• Journal of the Korean Society of Manufacturing Process Engineers
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• v.10 no.4
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• pp.38-43
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• 2011

Industrial reducer is in general use to Deck Crane. High-precision and high-efficient reducer is minimized the power-loss and energy-loss of a machine. So it contribute the price reduction and life extension. Reducer is usually using the Planetary gear reducer. Planetary gear reducer is composed the sun gear, planet gear, internal gear and casing. Industrial reducer's wear and breakage have a short-life. To solve this problem, it is using the profile-shifted-gear or tooth modification. This study was carried out the effect of addendum modification coefficient on tooth fillet bending strength to planetary reducer. Tooth fillet bending stress is calculate. And all parameter were expressed the function of addendum modification coefficient. And then stress concentration factor of tooth fillet curve was express the function of addendum modification coefficient using comparison between theory and finite element analysis.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.13 no.4
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• pp.73-78
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• 2004

The conventional SLT(Shear Lag Theory) which has been proven that it can not provide sufficiently accurate strengthening predictions in elastic regime when the fiber aspect ratio is small. This paper is an extented work to improve it by modifying the load transfer mechanism called NSLT(New Shear Lag Theory), which takes into account the stress transfer across the fiber ends and the SCF(Stress Concentration Factor) that exists in the matrix regions near the fiber ends. The key point of the model development is to determine the major controlling factor among the material and geometrical coefficients. It is found that the most affecting factor is the fiber/matrix elastic modulus ratio. It is also found that the proposed model gives a good result that has the capability to correctly predict the elastic properties such as interfacial shear stresses and local stress variations in the small fiber aspect ratio regime.

• Proceedings of the Korea Air Pollution Research Association Conference
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• 2001.11a
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• pp.435-436
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• 2001

대기 중 에어로졸 입자의 크기 분포를 측정하는 기기 중 광학적 입자 계수기(Optical Particle Counter)는 0.3$\mu\textrm{m}$에서 25$\mu\textrm{m}$ 사이의 입자의 크기를 개개의 입자에 대한 산란광의 강도를 측정하여 그 강도와 미리 정해진 강도와의 관계에 의해 입자의 크기를 추정한다(Chun et al., 2001). 본 연구에서는 2001년 4월 제주 고산에서 실시된 ACE-Asia(Asian Pacific Regional Aerosol Characterization Experiment) 집중 관측 기간 중 광학적 입자 계수기(Optical Particle Counter; HIAC/ROYCO 5230)를 이용하여 측정한 이 기간 중 에어로졸 입자의 크기 분포의 특성을 황사시와 비황사시, 그리고 강수시와 비강수시로 나누고 그 특징을 비교하여 보았다. (중략)

• School Mathematics
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• v.14 no.4
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• pp.409-429
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• 2012

This paper reports the process two 11th grade students went through in reinventing derivatives on their own via a context problem involving the concept of velocity. In the reinvention process, one of the students conceived a tangent line as the limit of a secant line, and then the other student explained to a peer that the slope of a tangent line was the geometric mean of derivative. The students also used technology to concentrate on essential thinking to search for mathematical concepts and help visually understand them. The purpose of this study was to provide meaningful implications to school practices by describing students' process of reinvention of derivatives. This study revealed certain characteristics of the students' reinvention process of derivatives and changes in the students' thinking process.

• Proceedings of the Korea Water Resources Association Conference
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• 2015.05a
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• pp.19-19
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• 2015

