• Journal of Korean Tunnelling and Underground Space Association
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• v.22 no.4
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• pp.367-381
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• 2020

This paper presents the seal material mixing ratio of tunnel umbrella arch reinforcement method. Currently, there is no clear standard for the proper gelation time and curing time of the Seal material in Korea, and the quality control is also difficult because it cannot be verified. In response, the ratio of the mixture of the seal material was composed of four types of indoor experiments, and the amount of gelation time and bleed was checked. In addition, a non-cart penetration test confirmed the curing time and compared the ratio of each combination. Further experiments on W/C 120% identified the effect of mixing speed and time on the seal material. A total of three field experiments were conducted based on indoor experiments, and the size and strength of bulb formation were compared by checking the curing time of the specimen and main injection. Comparisons show that the lower W/C, the stronger the strength, the larger the size of the bulb, and the faster the hardening time appears. Based on the results of the gelation time and curing time, it was deemed that the mixing ratio of W/C 120% is most appropriate when applied to the actual site.

• Proceedings of the Korea Water Resources Association Conference
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• 2009.05a
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• pp.1316-1320
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• 2009

최근 한반도지역의 시공간적 수문변화 및 지속시간 연최대강우 추세분석을 위하여 기상청에서 제공 되어지는 관측자료를 이용하여 분석을 실시하였다. 분석을 위하여 서울, 인천, 속초, 부산, 군산등 전국적인 분포를 보이는 60개소의 일강수량, 일평균기온, 일최고 및 최저기온, 일평균풍속, 일습도 자료를 수집하였다. 더불어 지속시간별 연최대강우 추세분석을 위하여 동일기간에 대한 시간자료를 수집하여 분석을 실시하였다. 일자료를 이용한 분석결과 분석기간의 년평균강수량은 1998년 이전 1342.2mm였으나, 1998년 이후는 1,511.6mm로서 최근의 강수량 증가를 확인할 수 있었다. 계절적으로는 비홍수기에 비하여 홍수기에 강수량 증가가 더욱 두드러졌으며, 수계별로는 낙동강과 섬진강의 경우가 한강과 금강등 기타 수계에 비하여 최근의 강수량 증가추세가 상대적으로 뚜렷한 것으로 분석되었다. 내륙과 해안지역의 분석결과에서는 해안지역의 년강수량이 내륙에 비하여 90mm 정도 높게 나타났으며, 지역별로는 동해안지역이 서해안과 남해안에 비하여 변화경향이 크게 나타났다. 일최고강수량 및 집중호우빈도 분석결과 수계별 분석의 경우 한강수계가 다른 수계에 비하여 상대적으로 큰 증가경향을 보였으며, 한편 섬진강수계는 다소 완만한 경향을 나타내고 있었다. 집중호우빈도 분석결과 역시 년강수량과 마찬가지로 동해안지역에서의 변화경향이 크게 나타나고 있었다. 무강수일수는 전국적으로 감소경향을 보이고 있어, 강수발생일당 강수량은 증가하는 경향을 보이고 있었다. 이러한 수문학적 변화경향을 세부적으로 살펴보기 위하여 수계별 대표지점을 선정하여 지속시간별(1hr, 2hr, 3hr, 4hr, 6hr, 12hr) 강우강도 추세분석을 실시하였다. 분석결과 지속시간에 따른 강우강도 역시 증가하는 경향을 나타내는 것을 확인하였으며 짧은 지속시간이 상대적으로 큰 증가경향을 나타내는 것으로 확인하였다. 하지만 정확한 분석을 위하여 보다 많은 관측소에 대한 추가분석이 필요할 것으로 판단되어 진다.

