호텔 식음료 부문의 선택속성에 따른 관계 지향 요인에 관한 연구

정광석,원홍석,안형찬 국제관광학회 2007 국제관광연구 Vol.4 No.2

다상 전류 중첩을 이용한 기어비 가변 마그네틱 기어의 토크 조절

정광석 한국생산제조학회 2019 한국생산제조학회지 Vol.28 No.6

By controlling the speed of one layer of a concentric magnetic gear, we can change the ratio of the rotational speed between the other two layers, which are composed of permanent magnets and ferromagnetic steel. This results in torque ratio between the layers that is not the inverse of the speed, unlike in a general speed reducer. The value of the torque ratio is determined from the pole ratio of the permanent magnets and steel teeth constituting the layers. In this study, we propose experimentally verified method of varying the torque of the output layer of a variable speed magnetic gear by superimposing another polyphase power source on the control coil. By setting the torque ratio inversely to the speed, constant power can be maintained and some of the coil's power can be supplied to the output side.

초음파 중합에 의한 polypyrrole 나노입자를 함유하는 메조포러스 TiO₂ 박막의 합성

정광석,조성호,송명근,김종득,Jang, Kwang-Suk,Cho, Sung-Ho,Song, Myung-Geun,Kim, Jong-Duk 한국화학공학회 2008 Korean Chemical Engineering Research(HWAHAK KONGHA Vol. No.

Using ultrasonic-induced polymerization of pyrrole, mesoporous $TiO_2$ thin film with polypyrrole nanoparticles was prepared. Polypyrrole nanoparticles were ultrasonically synthesized in the mother solution of mesoporous $TiO_2$ before spin-coating. The polypyrrole particles were well dispersed in the solution. After spin-coating and calcinations process, the nanocomposite films have well-organized pore channels without pore-collapse, and polypyrrole nanoparticles are well dispersed in mesoporous $TiO_2$ matrix. The pore size and light absorbance of the mesoporous nanocomposite thin films were controlled by using different template materials, and by using different amount of pyrrole monomer, respectively. 초음파 중합법을 이용하여 pyrrole을 중합시킴으로써 polypyrrole 나노입자를 합유하는 메조포러스 $TiO_2$ 박막을 합성하였다. 메조포러스 $TiO_2$ 박막을 만들기 위한 $TiCl_4$-계면활성제 용액에 pyrrole을 넣어주고 초음파 중합시킴으로써 용액 내에 polypyrrole 나노입자들이 잘 분산된 형태로 만들어졌다. 이 용액을 이용하여 spin-coating과 열처리를 함으로써 polypyrrole 나노입자를 합유하는 메조포러스 $TiO_2$ 박막을 제조하였다. 열처리 후에도 기공 구조는 잘 유지되었으며, polypyrrole 나노입자들이 박막 내에 잘 분산되었다. 주형물질인 계면활성제의 종류와 pyrrole의 양을 조절함으로써, 합성된 박막의 기공 크기와 빛의 흡광도를 조절하였다.

Contactless Transfer of Conductive Rod Using an Electrodynamic Wheel

정광석,원광민 한국정밀공학회 2011 International Journal of Precision Engineering and Vol.12 No.4

A novel electrodynamic wheel is proposed to convey a conductive rod. When rotating the spiral electrodynamic wheel around the conductive rod, a radial force and an axial force are generated, and are used to convey the rod without mechanical contact. However, even though the radial force acting on the rod is a repulsive force, the spatial stability of the rod is not always guaranteed in the uncontrolled mode. The stability depends fully on the operating condition. So, for the proposed conveyance system, the operating conditions for dynamic stability of the rod are clarified on the basis of dynamic analysis and finite element analysis (FEA) with experimental verification, thereby showing the feasibility of the proposed conveyance system. A test setup is designed and used to analyze the effect of the relative position between permanent magnets (PMs) constituting the wheel, and the pole number of PMs.

Active-layer Thickness Effects Related to the Threshold Voltage and Mobility Degradation in Poly-crystalline ZnO Thin-Film Transistors

정광석,김유미,박정규,양승동,윤호진,이희덕,이가원 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.58 No.51

The electrical and the physical characteristics of ZnO thin-film transistors (TFTs) with two different active layer thicknesses of 40 nm and 80 nm are investigated. A positive voltage shift and a mobility degradation were observed in all devices under a gate-bias stress. However, when the stress bias was removed, all ZnO TFTs recovered their original characteristics, which is regarded to be a result of pre-existing traps rather than stress-induced traps. In addition, through an XRD analysis and AFM topographies, we found that the thinner active layer thickness was, the smaller the grain size and the RMS roughness were. In order to clarify the pre-existing traps for various active layer thicknesses, we extracted the grain boundary trap density by using Levinson’s model, and we compared Hooge’s parameters based on a low-frequency noise analysis. TFTs with an active layer thickness of 40 nm have a higher grain boundary trap density and Hooge’s parameter value.

