• Proceedings of the Korean Geotechical Society Conference
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• 2006.03a
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• pp.86-95
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• 2006

Brillouin backscatter is a type of reflection that occurs when light is shone into an optical fibre. Brillouin reflections are very sensitive to changes in the fibre arising from external effects, such as temperature, strain and pressure. We report here several case studies on the measurement of strain using Brillouin reflections. A mechanical bending test of an I beam, deployed with both fiber optic sensors and conventional strain gauge rosettes, was performed with the aim of evaluating: (1) the capability and technical limit of the DTSS technology for strain profile sensing; (2) the reliability of strain measurement using fiber optic sensor. The average values of strains obtained from both DTSS and strain gauges (corresponding to the deflection of I beam) showed a linear relationship and an excellent one-to-one match. A practical application of DTSS technology as an early warning system for land sliding or subsidence was examined through a field test at a hillside. Extremely strong, lightweight, rugged, survivable tight-buffered cables, designed for optimal strain transfer to the fibre, were used and clamped on the subsurface at a depth of about 50cm. It was proved that DTSS measurements could detect the exact position and the progress of strain changes induced by land sliding and subsidence. We also carried out the first ever distributed dynamic strain measurement (10Hz) on the Korean Train eXpress(KTX) railway track in Daejeon, Korea. The aim was to analyse the integrity of a section of track that had recently been repaired. The Sensornet DTSS was used to monitor this 85m section of track while a KTX train passed over. In the repaired section the strain increases to levels of 90 microstrain, whereas in the section of regular track the strain is in the region of 30-50 microstrain. The results were excellent since they demonstrate that the DTSS is able to measure small, dynamic changes in strain in rails during normal operating conditions. The current 10km range of the DTSS creates a potential to monitor the integrity of large lengths of track, and especially higher risk sections such as bridges, repaired track and areas at risk of subsidence.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.11a
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• pp.363-363
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• 2008

The development of dry etching process for sapphire wafer with plasma has been key issues for the opto-electric devices. The challenges are increasing control and obtaining low plasma induced-damage because an unwanted scattering of radiation is caused by the spatial disorder of pattern and variation of surface roughness. The plasma-induced damages during plasma etching process can be classified as impurity contamination of residual etch products or bonding disruption in lattice due to charged particle bombardment. Therefor, fine pattern technology with low damaged etching process and high etch rate are urgently needed. Until now, there are a lot of reports on the etching of sapphire wafer with using $Cl_2$/Ar, $BCl_3$/Ar, HBr/Ar and so on [1]. However, the etch behavior of sapphire wafer have investigated with variation of only one parameter while other parameters are fixed. In this study, we investigated the effect of pressure and other parameters on the etch rate and the selectivity. We selected $BCl_3$ as an etch ant because $BCl_3$ plasmas are widely used in etching process of oxide materials. In plasma, the $BCl_3$ molecule can be dissociated into B radical, $B^+$ ion, Cl radical and $Cl^+$ ion. However, the $BCl_3$ molecule can be dissociated into B radical or $B^+$ ion easier than Cl radical or $Cl^+$ ion. First, we evaluated the etch behaviors of sapphire wafer in $BCl_3$/additive gases (Ar, $N_2,Cl_2$) gases. The behavior of etch rate of sapphire substrate was monitored as a function of additive gas ratio to $BCl_3$ based plasma, total flow rate, r.f. power, d.c. bias under different pressures of 5 mTorr, 10 mTorr, 20 mTorr and 30 mTorr. The etch rates of sapphire wafer, $SiO_2$ and PR were measured with using alpha step surface profiler. In order to understand the changes of radicals, volume density of Cl, B radical and BCl molecule were investigated with optical emission spectroscopy (OES). The chemical states of $Al_2O_3$ thin films were studied with energy dispersive X-ray (EDX) and depth profile anlysis of auger electron spectroscopy (AES). The enhancement of sapphire substrate can be explained by the reactive ion etching mechanism with the competition of the formation of volatile $AlCl_3$, $Al_2Cl_6$ or $BOCl_3$ and the sputter effect by energetic ions.

