• Journal of the Korean Operations Research and Management Science Society
• /
• v.25 no.4
• /
• pp.45-54
• /
• 2000

Estimation Problems of parameters of the failure process and the repair effect in repairable systems are considered. We propose estimation procedures in repairable systems without preventive maintenances. The failure process is modeled by a proportional age reduction model (Brown, Mahoney, Sivazlian [5]) which is able to consider both aging and repair effects. Maximum likelihood method is used to estimate the repair effect and parameters of intensity function simultaneously. simulations are performed to evaluate the accuracy of estimators. A numerical example is also presented.

• Proceedings of the Korean Society for Quality Management Conference
• /
• 2004.04a
• /
• pp.430-435
• /
• 2004

Nonhomogeneous Poisson Process is often used to model failure times which occurred in software reliability and hardware reliability models. It can be characterized by its intensity functions or mean value functions. Many parametric intensity models have been proposed to account for the failure mechanism in real situation. In this paper, we propose a Bayesian semiparametric approach based on beta-mixtures. Two real datasets are analyzed.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.24 no.1 s.173
• /
• pp.38-51
• /
• 2000

The study on the mechanical behavior of a spot-welded specimen is largely divided into the quasi-static overload failure analysis and the fatigue failure prediction. The main issue in an overload analysis is to examine the critical loads, thereby providing a generalized overload failure criterion. As the welding spot forms a singular geometry of an external crack type, fatigue failure of spot-welded specimens can be evaluated by means of a fracture parameter. In this study, we first present the limit loads of 4 representative types of single spot-welded specimens in terms of the base metal yield strength and specimen geometries. Recasting the load vs. fatigue life relationships experimentally, obtained here, we then predict the fatigue life of spot-weld specimens with a single parameter denoted the equivalent stress intensity factor. This crack driving parameter is demonstrated to successfully describe the effects of specimen geometry and loading type in a comprehensive manner. The suggested fatigue life formula for a single spot weld can play a key, role in the design and assessment of spot-welded panel structures, in that the fatigue strength of multi-spots is eventually determined by the fatigue strength of each single spot.

• Journal of Information Technology Applications and Management
• /
• v.24 no.2
• /
• pp.71-80
• /
• 2017

Software reliability is one of the most elementary and important problems in software development In order to find the software failure occurrence, the instantaneous failure rate function in the Poisson process can have a constant, incremental or decreasing tendency independently of the failure time. In this study, we compared the reliability performance of the software reliability model using the parameters of Pareto life distribution with the intensity decreasing pattern and the shape parameter of Erlang life distribution with the intensity increasing and decreasing pattern in the software product testing. In order to identify the software failure environment, the parametric estimation was applied to the maximum likelihood estimation method. Therefore, in this paper, we compare and evaluate software reliability by applying software failure time data. The reliability of the Erlang and Pareto life models is shown to be higher than that of the Pareto lifetime distribution model when the shape parameter is higher and the Erlang model is more reliable when the shape parameter is higher. Through this study, the software design department will be able to help the software design by applying various life distribution and shape parameters, and providing basic knowledge using software failure analysis.

• Proceedings of the Korean Geotechical Society Conference
• /
• 1999.03a
• /
• pp.277-284
• /
• 1999

This study describes the influence factors related to slope failure pattern and dimension in the southern Kyounggi area. Intrusive and metamorphic rocks are distributed in the study area. Geological condition, rainfall property and slope geometry are influence on slope failure characteristics in the study we& Geological factors related to slope failure are rock type, geological structure and weathering condition. Because of deep soil (RS-CW) depth of granite region, circular failure type is major failure pattern in granite region. Almost granite slopes with circular or surface failure pattern are failed during heavy rainfall season. But typical wedge failure type related to geological structure factor is a main failure pattern of metamorphic rock slope. Additionally failure dimension is influenced by geological factors and several factors, i.e. natural slope condition, failure type, rainfall intensity and etc. failure height/width ratio and thickness/length ratio of granite slope are 0.88 and 0.23. But the ratios of metamorphic rock slope are 1.36 and 0.19.

• Journal of Korean Neurosurgical Society
• /
• v.61 no.1
• /
• pp.97-104
• /
• 2018

