• Journal of the Korean Data and Information Science Society
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• 제13권2호
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• pp.243-250
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• 2002

This paper considers the problem of estimating parameters of the bivariate exponential distribution with a location parameter for a two-component shared parallel system using component data from system-level life test terminated at the time of the prespecified number of system failure. In the system-level life testing, there are three patterns of failure types ; 1) both component failed 2) both component censored 3) one is failed and the other is censored. In the third case, we assume that the failure time might be known or unknown. The maximum likelihood estimators are obtained for the case of known/unknown failure time when the other component is censored.

• Journal of applied mathematics & informatics
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• 제8권1호
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• pp.199-212
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• 2001

We consider a k-out-of-n system with repair under T-policy. Life time of each component is exponentially distributed with parameter $\lambda$. Server is called to the system after the elapse of T time units since his departure after completion of repair of all failed units in the previous cycle or until accumulation of n-k failed units, whichever occurs first. Service time is assumed to be exponential with rate ${\mu}$. T is also exponentially distributed with parameter ${\alpha}$. System state probabilities in finite time and long run are derived for (i) cold (ii) warm (iii) hot systems. Several characteristics of these systems are obtained. A control problem is also investigated and numerical illustrations are provided. It is proved that the expected profit to the system is concave in ${\alpha}$ and hence global maximum exists.

• 한국재료학회지
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• 제18권9호
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• pp.497-502
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• 2008

BGA test sockets failed earlier than the expected life-time due to abnormal signal delay, shown especially at the low temperature ($-50^{\circ}C$). Analysis of failed sockets was conducted by EDX, AES, and XRD. A SnO layer contaminated with C was found to form on the surface of socket pins. The formation of SnO layer was attributed to the repeated Sn transfer from BGA balls to pin surface and instant oxidation of fresh Sn. As a result, contact resistance increased, inducing signal delay. Abnormal signal delay at the low temperature was attributed to the increasing resistivity of Sn oxide with decreasing temperature, as manifested by the resistance measurement of $SnO_2$.

• Journal of Chest Surgery
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• 제32권11호
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• pp.1049-1051
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• 1999

We performed a reoperation of failed tricuspid mechanical valve in a 63-year-old female patient because the overgrown endothelial pannus had entrapped the prosthetic leaflets. Four years ago, the patient underwent mitral and tricuspid valve replacements with 31 and 33 mm Carbomedics, respectively. The patient showed symptoms of neck vein distention, abdominal distention and peripheral edema. The chest film, echocardiography and cineangiography confirmed the diagnosis of tricuspid valve. During the operation, we found the entrapped leaflets of the tricuspid valve in a partially closed state and the endothelial pannus had overgrown into the leaflets. Carpentier-Edward bovine pericardial valve was inserted and the patient was discharged with no significant events.

• The Korean Journal of Pain
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• 제4권2호
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• pp.162-167
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• 1991

Epidural steroid therapy has been well-established for the treatment of sciatica and low back pain. Disappointing results following surgical decompression or discectomy pain owing for to nerve root compression have led to trials of corticosteroids injected either systemically or into the intrathecal or epidural space to treat intervertebral disc. Epidural steroid is less effective in the patients with low back pain who have a history of surgical operation, so that the use of epidural morphine and methylprednisolone has been advocated for the amelioration of chronic low back pain in the post-laminectomy pain("failed back") syndrome over the past several years. We treated 47 patients with low back pain who had a history of one or two surgical procedures. We concluded that epidural steroid therapy is less effective in the patients with "failed back" syndrome than in the virgin back furthermore, there is a greater risk of complication such as inadvertent dural puncture and corresponding motor paralysis and headache.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2002년도 봄 학술발표회 논문집
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• pp.443-448
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• 2002

The cross sections of structural walls have various shapes such as T, L, and H-shaped. The L-shaped walls frequently appear in the comer of the structural plans. There are a little researches on the structural performance of L-shaped walls subjected to hi-directional loads. L-shaped wall subjected to hi-directional loads might be failed due to high compressive stress in the corner of the wall. L-shaped wall subjected to bi-directional(45$^{\circ}$ direction) loads was failed by the compressive failure more possible than that of one-directional(0$^{\circ}$ direction) loads. Therefore, in this paper, Two L-shaped wall specimens are chosen and presented. One is LCU specimen subjected to the bi-directional loads, the other is LCX specimen subjected to the one-directional loads. Also, the experimental results compared with the analytical results from nonlinear FEM analysis.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2004년도 춘계 학술발표회 제16권1호
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• pp.48-51
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• 2004

This paper is to study the response of flat plate slab-column connections consisting of various types of shear reinforcement and steel plate subjected to gravity loadings, mainly punching shear forces using the non-destructive testing, spectral analysis of surface waves and structural experiments. The base specimen failed due to punching shear generated from the gravity. The three other types of slab shear reinforcement and steel plate showed effective in resisting punching shear for these types of connections under gravity loading. This study has focused in evaluating the velocity response of a Surface wave during the early age as the poured concrete specimens have been hardened, the possibility of damage detection in the slab-column connection and the relationship between the punching shear forces and the surface wave velocities under the condition that the punching shear forces had gradually increased until the flat plate slab in slab-column connection had been failed.

• Journal of Korean Neurosurgical Society
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• 제56권6호
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• pp.496-499
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• 2014

Owing to the focal wall defect covered with thin fibrous tissues, an aneurysm arising from the dorsal wall of the internal carotid artery (ICA) is difficult to manage either surgically or endovascularly and is often associated with high morbidity and mortality. Unfortunately, the definitive treatment modality of such highly risky aneurysm has not yet been demonstrated. Upon encountering the complex intracranial pathophysiology of such a highly precarious aneurysm, a neurosurgeon would be faced with a challenge to decide on an optimal approach. This is a case of multiple paraclinoid aneurysms including the ICA dorsal wall aneurysm, presented with spontaneous subarachnoid hemorrhage. With respect to treatment, direct clipping with a Sundt graft clip was performed after multiple endovascular interventions had failed. This surgical approach can be a treatment modality for a blood blister-like aneurysm after failed endovascular intervention(s).

• 전기학회논문지
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• 제58권3호
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• pp.614-620
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• 2009

The force distribution in multi-legged robots is a constrained, optimization problem. The solution to the problem is the set points of the leg contact forces for a particular system task. In this paper, an efficient and general formulation of the force distribution problem is developed using linear programming. The considered walking robot is a quadruped robot with a locked-joint failure, i.e., a joint of the failed leg is locked at a known place. For overcoming the drawback of marginal stability in fault-tolerant gaits, we define safety margin on friction constraints as the objective function to be maximized. Dynamic features of locked-joint failure are represented by equality and inequality constraints of linear programming. Unlike the former study, our result can be applied to various forms of walking such as crab and turning gaits. Simulation results show the validity of the proposed scheme.

• 대한산업공학회지
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• 제30권3호
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• pp.250-260
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• 2004

This study considers a linear connected-(r,s)-out-of-(m,n):F lattice system whose components are ordered like the elements of a linear (m,n )-matrix. We assume that all components are in the state 1 (operating) or 0 (failed) and identical and s-independent. The system fails whenever at least one connected (r,s)-submatrix of failed components occurs. The purpose of this paper is to present an optimization scheme that aims at minimizing the expected cost per unit time. To find the optimal threshold of maintenance intervention, we use a genetic algorithm for the cost optimization procedure. The expected cost per unit time is obtained by Monte Carlo simulation. The sensitivity analysis to the different cost parameters has also been made.