• Progress in Medical Physics
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• v.12 no.1
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• pp.51-58
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• 2001

Synchrotron radiation (SR) has several advantages over convetional x-rays, including its phase, collimation, and high flux. A synchrotron radiation beamline 5C1 at Pohang Light Source (PLS) was recently built for imaging applications. We have shown that a SR imaging system is useful in imaging microscopic structures. SR with broad-band energy spectrum were adjusted to an object by Si wafers and their energy were approximately ranging from 6 keV to 30 keV. SR were passed through an object and finally transformed into visible lights by CdWO$_4$ scintillator screen. The visible lights which were reflected at an angle of 90 degrees by gold plated mirror were detected by a CCD camera and the image data were acquired using image acquisition system. A high-resolution phantom, capacitor, adult tooth, child tooth, cancerous breast tissue, and mouse lumbar vertebra were imaged with SR imaging system. The Objects were rotated within the field of view of the CCD detector, and their projection image data were obtained at 250 steps over 180 degrees rotation. Image reconstructions were carried out in a PC by using IDLTM(Research systems, Inc., US) program. The spatial resolution of the images acquired by the SR imaging system was measured with a high-resolution chart manufactured for several micrometer resolution. The specimens were also imaged with conventional x-ray radiography system to compare the image quality of radiography obtained with the SR imaging system. The results showed more structural details and high contrast images with SR imaging system than conventional x-ray radiography system. The SR imaging system may have a potential for imaging in biological researches, material applications, and clinical radiography.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.22 no.5
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• pp.510-515
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• 2011

In this paper, an artificial transmission line coupler with slotted-triangular patches, which is compact and spacesaving structure, is proposed. The proposed structure has specific features of not only convenience for adjusting the characteristic impedance and the phase of its coupled line by varying the lengths of the slots of the artificial transmission lines in designing a coupler but also the maximized coupling value at less than ${\lambda}$/4 electrical length so that it can be designed in compact and small dimensions, while conventional coupled line couplers are generally limited in compact and miniaturized designs by their ${\lambda}$/4 transmission lines. A fabricated 15 dB test-coupler at 2.4 GHz band by proposed design method shows good agreement with theory and simulation.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.37 no.3
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• pp.28-34
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• 2000

In this paper, we derive a spectral function and a new impedance profile of non-uniform tapered transmission lines by applying the Fourier transform to a linearized Riccati equation. We compensate the error which is from a linearized Riccati equation by adding a Taylor series to the impedance profile. Added terms remove discontinuities In the impedance profile at both ends of the non-uniform section. We show that a calculated spectrum approaches to a target spectrum of filter by an iterative method and numerical examples are given to illustrate the role of the phase function. As the design method which is shown in present paper provides a excellent adaptability for the design of non-uniform tapered transmission lines, the present method can be applied to design filters and impedance matching circuits with various passband characteristics.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.16 no.6
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• pp.87-94
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• 2002

As a section insulator dividing the electric railroad catenaries with different phases, the AC/DC section insulator which divides AC and DC railroad catenary have the complex structure, and suffer irregular abrasion on the surface or insulator rods when it is installed at the underground railroad. This paper intended as an investigation of the irregular abrasion of section insulators, provides the field measurements of abrasion level along insulator length and the abrasion patterns. The height variation of insulator parts and the balding length of insulators against pantograph's contact force are analysed experimentally, and the irregular abrasion mechanism is clarified with the help of theoretical analysis on the interaction between pantographs and section insulators. On the basis of experimental and theoretical analysis, the countermeasures to reduce the irregular abrasion are provided too.

• Proceedings of the KIPE Conference
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• 2016.07a
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• pp.235-236
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• 2016

본 논문에서는 400Hz 항공기용 3상 4선식 인버터의 전압 제어에 대해 연구하였다. 시스템에서 불평형이 발생하면 중성선 전류가 증가하며 이에 따라 출력전압 불균형 및 왜곡 증가 등 시스템에 심각한 문제를 발생시킨다. 전압의 크기를 제어해주는 RMS 제어의 경우 불평형 발생 시 전압의 크기는 정상적으로 제어가 가능하지만, THD가 상승하여 전력의 품질이 저하될 수 있다. 다른 제어 방식인 비례 공진(PR) 제어는 순시적으로 제어를 함으로써 전압의 크기뿐만 아니라 위상차 및 THD 감소 등의 향상된 전력 품질을 기대할 수 있다. 두 제어방법의 비교는 시뮬레이션 및 실험을 통해 수행하였으며, 두 제어방법 불평형 발생 시 모두 전압의 크기 오차가 3% 이하로 정상적으로 제어하는 것을 확인하였고, THD는 RMS 제어에 비하여 PR 제어의 결과가 2% 감소하는 것을 확인하였다.

