• The Korean Journal of Financial Management
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• v.14 no.1
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• pp.23-50
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• 1997

Shiller(1981)와 LeRoy-Porter(1951)에 의하여 시작된 분산한계검증(分散限界檢證)(variance bounds test)에 관한 연구는 주식시장에서 초과변동성(超過變動性)(excess volatility)의 존재를 통하여 주식시장(株式市場)의 효율성(效率性)을 검증하는 새로운 연구분야로서 주목을 받아왔다. 그리고 이들의 연구방법론을 응용하여 많은 효율적(效率的) 시장가설(市場假說)의 검증에 대한 연구가 이루어져 왔다. 본(本) 연구(硏究)는 이러한 연구(硏究)의 한 범주로써 한국주식시장(韓國株式市場)에서 분산한계검증(分散限界檢證)을 통하여 약형효율성(弱形效率性) 시장가설(市場假說)을 검증(檢證)하고자 하였으며 이를 위하여 먼저 Shiller (1981)의 배당평가모형(配當評價模型)을 이용한 사후적(事後的)인 합리적(合理的) 주가(株價)인 $P_t{^*}$의 추정방법(推定方法) 대신에 이 배당평가모형(配當評價模型)을 변형하여 $P_t{^*}$를 추정(推定)하는 방법을 제시하였다. 그리고 이 $P_t{^*}$를 기초로 Shiller(1981)의 분산한계검증식(分散限界檢證式)을 변형한 분산한계검증(分散限界檢證)의 조건식(條件式)을 유도하고 이에 의해 실증적(實證的) 검증(檢證)을 하였다. 한편, 이러한 검증과정(檢證過程)에서 시계열자료(時系列資料)의 특성상 사전적(事前的)으로 필요로 하는 실제주가(實際株價), $P_t$와 사후적(事後的)인 합리적(合理的) 주가(株價), $P_t{^*}$에 대한 단위근검정(單位根檢定)(unit root test)을 실시하였다. 아울러 $P_t$와 $P_t{^*}$의 선형관계(線形關係)의 안정성을 검정하기 위하여 공적분검정(共積分檢定)(cointegration test)도 실시하였다. 검증결과(檢證結果), Shiller(1981)의 분산한계검증식(分散限界檢證式)을 변형하여 유도된 효율성조건(效率性條件)을 만족시키는 범위(範圍)에 벗어나 한국주식시장(韓國株式市場)에서 주식시장(株式市場)의 비효율성(非效率性)을 배제할 수 없는 것으로 나타났다.

• Journal of the Korean Society for Nondestructive Testing
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• v.32 no.2
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• pp.170-176
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• 2012

In the nuclear industry, wall thinning defect of straight pipe occur the enormous loss in life evaluation and safety evaluation. To use non-destructive technique, we measure deformation, vibration, defect evaluation. But, this techniques are a weak that is the measurement of the wide area is difficult and the time is caught long. In the secondary side of nuclear power plants mostly used steel pipe, artificiality wall thinning defect make in the side and different thickness make to the each other, wall thinning defect part of deformation measure by using shearography. In addition, optical measurement through deformation, vibration, defect evaluation evaluate pipe and thickness defects of pressure vessel is to evaluate quantitatively. By shearography interferometry to measure the pipe's internal wall thinning defect and the variation of pressure use the proposed technique, the quantitative defect is to evaluate the thickness of the surplus. The amount of deformation use thickness of surplus prediction of the actual thickness defect and approximately 7 percent error by ensure reliability. According to pressure the amount of deformation and the thickness of the surplus through DB construction, nuclear power plant pipe use wall thinning part soundness evaluation. In this study, pressure vessel of thickness defect measure proposed nuclear pipe of wall thinning defect prediction and integrity assessment technology development. As a basic research defected theory and experiment, pressure vessel of advanced stability and soundness and maintainability is expected to contribute foundation establishment.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2017.05a
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• pp.166-166
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• 2017

