• 대한기계학회논문집
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• 제18권9호
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• pp.2331-2338
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• 1994

Experimental conditions of the optical shadow methods of caustics for measurement of the stress intensity factor and the J-integral in various materials(polycarbonate, PMMA, Al 5586D) are investigated. The necessary experimental requirements toe determine accurate values of the stress intensity factors and the J-integrals are described. The ratio of $r_o$ (radius of initial curve) to $r_p$ (plastic zone size) is selected as a parameter to verify the experimental limitation of the method of caustics in determination of fracture parameters. In this study, transmission caustics method was used for compact tension specimens made of polycarbonate and PMMA. while reflection caustics method was applied to c-shaped tension specimen made of Al 5586D. The appropriate ranges of $r_o/r_p$ tp determine accurate values of stress intensity factors were found to be 1.5~1.8. Existing experimental results have been obtained mainly by changing $r_p$ with different loads in $r_o/r_p$. However, in this study we could obtain varying $K_{caus}/K_{th}$ over the wide range of $r_o/r_p$ at fixed load conditions with newly designed optical arrangement. Thus, we could find the range in which theoretical and experimental results agree well each other by changing $r_o$ values only. In Al 5586D specimen, experimental caustics were located inside of the plastic zone, and $K_{caus}/K_{th}$ were found to be not unity in this range. It is found that $J_{caus}/J_{th}=1{\;}with{\;}r_o/t{\geq}0.8$ and the experimental plastic zone includes the contours of caustics.

• 대한기계학회논문집
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• 제18권10호
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• pp.2543-2553
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• 1994

Caustics method has been applied successfully to determine the fracture parameters such as stress intensity factor and the J-integral for elastic and/or elastic-plastic stress field around the crack tip. For stress fields at the vicinity of crack tip in the creep domain, no experimental report concerning fracture mechanics parameters by using the caustics method has been published up to date. This study investigated creep behavior at the vicinity of crack tips at high temperature($175^{\circ}C$) and attempted to determine of proper fracture parameters for A1 5086 H24 specimens by using the caustics method. The results obtained from the limited experimental investigation are as follows; $J_{th}/J_{caus}$ is found to approach to 1 more rapidly than $K_{th}/K_{caus}$ does during incipient period(within 80 minutes). It is confirmed that experimental $K_{caus}$ approached to theoretical $K_{th}$ after 80 minutes by analyzing the ratio of $K_{th}$ to $K_{caus}$. Unlike the case of room temperature, it is confirmed experimentally that caustics diameter enlarged gradually even the distance between specimen and screen keeps constant. It showed that initial curve of the caustics was initially located in the plastic zone, but it grew out rapidly into the elastic zone for Al 5086 H24 at $175^{\circ}C$. It is confirmed that caustics is a function of time, temperature and distance between specimen and screen at high temperature.

• 대한기계학회논문집
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• 제16권12호
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• pp.2226-2240
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• 1992

본 연구에서는 이방성체에 대한 구체적인 코스틱스 실험법을 확립하기 위하여 다음과 같은 연구를 수행 하였다. 첫째, 이방성체에 대한 코스틱스상 및 초기곡선의 사상방정식을 기하광학 및 Sih의 응력장을 이용하여 구하고, 이 식에 의한 이론상을 여러가지 경계조건하에서 컴퓨터 그래픽 하여 유도한 사상방정식의 타당성을 검토 하 였다.둘째, 본 논문에서 개발한 두 가지 종류의 직교이방성체를 사용하여 실험을 수행하고 실험에 의한 코스틱스상을 이론상과 비교, 검토 하였다.셋째, 이방성체의 코스틱스상으로부터 응력확대계수를 구하는 방법을 제시하고 이 방법을 실제 시편에 적용하여 신뢰 할수 있는 결과를 얻는 초기곡선의 범위를 결정 하였다. 그리고 이 범위에서 구한 응력확대 계수 값을 경계요소법을 이용한 변위외삽법에 의한 결과와 비 교함으로써 본 논문에서 제시하는 방법이 이방성체의 응력확대계수를 구하는 한 방법 으로 유효하게 사용될 수 있음을 밝혔다.

