• The Korean Journal of Ecology
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• 제24권6호
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• pp.335-339
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• 2001

The dynamic model was developed to simulate the photosynthetic rate of Phragmites communis stands in coastal ecosystem. The model was composed of the compartments of both climatic and biological variables. The former were photosynthetic photon flux density(PPFD), daily maximum- and minimum-temperature. The latter were combinations of the specific physiological responses of plant organs with the biomass of each organs. The PPFD and air temperature were calculated and using those values, gas exchange rate of each plant organ was calculated at every hour. The carbon budget was constructed using the modelled predictions. Analysis of annual productivity and fluxes showed that yearly gross population productivity, yearly population respiration and yearly net population productivity were 33.4, 21.3 and 12.1 $CO_2ton{\cdot}ha^{-2}{\cdot}yr^{-1}$, respectively. The final result was tested over two stands, produced promising predictions with regards to the levels of production attained. The model can be used to determine production potential under given climatic conditions and could even be applied to plant canopies with analogous biological characteristics.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2002년도 추계학술발표대회 논문집
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• pp.139-142
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• 2002

This study presents a mathematical model predicting the stress-strain behavior of fiber reinforced (FMMCs) and fiber/particle reinforced metal matrix composites (F/P MMCs). MMCs were fabricated by squeeze casting method using Al2O3 short fiber and particle as reinforcement, and A356 aluminum alloy as matrix. The fiber/particle ratios of F/P MMCs were 2:1, 1:1, 1:2 with the total reinforcement volume fraction of 20 vol.%, and the FMMCs were reinforced with 10 vol,%, 15 vol. %, 20 vol. % of fibers. Tensile tests were conducted and compared with predictions which were derived using laminate analogy theory and multi-failure model of reinforcements. Results show that the tensile strength of FMMCs with 10 vol.% of fiber was well matched with prediction, and as the fiber volume increases, predictions become larger than experimental results. The difference between the prediction and experiment is considered to be a result of matrix allowance of fiber damage in tensile loading. As the fiber volume fraction in FMMCs increases, the fiber damage increases and so that the tensile strength is reduced. The strength of F/P MMCs approaches more closely to the prediction than FMMCs reinforced with 20 vol.% of fibers because F/P MMCs contains small quantity of fibers and thus has a positive effect in fiber strengthening.

• 대한기계학회논문집
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• 제12권4호
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• pp.790-805
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• 1988

본 연구에서는 유리섬유 강화 에폭시 복합재료의 파괴 강도와 피로 수명을 정 규분포, 로그 정규 분포와 2모수 및 3모수 Weibull 분포 함수의 기대값으로 살펴 보았 다. 2연속 응력 피로 실험 [작은 응력에서 큰 응력으로의 실험(low-high test), 큰 응력에서 작은 응력으로의 실험(high-low test)]의 결과도 분포 함수들을 사용하여 분 석하였다. 비통계학적 누적 손상 법칙들(non-statistical cumulative damage rules) 을 2연속 응력 피로 수명 분산 예측에 이용하기 위해서 동등 순위 가정(equal rank assumption)을 확장하여 수정하였다. 수정한 누적 손상 모형은 Miner의 법칙, Brou- tman과 Sahu의 손상모형 및 Hashin과 Rotem의 모형 등이다.

• 한국지능시스템학회논문지
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• 제26권5호
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• pp.343-350
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• 2016

Remaining lifetime prediction of the underground gas pipeline plays a key role in maintenance planning and public safety. One of main causes in the pipeline failure is metal corrosion. This paper deals with estimating the pipeline reliability in the presence of corrosion defects. Because a pipeline has uncertainty and variability in its operation, probabilistic approximation approaches such as first order second moment (FOSM), first order reliability method (FORM), second order reliability method (SORM), and Monte Carlo simulation (MCS) are widely employed for pipeline reliability predictions. This paper presents a fuzzy inference based reliability method (FIRM). Compared with existing methods, a distinction of our method is to incorporate a fuzzy inference into quantifying degrees of variability in corrosion defects. As metal corrosion depends on the service environment, this feature makes it easier to obtain practical predictions. Numerical experiments are conducted by using a field dataset. The result indicates that the proposed method works well and, in particular, it provides more advisory estimations of the remaining lifetime of the gas pipeline.

• 한국산업정보학회논문지
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• 제18권6호
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• pp.95-101
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• 2013

소셜 미디어 정보는 실시간으로 가장 최신의 정보의 획득을 가능하게 하며, 확산 속도가 빠르고 형태의 제약 없이 유연하게 생산 및 유통할 수 있다는 강점이 있으며, 최근 경제변수들의 예측에 있어서 소셜 미디어 정보를 이용한 예측의 활용 방안에 대한 논의가 활발히 이루어지고 있다. 본 논문에서는 실업률을 예측함에 있어 소셜 미디어 정보 유형 중 하나인 Google Index 정보를 이용하여 시계열 모형 중 하나인 ARIMAX 모형과 ECM 모형을 적합하였고, 모형의 예측력을 비교하기 위해 기존의 ARIMA 모형과의 비교를 수행하였다. 또한, 소셜 미디어 정보 이용에 있어 Google Index 뿐만 아니라 국내 소셜 미디어 정보인 News Index와의 결합을 통해 예측력의 제고 가능성을 확인하였다. 본 연구에서 다루어진 분석 절차와 통계적 모형의 적합과정은 실업률 외의 주요 사회, 경제지표에도 적용될 수 있다.