금속 재료 중 철강은 기계적 특성이 우수하고 대량생산이 가능하여 선박, 건축, 자동차 등 다양한 분야에 기초재료로써 널리 사용되고 있다. 그러나 스테인리스강 등과 같은 일부 특수한 용도의 강을 제외하고는 부식환경에 취약한 특성을 가지기 때문에 내식성을 향상을 위한 표면처리에 관한 연구가 활발히 진행되고 있다. 가장 일반적으로 습식법(wet process)을 통해 표면상에 아연(Zn)을 도금해 사용하며, 아연이 자체적으로 포함한 희생양극(sacrificial anode) 및 차폐(barrier) 효과가 철강의 부식을 방지하게 된다. 하지만 산업의 고도화에 따라 더욱 가혹해진 노출환경으로 인해 고내식 강재에 대한 수요가 점차 증가하고 있으며, 아연코팅 층의 두께를 증가하여 내식성을 확보하는 방안은 미래 환경 및 자원적인 측면에서 근본적인 해결책으로 제시하기 어려움이 있다. 한편, 건식 프로세스(wet process)로 대별되는 PVD(physical vacuum deposition)에 의해 내식성을 향상시키고자 하는 연구들이 다양하게 진행되고 있다. 이것은 표면에 고순도 양질의 금속 막을 형성시킴으로써 외부환경과의 반응을 효과적으로 제어가 가능하며, 형성된 막은 그 물질의 고유 특성뿐만 아니라 제작 조건에 따른 표면의 기하학적 혹은 결정학적 구조에 의해 크게 영향을 받게 된다. 본 연구에서는 실용금속 중 이온화 경향이 가장 크고 산소와 반응하여 투과성이 작은 산화 피막 형성이 유리한 마그네슘(Mg)을 활용해 표면의 전기화학적 특성을 향상시켰다. 또한 금속 증착 중 진공도조절을 위해 도입되는 불활성 가스로 아르곤(Ar) 및 질소($N_2$)를 사용하여 표면에 형성한 막의 모폴로지 및 결정배향성이 내식성에 미치는 상관관계를 해석하고자 하였다. 실험방법으로 PVD법 중 비교적 간편하고 기초적인 지침을 제시하기 적합할 것으로 고려된 진공증착(vacuum evaporation)법을 이용해 아르곤 및 질소 분위기에서 진공도를 조절하며 용융아연도금상 Mg막을 형성하였다. 제작조건별 막의 기초 특성을 분석하기위해 SEM, EDS, XRD를 이용하였고, 결정배향성(crystal orientation) 분석을 위해 면간격(d-value)과 상대강도(relative intensity)를 확인하였다. 또한 내식성 평가로 염수분무(salt sprat test) 및 양극분극(anode polarization)을 각각 실시하였다. 실험결과에 따르면, Ar 및 $N_2$ 모두에서 가스압이 증가할수록 코팅층의 증착량은 적어지고 입상정(granular structure)의 모폴로지 형성 및 면간격과 상대강도가 증가하는 것이 확인되었다. 또한 쳄버 내 동일 진공도에서, $N_2$ 도입 시 Mg막은 더욱 치밀하고 미세한 입상정의 모폴로지로 형성되며 면간격과 상대강도는 더욱 증가한 것으로 나타났다. 내식성 평가에서 저진공 $N_2$ 조건에서 형성시킨 막이 가장 우수한 내식성이 나타났는데, 이는 상대적으로 불안정하고 반응하기 유리한 입계면적을 많이 포함한 입상정 모폴로지 및 표면에너지가 높은면의 면점유율 증가로 인해 외부환경과의 신속한 반응은 물론 안정적인 피막형성이 용이하였기 때문일 것으로 사료된다. 이상으로 Ar 및 $N_2$ 가스압 조건에 따른 고내식 Mg 막의 유효성을 확인하였고 향후 내식성을 향상시키는 방법으로 응용 가능할 것으로 생각된다.

• Journal of Korean Tunnelling and Underground Space Association
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• v.17 no.2
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• pp.75-90
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• 2015

As soil nails support a ground by the friction between nails and soils being reinforced, the length of soil nails is important factor for a ground stability. Thus, the soil nail length has to be accurately evaluated in order to secure a ground stability. The goal of this study is to suggest the applicability of the non-destructive method as the basic research for the evaluation of the soil nail length. First, the elastic and electromagnetic waves are adopted to select an applicable method for the soil nails connected by the coupler. Test results show that while the ultrasonic waves are not detected due to the coupler, the electromagnetic waves are free for the influence of the coupler. Second, electromagnetic waves are measured for combined soil nails with the length of 1 m~15 m for the investigation of the characteristics of electromagnetic waves. The travel time of the electromagnetic wave increases with an increase in the soil nail length. In addition, the ground cable is used to apply the electromagnetic waves to pre-installed soil nails. Test results show that the travel time of the electromagnetic wave by using the ground cable increases with an increase in soil nail length. This study demonstrates that the electromagnetic wave may be a promising method for the evaluation of the soil nail length.

• Journal of the Korean GEO-environmental Society
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• v.13 no.6
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• pp.91-100
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• 2012

Wireless monitoring system for the structural health evaluation has a limit to the reliability of measured response. The objective of this study is to evaluate an effective measurement range of the wireless monitoring system on the analyzed data. For the wireless monitoring system, Bluetooth and Wi-Fi are applied to datalogger-receiver and receiver-personal computer, respectively. For the model of the monopile structure response, a laboratory-scale monopile is manufactured with Mono Cast Nylon and a lateral loading is applied by hammer impacting. Strain gauges attached on the model monopile are connected with the datalogger. The distances of datalogger-receiver and receiver-personal computer are changed for the evaluation of the measurement range. Experimental results show that the receiving rates of the response remain almost constant within limited distance, while the receiving rates dramatically decrease out of effective range. In addition, the receiving rates affect on the measured natural frequencies of the model monopile. This study suggests that the effective range evaluation of the wireless monitoring system may be used for the determination of a monitoring distance to the monopile installed in the offshore wind farm.

