• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.4
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• pp.57-62
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• 2005

Satellite contamination from back-scattered molecules has long been analyzed using the BGK theory or the DSMC technique which are rather inefficient in that they are complicated or take a long time in the analysis. This study presents a new technique of estimating the back-scattering contamination, which is very simple and easy to use like the view factor method and also very accurate. This method, called the modified view factor method, is equivalent to the DSMC in so far as the molecular thermal velocity is much smaller than the satellite velocity and the mean free path much longer than the satellite.

• Proceedings of the Korea Water Resources Association Conference
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• 2015.05a
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• pp.287-291
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• 2015

본 연구에서는 두 지역의 실제 상수관망에 대해서 부정류해석을 수행하였고 각각의 상수관망에 필요한 부정류피해 최소화방안을 제시하였다. 첫 번째 대상지역은 베트남 호치민으로 148개 절점과 162개의 파이프로 이루어진 소블럭 상수관망이며 두 번째 대상지역은 파주시 광탄면으로 512개 절점과 527개의 파이프로 이루어진 세 개의 소블럭 상수관망이다. 두지역의 상수관망은 지형적면이나 규모면에서 다른 모습을 하고 있기 때문에 부정류해석 시 발생가능한 피해유형이 틀린 것으로 나타났다. 호치민의 경우 배수지의 높이가 낮고 도시 내 표고차가 없어서 관망 내 평균수압이 $1kg/cm^2$을 약간 상회하는 수준으로 수압이 낮고 수압차 역시 작다. 따라서 상수관망에서 일어날 수 있는 소요수량의 변화나 소화전 사용과 같은 작은 변화에도 역류발생이 빈번히 일어나는 것으로 나타났으며 역류발생이 잦은 파이프를 선정할 수 있었다. 상당히 많은 파이프에서 단기간 역류가 발생하는 것을 확인할 수 있었다. 짧은 기간에 발생하는 변화에 대한 단기간 역류는 교차연결(Cross-Connection)의 문제를 야기할 수 있다. 따라서 역류발생이 빈번히 일어나는 파이프 주위에 check valve나 역지밸브등의 설치를 통해 역류로 인한 피해를 최소화할 수 있다. 파주시 광탄면 지역의 소블럭 집합으로써 고저차가 많은 지역이다. 배수지 밸브개폐 시 발생 가능한 수충격에 대한 시뮬레이션과 펌프장정지로 인해 발생할 수 있는 수충격에 발생 시뮬레이션을 수행하였고 관망내에서 자주 발생하는 밸브개폐로 인한 시뮬레이션을 수행하였다. 그 결과 광탄의 경우 수충격 발생위험 지점은 배수지 근처로 나타났고 수격압이 최대 $2.5kg/cm^2$에서 $3.0kg/cm^2$까지 발생 가능한 것으로 나타났고 밸브개폐시간이 1-2초 지연되어도 상당히 큰 수격압을 줄일 수 있는 것으로 나타났다. 수충격압이 크게 발생할 수 있는 지역에 수충격피해 최소화를 위해 surge tank와 같은 장치를 설치해야 한다. 또한 발생가능한 수격압의 크기를 통계적기법을 통해 확률밀도함수로 나타낼 수 있었다. 이 결과는 앞으로 상수관망의 설계나 운영에서 수충격피해 방지 장치 및 설비를 시공할 때 장치의 규모나 용량을 결정할 때 유용한 정보가 될 것으로 판단된다.

• Childhood Kidney Diseases
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• v.16 no.1
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• pp.32-37
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• 2012

