• Journal of Korean Institute of Industrial Engineers
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• v.21 no.4
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• pp.507-517
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• 1995

The failure rate of an item depends on operational environment. When an item has a chance failure period and a wearout failure period in sequel, the severity of operational environment causes the increase in the slop of wearout failure rate or the increase in the magnitude of chance failure rate. For such a change of operational environment, this paper concerns the change of optimal preventive replacement time. Two preventive replacement policies, age replacement policy and periodic replacement policy with minimal repair, are considered. Investigated properties are: (a) in age replacement policy, optimal preventive replacement time increases as the chance failure rate increases and optimal preventive replacement time decreases as the slope of wearout failure rate increases, and (b) in periodic replacement policy with minimal repair, optimal preventive replacement time increases as the slope of wearout failure rate increases; however, the change of chance failure rate does not alter the optimal preventive replacement time.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.20 no.44
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• pp.263-271
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• 1997

This paper presents a preventive maintenance model for determining the preventive replacement period of a system in which a failure rate is affected by the cumulative damage of fault and inspection. Especially, the failure rate function is considered to be a function of the cumulative damage of the fault and inspection time. Types of replacement considered are preventive replacement and failure replacement. Failure rate and expected cost function between replacement are derived. An optimal policy is obtained that minimizes the average cost per unit time for preventive replacement, failure replacement, inspection and repair.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.22 no.4
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• pp.131-139
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• 2021

This study assessed the use of zeolite with high absorption performance in landscape paving concrete as a substitute for aggregate. The absorption performance and strength properties of paving concrete were investigated according to the replacement rate of the zeolite coarse aggregate, and the mechanical properties were investigated through strength tests. The absorption rate of the zeolite aggregate was 14%, which is 2.5 times higher than that of general aggregate. When zeolite coarse aggregate is applied to paving concrete, the absorption rate increases according to the replacement rate. The absorption rate was 5.2% at a replacement rate of 50%, which was 42% higher than that of general paving concrete. The compressive strength increased to 20% of the replacement rate and decreased at a higher replacement, but all the strengths in the construction standard code were satisfied. The flexural strength satisfied the code up to a replacement rate of 10%, but the strength decreased with increasing replacement rate, and the splitting tensile strength was greater than that of paving concrete using general aggregate up to a 20% replacement rate. Overall, zeolite coarse aggregate can be applied as a substitute.

• Journal of Chest Surgery
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• v.27 no.10
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• pp.838-845
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• 1994

From April, 1982 to December, 1992, multiple valve replacement was performed in 100 patients. Mitral and aortic valve replacement were done in 86 patients, 9 underwent mitral and tricuspid valve replacement, 4 patients underwent triple valve replacement and 1 patient underwent aortic and tricuspid valve replacement. Of the valve implanted, 100 were St. Jude, 64 Duromedics, 19 Carpentier-Edwards, 13 Bj rk-Shiley, 6 Ionescu-Shiley, and 2 Medronics.The hospital mortality rate was 15%[15 patients] and the late mortality rate was 7%[7 patients], the mortality rate was high in early operative period but decreased with time[20% at 1986, 18.2% at 1987, 9.5% at 1988, 11.1% at 1989, 12.5% at 1990, 11.8% at 1991, 0% at 1992]. The causes of death were low cardiac output in 8, sudden death in 3, CHF in 3, bleeding in 2, cerebral thromboembolism in 1, leukemia in 1, multiorgan failure in 1 and so on. The actuarial survival rate excluding operative death was 73% at 10 years.

• International Journal of Reliability and Applications
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• v.12 no.2
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• pp.117-122
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• 2011

In this paper, we suggest the optimal replacement policy following the expiration of repair warranty when the cost of minimal repair depends on the age of system. To do so, we first explain the replacement model under repair warranty. And then the optimal replacement policy following the expiration of repair warranty is discussed from the user's point of view. The criterion used to determine the optimality of the replacement model is the expected cost rate per unit time, which is obtained from the expected cycle length and the expected total cost for our replacement model. The numerical examples are given for illustrative purpose.

• Journal of Applied Reliability
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• v.11 no.4
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• pp.409-417
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• 2011

In this paper, we consider a replacement model following the expiration of warranty. In other words, this paper proposes the optimal replacement policy for a repairable system following the expiration of payable renewing replacement-non-renewing minimal repair warranty. The expected cost rate per unit time from the user's perspective is used to determine the optimality of the replacement policy. Thus, we derive the expressions for the expected cycle length and the expected total cost to obtain the expected cost rate per unit time. Finally, the numerical examples are presented for illustrative purpose.

