• 한국시뮬레이션학회논문지
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• 제19권4호
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• pp.43-50
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• 2010

최근 인터넷 전화는 기존 유선 전화에 비해 적은 비용으로 통화를 할 수 있다는 장점으로 인해 많은 인터넷 사용자들에 의해 사용되어지고 있다. Session Initiation Protocol(SIP)은 인터넷 전화의 세션 설정 및 해제를 위한 응용계층 프로토콜 표준이다. SIP는 주로 전송을 위해 UDP를 사용하고 있다. 따라서 INVITE 요청 메시지가 유실되는 경우, UDP 메시지의 신뢰성 있는 전송을 위하여 그 메시지는 적절한 타이머에 의해 재전송된다. 재전송은 사용자에 의해 보내진 메시지의 신뢰성 보장을 위해 유용할 지라도, SIP 프록시(Proxy) 서버의 과부하를 초래하는 원인이 되기도 한다. SIP 프록시 서버의 과부하로 인하여 입력되는 메시지가 많이 유실될 수 있다. 본 논문에서는 프록시 서버의 과부하를 효율적으로 해결하기 위한 비선형 과부하 제어 알고리즘을 제안한다. 제안된 알고리즘은 ns-2 시뮬레이터를 이용하여 성능을 시뮬레이션하였다. 시뮬레이션 결과는 기존의 선형 과부하 제어 알고리즘에 비해 제안된 알고리즘의 프록시 서버의 처리율이 약 12%정도 향상됨을 알 수 있었다.

• Pediatric Gastroenterology, Hepatology & Nutrition
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• 제27권4호
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• pp.215-223
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• 2024

Purpose: Patients who receive frequent blood transfusions are at an elevated risk of developing hepatic fibrosis due to iron overload in the liver. In this study, we evaluated the effectiveness of transient elastography (TE) (FibroScan^®) for assessing liver fibrosis in patients with pediatric cancer. Methods: We enrolled 106 consecutive cases of acute leukemia in individuals under 21 years of age. The participants were followed for 2 years. Based on their serum ferritin (SF) levels, the patients were divided into two groups: group 1 (SF≥300 ng/mL) and group 2 (SF<300 ng/mL). A liver FibroScan^® was performed, and a p-value of less than 0.05 was considered statistically significant. Results: Among the various parameters in the liver function test (LFT), alkaline phosphatase was significantly higher in a subgroup of patients aged 5-8 years in group 2 compared to those in group 1. The indices of liver fibrosis determined by TE, including the FibroScan score, controlled attenuation parameter score, steatosis percentage, and meta-analysis of histological data in viral hepatitis score, as well as indirect serum markers of liver fibrosis such as the aminotransferase (AST)/alanine aminotransferase (ALT) ratio, Fibrosis 4 score, and AST to platelet ratio index, did not differ significantly between the two groups. The association between the TE results and LFT parameters was only significant for ALT. Conclusion: Transfusion-associated iron overload does not have a significant correlation with severe liver fibrosis. FibroScan^® is not a sensitive tool for detecting early stages of fibrosis in survivors of pediatric leukemia.

• 한국생산제조학회지
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• 제7권2호
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• pp.54-61
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• 1998

This paper examines the crack growth behavior of 7075-T651 aluminum alloy for small tensile overload under high-low block loading condition. The cantilever beam type specimen with a chevron notch is used in this study. The crack growth and closure are investigated by compliance method. The applied initial stress ratios are R=-0.5 R=0.0 and R=0.25 Crack length, effective stress intensity factor range, ratio of effective stress intensity factor range and crack growth rate etc, are inspected with fracture mechanics estimate.

• 한국정밀공학회지
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• 제9권3호
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• pp.140-148
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• 1992

The effect of mechanical, properties in the plastic zone near the crack-tip was investigated, under various controlled loading conditions, i.e., ${\Delta}K$ increasing, ${\Delta}K$ decreasing, and single overload test. For both ${\Delta}K$ decreasing test and ${\Delta}K$ increasing test with constant stress ratio, it is found that the ratio of material constant m'( ${\Delta}K$ decreasing test) to material constant m( ${\Delta}K$ increasing test) is larger than 1 for n<0.1, and it is equal to 1 for 0.10.2. A modified crack growth rate equation based on Forman's equation which applied stable region of fatigue crack propagation in ${\Delta}K$ decreasing test is proposed. Within the limit of this single overload test, an empirical relation between among the retardation ratio (Nd/ $N^{*}$), the strain hardening exponent (n) and the percent peak load (%PL) has been established.established.

• 대한전기학회논문지:전력기술부문A
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• 제55권10호
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• pp.426-432
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• 2006

This paper describes the concepts of Static Line Rating (SLR) and Dynamic Line Rating (DLR) and the computational methods to demonstrate them. Calculation of the line capacity needs the heat balance equation which is also used for computing the reduced tension in terms of line aging. SLR is calculated with the data from the worst condition of weather throughout the year. Even now, the utilization ratio is obtained from this SLR data in Korea. DLR is the improved method compared to SLR. A process for DLR reveals not only improved line ratings but also more accurate allowed line ratings based on line aging and real time conditions of weather. In order to reflect overhead transmission line aging in DLR, this paper proposes the method that considers the amount of decreased tension since the lines have been installed. Therefore, the continuous allowed temperature for remaining life time is newly acquired. In order to forecast DLR, this paper uses weather forecast models, and applies the concept of Thermal Overload Risk Probability (TORP). Then, the new concept of Dynamic Utilization Ratio (DUR) is defined, replacing Static Utilization Ratio (SUR). For the case study, the two main transmission lines which are responsible for the north bound power flow in the Seoul metropolitan area are chosen for computing line rating and utilization ratio. And then line rating and utilization ratio are analyzed for each transmission line, so that comparison of the present and estimated utilization ratios becomes available. Finally, this paper proves the validity of predictive DUR as the objective index, with simulations of emergency state caused by system outages, overload and so on.

