• 대한기계학회논문집
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• 제17권9호
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• pp.2145-2152
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• 1993

The objective of this paper is to examine the detection limit, growth characteristics and notch curvature radius in short crack problem. Measurement techniques such as ultrasonic method and back-face strain compliance method were adopted. The fatigue crack growth rate of the short crack is slower than that of a long crack for a notched specimen. The characteristic of crack growth and crack closure is same as the case of a delay of crack growth caused by constant amplitude load for an ideal crack or single peak overload for a fatigue crack. The short crack is detected effectively by ultrasonic method. A short surface crack occurs in the middle of specimen thickness and is transient to a through crack depth is larger than the notch curvature radius.

• 한국해양공학회지
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• 제18권1호
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• pp.28-34
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• 2004

It is well known that tensile peak overloads may significantly delay suubsequent constant amplitude fatigue crack growth in many materials. Since real structures are usually subjected to complex load histories, the ability to predict accurate crack growth under realistic service conditions is of major engineering interest. This paper describes experiments on fatigue track growth in the integrally stiffened panel of 7075-T6 aluminum alloy. The effect of shape parameters and overload position on the fatigue crack growth behavior of integrally stiffened panels are discussed. Based on the experimental results, the following conclusions have been drawn: the overall fatigue crack growth retardation resulting from single overload in the stiffened panels was generally larger in the larger thickness ratio, although the retardation trends, according to the change in overload positions, were similar to those exhibited in the non-stiffened panels.

• 한국항공운항학회지
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• 제28권1호
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• pp.7-13
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• 2020

A significant growth in local air traffic volume is leading to airway congestion and flight delays especially for Incheon-China and Incheon-Europe sectors. A key method to increase the airway capacity is to place a supplemental airway parallel to the existing one and in cooperation between the aviation authorities between China and Korea, a dual airway track was implemented on December 6, 2018. Here, we use airline A's flight data to analyze the congestion change effect of the new airway. Results show total delay time to Europe is reduced 51% (13.4 to 6.6 minutes) as the delay distribution for 16-30 minutes, 31 minutes and greater decreased from 23.2% to 8.2% and 8.7% to 1.0% respectively. The delay to China also decreased but the drop is not as significant as flights to Europe. This is caused by the difference in flight distance, traffic volume, and characteristics of flights landing and transiting China. Flights to Europe show a broad distribution in altitude allocation and reduction in aircraft separation demonstrating the effectiveness of a dual airway track.

• 화약ㆍ발파
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• 제13권1호
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• pp.20-31
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• 1995

Many methods and techniques to reduce ground vibrations are well known. Some of them are to adopt electric milisecond detonators with a sequential blasting machine or an initiating system with an adequate number of delay intervals. The types of electric detonators munufactured in Korea include instantaneous, decisecond and milisecond delays byt numbers of delay intervals are only limite from No.1 to No.20 respectively. It is not sufficient to control accurately milisecond time with these detonators in tunnel excavation. Sequential fire time refers to adding an external time delay to a detonators norminal firing time to obtain sequential initiation and it is determined by sequential timer setting. To reduce the vibration level, sequential blasting machine with decisecond detonatore was adopted. A total of 134 blasting was recorded at various sites. Blast-to-structure distances ranged from 20.3 to 42.0 meter, where charge weight varied from 0.25 to 0.75 kg per delay. The results can be summarized as follow : 1. The effects of sequential blasting machine on the vibration level are discussed. The vibration level by S.B.M. are decreased approximately 14.38~18.05 to compare to level of conventional blasting and cycle time per round can be saved. 2. The empirical equations of particle velocity were obtained in S,B.M. and conventional blastin. $V=K(D/W^{1/3})-n$. where the values for n and k are estimated to be 1.665 to 1.710 and 93.59 to 137 respectively. 3. The growth of cracks due to vibrations are found but the level fall to within allowable value.

• 전기학회논문지
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• 제67권12호
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• pp.1587-1594
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• 2018

In south korea, the government make a plan to generate the 20% of the total electrical power as renewable source like wind generation and solar generation. This plan will accelerate the increase of fault current with power industry's growth. As the increase of fault current, the superconducting fault current limiter (SFCL) has been studied. In case that the SFCL is applied in power system, it can cause the overcurrent relay (OCR)'s trip delay because of the reduced fault current. In this paper, the overcurrent relay with voltage component was suggested to improve the OCR's trip delay caused by the SFCL and compensational constant was introduced to have the trip time similar to the trip time of case without the SFCL. For conforming the effect of the suggested OCR with voltage component, the PSCAD/EMTDC simulation modeling and analysis were conducted. Through the simulation, it was conformed that the trip delay could be improved by using the suggested OCR and compensational constant.

