• Journal of Wetlands Research
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• v.23 no.2
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• pp.173-182
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• 2021

It is important to extract and assess low-flow recession characteristics for water resources management in the upper reaches of a stream. It is difficult to express the groundwater flow recession characteristics for streamflow synthetically. The linear recession model has been widely used by baseflow recession analysis for reason of simplicity and convenience, but recent studies show that nonlinear recession models fit well, and the relationship between the reservoir storage of shallow unconfined aquifers and the groundwater discharge was to be identified as nonlinear in the literature based on the analysis of numerous streamflow recession curves. The objective of the study is to decode these nonlinear characteristics, including evaporation loss, storage, and recharge of groundwater using streamflow. By analyzing the observed time series of streamflow from the study area, which is the Pyeongchang River basin in Korea, the main components of the underlying groundwater balance, namely, discharge, evaporation loss, storage, and recharge, can be identified and quantified. As a result of the study, depletion of groundwater by evapotranspiration losses through the water uptake of tree roots was found to bias the recession curves and the estimated reservoir parameters. The seasonality of both rainfall and potential evaporation, analysis of the recession curves, stratified according to time of the year, allowed the quantification of evapotranspiration loss as a function of a calendar month and stored groundwater storage.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.5A
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• pp.566-573
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• 2004

A variable optical attenuator with a bending-sensitive fiber (BSF) that can be used in optical networks is developed. The proposed BSF consists of inner core, outer core, center dip and cladding. The proposed BSF is also very sensitive to mechanical perturbation, such as bending and pressure, making the light propagating in the BSF easily controlled and attenuated. The fabricated fiber-type variable optical attenuator using the proposed BSF (VOAFB) consisted of the BSF in a rectangular rubber ring with a fixed bend radius (BR) in a steady state. The variable optical attenuator using the proposed BSF (VOAFB) was able to attenuate the optical power by more than about -38㏈ with the gradient -88.4［㏈$.$$cm^{-1}$ /］ at (1540∼1560nm) based m adjusting the mechanical pressure applied to the upper surface of the rectangular rubber ring with the bent BSF. According to the experimental results when using the proposed VOAFB, the optical power was easily controlled by adjusting mechanical pressure and produced an insertion loss of 0.68㏈, polarization loss of 0.5㏈, and return loss of less than -60㏈.

• Journal of the Korean Society of Propulsion Engineers
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• v.13 no.2
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• pp.26-34
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• 2009

Secondary flow losses can be as high as 30~50% of the total aerodynamic losses for a turbo-machinery blade or stator row. These are important part for improving a turbine efficiency. Therefore, many studies have been performed to decrease the secondary flow losses. The present study deals with the chamfered leading-edge at a generic wing-body junction to decrease the horseshoe vortex, one of factors to generate the secondary flow losses, and investigates the vortex generation and the characteristics of the horseshoe vortex with the chamfered height, and depth of the chamfer by using $FLUENT^{TM}$. It was found that the total pressure loss for the best case can be decreased about 1.55% compare to the baseline case.

• Journal of the Institute of Convergence Signal Processing
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• v.2 no.2
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• pp.68-74
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• 2001

A design and implementation method for the UHF-band(800MHz) variable attenuator using the 3dB coupler is proposed. The 90 degree, 3-dB Coupler is used for the variable attenuator. The principal theory for the 3-dB coupler is introduced. The 3-dB Coupler is designed by the mathematical analysis and a computer simulation tool. A PIN diode is used for the variable resistor at UHF-band. The variable attenuator using the 3-dB coupler and the PIN diode is designed and implemented. The measured results for the variable attenuator by a network analyzer show that the insertion loss is below -l0dB, and the continuous variable attenuation range is about 10dB.

