• 전력전자학회논문지
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• 제24권4호
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• pp.229-236
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• 2019

This study proposes a DC-DC converter topology of solid-state transformer for low-voltage DC distribution. The proposed topology consists of a voltage balancer and bipolar DC-DC converter. The voltage and current equations are obtained on the basis of switching states to design the controller. The open-loop gain of the controller is achieved using the derived voltage and current equations. The controller gain is selected through the frequency analysis of the loop gain. The inductance and capacitance are calculated considering the voltage and current ripples. The prototype is fabricated in accordance with the designed system parameters. The proposed topology and designed controller are verified through simulation and experiment.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2001년도 춘계학술대회논문집
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• pp.78-84
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• 2001

In this paper, Power Flow Boundary Element Method(PFBEM) has been developed for one and two dimensional noise and vibration problems in the medium to high frequency ranges. Green functions used for PFBEM are the fundamental solutions of energy governing equations. Both direct and indirect methods of PFBEM have been formulated and numerically applied to predict the vibrational energy density and intensity distributions of simple beams, rectangular plates and L-type plates.

• 사물인터넷융복합논문지
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• 제9권1호
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• pp.105-115
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• 2023

본 연구는 디지털 기술 수용을 통하여 이용자를 스포츠에 직접적인 참여 확대로 유도할 수 있는 방안을 모색하고자 한다. 2022년 7월 1일부터 8월 30일까지 사물인터넷(IoT)을 적용한 홈트레이닝 이용자를 대상으로 설문조사를 실시하였다. 설문 조사는 비대면 자기기입식 방법으로 129명이 참여하였다. 자료 처리는 IBM사의 SPSS 21.0 프로그램을 활용하여 빈도분석, 탐색적 요인 분석, 신뢰도 분석, 상관관계분석, 다중회귀분석, 3단계 매개회귀분석을 실시하였다. 연구 결과는 다음과 같다. 첫째, 홈트레이닝 PPM 모델과 스포츠 직접 참여의 관계에서 용이성은 매개효과가 나타났다. 불만족 요인에서 단순 기능성은 완전매개효과가 나타났고, 비효율성은 부분매개효과가 나타났다. 만족 요인에서 유희성과 경험 가능성은 완전매개효과가 나타났다. 계류 요인에서 개인 혁신성은 완전매개효과가 나타났다. 둘째, 홈트레이닝 PPM 모델과 스포츠 직접 참여의 관계에서 유용성은 매개효과가 나타났다. 불만족 요인에서 단순 기능성은 완전매개효과가 나타났고, 비효율성은 부분매개효과가 나타났다. 만족 요인에서 유희성과 경험 가능성은 완전매개효과가 나타났다. 계류 요인에서 개인 혁신성은 부분매개효과가 나타났다. 이러한 연구를 통하여 스포츠 산업이 NFT, 메타버스, 가상·증강현실 등 디지털 기술의 확대로 소비지출 확대와 경제성장에 기여하길 기대한다.

• Journal of Biosystems Engineering
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• 제31권1호
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• pp.1-8
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• 2006

This study was conducted to identify the characteristics of PTO rattle noise of a direct engine-PTO driveline for agricultural tractors. In order to reduce production costs of agricultural tractors, a direct engine-PTO driveline was recently introduced to the tractors produced in Korea. This simplified drive line reduced a number of gears and counter shafts in previous one. However, it caused a severe rattle noise under an idle condition, which was perceived as intolerable by many tractor operators. PTO rattle noise was measured at two locations: one 3 em apart radially from the centerline of the PTO shaft and another 100 em apart backward from the PTO end and 160 em high from the ground. Characteristics of the rattle was analyzed using the data measured near the PTO shaft. It was found that the period of rattle noise was same as the explosion stroke of engine and its peak level was about 123 dB (A) with PTO engaged at an idle engine speed of 880 rpm. As the engine speed increased, the rattle noise decreased. The frequency band of the rattle was 0.5-2.0 kHz and the frequency of peak sound pressure was 1.4 kHz. When compared the rattle noise between the locally produced and imported tractors of the same type of PTO driveline, the former generated louder rattle noise than the imported one by 7 dB (A). It was suggested that the rattle noise of local tractors must be reduced at least by 7 dB (A) to meet the international level.