• Atmosphere
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• v.23 no.4
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• pp.471-483
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• 2013

Nighttime sea fog detection from satellite is very hard due to limitation in using visible channels. Currently, most widely used method for the detection is the Dual Channel Difference (DCD) method based on Brightness Temperature Difference between 3.7 and 11 ${\mu}m$ channel (BTD). However, this method have difficulty in distinguishing between fog and low cloud, and sometimes misjudges middle/high cloud as well as clear scene as fog. Using CALIPSO Lidar Profile measurements, we have analyzed the intrinsic problems in detecting nighttime sea fog from various satellite remote sensing algorithms and suggested the direction for the improvement of the algorithm. From the comparison with CALIPSO measurements for May-July in 2011, the DCD method excessively overestimates foggy pixels (2542 pixels). Among them, only 524 pixel are real foggy pixels, but 331 pixels and 1687 pixels are clear and other type of clouds, respectively. The 514 of real foggy pixels accounts for 70% of 749 foggy pixels identified by CALIPSO. Our proposed new algorithm detects foggy pixels by comparing the difference between cloud top temperature and underneath sea surface temperature from assimilated data along with the DCD method. We have used two types of cloud top temperature, which obtained from 11 ${\mu}m$ brightness temperature (B_S1) and operational COMS algorithm (B_S2). The detected foggy 1794 pixels from B_S1 and 1490 pixel from B_S2 are significantly reduced the overestimation detected by the DCD method. However, 477 and 446 pixels have been found to be real foggy pixels, 329 and 264 pixels be clear, and 989 and 780 pixels be other type of clouds, detected by B_S1 and B_S2 respectively. The analysis of the operational COMS fog detection algorithm reveals that the cloud screening process was strictly enforced, which resulted in underestimation of foggy pixel. The 538 of total detected foggy pixels obtain only 187 of real foggy pixels, but 61 of clear pixels and 290 of other type clouds. Our analysis suggests that there is no winner for nighttime sea fog detection algorithms, but loser because real foggy pixels are less than 30% among the foggy pixels declared by all algorithms. This overwhelming evidence reveals that current nighttime sea fog algorithms have provided a lot of misjudged information, which are mostly originated from difficulty in distinguishing between clear and cloudy scene as well as fog and other type clouds. Therefore, in-depth researches are urgently required to reduce the enormous error in nighttime sea fog detection from satellite.

• Economic and Environmental Geology
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• v.24 no.4
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• pp.421-434
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• 1991

Ground magnetic surveys were conducted at four areas where the Yangsan fault, the most prominent lineament in the Kyeongsang basin, appears to be passed through. For data processing, IGRF correction, upward continuation and reduction-to-the-pole were performed. The automatic inversion by using a matrix computation method, which takes the depth to bottom layer of the horizontal two layer structure as the model parameter, has been attempted to delineate the subsurface structure. Upward continuation of the surface magnetic map to the same level of the aeromagnetic survey (KIER, 1989) resulted in very similiar patterns to those of aeromagnetic data. Subsurface modeling of eight profile data show that the strike and dip of the Yangsan fault in study areas are $N6^{\circ}-15^{\circ}E$, and near vertical to somewhat eastward, repectively, despite of the local lithological contrast of each study area. It seems that the magnetic effect of faulting in the study area 1, which locates in the most northern part of the survey areas, is disturbed by that of igneous intrusion. At study area 2, the possibility of volcanic or igneous intrusion, which is 200-300 meters wide along the fault plane was presented. At study area 3, unlike other study areas, distinct fracture zone of 500-700 meters in width was revealed along the surface fault line. The andesitic rocks of the study area 4 have very high susceptibilities and the fault line on surface of this area was shifted about 500 meter eastward, as compared with the inferred fault line by the previous study.

