• Journal of the Korea Institute of Information and Communication Engineering
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• v.11 no.9
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• pp.1729-1733
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• 2007

In this paper, we have carried out some tests for analyzing the effects of optical fiber characteristics and piping structures in designing a Customer Cabling System with optical fibers. In this tests, the loss characteristics due to the number of curvatures and the radius of curvature with bending to establish an optical fiber have analyzed particularly. We can confirm that the test results satisfy the current technical regulations in both cases of the number of curvatures and the radius of curvatures. Also, in particular, since there is no loss in an optical cable under the current radius of curvature, that is 30mm, the radius criteria of curvature needs to be revised. These tests results will be so useful to revise and establish a customer cabling system for FTTH.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.10A
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• pp.1014-1019
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• 2006

The research deals with the measurement of electromagnetic wave propagation in subway tunnels at 2.65GHz. Measurements have been conducted in 4 different types of tunnel courses, a straight tunnel, two curved tunnels, with 245m and 500m radius of curvature, and a tunnel that has both straight and curved sections. we found that the path loss exponent for the line-of-sight(LOS) region inside all the tunnels is $1.31{\sim}2.19$. The path loss exponents for LOS regions in the tunnel is lower than $(3{\sim}4)$, which corresponds to the path loss exponent factor for outdoor cellular environments. The path loss exponents of the straight tunnel, two curved tunnels with 245m and 500m radius of curvature are 1.94, 2.92, and 4.34, respectively. This indicates that a smaller radius of curvature in tunnel results in a higher path loss exponent for nonline-of-sight(NLOS) region. The path loss exponents for the NLOS region in the combined and curved tunnel, which have the same radii of cuvature, are 5.88 and 4.34, respectively. Therefore, it can be concluded that the path loss characteristics in tunnel environments are infulenced by the radii of curvature as well as the LOS distance.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.7C
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• pp.529-533
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• 2008

In this paper, we have analysed the channel loss characteristics of optical fiber due to the changing of radius of curvatures and the number of cable banding, and due to the connection between different modes of fiber to derive revisions of technical regulation for FTTH. The results of test show that all conditions are satisfied the criteria(allowable radius of curvatures, 30mm) with the exception of conditions of 10mm radius in single mode case and show that source of light in multi mode fiber can't be delivered to single mode fiber. henceforth, we should study more intensively on the standards of connection between cables in the different modes.

• Journal of the Korean Society of Propulsion Engineers
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• v.22 no.5
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• pp.1-12
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• 2018

The streamline curvature method is essentially used for the design procedure of multi-stage axial turbines. Moreover, by using this method, it is possible to consider the turbine loss characteristics for real operating conditions at an early design stage. However, there is not enough relevant research in South Korea to support this. In the present study, the streamline curvature method and the empirical equation for calculating the mixing loss are employed to predict the performance of a multi-stage axial turbine with leakage flows. The proposed method is applied to the prediction of the performance of a five-stage axial turbine with leakage flows, as used for an industrial gas turbine of 86 MW in South Korea. The calculation result is compared with 3D CFD data, and the advantages and limitations of the streamline curvature method are described.

• Korean Journal of Optics and Photonics
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• v.9 no.3
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• pp.151-155
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• 1998

A new Fabry-Perot tunable filter has been built with simple construction, which does not require any additional aligning and/or beam-confining components for the reduction of the diffraction loss. For this feature, one of the two fibers for the filter is processed to have a concave mirror whose curvature is the same as that of the wavefront of the Gaussian beam from the first fiber. After high reflection coatings, the two fibers are aligned to result in an FP filter whose bandwidth, free spectral range, and insertion loss is 1.47nm, 52nm, 5.6dB respectively.

• Korean Journal of Optics and Photonics
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• v.8 no.3
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• pp.230-235
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• 1997

Coupling loss variation as the shape of fiber ends and the fiber arrangement in a fiber Fabry-Perot cavity, formed with two optical fibers with dielectric mirror coatings on their ends, is analyzed. For the intended features it is assumed that one of two fibers is processed to have a concave mirror whose curvature is the same as that of the wavefront of the Gaussian beam from the first fiber. In this assumption, it was turned out that the coupling loss at the cavity length of 15 ${\mu}{\textrm}{m}$ is less than 0.5% even with tilt angle of 0.2$^{\circ}$, curvature error of 70 ${\mu}{\textrm}{m}$, cavity length error of 8 ${\mu}{\textrm}{m}$, and lateral alignment error of 0.5 ${\mu}{\textrm}{m}$. Thus, low loss and high-finesse fiber Fabry-Perot filters whose cavity length is greater than several ${\mu}{\textrm}{m}$ can be obtained easily if the receiving fiber end is properly formed.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.38 no.10
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• pp.797-805
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• 2014

