• Title/Summary/Keyword: 특성 모델 검증

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Accurate Localization of Metal Electrodes Using Magnetic Resonance Imaging (자기공명영상을 이용한 금속전극의 정확한 위치 결정)

  • Joe, Eun-Hae;Ghim, Min-Oh;Ha, Yoon;Kim, Dong-Hyun
    • Investigative Magnetic Resonance Imaging
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    • v.15 no.1
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    • pp.11-21
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    • 2011
  • Purpose : Localization using MRI is difficult due to susceptibility induced artifacts caused by metal electrodes. Here we took an advantage of the B0 pattern induced by the metal electrodes by using an oblique-view imaging method. Materials and Methods : Metal electrode models with various diameters and susceptibilities were simulated to understand the aspect of field distortion. We set localization criteria for a turbo spin-echo (TSE) sequence usingconventional ($90^{\circ}$ view) and $45^{\circ}$ oblique-view imaging method through simulation of images with various resolutions and validated the criteria usingphantom images acquired by a 3.0T clinical MRI system. For a gradient-refocused echo (GRE) sequence, which is relatively more sensitive to field inhomogeneity, we used phase images to find the center of electrode. Results : There was least field inhomogeneity along the $45^{\circ}$ line that penetrated the center of the electrode. Therefore, our criteria for the TSE sequence with $45^{\circ}$ oblique-view was coincided regardless of susceptibility. And with $45^{\circ}$ oblique-view angle images, pixel shifts were bidirectional so we can detect the location of electrodes even in low resolution. For the GRE sequence, the $45^{\circ}$ oblique-view anglemethod madethe lines where field polarity changes become coincident to the Cartesian grid so the localization of the center coordinates was more facilitated. Conclusion : We suggested the method for accurate localization of electrode using $45^{\circ}$ oblique-view angle imaging. It is expected to be a novelmethodto monitoring an electrophysiological brain study and brain neurosurgery.

Introductions of Pre-Rake with Frequency Domain Equalizer and Cyclic Prefix Reduction Method in CDMA/TDD Multi-code Transmission (CDMA/TDD 다중코드 전송에서 주파수 도메인 등화기와 결합된 Pre-Rake 와 Cyclic Prefix 최소화 방법)

  • Lee, Jun-Hwan;Jeong, In-Cheol
    • Journal of Satellite, Information and Communications
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    • v.6 no.1
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    • pp.86-96
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    • 2011
  • In this paper we propose a Pre-rake system applied with a frequency domain equalizer in TDD/CDMA multi-code transmission. The Pre-rake system has been well known technique in TDD/CDMA to make a receiver simple. However, it still has residual losses of path diversity and signal to noise ratio (SNR). However, gathering all the residual paths demands an additional hardware such as a rake combiner at the receiver. For the reason Pre/Post-rake system has already been proposed at up/downlink correlated channel conditionunder the assumption of noisier channel. There is a trade-off between the first purpose of Pre-rake that makes hardware simple at the receiver and the performance improvement. From the point the frequency domain equalizer (FDE) can be considered in Pre/Post-rake to supply the receiver with the flexible equalizing methods with rather reduced complexity compared with time domain rake combiner or equalizers. Pre-rake itself increases the number of multipath, which results from the convolution of Pre-rake filter and wireless channel, and FDE must be well matched to Pre/Post-rake, while it considers the relationship of hardware complexity and the performance. In this paper, the Pre-rake/Post-FDE system is introduced at TDD/CDMA multi-code transmission. In addition, the cyclic prefix reduction method in the proposed system is introduced, and the theoretical analysis to the proposed system is given by assuming Gaussian approximation, and finally the numerical simulation results are provided.

Estimation of the amount of refrigerant in artificial ground freezing for subsea tunnel (해저터널 인공 동결공법에서의 냉매 사용량 산정)

  • Son, Youngjin;Choi, Hangseok;Ko, Tae Young
    • Journal of Korean Tunnelling and Underground Space Association
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    • v.20 no.2
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    • pp.255-268
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    • 2018
  • Subsea tunnel can be highly vulnerable to seawater intrusion due to unexpected high-water pressure during construction. An artificial ground freezing (AGF) will be a promising alternative to conventional reinforcement or water-tightening technology under high-water pressure conditions. In this study, the freezing energy and required time was calculated by the theoretical model of the heat flow to estimate the total amount of refrigerant required for the artificial ground freezing. A lab-scale freezing chamber was devised to investigate changes in the thermal and mechanical properties of sandy soil corresponding to the variation of the salinity and water pressure. The freezing time was measured with different conditions during the chamber freezing tests. Its validity was evaluated by comparing the results between the freezing chamber experiment and the numerical analysis. In particular, the freezing time showed no significant difference between the theoretical model and the numerical analysis. The amount of refrigerant for artificial ground freezing was estimated from the numerical analysis and the freezing efficiency obtained from the chamber test. In addition, the energy ratio for maintaining frozen status was calculated by the proposed formula. It is believed that the energy ratio for freezing will depend on the depth of rock cover in the subsea tunnels and the water temperature on the sea floor.