Purpose: The aim of this study is to investigate the renal ultrasonographic findings in children with vesicoureteral reflux (VUR). Methods: We retrospectively reviewed the medical records of 83 patients who were diagnosed with VUR and underwent ultrasonography at Ilsan hospital between January 2000 and December 2010. Results: Among 166 renal units, 108 (65.0%) were found to have vesicoureteral reflux (VUR). Fifty-one (73.9%) had VUR in renal units with abnormal ultrasonography (USG), whereas 57 (58.7%) had VUR in renal units with normal USG. Abnormal USG findings were independent risk factors for VUR (Odds ratio, 1.98; 95% CI, 1.01-3.89; $P$=0.045). In renal units with VUR, the number of normal USG finding was 52.8%, and the abnormal findings were as follows; increased cortical echogenicity 16.7%, hydronephrosis 17.6%, megaureter or ureter dilatation 8.3%, hydronephrosis and ureter dilatation 1.9%, duplication of ureter 1.9%, and atrophic kidney 0.9%. The prevalence of VUR was relatively higher in renal units with hydronephrosis (23/19, 82.6%), ureter dilatation (9/9, 100%), duplication of ureter (2/3, 66.6%), and atrophic kidney (1/1, 100%). Conclusion: Our study indicates that VUR was associated with abnormal USG findings. When there are abnormal USG findings such as hydronephrosis, ureter dilatation, duplication of ureter, and atrophic kidney in children with UTI, VCUG is recommended to detect VUR after controlling UTI.

• Transactions of the Korean Society of Mechanical Engineers
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• v.10 no.6
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• pp.947-958
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• 1986

물-증기 역류 성층이상유동에서의 평균 액체층 두께가 여러가지 경사각과 종횡비에 따라 측정되었다. 난류유동에 있어서 전단응력분포의 선형화와 von Karman의 혼합길이 이론을 근거로 평균 액체층의 두께에 대한 관계식이 제시되었으며 실험결과와 잘 일치하였음을 보였다. 접촉면에서의 조파저항이 고려되지 않은 해석결과는, 수평 성층유동의 경우에, 평균 액체층 두께보다는 오히려 파곡까지의 액체층 두께를 예측하고 있는 것으로 나타났다. 또한 평균 액체층 두께에 대한 실험 상관관계식이 계산시 편의를 위해 쉽게 인지할 수 있는 매개변수들의 항들롤 제시되었다.

• Childhood Kidney Diseases
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• v.2 no.2
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• pp.145-151
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• 1998

Purpose : DMSA renal scan is known as a valuable method for evaluating acute pyelonephritis and renal scar in patients with febrile urinary tract infection or vesicoureteral reflux. We made this study, to determine the most effective use of DMSA renal scan. Methods : 155 children were admitted to the Pediatric Department of Yonsei University, Severance hospital with the symptom of urinary tract infection from January, 1992 to June, 1995. DMSA scan, renal ultrasound and VCUG were performed. One consisted of 29 patients with the diagnosis of acute pyelonephritis without vesicoureteral reflux and the otherconsistedofllpatientswithvesicoureteralreflux. Results : The follow-up DMSA scans at mean $0.99{\pm}0.46$ months after the initial DMSA scans were performed in the 29 children with acute pyetonephritis. 21($72.4\%$) of 29 children showed normal DMSA scans. 8 children with abnormal DMSA scans had follow-up DMSA scans at 2.5 months after the initial scans and 6 of 8 children showed normal DMSA scans. Only 12($41.4\%$) of 29 children showed abnormal renal ultrasound. The data about DMSA scans in 32 children with vesicoureteral reflux showed that there were abnormal DMSA scans in Grade $I;25.0\%$, Grade $II;44.5\%$, Grade $III;64.3\%$, Grade $IV;92.9\%$ and Grade $V;100.0\%$. There was a significant difference in that 36 renal unit ($68.0\%$) on DMSA renal scan and 26 renal units ($49.1\%$) on renal ultrasound showed abnormal finding(P<0.05). Conclusion : DMSA renal scan is more useful than renal ultrasound for the diagnosis of acute pyelonephritis. It is considered that if the initial DMSA scan is abnormal, a follow-up DMSA scan must be performed after 10weeks (8-12weeks) and the change in DMSA scan evaluated.

• Childhood Kidney Diseases
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• v.5 no.1
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• pp.36-42
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• 2001

