• 대한기계학회논문집A
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• 제41권9호
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• pp.853-860
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• 2017

본 연구는 균열 발생 및 전파단계에서 하중모드 II의 영향을 평가하기 위해 피로균열 하한계 영역의 혼합모드 I+II 하중을 통해 실험적으로 평가하였다. 균열 발생단계(Stage I)에서는 혼합모드상태에서 하중작용 각도(${\theta}$)가 증가할수록 모드 II 영향으로 인하여 낮은 하중에서 균열이 발생하고, 균열 전파단계 (Stage II)에서는 균열전파 속도는 감소하였다. 다단계 하중작용 각도변화에 따른 하중모드 II영향은 균열전파단계 실험을 통해 평가하였다. 혼합모드 I+II 하중 작용 시 작용각도 ($0^{\circ}{\rightarrow}{\theta}{\rightarrow}60^{\circ}$) 증가에 따라 피로균열전파속도는 감소하였으며 늦게 발생한 균열에서도 마찬가지로 감소하였다. 작용각도가 ${\theta}{\geq}75^{\circ}$ 범위에서는 하중작용각도 증가에 따라 피로균열전파속도가 증가하고 피로수명이 감소하는 것을 확인하였다.

• 한국지반환경공학회 논문집
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• 제11권8호
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• pp.49-55
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• 2010

병렬터널의 이격거리가 근접할수록 응력집중으로 인하여 필라(pillar)의 파괴 위험이 큰 만큼 필라의 응력 검토 및 필라의 강도를 고려한 필라의 안정성 평가는 병렬터널의 이격거리 검토 시 매우 중요한 사항이다. 본 연구에서는 필라의 안정성을 구하는 방법 중 하나인 수치해석의 요소크기를 검토하여 필라부 안정성 검토에 대한 체계적인 분석을 제안하였다. 그 결과, 강도응력비는 요소크기에 따른 영향이 크게 없었고, 강도강소법에 의한 안전율은 요소가 작을수록 안전율이 작게 나왔다. 특히 지반이 풍화암인 경우 요소크기에 대한 안전율 값 차이가 크므로 지반이 불량한 경우 요소의 크기를 작게하는 것이 안정적인 결과를 나타냈다.

• 대한디지털의료영상학회논문지
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• 제16권1호
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• pp.27-33
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• 2014

The purpose of this study evaluated the hemo-dynamic information within 30 seconds clinically in 3D breast MRI. From January to March 2014, A total of 40 people were examined at 1.5 Tesla(Philips, Medical System, Achieva, The Netherlands) MRI equipments using 16 channel SENSE breast coil. The imaging parameters on vibrant are fellow as: $TR/TE/FA^{\circ}$/Matrix size/Slice thickness/Slab($5ms/2ms/10^{\circ}/180{\times}139{\times}2mm/80$). This study used a Gadovist and injected it with injection speed of 4 ml /sec by auto injector with 15 ml saline flushing. Firstly, for the delay time study, it divided three different delay time from immediately, 20 seconds, and 30 seconds. In quantitative analysis, the ROI signal intensities of tumor and surrounding tissues were measured retrospectively. In qualitative analysis, the image quality was scored from 1 to 5 point by one experienced radiological technologists as a visual test. The significance level of each delay time was evaluated with a one-way ANOVA(p<0.05). In the visual test, score levels on 30 seconds delay time was a little bit higher than others(p<0.05). The signal intensity of the tumor were $1445{\pm}360$, $1410{\pm}320$, $1510{\pm}415$ on immediately, 20 seconds, and 30 seconds and score levels were $4.18{\pm}0.85$, $3.54{\pm}0.94$, $4.45{\pm}0.74$(p<0.05). The data on immediate images showed better results than that others(p<0.05). Conclusively, Although it has been high scored in 30sec delay time for visual test in order to avoid failure in 20second, 30seconds delay time after contrast media administration, we recommend that the DCE 3D breast MRI commence immediately.