• The Journal of Engineering Geology
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• v.21 no.1
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• pp.15-24
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• 2011

To clarify the distribution of joints and fracture zones in the Cheongju granitic mass, we analyzed drill-core and geophysical well-logging data obtained at two boreholes located 30 m from each other. Lithological properties were investigated from the drill-core data and the samples were classified based on the rock mass rating (RMR) and on rock quality designation (RQD). Subsurface discontinuities within soft and hard rocks were examined by geophysical well-logging and cross-hole seismic tomography. The velocity structures constructed from seismic tomography are well correlated with the profile of bedrock depth, previously mapped from a seismic refraction survey. Dynamic elastic moduli, obtained from full waveform sonic and ${\gamma}-{\gamma}$ logging, were interrelated with P-wave velocities to investigate the dynamic properties of the rock mass. Compared with the correlation graph between elastic moduli and velocities for hard rock at borehole BH-1, the correlation points for BH-2 data showed a wide scatter. These scattered points reflect the greater abundance of joints and fractures near borehole BH-2. This interpretation is supported by observations by acoustic televiewer (ATV) and optical televiewer (OTV) image loggings.

• Proceedings of the Korean Vacuum Society Conference
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• 1999.07a
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• pp.115-115
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• 1999

GaN는 직접천이형 wide band gap(3.4eV) 반도체로서 청색/자외선 발광소자 및 고출력 전자장비등에의 응용성 때문에 폭넓게 연구되고 있다. 이러한 넓은 분야의 응용을 위해서는 열 적으로 안정된 Ohmic contact을 반드시 실현되어야 한다. n-type GaN의 경우에는 GaN계면에서의 N vacancy가 n-type carrier로 작용하기 때문에 Ti, Al, 같은 금속을 접합하여 nitride를 형성함에 의해서 낮은 접촉저항을 갖는 Ohmic contact을 하기가 쉽다. 그러나 p-type의 경우에는 일 함수가 크고 n-type와 다르게 nitride가 형성되지 않는 금속이 Ohmic contact을 할 가능성이 많다. 시료는 HF(HF:H2O=1:1)에서 10분간 초음파 세척을 한 후 깨끗한 물에 충분히 헹구었다. 그런 후에 고순도 Ar 가스로 건조시켰다. Pd와 Ni은 열적 증착법(thermal evaporation)을 사용하여 p-GaN에 상온에서 증착하였다. 현 연구에서는 열처리에 의한 Pd의 clustering을 줄이기 위해서 wetting이 좋은 Ni을 Pd 증착 전과 후에 삽입하였으며, monchromatic XPS(x-ray photoelectron spectroscopy) 와 SAM(scanning Auger microscopy)을 사용하여 열처리 전과 40$0^{\circ}C$, 52$0^{\circ}C$ 그리고 695$0^{\circ}C$에서 3분간 열처리 후의 온도에 따른 morphology 변화, 계면반응(interfacial reaction) 및 벤드 휨(band bending)을 비교 연구하였다. Nls core level peak를 사용한 band bending에서 Schottky barrier height는 Pd/Ni bi-layer 접합시 2.1eV를, Ni/Pd bi-layer의 경우에 2.01eV를 얻었으며, 이는 Pd와 Ni의 이상적인 Schottky barrier height 값 2.38eV, 2.35eV와 비교해 볼 때 매우 유사한 값임을 알 수 있다. 시료를 후열처리함에 의해 52$0^{\circ}C$까지는 barrier height는 큰 변화가 없으나, $650^{\circ}C$에서 3분 열처리 후에 0.36eV, 0.28eV 만큼 band가 더 ？을 알 수 있었다. Pd/Ni 및 Ni/Pd 접합시 $650^{\circ}C$까지 후 열 처리 과정에서 계면에서 matallic Ga은 온도에 비례하여 많은 양이 형성되어 표면으로 편석(segregation)되어지나, In-situ SAM을 이용한 depth profile을 통해서 Ni/Pd, Pd/Ni는 증착시 uniform하게 성장함을 알 수 있었으며, 후열처리 함에 의해서 점차적으로 morphology 의 변화가 일어나기 시작함을 볼 수 있었다. 이는 $650^{\circ}C$에서 열처리 한후의 ex-situ AFM을 통해서 재확인 할 수 있었다. 이상의 결과로부터 GaN에 Pd를 접합 시 심한 clustering이 형성되어 Ohoic contact에 문제가 있으나 Pd/Ni 혹은 Ni/Pd bi-layer를 사용함에 의해서 clustering의 크기를 줄일 수 있었다. Clustering의 크기는 Ni/Pd bi-layer의 경우가 작았으며, $650^{\circ}C$ 열처리 후에 barrier height는 Pd/Ni bi-layer의 경우에도 Ni의 영향을 받음을 알 수 있었다.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.26 no.3
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• pp.265-274
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• 1990

