• Communications for Statistical Applications and Methods
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• 제3권2호
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• pp.275-282
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• 1996

A life distribution F with survival function $\overline{F}$=1-F, finite mean $\mu$ and mean residual life m(t) is said to be NBUE(NWUE) if m(t)$\leq$($\geq$) .$\mu$ for t$\geq$0. This NBUE property can equivalently be characterized by the fact that $\varphi$(u)$\geq$($\leq$)u for 0$\leq$u$\leq$1, where $\varphi$(u) is the scaled total-time-on test transform of F. A generalization of the NBUE properties is that there is a value of p such that $\varphi$(u)\geq.u$ for 0$\leq$u$\leq$p and $\varphi$(u)\leq$$\leq$u$\leq$1, or vice versa. This means that we have a trend change in the NBUE property. In this paper we point out an error of Klefsjo's paper (1988). He erroneously takes advantage of trend change point of failure rate to calculate the empirical test size and power in lognormal distribution. We solves the trend change point of mean residual lifetime and recalculate the empirical test size and power of Klefsjo (1988) in mocensoring case.

• Journal of Chest Surgery
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• 제28권5호
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• pp.453-463
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• 1995

During 42 month period 91 consecutive patient underwent coronary artery bypass surgery. The mean age of these patient was 57 years [range from 28 to 78 years . There were 57 men and 34 women. The preoperative risk factors that include beyond the 50 % of total patients were male sex, obesity, hypo-high-density lipoproteinemia, smoking, hypercholesterolemia, hyper-low-density lipoproteinemia, hypertriglyceridemia and hypertension. Preoperatively 27 patients had stable angina pectoris and 39 patients of unstable angina pectoris. Twenty five patients had previous myocardial infarction history. The patterns of disease were 8 patients of single vessel involvement, 18 patients of double vessel involvement, 54 patients of triple vessel involvement and 11 patients of left main coronary artery disease. Fifty five patients were in Canadian Cardiovascular Society functional class III. Myocardial revascularization was performed under emergency conditions in 5 patients. Nine percent of patients had previous PTCA history. We performed 16 cases of sequential anastomosis, internal mammary artery harvest in 86 percent of total patients and total 284 distal anastomoses[mean 3.1 anastomosis per patient . The mean ACC time was 60.5 minutes and ECC time was mean 110 minutes. The combined surgeries were 16 cases of endarterectomy, 2 cases of LV aneurysmectomy, 1 case of Bentall operation, 1 case of repair of sinus of Valsalva, 1 case of ligation of coronary AV fistula and 1 case of excision of breast mass. The most common complication was wound infection[12 cases, 13 % . There was one hospital death due to postoperative respiratory failure and low output syndrome in patient with postinfarction VSD, LV aneurysm. Postoperative 88 patients were in Functional class I or II. The 99mTc-MIBI myocardial perfusion scan that used as evaluation of postoperative state was well correlated with patient`s symptoms instead of some disadvantages.

• Journal of Minimally Invasive Surgery
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• 제21권4호
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• pp.154-159
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• 2018

Purpose: Intussusception is a common cause of intestinal obstruction in children. While most patients can be treated by enema reduction, about 20% require surgery. We investigated the usefulness and feasibility of laparoscopic surgery and the intraoperative risk of bowel resection. Methods: We retrospectively reviewed pediatric patients who underwent surgery for intussusception from 2010 to 2017. We collected data for age, gender, body weight, associated symptoms, duration of symptoms, white blood cell count, operating time, and postoperative complications. Results: Of 155 patients, 37 (23.8%) underwent surgery due to enema reduction failure in 29 (78.3%), recurrence in 6 (16.3%), a suspicious lead point in 1, and suspicious ischemic change observed on ultrasonography in 1. The mean age was $26.8{\pm}18.9$ months (range, 3.5~76.7 months), and the mean body weight was $12.9{\pm}3.9kg$ (range, 5.4~22.2 kg). Laparoscopic surgery was successful in 29 patients (78.4%), and 7 (18.9%) needed bowel resection and anastomosis. The mean operating time was $56.7{\pm}32.8min$. A lead point was found in 3 patients in the bowel resection group (p=0.005); in addition, the operating time and hospital stay were longer in this group. There were no intra- or postoperative complications. Conclusion: Laparoscopic surgery was successful in 78.4% of the patients with a short hospital stay and early oral intake. The only predictive factor for bowel resection was the presence of a lead point. Laparoscopic surgery may be an optimal treatment intervention for children with intussusception, except for those who show initial peritonitis.

