• Journal of applied mathematics & informatics
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• 제25권1_2호
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• pp.67-83
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• 2007

The characteristics of steady two-dimensional laminar boundary layer flow of a viscous and incompressible fluid past a moving wedge with suction or injection are theoretically investigated. The transformed boundary layer equations are solved numerically using an implicit finite-difference scheme known as the Keller-box method. The effects of Falkner-Skan power-law parameter (m), suction/injection parameter ($f_0$) and the ratio of free stream velocity to boundary velocity parameter (${\lambda}$) are discussed in detail. The numerical results for velocity distribution and skin friction coefficient are given for several values of these parameters. Comparisons with the existing results obtained by other researchers under certain conditions are made. The critical values of $f_0$, m and ${\lambda}$ are obtained numerically and their significance on the skin friction and velocity profiles is discussed. The numerical evidence would seem to indicate the onset of reverse flow as it has been found by Riley and Weidman in 1989 for the Falkner-Skan equation for flow past an impermeable stretching boundary.

• The Journal of Asian Finance, Economics and Business
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• 제7권12호
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• pp.73-84
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• 2020

The study aims to investigate the dual effects of corruption control on economic growth in relationship with the stock market and trade openness in developing countries. The study used difference S-GMM method on the dynamic panel data model in the period (2002-2017) with data collected from the World Bank. The study discovers the dominant impacts of corruption control in the relationship with the stock market on economic growth. At the same time, the study also confirms the overwhelming impact of corruption control in the relationship between trade openness and economic growth in the developing countries. In addition, the study shows that inefficient stock markets in developing countries will not promote economic growth. Meanwhile, the long-standing credit market has a positive impact on economic growth. With the strong development of stock market and trade openness in the period (2002-2017), control on corruption in developing countries does not get better in time with the increase in demand. The findings of this study suggest a number of solutions to strengthen corruption control, leading to the increased efficiency on the stock market and as well as encouraging the positive effects of trade openness to contribute to promoting economic growth in developing countries.

• Journal of Electrical Engineering and Technology
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• 제12권1호
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• pp.45-52
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• 2017

This paper deals with the operation strategy of reactive power in a multi-infeed HVDC (MIHVDC) system, in which several converters are connected to the same or nearby separate AC buses. The potential problems concerning a MIHVDC system when feeding a weak AC network are as follows: the need for coordination of the recovery control, the possibility of voltage instability or low quality of the area connected to the MIHVDC system, and the risk of mutual commutation failures. These problems in MIHVDC systems are similar to those in single-infeed HVDC (SIHVDC) systems, but the differences with the phenomenon of the SIHVDC system are the interactions between converters. The main reason for the potential problems of HVDC systems (MIHVDC or SIHVDC) is voltage variation; therefore, to mitigate the voltage variations, the performances of the HVDC system should be enhanced. Consequently, to mitigate the potential problems of MIHVDC systems, several solutions are suggested in this study, including installing STATCOM and installing a line arrester on the tower. The study results will be applied to a multi-infeed HVDC system in Korea.

• 대한기계학회논문집A
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• 제24권4호
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• pp.894-900
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• 2000

Optimization of chassis frame is performed according to the minimization of eleven responses representing one total frame weight, three natural frequencies and seven strength limits of chassis frame that are analyzed by using each response surface model from D-optimal design of experiments. After each response surface model is constructed form D-optimal design and random orthogonal array, the main effect and sensitivity analyses are successfully carried out by using this approximated regression model and the optimal solutions are obtained by using a nonlinear programming method. The response surface models and the optimization algorithms are used together to obtain the optimal design of chassis frame. The eleven-polynomial response surface models of the thirteen frame members (design factors) are constructed by using D-optimal Design and the multi-disciplinary design optimization is also performed by applying dual response analysis.

• 한국경영과학회지
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• 제23권2호
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• pp.187-200
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• 1998

This paper presents an original approach for solving short-term power scheduling in extended power system with two fuels in a unit and a limited fuel using Lagrangian relaxations. The underlying model incorporates the full set of costs and constraints including setup, production, ramping, and operational status, and takes the form of a mixed integer nonlinear control problem. Moreover, the mathematical model developed includes two fuels in a unit and a limited fuel, regulation reserve requirements of prespecified group of units. Lagrangian relaxation is used to disaggregate the model by generator into separate subproblems which are then solved with a nested dynamic program including empirical knowledges. The strength of the methodology lies partially in its ability to construct good feasible solutions from information provided by the dual. Thus, the need for branch-and-bound is eliminated. In addition, the inclusion of two fuels in a unit and a limited fuel provides new insight into the limitations of current techniques. Computational experience with the proposed algorithm indicates that Problems containing up to 23 units including 8 unit used two fuels and 24 time periods can be readily solved in reasonable times. Duality gaps of less than 4％ were achieved.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제11권3호
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• pp.1357-1372
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• 2017

