• 한국정보통신학회논문지
• /
• 제10권9호
• /
• pp.1654-1662
• /
• 2006

Ad-hoc 네트워크는 무선 링크들로 구성 된 멀티-홉 네트워크이다. 그리고 무선 링크의 전송 특성은 유선에 비해 보다 불안정 한 상태이다. 그러므로 Ad-hoc 네트워크에서는 패킷 손실이 자주 발생하고, 패킷 손실에 의한 TCP 연결 실패는 TCP 성능을 심각하게 저하시킨다. 또한, TCP 성능저하는 무선채널에서 데이터 패킷과 ACK 패킷의 충돌에 의해서 발생한다. 본 논문에서는 ODA(Ordering-Delayed ACK)지연 알고리즘을 제안하고, ODA 알고리즘과 지연 ACK 알고리즘을 이용하여 무선 Ad-hoc 네트워크의 성능을 향상시키고자 한다. 제안된 ODA알고리즘은 무선 Ad-hoc 네트워크에서의 수신 측에서 데이터 패킷의 수를 순서 적으로 증가시킨다. 본 논문에서는 NS-2를 이용하여 컴퓨터시뮬레이션을 수행하였다. 시뮬레이션 결과, 제안된 ODA 알고리즘은 기존의 지연 ACK 알고리즘에 비해서 무선 멀티-홉 Ad-hoc 네트워크 환경에서 채널 용량이 증가되고 네트워크의 성능이 향상됨을 확인할 수 있었다.

• 품질경영학회지
• /
• 제44권2호
• /
• pp.373-388
• /
• 2016

Purpose: This paper suggests a hierarchical time delay model to evaluate failure risks in FMEA(failure modes and effects analysis). In place of the conventional RPN(risk priority number), a more reasonable and objective risk metric is proposed under hierarchical failure cause structure considering time delay between a failure mode and its causes. Methods: The structure of failure modes and their corresponding causes are analyzed together with the time gaps between occurrences of causes and failures. Assuming the severity of a failure depends on the length of the delayed time for corrective action, a severity model is developed. Using the expected severity, a risk priority metric is defined. Results: For linear and quadratic types of severity, nice forms of expected severity are derived and a meaningful metric for risk evaluation is defined. Conclusion: The suggested REM(risk evaluation metric) provides a more reasonable and objective risk measure than the conventional RPN for FMEA.

• Journal of Chest Surgery
• /
• 제9권2호
• /
• pp.148-156
• /
• 1976

Acute respiratory failure has become an increasingly frequent cause of death following shock or trauma. Interstitial or diffuse alveolar edema, as chief pathophysiologic change of acute respiratory insufficiency, can be the result of sepsis, fat embolism, cardiac failure, lung congestion, and oxygen toxicity. These pulmonary problems are extremely difficult to treat without early recognition of their development and aggressive management. If the treatment is delayed, the progressive respiratory failure is almost uniformly fatal. Authors have experienced two cases of acute respiratory insufficiency following the blunt chest trauma, which were healed uneventfully. Literatures were briefly reviewed.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2001년도 추계학술대회논문집A
• /
• pp.155-160
• /
• 2001

This paper describes a probabilistic fracture mechanics (PFM) analysis based on Monte Carlo (MC) simulation. In the analysis of CANDU pressure tube, it is necessary to perform the PFM analyses based on statistical consideration of flaw generation time. A depth and an aspect ratio of initial semi-elliptical surface crack, a fracture toughness value, delayed hydride cracking (DHC) velocity, and flaw generation time are assumed to be probabilistic variables. In all the analyses, degradation of fracture toughness due to neutron irradiation is considered. Also, the failure criteria considered are plastic collapse, unstable fracture and crack penetration. For the crack growth by DHC, the failure probability was evaluated in due consideration of flaw generation time.

• 대한산업공학회지
• /
• 제33권2호
• /
• pp.273-281
• /
• 2007

The decision of how long performing system burn-in must be answered with a probabilistic model of a system lifetime at which infant mortality failures created during assembly processes are quantified. In this paper, we propose such a model which is modified from previous results. Using the system model, we derived system reliability in terms of component and system burn-in times for the two cases of minimal repair at system failure and of component replacement and connection repair at their failure times. The procedure is illustrated with a bridge system and the optimal system burn-in times are obtained for maximizing system reliability. The result suggests that an assumption of minimal repair at system failure may underestimate the optimal burn-in time in practice.

• Tuberculosis and Respiratory Diseases
• /
• 제42권6호
• /
• pp.951-954
• /
• 1995

Diagnostic procedures in pregnant wowen is limited and is usually delayed, especially so if she is on mechanical ventilation. A 28-year-old pregnant woman with severe dyspnea was referred to our hospital under the impression of miliary tuberculosis. The respiratory failure was so severe that patient had to be managed with mechanical ventilator under clinical impression of overwhelming pneumonia or pulmonary tuberculosis. But the patient's conditions deteriorated. Bronchoscopy and blind transbronchial lung biopsy performed to determine the nature of the etiology, and to our surprise, revealed squamous cell carcinoma of the lung.

