• 한국초전도ㆍ저온공학회논문지
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• 제21권1호
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• pp.10-14
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• 2019

Radio-frequency (RF) amplifiers based on direct current (DC) superconducting quantum interference device (SQUID) have low-noise performance for precision physics experiments. Gain curves of SQUID RF amplifiers depend on several parameters of the SQUID and operation conditions. We are developing SQUID RF amplifiers for application to measure very weak RF signals from ultra-low-temperature high-magnetic-field microwave cavity in axion search experiments. In this study, we designed, fabricated and characterized SQUID RF amplifiers with different SQUID parameters, such as number of input coil turn, shunt resistance value of the junction and coupling capacitance in the input coil, and compared the results.

• Current Applied Physics
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• 제18권11호
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• pp.1381-1387
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• 2018

One dimensional (1D) grating has been fabricated (using focused ion beam) on 50 nm gold (Au) film deposited on higher refractive index Gallium phosphate (GaP) substrate. The sub-wavelength periodic metal nano structuring enable to couple photon to couple with the surface plasmons (SPs) excited by them. These grating devices provide the efficient control on the SPs which propagate on the interface of noble metal and dielectric whose frequency is dependent on the bulk electron plasma frequency of the metal. For a fixed periodicity (${\Lambda}=700 nm$) and slit width (w = 100 nm) in the grating device, the efficiency of SPP excitation is about 40% compared to the transmission in the near-field. Efficient coupling of SPs with photon in dielectric provide field localisation on sub-wavelength scale which is needed in Heat Assisted Magnetic recording (HAMR) systems. The GaP is also used to emulate Vertical Cavity Surface emitting laser (VCSEL) in order to provide cheaper alternative of light source being used in HAMR technology. In order to understand the underlying physics, far-and near-field results has been compared with the modelling results which are obtained using COMSOL RF module. Apart from this, grating devices of smaller periodicity (${\Lambda}=280nm$) and slit width (w = 22 nm) has been fabricated on GaP substrate which is photoluminescence material to observe amplified spontaneous emission of the SPs at wavelength of 805 nm when the grating device was excited with 532 nm laser light. This observation is unique and can have direct application in light emitting diodes (LEDs).

• 한국재료학회지
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• 제32권8호
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• pp.339-344
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• 2022

The lattice oxygen mechanism (LOM) is considered one of the promising approaches to overcome the sluggish oxygen evolution reaction (OER), bypassing -OOH^* coordination with a high energetic barrier. Activated lattice oxygen can participate in the OER as a reactant and enables O^*-O^* coupling for direct O₂ formation. However, such reaction kinetics inevitably include the generation of oxygen vacancies, which leads to structural degradation, and eventually shortens the lifetime of catalysts. Here, we demonstrate that Se incorporation significantly enhances OER performance and the stability of NiFe (oxy)hydroxide (NiFe) which follows the LOM pathway. In Se introduced NiFe (NiFeSe), Se forms not only metal-Se bonding but also Se-oxygen bonding by replacing oxygen sites and metal sites, respectively. As a result, transition metals show reduced valence states while oxygen shows less reduced valence states (O^-/O₂^2-) which is a clear evidence of lattice oxygen activation. By virtue of its electronic structure modulation, NiFeSe shows enhanced OER activity and long-term stability with robust active lattice oxygen compared to NiFe.

• 한국근적외분광분석학회:학술대회논문집
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• 한국근적외분광분석학회 2001년도 NIR-2001
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• pp.3114-3114
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• 2001

