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김건우 ( Geonwoo Kim ),김재윤 ( Jaeyun Kim ),김찬우 ( Chanwoo Kim ),윤창빈 ( Changbin Yoon ),최지호 ( Jiho Choi ),윤희철 ( Heecheol Yoon ),박완일 ( Wan-il Park ) 전북대학교 과학교육연구소 2019 과학과 과학교육 논문지 Vol.44 No.2
만유인력 법칙의 구조를 이론적으로 이해하고, 거리-역제곱법칙을 실험으로 검증해 보았다. 이론적으로는, 만유인력 법칙의 수학적 구조를 뉴턴의 제 2 운동법칙을 통해 추론해 보고 뉴턴이 했던 것과 같이 달의 공전을 이용하여 거리의 역제곱 법칙이 성립함을 확인해 보았다. 실험적으로는, 정밀저울을 이용하여 일정한 질량을 가진 분동의 높이 변화에 따른 무게변화를 측정함으로써 중력가속도의 크기 변화를 측정하고, 이로부터 만유인력의 법칙이 가진 거리-역제곱 법칙을 실험적으로 검증해 보았다. We inspected the theoretical structure of the law of universal gravity, and verified it experimentally. Theoretically, we deduced the mathematical structure of the law of universal gravity from Newton’s second law of motion, and confirmed the law of inverse square-distance via moon’s orbital motion as Newton did. Experimentally, in order to verify the law of inverse square-distance, a characteristic of the law of universal gravity, using a precision scale, we measured the variation of the magnitude of the gravitational acceleration as a function of the hight from the ground by measuring the weight of a weight having a given mass.
KR60 레일의 결함 탐상을 위한 위상배열 초음파 변환기 개발 (Ⅰ)
김건우(Geonwoo Kim),서무경(Mu-Kyung Seo),최남경(Namkyoung Choi),김기복(Ki-Bok Kim),권세곤(Segon Kwon),김영철(Young-cheol Kim) 한국비파괴검사학회 2017 한국비파괴검사학회지 Vol.37 No.6
현재 우리나라 철도 레일의 초음파 탐상은 복수의 단일 초음파 변환기를 이용한 탐상이다. 단일 초음파 탐상의 한계를 극복하기 위해, 본 연구에서는 CIVA 시뮬레이션을 이용하여 KR60 레일의 결함 탐상을 위한 최적 위상배열 초음파 변환기를 설계하고, 그 탐상 결과를 분석하였다. 상용 위상배열 초음파 변환기를 KR60 레일의 비파괴 탐상에 이용할 경우 레일의 기하학적 특성에 따라 검출 가능한 결함의 종류가 제한되었다. 따라서, KR60 레일의 구조적 특징과 결함의 위치와 형상에 따라 위상배열 초음파 변환기의 제원(중심주파수, 대역폭, 집속 깊이, 소자 길이, 너비, 높이 등)을 도출하였으며, 도출된 위상배열 초음파 변환기의 음장과 다양한 인공결함에 대한 S-scan 이미지를 비교·분석하였다. Ultrasonic testing for the KR60 railway in Korea has been conducted by single element ultrasonic testing. In this study, to overcome the limits of single element ultrasonic testing, phased array ultrasonic transducers for detecting defects on the KR60 rail were designed and analyzed based on the inspection results obtained by CIVA software simulation. It was difficult to detect various defects using commercial phased array ultrasonic transducers because of geometric features of KR60 railroad. Therefore, according to the geometric characteristics of the KR60 railroad, the specifications of phased array ultrasonic transducers for the KR60 rail were determined such as nominal frequency, bandwidth, focusing length, width, height, length of piezo-electric material, etc. The acoustic field of the phased array ultrasonic transducers and their S-scan images of artificial defects on the KR60 rail were compared and analyzed.
KR60 레일의 결함 탐상을 위한 위상배열 초음파 변환기 개발 (Ⅱ)
김건우(Geonwoo Kim),서무경(Mu-Kyung Seo),최남경(Namkyoung Choi),김기복(Ki-Bok Kim),권세곤(Segon Kwon),김영철(Young-cheol Kim) 한국비파괴검사학회 2017 한국비파괴검사학회지 Vol.37 No.6
본 연구에서는 KR60 레일 두부와 복부의 기하학적 형상 및 재질에 최적화된 위상배열 초음파 변환기를 CIVA 시뮬레이션 결과를 바탕으로 제작하였으며, 제작된 위상배열 초음파 변환기의 성능 평가를 위해 상용 위상배열 초음파 변환기와의 비교 실험을 진행하였다. 성능 평가는 KR60 레일에 표준인공결함을 제작하고 개발된 위상배열 초음파 변환기와 상용 위상배열 초음파 변환기의 감도와 상용 위상배열 초음파 변환기의 반사 신호 획득 제한 구역에서의 반사 신호 획득 가능 여부에 초점을 두었다. In this study, phased array ultrasonic transducers which are optimized in terms of the geometric and material features for detecting defects on head and body parts of the KR60 rail were fabricated based on CIVA simulation results. For the performance test of developed phased array ultrasonic transducers, these were compared with a commercial phased array ultrasonic transducer was compared. A performance test was conducted by comparing the sensitivities of the two types of phased array ultrasonic transducers, focusing on detecting defects that could not be inspected by commercial phased array ultrasonic transducers.