• Journal of The Korean Association For Science Education
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• v.28 no.1
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• pp.32-46
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• 2008

The purpose of this study was to analyse the qualitative and quantitative characteristics of paper-pencil tests for exploring its appropriateness as a selection tool of the gifted in science. For this purpose, we developed two (internal and external) item analysis frameworks, and applied these frameworks to analyse qualitative characteristics. Also, we analysed the relationship between two characteristics. The results of analysing qualitative characteristics revealed that the portion of items with acceleration context exceeding middle school curriculum level was relatively large, which caused low content validity. Furthermore, there was considerable deviation in content and context by subject matter and year, which caused test unstability. Items measuring knowledge domain was the most prevalent, and too much weight on data interpretation & analysis domain in inquiry process skills. In case of creativity test, the portion of items measuring convergent thinking was much larger than that of divergent or associative thinking. Most of these items were represented by using pictures and tables rather than using graphs. Item types of multiple-choice and short answers were superior to essay types. Discrimination index, on the whole, was appropriate (above 0.3), but item difficulty showed a vast deviation ($0.01{\sim}0.90$). Correlation coefficients among subject matters and test tools were very low, and test reliabilities were also low. Low item difficulty & high discrimination index item types were distinguishable. Items with acceleration context were more discriminating than enrichment context. Implications of developing quality paper-pencil test items in the selection of gifted students are discussed.

• Journal of Korean Society of Transportation
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• v.25 no.6
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• pp.19-31
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• 2007

When estimating the benefits from an investment project in the transportation sector, errors caused by many factors may exist. This study focuses on user equilibrium traffic assignment methods and stopping criteria. According to previous studies, when using a user equilibrium assignment model, the benefits of travel time savings can be effected by the relative gap value. As the stopping criteria decreases, the time needed for traffic assignment increases, so that lowering the criteria cannot be the best solution. Therefore, an effort is necessary to reduce this change rate and thus improve reliability. This paper considers three methods: reducing the links subject to benefit calculation, extracting sub-area O/D tables and networks, and applying the mean value of successive traffic assignment results. The results of the analysis show that the method using the mean value of five results is more proper than the other methods. Using the sub-area analysis method, if the study area is small the benefits of a project might be over- or under-estimated. This paper used a nationwide O/D table and network at peak time as a case study. The resulting patterns can differ according to basic data to be used in analysis. So further analysis using the data from metropolitan areas are needed.

• Food Science of Animal Resources
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• v.28 no.5
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• pp.549-554
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• 2008

Liposomes were prepared from egg yolk phospholipids to study their physical properties and stability at various storage conditions. Under storage conditions at different pH levels, the particle sizes of liposomes increased at the range of pH 1-2, and the absolute values of $\xi$-potentials were reduced at the range of pH 1-4. The leakage of sulforhodamine B (SRB), a fluorescent dye which is encapsulated in the liposome, increased greatly at pH 2-4. At different storage temperatures, the particle size of liposomes increased from the 10 days of storage at $4^{\circ}C$ and the 40 days at 20 and $35^{\circ}C$. The $\xi$-potentials decreased slightly later during storage under 4, 20 and $35^{\circ}C$. At the storage temperature of $50^{\circ}C$, the leakage of SRB was the greatest. Therefore, we concluded that the pH conditions lower than pH 6 and high temperature of $50^{\circ}C$ are not conducive to storing liposomes. The results obtained here may prove helpful in developing liposome-based encapsulation and diagnostic reagents.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.40 no.4
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• pp.360-366
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• 2004

This paper presents a method analyzing the motion of cylindrical buoy moored at 2 points and tensions action on each mooring line under the action of periodic waves. It was found that submersible buoy was more effective than floating one in the severe conditions considering its dynamic motions, wave forces, and mooring line tensions. The wave induced its dynamic responses and mooring line tensions peak when the ratio d/${\lambda}$ of the buoy length d to the waves length ${\lambda}$ was 0.66 due to its natural frequency. The results of this study were in agreement with the existing measurement ones, however, further verifications are needed considering resonance of cylindrical buoy and its displacements to wave height by a series of model tests.

• Journal of Korean Tunnelling and Underground Space Association
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• v.15 no.5
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• pp.483-496
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• 2013

This paper presents the shield TBM technology in soft ground tunnelling. In order to perform this study, a scale model test was carried out using the developed small scaled shield TBM machine. The various instrumentations were conducted during the simulation of tunnelling. In addition, the ground behavior due to the shield TBM operation parameters was measured during the simulation. Based on the simulation results, the stability of the ground was evaluated and the fundamental shield TBM tunnelling technique in the soft ground was suggested. In conclusion, design's reliability through laboratory small scale model test about Shield-TBM section was obtained, and both the improvement plan for safety during construction and the construction plan for securing airport runway's safety during tunnel passing by Shield-TBM propulsion were suggested.