• 대한전기학회논문지
• /
• 제43권7호
• /
• pp.1206-1213
• /
• 1994

This paper presents the operation principle and design rule of the Rogowski coil which can measure the transient current and describes the calibration and application experimental results for performance evaluation. It is obtained that the response curves of the Robowski coil with the turns of 300 and the passive integrator to sinusoidal input give a good linearity up to the frequency of 500 [kHz] and the current measurement system gaving the Rogowski coil is the frequency bandwidth of 40 [Hz]~700 [kHz]. As an application experiment for the fabricated modeling power transmission line, the impulse current, which limitates the direct lightning return stroke to overhead ground wire, is measured by the Rogowski coil and its fast Fourier transformation is carried out. The equivalent circuit of the Rogowski coil considering the stray capacitances is proposed, and the theoretical analysis is in good agreement with the measurement results. Also, it is found that for high frequency domain the stray capacitance such as a distributed capacitance to the shield and the capacitance between windings of coil should be considered in designing the Rogowski coils since the resonance originates from the stray capacitance and the self-inductance of the Rogowski coil.

• 대한전기학회:학술대회논문집
• /
• 대한전기학회 2000년도 하계학술대회 논문집 B
• /
• pp.1260-1263
• /
• 2000

Vector control of a single phase induction machine(SPIM) is usually employed by mechanical methods than electrical ones. The disadvantage of a SPIM has large noise at the starting. Using auxiliary winding which is only utilized for starting, the SPIM can be controlled with the vector control method. Regarding a auxiliary winding one phase, the SPIM is analyzed by the unsymmetrical two phase motor and phase transformation is unnecessary such as three phase IM. Including a auxiliary winding, SPIM is modeled by mathematical getting by component of turns ratio with main to auxiliary winding. It will be take with complicated resultant formula, by comparison to symmetrical three phase TM. For using the vector control theory, it must be decoupled of rotor flux and torque component. stator current is controlled and decoupled. This paper presents a variable-speed control system of SPIM, which to decoupled with flux and torque component and to use machine equivalent circuit referred to rotor, conventionally three phase IM by similar method.

• Structural Engineering and Mechanics
• /
• 제33권4호
• /
• pp.429-446
• /
• 2009

Three-scale homogenization procedure is proposed in this paper to provide estimates of the effective thermal conductivities of porous carbon-carbon textile composites. On each scale - the level of fiber tow (micro-scale), the level of yarns (meso-scale) and the level of laminate (macro-scale) - a two step homogenization procedure based on the Mori-Tanaka averaging scheme is adopted. This involves evaluation of the effective properties first in the absence of pores. In the next step, an ellipsoidal pore is introduced into a new, generally orthotropic, matrix to make provision for the presence of crimp voids and transverse and delamination cracks resulting from the thermal transformation of a polymeric precursor into the carbon matrix. Other sources of imperfections also attributed to the manufacturing processes, including non-uniform texture of the reinforcements, are taken into consideration through the histograms of inclination angles measured along the fiber tow path together with a particular shape of the equivalent ellipsoidal inclusion proposed already in Sko ek (1998). The analysis shows that a reasonable agreement of the numerical predictions with experimental measurements can be achieved.

• 한국안전학회지
• /
• 제27권6호
• /
• pp.59-63
• /
• 2012

The use of dry chemical powder has been increased as it can be stored for a long period and sustain in stable condition compared to gas or liquid phase extinguishing agents. A new type of dry chemical powder using Zeolite was produced in the research. Chemical powder was adsorbed into Zeolite 13X, a porous material appearing negative catalytic effect, to create extinguishing powder obtaining core shell structure and measured physical properties and run a small scale fire extinguishment. SEM, XRD, TA analysis was also executed, and extinguishing characteristics were measured by fire extinguishing experiment on oil pool fire. The experiment showed that the average particle size of Zeolite 13X was equivalent, indicating about $3{\pm}1{\mu}m$ and thermal analysis result illustrated that Zeolite 13X showed exothermic reaction peaks at $900^{\circ}C$ due to solid-state transformation. Extinguishing characteristics on oil fire of $NaHCO_3$/Zeolite 13X and $NH_4H_2PO_4$/Zeolite were improved, influenced by adsorbed extinguishing powders on Zeolite 13X and Zeolite 13X that contains high phase transition temperature.

