• 대한자기공명의과학회:학술대회논문집
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• 대한자기공명의과학회 2002년도 제7차 학술대회 초록집
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• pp.15-29
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• 2002

MRI에서 펄스 시퀀스(pulse sequence)란 고주파 RF(radiofrequency) 펄스 및 경사자장(gradient) 펄스를 가하고 MR 신호를 획득하는 순서를 시간대별로 도식화 한 pulse diagram을 이야기한다. 이러한 pulse sequence는 실제로 영상을 획득하기 위한 RF amplifier, gradient amplifier 등의 하드웨어를 순차적(sequential)으로 구동하는 역할을 한다. 따라서 이러한 pulse sequence는 현재 임상적으로 사용되는 다양한 영상기법들을 이해하는데 필수적이다.

• Journal of Electrical Engineering and Technology
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• 제13권3호
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• pp.1265-1274
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• 2018

This paper proposes a virtual flux (VF) and positive-sequence power based control strategy to improve the performance of grid-interfaced three-phase voltage source converters against unbalanced and distorted grid conditions. By using a second-order generalized integrator (SOGI) based VF observer, the proposed strategy achieves an AC voltage sensorless and grid frequency adaptive control. Aiming to realize a balanced sinusoidal line current operation, the fundamental positive-sequence component based instantaneous power is utilized as the control variable. Moreover, the fundamental negative-sequence VF feedforward and the harmonic attenuation ability of a sequence component generator are employed to further enhance the unbalance regulation ability and the harmonic tolerance of line currents, respectively. Finally, the proposed scheme is completed by combining the foregoing two elements with a predictive direct power control (PDPC). In order to verify the feasibility and validity of the proposed SOGI-VFPDPC, the scenarios of unbalanced voltage dip, higher harmonic distortion and grid frequency deviation are investigated in simulation and experimental studies. The corresponding results demonstrate that the proposed strategy ensures a balanced sinusoidal line current operation with excellent steady-state and transient behaviors under general grid conditions.

• East Asian mathematical journal
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• 제22권1호
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• pp.53-59
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• 2006

We introduce the resistant length and examine its properties. And consider the applications of resistant length to the boundary behavior of conformal mappings. We obtain the theorems in the connection with the resistant length zero and the fundamental sequences. The method of resistant length leads a simple proofs of theorems.

• 충청수학회지
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• 제26권1호
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• pp.243-248
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• 2013

In this paper, we introduce the mathematical resistance and examine its properties and consider the applications of mathematical resistance to conformal mappings. We obtain the theorems in the connection with "the mathematical resistance zero" and "the fundamental sequences".

• 호남수학학술지
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• 제22권1호
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• pp.31-36
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• 2000

In this paper, we introduce the extremal length and examine its properties and consider the applications of extremal length to conformal mappings. We obtain the theorems in the connection with "the extremal length zero" and "the fundamental sequences".

• Journal of Electrical Engineering and Technology
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• 제8권3호
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• pp.499-506
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• 2013

The accurate estimation of a fault location is desired in distance protection schemes for transmission lines in order to selectively deactivate a faulted line. However, a typical method to estimate a fault location by calculating impedances with voltages and currents at relaying points may have errors due to various factors such as the mutual impedances of lines, fault impedances, or effects of parallel circuits. The proposed algorithm in this paper begins by extracting the fundamental phasor of the positive sequence currents from the three phase currents. The second-order difference of the phasor is then calculated based on the fundamental phasor of positive sequence currents. The traveling times of the waves generated by a fault are derived from the second-order difference of the phasor. Finally, the distance from the relaying point to the fault is estimated using the traveling times. To analyze the performance of the algorithm, a power system with EHV(Extra High Voltage) untransposed double-circuit transmission lines is modeled and simulated under various fault conditions, such as several fault types, fault locations, and fault inception angles. The results of the simulations show that the proposed algorithm has the capability to estimate the fault locations with high speed and accuracy.

