• Korean Journal of Materials Research
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• v.12 no.4
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• pp.254-258
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• 2002

To realize channel cross-connecting in optical communications systems, a high speed optical matrix switch was fabricated using z-cut $LiNbO_3$. For switch fabrication was design bending structure and coupling length and four $2{\times}2$ directional couplers were integrated on one substrate far construction of a $4{\times}4$ switch. Single-mode optical waveguides were formed by Ti-diffusion at a wet $O_2$ atmosphere. Ti-diffusion profile, refractive index variation and waveguide morphology were analyzed by Prism coupler and optical microscopy, respectively.

• ETRI Journal
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• v.42 no.1
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• pp.7-16
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• 2020

Assuming omnidirectional antenna reception, the ITU-R recently developed a new propagation model on building entry loss (BEL) for 5G millimeter-wave frequency sharing and compatibility studies, which is a simplified outdoor-to-indoor path loss model. Considering the utilization of high-gain narrow-beamwidth beamforming, the omnidirectional-based ITU-R BEL model may not be appropriate to predict propagation characteristics for directional beamforming scenarios. This paper studies the effects of beamwidth on the ITU-R BEL model. This study is based on field measurements collected with four different beamwidth antennas: omnidirectional, 10° horn, 30° horn, and 60° horn. The measurement campaigns were conducted at two types of building sites: traditional and thermally efficient buildings. These sites, as well as the measurement scenarios, were carefully chosen to comply with the ITU-R BEL measurement guidelines and the ITU-R building types. We observed the importance of accurate beam alignment from the BEL variation range. We were able to quantify the beamwidth dependency by fitting to a model that is inversely proportional to the beamwidth.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.42 no.3
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• pp.134-147
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• 2006

A model experiment using circulation water channel was carried out to investigate the dynamic characteristics of bottom trawl net which can be used in sea mount of North Pacific. Hydrodynamic resistance and shape variation according to the flow velocity and angle of hand rope transformation for net were measured, and experimental value was analyzed as the value of full-scale bottom trawl net. The results summarized are as follows; At the $30^{\circ}$ of angle of hand rope to net, hydrodynamic resistance varied from 0.5kgf to 2.68kgf as the flow velocity increased between 0.31m/s and 0.92m/s, and formula of hydrodynamic resistance for the model net was $F_m=3.04\;{\cdot}\;{\upsilon}^{1.53}$. At the fixed angle of hand rope, Net height was low and Net width was high according to the increase of flow velocity, and in addition, vertical opening was low and Net width was high by the increase of angle of hand rope at the fixed flow velocity. At the $30^{\circ}$ of angle of hand rope to net, net opening area was $0.214m^2$ as flow velocity was 0.61m/s, and formula of net opening area for the model net was $S_m=-0.22{\upsilon}+0.35$. At the $30^{\circ}$ of angle of hand rope to net, catch efficiency seemed to be highest as $0.319m^3/s$ of filtering volume at the 0.76m/s(51kt's) of flow velocity. Shape variation of net showed the gradual laminar transform for the variation of flow velocity but there needed some improvements due to the occurrence of shortening at the ahead of wing net.

• Journal of the Korean Society of Hazard Mitigation
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• v.1 no.3 s.3
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• pp.93-102
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• 2001

In this study, the characteristics of river bed profile fluctuation are become possible to be used effectively in future estimation of Taehwa river general development plan through analysis and examination according to the effects of sediment protection weir located in the area of the estuary of Taehwa river's main channel using HEC-6 model. The flow conditions needed in analysis of the characteristics of river bed profile fluctuation refer the conditions of flow which secures 95 days in a year, flood flow, and design flood examined in the estimation of Taehwa river maintenance basic plan. First, in analysis result of river bed variation range, there is no significant variation in upstream section from Samho-gyo while there are the more active erosion and sedimentation as the more flow in downstream from Samho-gyo. Next, from the result of the capacity of sediment transfer, it is analyzed that sediment transfer capacity in the area of estuary of Taehwa river has no significant difference in before and after removal of the sediment protection weir when design flood flows while it is estimated that the more flow, the bigger sediment transfer capacity. Therefore, it is thought that the installation of a suitable hydraulic structure at the lowest point of Dong-chun tributary joins from the downstream of Taehwa river can be a good device to reduce the accumulation of sediments at the lowest point of Taehwa river considering the reduction plan of sediment inflow caused by removal of the sediment protection weir.

