• 한국지반공학회논문집
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• 제33권1호
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• pp.79-91
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• 2017

반복단순전단시험기를 이용하여 해양실트질 모래의 상대밀도 변화에 따른 비배수전단파괴 거동에 대해 평균전단응력과 반복전단응력이 미치는 영향을 평가하였다. 시험결과 반복전단 변형모드는 상대밀도가 달라지더라도 유사한 양상을 보였으며, 평균전단응력과 반복전단응력으로부터 큰 영향을 받았다. 파괴에 필요한 반복하중 횟수는 반복전단응력비, 상대밀도, 그리고 평균전단응력비의 순서로 좌우되는 것으로 나타났다. 본 논문에서는 조밀한 지반과 느슨한 지반에서 상대밀도 변화에 따른 응력기반 파괴경로의 변화를 2차원과 3차원으로 제시하였으며, 3차원 파괴선도는 조밀한 지반 조건에 대해서만 한정된 한계점을 보완하여 지반의 상대밀도에 따라 반복전단응력비, 평균전단응력비, 반복하중 횟수 등의 설계 조건을 결정 할 수 있는 아주 유용한 설계도구로 활용 가능하다.

• 임산에너지
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• 제20권2호
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• pp.58-68
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• 2001

본 연구는 상대광도 차이에 따른 구상나무(Abies koreana Wilson) 유묘의 생장과 물질생산에 대하여 구명하고자 자연전광이 100, 50, 30, 10% 및 2%로 조절된 피음포지에서 구상나무 5년생 포트묘를 사용하여 24개월간 실시하였으며 다음과 같은 결과를 얻었다. 1. 3회의 수고생장을 측정한 결과, 가장 낮은 생장치를 기록한 2% 처리구를 제외하고 처리구 간에 큰 차이를 보이지 않았다. 2. 근원경생장은 상대광도가 낮아짐에 따라 단계적으로 감소하는 경향이 뚜렷하게 나타났다. 3. 상대적으로 낮은 광도에서 자란 유묘의 다음해 생장시작 시기가 늦어졌으며, 신엽의 갯수 및 신초의 갯수, 신초의 길이도 감소하였다. 4. 지상부와 지하부, 엽중량을 포함한 총 건물생산량은 광도가 감소할수록 점진적으로 감소하였다. 5. 구엽의 건물량에 대한 신엽의 건물량의 비율은 1년간 피음처리한 경우 0.99±0.25∼1.06±0.06으로서 100, 50, 30% 처리구에서 비슷하게 높았고, 10%와 2% 처리구에서 각각 0.60±0.04, 0.52±0.03으로서 그 비율이 상대적으로 낮았다. 2년간 피음처리한 경우에는 0.79±0.04∼1.00±0.03으로서 100, 50, 30, 10% 처리구에서 비슷하였고, 2% 처리구에서 0.29±0.03으로 매우 낮은 비율로 나타났다. 6. T/R율은 1년간 피음처리한 유묘의 경우 3.35±0.33∼4.61±0.25로서 100, 50, 30, 10% 처리구 간에 비슷하였으며, 2% 처리구에서는 7.36±0.15로서 다른 처리구에서보다 높게 나타났다. 2년간 피음처리한 유묘의 T/R율은 상대광도 2% 처리구의 2.01±0.14를 제외하고는 1.76±0.11∼3.12±0.19로서 상대광도가 감소할수록 높게 나타났다.

• Investigative Magnetic Resonance Imaging
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• 제6권1호
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• pp.55-63
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• 2002

목적 급성 허혈성 뇌졸중에서 관류 MR영상으로 측정한 상대적 뇌혈용적과 단광자방출전산화단층촬영으로 측정한 상대적 뇌혈류량이 나중에 발생할 뇌경색을 예측할 수 있는지 알아보고자 하였다. 대상 및 방법 급성 일측성 중대뇌동맥 폐색 환자에서 증상 발생 6시간 이내에 관류 MR영상과 99mTc-HMPAO 단광자방출전산화단층촬영을 모두 시행한 13명을 대상으로 하였다. 동맥 폐색에 의한 허혈 부위와 반대측 정상 부위에서 각 관류 변수를 측정하여 그 비(허혈 부위 관류변수 값 / 정상 부위 관류 변수 값)를 구한 후, 나중에 경색으로 이행할 부위와 그렇지 않을 부위를 판별할 수 있는 관류변수 비의 절단값을 계산하였다. 결과 : 경색으로 이행한 부위와 그렇지 않은 부위에서 상대적 뇌혈용적 비의 평균값은 각각 $0.58{\pm}0.27{\;}and{\;}0.99{\pm}0.17$ (p<0.001)이었고, 상대적 뇌혈류량 비의 평균 값은 $0.41{\pm}0.22{\;}and{\;}0.71{\pm}0.14$ (p<0.001)이었다. 경색으로 이행할 부위와 그렇지 않을 부위를 판별하는 절단값은 상대적 뇌혈용적 비가 0.80, 상대적 뇌혈류량 비가 0.56이었다. 각 절단값의 민감도, 특이도, 능률은 뇌혈용적 비가 80.6, 87.5, 82.7%이었고 상대적 뇌혈류량 비가 72.2, 75.0, 73.0%이었다. (두 관류변수 사이에서 p>0.05). 결론 : 급성 허혈성 뇌졸중에서 상대적 뇌혈용적과 상대적 뇌혈류량의 측정은 뇌경색의 발생을 예측하는 데에 유용한 것으로 사료된다.