• Journal of Integrative Natural Science
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• v.14 no.4
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• pp.197-204
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• 2021

Under the two-phase warranty, the warranty period is divided into two intervals, one of which is for renewing replacement warranty, and the other is for minimal repair warranty. Jung^[13] discusses the two types of extended two-phase warranty models. In this paper, we suggest the replacement model after the extended two-phase warranty that has been proposed by Jung^[13]. To determine the optimal replacement policy, we adopt the expected cost rate per unit time. So, the expressions for the total expected cost, the expected length of the cycle and the expected cost rate per unit time from the user's point of view are derived. Also, we discuss the optimal replacement policy and the uniqueness of the solution for the optimization. Furthermore, the numerical examples are provided to illustrate the proposed the replacement model.

• Journal of Chest Surgery
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• v.33 no.2
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• pp.160-166
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• 2000

Background: The purpose of this study is to evaluate and analyze the surgical results in patients undergoing operations for multiple for multiple valvular heart diseases. Material and method: From April 1982 to June 1997 multiple valve replacement was performed in 150 patients mitral and aortic valve replacement were done in 135 patients mitral and tricuspid valve replacements in 10 patients triple replacements in 4 patients and aortic and tricuspid valve replacement in 1 patient. Of the valves implanted 157 were St. Jude 104 Duromedics 20 Carpenter-Edwards 6 Bjork-Shiley 6 Ionescu-Shiley and 2 Medtronics. Result: The hospital mortality rate was 10.7% (16/150) and the late mortality rate was 7.2% (8/134) The mortality rate was high in early operative period but decreased with time. The causes of death were low cardiac output in 9 sudden death in 3 congestive heart failure in 3 bleeding in 2 cerebral thrombosis in 1 leukemia in 1 multiorgan failure in 1 and so on . The actuarial survival rate excluding operative death was 83.1% at 15 years. Conclusion: With a follow-up now extending to 15 years the multiple valve replacement continues to be reliable procedure with relatively low mortality and morbidity.

• Food Science of Animal Resources
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• v.24 no.3
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• pp.216-220
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• 2004

To investigate the effect of feeding the fermented food wastes (FFW) on meat quality, twenty pigs produced from four treatments with different mixing rates of FFW [100% concentrate (control), 25% replacement with FFW (25% FFW), 50% replacement with FFW (50% FFW) and 100% fermented food wastes (100% FFW)] were slaughtered. Carcass characteristics were differentiated if FFW replacement rate was higher than 50%. The proximate compositions of hams and loins in control pigs were not different from (p>0.05) those of the FFW replacements, regardless of mixing rate of FFW replacement. Drip loss of pork loin increased (p<0.05) with increased rate of FFW replacement. Hunter color values were affected (p<0.05) by the FFW replacement and storage time, while not significantly changed (p>0.05) when replaced with lower than 25% FFW. With replacing more than 50% FFW, redness values tended to be decreased, while yellowness values increased. Aerobic plate counts (APC) were rapidly increased 12 d for the control and 8 d for FFW replacement, and microbial stability seemed to be lowered when the rate of FFW replacement rate was more than 50%. These results indicated that the replacement of concentrate diets with FFW was still nutritious feedstuffs for pig diet, however, no more than 50% FFW replacement was recommended to have similar effect to those with the control (100% concentrate).

• Journal of the Korea Institute of Building Construction
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• v.6 no.3 s.21
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• pp.107-114
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• 2006

In this study, the experiment was carried out to investigate and analyze the engineering properties of concrete using fine aggregate of PS bal slagl. The main experimental variables were water/cement ratio 30, 40, 50(%), water content $170kg/m^3$, replacement ratio of slag fine aggregate 0, 25, 50, 75(%) in experiment I and water/cement ratio 30, 40, 50(%), water content 165, 170, 175($kg/m^3$), replacement ratio of fine aggregate of PS ball 0, 50 in experiment II. According to the test results, the principle conclusions are summarized as follows (1) The workability of slag fine aggregate-mixed concrete tends to improve, as the replacement rate increases. (2) The air content of slag fine aggregate-mixed concrete tends to decrease, as the replacement rate increases. (3) The unit volume weight of slag fine aggregate-mixed concrete tends to significantly increase, as the replacement rate increases. (4) The compressive strength of slag fine aggregate-mixed concrete tends to show more increasing propensity, in case the curing period is relatively long, as the replacement rate increases.