최근 기후변화로 인해 집중호우 및 게릴라성 폭우의 발생빈도가 증가하고 있다. 또한, 도시화 및 산업화로 인해 불투수지역이 증가하여 첨두강우의 도달시간은 짧아지고, 강우강도는 증가하는 현상을 보이고 있다. 이로 인해 도시유역에서는 우수관의 통수능 부족으로 인한 홍수가 빈번히 발생하고 있다. 본 연구에서는 EPA-SWMM User's manual에서 제공하는 예제 관망도를 이용하여 SWMM 모형 매개변수들 간의 상관관계 분석을 수행하였다. 사전 조사 및 분석을 통해 유역폭, 관조도계수, 불투수유역 조도계수, 투수유역 조도계수, 불투수면적 비율 등 총 5개의 매개변수를 분석 대상으로 선정하였다. 매개변수들 간의 상관관계를 분석한 결과 유역폭-관조도계수, 유역폭불투수유역조도계수, 불투수면저 비율-투수유역 조도계수가 양의 기울기를 가지는 1차 선형함수 형태를 보였다. 즉, 예로 유역폭이 증가하면 관조도계수 또한 증가하는 경향을 보였다. 반대로 유역폭-불투수면적비율, 불투수유역 조도계수-관조도계수의 경우 음의 기울기를 가지는 상관관계를 보였으며 특히, 유역폭-불투수면적비율의 경우 2차 회귀곡선을 가지는 감소경향을 보였다. 본 연구의 결과를 활용하여 향후 우수관 설계를 수행한다면 내수침수 저감에 실무적인 도움을 줄 수 있을 것으로 판단된다.

• Proceedings of the Korea Water Resources Association Conference
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• 2008.05a
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• pp.613-618
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• 2008

본 연구에서는 개수로 마찰흐름 특성에 관한 연구로서 유량조사사업단(2006)의 우리나라 3대강 유역 하천자료와 미국의 Colorado지역 록키산맥 하천 관측자료를 통하여 개수로의 흐름특성을 집중적으로 검토하였다. 개수로 설계에 있어 수로의 흐름해석 및 마찰계수의 정확한 산정은 수로설계의 근간이 된다. 하지만 일반적으로 사용하고 있는 Manning(1889)식은 개수로 흐름특성을 판단하기에 너무 단순하여 상이한 결과를 보임에도 불구하고 단순성에 기인하여 사용되는 것으로 판단된다. Bazin(1865)과 Varwick(1945)의 개수로 실험결과를 보면 Nikuradse(1933)의 원형관수로 실험결과와 마찬가지로 층류, 천이층류, 완난류, 천이난류, 전난류 등 다섯 가지의 흐름특성이 존재함을 알 수 있다. 또한, 개수로 마찰계수의 특성변화를 보면 조고 또는 조도가 증가함에 따라 마찰계수가 상향으로 평행 이동하는 것을 볼 수 있다. 실험결과로부터 확인되는 이러한 흐름 특성이 현장에서도 분명히 나타날 것으로 판단하며 이러한 가설에 근거하여 각 하천의 관측자료를 분석하였다. 유량조사사업단의 우리나라 3대강 유역 하천 관측자료(2006)를 레이놀즈수의 함수인 완난류 흐름으로 전제하고 물의 기본적인 성질과 하천의 경사, 수심, 조고 등의 영향을 고려한 무차원수를 도입하여 마찰계수의 2차적인 분포특성을 파악하고자 하였다. 하지만 관측된 자료로부터 무차원수를 도입하여 산정된 마찰계수분포를 보면 마찰계수가 급격히 증가하고 추정된 유속과 관측된 유속을 비교하면 추정된 유속이 산개되는 경향이 나타났다. 이러한 문제점은 유량관측시 관측지점의 수면경사 및 하상경사의 미관측으로 하천정비기본계획상에 제시된 지형으로부터 하상경사를 추정하여 마찰계수와 유속을 산정하였다. 또한 하천정비기본계획상에 제시된 Manning의 조도계수를 이용하여 Ganguillet&Kutter(1869) 산정식과 Manning(1889) 산정식으로 부터 유속을 산정한 결과 오차가 크게 발생한 것을 확인하였으며, 실제 관측자료에 적합하도록 조도계수를 재 산정하였다. 논문의 분량 제한상 분석과정은 추후 논문에 제시하기로 하고 분석결과와 수위관측에서의 문제점을 제시하였다.