• 국제학술발표논문집
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• The 8th International Conference on Construction Engineering and Project Management
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• pp.50-59
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• 2020

The 21st century is witnessing a rapid growth of tall buildings in urban centers globally to create more urban space for an anticipated urban population. Tall buildings, however suffer from incessant delays and sometimes total abandonment. Consequently, this study investigated and ranked the causes of delay in tall building projects, while focusing on the Gulf Cooperation Council (GCC) countries. Initially, 36 common delay causes investigated globally were categorized into 9 groups, and then further ranked utilizing the Relative Importance Index (RII) through a questionnaire survey. Tall building professionals in the GCC countries (Saudi Arabia, United Arab Emirates, Bahrain, Kuwait, Oman and Qatar) were contacted. The respondents' categories include Consultants, Contractors, and Clients' Representatives/Facility Managers. The results reveal that the top three causes include "client's cash flow problems/delays in contractor's payment", "contractor's financial difficulties", and "poor site organization and coordination between various parties". The findings from this study could help construction professionals develop guidelines and controls for delay mitigation, as well as support them in risk-based decision making in the planning of tall building projects.

• Child Health Nursing Research
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• 제19권1호
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• pp.12-20
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• 2013

목적 본 연구는 영유아의 발달지연의심에 영향 미치는 요인을 파악하여 영유아의 성장발달 지연 예방 프로그램 개발에 기초자료를 제공하고자 시도하였다. 방법 연구대상은 B시 16개구 보건소를 방문한 0-6세까지의 영유아와 그의 어머니로 총 133명이었고, 영유아의 발달검사를 위해서는 한국형 덴버 II 도구를 사용하였으며, 자료분석은 SPSS 19.0을 이용하여 ${\chi}^2$-test와 Fisher's exact test, 다중 로지스틱 회귀분석을 실시하였다. 결과 신체계측 결과 체중 3백분위 미만은 7.5%였고, 현재체중 백분위가 출생시 체중백분위보다 성장곡선 두 칸 이상 감소한 경우는 8.4%였다. 한국형 덴버 II 결과에 의한 발달지연의심 비율은 9.8%였다. 영유아의 발달지연의심 예측요인은 체중백분위 변화, 경제상태, 어머니가 지각한 아동의 발달상태였다. 즉, 출생시 체중백분위가 '감소'하는 경우가 '유지'되는 경우보다 발달지연의심이 나타날 확률이 6.69배 높았고, 경제상태가 '하'인 경우가 '중'인 경우보다 발달지연의심이 나타날 확률이 6.26배 높았으며, 어머니가 지각한 아기의 발달상태가 '의심'인 경우가 '정상'인 경우보다 발달지연의심 비율이 4.99배 높게 나타났다. 결론 영유아들의 건강한 성장발달을 위해서는 출생 시부터 주기적으로 아동의 성장발달상태를 관리하는 정부차원의 시스템 구축이 필요하고, 특히 저소득층 및 1세 이하의 영아들을 위한 보다 짧은 주기의 성장발달평가 프로그램이 필요하다.

• 한국시스템다이내믹스연구
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• 제17권2호
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• pp.5-32
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• 2016

Purpose of this paper is to review series of Limits to Growth studies from its original Rome Club Report published in 1972 to the most recent one in 2012 by Jorgen Randers and finds its implications on concept and strategy of sustainable development. For this purpose first, this paper reviewed series of Limits to Growth studies in details with focus on scenarios used in simulation of world model. Second, response to the original Limit to Growth was reviewed and to see validity of its scenario based simulations, simulated results of interest variables and actual historical data up to the year 2010 was compared. Third, structure and key arguments in both studies, Limit to Growth studies and Our Common Future was explained and compared. Finally, implications of the Limit to Growth studies on concept and strategy for sustainable development was discussed. Based on the comparison, this paper argued that even if the term sustainable development was not used in the Limit to Growth at all, concept and strategies for sustainable development implied in the Limit to Growth are more clear and specific than those of Our Common Future. Since Limit to Growth studies were simulation based ones that produce detailed behaviors on interest variables, it clarifies more clearly the abstract concept of sustainable development and thus, provides specific guidelines for the direction of sustainable policy which has been suffering long from vagueness of concept of sustainable development.

• 한국작물학회:학술대회논문집
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• 한국작물학회 2001년도 춘계 학술대회지
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• pp.200-201
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• 2001

• 한국작물학회:학술대회논문집
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• 한국작물학회 2021년도 추계학술대회
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• pp.154-154
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• 2021