• Journal of the Korea institute for structural maintenance and inspection
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• v.15 no.3
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• pp.116-124
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• 2011

In this study, a new method to estimate the bridge deflection is developed by using Wireless Tilt Sensor. Most of evaluations of structural integrity, it is very important to measure the geometric profile, which is a major factor representing the global behavior of civil structure, especially bridges. In the past, Because of the lack of appropriate methods to measure the deflection curve of bridges on site, the measurement of deflection had been done restrictly within just a few discrete points along the bridge. Also the measurement point could be limited to locations installed with displacement transducers. So, in this study, the deflection of the structure was measured by wireless tilt sensor instead of LVDT(Linear Variable Differential Transformer). Angle change of tilt sensor shows structural behavior by the change of the resistor values which is presented to voltage. Moreover, the maximum deflection was calculated by changing the deflection angle which was calculated as V(measured voltage) ${\times}$F(factor) to deflection. The experimental tests were carried out to verify the developed deflection estimation techniques. Because the base of tilt measuring is the gravity, uniform measurement is possible independent of a measuring point. Also, measuring values were showed very high accuracy.

• Journal of the Korea institute for structural maintenance and inspection
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• v.22 no.1
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• pp.176-182
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• 2018

The purpose of this study was to investigate the safety and rationality of buckling strength and length coefficient by comparing with the design standards of domestic and foreign compression materials based on the buckling test results of circular steel pipe with ball joints. The types of round steel pipes selected for buckling performance evaluation were ø$48.6{\times}2.8t$, ø$60.5{\times}3.2t$ and ø$76.3{\times}3.2t$. For the design of domestic and foreign compression materials, Korea 's Load Resistance and Factor Design, Japan' s Limit State Design, and British Standard BS5950 standard were applied. In this study, we compared and analyzed the buckling performance between the experimental results of the previous research and the domestic and foreign design standards. The results were summarized as follows. As a result of applying the full length of the member to the buckling length in the compression materials design standards of each country, it was 64-89% of the buckling strength by the experiment. Therefore, it is deemed desirable to perform the member design according to the current design standard formula for safety. Experimental results show that the measured buckling strength was 1.02-1.43 times higher than the buckling strength of pure cylindrical steel tubes in the design standards of Korea, Japan and the United Kingdom compression materials. Consequently, it seemed that the buckling strength of individual member in the design of space frame structure should be considered buckling coefficient as the length of pure round steel pipe rather than the length of inter-node.

• Fire Science and Engineering
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• v.28 no.3
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• pp.62-71
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• 2014

The importance of the firefighting education & Training is being magnified in order to enhance and strengthen a firefighters' ability and to reduce the firefighters' fatality and casualty. Therefore, It is needed to expand the facilities. In this study, with a comparative analysis of the global firefighting education & training facilities for fire suppression, we try to present the necessity and the basic contents of the establishing the installation criteria for the domestic firefighting education & training facilities. It has to contain specific purpose of the training and minimum standards for the structures with a guarantee of an international level. Naturally, the top priority is a safety of trainees and trainers. And, it should pay attention to a higher effectivity of the training course with a active reflection of the standard operation procedures' scenarios. Simultaneously, by securing a similarity and a compatibility to the other standards, it must maintain the balance of a whole standard.

• Journal of Korean Society of Transportation
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• v.27 no.2
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• pp.95-105
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• 2009

Traffic accidents on highways are likely to happen when there is an imbalance in the complex relationships among key elements such as road geometries, driver related factors, and mechanical performances. The Demand-Effort Model (DEM), which evaluates highway safety, can be explained by the imbalance, which occurs when the level of demand of the driver's attention to the road environment exceeds that of the response from the driver. This study suggests a new model that improves the reliability of the current DEM through the reinterpretation on the physiological signals with the help of the Neural Network Model (NNM). The data were collected from 149 subjects, who drove a test vehicle on the Yongdong, Honam, and Seohaean Expressways in Korea. Three important results could be drawn from the recursive tests as follows; (1) Only 5 out of 10 parameters on the physiological signals which are currently used were proven to be meaningful through the Normality Test, Cluster Analysis, and Mann-Whitney Analysis. (2) The revised DEM, which internally uses the NNM, showed more reliable results than existing DEM. Group 1, which is based on the new DEM showed 80.0% of accuracy in measuring the level of driver's efforts, however, that of Group 2 based on the current DEM was 74.3%. (3) Field tests on the Honam Expressway showed lower 'type II error' with the new DEM (40.5%) than the old DEM (58.8%). The DEM is designed as a quick and easy way to determine highway safety prior to the minute road safety audit (RSA) by a professional audit team. Then a new DEM, which is based on the NNM, needs to be considered since it showed higher reliability and lower error.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.08a
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• pp.395-396
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• 2011