• 한국음향학회지
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• 제40권4호
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• pp.370-381
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• 2021

본 논문에서는 수중 통신에서 은밀성과 성능 향상을 위해 직접 수열 확산 방식 기반 다중 밴드 기법을 사용한 부 대역 Frequency Shift Keying(FSK) 신호의 효율적인 송수신 구조를 제시하였다. 은밀성적인 측면에서는 Pseudo Noise(PN) 부호의 chip을 직접 곱하는 직접 수열 대역 확산 방식을 적용하였으며, 성능적인 측면에서는 다중 경로 특성, 도플러 확산 등으로 인한 성능 감쇠를 극복하기 위해 다중 밴드, 터보 등화, 각 밴드별 가중치 알고리즘을 적용하였다. 시뮬레이션 결과를 바탕으로, 송수신기 사이의 거리가 약 300 m ~ 500 m인 호수에서 기동 실험을 하여 대역확산 신호의 chip 수를 8개, 32개로, 다중 밴드 수는 4개 일 때의 성능을 분석하였으며, chip 수가 증가할수록, 터보 등화 기법 적용 시 반복횟수가 증가할수록 성능이 향상되었고, 다중 밴드에서 프리엠블 오류율을 분석하여 밴드 별 가중치를 적용 시 더 많은 패킷 전송 성공률을 나타냈다.

• 임상간호연구
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• 제25권1호
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• pp.55-66
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• 2019

Purpose: This study was done to assess development and postnatal care interventions in postnatal care intervention records for maternity ward nurses in tertiary hospitals and women's hospitals in South Korea. Methods: This mixed-method research was a Time-Motion (TM) study. Data were collected through external observation of 12 nurses in 4 wards over 24 hours. Mann-Whitney U test and independent t-test were employed for the analysis of frequency and provision time of direct/indirect care activity. $x^2$ (Fisher's exact test) was utilized to determine the difference in frequency between two groups. IBM SPSS 22.0 statistical program was employed for calculation. All statistical significance levels were at ${\alpha}=.05$. Results: According to the KPCS-1 (Korean Patient Classification System-1), women's hospitals are group 3 and tertiary hospitals, group 4. With respect to time difference in direct care, tertiary hospitals showed 791 minutes and women's hospitals, 399 a difference of 392 minutes. For time difference in indirect care, women's hospitals had 2,415 minutes while tertiary hospitals, 2,080, a difference of 335 minutes for women's hospitals. No difference was found in the average total care workload between the two institutions. Individual time also showed no difference (p>.05). Conclusion: High-risk maternal care strength in tertiary hospitals and breast-feeding strength in women's hospitals need to be benchmarked with each other.

• 한국도로학회논문집
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• 제10권4호
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• pp.139-150
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• 2008

본 연구는 도로연장측면에서 본선에 비해 상대적으로 연결로에서 발생하는 사고빈도가 높고, 교통사고가 증가하는 추세인 고속도로 연결로의 교통사고 예측모형의 개발에 초점을 두었다. 연결로 유형별(직결, 준직결, 루프)로 통계적으로 유의한 사고인자를 선정하고, 사고율과의 관계가 비선형 임을 분석하여 변수를 변형(Variables Transformation)하여 All possible 방식으로 예측모형을 개발하고, 통계적 진단 및 검증을 거쳐 유의성을 확인하였으며 이에 기존 개발 모형에 비해 예측력이 더욱 우수한 결과를 보였다. 개발된 사고예측모형은 보다 비용면에서 효율적이고, 안전한 트럼펫형 IC 연결로의 설계와 연결로 교통사고 원인분석에 활용될 수 있을 것으로 기대된다.