Comparison of Local Mean Temperature Equations for GPS-based Precipitable Water Vapor Determination (GPS 가강수량 결정을 위한 한국형 평균온도식 비교)

  • Ha, Ji-Hyun;Park, Kwan-Dong
    • Journal of Astronomy and Space Sciences
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    • v.25 no.4
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    • pp.425-434
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    • 2008
  • The mean temperature equation is a key factor in calculating GPS meteorological information. A local mean temperature equation should be used to improve accuracy of GPS PWV (Precipitable Water Vapor). In this paper, four local mean temperature equations, HP, $HP_M,\;HPt_Y,\;and\;HPt_M$ from Ha & Park (2008) were used to analyze the effects of local models in determining GPS PWV. Four different sets of GPS PWVs were compared with radiosonde PWV to validate the accuracies of local models. GPS PWVs of four local models have similar trends compared against radiosonde PWV. The bias and RMS error were the same level: the bias is ${\sim}3mm$ and the RMS is ${\sim}3.6mm$ after the bias was removed. Especially, with $HPt_Y\;and\;HPt_M$ models one can obtain accurate PWVs even without surface temperature measurements. And we investigated dry bias of radiosonde measurements depending on sensor types and observation time at Sokcho weather station. After the radiosonde sensor equipment was changed from RS80-15L to GRS DFM-06, dry bias of radiosonde PWV decreased about 18.2% during daytime (KST 09:00), and 16.1% during nighttime (KST 21:00).

Adolescents' Information-seeking Behavior for Gender Identity in a Community-driven Knowledge Site (청소년들의 성 정체성에 관한 지식검색 커뮤니티 정보탐색행태)

  • Yi, Da Jeong;Yi, Yong Jeong
    • Journal of the Korean Society for information Management
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    • v.36 no.4
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    • pp.161-181
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    • 2019
  • People begin to recognize sexual orientation or gender identity in adolescence, and adolescents frequently use an accessible and anonymous anonymity knowledge retrieval community to explore sensitive health information about gender. This study attempted to observe their information search behavior based on questions and answers about adolescents' gender identity in the knowledge retrieval community. First, we wanted to examine their information needs and to investigate what factors they preferred to answer by comparing the characteristics of the answers adopted with the non-adopted answers among the answers provided in the questions they shared. To this end, Naver, Korea's representative knowledge search community. In Knowledge-iN, a total of 358 sets of data were analyzed, consisting of responses adopted over three years from January 2016 to December 2018. As a result, adolescents with concerns about gender identity demanded information about definition or confusion about gender identity. In the responses adopted by the users, the factors that gave empathy and positive feelings were higher than those that were not adopted, whereas the negative responses were higher in the unaccepted answers. This study is meaningful in that it analyzes the information needs and information search behaviors of adolescents with no established gender identity, expands the discussion in the information search field, and confirms cognitive and emotional models for information evaluation of health information users. Also, based on the research results, we propose practical implications for effective information services on gender identity that social media should provide to young people.

Study of Multi Floor Plant Layout Optimization Based on Particle Swarm Optimization (PSO 최적화 기법을 이용한 다층 구조의 플랜트 배치에 관한 연구)

  • Park, Pyung Jae;Lee, Chang Jun
    • Korean Chemical Engineering Research
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    • v.52 no.4
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    • pp.475-480
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    • 2014
  • In the fields of researches associated with plant layout optimization, the main goal is to minimize the costs of pipelines for connecting equipment. However, what is the lacking of considerations in previous researches is to handle the multi floor processes considering the safety distances for domino impacts on a complex plant. The mathematical programming formulation can be transformed into MILP (Mixed Integer Linear Programming) problems as considering safety distances, maintenance spaces, and economic benefits for solving the multi-floor plant layout problem. The objective function of this problem is to minimize piping costs connecting facilities in the process. However, it is really hard to solve this problem due to complex unequality or equality constraints such as sufficient spaces for the maintenance and passages, meaning that there are many conditional statements in the objective function. Thus, it is impossible to solve this problem with conventional optimization solvers using the derivatives of objective function. In this study, the PSO (Particle Swarm Optimization) technique, which is one of the representative sampling approaches, is employed to find the optimal solution considering various constraints. The EO (Ethylene Oxide) plant is illustrated to verify the efficacy of the proposed method.