• 한국환경보건학회지
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• 제21권4호
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• pp.24-31
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• 1995

Gas sensing element, $\alpha-Fe_2O_3$ was synthesized by dehydration, reduction, and oxidation of $\alpha-FeOOH$, which was synthesized with $FeSO_4\cdot 7H_2O$ and NaOH. They were produced as a bulk-type, a thick film-type. Then, their responses and mechanisms of response to the gas of carbon monoxide were studied. The qualities of gas sefising elements are decided by the structure and the relative surface area. In the process of $\alpha-FeOOH$ synthesis, the effects of reaction conditions as the equivalent ratio, on the structure and the relative surface area of gas sensing element were observed. The changes of the structure were measured with XRD, SEM,TG-DTA and BET. The resistance changes of the synthesized gas sensor in the air were measured. The response ratio were also measured for the changes of working temperature and gas concentration. As a result of analysis with XRD, it was confirmed that the the best conditions for the synthesis of $\alpha-FeOOH$ were equivalent ratio 0.65. The thick film-type element of $\gamma-Fe_2O_3$ responded more quickly than the bulk-type did. The structure and the relative surface area of the $\rho-FeOOH$ were confirmed as the important factors deciding gas response charcteristics.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2008년도 추계 학술발표회
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• pp.1290-1295
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• 2008

The relative density of soil indicate loose and dense state of sand. Because sand is low compressibility, initial relative density of sand is important effect factor of compression and shear behavior. To measure exactly relative density, the exactly maximum and minimum void ratio was determinated by laboratory tests. Generally, vibrating table method is adapted for minimum void ratio(KS F 2345). However KS F 2345 is not consider the particle break during the vibrating table test. In this study, The minimum void ratio is compared with a method of Pluviation and Vibrating table test results using the K-7(crushed sand). It is concluded that the K-7 sand particles were crushed during the vibrating table test and vibrating table test is not a suitable test for a crushed sand $e_{min}$.

• Geomechanics and Engineering
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• 제22권2호
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• pp.165-171
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• 2020

Laboratory determination of strength and deformation behavior of clean sands and gravels has always been challenging due to the difficulty in obtaining their undisturbed samples. An alternative solution to this problem is to develop correlations between mechanical properties of cohesionless soils and their gradation characteristics. This study presents database of 3 natural sands with 11 varying particle size gradation curves to allow investigating relationships between mean particle size, maximum and minimum void ratio, relative density and shear strength of the test soils. Direct shear tests were performed at relative densities of 50, 75 and 95% to explore the effects of gradation and density on the angle of internal friction of the modeled sand samples. It is found that the mean grain size D₅₀ bears good correlations with void ratio range (e_max - e_min) and peak angle of internal friction 𝜙'_peak. The generated regression models are in good agreement with published literature and can be considered as reliable for natural sands in Pakistan. These empirical correlations can save considerable time and efforts involved in laboratory and field testing.

• 한국농공학회논문집
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• 제48권6호
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• pp.79-85
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• 2006

A simulation was done to analyze the seepage problems due to seawater intrusion through the embedded rock layers on heterogeneous layers of sea-dike. Numerical analysis with SAMTLE(developed by author) was done by taking various relative permeability $ratio(R_r/R_e)$. These results showed, when the sed-dike is newly designed, operated, and maintained considering the safety of sea-dike in seepage problems, these embankment materials are prudently chosen. The permeability of the soil materials, within the range of salinity management in freshwater, is comparatively high, however, the permeability of rock materials for bottom rock layer is low. Therefore, when the relative permeability $ratio(R_r/R_e)$ is bellow 10 it is safety in seepage problems of sea-dike.

• 기술혁신연구
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• 제6권2호
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• pp.178-207
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• 1998

This article suggests a methodology to decide the priority of investment project for venture business under the dynamic circumstance. By the Monte Carlo procedure on the probability distribution of cost and revenue, the model simulates the investment project to estimate profit ratio and risk. The profit ratio is calculated on the yearly basis for the relative comparison. The project risk is calculated as semi-variance under the target yield. After sufficient simulations in this fashion for several projects, the efficient projects with more profit and less risk are selected by the dominance principle. Then the regression equation of the selected projects is produced to find the relative value of the projects. The relative value is obtained through dividing the raw profit ratio by the estimated one on the equation. This value shows the degree to which the simulated project yields over the equation. The priority of investment is decided by this value. An examplary venture business of chemical development for semi-conductor is presented as a case study.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2004년도 추계학술대회논문집
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• pp.662-665
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• 2004

In this paper, based on shaking table test results on a seismically isolated bridge model, an inelastic numerical model is refined by using Bouc-Wen model representing the hysteretic behavior of isolators. Seismic responses of isolated bridges are numerically investigated varying with relative stiffness ratios, which is a ratio of the effective stiffness of isolator to the lateral stiffness of bridge pier. From the results, it is found that an adequate range of relative stiffness ratio could be defined for seismic design of isolated bridges without considering the flexibility of piers.

• Journal of Mechanical Science and Technology
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• 제17권8호
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• pp.1196-1202
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• 2003

The concept of hydrogen enriched LPG fuelled engine can be essentially characterized as low emissions and reduction of backfire for hydrogen engine. The purpose of study is obtaining low-emission and high-efficiency in LPG engine with hydrogen enrichment. In order to determine the ideal compression ratio, a variable compression ratio single cylinder engine was developed. The objective of this paper is to clarify the effects of hydrogen enriched LPG fuelled engine on exhaust emission, thermal efficiency and performance. The compression ratio of 8 was selected to minimize abnormal combustion. To maintain equal heating value, the amount of LPG was decreased, and hydrogen was gradually added. In a similar manner, the relative air-fuel ratio was increased from 0.8 to 1.3 in increment of 0.1, and the ignition timing was controlled to be at MBT each case.