The purpose of this study was to investigate the drag and lift characteristics of the cavitator of a supercavitating underwater vehicle and the pressure loss due to water intake. These investigations were performed by changing the diameter, velocity, radius of curvature of the intake, and angle of attack of the cavitator. With increasing ratio of the intake diameter to the cavitator diameter ratio($d/D_1$), the drag coefficient and the pressure loss coefficient of the water intake decreased. The greater the increase in the ratio of the intake velocity-to-free stream velocity ratio(S), the smaller was the decrease in the drag coefficient and the lift coefficient. When the intake had a radius of curvature(c), the pressure loss coefficient decreased. On the contrary, the effect of the radius of curvature on the drag coefficient was imperceptible. For angles of attack (${\alpha}$) of the caviatator in the range of $0^{\circ}$ to $10^{\circ}$, the drag coefficient and the pressure loss coefficient changed slightly, whereas the lift coefficient increased linearly with increasing angle of attack.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.15 no.4
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• pp.185-190
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• 2015

In this paper we characterized and designed the waveguide antipodal finline transition at 57-65GHz frequency band in V-band for 5G mobile communication systems. Especially, we proposed the design method of spline taper for finline tapers by means of increasing curvature from linear taper. We could perform optimization more effectively by excluding improper regions for optimal performance from optimization using the method. Return losses and insertion losses of antipodal finline transitions were mainly affected by the taper shape of the finline. The resonances in the structure of the finline transition were the strongest enemies who deteriorate the performance of the transition. And we alleviated the resonances using semicircle shaped patch. The designed antipodal finline transition showed good performance as it showed less than -24.2dB of return loss and -0.24dB of insertion loss in the band(57-65GHz) which we suppose to use.

• Transactions of the Korean Society of Mechanical Engineers
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• v.15 no.3
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• pp.789-798
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• 1991

본 연구에서는 원통형 구조물의 진동해석을 위하여 통계에너지 분석방식(st- atistical energy analysis:SEA)이 사용되었다. SEA는 4개의 물리적 변수인 구조물 질량(Mi), 주파수대역에 존재하는 고유진동수(Ni), 내부손실계수(internal loss fact- or) 및 상호손실계수(coupling loss factor)를 이용하여 구조물의 진동수준과 구조물 상호간의 에너지 교환을 해석하는 방법으로서 비록 넓은 주파수 범위에 걸쳐 정확한 진동예측을 하기에는 어느정도 오차가 예상되는 단점이 있으나 진동해석이 용이하고 복잡한 계산을 필요로 하지 않기 때문에 대형구조물의 진동해석에 많이 사용되고 있 는 기법이다. 따라서 연구의 대상인 원통형 구조물의 고유진동수를 예측하기 위하여 일차적으로 반경에 의한 곡률영향을 배제시킨 평판에 대한 분석이 시도되었다. 이와 함께 주어진 주파수 대역에 걸쳐 평판및 원통형 구조물의 고유진동수의 차이를 비교하 였다.그결과로부터 원통형 구조물에 대한 고유진동수 계산식을 평판구조물의 굽힘 강성과 곡률반경으로 야기되는 표면응력에 의한 함수로 표현하였다.

• Journal of the Korean Institute of Intelligent Systems
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• v.20 no.5
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• pp.624-630
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• 2010

As electrocardiogram(ECG) signals are generally sampled with a frequency of over 200Hz, a method to compress diagnostic information without losing data is required to store and transmit them efficiently. In this paper, an ECG signal compression method, which uses feature points based on curvature, is proposed. The feature points of P, Q, R, S, T waves, which are critical components of the ECG signal, have large curvature values compared to other vertexes. Thus, these vertexes are extracted with the proposed method, which uses local extremum of curvatures. Furthermore, in order to minimize reconstruction errors of the ECG signal, extra vertexes are added according to the iterative vertex selection method. Through the experimental results on the ECG signals from MIT-BIH Arrhythmia database, it is concluded that the vertexes selected by the proposed method preserve all feature points of the ECG signals. In addition, they are more efficient than the AZTEC(Amplitude Zone Time Epoch Coding) method.