• 대한치과보철학회지
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• 제43권6호
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• pp.736-744
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• 2005

Statement of problem. Initial stability of implant is an important factor for predicting osseointegration. It requires a rapid, non-invasive, user-friendly technique to frequently assess the implant stability and the degree of osseointegration. Purpose. The aim of this study was to evaluate the correlation between the resonance frequency analysis (RFA) and the radiographic method for peri-implant bone change under in vitro conditions. Material and Method. Twenty implants of 3.75 mm in diameter(Neoplant, Neobiotech, Korea) were used. To simulate peri-implant bone change, 2 mm-deep $45^{\circ}$ range horizontal defect and 2 mm-deep $90^{\circ}$ range horizontal defect area were serially prepared perpendicular to the X-ray beam after conventional implant insertion. Customized film holding device was fabricated to standardize the projection geometry for serial radiographs of implants and direct digital image was obtained. ISQ values and gray values inside threads were measured before and after peri-implant bone defect preparation. Results. Within a limitation of this study, ISQ value of resonance frequency analysis was changed according to peri-implant bone change (p<0.05) and gray value of radiographic method was changed according to peri-implant bone change (p<0.05). There was no correlation between the ISQ value and the gray value for peri-implant bone change (p>0.05). But, in horizontal defect condition, relatively positive correlation were between ISQ and gray values(r=0.663). Conclusion. This results provided a possibility that peri-implant bone change may be evaluated by both RFA and radiographic method.

• 한국치위생학회지
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• 제18권6호
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• pp.1025-1035
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• 2018

Objectives: This study examined dental hygiene students' frequency of participation in community volunteer activities, job consciousness, depression, and self-esteem, and then identified the correlation among them. We also analyzed the moderating effect of depression and self-esteem on the correlation between participation in community volunteer activities and job consciousness. Methods: We surveyed 312 dental hygiene students attending four universities in South Chungcheong Province, Korea, from May 2 to June 15, 2016, through direct visits. They were given structured questionnaires containing four items on community volunteer activities, three on job consciousness, ten on self-esteem, and 13 on depression. To examine the moderating effect of depression and self-esteem, we performed analysis of variance, correlation analysis, and structural equation modeling analysis (based on the path analysis model and by inserting interaction terms) using SPSS and AMOS. Results: We observed a negative correlation between self-esteem and depression (r=-0.062) but a positive correlation between self-esteem and job consciousness (r=0.125). Depression and job consciousness had a negative correlation (r=-0.176). Depression had a statistically significant impact on job consciousness (r=-0.519, p<0.01). The interaction term between depression and frequency of community volunteer activities also had a statistically significant influence on job consciousness (r=0.090, p<0.05). These findings indicate that depression moderates the correlation between frequency of community volunteer activities and job consciousness at a statistically significant level. Conclusions: More frequent participation in volunteer activities enhances dental hygiene students' self-esteem, reduces depression, and raises job consciousness. The positive impact of volunteering on self-esteem, depression, and job consciousness warrants encouraging students' participation in community volunteer activities, creating supportive structures, and developing various volunteer programs relevant to the students' area of study.

• 패션비즈니스
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• 제3권2호
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• pp.67-76
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• 1999

The purpose of the study was to investigate customer shopping orientations of non-store shoppers and identify differences shopping orientations among groups determined by amount and frequency of purchase by various direct marketing media. The subjects were male and female consumers who aged over twenty and resided in Seoul, Kungki or Masan area. A questionnaire was developed by the researchers, and distributed to 770 people. A sample of 747 consumers responded to the questionnaire, and 732 questionnaires were used for analysis. Frequency count and percentage, factor analysis, analysis of variance (ANOVA) and Tukey's test were used for statistical analysis. Consumer shopping orientations were classified into 4 factors: pleasure, economy/value, and convenience I & II. Among groups of heavy shoppers, light shoppers, and non-shoppers, there were significant differences in their shopping orientations. Also, within groups, there were significant differences among their shopping orientation factors. All three groups had significantly stronger orientation toward convenience I than pleasure and convenience II. Also, within other purchase groups (fashion-good purchasers, other-good purchasers, and non-purchasers) showed the same shopping orientations as the former groups. On the basis of the above results, this study is expected to be useful for catalog retailers to develope effective marketing strategies and provide their customers new buying motives.