• Proceedings of the Korean Society of Computer Information Conference
• /
• 2022.07a
• /
• pp.3-5
• /
• 2022

혼합 중요도(mixed criticality) 시스템은 안전에 중요한 기능을 우선시하도록 하는 추가적인 안전 요구사항이 존재한다. 그러나 기존 실시간 시스템의 설계로는 이를 만족하지 못하며, 높은 중요도 태스크가 다른 낮은 중요도 태스크로부터 간섭을 받아 데드라인 미스와 같은 문제를 일으키는 중요도 역전(criticality inversion) 문제가 발생할 수 있다. 이러한 중요도 역전 문제를 해결하기 위해 주기 변환(period transformation) 기법을 사용할 수 있지만, 스케줄링 오버헤드의 증가로 인해 오히려 전반적인 태스크의 응답시간이 증가하는 또 다른 문제가 발생하게 된다. 본 논문에서는 주기 변환과 스케줄링 오버헤드 간의 트레이드오프 관계를 설명하고, 실시간 리눅스 시스템에서 해당 문제점을 재연한 후 주기 변환의 적정선을 분석하고자 실험을 진행하였다. 그 결과, 중요도 역전 문제를 해결하기 위한 주기 변환을 그대로 적용할 경우, 문맥 교환이 48.7% 증가 및 스케줄링 오버헤드가 28.7% 증가로 인해 전반적인 응답시간이 증가하여 데드라인 미스가 다수 발생하는 결과를 확인할 수 있었다.

• Sleep Medicine and Psychophysiology
• /
• v.7 no.1
• /
• pp.34-42
• /
• 2000

Objectives: Periodic limb movements in sleep(PLMS) is a moderately prevalent disorder, of which pathophysiology remains largely unknown. PLMS has been reported to be common in patients with obstructive sleep apnea syndrome(OSAS), but reports on their relationship have been inconsistent in previous studies. Inconsistency of results may be attributable to insufficient number of the study subjects. We attempted to explore the influence of OSAS on PLMS in a large number of subjects. Methods: Three hundred and twenty subjects(M : F=192:128) with PLMS, as identified by the nocturnal polysomnography, were studied. Sample mean age was 53.1(SD=15.1) years and their mean periodic limb movement index(PLMI) is 25.2/hr (SD=24.8). PLMS subjects were divided into two groups, based on the presence or absence of OSAS. Periodic limb movement indices and sleep parameters between two groups were analyzed to evaluate the effects of OSAS on PLMS. Results: Each of PLMI and PLMI with arousal(PLMAI) correlated positively with age. PLMI of men was larger than that of women (p<0.01). The presence of comorbid OSAS independently had influence on PLMI(t=-2.20, p<0.05), but not PLMAI. There were no significant differences between the two groups in their PLMI, PLMAI and sleep parameters. However, the two groups differed in PLMI-correlated sleep parameters. In PLMS subjects with comorbid OSAS, PLMI was negatively correlated with each of slow wave sleep time and REM sleep time. In subjects without comorbid OSAS, PLMI was negatively correlated with sleep efficiency. Conclusion: PLMS patients with OSAS turned out to have increased PLMI than those without OSAS We suggest that OSAS patients may have subtle autonomic arousals and these arousals could, in part, express themselves as PLM.

• Pediatric Gastroenterology, Hepatology & Nutrition
• /
• v.7 no.1
• /
• pp.61-73
• /
• 2004

Purpose: Liver function test abnormalities have been reported frequently in patients receiving total parenteral nutrition (TPN). In adults, it is known that liver complications decrease with the use of cyclic parenteral nutrition (CPN), especially if the shift to cycling was not too late. However, there are few studies about the effects of cycling on liver injury in children beyond the neonatal period. The aim of this study is to evaluate the effect of the early use of CPN on total parenteral nutrition induced hepatic dysfunction. Methods: Twelve sets of CPN in 11 children (2 months to 17 years) were included in this study. Data on underlying diseases, age, length of time on TPN, macronutrient intake, complications, and biochemical parameters were collected from clinical records. All children had received CPN in the early period of persistent transaminase elevation or cholestasis complicated by previous continuous PN. The duration of infusion off-time in CPN was 2 hours in patients less than 3 months of age and 4 hours in the older children. Results: All 12 cases showed elevated aminotransferase and 5 of them also showed cholestasis. Serum total bilirubin concentration was normalized in all 5 cases with median periods of 8 days (p<0.05) after initiation of CPN. ALT either decreased significantly or was normalized in all cases with median periods of 30 days (p<0.05) on CPN. The CPN was well tolerated without significant complication except for one case of hyperglycemia. Conclusion: The early use of cyclic parenteral nutrition had a beneficial effect in improving hepatic dysfunction complicated by TPN in children.

• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.24 no.2
• /
• pp.120-127
• /
• 2012

Exploratory data analysis was carried out by using the long-term wave climate data in Sokcho coastal zone. The main features found in this study are as follows. The coefficient of variations on the wave height and period are about 0.11 and 0.02, respectively. It also shows that the annual components of the wave height and period are dominant and their amplitudes are 0.24 m and 0.56 seconds, respectively. The amount of intra-annual variation range is about two times greater than that of the inter-annual variation range. The distribution shapes of the wave data are very similar to the log-normal and GEV(generalized extreme value) functions. However, the goodness-of-fit tests based on the KS test show as "rejected" for all suggested density functions. Then, the structure of the timeseries wave height data is roughly estimated as AR(3) model. Based on the wave duration results, it is clearly shown that the continuous and maximum duration is decreased as a power function shape and the total duration is exponentially decreased. Meanwhile, the environment of the Sokcho coastal zone is classified as a wave-dominated environment.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
• /
• v.13 no.4
• /
• pp.243-251
• /
• 2015

Nuclear power is currently the second largest power supply method in Korea and the number of nuclear power plants are planned to be increased as well. However, clear management policy for spent fuels generated from nuclear power plants has not yet been established. The back-end fuel cycle, associated with nuclear material flow after nuclear reactors is a collection of technologies designed for the spent fuel management and the spent fuel management policy is closely related with the selection of a nuclear fuel cycle. Cost is an important consideration in selection of a nuclear fuel cycle and should be determined by adding external cost to private cost. Unlike the private cost, which is a direct cost, studies on the external cost are focused on nuclear reactors and not at the nuclear fuel cycle. In this research, external cost indicators applicable to nuclear fuel cycle were derived and quantified. OT (once through), DUPIC (Direct Use of PWR SF in CANDU), PWR-MOX (PWR PUREX reprocessing), and Pyro-SFR (SFR recycling with pyroprocessing) were selected as nuclear fuel cycles which could be considered for estimating external cost in Korea. Energy supply security cost, accident risk cost, and acceptance cost were defined as external cost according to precedent and estimated after analyzing approaches which have been adopted for estimating external costs on nuclear power generation.

• Sleep Medicine and Psychophysiology
• /
• v.4 no.2
• /
• pp.147-155
• /
• 1997

To assess the reliability of chronobiological models of sleep/wake regulation, it is necerssary that the models predict the data which has been studied in sleep research, and they should be generalized across all ages. To date, many adult human data on such models have accumulated, yet it is evident that a comprehensive theory of the biorhythmic aspects of sleep/wake states has not established. Circadian rhythms such as the time going to bed, sleep onset, slow wave sleep pressure, periodicity of REM sleep, daytime performance, and early evening alertness are resumed everyday. Even in adult humans, sleep is inherently polyphasic. In both the disentrained and entrained states, naps when allowed tend to recur in a temporally lawful manner. The monophasic sleep pattern of most industrial societies therefore appears to be purely of social origin. The endogenous biorhythmic nature of circasemidian sleep tendency is supported by the ubiquity of the phenomenon across all ages. The NREM/REM sleep cycle within sleep with its inherent physiological, endocrine, and neurochemical fluctuations represents the best-documented ultradian sleep rhythms. Also, a daytime ultradian variation in sleepiness with a periodicity similar to nocturnal NREM/REM cycle(BRAC hypothesis) is suggested. This review article provides a brief synoptic review of the evidences for circadian, circasemidian, and ultradian sleep/wake rhythms, and then the authour will suggest the issues which expedite fuller modeling of sleep/wake system, to be further discussed.

