground logistics tunnel-based cargo transportation system," define system components through analysis from a hierarchical perspective, and the functions of each component were analyzed and defined. We identified what interfaces the components have at each stage of the operating process. Lastly, we defined a detailed operation scenario based on the previously derived results, deriving target system functional requirements.

• Journal of Korean Tunnelling and Underground Space Association
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• v.15 no.5
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• pp.505-522
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• 2013

Previously, a new concept of indexing methodology has been proposed for quantitative assessment of tunnel collapse hazard level at each tunnel face with respect to the given geological data, design condition and the corresponding construction activity (Shin et al, 2009a). In this paper, 'linear' model, in which weights of influence factors are invariable, and 'non-linear' model, in which weights of influence factors are variable, are taken into account with some examples. Then, the 'non-linear' model is validated by using 100 tunnel collapse cases. It appears that 'non-linear' model allows us to have adapted weight values of influence factors to characteristics of given tunnel site. In order to make a better understanding and help for an effective use of the system, a series of operating processes of the system are built up. Then, by following the processes, the system is applied to a real-life tunnel project in very weak and varying ground conditions. Through this approach, it would be quite apparent that the tunnel collapse hazard indices are determined by well interlinked consideration of face mapping data as well as design/construction data. The calculated indices seem to be in good agreement with available electric resistivity distribution and design/construction status. In addition, This approach could enhance effective usage of face mapping data and lead timely and well corresponding field reactions to situation of weak tunnel faces.

• Tunnel and Underground Space
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• v.14 no.5
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• pp.373-380
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• 2004

In this study, the emission rate of pollutant was modified according to the published standards, and the distribution of pollutant concentration was analyzed for each vehicle velocity. This modified emission rate was applied to a model tunnel and it was proved that the required air quantity was reduced to 49%, compared to the PIARC method. From the simulation result, it was proved by using statistics that the most sensitive factor among them is the friction coefficient and it was modified to the value in the range of 0.018 to 0.021. It is also expected that the required air quantity can be decreased form 14.4% to 19.2% according as the coefficient is applied to the domestic model tunnels. In conclusion, it is proposed that the number of jet fans can be reduced and the annual operating cost can be curtailed as well.

• Journal of the Society of Naval Architects of Korea
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• v.39 no.2
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• pp.1-10
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• 2002

Hull-propeller-rudder interactions are studied by the iterative computational procedures. Hull effects on the propeller are reflected through the effective velocities computed by the vortex ring method which used the measured nominal wake as input data. A potential based panel method has been developed to solve the propeller-rudder interactions using the obtained effective velocities. Steady flow characteristics around the rudder surface can be obtained by computing the induced velocities on the rudder by the propeller and vice versa are computed by the iterative manner until the converged solutions are obtained. Flow characteristics around the propeller and the rudder are measured by Laser Doppler Velocimetry(L.D.V.) in large cavitation tunnel at Samsung Heavy industries. The gap flow model is adopted to solve the characteristics of the horn rudder. Numerical results are compared with the experimental values and the computed velocity fields and pressure distributions with rudder angle on the horn rudder surface show good agreement with measured ones in large cavitation tunnel.