Energy harvesting techniques, particularly radio frequency energy harvesting (RF-EH) techniques, which are known to provide feasible solutions to enhance the performance of energy constrained wireless communication systems, have gained increasing attention. In this paper, we consider a wireless-powered cooperative communication network (WPCCN) for transferring energy in the downlink and forwarding signals in the uplink. The objective is to maximize the average transmission rate of the system, subject to the total network power constraint. We formulate such a problem as a form of wireless energy transmission based on resource allocation that searches for the joint subcarrier pairing and the time and power allocation, and this can be solved by using a dual approach. Simulation results show that the proposed joint optimal scheme can efficiently improve system performance with an increase in the number of subcarriers and relays.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제54권5호
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• pp.185-189
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• 2005

This paper focuses on the design for Rx/Tx switch module of GSM(global standard mobile) band, characterization of a miniature, low power and dual-band implementation of the front-end switch module with low-pass filer And the effort to make agreement between the simulated design and the measured data for these solutions takes the place through accumulated design and manufacturing data library. We present the design, modeling and measurement of switch module integrating GSM Rx/Tx switching circuit and LPF(low pass filter) on a LTCC(low temperature co-fired ceramic) substrate. For GSM application, insertion and return loss of the low pass filter designed was less than 0.3 dB which was less than 12.7 dB at 900 MHz. The LTCC switch module contained 10 embedded passives and 3 surface mount components integrated on 4.6$\times$4.8$\times$1.2 mm, 6-layer multi-layer integrated circuit. The insertion loss of switch module measured at 900 MHz was 11 dB. In both of the design approach yielded excellent agreement between measured and simulated results.

• Journal of Positioning, Navigation, and Timing
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• 제9권1호
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• pp.15-21
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• 2020

In October 2019, the European Galileo navigation system operates a total of 24 satellites, two of them are in the testing phase. There are enough satellites in operation to enable precise point positioning (PPP) using Galileo signals. The number of visible satellites for Galileo in South Korea is investigated. In addition, to assess the latest performance of the Galileo kinematic PPP, data received at DAEJ reference station from October 1 to October 7, 2019, are analyzed. Galileo kinematic PPP presents some results in two categories, single-frequency PPP (SPPP) and dual-frequency PPP (DPPP). The positioning accuracy for Galileo kinematic SPPP solutions is less than 1 m root mean square (RMS) in all direction components. The Galileo kinematic DPPP achieves the positioning accuracy with an RMS value of less than 7 cm in all direction components. The results show that the latest performance of Galileo kinematic PPP at DAEJ station in South Korea is still relatively poor compared to GPS kinematic PPP. However, the residuals of Galileo code measurements are smaller than those of GPS code measurements.

• Journal of Photoscience
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• 제3권3호
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• pp.153-158
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• 1996

The effects of $\alpha$- and $\beta$-cyclodextrins (CD) on the twisted intramolecular charge transfer (TICT) behavior of p-N,N'-dimethylaminobenzoic acid (DMABA) in buffered aqueous solution have been investigated by examining formation and decay behaviors of the TICT-typical dual fluorescence. The ratio of the TICT emission to the normal emission (I$_a$/I$_b$) increases linearly $\alpha$-CD concentration increases, while in the presence of $\beta$-CD it shows nonlinear dependences on the CD concentration. The analysis of the CD-dependent changes of the I$_a$/I$_b$ and absorption spectra demonstrates formation of 1:1 inclusion complexes between DMABA and CDs. The decay time of the normal emission (ca. 700 ps) is little affected by the formation of $\alpha$-CD inclusion complex, whereas it increases upto ca. 1.6 ns upon formation of $\beta$-CD inclusion complex. The TICT emission for the $\beta$-CD inclusion complex exhibits two decay components while it shows a single component for the $\alpha$-CD inclusion complex, indicating formation of one or two types of inclusion complex in the presence of $\alpha$-CD or $\beta$-CD, respectively. These results are attributed to the CD cavity size dependence on patterns of complexation between CDs and DMABA. The CD size dependences of the TICT fluorescence properties with the orientation of the guest molecule demonstrate that the specific hydrogen bonding between the carboxylic acid group and water plays an important role in the excited-state TICT.

• 대한기계학회논문집B
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• 제38권5호
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• pp.407-412
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• 2014

가스하이드레이트 원리를 이용한 신개념의 해수담수화 장치를 제안하였다. 본 연구의 연속식 장치는 하이드레이트를 제조하고, 듀얼실린더의 압축공정에 의해 해수로부터 순수의 하이드레이트 펠릿화가 가능하다. 해수 샘플로부터 용존된 각 이온들의 제거 효율이 유도결합플라즈마분광광도계(ICP-AES)와 이온크로마토그래피(IC)에 의해 분석되었다. 본 연구에서 제안된 방법과 장치를 이용한 해수담수화시 형성된 하이드레이트 결정과 고농도의 염농축액과의 분리에 어려움이 있지만, 이를 해결함으로 좀더 효율적인 해수담수화 공정 적용이 가능할 것으로 판단된다.