본 논문에서는 30% 내외의 평균반사율을 가지는 다결정 실리콘 태양전지의 입사광 손실을 최소화하여 광전변환효율 극대화를 구현하기 위해서 SF6/O2 혼합가스를 이용한 RIE 표면 texturing 공정을 수행하였다. 현재 다결정 실리콘 태양전지는 다양한 방향의 grain을 가지기 때문에 단결정 실리콘에 적용되는 습식 식각 방식이 다결정 실리콘 표면 texturing에 적절하지 않은 것으로 알려져 있다. 이를 개선하기 위해서 이방성 식각 특성을 가지는 다양한 texturing 방법이 시도되고 있다. 대표적으로 기계적인 방식의 V-grooving, 레이저 grooving, 플라즈마 건식식각을 이용한 texturing 및 산 용액을 이용한 texturing 등의 연구가 보고되고 있다. 그 중에서 플라즈마 건식식각 방식의 하나인 RIE를 이용한 표면 texturing 공정이 간단한 공정과 산업계 응용의 용이성 때문에 활발히 연구되어 왔다. 특히 Sandia group과 일본 Kyocera사의 연구 결과에서는 그 가능성을 입증하고 있다. 본 연구에서는 공정의 단순화와 안전한 공정을 위해서 SF6/O2 혼합 가스를 이용하여 마스크 패턴 공정없이 RIE texturing 공정을 수행하였으며, RIE-textured 다결정 실리콘에 대해서 태양전지를 제작하여 표면 texturing이 광전변환효율에 미치는 영향에 대해서 분석하였다. 그 결과 SF6/O2 혼합 가스를 이용한 RIE texturing은 다결정 실리콘 표면에 주로 needle 구조를 형성하는 것을 확인하였다. 각 texturing 조건별 반사율의 차이는 needle 구조의 조밀도와 관련되는 것을 알 수 있었으며, 동일 공정 parameter 상에서 식각 시간 1, 2, 3, 4, 5분 기준 시간에 따른 표면 구조 분석 결과 seed 가 형성되고 그에 따라서 needle 형태로 식각되는 과정을 관찰하였다. 반사율은 분당 약 4%씩 낮아져 5분 식각 후 14.45% 까지 낮아졌으며, 표면 구조에서 폭은 약 30 nm로 모두 일정하며, 길이가 약 20, 30, 50, 80, 100 nm으로 증가되었다. 이 결과로 보아 seed로부터 needle 구조가 심화되어가는 것을 알 수 있었다. 시간에 따른 RIE texturing 후 제작된 태양전지는 효율이 1분 식각 기준 15.92%에서 약 0.35% 씩 낮아져 5분 식각 후 14.4%로 낮아졌다. Voc 는 texturing 시간에 관계없이 일정하며 Isc가 점점 감소되는 것으로 확인되었다. EQE 결과도 이와 동일하게 RIE texturing 시간이 길어질수록 전체 파장 범위에서 일정하게 낮아지는 것이 관찰되었다. Electroluminescence(EL) 이미지 결과 texturing 시간이 길어진 태양전지일수록 점점 어두운 이미지가 나타나 5분 식각의 경우 가장 어두운 결과를 나타내었다. 이런 결과는 한 가지 이유보다는 복합적인 문제로 예상되는데 궁극적으로는 RIE 공정 후 표면에 쌓인 charged particle들이 trap 준위를 형성하여 효율 및 공정상에 영향을 미친 것으로 보이며, 특히 잔류 O기가 불균일한 산화막을 형성하는 것으로 예상된다. 또한 EL 분석 결과를 볼 때 RIE texturing 공정이 길어질수록 불안정한 pn-junction을 형성하는 것을 확인하였으며, emitter 층 형성 후 PSG (phosphorous silica glass) 공정에서 needle의 상부 구조가 무너지면서 면저항이 증가된 결과로 분석된다. PSG 제거 후 측정된 면저항의 경우 3분 texturing 샘플부터 면저항이 약 4${\Omega}/sq$ 정도 증가됨을 확인하였다.