• Proceedings of the KSME Conference
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• 2001.06d
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• pp.660-664
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• 2001

Ringbom Stirling engine which is a kind of low temperature difference model Stirling engine is manufactured and its characteristics are measured at some temperature differences. Pressure, displacer position and rotation speed are measured. Displacer position and rotation speed are detected by photo-sensor. The hot side of Ringbom Stirling engine is warmed by electric heater. The cold side of Ringbom Stirling engine is cooled by the air. This result may be useful for further design and manufacture of Ringbom Stirling engine. Also, it would be used as an educational material for mechanical engineering students.

• Proceedings of the Korea Air Pollution Research Association Conference
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• 2003.05b
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• pp.364-365
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• 2003

모델에 입력되는 지형자료의 형태는 좌표별 고도가 체계적으로 정리된 DEM(Digital Elevation Model)형태를 사용할 수 있으며, 과거에는 이러한 지형자료를 얻기 위해 대상지역의 지형도 중 등고선을 대상으로 좌표별 고도수치를 정리하여 구축하거나, 섬세한 지형자료를 구축하고자 할 경우 각 고도별 등고선자료를 scan한 후에 각 등고선별 고도자료의 위상관계를 설정해 주는 작업을 진행하였으나, 두 방법 모두 상당량의 수정작업과 반복작업이 요구되는 단점을 갖고 있었다. 그러나 국립지리원 주도로 1998년 9월부터 시작된 NGIS(National Geogralhic Information Sydtem)사업에 의해 구축된 수치지도를 이용하여 등고선별 고도자료를 추출하고, 이를 가공하여 모델의 입력자료로 활용하는 방법이 최근에 소개되고 있으며, 지형자료의 구축에 소요되는 시간 및 정확한 자료를 구축할 수 있다. (중략)

• The Proceedings of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.8 no.5
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• pp.70-75
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• 1994

본 논문은 상정사고에 기인한 선로의 과부하 해소 대책을 수립함에 있어서 가능한 한 부하차단없이 발전력재배분만으로 과부하해소를 시도하는 새로운 앨고리즘을 제시한다. 신속한 발전력 변화분을 계산하기 위하여 선로 과부하량과 상태변수($\Delta$$\theta$) 및 상태변수($\Delta$$\theta$)와 발전력 사이의 선형적인 관계를 이용하여 우선 과부하선로 양단모선 전압의 위상각 변화분을 계산하고 이에 대한 발전력 변화분을 계산하였다. 이 때 모든 Jacobian요소를 계산하지 아니하고 과부하선로 양단 모선번호에 해당하는 2열의 요소중 발전기 모선(slack 모선 제외)번호에 해당하는 행의 요소만 구함으로써 최소한의 요소를 이용하여 신속하게 계산토록 하였다.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.27 no.11
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• pp.1534-1541
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• 2003

A new window-based, user-friendly fringe analysis system is developed, especially for analyzing noisy interferograms. The system integrates three major techniques, that is fringe tracking, Phase shifting, and Fourier transform, into a single shell by employing a unified procedure. Since the system is made in a modular fashion and all processing modules can be shared for any technique, a user can select necessary modules and easily edit the applying order of them based on the user's analysis strategy, which should be changed depending on the noise level of the image. The system provides a high-level GUI and a variety of image handling tools and therefore users can easily access the system and produce the optimal results without giving up in the middle of a process even for severely noise-contaminated interferometric images.

• Proceedings of the Korea Information Processing Society Conference
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• 2003.11a
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• pp.169-172
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• 2003

최근에 대규모 병렬컴퓨터의 새로운 위상으로 HHN(m;n,h) 그래프가 제안되었다. HHN(m;n,h) 그래프는 하이퍼큐브에 기반한 계층적인 상호 연결망이며, 노드개수가 유사한 하이퍼큐브보다 작은 노드 분지수와 작은 링크의 수를 가지고 있기 때문에 대규모 병렬 컴퓨터를 구성하는 상호 연결망이지만, 심플 라우팅 알고리즘에 기반한 경로를 구성함으로써 불필요한 라우팅 경로를 갖는 단점이 있다. 따라서 본 논문에서는 심플 라우팅 알고리즘보다 평균거리가 개선된 새로운 라우팅 알고리즘을 제안하고, HHN(3;3,2)를 기준으로 비교하였을 때 대략 32%정도 향상됨을 보인다.