Kim, Suyong,Dangol, Manita,Kang, Geonwoo,Lahiji, Shayan F.,Yang, Huisuk,Jang, Mingyu,Ma, Yonghao,Li, Chengguo,Lee, Sang Gon,Kim, Chang Hyun,Choi, Young Wook,Kim, So Jeong,Ryu, Ja Hyun,Baek, Ji Hwoon,K American Chemical Society 2017 Molecular Pharmaceutics Vol.14 No.6
<P>Dissolving microneedle (DMN), a transdermal drug delivery system in which drugs are encapsulated in a biodegradable polymeric microstructure, is designed to dissolve after skin penetration and release the encapsulated drugs into the body. However, because of limited loading capacity of drugs within microsized structures, only a small dosage can be delivered, which is often insufficient for patients. We propose a novel DMN application that combines topical and DMN application simultaneously to improve skin permeation efficiency. Drugs in pretreated topical formulation and encapsulated drugs in DMN patch are delivered into the skin through microchannels created by DMN application, thus greatly increasing the delivered dose. We used 4-n-butylresorcinol to treat human hyper pigmentation and found that sequential application of serum formulation and DMNs was successful. In skin distribution experiments using Alexa Fluor 488 and 568 dyes as model drugs, we confirmed that the pretreated serum formulation was delivered into the skin through microchannels created by the DMNs. In vitro skin permeation and retention experiments confirmed that this novel combined application delivered more 4-n-butylresorcinol into the skin than traditional DMN-only and serum-only applications. Moreover, this combined application showed a higher efficacy in reducing patients' melanin index and hyperpigmented regions compared with the serum-only application. As combined application of DMNs on serum-treated skin can overcome both dose limitations and safety concerns, this novel approach can advance developments in transdermal drug delivery.</P>
Kim, Young Gon,Baek, Geonwoo,Han, Seunghak,Choi, Yojong,Kim, Junseong,Jeon, Haeryong,Ko, Tae Kuk The Korea Institute of Applied Superconductivity a 2019 한국초전도저온공학회논문지 Vol.21 No.4
Recently, many studies have been reported on the magnetoresistance and Hall effect of REBCO thin films and bulk. The voltage interferes quench detection of high-temperature superconducting magnet and generates leakage current in no insulation high-temperature superconducting coil. Therefore, in this paper, experiments on magnetoresistance and Hall effect of commercial YBCO and GdBCO tapes have been carried out. As a result, anomalous voltages expected for the magnetoresistance and Hall effect of REBCO tapes were observed and analyzed. In addition, the voltage characteristics of REBCO have been identified, and the Hall coefficient are calculated for use in high magnetic field magnet applications.
Kim, Junseong,Lee, Woo Seung,Kim, Jinsub,Song, Seunghyun,Nam, Seokho,Jeon, Haeryong,Baek, Geonwoo,Ko, Tae Kuk The Korea Institute of Applied Superconductivity a 2016 한국초전도저온공학회논문지 Vol.18 No.3
Recently, production technique and property of the High-Temperature Superconductor (HTS) tape have been improved. Thus, the study on applying an HTS magnet to the high magnetic field application is rapidly increased. A Nuclear Magnetic Resonance (NMR) spectrometer requires high magnitude and homogeneous of central magnetic field. However, the HTS magnet has fabrication errors because shape of HTS is tape and HTS magnet is manufactured by winding HTS tape to the bobbin. The fabrication errors are winding error, bobbin diameter error, spacer thickness error and so on. The winding error occurs when HTS tape is departed from the arranged position on the bobbin. The bobbin diameter and spacer thickness error occur since the diameter of bobbin and spacer are inaccurate. These errors lead magnitude and homogeneity of central magnetic field to be different from its ideal design. The purpose of this paper is to investigate the effect of winding error, bobbin diameter error and spacer thickness error on the central field and field homogeneity of HTS magnet using the virtual NMR signals in MATLAB simulation.
Characterization of a 20-inch Micro Channel Plate Photomultiplier Tube
Geonwoo Kim,Jik Lee,Hongjoo Kim 한국물리학회 2022 새물리 Vol.72 No.6
There is a proposal to construct a large neutrino detector in Korea, called Korean Neutrino Observatory (KNO), which consists of a large water tank and several tens of thousands of photosensors placed deep underground for neutrino detection. A 20-inch-diameter photosensor including a microchannel plate-photomultiplier Tube (MCP-PMT) is a candidate for the KNO due to its large photo-coverage. We characterized a 20-inch MCP-PMT by measuring its properties, including single photoelectron charge resolution, gain, signal-to-noise performance, dark count rate, after-pulse ratio, and timing performance. We present our measurements of its properties and compare them with those of a previous study.<br/>
Geonwoo Kim,Young-In Hwang,서무경,Ki-Bok Kim 대한기계학회 2020 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.34 No.8
In this study, two simple electrical impedance tuning methods derived from Krimholtz, Leedom, and Matthaei (KLM) modeling were proposed for increasing the sensitivity of a piezo-electric material-based ultrasonic transducer. In the first method, the reactance components of the ultrasonic transducer were removed, and in the other method, the electrical impedance of an ultrasonic transducer was matched to that of the ultrasonic system. To these ends, electrical circuits composed of inductors and capacitors were de-signed and KLM simulations of the two methods were performed. To verify the simulation results, ultrasonic transducers were fabricated and operated under the same conditions as in the simulations, and the experimental results were compared with the simulated results. In conclusion, the electrical tuning method (elimination of the reactance compo-nents) was more effective and the transducer circuit structure was simpler. The experi-mental results showed good agreement with the KLM simulation results.