Objective : Diffusion-weighted magnetic resonance imaging (DW-MRI) has proven useful in the study of the natural history of ischemic stroke. However, the potential of DW-MRI for the evaluation of chronic subdural hematoma (CSDH) has not been established. In this study, we investigated DW-MRI findings of CSDH and evaluated the impact of the image findings on postoperative outcomes of CSDH. Methods : We studied 131 CSDH patients who had undergone single burr hole drainage surgery. The images of the subdural hematomas on preoperative DW-MRI and computed tomography (CT) were divided into three groups based on their signal intensity and density : 1) homogeneous (iso or low) density on CT and homogeneous low signal intensity on DW-MRI; 2) homogeneous (iso or low) density on CT and mixed signal intensity on DW-MRI; and 3) heterogeneous density on CT and mixed signal intensity on DW-MRI. On the basis of postoperative CT, we also divided the patients into 3 groups of surgical outcomes according to residual hematoma and mass effect. Results : Analysis showed statistically significant differences in surgical (A to B : p<0.001, A to C : p<0.001, B to C : p=0.129) and functional (A to B : p=0.039, A to C : p<0.001, B to C : p=0.108) outcomes and treatment failure rates (A to B : p=0.037, A to C : p=0.03, B to C : p=1) between the study groups. In particular, group B and group C showed worse outcomes and higher treatment failure rates than group A. Conclusion : CSDH with homogeneous density on CT was characterized by signal intensity on DW-MRI. In CSDH patients, performing DW-MRI as well as CT helps to predict postoperative treatment failure or complications.

• The Journal of Korean Physical Therapy
• /
• v.30 no.5
• /
• pp.181-186
• /
• 2018

Purpose: This study investigated the effects of home-based exercise intensity on the aerobic capacity and 1 year re-hospitalization rate in patients with chronic heart failure (CHF). Methods: Forty seven patients with CHF (males 33, females 14, age $61.3{\pm}9.8years$) participated in this study. The patients were allocated randomly to 3 groups in accordance with home-based exercise intensity: no home based exercise (NHE, 40%, n=19), moderate intensity home-based exercise (MIHE, 43%, n=20), and high intensity home based exercise (HIHE, 17%, n=8). All patients completed the symptom-limited cardiopulmonary exercise (CPX) test safely at the cardiac rehabilitation hospital. Results: The NHE group significantly showed lower peak $VO_2$ and a higher $VE/VCO_2$ slope than the MIHE (p<0.05) and HIHE (p<0.01) groups. On the other hand, the NHE group did not show significant differences in the other hemodynamic responses, such as heart rate (HR) max, HR reserve, maximal systolic blood pressure (SBP), and SBP reserve. Nine out of 19 NHE patients (47%) were re-hospitalized related to heart disease and two out of 20 MIHE (10%) patients were re-hospitalized, but nobody in the HIHE group were re-hospitalized within 1 year from the CPX test. Conclusion: In patients with CHF, home-based self-exercise is one of the important factors for reducing the re-hospitalization rate. In addition, improved aerobic capacity is strongly associated with a lower re-hospitalization rate. In particular, re-hospitalized CHF patients showed significant differences in respiratory parameters and hemodynamic parameters compared to the non-re-hospitalized patients.

• Earthquakes and Structures
• /
• v.18 no.4
• /
• pp.519-526
• /
• 2020

Non-stationary random seismic response and reliability of multi-degree of freedom hysteretic structure system are studied based on the cumulative damage failure mechanism. First, dynamic Eqs. of multi-degree of freedom hysteretic structure system under earthquake action are established. Secondly, the random seismic response of a multi-degree freedom hysteretic structure system is investigated by the combination of virtual excitation and precise integration. Finally, according to the damage state level of structural, the different damage state probability of high-rise frame structure is calculated based on the boundary value of the cumulative damage index in the seismic intensity earthquake area. The results show that under the same earthquake intensity and the same floor quality and stiffness, the lower the floor is, the greater the damage probability of the building structure is; if the structural floor stiffness changes abruptly, the weak layer will be formed, and the cumulative damage probability will be the largest, and the reliability index will be relatively small. Meanwhile, with the increase of fortification intensity, the reliability of three-level structure fortification is also significantly reduced. This method can solve the problem of non-stationary random seismic response and reliability of high-rise buildings, and it has high efficiency and practicability. It is instructive for structural performance design and estimating the age of the structure.

• International Journal of Quality Innovation
• /
• v.5 no.1
• /
• pp.110-121
• /
• 2004

There is a new trend of incorporating software coverage metrics into software reliability modelling. This paper proposes a coverage-based software reliability growth model. Firstly, the failure rate function in coverage is analytically derived. Then it is shown that the number of detected faults follows a Nonhomogeneous Poisson distribution of which intensity function is the failure rate function in coverage. Practical applicability of the proposed models is examined by illustrative numerical examples.

• Journal of the Korean Society for Precision Engineering
• /
• v.18 no.1
• /
• pp.111-116
• /
• 2001

A practical scheme to reduce failure of the PCB(Printed Circuit Board) of a monitor is introduced using deformed mode shape under mechanical shock. When the monitor is given critical shock loads, cracks are commonly initiated at the tip of a hole on the PCB. Accordingly, a deformed mode shape of the PCB is obtained using a FEM code to define a weak point on the PCB under mechanical shock, and then the position and direction of the hole is determined to prevent the failure at the critical mode shape. Also, the stress intensity factor around the weak point on the PCB is calculated to check the possibility of fracture by normal tensile stress. In conclusion, present research is useful to assist the practical design of components-layout on the PCB.