• 대한수학회지
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• 제31권4호
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• pp.609-618
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• 1994

F. Rhodes [2] introduced the fundamental group $\sigma(X, x_0, G)$ of a transformation group (X,G) as a generalization of the fundamental group $\pi_1(X, x_0)$ of a topological space X and showed a sufficient condition for $\sigma(X, x_0, G)$ to be isomorphic to $\pi_1(X, x_0) \times G$, that is, if (G,G) admits a family of preferred paths at e, $\sigma(X, x_0, G)$ is isomorphic to $\pi_1(X, x_0) \times G$. B.J.Jiang [1] introduced the Jiang subgroup $J(f, x_0)$ of the fundamental group of X which depends on f and showed a condition to be $J(f, x_0)$ = Z(f_\pi(\pi_1(X, x_0)), \pi_1(X, f(x_0)))$.

• 한국전자파학회논문지
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• 제19권8호
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• pp.862-877
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• 2008

두 종류의 넓은 대역폭을 갖는 ring hybrids(하나는 coupled line이 포함되어 있고, 다른 하나는 left-handed transmission line을 포함한 ring hybrids)가 비교되었으며, 비교 결과로부터 coupled line을 포함한 ring hybrid가 모든 면에서 우수한 특성을 가짐을 보여줬다. 그러나, coupled line을 포함한 ring hybrid는 -3 dB coupling power를 가질 경우에 한해서만이 perfect matching이 이루어지기 때문에, perfect matching을 갖는 coupled line ring hybrid는 2차원으로 구현하기는 거의 불가능하다. 이 문제를 해결하기 위해서 coupled line을 해석했고, 그 해석 결과로부터 coupling coefficient에 관계없이 어느 경우에도 perfect matching을 이룰 수 있는 설계 식을 유도했다. 이 설계식을 이용하여, transmission line의 길이가 ${\pi}$보다 큰 경우에도 적용될 수 있는 크기를 줄이기 위한 새로운 형태의 transmission line 등가회로를 제시했다. 이 새로운 형태의 transmission line의 등가회로를 이용하면 기존의 ring hybrid의 $3\;{\lambda}/4$의 transmission line을 줄이는 데 사용할 수 있기 때문에 ring hybrid의 크기를 더욱 줄이는데 장점이 될 수 있다. 이 등가회로를 증명하기 위해서, coupling power를 고정하고 또는 transmission line의 길이를 고정하는 2가지 형태의 simulation을 하였으며, 대역폭은 coupled line의 coupling power에 직접적인 상관 관계가 있음을 보였다. 기존의 등가회로와 새로운 형태의 등가회로를 이용하여, 작고 넓은 대역폭을 가지는 ring hybrid를 제시하였다. 새로 제시된 ring hybrid를 이용하여, 기존의 ring hybrid와 비교하였다. 비교 결과로부터, 본 논문에서 제시한 ring hybrid의 전체 ring 둘레가 1/3보다 더 작음에도 불구하고, 대역폭이 훨씬 넓음을 보여줬다. 작고 넓은 대역폭을 가지는 ring hybrid를 측정했으며, 측정 결과는 -2.78 dB, -3.34 dB, -2.8 dB, -3.2 dB의 power division 특성을 보여줬으며, matching과 isolation은 20 % 이상의 대역폭에서 -20 dB보다 좋은 특성을 보여줬다.

• 한국전자파학회논문지
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• 제11권1호
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• pp.76-83
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• 2000

본 논문에서는 세라믹 동축 공진기와 Varactor Diode를 이용하여 800MHz~900MHz에서 2단 가변 대역통과 여파기를 설계 제작하였다. ABCD Parameter를 이용하여 $\pi$형 Inverter를 T형 등가회로로 변환하여 Varactor Diode 수를 2개로 최적화하였다. 가변대역은 800MHz~900MHz이며 삽입손실을 $405dB\pm0.5dB$ 이내 반사손실은 15dB 이상으로 설계하였다. 제작된 대역통과 여파기는 Simulation 결과와 잘 일치하였다.

• Bulletin of the Korean Chemical Society
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• 제31권3호
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• pp.577-581
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• 2010

Spiro[fluorene-9,4'-[4H]indeno[1,2-b]furan] was synthesized, and its $\pi$-conjugation was efficiently elongated using palladium-catalyzed C-H arylation of a furan moiety. The resulting $\pi$-conjugated compounds showed intense fluorescence and extremely high thermal stability.