• Nuclear Engineering and Technology
• /
• 제45권4호
• /
• pp.477-488
• /
• 2013

The PLC (Programmable Logic Controller) has been widely used to implement real-time controllers in nuclear RPSs (Reactor Protection Systems). Increasing complexity and maintenance cost, however, are now demanding more powerful and cost-effective implementation such as FPGA (Field-Programmable Gate Array). Abandoning all experience and knowledge accumulated over the decades and starting an all-new development approach is too risky for such safety-critical systems. This paper proposes an RPS software development process with a platform change from PLC to FPGA, while retaining all outputs from the established development. This paper transforms FBD designs of the PLC-based software development into a behaviorally-equivalent Verilog program, which is a starting point of a typical FPGA-based hardware development. We expect that the proposed software development process can bridge the gap between two software developing approaches with different platforms, such as PLC and FPGA. This paper also demonstrates its effectiveness using an example of a prototype version of a real-world RPS in Korea.

• Advances in nano research
• /
• 제12권3호
• /
• pp.319-336
• /
• 2022

Evaluating the temporal and spatial changes in the ecosystem service value (ESV) of the Sanjiangyuan Nature Reserve is important for understanding the impact of human activities on natural ecosystem and guiding ecosystem restoration and environmental pollution control. In this study, remotely sensed land-cover data and the equivalent factor method were used to analyze the spatiotemporal evolution characteristics of the ESV in Sanjiangyuan Nature Reserve from 1992 to 2015, and regression analysis was employed to determine the factors driving changes in the ESV. The results show that grassland was the main type of ecosystem in the study area, and the transformation of grassland into bare areas was the primary change in land cover. Additionally, the ESV in the study area first decreased and then increased, with an annual growth rate of 0.69%. The ESV mainly increased in the north of the Yellow River's source area, and mainly decreased in the northwest of the Yangtze River's source area. Finally, the gross output value of agriculture, urbanization rate and proportion of secondary industry were found to be the main factors driving the ESV in the study area.

• 한국정보과학회논문지:데이타베이스
• /
• 제34권1호
• /
• pp.18-34
• /
• 2007

온라인 분석 처리(OLAP, On-Line Analytical Processing)에서는 다양한 분석을 효과적으로 처리하기 위해, 다차원 구조의 데이타를 열에 차원 애트리뷰트의 값이 표시되는 넓은 형태의 수평 테이블로 표현한다. 관계형 테이블들은 보통 애트리뷰트의 개수에 제한이 있으므로 이러한 수평 테이블을 직접저장하기 어렵고, 저장하더라도 많은 수의 널(null) 간을 갖는 희박(sparse) 테이블이 되기 쉽다. 따라서 관계 데이타베이스에서는 이러한 수평 테이블을 차원의 이름을 열로 갖는 수직 테이블로 바꾸어 저장할 수 있다. 이렇게 할 경우, 수평 뷰 테이블에 대한 OLAP 질의를 저장된 수직 테이블에 대한 질의로 변환하는 작업이 필요하다. 본 논문에서는 전통적인 관계 대수 연산자들 외에 최근 DBMS 버전들이 제공하는 PIVOT 연산자를 사용하여 수평적인 뷰의 질의를 효율적으로 변환하는 방법을 제안하였다. 이를 위해 PIVOT 연산과 동등한 관계 대수식을 만들고 이를 증명하였으며, 이 PIVOT 연산을 사용하여 수평적인 테이블에 대한 질의를 수직적인 테이블에 대한 질의로 변환하는 방법을 제시하였다. 또한 실험을 통해 제안한 변환 방법이 기존 방법에 비해 성능이 더욱 우수함을 보였다.