• 대한수학회보
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• 제59권3호
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• pp.697-707
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• 2022

It is well known that the continued fraction expansion of ${\sqrt{d}}$ has the form $[{\alpha}_0,\;{\bar{{\alpha}_1,\;{\ldots},\;{\alpha}_{l-1},\;2_{{\alpha}_0}}]$ and ${\alpha}_1,\;{\ldots},\;{\alpha}_{l-1}$ is a palindromic sequence of positive integers. For a given positive integer l and a palindromic sequence of positive integers ${\alpha}_1,\;{\ldots},\;{\alpha}_{l-1},$ we define the set $S(l;{\alpha}_1,\;{\ldots},\;{\alpha}_{l-1})\;:=\;\{d{\in}{\mathbb{Z}}{\mid}d>0,\;{\sqrt{d}}=[{\alpha}_0,\;{\bar{{\alpha}_1,\;{\ldots},\;{\alpha}_{l-1},\;2_{{\alpha}_0}}],\;where\;{\alpha}_0={\lfloor}{\sqrt{d}}{\rfloor}\}.$ In this paper, we completely determine when $S(l;{\alpha}_1,\;{\ldots},\;{\alpha}_{l-1})$ is not empty in the case that l is 4, 5, 6, or 7. We also give similar results for $(1+{\sqrt{d}})/2.$ For the case that l is 4, 5, or 6, we explicitly describe the fundamental units of the real quadratic field ${\mathbb{Q}}({\sqrt{d}}).$ Finally, we apply our results to the Mordell conjecture for the fundamental units of ${\mathbb{Q}}({\sqrt{d}}).$

• Geomechanics and Engineering
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• 제15권3호
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• pp.911-917
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• 2018

This paper concerns a numerical investigation on the effect of construction sequence on three-arch (3-Arch) tunnel behavior. A three-arch tunnel section adopted in a railway tunnel construction site was considered in this study. A calibrated 3D finite element model was used to conduct a parametric study on a variety of construction scenarios. The results of analyses were examined in terms of tunnel and ground surface settlements, shotcrete lining stresses, loads and stresses developed in center column in relation to the tunnel construction sequence. In particular, the effect of the side tunnel construction sequence on the structural performance of the center structure was fully examined. The results indicated that the load, thus stress, in the center structure can be smaller when excavating two side tunnels from opposite direction than excavating in the same direction. Also revealed was that no face lagging distance between the two side tunnels impose less ground load to the center structure. Fundamental governing mechanism of three-arch tunnel behavior is also discussed based on the results.

• 한국컴퓨터정보학회논문지
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• 제10권5호
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• pp.1-10
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• 2005

다중 서열 정렬(multiple sequence alignment, MSA)은 단백질과 핵산 서열들의 분석에 필요한 가장 중요한 도구이다. 생물학적인 서열들은 그들 사이의 유사성과 차이점을 보여주기 위하여 각각의 서열들을 수직적으로 정렬한다. 본 논문에서는 클러스터링 분기를 이용하여 두 그룹의 서열들 사이에서 정렬을 수행하는 효율적인 그룹 정렬 방법을 제안하였다. 제안한 알고리즘(Multiple Sequence Alignment using Clustering Divergence : CDMS)은 하향식 발견 방법인 트리 형태의 병합을 위해 클러스터링 방법으로 구축하였다. 클러스터링 방법은 가장 긴 거리를 가지는 서열을 두 개의 클러스터로 나눌 수 있다는 것에 기초하였다. 제안한 새로운 서열 정렬 알고리즘은 기존의 Clustal W알고리즘 보다 질적 향상과 처리 시간 단축 O($n^{3} L^{2}$)이 기대된다.

• Journal of Power Electronics
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• 제16권4호
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• pp.1513-1525
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• 2016

Rapid and accurate phase synchronization is critical for the reliable control of grid-tied inverters. However, the commonly used software phase-locked loop methods do not always satisfy the need for high-speed and accurate phase synchronization under severe grid imbalance conditions. To address this problem, this study develops a novel open-loop phase locking scheme based on a synchronous reference frame. The proposed scheme is characterized by remarkable response speed, high accuracy, and easy implementation. It comprises three functional cascaded blocks: fast orthogonal signal generation block, fast fundamental-frequency positive sequence component construction block, and fast phase calculation block. The developed virtual orthogonal signal generation method in the first block, which is characterized by noise immunity and high accuracy, can effectively avoid approximation errors and noise amplification in a wide range of sampling frequencies. In the second block, which is the foundation for achieving fast phase synchronization within 3 ms, the fundamental-frequency positive sequence components of unsymmetrical grid voltages can be achieved with the developed orthogonal signal construction strategy and the symmetrical component method. The real-time grid phase can be consequently obtained in the third block, which is free from self-tuning closed-loop control and thus improves the dynamic performance of the proposed scheme. The proposed scheme is adaptive to severe unsymmetrical grid voltages with sudden changes in magnitude, phase, and/or frequency. Moreover, this scheme is able to eliminate phase errors induced by harmonics and random noise. The validity and utility of the proposed scheme are verified by the experimental results.