Purpose : Vesicoureteral reflux is the most commonly inherited disease detected in children with urinary tract infection. The incidence of vesicoureteral reflux among siblings of children with known vesicoureteral reflux is 8$\%$ to 45$\%$ according to different authors. Family screening of a patient with vesicoureteral reflux is important in order to prevent reflux nephropathy. The purpose of this study is to determine the incidence of vesicoureteral reflux in asymptomatic family of children with vesicoureteral reflux and the factors which influence the family history. Methods : The study group consisted of 27 families of patients with vesicoureteral reflux. The total number in the group were 79 persons. BUN, Cr, urineanalysis, voidingcystourethrography(VCUG) and 99mTc -dimercaptosuccinic acid(DMSA) renal scan were performed oil tile siblings. As for tile parents the same tests were performed except the VCUG. Results : The abnormality was detected in 7 of 27 families(25.9$\%$). Vesicoureteral reflux was detected in 5 of 20 siblings and renal scar ns detected in 3 of 32 parents. In children with vesicoureteral reflux, renal scar was detected in 24 of 32 children. Between the group with the abnormality in its family(Group A) and the group without the abnormality in its family(Group B), There was no difference of creatinine clearance between two groups. More renal scars were detected in group A according to the DMSA(A:100$\%$, B:75$\%$. t-test P<0.05). There was no difference of grade of VCUG between two groups. There was no difference between one site and both sites in two groups. In tile case of tile siblings with vesicoureteral reflux, there was high incidence of renal scar in a patient with vesicoureteral reflux according to the DMSA. Conclusion : It is important to screen vesicoureteral reflux and renal scar in case of urinary tract infection to prevent reflux nephropathy. This study implies that it is necessary to screen the family of a patient with vesicoureteral reflux especially with renal scar. (J, Korean Soc Pediatr Nephrol 5 : 36- 42, 2001)

• Pediatric Gastroenterology, Hepatology & Nutrition
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• v.7 no.2
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• pp.163-169
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• 2004

Purpose: Many diagnostic modalities have been used for diagnosis of gastroesophageal reflux disease (GERD). Feeding materials during esophageal pH monitoring may interfere the result of examination and esophageal pH monitoring can not diagnose GER in case of alkaline reflux. The purpose of our study is to evaluate whether scintigraphy can substitiute 24 hr pH monitoring in children with GERD. Methods: From March 2002 to June 2003, 23 patients (12 boys and 11 girls, mean age 27 months) who have been admitted to Hanyang University Hospital presented with GER symptoms (recurrent vomiting, cough, chest pain, irritability) were included in the study. Scintigraphy and 24 hr pH monitoring were performed in all patients. Results: Six out of the 23 patients (26.1%) had evidence of GER on 24 hr pH monitoring, whereas nine of 23 patients (39.2%) exhibited GER by scintigraphy. Two out of the 23 patients could not be tested because of irritability. Three (14.3%) patients had evidence of GER on both 24 hr pH monitoring and scintigraphy, three (14.3%) patients on only 24 hr pH monitoring, six (28.6%) patients on only scintigraphy, and nine (42.9%) patients had no evidence of GER on both methods. No correlation was observed between 24 hr pH monitoring and scintigraphic results by Fisher's exact test (p=0.523) or Kendal's tau (t=0.678). Conclusion: The results of this study demonstrated that there was no correlation between 24 hr pH monitoring and scintigraphy. Therefore these modalities could be used as complementary tests to diagnose GERD.

• Childhood Kidney Diseases
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• v.2 no.2
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• pp.138-144
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• 1998

Purpose : The use of cyclosporine and mitomycin in various immunologic or neoplastic disorders has been known to cause wide-ranged nephrotoxic effects including thrombotic microangiopathy. However, the mechanism of nephrotoxicity of these drugs has not been studied adequately, so that present experimental study has been undertaken to find out whether these drugs can cause direct damage to the kidney and to clarify the pathogenetic mechanism of nephrotoxic effect of these drugs. Materials and methods : Sprague-Dawley rats weighing 250-300 gm were used for experimental animals and unilateral renal perfusion technique, modified from the method described by Hoyer et al was used. Isolation of left kidney from systemic circulation was made by clamping aorta and left renal vein and a hole was punctured in the anterior wall of the left renal vein. Cyclosporine (2.5 mg in 4 ml solution) and mitomycin (1.6 mg in 4ml solution) were infused through left renal artery and normal saline was used in control rats. Forty-eight hours after infusion of the drugs, animals were sacrificed and left kidney removed and processed for histologic examination. Total ischemic time of left kidney was less than 15 minutes: Results : Cyclosporine-perfused group showed severe swelling of glomerular endothelial ceil along with swelling of glomerular epithelial cell and interstitial vascular endothelial cell. Mitomycin-perfused group also showed severe swelling of glomerular endothelial and epithelial cells. And in addition to these findings, they demonstrated platelets aggregation, swelling and degranulation of platelets and fibrin accumulation in some of the capillaries, indicating occurrance of thrombotic microangiopathy. Conclusion : present experiment indicates that cyclosporine and mitomycin can cause direct toxic injury to renal endothelial cell. And this direct toxic damage to endothelial cell seems to be an important initiating event for the development of thrombotic microangiopathy.