• 전자공학회논문지B
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• 제31B권1호
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• pp.34-40
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• 1994

The design and implementation of a fuzzy self-organizing controller for an environmental temperature chamber is discussed. The chamber is a non-linear, time-variant system with delay-time and dead-time. And the parameter tuning is required in PI control when the performance degraded. However the proposed fuzzy-SOC monitors the performance of the process. modifies the data base, and performs the delay-time compensation based on the idealized process model. A series of experiments was performed for the conventional PI and the fuzzy-SOC. These experimental results show the usefulness of the fuzzy-SOC.

• 충청수학회지
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• 제14권1호
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• pp.1-6
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• 2001

We investigate the relationships between the Gottlieb groups and the generalized Gottlieb groups, and study some properties of the generalized Gottlieb groups. Lee and Woo [5] proved that $G_n(X,i_1,X{\times}Y){\simeq_-}G_n(X){\oplus}{\pi}_n(Y)$. We can easily re-prove the above main theorem of [5] using some properties of the generalized Gottlieb groups, and obtain a more powerful result as follows; if $F{\rightarrow}^iE{\rightarrow}^pB$ is a homotopically trivial fibration, then $G_n(F,i,E){\simeq_-}{\pi}_n(B){\oplus}G_n(F)$.

• Journal of Electrical Engineering and Technology
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• 제12권5호
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• pp.1821-1834
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• 2017

Medium voltage control applications due to obtain better output voltage and reduced electro-magnetic interference multi level inverter is used. In closed loop control with inverter, the PI controller does not operate satisfactorily when the operating point changes. This paper presents the performance of Co-Efficient diagram PI controller based indirect vector controlled induction motor drive fed from three-level inverter under different operating conditions (dynamic and steady state). The proposed Co-Efficient diagram PI controller based three level inverter significantly reduces the torque ripple compared to that of conventional PI controller. The performance of the indirect vector controlled induction motor drive has been simulated at different operating conditions. For three-level inverter control, a simplified space vector modulation technique is implemented, which reduces the coordinate transformations complications in the algorithms. The performance parameters, torque ripple contents and THD of induction motor drive with three-level inverter is compared under different operating conditions using CDM-PI and conventional PI controllers.

• 산업기술연구
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• 제26권B호
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• pp.227-231
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• 2006

This paper presents a robust speed control method of induction motors(IM) using a Non-linear PI controller(NPI). NPI is high gain controller in region of small error, and low gain controller in region of large error. So in steady state, system will be robust against variation of load torque. The simulation and experiment results confirm the validity of proposed control scheme.

• 대한수학회보
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• 제56권2호
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• pp.491-499
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• 2019

The problem of finding fast computing methods for Bernoulli numbers has a long and interesting history. In this paper, the author provides new proofs for two lacunary recurrence relations with gaps of length four and eight for the Bernoulli numbers. These proofs invoked the fact that the nth powers of ${\pi}^2$, ${\pi}^4$ and ${\pi}^8$ can be expressed in terms of the nth elementary symmetric functions.

• Korean Journal of Radiology
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• 제21권12호
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• pp.1326-1333
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• 2020

Objective: To evaluate urologist satisfaction on structured prostate MRI reports, including report with tumor-node-metastasis (TNM) staging (report B) and with Prostate Imaging Reporting and Data System (PI-RADS) score with/without TNM staging (report C, report with PI-RADS score only [report C-a] and report with PI-RADS score and TNM staging [C-b]) compared with conventional free-text report (report A). Materials and Methods: This was a prospective comparative study. Altogether, 3015 prostate MRI reports including reports A, B, C-a, and C-b were rated by 13 urologists using a 5-point Likert Scale. A questionnaire was used to assess urologist satisfaction based on the following parameters: correctness, practicality, and urologist subjectivity. Kruskal-Wallis H-test followed by Nemenyi test was used to compare urologists' satisfaction parameters for each report type. The rate of urologist-radiologist recalls for each report type was calculated. Results: Reports B and C including its subtypes had higher ratings of satisfaction than report A for overall satisfaction degree, and parameters of correctness, practicality, and subjectivity (p < 0.05). There was a significant difference between report B and C (p < 0.05) in practicality score, but no statistical difference was found in overall satisfaction degree, and correctness and subjectivity scores (p > 0.05). Compared with report C-b (p > 0.05), report B and C-a (p < 0.05) showed a significant difference in overall satisfaction degree and parameters of practicality and subjectivity. In terms of correctness score, neither report C-a nor C-b had a significant difference with report B (p > 0.05). No statistical difference was found between report C-a and C-b in overall satisfaction degree and all three parameters (p > 0.05). The rate of urologist-radiologist recalls for reports A, B, C-a and C-b were 29.1%, 10.8%, 18.1% and 11.2%, respectively. Conclusion: Structured reports, either using TNM or PI-RADS are highly preferred over conventional free-text reports and lead to fewer report-related post-hoc inquiries from urologists.