• Journal of Positioning, Navigation, and Timing
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• 제4권2호
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• pp.73-77
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• 2015

Global Positioning System (GPS) Precise Point Positioning (PPP) has been extensively used for geodetic applications. Since December 2012, BeiDou navigation satellite system has provided regional positioning, navigation and timing (PNT) services over the Asia-Pacific region. Recently, many studies on BeiDou system have been conducted, particularly in the area of precise orbit determination and precise positioning. In this paper PPP method based on BeiDou observations are presented. GPS and BeiDou data obtained from Mokpo (MKPO) station are processed using the Korea Astronomy and Space Science Institute Global Navigation Satellite System (GNSS) PPP software. The positions are derived from the GPS PPP, BeiDou B₁/B₂ PPP and BeiDou B₁/B₃ PPP, respectively. The position errors on BeiDou PPP show a mean bias < 2 cm in the east and north components and approximately 3 cm in the vertical component. It indicates that BeiDou PPP is ready for the precise positioning applications in the Asia-Pacific region. In addition, BeiDou tropospheric zenith total delay (ZTD) is compared to GPS ZTD at MKPO station. The mean value of their difference is approximately 0.52 cm.

• Current Optics and Photonics
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• 제6권1호
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• pp.104-113
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• 2022

We present a method to count the overall length of the zoom system in an initial design stage. In a zoom-lens design using the concept of the group, it has been very hard to precisely estimate the overall length at all zoom positions through the previous paraxial studies. To solve this difficulty, we introduce T_eq as a measure of the total track length in an equivalent zoom system, which can be found from the first order parameters obtained by solving the zoom equations. Among many solutions, the parameters that provide the smallest T_eq are selected to construct a compact initial zoom system. Also, to obtain an 8× four-group zoom system without moving groups, tunable polymer lenses (TPLs) have been introduced as a variator and a compensator. The final designed zoom lens has a short overall length of 29.99 mm, even over a wide focal-length range of 4-31 mm, and an f-number of F/3.5 at wide to F/4.5 at tele position, respectively.

• Journal of electromagnetic engineering and science
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• 제9권1호
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• pp.17-24
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• 2009

In recent years, OFDMA(orthogonal frequency division multiple access) and SC-FDMA(Single Carrier Frequency Division Multiple Access) have been widely studied for the uplink of a mobile communication system. In this paper, PAPR(Peak-to-Average Power Ratio) and BER(Bit Error Rate) performance of the OFDMA and SC-FDMA systems are studied in relation to the uplink of a mobile communication system. Three kinds of sub-carrier allocation methods in the OFDMA system and 2 kinds of sub-carrier allocation methods in SC-FDMA system are suggested to compare and improve system performance. Simulation results show that in the OFDMA system, the first sub-band allocation method has better PAPR reduction performance than the other methods. In the SC-FDMA system, the distributed allocation method offers similar P APR, compared with the sub-band allocation method. P APR can be further reduced by adding a spectrum shaping filter with an appropriate roll of factor. Furthermore, it is found that on average, SC-FDMA can reduce the PAPR by more than 5 dB compared to OFDMA, when the total sub-carrier number is 1,024 and the sub-carrier number allocated to each user changes trom 8 to 512. Because of the frequency diversity and low PAPR characteristics, SC-FDMA system of the distributed sub-carrier allocation method can achieve better BER performance than the OFDMA system.

• 전력전자학회논문지
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• 제28권1호
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• pp.68-75
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• 2023

This paper proposes a three-phase single-stage AC-DC converter for the small wind generation system. Input power factor improvement and insulated output can be implemented with the proposed three-phase single-stage AC-DC converter under the wide power generation voltage (80-260 V_ac) and frequency (10-42 Hz) in a small wind power generation (WPG) system. The proposed converter is also capable of zero-voltage switching in the primary-side switches and zero-current switching in the secondary-side diodes by phase-shift control at a fixed switching frequency. In addition, it is possible to control a wide output voltage (V_o: 39 V_DC-60 V_DC) by varying the link voltage and improving the input power factor (PF) and the total harmonic distortion factor (THD_i). Simulation and experimental results verified the validity of the proposed converter.

• 한국추진공학회지
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• 제18권2호
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• pp.86-92
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• 2014

나로우주센터에 구축되는 연소기 연소시험설비(CCTF)에는 한국형발사체(KSLV-II)에 적용된 터보펌프식 엔진의 가스발생기 시험시 생성되는 연료과잉가스를 연소시키기 위한 후연소시스템이 포함되어 있다. 후연소시스템은 $O_2$와 $CH_4$ 가스를 공급받아 연료과잉가스를 소모시킨다. 본 연구는 연소기 연소시험설비의 상세설계 자료를 바탕으로 후연소시스템의 가스공급시스템에 대해 AMESim 상용프로그램을 이용하여 해석하였다. 그 결과 상세설계에 적용된 레귤레이터, 공급배관, 오리피스크기 등으로 가스사용량을 예측하고, 상세설계의 타당성을 검증하였다.