• International Journal of Highway Engineering
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• v.12 no.3
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• pp.131-137
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• 2010

In this paper, overseas criteria and research results were reviewed to develop a rational criterion proper to domestic airport runways on measurement of friction coefficient and removal of rubber deposit. The friction coefficients of the runways of the Incheon International Airport were measured by the ASFT(Airport Surface Friction Tester) from August 2007 to July 2009 and the data at intensively landed points were analyzed. Variation of the friction coefficient due to accumulation and removal of tire rubber was analyzed and seasonal influence on the variation were investigated by pavement types. The friction coefficient steadily decreased over a long term despite periodical removal of the rubber deposits. The variation of the friction coefficient in summer was larger than other seasons and asphalt pavement was more sensitive to the seasonal influence than concrete pavement. The friction coefficient of the asphalt pavement with macro texture was even larger than that of early age concrete pavement with micro texture. The variation of the friction coefficient of the asphalt pavement due to the deposit and removal of the tire rubber was also larger than that of the concrete pavement.

• Journal of Digital Convergence
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• v.18 no.6
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• pp.33-44
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• 2020

The main objective of this study is to measure the concentration and deconcentration of the domestic freight forwarding system which illustrate the development trends in this industry. In this study, Herfindal-Hirschman index (HHI), shift-share analysis (SSA), and GINI coefficient combined with Lorenz curves were employed to investigate the domestic freight forwarders. The results are as follows: first, the HHI was used to assess the concentration of domestic freight forwarders in Vietnam. The downward trend from 0.117 in 2008 to 0.083 in 2018 indicate the deconcentration of domestic freight forwarders in Vietnam. Second, the SSA results indicated that the company Transimex showed the best performance with a shift effect of million VND 1,906,515 and a ABSGR value of million VND 2,158,232. Third, the GINI index go down from 0.468 to 0.393 in 2008-2018 as follow and the Lorenz curves covered a large part which make more demonstrate the deconcentration trend of freight forwarding in Vietnam. The results show that deconcentration is a trend in 2008-2018. The results of this study provides relevant data on freight forwarders which are not easily accessible to related stakeholders.

• Journal of Digital Convergence
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• v.18 no.6
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• pp.65-79
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• 2020

With the rapid development of China's economy, the aviation industry, as an important part of transportation services, has undoubtedly achieved rapid development. However, there is hardly any academic work that was based on the development of the top airlines in the Chinese airline industry. Hence, this study provides empirical research that takes into account the longitudinal development of the top 20 airlines in China from 2009 to 2018. The throughput volumes (cargo and passenger) of the airlines were analyzed by concentration indicators, namely the concentration ratio (CR), the Herfindahl- Hirschman index (HHI), the Gini coefficient, and the shift-share analysis (SSA). In this paper, the top 20 airlines have been analyzed in terms of the passenger and cargo throughput from 2009 to 2018. The calculation results of CR6, HHI and the Gini coefficient show that the airlines were extremely deconcentrated. In addition, by comparing the ABSGR of passenger and cargo throughput, it is shown that China's aviation industry is dominated by four airlines- Air China, China Eastern Airlines, China Southern Airlines and Hainan Airlines. In the future study, it is necessary to explore growth strategies to find niche markets for passenger and cargo transportation.

• Journal of the Korean Society for Nondestructive Testing
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• v.26 no.5
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• pp.329-335
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• 2006

It is necessary to study on the stress concentration experimentally, which is the main reason to avoid mechanical dilapidation and failure, when designing a mechanical structure. Stress concentration factor of a specimen of cantilever beam with a circular hole in the center was measured using both strain gage and photoelastic methods in this paper. In strain-gage measurement, three strain gages along the line near a hole of the specimen were installed and maximum strain was extrapolated from three measurements. In photoelastic measurement, two methods were employed. First, the Babinet-Soleil compensation method was used to measure the maximum strain. Secondly, photoelastic 4-step phase shilling method was applied to observe the strain distribution around the hole. Measurements obtained by different experiments were comparable within the range of experimental error.