• Bulletin of the Korean Mathematical Society
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• v.56 no.6
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• pp.1617-1642
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• 2019

In this paper, we study a theory for the structure of ${\tau}_w$-Loewy series of modules over commutative rings, where ${\tau}_w$ is the hereditary torsion theory induced by the so-called w-operation, and explore the relationship between ${\tau}_w$-Loewy modules and w-Artinian modules.

• Bulletin of the Korean Mathematical Society
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• v.59 no.1
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• pp.141-154
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• 2022

Let R be a commutative ring with identity. Denote by w𝒫_w the class of weak w-projective R-modules and by w𝒫_w^⊥ the right orthogonal complement of w𝒫_w. It is shown that (w𝒫_w, w𝒫_w^⊥) is a hereditary and complete cotorsion theory, and so every R-module has a special weak w-projective precover. We also give some necessary and sufficient conditions for weak w-projective modules to be w-projective. Finally it is shown that when we discuss the existence of a weak w-projective cover of a module, it is enough to consider the w-envelope of the module.

• Proceedings of the KIEE Conference
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• 1990.11a
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• pp.231-234
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• 1990

This paper shows real-time control technique of voltage-reactive power using the fuzzy theory. Here, major benefits of applying the fuzzy set theory as follow. First, heuristic knowledge of operator has been used in the operation and control of power system. Second, difficulties in traditional multi-objective numerical solution methods have been solved. Also, to achieve optimizing process on the voltage-reactive power control conventional search method have been used.

• East Asian mathematical journal
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• v.19 no.1
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• pp.63-71
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• 2003

In his invited lecture presented during the First Conference of the Mathematical Society of the Republic of Moldova($Chi\c{s}in\v{a}u$, August 2001) W. A. Dudek posed several open problems on the role and properties of the skew element in the theory of n-ary groups. In this note we give the partial solutions of some of these problems.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.56 no.3
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• pp.524-530
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• 2007

This paper presents a new and simple method for sensorless operation of matrix converter drives using a constant air-gap flux and the imaginary power flowing to the motor. To improve low-speed sensorless performance, the non-linearities of a matrix converter drive such as commutation delays, turn-on and turn-off times of switching devices, and on-state switching device voltage drop are modelled using PQR transformation and compensated using a reference power control scheme. The proposed compensation method is applied for high performance induction motor drives using a 3 kW matrix converter system. Experimental results are shown to illustrate the feasibility of the proposed strategy.

• Proceedings of the KIEE Conference
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• 1998.07b
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• pp.737-739
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• 1998

This presentation describes an experiment to intergrated control, protection and measurement system configulation at KOWACO's Yongdam hydro-power station currently constructed by discrete electronic and electromechenical devices. The experiment is designed to exploit existing microcomputer technologies, digital signal processors, m/w&fiber optic communications. The theory of operation and advantages of the intergrated approach are discussed.

• Journal of Biosystems Engineering
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• v.34 no.2
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• pp.89-94
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• 2009

Aerial application using an agricultural unmanned helicopter was suggested for an alternative against current pesticide application methods. Centrifugal clutches play important roles in the performance and safety of the helicopter operation. A previous study analyzed and verified the power transfer theory of the guide type centrifugal clutch. Based on the clutch theory, optimal designs of the clutch became possible and feasible using a simulation method. Design criteria of the clutch were the power transfer capacity of 24.66 kW(33.5 PS) at the rated engine speed and the engaging range speed of 3,000${\sim}$3,500 rpm. Various designs were accomplished using the simulation. An optimal clutch was simulated by determining the values of spring constant and mass of friction sector, which were 94,700 N/m and 123.7 g, respectively. The design performed the power capacity of 24.86 kW(33.8 PS) and engagement speed of 3,069 rpm, meeting the design criteria. Using the designed clutch, an efficient transfer of the power would be possible for the unmanned agricultural helicopter.

• Journal of Distribution Science
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• v.18 no.8
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• pp.75-87
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• 2020

Purpose: This study uses the protection motivation theory and information processing theory to discuss the high number of fraud phenomenon in Indonesia which causes worries to the internet users. The second problem is the large amount of information transparency in e-commerce which actually hinders the users in making decisions so it causes a negative behavior pattern, namely discontinue usage intention. Design/methodology: Therefore, this research hopes to provide insight to the online or e-commerce business community, especially for Tokopedia, to develop its business from understanding the factors influencing consumer attitude when shopping online. The sample are students from Universitas Indonesia, Institut Teknologi Bandung, Institut Pertanian Bogor, Universitas Gadjah Mada and Institut Teknologi Surabaya, with total 900 respondents. Result: The results of this research indicate that ubiquitous connectivity (UC) variable significantly affects variables such as the privacy concern (PC), information transparency (IT) and information overload (IO). PC and IO variables also significantly affect Discontinue Usage Intention (DUI). Conclusion: This study gives a new perspective that despite the phenomenon, the millennial generation especially are not entirely concerned about the privacy concern, however, this study clearly shows that the privacy issue in the digital word continues to be something that needs to be cared for.

• Journal of Power Electronics
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• v.13 no.6
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• pp.919-927
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• 2013

This paper proposes a Boundary Current Mode (BCM) control scheme to realize soft switching on a conventional single phase full bridge DC/AC inverter. This technique with the advantages of no auxiliary components, low cost, high efficiency, and simple in control, is attractive for micro-inverter applications. The operation principle and characteristic waveforms of the proposed soft switching technique are analyzed in theory. A digital controller is provided based on that theory. To balance the requirements of efficiency, switching frequency, and inductor size, the design considerations are discussed in detail to guide in BCM inverter construction. A 150W prototype is built under these guidelines to implement the BCM control scheme. Simulation and experiment results demonstrate the feasibilities of the proposed soft switching technique.

• Korean Journal of Optics and Photonics
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• v.10 no.4
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• pp.311-317
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• 1999

Unidirectional single-mode operation of a diode-pumped Nd:YAG laser with a planar semimonolithic ring cavity has been demostrated at 1064 nm. The semimonolithic cavity consists of a laser active medium placed in a magnetic field, a crystal quartz plate, and an output coupling mirror. They form an optical diode by acting each part as a Faraday rotator, a reciprocal polarization rotator and a partial polarizer, respectively. An eigenpolarization theory for the cavity configuration was presented and losses for the eigenmodes were calculated. A pump-limited single-mode output power of 155 mW and a slope efficiency of 17% were obtained when the laser was pumped by a 1.2 W, 809 nm diode-laser. A laser linewidth of less than 100 kHz is inferred from a beat note frequency spectrum between two identical laser systems and continous single-mode tuning range was more than 2 GHz.