• Proceedings of the Korea Water Resources Association Conference
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• 2023.05a
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• pp.422-422
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• 2023

최근 발생되고 있는 도시지역에서의 침수피해는 과거와는 다른 양상으로 발생되고 있으며, 이로 인해 많은 재산피해와 소중한 인명피해가 발생되고 있다. 도시지역의 침수피해는 다양한 원인에 의해 피해가 발생된다. 기후변화로 인해 발생되는 높은 강우강도의 집중호우로부터 도시 피복의 불투수화나 부족한 우수유출저감시설로 인한 침투비율의 감소에 따른 유출량의 증대, 짧은 도달시간으로 인한 빠른 하천수위의 상승, 빠른 하천수위의 상승으로 인해 발생되는 하수도의 만관에 따른 관수로화로 인한 역류 발생, 역류된 홍수류의 도시 내 저지대로의 유입, 최대 조위와 맞물려 발생되는 홍수류 배제의 어려움 등은 도시침수라는 결과를 제공하는 주요 원인으로 작동하고 있다. 이러한 현실은 도시지역에서의 침수대책의 수립에 있어 과거와는 다른 특정한 대책의 수립이 필요하다는 점을 시사해 주고 있다. 특히 도시침수를 발생시키는 주요 원인에 대한 개별적인 대책수립보다는 도시침수의 발생확률이 높은 지역에 대해서는 이러한 원인을 종합적으로 고려하여 이를 방어할 수 있는 효율적이고 실제적인 계획을 수립할 필요가 있다. 우리나라는 현재 행정안전부의 자연재해저감종합계획, 환경부의 특정하천유역치수계획 및 하수도정비기본계획을 기본으로 소하천정비기본계획, 하천기본계획 등 소관 부처를 달리하는 다양한 계획들을 수립하여 홍수로부터 귀중한 자산을 보호하려는 노력을 시행하고 있다. 이러한 계획들은 주로 홍수에 대비하고자 하는 특정 구조물의 설계를 중심으로 하고 있으며, 설계에는 항상 경제성의 개념이 수반되므로 설계용량을 초과하는 자연재해의 발생에 대해서도 홍수 발생에 대비하기 위해서는 홍수예보 및 재난대응체계의 운용과 같은 비구조물적인 대책도 매우 중요하게 활용되어야 한다. 이와 같은 현실에서 도시지역의 침수피해를 방지하기 위해서는 이제 과거와는 달리 개별법에 의해 수립되는 각종 계획들을 특정공간에 대해서 종합적으로 고찰하고 최적화하여 현실적이고 효율적인 하나의 계획으로 수립될 필요가 있으며, 하천을 중심으로 시행되고 있는 홍수예보와 유사한 도시침수예보와 같은 비구조물적 대책의 기술적 제고와 시행의 확산이 매우 시급한 실정이다. 본 연구에서는 최근 발의된 「도시하천유역 침수피해방지대책법(안)」의 경과와 이 법률에서 다루고 있는 주요 내용들을 살펴봄으로써 향후 우리나라가 지향해야 할 도시지역의 침수피해에 어떻게 대응해나가야 하는지에 관해 살펴보았다.

• Journal of the Korean Vacuum Society
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• v.10 no.1
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• pp.1-9
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• 2001

Pumping characteristics of a turbomolecular pump are influenced by interrelations of the down-stream and upstream pumping speeds (transmission probabilityxaperture conductance), and of gas flow rates (pumping speedxentrance pressure) in two directions. The pumping speed, one of the most important items characterized the performance of a pump, is given by dividing the net flow rate, that is, the difference between the counter flow rates by the pressure at the pumping port. The maximum compression ratio is defined as the ratio of the downstream pumping speed to the upstream one. Because these directional characteristics affect each other and are functions of the pressures of both sides, it is difficult to distinguish the relevant factors. However, quasi-quantitative analyses on them can be done if considering carefully the results of measuring the pumping speed and the maximum compression ratio.