• Journal of the Korean Society for Railway
• /
• v.8 no.5
• /
• pp.439-443
• /
• 2005

The biggest challenge bridge agencies face is the maintenance of bridges, keeping them safe and serviceable, with limited funds. To maintain the bridges effectively, there is and urgent need to predict their remaining life from a system reliability viewpoint. In this paper, a model using lifetime functions to evaluate the overall system probability of survival of a rail road bridge is proposed. In this model, the rail load bridge is modeled as a system. Using the model, the lifetime of the rail road bridge is predicted.

• The Journal of Fisheries Business Administration
• /
• v.25 no.2
• /
• pp.103-114
• /
• 1994

We consider the continous, deterministic, infinite horiton, perishable item inventory, within the setting of a retail sector, in which the price for an item is dependent on the lifetime of inventory. Replenishment cost is kept constant but the carrying cost per units is allowed to vary according to product lifetime. Tro possibilities of variation are considered : (1) Product lifetime is longer than cycletime and (2) Product lifetime is shorter than cycletime. We find the optimal policies and decision rules for perishable product.

• Proceedings of the IEEK Conference
• /
• 2003.11c
• /
• pp.140-144
• /
• 2003

A sensor network consists of many low-cost, low-power, and multi-functional sensor nodes. One of most important issues in of sensor networks is to increase network lifetime, and there have been researches on the problem. In this paper, we propose a routing mechanism to prolong network lifetime, in which each node adjusts its transmission power to send data to its neighbors. We model the energy efficient routing with power control and present an algorithm to obtain the optimal flow solution for maximum network lifetime. Then, we derive an upper bound on the network lifetime for specific network topologies.

• 한국정보디스플레이학회:학술대회논문집
• /
• 2007.08a
• /
• pp.625-627
• /
• 2007

We demonstrated high power efficiency and long lifetime in organic light-emitting diode (OLED) using new electron transport materials (ETMs). Electroluminescent device with these ETMs showed lower driving voltage than that with $Alq_3$. The device lifetime with a new ETM was 2 times longer than that with $Alq_3$.

• Journal of Korean Society for Quality Management
• /
• v.25 no.2
• /
• pp.1-14
• /
• 1997

This paper considers maximum likelihood (ML) estimation of lifetime distribution under stress bounded ramp tests in which the stress is increased linearly from used condition stress to the stress u, pp.r bound. The following assumptions are used: exponential lifetime distribution under a constant stress, an inverse power law relationship between stress and mean of exponential lifetime distribution, and a cumulative exposure model for the effect of changing stress. Likelihood equations for the parameters involved in the model and asymptotic distribution of the estimators are obtained, and a numerical example is given.

• Journal of Korean Society for Quality Management
• /
• v.26 no.1
• /
• pp.161-171
• /
• 1998

Kim and Kim (1997) developed a method of estimating the mean lifetime based on the augmented data after imputing censored observations. Assuming the linear relationship between lifetime and covariates, and then introducing the procedure of Buckley and James (1979) to estimate the mean lifetimes of censored observations, they proposed a mean lifetime estimator and its consistency under the regularity conditions. In this article, the Kim and Kim's estimator is compared with the estimator introduced by Gill (1983) through simulations under the various configurations. Also, their estimator is illustrated with two real data sets.

• Asian Pacific Journal of Cancer Prevention
• /
• v.17 no.8
• /
• pp.4083-4088
• /
• 2016

Background: Physical inactivity has been identified as the fourth leading risk factor for global mortality and is associated with increased breast cancer diagnosis and recurrence. Purpose: To examine the association between adult lifetime physical activity and breast cancer risk in a case-control analysis. Materials and Methods: This study involved 122 cases of breast cancer and 121 controls in the state of Kelantan in Malaysia. A comprehensive measure of lifetime physical activity was used to assess occupational, household, and recreational/sports activity. For every type of activity, a metabolic equivalent (MET) score was assigned using the compendium of physical activities. MET-hours/week per year for all types of activities at different levels of intensities for different age groups were calculated. Logistic regression analysis was used to estimate odds ratios between various measures of physical activity and breast cancer risk. Conclusions: The mean MET-hours/week per year for all activities were 120.0 and 132.9 of MET-hours/week per year for cases and controls respectively. Household activities accounted for about 70% of the total lifetime physical activities. Only about 2.5% of the total lifetime physical activities were in the form of recreational/sports. This study found no association between lifetime occupational and recreational/sports physical activities with breast cancer risk among Kelantanese women. However, higher intensity lifetime household activities seemed to significantly reduce risk of breast cancer.