• Asian-Australasian Journal of Animal Sciences
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• 제25권4호
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• pp.496-501
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• 2012

Thirty-five available feeds were fermented in vitro in order to investigate their soluble total organic carbon (TOCs) and methane ($CH_4$) production rate. A fermentation reactor was designed to capture the $CH_4$ gas emitted and to collect liquor from the reactor during in vitro fermentation. The results showed that $CH_4$ production rate greatly varied among feeds with different ingredients. The lowest $CH_4$-producing feeds were corn gluten feed, brewer's grain, and orchard grass among the energy, protein, and forage feed groups, respectively. Significant differences (p<0.05) were found in digestibility, soluble total organic carbon (TOCs), and $CH_4$ emissions among feeds, during 48 h of in vitro fermentation. Digestibility and TOCs was not found to be related due to different fermentation pattern of each but TOCs production was directly proportional to $CH_4$ production (y = 0.0076x, $r^2$ = 0.83). From this in vitro study, TOCs production could be used as an indirect index for estimation of $CH_4$ emission from feed ingredients.

• 센서학회지
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• 제33권3호
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• pp.179-184
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• 2024

In the car industry, welding is a fundamental linking technique used for joining components, such as steel, molds, and automobile parts. However, accurate inspection is required to test the reliability of the welding components. In this study, we investigate the detection of weld beads using 2D image processing in an automatic recognition system. The sample image is obtained using a 2D vision camera embedded in a lighting system, from where a portion of the bead is successfully extracted after image processing. In this process, the soot removal algorithm plays an important role in accurate weld bead detection, and adopts adaptive local gamma correction and gray color coordinates. Using this automatic recognition system, geometric parameters of the weld bead, such as its length, width, angle, and defect size can also be defined. Finally, on comparing the obtained data with the industrial standards, we can determine whether the weld bead is at an acceptable level or not.

• 한국해양공학회:학술대회논문집
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• 한국해양공학회 2006년 창립20주년기념 정기학술대회 및 국제워크샵
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• pp.311-314
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• 2006

This paper concerns about total dynamic analysis of integrated mining system. This system consists of vertical steel pipe, intermediate buffer station, flexible pipe and self-propelled miner. The self-propelled miner and buffer are assumed as rigid-body of 6-dof. Discrete models of vertical steel pipe and flexible pipe are adopted, which are obtained by means of lumped-parameter method. The motion of mining vessel is not considered. Instead, the motion of mining vessel is taken into account in form of various boundary conditions (e.g. forced excitation in slow motion and/or fast oscillation and so on). A terramechanics model of extremely soft cohesive soil is applied to the self-propelled miner. The hydrodynamic forces and moments are included in the dynamic models of vehicle and lifting pipe system. Hinged and fixed constraints are used to define the connections between sub-systems (vertical steel pipe, buffer, flexible pipe, miner). Equations of motion of the coupled model are derived with respect to the each local coordinates system. Four Euler parameters are used to express the orientations of the sub-systems. To solve the equations of motion of the total dynamic model, an incremental-iterative formulation is employed. Newmark-b method is used for time-domain integration. The total dynamic responses of integrated mining system are investigated.

• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2017년도 학술발표회
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• pp.181-181
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• 2017

Low impact development (LID) practices has become important to mitigate the damage from natural disasters in urban areas. Thereby many hydrological simulation models can simulate the hydrological impact of LID practices. However, commonly used models are not able to provide specific information to most users such as where LIDs should be placed and what kind of LID should be designed. In this study, a decision support system which can be used with the EPA's SWMM was developed for the determination of LID types and locations of LID practices, named Water Management Prioritization Module (WMPM), was applied to a urbanized university campus. Eight sub-catchments were selected as feasible candidate areas for the planning of LID practices. Pre-designated infiltration trenches and permeable pavements were applied to each selected sub-catchments, followed by peak and total runoffs comparison between before/after planning of LIDs. Moreover, TOPSIS, one of a multi-criteria decision analysis method was used in the procedure of selecting target sub-catchment areas and final prioritization of LID types and locations. As a result, sub-catchments S4 with permeable pavements and S16 with infiltration trenches has shown the most decrease in total and peak runoffs, respectively. Therefore, WMPM was found to be effective in determining the best alternative among various scenarios generated and simulated.

• 가정과삶의질연구
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• 제24권4호
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• pp.75-92
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• 2006

This study examines the psychological independence in the family system of unmarried women to see how well they become psychologically independent within the relationships with family. A total of 452 subjects of the study were sampled from 20 to 30 unmarried women living in Seoul, Incheon and Gyeonggi-do. The results of the study are as follows: First, the scores of unmarried women's perception of family system were normal category. The scores of family system of unmarried women showed to be distributed to high scores among the overall ranges of scores which means they recognized their family system in general in a healthy way. Second, the level of the subjects' psychological independence from their fathers was shown to be higher than that from their mothers. The result means unmarried women were more dependent on their mothers than fathers. Third, the family system of unmarried women affected the level of psychological independence from their parents. The sub-factors of the family system significantly affected the level of psychological independence. Particularly, enmeshed and disengaged boundary and cooperative factors between spouses and generations affected the level of psychological independence. Fourth, the family system affected each sub-factor of psychological independence of unmarried women. Even though family system were different depending on each sub-factor of psychological independence, they affected the level of psychological independence.