• Animal cells and systems
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• 제13권2호
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• pp.105-112
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• 2009

In this study, the effects of iron on cytochrome c oxidase (CcO) in rat lung mitochondria were examined. Similar to liver mitochondria, iron accumulated considerably in lung mitochondria (more than 2-fold). Likewise, the reactive oxygen species and nitric oxide (NO) content of mitochondria were increased by more than 50% and 100%, respectively. NO might be produced by nitric oxide synthase (NOS), eNOS and iNOS type, with particular contribution by NOS in mitochondria. The respiratory control ratio of iron overloaded lung mitochondria dropped to nearly 50% due to increased state 4. Likewise, cytochrome c oxidase activity was lowered significantly to approximately 50% due to excess iron. Real-time PCR revealed that the expression of isoforms 1 and 2 of subunit IV of CeO was enhanced greatly under excess iron conditions. Taken together, these results show that oxidative phosphorylation within lung mitochondria may be influenced by iron overload through changes in cytochrome c oxidase and NO.

• Steel and Composite Structures
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• 제12권3호
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• pp.231-248
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• 2012

This research aims to investigate the structural behavior of concentrically braced frames after element loss by performing nonlinear static and dynamic analyses such as Time History Analysis (THA), Pushdown Analysis (PDA), Vertical Incremental Dynamic Analyses (VIDA) and Performance-Based Analysis (PBA). Such analyses are to assess the potential and capacity of this structural system for occurrence of progressive collapse. Besides, by determining the Failure Overload Factors (FOFs) and associated failure modes, it is possible to relate the results of various types of analysis in order to save the analysis time and effort. Analysis results showed that while VIDA and PBA according to FEMA 356 are mostly similar in detecting failure mode and FOFs, the Pushdown Overload Factors (PDOFs) differ from others at most to the rate of 23%. Furthermore, by sensitivity analysis it was observed that among the investigated structures, the eight-story frame had the most FOF. Finally, in this research the trend of FOF and the FOF to critical member capacity ratio for the plane split-X braced frames were introduced as a function of the number of frame stories.

• 전기학회논문지
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• 제63권10호
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• pp.1328-1336
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• 2014

This paper proposes Power System Health Index(PSHI) newly. The paper describes several kind of power system health indices based on two main categories, which are adequacy and security. In adequacy, four kinds of health indices of Frequency, Voltage, Reserve(Operating Reserve Power and Frequency Regulation Reserve Power) and Overload of lines and transformers are proposed. In security, four kinds of health indices of Voltage(154kV, 345kV and 765kV), Overload of lines and transformers, Power flow constraint among areas and SPS are proposed. All indices are mapped with three domains, which are indicated as Health, Margin and Risk, defined with expert interview. While domains of health, margin and risk is defined similar with the conventional well being analysis of power system. The criterion of the domains is proposed using an interview with expert operators and practical reliability codes in Korea. The several kinds of health index functions, which are linear ratio, piecewise linear ration and reverse ratio function etc. are developed in this paper. It will be expected that the developed health indices can help operators to control power system more successfully and also prevent power system from accident as like as black out in future because operator can make a decision immediately based on more easily visual information of system conditions from too much indices acquisition of complex power system.

• 한국ITS학회 논문지
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• 제18권6호
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• pp.76-95
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• 2019

자중계는 화물차 운전자들이 자신의 화물무게를 인지하지 못해서 생기는 부득이한 과적을 방지하기 위해서 반드시 필요한 기술이다. 본 연구에서는 자중계의 일본의 의무장착 사례와 국내 활용현황에 대하여 조사하고 자중계와 GPS, 모뎀을 연동한 IoT 관제시스템을 시험차량에 설치한 후 원격 모니터링을 통해 과적운행패턴을 규명하고, 자중계 설치 시 과적 예방효과와 운송 효율성에 대하여 분석하고자 하였다. 장기 모니터링 데이터를 분석한 결과, 자중계 설치 후 운전자가 화물중량을 인지함으로써 과적율과 과적 중량이 감소되는 효과를 확인하였으며, 건설기계 차량의 경우 운송거리 단축에 의한 운송효율이 높아지는 결과를 확인하였다. 또한 단속지점의 GPS 좌표와 화물차량의 이동경로를 매칭하여 과적상태인 경우 회피 운행경로를 분석하였으며, 적재물의 종류에 따른 운행거리와 적재중량을 분석하였다.

• Journal of Welding and Joining
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• 제14권2호
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• pp.79-89
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• 1996

일정진폭하중과 과대하중비 2.5의 단일 인장과대하중에 의한 4140강 용접부 의 피로균열성장거동을 실온과 -45.deg.C의 저온에서 피로시험과 파면관찰을 통하여 고찰하였다. 이때, 용접부 미시조직의 영향을 평가하기 위해 모재(parent metal), 열영향부(as-welded HAZ), 열처리된 열영향부(PWHT HAZ)로 나누어 응력비 0과 0.5로 CT시험편을 이용하여 피로시험을 실시하였다. 피로균열성장거동은 재료의 미시조직과 온도변화보다는 응력비에 크게 영향을 받았으며, 단일 과대하중에 의한 피로균열성장 지연효과가 모든 재료에서 상당히 크게 나타났다. 전자현미경에 의한 피로파면 관찰 결과, 실온에서는 연성의 스트라이에이숀과 -45.deg.C에서는 의벽개파면과 같은 피로 균열성장거동을 나타내고 있다.