• 한국측량학회지
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• 제27권2호
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• pp.119-127
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• 2009

다양한 차세대 위성항법시스템들이 개발되고 있지만, 현재 사용자가 측위에 이용할 수 있는 위성항법시스템은 GPS와 GLONASS 뿐이다. 이 연구에서는 GLONASS의 궤도력 중에서 알마낙을 이용하여 위성궤도를 예측하고 예측궤도의 정확도를 평가하였다. 예측궤도를 생성하기 위하여 알마낙 파일에 포함되어 있는 케플러 궤도요소와 궤도방정식을 이용하였으며, 그 결과는 정밀궤도력과의 좌표 비교를 통하여 정확도를 검증하였다. 그 결과, 7일 동안 예측한 위성궤도의 3차원 최대오차는 155.4km로 나타났으며, RMS 오차는 56.3km로 나타났다. 또한 실제관측 결과와의 비교를 통해 궤도오차가 위성의 가시성을 분석하는데 무리가 없는 수준임을 확인하였다.

• 융합보안논문지
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• 제18권5_2호
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• pp.29-34
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• 2018

전쟁은 국제 사회에서 국가의 외교 정책, 안보, 영광, 위상 때문에 일어날 수 있다. 이 논문은 1945년 이후 세계전쟁을 정리하여 전쟁의 형태 변화를 분석하고자 한다. 주요 자료는 캠브리지 대학에서 발표한 자료를 근거로 하였다. 위 사실을 통해 3가지 중요한 결론에 도달하게 된다. 첫째, 1945년 이후에 발생한 전쟁 중 겨우 18%만이 국가 대 국가 형태의 전쟁이었던 것으로 보아 이전보다 국가 간의 전쟁이 급격히 감소했다는 사실이다. 둘째, 전쟁은 모든 지역에서 비슷한 형태로 일정한 규칙을 지니고 일어날 것이라는 현실주의자와 신 현실주의자들의 예측이 빗나갔다는 점이다. 지난 50년 동안 국가 간의 전쟁이 없었던 지역은 3군데나 있었다. 또 같은 기간 동안에 유럽과 북아메리카에서는 어떠한 형태의 전쟁도 일어나지 않았다. 마지막으로, 가장 중요한 사실은 열강들에 의한 전쟁이 없었다는 점이다. 1945년 이후 대부분의 전쟁은 '국가의 자유'를 위한 전쟁이었다. 이들 전쟁은 국가 내에 존재하는 비합법적인 통치를 종식시키는 것이 목적이었다. 미래의 전쟁형태 변화에 대한 여러 측면에서 지속적인 분석이 필요한 시점이다.

• Steel and Composite Structures
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• 제43권3호
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• pp.403-417
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• 2022

Recently, there has been an increasing demand for buildings that allow rapid assembly of construction elements, have ample open space areas and are flexible in their final intended use. Accordingly, researchers have developed new competitive structures in terms of cost and efficiency, such as cold-formed steel and timber composite floors, to satisfy these requirements. Cold-formed steel and timber composite floors are light floors with relatively high stiffness, which allow for longer spans. As a result, they inherently have lower fundamental natural frequency and lower damping. Therefore, they are likely to undergo unwanted vibrations under the action of human activities such as walking. It is also quite expensive and complex to implement vibration control measures on problematic floors. In this study, a finite element model of a composite floor reported in the literature was developed and validated against four-point bending test results. The validated FE model was then utilised to examine the vibration behaviour of the investigated composite floor. Predictions obtained from the numerical model were compared against predictions from analytical formulas reported in the literature. Finally, the influence of various parameters on the vibration behaviour of the composite floor was studied and discussed.

• Geomechanics and Engineering
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• 제31권5호
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• pp.453-460
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• 2022

It is essential for geotechnical engineers to conduct studies and make predictions about the stability of slopes, since collapse of a slope may result in catastrophic events. The Gaussian process regression (GPR) approach was carried out for the purpose of predicting the factor of safety (FOS) of the slopes in the study that was presented here. The model makes use of a total of 327 slope cases from Iran, each of which has a unique combination of geometric and shear strength parameters that were analyzed by PLAXIS software in order to determine their FOS. The K-fold (K = 5) technique of cross-validation (CV) was used in order to conduct an analysis of the accuracy of the models' predictions. In conclusion, the GPR model showed excellent ability in the prediction of FOS of slope stability, with an R² value of 0.8355, RMSE value of 0.1372, and MAPE value of 6.6389%, respectively. According to the results of the sensitivity analysis, the characteristics (friction angle) and (unit weight) are, in descending order, the most effective, the next most effective, and the least effective parameters for determining slope stability.

• Steel and Composite Structures
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• 제50권2호
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• pp.183-199
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• 2024

In this paper, a closed-form rigorous solution for interfacial stress in continuous steel beam with variable section strengthened with bonded prestressed FRP plates and subjected to a uniformly distributed load is developed using linear elastic theory and including the variation of fiber volume fractions with a longitudinal orientation of the fibers of the FRP plates. The results show that there exists a high concentration of both shear and normal stress at the ends of the laminate, which might result in premature failure of the strengthening scheme at these locations. The theoretical predictions are compared with other existing solutions. Overall, the predictions of the different solutions agree closely with each other. A parametric study has been conducted to investigate the sensitivity of interface behavior to parameters such as laminate and adhesive stiffness, the thickness of the laminate and the fiber volume fractions where all were found to have a marked effect on the magnitude of maximum shear and normal stress in the composite member. This research gives a numerical precision in relating to the others studies which neglect the effect of prestressed plate and the shear lag impact. The physical and geometric properties of materials are taken into account, and that may play an important role in reducing the interfacial stresses magnitude.