• 대한수학회지
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• 제44권3호
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• pp.719-731
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• 2007

R is called a right ${\Pi}-coherent$ ring in case every finitely generated torsion less right R-module is finitely presented. In this paper, we define a dimension for rings, called ${\Pi}-coherent$ dimension, which measures how far away a ring is from being ${\Pi}-coherent$. This dimension has nice properties when the ring in question is coherent. In addition, we study some properties of ${\Pi}-coherent$ rings in terms of preenvelopes and precovers.

• Journal of Photoscience
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• 제5권2호
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• pp.69-71
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• 1998

Electronic structures and excited states for pyrazinylquinoxalinylethylene are investigated using PM3-UHF-CI and Molecular Mechanics force field. The results indicate that pyrazinylquinoxalinylethylene has extensively mixed ($\pi$, $\pi$$^*$) and (n, $\pi$$^*$) states while the (n, $\pi$$^*$) transition band does not appear in the absorption spectrum clearly and seems to be submerged under the more intense ($\pi$, $\pi$$^*$) bands.

• Kyungpook Mathematical Journal
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• 제59권3호
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• pp.391-401
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• 2019

A module is said to be ${\pi}$-extending provided that every projection invariant submodule is essential in a direct summand of the module. In this article, we focus on the class of modules having the ${\pi}$-extending property by looking at the singularity of quotient submodules. By doing so, we provide counterexamples, using hypersurfaces in projective spaces over complex numbers, to show that being generalized ${\pi}$-extending is not inherited by direct summands. Moreover, it is shown that the direct sums of generalized ${\pi}$-extending modules are generalized ${\pi}$-extending.

• 전력전자학회논문지
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• 제22권1호
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• pp.60-66
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• 2017

This paper presents the design of a proportional-integral (PI)-proportional-derivative (PD) position controller without using a speed controller in motor drive systems. Unlike the existing PI-PD position controller design methods, the proposed controller is designed by reducing the entire position control system to a second-order transfer function. Thus, the gain values for the PI-PD position controller can be determined easily by a given bandwidth of the position controller. The PI-PD position controller designed by the proposed method is adopted for position control in an interior permanent magnet synchronous motor drive system to confirm the validity of the proposed design method. The effectiveness of the proposed design method is confirmed through experiments.

• 제어로봇시스템학회논문지
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• 제12권3호
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• pp.221-226
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• 2006

In this paper, we study an approach to design a Fuzzy PI controller in HVDC(High Voltage Direct Current) system. In the rectifier of traditional HVDC system, turning on, turning off, triggering and protections of thyristors have lots of problems that can make the dynamic instability and cannot damp the dynamic disturbance efficiently. In order to solve the above problems, we adapt Fuzzy PI controller for the fire angle control of rectifier. The performance of the Fuzzy PI controller is sensitive to the variety of scaling factors. The design procedure dwells on the use of evolutionary computing(Genetic Algorithms, GAs). Then we can obtain factors of the Fuzzy PI controller by Genetic Algorithms. A comparative study has been performed between Fuzzy PI controller and traditional PI controller, to prove the superiority of the proposed scheme.

• 대한수학회보
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• 제32권1호
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• pp.45-56
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• 1995

D. H. Gottlieb [1, 2] studied the subgroups $G_n(X)$ of homotopy groups $\pi_n(X)$. In [5, 7, 10], the authors introduced subgroups $G_n(X, A)$ and $G_n^{Rel}(X, A) of \pi_n(X)$ and $\pi_n(X, A)$ respectively and showed that they fit together into a sequence $$ \cdots \to G_n(A) \longrightarrow^{i_*} G_n(X, A) \longrightarrow^{j_*} G_n^{Rel}(X, A) \longrightarrow^\partial $$ $$ \cdots \to G_1^{Rel}(X, A) \to G_0(A) \ to G_0(X, A) $$ where $i_*, j_*$ and \partial$ are restrictions of the usual homomorphisms of the homotopy sequence $$ \cdot \to^\partial \pi_n(A) \longrightarrow^{i_*} \pi_n(X) \longrightarrow^{j_*} \pi_n(X, A) \to \cdot \to \pi_0(A) \to \pi_0(X) $$.

• 대한수학회보
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• 제53권3호
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• pp.925-942
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• 2016

We study the structure of rings whose principal right ideals contain a sort of two-sided ideals, introducing right ${\pi}$-duo as a generalization of (weakly) right duo rings. Abelian ${\pi}$-regular rings are ${\pi}$-duo, which is compared with the fact that Abelian regular rings are duo. For a right ${\pi}$-duo ring R, it is shown that every prime ideal of R is maximal if and only if R is a (strongly) ${\pi}$-regular ring with $J(R)=N_*(R)$. This result may be helpful to develop several well-known results related to pm rings (i.e., rings whose prime ideals are maximal). We also extend the right ${\pi}$-duo property to several kinds of ring which have roles in ring theory.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2001년도 하계학술대회 논문집
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• pp.369-372
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• 2001

We studied the electro-optical (EO) performance in the vertical-alignment (VA) - l/4$\pi$ cell photoaligned with polarized UV exposure on a homeotropic photopolymer surfaces. Excellent voltage-transmittance curve in the VA - l/4$\pi$ cell photoaligned with polarized UV exposure for 3 min on the photopolymer containing cholesterol group of 8% can be achieved. The V-T characteristics in the VA-l/4$\pi$ cell photoaligned on the photopolymer surface can be improved by increasing cholesteryl group. For response time measurement, the transmittance characteristics of the VA-l/4$\pi$ cell photoaligned on the photopolymer surface was better than that of the VA-l/4$\pi$ cell rubbingaligned on a polyimide(Pl) surface.

• 전자공학회논문지SC
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• 제47권6호
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• pp.1-5
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• 2010

본 논문에서는 PI 제어기를 설계해야 하는 경우인 임계 주파수 부근에서 이득 감소가 적은 시스템을 구별할 수 있는 알고리즘을 제안하였다. 임계 주파수 부근에서 이득감소가 적은 시스템을 구별하기 위해 시간 지연 요소를 이용하여 이득 감소율을 구하는 방법을 제안하였다. 또한 크기 마진과 위상 마진이 주어진 경우 PI 제어기를 설계하는 방법을 제안하였다. 제안된 알고리즘은 시간 지연요소와 포화함수를 이용하여 PI 제어가 가능한 한점의 좌표값을 계산하는 방법을 사용하였다. 제안된 방법은 시뮬레이션을 통해 타당성을 검증하였다.

• 한국식물병리학회지
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• 제14권3호
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• pp.212-216
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• 1998

Capsicum pepper selections fro PI163192, PI241670, PI244670, PI271322, PI308787, PI322719, and PI369994 were confirmed to be non-hypersensitively resistant to race 3 of Xanthomonas campestris pv. vesicatoria. A resistant cultivar,‘SR’, was shown to be hypersensitive. Four Koran local cultivars, a cytoplasmic male sterile line (A-line) and its maintainer (B-line) were highly susceptible. The resistant selections and cultivars were crossed with a male sterile A-line (Smsms) and fertility of their F1 hybrids was examined by observing he pollen production, testing pollen germination, and quantifying the amount of pollen produced per anther to identify the genotype interacting with the male sterile cytoplasm. The seven resistant PI selections turned out to be restorers (N(S)MsMs) and‘SR’to be a maintainer (Nmsms).