• 품질경영학회지
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• 제22권1호
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• pp.113-121
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• 1994

Present worth of warranty cost for an irrepairable item is derived under free-replacement, prorata and hybrid warranty policies, respectively. In this paper, it is assumed that the lifetime distribution is a Gamma, and warranty period is not renewed but maintained as promised at the selling time regardless of replacements due to warranty contract. A numerical example on the relationship between present worth of warranty cost and mean time to failure is included.

• 한국초전도ㆍ저온공학회논문지
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• 제15권4호
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• pp.6-9
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• 2013

Korea Superconducting Tokamak Advanced Research (KSTAR) has a helium refrigeration system (HRS) with the cooling capacity of 9 kW at 4.5 K. Main cold components are composed of 300 tons of superconducting (SC) magnets, main cryostat thermal shields, and SC current feeder system. The HRS comprises six gas storage tanks, a liquid nitrogen tank, the room temperature compression sector, the cold box (C/B), the 1st stage helium distribution box (DB#1), the PLC base local control system interconnected to central control tower and so on. Between HRS and cold components, there's another distribution box (DB#2) nearby the KSTAR device. The entire KSTAR device was constructed in 2007 and has been operated since 2008. This paper will present the maintenance result of the KSTAR HRS during the campaign and discuss the operation record and maintenance history of the KSTAR HRS.

• Journal of the Korean Association of Oral and Maxillofacial Surgeons
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• 제49권1호
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• pp.13-20
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• 2023

Objectives: Ultra-wide implants may be used as a replacement if existing implants fail. This study was conducted to evaluate the factors influencing the prognosis and failure of ultra-wide implants. Patients and Methods: This study evaluated whether sex, age, site, diameter, length, additional surgery, implant stability (primary and secondary), and reason for ultra-wide implant placement affect the 5-year survival and success rates and marginal bone loss (MBL) of ultra-wide implants. Seventy-eight ultra-wide implants that were placed in 71 patients (39 males and 32 females) from 2008 to 2010 were studied. One-way ANOVA analysis was conducted to evaluate the statistical significance of MBL according to the patient's sex, implant site, and diameter. Independent sample t-tests were used to determine the statistical significance of MBL analysis which was used to determine the significance of the 5-year success and survival rates related to the variables. One-way ANOVA was conducted to evaluate the statistical significance of sex, implantation site, diameter, and MBL. Independent sample t-tests were used to evaluate the correlation between implantability and MBL for implantation reasons, while additional surgery, length, and Kaplan-Meier analysis were used to evaluate 5-year survival and success rates. Results: The mean age of patients was 54.2 years with a survival rate of 92.3% and a success rate of 83.3% over a mean 97.8-month period of observation. MBL averaged 0.2 mm after one year of prosthetic function loading and 0.54 mm at the time of final observation. Success rates correlated with primary stability (P=0.045), survival rates correlated with secondary stability (P=0.036), and MBL did not correlate with any variables. Conclusion: Ultra-wide implants can be used to achieve secure initial fixation in the maxillary and mandibular molar regions with poor bone quality or for alternative purposes in cases of previous implant failure.

• Journal of Chest Surgery
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• 제33권6호
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• pp.469-475
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• 2000

Background: Thoracic aortomyoplasty is one of the surgical treatment for heart failure and has advantages over artificial heart or intraaortic balloon pumps. It uses autogenous skeletal muscles and solves problems such as energy source. However its use in clinical settings has been limited. This preliminary study was designed to develop surgical technique and to determine the effect of acute descending thoracic aortomyoplsty. Material and Method: Thirteen adult Mongrel dogs were used. The left latissimus dorsi muscle was wrapped around the descending aorta under general anesthesis. Swan-Ganz and microtipped Millar catheter were used for the hemodynamics and endocaridial viability ratio. Data were collected with myostimulator on and off in normal hearts and the ischemic hearts. Result: In normal hearts, the mean aortic diastolic pressure increased from 72$\pm$15mmHg at baseline to 78$\pm$13mmHg with stimulator on. Coronary perfusion pressure increased from 61$\pm$11mmHg to 65$\pm$9mmHg. Diastolic time increased from 0.288$\pm$0.003 msec to 0.290$\pm$0.003msec. Systolic time decreased from 0.164$\pm$0.002msec to 0.160$\pm$0.002 msec. Endocardial viability ratio increased from 1.21$\pm$0.22 to 1.40$\pm$0.18. In ischemic hearts, mean aortic diastolic pressure incrased from 56$\pm$21mmHg at baseline to 61$\pm$15mmHg with stimulator on. Coronary perfusion pressure increased from 48$\pm$17mmHg to 52$\pm$15mmHg. Diastolic time increased from 0.290$\pm$0.003 msec to 0.313$\pm$0.004msec. Systolic time decreased from 0.180$\pm$0.002 msec to 0.177$\pm$0.003 msec. Endovascular viability ratio increased from 0.9$\pm$0.31 to 1.1$\pm$0.31. The limited number of cases ruled out the statistic significance. Conclusion: Descending thoracic aortomyoplasty is a simple operation designed to use patient's own skeletal muscles. It trends to increase diastolic augmentation and coronary perfusion pressure. Modification of surgical technique and stimulator protocol would maximize the effect to assist the heart.