During the last years phytochemistry and phytopharmaceutical applications have developed rapidly and so there exists a high demand for faster and more efficient analysis techniques. Therefore we have established a near infrared transflectance spectroscopy (NIRS) method that allows a qualitative and quantitative determination of new polyphenolic pharmacological active leading compounds within a few seconds. As the NIR spectrometer has to be calibrated the compound of interest has at first to be characterized by using one or other a combination of chromatographic or electrophoretic separation techniques such as thin layer chromatography (TLC), high performance liquid chromatography (HPLC), capillary electrophoresis (CE), gas chromatography (GC) and capillary electrochromatography (CEC). Both structural elucidation and quantitative analysis of the phenolic compound is possible by direct coupling of the mentioned separation methods with a mass spectrometer (GC-MS, LC-MS/MS, CE-MS, CEC-MS) and a NMR spectrometer (LC-NMR). Furthermore the compound has to be isolated (NPLC, MPLC, prep. TLC, prep. HPLC) and its structure elucidated by spectroscopic techniques (UV, IR, HR-MS, NMR) and chemical synthesis. After that HPLC can be used to provide the reference data for the calibration step of the near infrared spectrometer. The NIRS calibration step is time consuming, which is compensated by short analysis times. After validation of the established NIRS method it is possible to determine the polyphenolic compound within seconds which allows to raise the efficiency in quality control and to reduce costs especially in the phytopharmaceutical industry.

• Structural Engineering and Mechanics
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• 제86권2호
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• pp.221-235
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• 2023

To calculate the vibrations of a tout cable subjected to axial support excitations, a nonlinear relationship of cable force and the support displacement under static situations are employed to depict the quasi-static vibration of the cable. The dynamic components of quasi-static vibration are inputted as "direct loads" to cause the parametric vibrations on the cable. Both the governing equations of motion and deformation compatibility for parametric vibrations are then derived, which indicates the high coupling of cable parametric force and deformation. Numerical solutions, based on the finite difference method, are put forward for the parametric vibrations, which is validated by the finite element method under periodic axial support excitations. For the quasi-static response, the shorter cables are more sensitive to support excitations than longer ones at small cable force. The quasi-static cable force makes the greatest contribution to the total cable force, but the parametric cable force is responsible for the occurrence of cable loosening at large excitation amplitudes. Moreover, this study also revealed that the traditional approach, assuming a linear relationship between quasi-static cable force and axial support displacement, would result in some great error of the cable parametric responses.

• 한국물환경학회지
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• 제39권1호
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• pp.87-101
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• 2023

The constituents of a watershed control a wide range of ecosystem processes, such as, carbon sequestration, nutrient retention, and biodiversity preservation. Maintenance of a healthy watershed is advantageous to humans in many direct and indirect ways. Dissolved organic matter fluorescence analysis is one of the most commonly utilized parameters for water quality measurement, pollution source tracking, and determination of the ecological state of a watershed. Throughout the recent decades, the advancement in data processing, instrumentation, and methods has resulted in many improvements in the area of watershed study with fluorescence analysis. The current trend of coupling advanced instrumentations and new comparative parameters, such as, microplastics of different types, antibiotics, and specific bacterial contaminants have been reported in watershed studies. However, conventional methodologies for obtaining fluorescence excitation emission matrices and for calculating the fluorescence and spectral indices are preferred to advanced methods, due to their easiness and simple data collection. This review aims to gain a general understanding of the use of dissolved organic matter fluorescence analysis for diagnosis and source identification of watershed pollutions, by focusing on how the studies have utilized fluorescence analysis to improve existing knowledge and techniques in recent years.

• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2021년도 학술발표회
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• pp.206-206
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• 2021

The necessity for appropriate management of water resources infrastructures such as reservoirs, levees, and dikes is increasing due to unexpected hydro-climate irregularities and rising water demands. To meet this need, past studies have focused on advancing theoretical optimization algorithms such as nonlinear programming, dynamic programming (DP), and genetic programming. Yet, the optimally derived theoretical solutions are limited to be directly implemented in making release decisions in the real-world systems for a variety of reasons. This study first aims to comparatively analyze the two prominent optimization methods, DP and evolutionary multi-objective direct policy search (EMODPS), under historical inflow series using K-fold cross validation. A total of six optimization models are formed each with a specific formulation. Then, one of the optimization models was coupled with the actual zone-based hedging rule that has been adopted in practice. The proposed methodology was applied to Boryeong Dam located in South Korea with conflicting objectives between supply and demand. As a result, the EMODPS models demonstrated a better performance than the DP models in terms of proximity to the ideal. Moreover, the incorporation of the real-world policy with the optimal solutions improved in all indices in terms of the supply side, while widening the range of the trade-off between frequency and magnitude measured in the sides of demand. The results from this study once again highlight the necessity of closing the gap between the theoretical solutions with the real-world implementable policies.