• Structural Engineering and Mechanics
• /
• 제78권5호
• /
• pp.545-556
• /
• 2021

The present experimental study evaluated the seismic performance of six engineered cementitious composite (ECC) columns strengthened with carbon fiber reinforced polymer (CFRP) laminates under cyclic lateral loading. The ECC columns damaged and crushed in the first stage of cyclic tests were repaired using the ECC with a certain polyvinyl alcohol (PVA) fiber and strengthened with flexural and sheer CFRP laminates and then re-assessed under the cyclic loading. The effects of some variables were examined on lateral displacement, energy absorption and dissipation, failure modes, crack patterns, load bearing capacity and plasticity, and the obtained results were compared with those of the first stage of cyclic tests. The results showed that retrofitting the ECC columns can improve their performance, plasticity and load-bearing threshold, delayed the concrete failure, changed the failure modes and increased the energy absorbed by the strengthened columns element by over 50%.

• Journal of Chest Surgery
• /
• 제26권12호
• /
• pp.915-919
• /
• 1993

The management of Patent Ductus Arteriosus[PDA] with heart failure and cardiac cachexia in premature infants have been a disturbing and controversial problem in the field of pediatric cardiovascular surgery.We analysed our experiences to determine the rationale of surgical closure of PDA in infants . During a period of 7 years from January 1986 to December 1992, 12 infants under 2 months of age underwent operations for "hemodynamically significant" PDA which had caused severe heart failure.There were 6 male and 6 female patients. Their mean gestational age was 33.8 weeks and their mean body weight was 1990 g. ranged from 710 g. to 2900 g. Mean age at operation was 28.5days. Seven patients had history of Indomethacin trial. All patients were operated with double ligation technique under general anesthesia.There was no mortality and blood transfusion was not necessary in any patient during the operation.In all cases, we could confirm the complete closure of PDA after operation by follow-up echocardiography.Two patients died during their hospital stay and 1 patient died at 6 months after operation. The causes of death were sepsis with congestive heart failure, necrotizing entero colitis and pneumonia respectively.We can not detect any operation related complication which resulted in permanent sequelae as well as delayed complications related to nerve damage. These results indicate that surgical ligation of PDA in infants with severe heart failure is relatively safe and effective.effective.

• Journal of Korean Dental Science
• /
• 제8권2호
• /
• pp.82-88
• /
• 2015

Purpose: To evaluate the effect of light-curing on the immediate and delayed micro-shear bond strength (${\mu}SBS$) between yttria-tetragonal zirconia polycrystal (Y-TZP) ceramics and RelyX Ultimate when using Single Bond Universal (SBU). Materials and Methods: Y-TZP ceramic specimens were ground with #600-grit SiC paper. SBU was applied and RelyX Ultimate was mixed and placed on the Y-TZP surface. The specimens were divided into three groups depending on whether light curing was done after adhesive (SBU) and resin cement application: uncured after adhesive and uncured after resin cement application (UU); uncured after adhesive, but light cured after resin cement (UC); and light cured after adhesive and light cured resin cement (CC). The three groups were further divided depending on the timing of ${\mu}SBS$ testing: immediate at 24 hours (UUI, UCI, CCI) and delayed at 4 weeks (UUD, UCD, CCD). ${\mu}SBS$ was statistically analyzed using one-way ANOVA and Student-Newman-Keuls multiple comparison test (P<0.05). The surface of the fractured Y-TZP specimens was analyzed under a scanning electron microscope (SEM). Result: At 24 hours, ${\mu}SBS$ of UUI group ($8.60{\pm}2.06MPa$) was significantly lower than UCI group ($25.71{\pm}4.48MPa$) and CCI group ($29.54{\pm}3.62MPa$) (P<0.05). There was not any significant difference between UCI and CCI group (P>0.05). At 4 weeks, ${\mu}SBS$ of UUD group ($24.43{\pm}2.88MPa$) had significantly increased over time compared to UUI group (P<0.05). The SEM results showed mixed failure in UCI and CCI group, while UUI group showed adhesive failure. Conclusion: Light-curing of universal adhesive before or after application of RelyX Ultimate resin cement significantly improved the immediate ${\mu}SBS$ of resin cement to air-abrasion treated Y-TZP surface. After 4 weeks, the delayed ${\mu}SBS$ of the non-light curing group significantly improved to the level of light-cured groups.

• 한국지진공학회논문집
• /
• 제25권5호
• /
• pp.213-221
• /
• 2021

Many Korean domestic masonry structures constructed since 1970 have been found to be vulnerable to earthquakes because they lack efficient lateral force resistance. Many studies have shown that the brick and mortar suddenly experience brittle fracture and out-of-plane collapse when they reach the inelastic range. This study evaluated the seismic retrofitting of non-reinforced masonry with Hybrid Super Coating (HSC) and Cast, manufactured using glass fiber. Four types of specimen original specimen (BR-OR), one layered HSC (BR-HS-O), two-layered HSC (BR-HS-B), one layered HSC, and Cast (BR-CT-HS-O) were constructed and analyzed using compression, flexural tensile, diagonal compression, and triplet tests. The specimen responses were presented and discussed in load-displacement curves, maximum strength, and crack propagation. The compressive strength of the retrofit specimens slightly increased, while the flexural tensile strength of the retrofit specimens increased significantly. In addition, the HSC and Cast also produced a considerable increase in the ductile response of specimens before failure. Diagonal compression test results showed that HSC delayed brittle cracks between the mortar and bricks and resulted in larger displacement before failure than the original brick. The triplet test results confirmed that the bonding strength of the retrofit specimens also increased. The application of HSC and Cast was found to restrain the occurrence of brittle failure effectively and delayed the collapse of masonry wall structures.