A Case Study on Impact Factor of Bridge in Tunnels Subjected to Moving Vehicle Load (터널내 교량의 이동차량하중 작용시 충격계수에 대한 사례연구)

  • 김재민;이중건;이익효;이두화
    • Tunnel and Underground Space
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    • v.9 no.3
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    • pp.185-193
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    • 1999
  • This paper presents results of dynamic analysis for a bridge in intersection part of two tunnels subjected to moving vehicle load. Since such a bridge system is very unusual due to the fact that it is located in tunnel, the dynamic characteristics of the structure can not be assumed as conventional one. The structure investigated in this study it a reinforced concrete bridge in the intersection part of Namsan Tunnel-1 and Tunnel-2 in Seoul. It is supported by temporary steel structure which shall be constructed during the period of replacing lining in Tunnel-2. Dynamic analysis was carried out for the system using a finite element model constructed by general purpose FE program SAP2000. For this purpose, the structure, lining of tunnels, and surrounding rock were represented by finite elements, while the rock region it truncated and on its outer boundary viscous dampers were placed to simulate radiation of elastic waves generated tunnels. Several types of vehicle with various driving velocities were considered in this analysis. The FE model including vehicle loadings was verified by comparing calculated peak particle velocity with the measured one. From the analysis, the impart factor for the bridge was estimated as 0.21, which indicates that the use of upper bound for the impact factor in design code is reasonable for this kind of bridge system.

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Static Fluid-Structure Coupled Analysis of Low-Pressure Final-Stage Turbine Blade (발전용 저압터빈 최종단 블레이드의 정적 유체-구조 연계해석)

  • Kwon, Sun-Guk;Lee, Young-Shin;Bae, Yong-Chae
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.34 no.8
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    • pp.1067-1074
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    • 2010
  • In this study, a loosely coupled fluid-structure interaction (FSI) analysis was conducted for a low-pressure (LP) final-stage rotor blade. Preliminary FSI analyses of a $15^{\circ}$ sweptback wing and a NASA Rotor 37 compressor blade were performed for verifying the boundary conditions. The results were compared with the established literatures for each model. The FSI analysis of the $15^{\circ}$ sweptback wing was carried out under both stable and unstable conditions. The excessive deformation of the wing was observed within 0.05 s under the unstable condition which is higher than the divergence speed of a wing compared with the stable condition. On the basis of the results of a steady-state study, an unsteady state FSI analysis was conducted for a NASA Rotor 37. Different deformations were observed at trailing edge of the blade in the static FSI and dynamic FSI analysis. A 3D FE model of a LP rotor was generated from the span-wise section data. In order to develop a reasonable model, an impact test was performed and compared to the FE model. Using this FE model, the steady-state FSI analysis was performed successfully.

A Study on the Startup Growth Stage in Korea (스타트업 성장단계 구분에 대한 탐색적 연구)

  • Kim, Sunwoo;Kim, Kangmin
    • Asia-Pacific Journal of Business Venturing and Entrepreneurship
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    • v.15 no.2
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    • pp.127-135
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    • 2020
  • The purpose of this paper is to classify individual startups by growth stage based on data-based quantitative criteria. This is to provide a basis for systematic support for government startups based on accurate statistics on the startup growth process. This startups were the TIPS (Tech Incubator Program for Startup) support company, which used a relatively reliable startup. We found seed money to complete MVP (Minimum Viable Product) within 1.5 years after establishment, verified PMF (Product-Market Fit) within 1 year, attracted Series A investment within 2.5 years after establishment, and successfully commercialized it. It attracted Series B investment for stable growth within 1.5 years (Series B investment within 4 years from start-up). The results of the study, the division of government programs that support stage-based startup commercialization, that is, within three years and within seven years of establishment, is significant to date. Three directions are suggested for future research. First, develop indicators for monitoring startup growth stages. Second, it continuously updates the annual changes and tracks the growth stages of individual startups. Third, we discover the successful growth law of technology-based startups by applying in-depth case analysis of successful startups to the model.

A Study on the Selection of Target Ship for the Protection of Submarine Power Cable (해저 동력케이블 보호를 위한 대상 선박 선정에 관한 연구)

  • Lee, Yun-sok;Kim, Seungyeon;Yu, Yungung;Yun, Gwi-ho
    • Journal of the Korean Society of Marine Environment & Safety
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    • v.24 no.6
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    • pp.662-669
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    • 2018
  • Recently, the installation of submarine power cables is under consideration due to the increase of electric power usage and the development of the offshore wind farm in island areas, including Jeju. In order to protect power cables installed on the seabed, it is necessary to calculate the burial depth based on the characteristics of anchoring, dragging and fishing, etc. However, there is no design standard related to the size of target ships to protect the cables in Korea. In this study, we analyzed the design standards for the protection of domestic submarine pipelines similar to submarine cables, and developed the risk matrix based on the classification by emergency anchoring considering the installation environment, then designed the size of target ships according to the cumulative function scale by ship size sailing through the sea concerned. Also, we linked marine accident conditions, such as anchoring, dragging, etc. and the environmental conditions such as current, sea-area depth of installation etc. to the criteria of the protection of submarine cable, and examined the size of specific target ships by dividing the operating environment of ships into harbor, coastal and short sea. To confirm the adequacy and availability of the size of target ships, we verified this result by applying to No. 3 submarine power cables, which is to be installed in the section from Wando to Jeju Island. This result is expected to influence in the development of a protection system for submarine cables and pipelines as well as the selection of anchor weight according to the determination of burial depth.