비선형 시계열 하천생태모형 개발과정 중 시간지연단계와 입력변수, 모형 예측성 간 관계평가

정광석,김동균,윤주덕,라긍환,김현우,주기재,Jeong, Kwang-Seuk,Kim, Dong-Kyun,Yoon, Ju-Duk,La, Geung-Hwan,Kim, Hyun-Woo,Joo, Gea-Jae 한국하천호수학회 2010 생태와 환경 Vol.43 No.1

In this study, we implemented an experimental approach of ecological model development in order to emphasize the importance of input variable selection with respect to time-delayed arrangement between input and output variables. Time-series modeling requires relevant input variable selection for the prediction of a specific output variable (e.g. density of a species). Inadequate variable utility for input often causes increase of model construction time and low efficiency of developed model when applied to real world representation. Therefore, for future prediction, researchers have to decide number of time-delay (e.g. months, weeks or days; t-n) to predict a certain phenomenon at current time t. We prepared a total of 3,900 equation models produced by Time-Series Optimized Genetic Programming (TSOGP) algorithm, for the prediction of monthly averaged density of a potamic phytoplankton species Stephanodiscus hantzschii, considering future prediction from 0- (no future prediction) to 12-months ahead (interval by 1 month; 300 equations per each month-delay). From the investigation of model structure, input variable selectivity was obviously affected by the time-delay arrangement, and the model predictability was related with the type of input variables. From the results, we can conclude that, although Machine Learning (ML) algorithms which have popularly been used in Ecological Informatics (EI) provide high performance in future prediction of ecological entities, the efficiency of models would be lowered unless relevant input variables are selectively used.

Machine Learning Application to the Korean Freshwater Ecosystems

정광석,김동균,전태수,주기재 한국생태학회 2005 Journal of Ecology and Environment Vol.28 No.6

ecosystem research. Currently, many studies have been carried out to find the patterns of environmental impact on dynamics of communities in aquatic ecosystems. Ecological models popularly adapted by many researchers have been a means of information processing in dealing with dynamics in various ecosystems. The up-to-date trend in ecological modelling partially turns to the application of ML to explain specific ecological events in complex ecosystems and to overcome the necessity of complicated data manipulation. This paper briefly introduces ML techniques applied to freshwater ecosystems in Korea. The manuscript provides promising information for the ecologists who utilize ML for elucidating complex ecological patterns and undertaking modelling of spatial and temporal dynamics of communities.

몰드변압기에서 용량성 프로브에 의한 부분방전 검출 기술

정광석,박대원,차현규,차상욱,길경석,Jung, Kwang-Seok,Park, Dae-Won,Cha, Hyeon-Kyu,Cha, Sang-Wook,Kil, Gyung-Suk 한국전기전자재료학회 2011 전기전자재료학회논문지 Vol.24 No.4

This paper dealt with a partial discharge (PD) detection method for insulation diagnosis in cast-resin transformers. To detect PD pulse, a planar-capacitive probe was designed and fabricated. The probe has no insulation problem and can be installed on cast-resin transformers even in operation since it does not connect with high voltage conductor. The PD measurement system consists of the capacitive probe, a coupling network of 100 [kHz] low-cutoff frequency, and an amplifier with a gain of 40 [dB] and a frequency bandwidth of 500 [Hz]~45 [MHz]. A plane-needle and a plane-plane electrode system were fabricated to simulate insulation defects in a cast-resin transformer. Sensitivity of the PD measurement system, which is evaluated by a standard calibrator was 0.35 [mV/pC] for positive and 0.45 [mV/pC] for negative, respectively. The PD detection by the capacitive probe was less sensitive than that by a coupling capacitor according to IEC 60270, but we could analyze the magnitude and the phase distribution of PD pulse.

자기 포커싱 방법을 적용한 감속 장치의 자기력 특성에 관한 연구

정광석,Jung, Kwangsuk 한국교통대학교 융복합기술연구소 2021 융ㆍ복합기술연구소 논문집 Vol.11 No.1

The magnetic gear, which amplifies the torque by filtering the magnetic field generated by the low-speed permanent magnet with a modulator, can exclude gear contact and can be effectively applied when there are environmental restrictions. In this paper, we discuss the magnetic force characteristics of a magnetic gear using a magnetic focusing array that replaces a general permanent magnet array magnetized in a radial direction along the circumferential direction. The torque increasing effect of the discussed array, known as an arrangement that increases the principal component by focusing a radial magnetic field, is compared with that of a general magnetic gear. In particular, in a magnetic gear using such an array, the sensitivity of torque according to variables is analyzed to see how various variables known as factors affecting torque have an effect.

Low-Frequency Noise 측정을 통한 Bottom-Gated ZnO TFT의 문턱전압 불안정성 연구

정광석,김영수,박정규,양승동,김유미,윤호진,한인식,이희덕,이가원,Jeong, Kwang-Seok,Kim, Young-Su,Park, Jeong-Gyu,Yang, Seung-Dong,Kim, Yu-Mi,Yun, Ho-Jin,Han, In-Shik,Lee, Hi-Deok,Lee, Ga-Won 한국전기전자재료학회 2010 전기전자재료학회논문지 Vol.23 No.7

Low-frequency noise (1/f noise) has been measured in order to analyze the Vth instability of ZnO TFTs having two different active layer thicknesses of 40 nm and 80 nm. Under electrical stress, it was found that the TFTs with the active layer thickness of 80 nm shows smaller threshold voltage shift (${\Delta}V_{th}$) than those with thickness of 40 nm. However the ${\Delta}V_{th}$ is completely relaxed after the removal of DC stress. In order to investigate the cause of this threshold voltage instability, we accomplished the 1/f noise measurement and found that ZnO TFTs exposed the mobility fluctuation properties, in which the noise level increases as the gate bias rises and the normalized drain current noise level($S_{ID}/{I_D}^2$) of the active layer of thickness 80 nm is smaller than that of active layer thickness of thickness 40 nm. This result means that the 80 nm thickness TFTs have a smaller density of traps. This result correlated with the physical characteristics analysis performmed using XRD, which indicated that the grain size increases when the active layer thickness is made thicker. Consequently, the number of preexisting traps in the device increases with decreasing thickness of the active layer and are related closely to the $V_{th}$ instability under electrical stress.