• 대한임상독성학회지
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• 제10권2호
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• pp.91-96
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• 2012

Purpose: A retrospective study with a literature review was conducted to identify the clinical characteristics and prognosis after the acute ingestion of glacial acetic acid. Methods: The medical records of 20 patients,who had presented to the emergency department of Ajou University Hospital complaining of the acute ingestion of glacial acetic acid between January 2006 and December 2011, were examined retrospectively. Results: Among the 172 patients admitted for caustics injury, 20 patients ingested glacial acetic acid. The mean age of the patients was $55{\pm}23.5$, and the mean volume of the acid was $84.5{\pm}71.3$ ml. The clinical features included 1) oral ulcers in 12 patients (63.2%), 2) respiratory difficulties in 11 patients (57.9%), 3) oliguria in 8 patients (42.1%), 4) renal toxicity in 7 patients (36.8%), 5) hepatic failure in 7 patients (36.8%), 6) disseminated intravascular boagulopathyin 7 patients (36.8%), 7) low blood pressure in 8 patients (42.1%), and 8) mental changes in 9 patients (47.4%). Ten patients required endotracheal intubation. Nine patients were admitted to the intensive care unit, and 5 patients expired. Conclusion: The ingestion of glacial acetic acid can cause severe symptoms, such as metabolic acidosis, multiple organ failure and upper airway swelling frequently and has a high mortality rate. Therefore, aggressive treatment, including endotracheal intubation, should be considered at the early stages.

• Journal of Information Processing Systems
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• 제17권4호
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• pp.737-753
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• 2021

As the demand for high-quality rendering for mixed reality, videogame, and simulation has increased, global illumination has been actively researched. Monte Carlo path tracing can realize global illumination and produce photorealistic scenes that include critical effects such as color bleeding, caustics, multiple light, and shadows. If the sampling rate is insufficient, however, the rendered results have a large amount of noise. The most successful approach to eliminating or reducing Monte Carlo noise uses a feature-based filter. It exploits the scene characteristics such as a position within a world coordinate and a shading normal. In general, the techniques are based on the denoised pixel or sample and are computationally expensive. However, the main challenge for all of them is to find the appropriate weights for every feature while preserving the details of the scene. In this paper, we compare the recent algorithms for removing Monte Carlo noise in terms of their performance and quality. We also describe their advantages and disadvantages. As far as we know, this study is the first in the world to compare the artificial intelligence-based denoising methods for Monte Carlo rendering.

• 대한임상독성학회지
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• 제13권2호
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• pp.87-94
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• 2015

Purpose: We investigated comparison of clinical characteristics and prognosis by initial endoscopic severity in caustic injury and then discussed predisposing factors which can be helpful in predicting the prognosis and determining the treatment. Methods: This study was a retrospective review of medical records from patients over the age of 15, who underwent initial endoscopy for caustic injury from April 2007 through November 2014. Patients were classified according to two groups based on the initial endoscopic finding by Zargar's classification: patients with grade 0, I, IIa at esophagus (low risk group) and patients with grade IIb, IIIa, IIIb at esophagus (high risk group). The two groups were then compared. Results: A total of 55 patients were included (low risk group [n=44] vs. high risk group [n=11]). Old age (p<0.001), large amount of ingestion (p<0.05), oropharyngeal symptoms (p<0.01), high SOFA score (p<0.001), high WBC count (p<0.05), low base excess (p<0.01), and HCO3 (p<0.05) were statistically significant factors in the high risk group. A poor prognosis was observed for hospital stay (p<0.001), ICU admission (p<0.001), mortality (p<0.01), and stricture (p<0.001) in the high risk group. Conclusion: Clinical characteristics including age, amount of ingestion, oropharyngeal symptoms, SOFA score, WBC count, base excess, and $HCO_3$ can be helpful in the decision to undergo initial endoscopy and risk assessment by initial endoscopic severity can be helpful in predicting prognosis and determining the treatment plan.