• Journal of Korean Society of Industrial and Systems Engineering
• /
• v.40 no.3
• /
• pp.92-98
• /
• 2017

The rapid growth of engineering technology and the emergence of systemized and large-scale engineering systems have resulted in complexity and uncertainty throughout the lifecycle activities of engineering systems. This complex and large-scale engineering system consists of numerous components, but system failure can be caused by failure of any one of a number of components. There is a real difficulty in managing such a complex and large-scale system as a part. In order to efficiently manage the system and have high reliability, it is necessary to structure a system with a complex structure as a sub-system. Also, in the case of a system in which cause of failures exist at the same time, it is required to identify the correlation of the components lifetime and utilize it for the design policy or maintenance activities of the system. Competitive risk theory has been used as a theory based on this concept. In this study, we apply the competitive risk theory to the models with combined structure of series and parallel which is the basic structure of most complex engineering systems. We construct a competing risks model and propose a mathematical model of net lifetime and crude lifetime for each cause of failure, assuming that the components consisting a parallel system are mutually dependent. In addition, based on the constructed model, the correlation of cause of failure is mathematically analyzed and the hazard function is derived by dividing into net lifetime and crude lifetime.

• Nuclear Engineering and Technology
• /
• v.55 no.3
• /
• pp.919-926
• /
• 2023

To analyze the cause of the destruction of thin, carbon-backed lithium fluoride targets during a measurement of the fusion of ⁷Li and ¹⁷O, we estimate theoretically the lifetimes of carbon and LiF films due to sputtering, thermal evaporation, and lattice damage and compare them with the lifetime observed in the experiment. Sputtering yields and thermal evaporation rates in carbon and LiF films are too low to play significant roles in the destruction of the targets. We estimate the lifetime of the target due to lattice damage of the carbon backing and the LiF film using a previously reported model. In the experiment, elastically scattered target and beam ions were detected by surface silicon barrier (SSB) detectors so that the product of the beam flux and the target density could be monitored during the experiment. The areas of the targets exposed to different beam intensities and fluences were degraded and then perforated, forming holes with a diameter around the beam spot size. Overall, the target thickness tends to decrease linearly as a function of the beam fluence. However, the thickness also exhibits an increasing interval after SSB counts per beam ion decreases linearly, extending the target lifetime. The lifetime of thin LiF film as determined by lattice damage is calculated for the first time using a lattice damage model, and the calculated lifetime agrees well with the observed target lifetime during the experiment. In experiments using a thin LiF target to induce nuclear reactions, this study suggests methods to predict the lifetime of the LiF film and arrange the experimental plan for maximum efficiency.

• Journal of IKEEE
• /
• v.27 no.4
• /
• pp.556-560
• /
• 2023

In this study, the impact of Nitrogen implantation process on deep-level defects and lifetime in 4H-SiC Epi surfaces was comparatively analyzed. Deep Level Transient Spectroscopy (DLTS) and Time Resolved Photoluminescence (TR-PL) were employed to measure deep-level defects and carrier lifetime. As-grown Schottky Barrier Diodes (SBDs) exhibited energy levels at 0.16 eV, 0.67 eV, and 1.54 eV, while for implantation SBD, defects at 0.15 eV were observed. This indicates a reduction in defects associated with energy levels Z_1/2 and EH_6/7, known as lifetime killers, as impurities from nitrogen implantation replace titanium and carbon vacancies.