• Korean Journal of Environment and Ecology
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• v.15 no.4
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• pp.361-368
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• 2002

The valley forests located at the east-facing slope and the west facing slope in Hambaeksan area were studied to investigate forest structure in relation to aspect and altitude of the slope. There was little difference in density. mean DBH and basal area of the tree layer between east-facing slope and west-facing slope. The importance percentages of Tilia amurensis and Betula costata in west-facing slope were higher than those in east-facing slope. However, the importance percentages of Quercus mongilica and Fraxinus rhynchophylla in the west facing slope were lower than those in east-facing slope. Species diversity of the west-facing slope was 1.415 and that of the east-facing slope was 1.328. Elevation trends were also found for forest structure. As elevation Increased basal area and mean height of the tree layer decreased in both of east-facing slope and west-facing slope. There was a tendency that number of species, species diversity and evenness decreased with increasing elevation. The importance percentage of Quercus mongolica increased with increasing elevation while those of Betula costata and Maackia amurensis decreased. The result of cluster analysis for the tree and subtree layer indicated that the studied forests were classified into the mixed forest community of broad-leaved tree species at west-facing slope and the low and middle elevation belts of east-facing slope and Quercus mongolica community at the high elevation belt of east-facing slope. Quercus mongolica was significantly and positively correlated with Symplocos chinensis for. pilosa, Acer tschonoskii var. rubripes and deutzia glabrata. Betula costata was significantly and negatively correlated with Quercus mongolica and Acer pseudo-sieboldianum.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.22 no.3
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• pp.191-201
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• 2010

The breakwaters are designed by considering the cost optimization because a human risk is seldom considered. Most breakwaters, however, were constructed without considering the cost optimization. In this study, the optimum return period, target failure probability and the partial safety factors were evaluated by applying the cost optimization to the rubble mound breakwaters in Korea. The applied method was developed by Hans F. Burcharth and John D. Sorensen in relation to the PIANC Working Group 47. The optimum return period was determined as 50 years in many cases and was found as 100 years in the case of high real interest rate. Target failure probability was suggested by using the probabilities of failure corresponding to the optimum return period and those of reliability analysis of existing structures. The final target failure probability is about 60% for the initial limit state of the national design standard and then the overall safety factor is calculated as 1.09. It is required that the nominal diameter and weight of armor are respectively 9% and 30% larger than those of the existing design method. Moreover, partial safety factors considering the cost optimization were compared with those calculated by Level 2 analysis and a fairly good agreement was found between the two methods especially the failure probability less than 40%.

• Journal of the Korean Geosynthetics Society
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• v.8 no.4
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• pp.9-17
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• 2009

This research was intended to verify the stability of landfill final cover using SRSL(Self Recovering Sustainable Liner) with regard to differential settlements due to the degradation of waste and so on in a waste landfill. Numerical analysis was performed using FLAC 2D software program with input parameters based on soil characteristic tests and reference data after the blank was designed in order to represent the decomposition condition of waste. The maximum settlement of landfill cover was calculated to investigate the structural stability of landfill cover with the different condition of settlement width, settlement depth, and number of differential settlements. The allowable maximum deformation rate of SRSL, which was calculated using field permeability tests, was 6 mm. The analysis showed that SRSL was stable in case of a differential settlement width not exceeding 24.5% of total cover width.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.39 no.3
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• pp.451-460
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• 2019

It is critical for Korea to make effective use of limited space as it has dense population and high traffic volume compared to its terrestrial area. To resolve this issue, diverse types of underground structures have increasingly been applied so far, and one of the most representative structures is double-deck tunnel. The construction period of the middle slab in the double deck tunnel constructed at the great depth can be considered as an important part after the tunnel lining construction in the whole process. In order to minimize the construction period required for construction of the middle slab in the double deck tunnel, it was proposed a method of the precast intermediate slab. In this study, it is suggested a mechanical construction process with dedicated equipments developed to improve the safety and the workability of erection of the precast middle slab than the current construction method using the existing mobile crane.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.13 no.4
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• pp.675-683
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• 2009

RC6 which has different algorithm of encryption and decryption has been proposed to have the same algorithm between encryption and decryption through inserting symmetry layer using simple rotate and logical operation. That means the half of whole RC6 round uses encryption algorithm and the rest of it uses decryption one and symmetry layer has been put into the middle of encryption and decryption. The proposed RC6 algorithm has no difference with the original one in the speed of process. However it is quite safe because by inserting symmetry layer the path of high probability which is needed for differential and linear analysis is cut off so that it is hard to be analyzed. The proposed symmetry layer algorithm can be easily applied to the algorithm which has different encryption and decryption and make it same, and it can be good idea to be used to design a new block cipher algorithm.