• The Journal of the Acoustical Society of Korea
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• v.42 no.4
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• pp.305-312
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• 2023

Physics-Informed Neural Network (PINN) is used to invert bubble size distributions from attenuation losses. By considering a linear system for the bubble population inversion, Adaptive Learned Iterative Shrinkage Thresholding Algorithm (Ada-LISTA), which has been solved linear systems in image processing, is used as a neural network architecture in PINN. Furthermore, a regularization based on the linear system is added to a loss function of PINN and it makes a PINN have better generalization by a solution satisfying the bubble physics. To evaluate an uncertainty of bubble estimation, deep ensemble is adopted. 20 Ada-LISTAs with different initial values are trained using the same training dataset. During test with attenuation losses different from those in the training dataset, the bubble size distribution and corresponding uncertainty are indicated by average and variance of 20 estimations, respectively. Deep ensemble Ada-LISTA demonstrate superior performance in inverting bubble size distributions than the conventional convex optimization solver of CVX.

• Proceedings of the Korea Society for Industrial Systems Conference
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• 1997.11a
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• pp.211-220
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• 1997

체비셰프 삽입손실법을 이용하여 선택도가 높은 대역 여파기를 설계한다. 체비셰프 방식은 차단주파수 근방 곡선의 경사가 버터워쓰에 비해 급격하게 떨어지는 특징을 가진다. 인접 채널의 간섭을 최소화 하기위해 차단 대역의 감쇄를 70db이상으로 유지한다. 중심주파수는 885MHz에서 통과대역폭 10MHz의 여파기를 제작하였다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.23 no.9A
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• pp.2391-2401
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• 1998

An L-band (1435-MHz~1535MHz) omnidirectional circular polarized wave antenna is designed and evaluated for transmitting/receiving of vehicle data. Conventioanl linear polarized wave antenna can not receive clearly all of the vehicle data which come from the wide driving test range on account of distortion. To vercome this problem, an omnidirectional circular polarized wave antenna is reuaried an designed. For the design, first of all, the charcteristics, design principle and theoretical background of circular polarized wav ewith a little signal loss ahve been reviewed. The characteristics of th edesigned antenna are analyzed wave with a little signal loss have been reviewed. The characteristics of the designed antenna is increased over 5dB comparing to that of linear polarized wave. Our results also demonstrate that the strength of vehicle data is flat enough over the full test range using this new antenna.

• Proceedings of the Korea Electromagnetic Engineering Society Conference
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• 2000.11a
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• pp.255-258
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• 2000

최근 경제 활동의 증가로 인하여 통신 서비스에 대한 이동성, 편의성, 및 개인에 대한 요구가 증대되고 있다. 현재 세계각국에서는 이동통신 서비스인 셀룰라 이동통신과 개인 휴대 통신인 PCS(Personal Communication System)가 상용화되고 있다. 1900MHz 대역은 셀룰라 800 MHz에 비해 전파 특성상 전파환경에 따른 전파의 감쇄 및 회전손실 등으로 인한 전파 경로 손실이 증가 할 것으로 본다. 본 논문에서는 바다 해수면의 영향에 따른 800MHz대역과 1900MHz 대역에서 주파수에 따른 경로 손실 차를 실측 Data를 이용하여 비교하였으며 실측 Data를 이용하여 전파모델을 만들어 LGE에서 자체 개발한 전파 분석 시뮬레이션 툴로 Coverage 영역을 비교하였다.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.13 no.10
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• pp.1071-1077
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• 2002

In this paper, we have studied the dependence of insertion loss of the pressed microstrip PBG ring consisting of coupled two microstrip lines. When the distance decreases, two or three attenuation poles are created by the coupling between the lines. Thus the pressed PBG ring exhibits a wide stop band and sharp cutoff characteristics.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.13 no.10
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• pp.1078-1082
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• 2002

In this paper, we have studied the dependence of insertion loss of a microstrip stepped impedance lowpass filter with coupled open stubs. Coupling mechanisms in the filter depend not only on the transmission line width of the filter but also the gap width of coupled open stubs and three attenuation poles are created with the proper conditions. Also edge capacitance between open stubs play an important role in having three attenuation Poles. We verify the results by obtaining [S] matrices.