• Tuberculosis and Respiratory Diseases
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• 제73권2호
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• pp.100-106
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• 2012

Background: There are a plethora of literatures showing that high-intensity intensive care unit (ICU) physician staffing is associated with reduced ICU mortality. However, it is not widely used in ICUs because of limited budgets and resources. We created a critical care team (CCT) to improve outcomes in an open general ICU and evaluated its effectiveness based on patients' outcomes. Methods: We conducted this prospective, observational study in an open, general ICU setting, during a period ranging from March of 2009 to February of 2010. The CCT consisted of five teaching staffs. It provided rapid medical services within three hours after calls or consultation. Results: We analyzed the data of 830 patients (157 patients of the CCT group and 673 patients of the non-CCT one). Patients of the CCT group presented more serious conditions than those of the non-CCT group (acute physiologic and chronic health evaluation II [APACHE II] 20.2 vs. 15.8, p<0.001; sequential organ failure assessment [SOFA] 5.5 vs. 4.6, p=0.003). The CCT group also had significantly more patients on mechanical ventilation than those in the non-CCT group (45.9% vs. 23.9%, p<0.001). Success rate of weaning was significantly higher in the CCT group than that of the non-CCT group (61.1% vs. 44.7%, p=0.021). On a multivariate logistic regression analysis, the increased ICU mortality was associated with the older age, non-CCT, higher APACHE II score, higher SOFA score and mechanical ventilation (p<0.05). Conclusion: Although the CCT did not provide full-time services in an open general ICU setting, it might be associated with a reduced ICU mortality. This is particularly the case with patients on mechanical ventilation.

• Geomechanics and Engineering
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• 제14권4호
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• pp.367-376
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• 2018

Samples composed of coal and rock show different mechanical properties of the pure coal or rock mass. For the same coal seam with different surrounding rocks, the frequency and intensity of rock burst can be significantly different in. First, a method of measuring the strain variation of coal in the coal-rock combined sample was proposed. Second, laboratory tests have been conducted to investigate the influences of rock lithologies, combined forms and coal-rock height ratios on the deformation and failure characteristics of the coal section using this method. Third, a new bursting liability index named combined coal-rock impact energy speed index (CRIES) was proposed. This index considers not only the time effect of energy, but also the influence of surrounding rocks. At last, a new approach considering the influences of roof and/or floor was proposed to evaluate the impact capability of coal seam. Results show that the strength and elastic modulus of coal section increase significantly with the coal-rock height ratio decreasing. In addition, the values of bursting liability indexes of the same coal seam vary greatly when using the new approach. This study not only provides a new approach to measuring the strain of the coal section in coal-rock combined sample, but also improves the evaluation system for evaluating the impact capability of coal.

• 한국지진공학회논문집
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• 제3권2호
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• pp.9-18
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• 1999

현행 내진설계 기준과는 달리 내진설계기준연구(II) 에서는 6층 미만의 건물도 내진설계를 적용하도록 제안하고 있다 이 제안서가 향후 내진설계 기준의 근간이 된다면 저층 건물에 대하여서도 내진설계가 수행되어야 할 것으로 예상된다 지진의 세기로 구분할 때 국내의 약지진동 지역으로 구분되며 이와 같은 지역에서의 저층 건물의 초과강도 계수 $\Omega$는 매우 크다고 기조의 연구자들이 보고하고 있다 따라서 본 연구에서는 국내 4층 RC 모멘트 연성 골조의 경우에$\Omega$를 고찰하고자 스팬과 경간(bay)를 변화시키면서 모델을 설계하고 이를 2차원 push-over 해석하였다 수치해석 결과 경간의 수 또는 스팬 길이가 증가함에 따라$\Omega$의 값이 증가하는 추세를 보였다 이는 내진설계시 우발 비틀림 모멘트를 고려함으로 스팬 길이 또는 경간 수의 증가에 비하여 외부기중의 설계강도증가율이 크기 때문이다 또한 외부 기둥의 강도증가는 강기동-약보 모델에 근접한 붕괴기구를 형성하므로 $\Omega$의 증가에 영향을 미치는 것으로 고찰되었다

• Radiation Oncology Journal
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• 제38권1호
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• pp.60-67
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• 2020