• 대한임상독성학회지
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• 제12권2호
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• pp.70-76
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• 2014

Purpose: Endoscopy has been recommended as a primary procedure for determining the extent of damage and prognosis in patients with caustic ingestions. Endoscopy within the first 24 hours has been suggested, however, such immediate endoscopy is not always possible. Therefore, we wanted to determine complications and possible delayed sequelae after the endoscopy performed dependent on time, including less than 24 hours and more than 24 hours, after ingestion of relatively high toxic caustic agents. Methods: From January 2005 to May 2013, 105 consecutive patients were diagnosed with caustic poisoning in the emergency department of the Wonju Severance Christian Hospital. Out of 95 patients who underwent endoscopy, while excluding 49 patients who ingested sodium hypochlorite and 15 patients due to insufficient data, 41 patients were ultimately included. We compared general characteristics, complications related to endoscopy, late sequelae, total admission length, and mortality between two groups. Results: Twenty eight patients (68.3%) were diagnosed with acid ingestion. Median endoscopy time was 17.8 (IQR 9.7-36.9) hours and performed in 16 patients (39%) after 24 hours. There were no complications, such as perforation and bleeding in either endoscopy within 24 hours group or endoscopy after 24 hours group. In addition, no difference in ingested materials, endoscopy grade, or late sequelae was observed between endoscopy within 24 hours group and endoscopy after 24 hours group. Conclusion: No difference in complications and late sequelae was observed between endoscopy within 24 hours group and endoscopy after 24 hours group when endoscopy was performed based on a clinician's assessment.

• Clinical and Experimental Pediatrics
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• 제52권4호
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• pp.446-452
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• 2009

목 적 : 소아 부식식도염 환자에서 후기 합병증 예측을 위한 조기내시경 검사의 유용성에 대해서 분석하고자 하였다. 방 법 : 1989년 1월부터 2007년 12월까지 빙초산과 가성소오다 등의 부식성물질 섭취 후 급성기에 서울대학교 어린이병원과 분당서울대학교병원에 내원하여 내시경을 시행한 34명의 환자를 대상으로 내시경 검사와 의무기록 조사 및 보호자 전화면담을 통하여 정보를 수집하였다. 결 과 : 식도의 내시경 소견을 보면 grade 0, grade 1, grade 2a, grade 2b, grade 3인 경우가 각각 8명, 2명, 7명, 13명, 4명이었다. 구토, 침흘림, 삼킴곤란 등의 증상의 유무는 내시경상 식도 점막 손상의 유무와 유의한 상관관계를 보이지 않았다. 구강 손상의 유무는 내시경상 식도 점막 손상의 유무와 유의한 상관관계를 보였다(P=0.014). 내시경 시행 후 점막째짐, 출혈, 천공 등의 합병증은 발생하지 않았다. 협착은 12명(36.3%)의 환아에서 발생하였고, 식도의 협착은 11명, 유문부의 협착은 1명이었다. 식도 점막 손상의 정도가 심해질수록 식도협착이 많이 발생하는 경향을 보였다(P=0.002). 식도협착이 있었던 11명 중 2명(18.1%)은 반복적인 식도확장술만으로 증상이 호전되었고, 나머지 7명(63.6 %)은 수술이 필요하였다. 결 론 : 부식성 물질을 실수로 섭취한 소아에서 내시경 검사는 안전하고 유용한 검사이며, 점막 손상의 정도와 부위를 확인함으로써 후기 합병증 발생 예측에 도움이 되기 때문에 조기에 식도내시경을 시행하는 것이 필요하다.