• 한국산업보건학회지
• /
• 제16권4호
• /
• pp.398-412
• /
• 2006

The purpose of this study is to investigate the relationship between the acceleration of vibration by the powered hand tools used in the shipbuilding industry, and to develop the prospective prevalence model for the hand-arm vibration syndrome among the shipbuilding workers.The acceleration levels and frequencies of six types of grinder were measured using the ISO5349 method along with the time of exposure to the vibration from the powered hand tools. Medical examination for 114 workers were performed using the cold provocation test. Comparisons were made between the estimated prevalence of hand-arm vibration syndrome from ISO5349 and the observed values from the medical examinations. By multiple regression, we developed the prospective prevalence model of hand-arm vibration syndrome produced by the hand tools used in the shipbuilding industry. 4 hour-energy-equivalent frequency-weighted accelerations were $6.23m/s^2$ in the grinding job done after welding, and $13.39m/s^2$ in the grinding job done before painting. The mean exposure time while holding powered hand tools was 4.64 hours. Prevalence rates of Raynaud's Phenomenon were 12.04% in the grinding after soldering, and 42.9% in the grinding before painting measured using the ISO5349 method. After exposure to vibration for 10.79 years, about a half of the workers in the grinding after welding could developed Raynaud's Phenomenon. For the workers in the grinding before painting, the latency was 5.02 years. The ISO equation for dose response relationship was not significantly correlated with observed recovery rates of finger skin temperatures, blood flows and amplitudes of nerve conduction velocities. A multiple regression model for dose-response relationship was proposed from the results. Recovery rate of the skin temperatures = -0.668+ 0.337 ${\times}$ 4 hour energy equivalent frequency-weighted accelerations + 0.767 ${\times}$ duration of vibration exposure(years) The validity was proved by multiple regression analysis after correlation transformation and regression results based on model-building data and validation data.

• 한국전자파학회논문지
• /
• 제24권6호
• /
• pp.602-612
• /
• 2013

본 논문에서는 주파수 5.3 GHz에서 소형화된 branch line 커플러와 $360^{\circ}$ 이상의 위상천이를 보일 수 있는 가변 리액턴스 부하를 결합하여 소형화된 위상천이기의 설계를 보였다. 위상천이기의 소형화를 위하여, branch line 커플러의 새로운 구조를 제안하였다. 새로운 branch line 커플러는 전송선의 T 및 ${\pi}$형 등가회로 변환 방법을 이용하여 소형화하였다. 소형화된 branch line 커플러는 일반적인 구조에 비해 50 % 이상 소형의 크기를 가진다. 넓은 위상천이량을 갖기 위하여 전송선에 버렉터 다이오드 두 개를 입력과 출력에 연결한 부하 구조를 채택하였다. 특히, 조정 전압에 대한 위상천이량이 완만하도록 임피던스 변환기 역할을 하는 전송선을 설계된 부하 구조에 추가하여 구조를 보완하였다. 추가된 임피던스 변환기에 사용된 전송선 및 선정된 부하 구조의 전송선은 소형화에 장애가 되기 때문에 이를 집중 소자로 등가하여 소형화하였다. 제작된 위상천이기는 $15{\times}15mm^2$의 소형의 크기를 가지며, 조정 전압 0~10 V 범위의 경우, 중심 주파수 5.3 GHz에서 삽입 손실은 약 -4~-6 dB, 반사 손실은 -20 dB 이하, 약 $480^{\circ}$의 넓은 위상천이를 보였다.

• 한국임상보건과학회지
• /
• 제8권1호
• /
• pp.1362-1368
• /
• 2020

Purpose. In this study, The change of the accommodation function due to the use of a smartphone was objectively evaluated using an Auto Refractokeratometer and was to investigate the effect of accommodation response and microfluctuations of accommodation on stable fatigue. Methods. Twenty subjects (20 males, 20 females) who had no abnormalities in ophthalmic disease and strabismus, diplopia, suppression, convergence and ocular movement, and corrected visual acuity and unaided visual acuity of 0.8 or more were performed. The average age of the participants is (21.78 ± 1.78) years old. The refractive power of the eye was measured using an Auto Refractokeratometer (Speedy-i K-model, Righton Mfg Co. Tokyo Japan), and the equivalent spherical power was automatically calculated from the measured refractive power. The accommodation response amount was calculated for the accommodation stimulation amount in 8 steps in 0.5D increments from + 0.50D to -3.00D in the calculated equivalent spherical power. The microfluctuations of accommodation in the high frequency region was calculated according to the change in the amount of the accommodation stimulus. At this time, the spectral power of the microfluctuations of accommodation was analyzed by Fast Fourier Transformation (FFT). Results. After using the smartphone, it was found that the accommodation response to accommodation stimulation decreased and the microfluctuations of accommodation increased. Conclusions. It can be said that the use of a smartphone affects the accommodation response and the microfluctuations of accommodation, thereby causing a accommodative stable fatigue. Therefore, it is thought that the use of a smartphone for a long time may bring about a change in the accommodation function.