Purpose: We performed three-dimensional (3D) dose reconstruction-based pretreatment verification to evaluate gamma analysis acceptance criteria in volumetric modulated arc therapy (VMAT) for prostate cancer. Materials and Methods: Pretreatment verification for 28 VMAT plans for prostate cancer was performed using the COMPASS system with a dolphin detector. The 3D reconstructed dose distribution of the treatment planning system calculation (TC) was compared with that of COMPASS independent calculation (CC) and COMPASS reconstruction from the dolphin detector measurement (CR). Gamma results (gamma failure rate and average gamma value [GFR and γAvg]) and dose-volume histogram (DVH) deviations, 98%, 2% and mean dose-volume difference (DD_98%, DD_2% and DD_mean), were evaluated. Gamma analyses were performed with two acceptance criteria, 2%/2 mm and 3%/3 mm. Results: The GFR in 2%/2 mm criteria were less than 8%, and those in 3%/3 mm criteria were less than 1% for all structures in comparisons between TC, CC, and CR. In the comparison between TC and CR, GFR and γAvg in 2%/2 mm criteria were significantly higher than those in 3%/3 mm criteria. The DVH deviations were within 2%, except for DD_mean (%) for rectum and bladder. Conclusions: The 3%/3 mm criteria were not strict enough to identify any discrepancies between planned and measured doses, and DVH deviations were less than 2% in most parameters. Therefore, gamma criteria of 2%/2 mm and DVH related parameters could be a useful tool for pretreatment verification for VMAT in prostate cancer.

• 한국지반공학회논문집
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• 제21권8호
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• pp.45-53
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• 2005

강우에 의한 표면파괴는 세계적으로 흔히 볼 수 있는 사면파괴의 형태이다. 본 연구에서는 침투가 사면 표면의 안정에 미치는 영향을 평가하기 위해 일차원 침투모델을 이용한 무한사면 해석법을 연구하였다. 2층으로 구성된 지반에서 임의의 강우에 의해 유발되는 얕은 사면파괴의 가능성을 평가하기 위해서 Green-Ampt모델에 바탕을 둔 수정 GAML(Green-Ampt-Mein-Larson) 모델을 확장하여 재현기간에 따른 강우강도와 지속시간이 고려되는 침투거동을 예측하였다. 예측된 침투거동과 비교하기 위하여 일련의 수치해석이 수행되었다. 그 결과에 의하면 적절하게 선택된 입력값을 사용하면 제안된 간략법이 더욱 엄밀한 해석법인 유한요소해석과 근사한 합리적인 결과를 줌을 알 수 있다.

• 한국항해항만학회:학술대회논문집
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• 한국항해항만학회 2015년도 추계학술대회
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• pp.322-323
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• 2015

육지초인용으로 사용하고 있는 전구식 회전형 대형등명기는 고압방전등을 사용하고 있어 고장발생 빈도가 높고 긴급수리에 장시간이 소요되어 기능 유지가 어려우며, 제품 가격이 높아 신규 설치 시 및 등명기 교체 시 비용 부담이 가증되는 문제점이 대두되고 있다. 따라서 기존 광원(메탈할라이트 램프 또는 텅스텐할로겐 램프)의 문제점을 개선하고, 국제항로표지협회(IALA)에서 권고하는 규격을 만족하는 효율성과 안정성이 뛰어난 대형 LED등명기 기술개발의 필요하게 되었다. 본 연구에서는 대용량 LED 모듈 및 반사경을 적용한 광학계를 설계하고, 광도와 반사경의 회전속도 제어하는 광출력/등질 제어시스템을 개발하여 20M부터 27M까지의 광달거리의 광도 가변형 육지초인용 LED 대형 등명기 개발을 수행하였다.

• Computers and Concrete
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• 제2권6호
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• pp.423-437
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• 2005

In this study two single-bay, three-storey space frames, one with brick masonry infill in the second and third floors representing a soft-storey frame and the other without infill were designed and their 1:3 scale models were constructed according to non-seismic detailing and the similitude law. The models were excited with an intensity of earthquake motion as specified in the form of response spectrum in Indian seismic code IS 1893-2002 using a shake table. The seismic responses of the soft-storey frame such as fundamental frequency, mode shape, base shear and stiffness were compared with that of the bare frame. It was observed that the presence of open ground floor in the soft-storey infilled frame reduced the natural frequency by 30%. The shear demand in the soft-storey frame was found to be more than two and a half times greater than that in the bare frame. From the mode shape it was found that, the bare frame vibrated in the flexure mode whereas the soft-storey frame vibrated in the shear mode. The frames were tested to failure and the damaged soft-storey frame was retrofitted with concrete jacketing and, subjected to same earthquake motions as the original frames. Pushover analysis was carried out using the software package SAP 2000 to validate the test results. The performance point was obtained for all the frames under study, therefore the frames were found to be adequate for gravity loads and moderate earthquakes. It was concluded that the global nonlinear seismic response of reinforced concrete frames with masonry infill can be adequately simulated using static nonlinear pushover analysis.