• Journal of the Korean Institute of Telematics and Electronics B
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• v.32B no.6
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• pp.932-942
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• 1995

A spacecraft power system can be divided into two types : DET system(Direct Energy Transfer system) and PPT system(Peak Power Tracking system). In a DET system employing the regulated bus voltage control method, the battery charger and discharger are widely used for the bus voltage regulation. The battery charger has two different modes of operation. One is the bus voltage regulation mode and the other is the charge current regulation mode. The battery discharger is employed to provide the power when the spacecraft is in the earth's shadow or the sun is eclipsed. The operating mode, charging or discharging, is selected by a power control circuit. In this paper, small-signal dynamic characteristics of battery charging and discharging system are analyzed to facilitate design of control loop for optimum performance. Control loop designs in various operating modes are discussed. Anaylses are verified through experiments.

• Proceedings of the Korean Institute of Intelligent Systems Conference
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• 2006.05a
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• pp.293-296
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• 2006

본 논문에서는 기타를 배우는 초보자가 조율을 쉽게 할 수 있도록 지원하는 시스템을 구현하였다. 본 시스템은 입력된 기타음에서 A/D 변환 및 FFT를 이용하여 pitch를 추출하였다. 기타음 인식 알고리즘을 적용하여 줄감개의 조작량과 조작 방향을 '약 $45^{\circ}$정도 감아라.', '아주조금 풀어라.' 등과 같은 언어적 표현으로 나타내어 조율 할 수 있게 하였다. 기타를 처음 접해보는 피험자들에게 본 시스템을 적용시켜 본 결과 피험자들은 시스템의 언어표현과 적절한 조작 횟수에 대하여 만족감을 나타내었고 조율 결과도 숙련자의 조작과 동일한 효과를 얻을 수 있었다.

• Journal of Electrical Engineering and information Science
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• v.3 no.1
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• pp.14-20
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• 1998

The resistive shunting for the fine control of a Direct Energy Transfer(DET) systems is fully developed, but the non-resistive shunting using variable size solar array segments is in progress. This paper presents the spacecraft power control through switching of solar array segments, which uses a fully regulated DET power regulation. This method eliminates a dissipative element and removes the associated design limitations which arise from the dissipative elements for radiating cooling in deep space. The switching shunt regulator comprises the switched Solar Array Shunt(SAS) modules that regulate the solar array power. These SAS modules connect/disconnect the solar array segments to/from the bus according to the loading in the main bus without significant variations in the dissipation level. In this paper, twelve segments are used in the shunting. In order to verify the basis of analysis, the computational result of an analytic loop gain is performed.

• Korean Journal of Mathematics
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• v.20 no.3
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• pp.285-291
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• 2012

Let $M_n$ be the algebra of all complex $n{\times}n$ matrices and ${\phi}:M_n{\rightarrow}M_n$ a surjective map (not necessarily additive or multiplicative) satisfying one of the following equations: $${\det}({\phi}(A){\phi}(B)+{\phi}(X))={\det}(AB+X),\;A,B,X{\in}M_n,\\{\sigma}({\phi}(A){\phi}(B)+{\phi}(X))={\sigma}(AB+X),\;A,B,X{\in}M_n$$. Then it is an automorphism, where ${\sigma}(A)$ is the spectrum of $A{\in}M_n$. We also show that if $\mathfrak{A}$ be a standard operator algebra, $\mathfrak{B}$ is a unital Banach algebra with trivial center and if ${\phi}:\mathfrak{A}{\rightarrow}\mathfrak{B}$ is a multiplicative surjection preserving spectrum, then ${\phi}$ is an algebra isomorphism.

• Korean Journal of Mathematics
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• v.7 no.2
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• pp.159-166
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• 1999

For classical elliptic pseudodifferential operators $A({\lambda})$ of order $m$ > 0 with parameter ${\lambda}$ of weight ${\chi}$ > 0, it is known that $logDet_{\theta}A({\lambda})$ admits an asymptotic expansion as ${\theta}{\rightarrow}+{\infty}$. In this paper we show, with some assumptions, that the coefficients of ${\lambda}^-{\frac{n}{\chi}}$ can be expressed by the values of zeta functions at 0 for some elliptic ${\psi}$DO's on $M{\times}S^1{\times}{\cdots}{\times}S^1$ multiplied by $\frac{m}{c_{n-1}}$.

