• Journal of Electrical Engineering and Technology
• /
• v.2 no.3
• /
• pp.386-390
• /
• 2007

At recent times, an essential issue in the replacement of the old analogue I&C to computer-based digital systems in nuclear power plants becomes the quantitative software reliability assessment. Software reliability models have been successfully applied to many industrial applications, but have the unfortunate drawback of requiring data from which one can formulate a model. Software that is developed for safety critical applications is frequently unable to produce such data for at least two reasons. First, the software is frequently one-of-a-kind, and second, it rarely fails. Safety critical software is normally expected to pass every unit test producing precious little failure data. The basic premise of the rare events approach is that well-tested software does not fail under normal routine and input signals, which means that failures must be triggered by unusual input data and computer states. The failure data found under the reasonable testing cases and testing time for these conditions should be considered for the quantitative reliability assessment. We presented the quantitative reliability assessment methodology of safety critical software for rare failure cases in this paper.

• Journal of the Korea Society for Simulation
• /
• v.8 no.3
• /
• pp.77-89
• /
• 1999

Simulating rare events, such as probability of cell loss in ATM networks, machine failure in highly reliable systems, requires huge simulation efforts due to the low chance of occurrence. Importance Sampling (IS) has been applied to accelerate the occurrence of rare events. However, it has a drawback of effective biasing scheme to make the estimator of IS unbiased. Adaptive Importance Sampling (AIS) employs an estimated sampling distribution of IS to the system of interest during the course of simulation. We propose Nonparametric Adaptive Importance Sampling (NAIS) technique which is nonparametrical version of AIS. We test NAIS to estimate a probability of rare event in M/M/1 queueing model. Comparing with classical Monte Carlo simulation, the computational efficiency and variance reductions gained via NAIS are substantial. A possible extension of NAIS regarding with random number generation is also discussed.

• KIEE International Transactions on Power Engineering
• /
• v.5A no.2
• /
• pp.103-108
• /
• 2005

Catastrophic failures in power systems are rare but not uncommon events. Protection systems play an important role in the progression of events during a catastrophic failure. This paper will examine some of the historical records, and suggest possible improvements to protection systems which can have a positive impact on power system performance during catastrophic failures.

• The Bulletin of The Korean Astronomical Society
• /
• v.42 no.2
• /
• pp.66.1-66.1
• /
• 2017

Nuclear reactions in explosive stars such as novae, X-ray bursts, and supernovae are responsible for producing many of the elements that make up our world. Exotic nuclei not normally found on earth can play an important role in these events due to the extreme conditions that occur in the explosion. A frontier area of research involves utilizing beams of radioactive nuclei to improve our understanding of these explosions and the implications on cosmic element production. At the future radioactive ion beam facility of Korea, RAON, we will measure astrophysically important reactions using exotic beams to probe the details of cosmic events. Details of RAON and possible day-1 experiments at the facility will be presented.

• Clinical and Experimental Pediatrics
• /
• v.50 no.8
• /
• pp.726-731
• /
• 2007

This review describes the wide spectrum of paroxysmal events during sleep in infancy and childhood. The differential diagnosis between sleep-related non-epileptic paroxysmal events and epileptic seizures is difficult in special occasions. The nocturnal frontal lobe seizure and of the more common nonepileptic paroxysmal events during sleep are described. The main differentiating features characterizing parasomnias are: onset in early childhood, rare episodes of long duration, relatively lower frequency per night, absence of stereotypy, gradual disappearance of older age. Video-polysomnography is the gold standard to diagnosing and differentiating parasomnias from nocturnal frontal lobe seizures.

• Investigative Magnetic Resonance Imaging
• /
• v.25 no.3
• /
• pp.193-196
• /
• 2021

Congenital absence of the bilateral internal carotid arteries (ICA) is a very rare occurrence. Recognition of this rare anomaly is important, when considering intracranial endovascular interventions in the event of thromboembolic events with revascularization, transsphenoidal surgery, and the surveillance and detection of associated cerebral aneurysms. We report a case of a 25-year-old man who presented with headache since 2 years ago, and was incidentally discovered to have a congenital bilateral absence of ICAs.

• Journal of Animal Science and Technology
• /
• v.63 no.1
• /
• pp.77-90
• /
• 2021

This study aimed to assess the impact of abnormal climate events on the production of Italian ryegrass (IRG), such as autumn low-temperature, severe winter cold and spring droughts in the central inland, southern inland and southern coastal regions. Seasonal climatic variables, including temperature, precipitation, wind speed, relative humidity, and sunshine duration, were used to set the abnormal climate events using principal component analysis, and the abnormal climate events were distinguished from normal using Euclidean-distance cluster analysis. Furthermore, to estimate the impact caused by abnormal climate events, the dry matter yield (DMY) of IRG between abnormal and normal climate events was compared using a t-test with 5% significance level. As a result, the impact to the DMY of IRG by abnormal climate events in the central inland of Korea was significantly large in order of severe winter cold, spring drought, and autumn low-temperature. In the southern inland regions, severe winter cold was also the most serious abnormal event. These results indicate that the severe cold is critical to IRG in inland regions. Meanwhile, in the southern coastal regions, where severe cold weather is rare, the spring drought was the most serious abnormal climate event. In particular, since 2005, the frequency of spring droughts has tended to increase. In consideration of the trend and frequency of spring drought events, it is likely that drought becomes a NEW NORMAL during spring in Korea. This study was carried out to assess the impact of seasonal abnormal climate events on the DMY of IRG, and it can be helpful to make a guideline for its vulnerability.

• Wind and Structures
• /
• v.15 no.2
• /
• pp.163-176
• /
• 2012

Damaging winds, associated with a variety of weather phenomena, are frequently experienced in New Zealand. Observations and modelling of two recent extreme wind events; the Taranaki tornado outbreak of July 2007, and the Greymouth down-slope easterly wind storm of July 2008 are described in detail here. Post-event engineering damage surveys, rare for New Zealand, were done for these storms and the results are summarized here. Finally, the issue of sampling extreme wind events is raised and the need to include detailed numerical modelling analysis to understand wind gust climatologies at observing sites and extending these to wider regions is discussed.

• Proceedings of the Korean Operations and Management Science Society Conference
• /
• 1995.04a
• /
• pp.966-966
• /
• 1995

• 한국데이터정보과학회:학술대회논문집
• /
• 2001.10a
• /
• pp.87-97
• /
• 2001

We consider a stable tandem network which consists of two M/M/1 queues. The optimal changes of measure to run the fast simulation for the probability of rare events such as buffer overflows are obtained.