• Smart Structures and Systems
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• 제31권1호
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• pp.69-78
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• 2023

The purpose of this paper is to develop a scalable grey predictive controller with unavoidable random delays. Grey prediction is proposed to solve problems caused by incorrect parameter selection and to eliminate the effects of dynamic coupling between degrees of freedom (DOFs) in nonlinear systems. To address the stability problem, this study develops an improved gray-predictive adaptive fuzzy controller, which can not only solve the implementation problem by determining the stability of the system, but also apply the Linear Matrix Inequality (LMI) law to calculate Fuzzy change parameters. Fuzzy logic controllers manipulate robotic systems to improve their control performance. The stability is proved using Lyapunov stability theorem. In this article, the authors compare different controllers and the proposed predictive controller can significantly reduce the vibration of offshore platforms while keeping the required control force within an ideal small range. This paper presents a robust fuzzy control design that uses a model-based approach to overcome the effects of modeling errors. To guarantee the asymptotic stability of large nonlinear systems with multiple lags, the stability criterion is derived from the direct Lyapunov method. Based on this criterion and a distributed control system, a set of model-based fuzzy controllers is synthesized to stabilize large-scale nonlinear systems with multiple delays.

• 국제교류와 융합교육
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• 제4권1호
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• pp.35-56
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• 2024

이 연구는 중국 의무교육단계 학생 부담경감 최신정책 '쌍감'정책을 중심으로 Kingdon의 정책흐름모형을 활용하여 정책의 흐름을 분석하였다. 데이터의 직관적인 반영, 현행 정책의 피드백 등으로 문제의 흐름을 구성하였다. 중국 정부의 높은 관심, 정치협상회의 위원과 전문가의 건언, 학교 현장과 이해관계자의 강한 요구 등은 정책대안의 흐름을 구성하였다. 집권당의 집권 이념과 교육 지침, 국민 정서, 전환기 이익 게임 등은 정치의 흐름을 구성한 것이다.문제의 흐름,정책대안의 흐름, 정치의 흐름 세 가지 흐름이 결합되어 '정책의 창'이 열리게 된 것으로 분석되었다.

• 대한약리학회지
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• 제29권2호
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• pp.245-252
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• 1993

Amiloride는 $Na{^+}$ channels를 선택적으로 억제하는 potassium sparing diuretic이다. 본 연구에서는 amiloride와 아데노신 수용체의 상호작용을 밝히고자, 흰쥐에서 얻은 crude adipocytic membrane fractions의 adenylyl cyclase activity를 여러 조건하에서 측정하였다. 우선 GTP가 isoproterenol-stimulated adenylyl cyclase activity에 미치는 영향을 조사함으로서 $G_i$ protein (inhibitory guanine nucleotide binding protein)의 기능을 알아보았다. 그 결과 amiloride는 높은 GTP 농도에서 isoproterenol-stimulated adenylyl cyclase의 활성을 억제하는 것을 관찰할 수 없었다. 이와는 대조적으로 amiloride 존재 하에서 2-chloroadenosine을 사용하여 아데노신 수용체를 경유한 isoproterenol-stimulated adenylyl cyclase activity가 억제되는 정도를 측정하였을 때, 2-chloroadenosine의 농도에 따라 큰 변화 없거나 오히려 억제 효과가 더욱 크게 나타났다. 그러나 위와 같은 조건하에서 propranolol에 의한 isoproterenol-stimulated adenylyl cyclase activity의 억제는 amiloride에 의해서 유의하게 변하지 않는 것으로 보아서, 수용체를 매개로 한 $G_s$ protein의 기능은 amiloride에 의해 영향을 받지 않는 것으로 생각된다. 그리고 amiloride에 의해 증가된, 2-chloroadenosine-mediated adenylyl cyclase의 억제 효과는 150mM NaCl 존재 하에서도 그대로 유지되었다. 이러한 결과로 보아 amiloride는 아데노신 수용체와 결합하여 $G_i$ proteins과의 coupling을 용이하게 할 뿐만 아니라, $G_i$ protein을 선택적으로 변화시켜 $G_i$ protein의 GTP 의존적인 adenylyl cyclase의 억제 기능을 제거하는 두 작용을 갖는 것으로 사료된다.