• Honam Mathematical Journal
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• v.31 no.4
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• pp.515-527
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• 2009

Let R be a commutative ring with identity. Then we prove $M_n(R)=GL_n(R)$ ${\cup}${$A{\in}M_n(R)\;{\mid}\;detA{\neq}0$ and det $A{\neq}U(R)$}${\cup}Z(M-n(R))$ where U(R) denotes the set of all units of R. In particular, it will be proved that the full matrix ring $M_n(F)$ over a field F is the disjoint union of the general linear group $GL_n(F)$ of degree n over the field F and the set $Z(M_n(F))$ of all zero-divisors of $M_n(F)$. Using the result and universal mapping property we prove that $M_n(F)$ is its total ring of fractions.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2013.10a
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• pp.331-337
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• 2013

Acoustic Emission technique is widely applied to develop the early fault detection system, and the problem about a signal processing method for AE signal is mainly focused on. In the signal processing method, envelope analysis is a useful method to evaluate the bearing problems and Wavelet transform is a powerful method to detect faults occurred on rotating machinery. However, exact method for AE signal is not developed yet. Therefore, in this paper two methods which are Hilbert transform and DET for feature extraction. In addition, we evaluate the classification performance with varying the parameter from 2 to 15 for feature selection DET, 0.01 to 1.0 for the RBF kernel function of SVR, and the proposed algorithm achieved 94% classification accuracy with the parameter of the RBF 0.08, 12 feature selection.

• Journal of Korea Multimedia Society
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• v.25 no.6
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• pp.769-782
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• 2022

A study on agricultural automation became more important. In Korea, sweet persimmon farmers spend a lot of time and effort on classifying profitable persimmons. In this paper, we propose and implement an efficient grading algorithm for persimmons before shipment. We gathered more than 1,750 images of persimmons, and the images were graded and labeled for classifications purpose. Our main algorithm is based on EfficientDet object detection model but we implemented more exquisite method for better classification performance. In order to improve the precision of classification, we adopted a machine learning algorithm, which was proposed by PyCaret machine learning workflow generation library. Finally we acquired an improved classification model with the accuracy score of 81%.

• The Bulletin of The Korean Astronomical Society
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• v.34 no.1
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• pp.173.2-173.2
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• 2009

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.225-225
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• 2016

PHOLED devices which have the structure of ITO/HAT-CN(5nm)/NPB(50nm)/EML(47nm)/TPBi(10nm)/Alq3(20nm)/LiF(0.8nm)/Al(100nm) are fabricated to investigate the diffusion length of the triplet exciton by using double-quantum-well(DQE) EML structure. To fabricate DQW structures, Ir(ppy)3(2% wt) and Ir(btp)2(8% wt) are used as green and red emission zones, respectively. In DQW structured EML, as shown in Fig. 1, 1nm thick layers of green and red emission zones are located middle of the EML, and the distance between these wells(x) is changed from 0nm to 10nm. As shown in Fig. 2, the emission spectra from DQW PHOLED devices are changed with different x. The intensity of the green emission(520nm) is decreased when x is decreased, and it goes to near zero when x=0nm. This behavior can be identified as the diffusion of the triplet excitons from Ir(ppy)3 to Ir(btp)2 by the Dexter energy transfer(DET). From the external quantum efficiency(EQE) of the red emission, as shown in Fig. 3, the diffusion length of the triplet excitons can be determined by the equation of DET rate, R=A Exp(-2RDA/L), where RDA is donor-acceptor distance and L is the sum of the van der Wals radii. As a result, the measured data of the red EQEs with different x are identified to theoretical result from the equation of DET rate(Fig. 4). From this results, we could confirm that the diffusion length of the triplet excitons can be determined by using DQW structure and this method is very useful to investigate the behavior of the excitons in PHOLEDs.