• Korean Journal of Digital Imaging in Medicine
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• v.15 no.2
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• pp.55-61
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• 2013

The purpose of this study is to evaluate image blurring according to variation of the ETL and propose the clinically appropriate ETL range. SIEMENS MAGNETOM Skyra 3.0T and 20 channel head coil were used for the study. MRI phantom was kept the lines horizontally to three direction(X,Y,Z) of the coil and T1, T2 weighted images that used the fast spin echo technique acquired. The ETL with increase of 10 was applied from 10 to 80. In addition, the ETL with increase of 1 was applied in the interval statistically significant differences occurred. And T1, T2 weighted images that used the conventional spin echo technique acquired to compare image blurring of the images that used the fast spin echo technique. The slope of lattice in the images was measured using Image J 1.47v program to evaluate image blurring. And image blurring was determined by the degree of the slope. The statistical significance of both techniques was evaluated by the Kruskal-Wallis test of the SPSS 17.0v. And the correlation of the ETL and image blurring was evaluated quantitatively by regression analysis. The slope of the T1, T2 weighted images that used fast spin echo technique decreased as contrasted with conventional spin echo technique. In the result of the Kruskal-Wallis test, the T1, T2 weighted images that used fast spin echo technique made a significant difference with conventional spin echo technique. Particularly, in the Tomhane' T2 test, the T1, T2 weighted images made a significant difference from ETL 22 and 31 respectively. In the result of the regression analysis, the R-squared of the T1, T2 weighted images are 0.762 and 0.793. It is difficult to apply the long ETL in the T1 weighted image caused by the short TR and multi-slices study. Therefore, clinical impact according to variation of the ETL is very slight in the T1 weighted images. But the application of the proper ETL is demanded in T2 weighted images using the fast spin echo technique in order to prevent image blurring.

• Journal of Korea Water Resources Association
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• v.39 no.7 s.168
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• pp.605-615
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• 2006

In order to analyze movement of soil moisture, Time Domain Reflectometry(TDR) with multiplex system has been installed at the Bumreunsa hillslope of Sulmachun Watershed to configure spatial-temporal variation pattern considering seasonal characteristic. An intensive surveying was performed to build a refined digital elevation model(DEM) and flow determination algorithms with inverse surveying have been applied to establish an efficient soil moisture monitoring system. Soil moisture data were collected through an intensive and long term monitoring 380 hrs in November of 2003 and 1037 hrs in May and June of 2004. Soil moisture data shows corresponding variation characteristics of soil moisture on the up slope, buffer, main channel zones of the hillslope which were classified from terrain analysis. Measured soil moisture data were discussed in conjunction with flow characteristic through terrain analysis. Regardless season, immediate responses of soil moisture about rainfall looks similar but recession and recharge are primary characteristics of intermediate soil moisture variation for spring to summer and fall to winter season, respectively.

• Korean Journal of Remote Sensing
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• v.24 no.4
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• pp.273-287
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• 2008

Characteristics of skin-bulk sea surface temperature (SST) differences in the Northeast Asia seas were analyzed by utilizing 845 collocated matchup data between NOAA/AVHRR data and oceanic in-situ temperature measurements for selected months from 1994 to 2003. In order to understand diurnal variation of SST within a few meters of the upper ocean, the matchup database were classified into four categories according to day-night and drifter-shipboard measurements. Temperature measurements from daytime drifters showed a good agreement with satellite MCSST (Multi-Channel Sea Surface Temperature) with an RMS error of about $0.56^{\circ}C$. Poor accuracy of SST with an rrns error of $1.12^{\circ}C$ was found in the case of daytime shipboard CTD (Conductivity, Temperature, Depth) measurements. SST differences between MCSST and in-situ measurements are caused by various errors coming from atmospheric moist effect, coastal effect, and others. Most of the remarkable errors were resulted from the diurnal variation of vertical temperature structure within a few meters as well as in-situ oceanic temperatures at different depth, about 20 cm for a satellite-tracked drifting buoy and a few meters for shipboard CTD or moored buoy. This study suggests that satellite-derived SST shows significant errors of about ${\pm}3^{\circ}C$ in some cases and therefore it should be carefully used for one's purpose on the base of in-depth understanding of skin-bulk SST difference and vertical temperature structure in regional sea.