The temperature inversions were studied on the basis of Digital Memory Bathythermography(DBT) data collected by training ship, Pusan 402, of the National Fisheries University of Pusan in August 23~25, 1986 and Fisheries Reserach and Development Agency of Korea in August, 1986, The results were as follows; Among the 67 stations of studied area, occurrence frequency of temperature inversion was 58.20%, And the frequency of onefold occurrence of temperature inversion at its profile of each station was 13.42%. of twofold occurrence was 20.80%, and of threefold occurrence was 23.88%. In the studied area, the temperature inversion usually occurred below the 40m depth and its layers also located below the thermocline. The temperature range of its inversion was from 14$^{\circ}C$ to 16$^{\circ}C$. The temperature inversion in the study area was oaused by the interaction between Tsushima Warm Current and Korea Coastal Waters.

• Journal of the Institute of Electronics Engineers of Korea SP
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• v.42 no.2 s.302
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• pp.101-112
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• 2005

As we perceive the world as 3-dimensional through our two eyes, we can extract 3-dimensional information from stereo images obtained from two or more cameras. Since stereo images have a large amount of data, with recent advances in digital video coding technology, efficient compression algorithms have been developed for stereo images. In order to compress stereo images and to obtain 3-D information such as depth, we find disparity vectors by using disparity estimation algorithm generally utilizing pixel differences between stereo pairs. However, it is not unusual to have stereo images having different intensity values for several reasons, such as incorrect control of the iris of each camera, disagreement of the foci of two cameras, orientation, position, and different characteristics of CCD (charge-coupled device) cameras, and so on. The intensity differences of stereo pairs often cause undesirable problems such as incorrect disparity vectors and consequent low coding efficiency. By compensating intensity differences between left and right images, we can obtain higher coding efficiency and hopefully reduce the perceptual burden of brain to combine different information incoming from two eyes. We propose several methods of intensity compensation such as local intensity compensation, global intensity compensation, and hierarchical intensity compensation as very simple and efficient preprocessing tool. Experimental results show that the proposed algerian provides significant improvement in coding efficiency.

• Journal of the korean academy of Pediatric Dentistry
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• v.30 no.2
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• pp.298-307
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• 2003

The purpose of this study was to investigate the distribution and differences of the cephalometric measurements between normal occlusion and the class III malocclusion. Kim's analysis was achieved and compared on both the 141 elementary school students with proper profile and normal occlusion and the class III malocclusion group at the age of 7 to 9, in Gwang-ju area and the results were as follows; 1. The ODI, APDI, IIA, UL showed statistically significant differences between normal occlusion and class III malocclusion(p<0.01). But, no significant difference existed in both CF and EI. 2. The mean value of ODI was 72.62, APDI 80.47 IIA 121.37 in normal occlusion. 3. The mean value of ODI was 64.45, APDI 87.31 IIA 129.89 in class III malocclusion. 4. ODI decreased as APDI increased, and the correlation coefficient was -0.576 in both normal occlusion and class III malocclusion. 5. The correlation coefficient related to EI was CF 0.777, LL -0.670, UL -0.588, IIA 0.485. It means that UL and LL were very sensitively reflected on EI.

• Journal of the Korean GEO-environmental Society
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• v.19 no.5
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• pp.23-31
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• 2018

The dredging project became more important with the recent construction of off shore structures and reclamation projects. Accordingly, more exact quantitative estimation of the dredged amount should be required. The sub-sea ground information can be obtained generally by the boring investigation and the dredged amount can be estimated based on the depth or the deeper bound of a ceratin layer via 3D visualization program. During the estimation process, the input DB should be constructed with 1D elevation information from boring investigation for the spatially approximated distribution of a deeper bound of each ground layer. The input DB can be varied with the application of the borings and the approximation targets. Therefore, the 3D visualized ground profile and dredged amounts are compared on the actively dredged sites, vicinity of Saemangeum area and outer port area in Gunsan with regard to the input DB construction methods. Conclusively, the input DB based on the spatially approximated depths show higher precision results and more reasonable 3D visualized ground profiles.