• Journal of Animal Science and Technology
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• v.50 no.3
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• pp.373-380
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• 2008

This study was undertaken to investigate the effects of feed withdrawal time(FWT) before transport in farm(<2 hrs, 2~4 hrs, 4~6 hrs) and total feed withdrawal time(TFWT) before slaughter(<8 hrs, 8~12 hrs, >12 hrs) on carcass defects, grades and meat quality of broilers. FWT of 2~4 hrs before transport in the farm showed lower incidences of dead-on-arrival chicks(p<0.05) and bruising chicks, and a little higher incidences of 1st or 2nd carcass grade compared to shorter than 2 hrs or 4~6 hrs of FWT in the farm. In the meat quality of breast meat, FWT of 2~4 hrs in the farm tended to show higher pH and water holding capacity(WHC), and lower drip loss, cooking loss and shear force values compared to shorter than 2 hrs or 4~6 hrs of FWT in the farm. In the total microbial counts of breast meat during 7 days of cooler storage, FWT of 2~4 hrs in the farm showed significantly lower value than shorter than 2 hrs of FWT in the farm. In the carcass defects and grades by TFWT before slaughter, TFWT shorter than 8hrs showed lower(p<0.05) incidences of dead-on-arrival chicks and bruising chicks, and higher(p<0.05) incidences of 1st carcass grade than TFWT longer than 12 hrs before slaughter. In the meat quality of broiler breast meat, TFWT longer than 12hrs before slaughter showed lower(p<0.05) pH and WHC values, and a little higher drip loss, cooking loss and shear force values compared to TFWT shorter than 8 hrs or 8~12 hrs before slaughter. In the total microbial counts of broiler breast meat during 7 days of cooler storage, TFWT longer than 12 hrs before slaughter tended to show higher value than TFWT shorter than 8 hrs or 8~12 hrs before slaughter. As a result, 2~4 hrs of feed withdrawal time before transport in the farm and total feed withdrawal time shorter than 8hrs or 8~12hrs before slaughter could be recommended for the production of high quality broiler meat.

• Journal of Aerospace System Engineering
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• v.14 no.3
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• pp.17-23
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• 2020

In this paper, the efficient periodic unsteady flow analysis is developed by using a Chebyshev collocation operator applied to the time differential term of the governing equations. The partial implicit time integration method was also applied in the governing equation for a fluid, which means flux terms were implicitly processed for a time integration and the time derivative terms were applied explicitly in the form of the source term by applying the Chebyshev collocation operator. To verify this method, we applied the 1D unsteady Burgers equation and the 2D oscillating airfoil. The results were compared with the existing unsteady flow frequency analysis technique, the Harmonic Balance Method, and the experimental data. The Chebyshev collocation operator can manage time derivatives for periodic and non-periodic problems, so it can be applied to non-periodic problems later.

• Journal of the Korean Society of Food Science and Nutrition
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• v.44 no.7
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• pp.1007-1015
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• 2015

This study investigated the correlation between smartphone addiction and eating behaviors of 288 elementary school students (fifth and sixth grades) in the Ansan area. Addiction and normal groups consisted of 29 (10.1%) and 259 students (89.9%). Average usage time of the smartphone addiction group was higher than that of the normal group (P<0.001). Percentages of using a smartphone when eating meals as well as skipping meals due to using a smartphone were also higher in the addiction group than the normal group (P<0.01). Degree of reduction of physical activity and sleep disorders due to using a smartphone were higher in the addiction group than the normal group (P<0.001). However, nutritional knowledge related to protein and dietary life scored lower in the addiction group than the normal group (P<0.05). Correlation between smartphone usage time and eating behaviors was as follows: smartphone usage time on weekdays increased with elevated usage time on weekends in the addiction group (+0.742) (P<0.001) and the normal group (+0.762) (P<0.001). Frequency of snack intake in the addiction group increased with elevated usage time on weekdays (+0.460) (P<0.05). Sleeping time of the normal group decreased with elevated usage time on weekdays (-0.150) (P<0.05), and good eating behaviors decreased with elevated usage time the on weekend (-0.143) (P<0.05). Consequently, smartphone addiction in elementary school students showed negative eating behaviors. Therefore, effective nutritional education programs and national support policy are required to solve problems of unhealthy eating behaviors from smartphone usage in elementary school students.