• 전자공학회논문지 IE
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• v.48 no.4
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• pp.13-18
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• 2011

In this paper, we have examined electrical characteristics of LDO regulator according to the process variation using a 1 ${\mu}m$ 20 V high voltage CMOS process. The electrical analysis of LDO regulator have been performed with three kind of SPICE parameter sets (Typ : typical, FF : fast, SS : slow) by process variation which cause change of SPICE parameter such as threshold voltage and effective channel length of MOS devices. From simulation results, we confirmed that in case of SS type SPICE parameter set, the LDO regulator has 3.6 mV/V line regulation, 0.4 mV/mA load regulation and 0.86 ${\mu}s$ output voltage settling time. And in case of Typ type SPICE parameter set, the LDO regulatorhas 4.2 mV/V line regulation, 0.44 mV/mA load regulation and 0.62 ${\mu}s$ output voltage settling time. Finally, in the FF type SPICE parameter set, the LDO regulator has 7.0 mV/V line regulation, 0.56 mV/mA load regulation and 0.27 ${\mu}s$ output voltage settling time.

• Proceedings of the Korea Water Resources Association Conference
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• 2005.05b
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• pp.1143-1147
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• 2005

인간생활을 하면서 하천을 건너다니기 위해 많은 교량을 설치하여 이용하고 있으며, 현재도 어느 지역 언 하천에선가 교량을 건설 중에 있다. 이러한 교량을 설치할 때 교량의 교각을 설치하는 위치는 경제성이나 구조의 설계 안전성에 의해 노선을 결정하고 설치하고 있다. 물론 하천설계기준이나 도로설계요령에 의하면 설치기준이나 세굴 등에 대한 고려사항을 제시하고 있고 이를 맞추기 위해 노력하고 있다. 그러나 이러한 설계기준에서의 제안은 대부분 일반 직선하천에서 구해진 공식이나 경험에 의해 나타내어진 값이다. 따라서 수리현상이 불규칙적이고 복잡한 합류부에 적용하기에는 다소 역부족이다. 본 실험 연구에서는 합류부를 지닌 하천에서의 교각 설치 위치에 따른 세굴의 영향 및 합류각도에 따른 영향을 분석하기 위해 수리실험을 통해 결과를 도출하고자 하였으며, 그 결과 합류되는 각도에 따라 교각의 최대세굴심이 큰 차이를 나타내고 있으나, 합류부를 지닌 수로에서의 세굴심은 유속이 가장 빠른 곳에서 최대세굴심이 나타나지 않으며 유속보다 접근각도 및 흐름에 의한 하향류에 의해 영향을 받기 때문에 기존의 공식에 의해 계산할 수 없으며 실험을 통한 계산을 하거나 가급적 하천의 중앙부에 설치하는 것을 피해야 할 것으로 판단된다.

• Proceedings of the Korea Water Resources Association Conference
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• 2019.05a
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• pp.135-135
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• 2019

수제는 만곡부의 유로 조정이나 하상보호와 같은 하천공학적인 목적을 가진 수공구조물이다. 본 연구에서는 개수로 만곡부에 수제 설치 시 외측벽과 수제 사이의 거리에 따라 하상변동이 어떤 차이가 있는지를 파악하기 위해 이동상 수리실험을 했다. 본 연구에서는 폭 1.45 m, 길이 24 m인 $90^{\circ}$ 만곡수로에 $4.2{\times}8.4cm$의 직사각형 단면 수제를 외측으로부터 이격하여 2열로 설치하였다. 하상재료는 $d_{50}$이 3.3 mm인 잔자갈을 사용했고 하상경사는 1/300로 하였다. 실험은 평균 유량 163 l/s를 3시간 동안 공급했고, 종료 후 만곡부의 주요횡단면별 하상고를 측정했다. 여기서 실험별 이격거리는 8.4 cm, 14 cm, 19.6 cm로 하였다. 실험 결과 외측벽과 수제 사이의 거리가 멀어질수록 만곡부의 최대세굴심은 커지고 그 발생 위치는 하류로 이동하는 경향을 보였다. 만곡부 최대세굴이 발생한 횡단면 형상은 만곡 내측에서 외측방향으로 무차원 위치 $y_1$(=내측에서의거리/폭)가 0.27보다 작으면 퇴적에 의해 하상이 상승하고, 0.35보다 클 때는 세굴에 따른 하상저하가 나타났다. 만곡 외측벽 부근 하상은 이격거리가 짧을수록 수제 설치에 의한 하상고 변화가 작았다.