• 산업경영시스템학회지
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• 제21권47호
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• pp.1-10
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• 1998

Testing high reliability devices under nomal operating condition is difficult, because the devices are not likely to fail in the relatively short time available for tests. For most applications it is necessary to accelerate the causes of failure by increasing a stress above its nomal value. Previous accelerated life test(ALT) plans have shown how to find optimum allocation, lowest stress and sample size subject to minimizing the variance of mean life estimator. In these ALT plans, the highest acceptable test-stress was assumed to be specified in advance by the experimenter but there is no guidance for selecting it. This assumption is, however, inappropriate for many applications. Testing devices at too-high stress levels can invalidate the extrapolation model, or introduce failure mechanisms that are not anticipated under nomal operating conditions. In this paper, we propose new 4:2:1 compromise plans using Min-Max method to minimize this risk and present minimized test-stress levels(max, middle, min), and find sample allocation based on Min-Max 4:2:1 compromise plans. In result, we compare previous 4:2:1 compromise plans specified maximum test-stress with Min-Max 4:2:1 compromise plans minimized maximum test-stress.

• 한국정보전자통신기술학회논문지
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• 제8권6호
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• pp.483-490
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• 2015

소프트웨어의 디버깅과정에서 오류 발생의 시간을 기반으로 하는 많은 소프트웨어 신뢰성 모델이 제안되어 왔다. 무한고장 모형과 비동질적인 포아송 과정에 의존한 소프트웨어 신뢰성 모형을 이용하면 모수 추정이 가능하다. 소프트웨어를 시장에 인도하는 결정을 내리기 위해서는 조건부 고장률이 중요한 변수가 된다. 무한 고장 모형은 실제 상황에서 다양한 분야에 사용된다. 특성화 문제, 특이점의 감지, 선형 추정, 시스템의 안정성 연구, 수명을 테스트, 생존 분석, 데이터 압축 및 기타 여러 분야에서의 사용이 점점 많아지고 있다. 통계적 공정 관리 (SPC)는 소프트웨어 고장의 예측을 모니터링 함으로써 소프트웨어 신뢰성의 향상에 크게 기여 할 수 있다. 컨트롤 차트는 널리 소프트웨어 산업의 소프트웨어 공정 관리에 사용되는 도구이다. 본 논문에서 NHPP에 근원을 둔 로그 포아송 실행시간 모형, 즉,Musa-Okumo 모형과 파우어 로우(Power-law) 모형의 평균값 함수를 이용한 통계적 공정관리 차트를 이용한 제어 메커니즘을 제안하였다.

• 정보처리학회논문지D
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• 제9D권3호
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• pp.389-398
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• 2002

본 논문에서는 비동질 포아송 과정에 기초한 소프트웨어 오류 현상에 대한 신뢰도 모형을 고려하고 사전정보를 이용한 베이지안 추론을 시행하였다. 고장 패턴은 NHPP에 대한 강도함수와 평균값 함수로서 나타낼 수 있다. 따라서 본 논문에서는 기존의 모형인 Goel이 제시한 모형과 신뢰성 분포로 많이 사용되는 와이블 분포의 특수형태인 레일리분포와 라플라스 분포를 이용한 모형을 제시하여 베이지안 추론을 시행하고 또, 효율적 모형을 위한 모형선택으로서 편차자승합을 이용하여 비교하였다. 모수의 추정을 위해서 마코브체인 몬테카를로 기법중에 하나인 깁스샘플링을 이용한 근사추정 기법이 사용되었다. 수치적인 예에서는 실측자료인 NTDS 자료를 이용하여 모수 및 신뢰도를 추정하였고 편차자승합을 이용한 모형비교의 결과를 나열하였다.