• Journal of the Institute of Electronics Engineers of Korea CI
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• v.37 no.4
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• pp.9-15
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• 2000

The purpose of this paper is to minimize the a slack computation time of the scheduling of a soft aperiodic real-time tasks in a fixed priority real-time system. The proposed algorithm reduces the computation overhead at on-line time and supports the maximum slack time assigned for aperiodic real-time tasks. The proposed algorithm has 10~20% more response time for aperiodic real-time tasks than that of Slack Stealing Algorithm that offers optimal response time in fixed priority real-time system. However, the performance of the proposed algorithm is seven times better in a scheduling overhead.

• Journal of the Korean Institute of Telematics and Electronics
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• v.18 no.6
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• pp.1-8
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• 1981

A new desio method of decentraliaed stabilizing controller is proposed for large scale discretetime systems with delays in interconnections. Gain parameters of the local stabilizing controller are determined by utilizing the well-knowon Nyquist array technique in the complex q-plane, where .

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.9
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• pp.34-40
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• 2005

In present study, a two dimensional unsteady Navier-Stokes solver has been developed using the Diagonalized ADI (DADI) method and implicit dual time stepping method. The jacobian matrices in steady state Navier-Stokes equations are introduced from inviscid flux terms. The implicit treatment of artificial dissipation terms results in a block penta-diagonal matrix system and it becomes a scalar penta-diagonal matrix by diagonalization. In steady state equations about fictitious time, a new residual including a real time derivative term is introduced. From a converged solution about fictitious time, a real time unsteady solution can be obtained, which is called 'implicit dual time stepping method'. For code validation, an oscillating flat plate, a regular Karman vortices past a circular cylinder and shock buffeting around a bicircular airfoil problems are numerically solved. And they are compared with a theoretical solution, experiments and other researcher's computations.

• Proceedings of the Korean Nuclear Society Conference
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• 1996.05d
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• pp.241-246
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• 1996

지진시 미끄럼 등과 같이 전형적인 비선형거동을 하는 구조물에 대한 동적해석을 수행하는 경우 먼저 입력지진의 가속도 시간이력에 대한 기준선 조정이 필요할 때가 있다. 인공적으로 작성된 지진기록의 경우 때로 가속도 시간이력을 적분하여 속도 및 변위 시간이력을 얻었을 때 증가하는 형태로 나타나 이로 인하여 비선형응답이 비정상적으로 커질 수 있기 때문이다. 본 논문에서는 바닥이 마찰거동을 하는 구조물에 대해 간단히 모델하여 이러한 예를 보였으며 또한 주로 사용되는 기준선 조정방법들의 응답영향을 비교하였다. 그 결과 입력지진의 기준선 조정을 하지 않는 것이 항상 보수적인 결과만을 보여 주지 않는다는 점과 기준선 조정의 방범에도 표준화가 필요하다는 점을 파악할 수 있었다.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2010.04a
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• pp.742-745
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• 2010

본 논문은 초고층구조물의 해석방법으로 탄성변형과 아울러 시간의존성을 가진 크리프와 건조수축에 의한 비탄성변형을 고려한 비선형 시공단계 해석법을 제시한다. 기존의 초고층구조물 해석에서 주로 행하는 기둥 축소량 해석은 실무자의 경험과 프로그램을 통한 간략화에 맞추어져 있다. 이는 실제 시공 시 발생하는 구조해석 요소들을 충분히 반영하지 못하여 계산 값과 실제 값 사이에 오차가 발생된다. 비선형 시공단계 해석은 실제 시공 때 발생되는 해석변수들을 고려한 단계별 해석의 수행이 가능하며, 시간의 의존성을 가진 creep과 shrinkage의 효과를 함께 고려하여 일괄해석의 문제점을 구조해석 단계에서 실제상황에 가까운 해석을 가능하게 할 수 있다. 이를 위해 시공단계해석이 가능한 범용 프로그램을 이용한 50층 규모의 3차원 골조 프레임 모델 예제 해석을 통하여 기존 해석법들과의 비교, 분석으로 시간의 의존성을 고려한 시공단계해석의 필요성을 제시한다. 본 논문에는 범용프로그램인 SAP2000(ver.14)와 CEB-FIP모델 코드를 사용 하였다.