• Journal of the Korea Institute of Building Construction
• /
• v.10 no.1
• /
• pp.193-198
• /
• 2010

This study aimed at presenting the improvement plan for estimation of the repair and replacement cycle to analyze these current problems by considering the repair and replacement cycle theoretically and examining estimation status of home and abroad, and then drawing implication and problem based on brainstorming and expert opinion. The findings of a study is as follows. First, the problem is, for the domestic, that there is no clear standard of division to the cycle of repair and replacement and the repair and replacement cycle considering capability to deal with the change by construction method, development of the function of material and the number of years of progress is not being applied. That is, an estimation of economical repair and replacement cycle which considers the case that a large scale repair with the level of remodeling is done between 25 years and 35 years is necessary. For estimating the repair and replacement cycle, foreign country is providing this according to the use or the level of function of a building, but it is not the case for the domestic. A characteristic of each building should be reflected and the standard of estimation of the repair and replacement cycle to new construction material or method should be prepared to improve this. In addition, the method of classification of the subject item for the repair and replacement is necessary to be reorganized to be able to apply the standard of initial construction item of a building. Also, it is considered that a service standard which can reset the repair and replacement cycle based on status of a building with escape from the existing definite setup of the repair and replacement cycle through the management of background data of the repair and replacement is going to be necessary.

• Journal of the Korean Society for Railway
• /
• v.20 no.5
• /
• pp.569-576
• /
• 2017

The electromagnetic valve of pneumatic doors of EMUs has a high failure rate due to air leakage because it supplies air on and off to operate the doors repeatedly. The electromagnetic valve is a very important safety component for which a very high reliability is required because failure makes it impossible to operate the passenger cars. However, domestic urban railway operators maintain electronic valves of the EMU door under a fixed cycle with a spare period according to the full overhaul cycle of the EMU. An improvement of the current maintenance cycle was suggested based on the reliability function and mission reliability. Using the statistical program MINITAB for the operational data of EMU line 6, we analyzed the characteristics of the fault distribution and derived the shape and scale parameters of the reliability function. If we limit the specific reliability probability to under a certain failure rate and calculate its statistical parameters, we can calculate the allowable inspection period with mission reliability. Through this study, we suggested a maintenance period based on RCM (reliability centered-maintenance) to improve the reliability of electromagnetic valves from 68% to 95%.

• Journal of Energy Engineering
• /
• v.25 no.2
• /
• pp.52-64
• /
• 2016

The production of nuclear energy from thorium which is non-fissile material was a main issue until the middle of 1970's, because of the thorium's abundance as energy resources, its capability of breeding fissile material U233, and the reduction of long-lived actinides. However, to use thorium as nuclear fuel, some obstacles such as the necessities of external neutron source and long-term neutron irradiation for effective breeding, and the production of high radioactive isotopes in the course of thorium breeding cycle should be overcome. The difficulties to resolve these cons of thorium cycle became the reason of interruption of the related researches in the middle of 1970's. But in the 21st century, the change of societal perspective regarding nuclear energy and the appearance of accelerator-driven nuclear reactor shift those cons into pros and rehabilitate the study of thorium. The high activity of thorium cycle turned out to be a good option as higher resistance and easier detectibility of nuclear proliferation and the employment of subcritical accelerator-driven reactor as external neutron sources is considered to enhance the nuclear safety. In this study we compare the thorium cycle with the currently-used uranium cycle and analyze the technical status and perspective of thorium researches which use accelerator-driven reactors.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.21 no.1
• /
• pp.439-447
• /
• 2020

Re-coating of the mirror is one of the important things to maintain the performance of a telescope. The metal coated on the mirror reflects light, and if the reflectance decreases, then the telescope's performance decreases, so the mirror must be periodically recoated. It is important to predict re-coating cycles for military telescopes and to develop maintenance plans not only for performance, but also for the telescope's availability for missions and the maintenance costs for long-term use. However, most similar telescopes used for astronomy research determine recoating cycles based on experience and operating conditions, and not for prediction of recoating. Therefore, this study predicts the cleaning cycles and re-coating cycles of a military telescope's mirror by using simulation. First, this study analyzed similar cases of domestic and foreign astronomy research institutes and the study also reviewed the need for re-coating and predicting re-coating cycles. Second, this study developed simulation for predicting cleaning and re-coating cycles according to data analysis and modeling. Finally, the study predicts cleaning cycles and re-coating cycles according to varying reflectance reduction (5%, 10%, 15%, 20%) and cleaning conditions (per 3 months, 6 months, 1 year and 2 years). As a result, this study suggests reference criteria to develop the planning for military telescopes and their maintenance.