• Journal of the Korean Society for Railway
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• v.20 no.3
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• pp.349-355
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• 2017

Failures of railway systems can result in train delays or accidents, and therefore high reliability is required to ensure safety of railway systems. To improve reliability, railway systems are designed with redundant systems so that the standby system will continue to function normally even if the primary system fails. Generally, overall system reliability can be evaluated by the reliabilities of the parts of the whole system and the reliability of the redundant system considering common failures in case of each system is not conform physical, functional and process independent. In this study, the reliability of the hot-standby sparing system is analyzed the independent systems and dependent systems with common failures. The reliability for the standby system can be effectively analysed using Markov models, which can model the redundant configuration and the state transition.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.08a
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• pp.182.2-182.2
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• 2013

최근 산화아연이나 산화주석을 기반으로 한 산화물 박막 트랜지스터의 연구가 활발히 진행중이다. 2004년 Hosono 그룹에서 비정질 InGaZnO (IGZO) 박막을 이용한 TFT소자 제작을 보고하고 우수한 특성을 확인 후 산화물 TFT 소자기술에 대한 전 세계적인 연구개발의 발판이 마련되었다. 그러나 다성분계 화합물로 이루어진 산화물 반도체의 경우 복잡한 성분 조합과 조절이 어렵고, 장비의 제약으로 상용화에 어려움을 겪고 있다. 산화아연의 경우 증착시 쉽게 결정화가 이루어져 대면적 균일성을 확보하기 어렵고, 결정립계에 의한 이동도 저하, DC 신뢰성 저하의 문제가 발생한다. 이에 비해 산화주석의 경우 증착공정에 따라 비정질상과 결정립상을 조절할 수 있다. 하지만, 현재까지 발표된 산화주석 기반의 박막 트랜지스터는 내부 캐리어의 조절이 상대적으로 어려운 단점이 보고되었다. 본 연구에서는 산화 주석기반의 박막 트랜지스터를 제작하고 이에 Zr이온을 도핑하여 소자 특성을 개선시키고 동작모드를 조절하는 연구를 진행하였다. Bottom gate 형식의 ZrSnO TFT를 제작하였고 전이 특성을 살펴본 결과 Zr의 함량이 늘어날수록 이동도는 감소하는 경향이 나타났다. 또한 Zr의 미량 함량에도 불구하고 산소결핍에 의한 캐리어 생성을 억제하여, 소자 특성을 공정조건에 따라 조절할 수 있는 가능성을 확인 했다.

• Journal of KIISE:Computer Systems and Theory
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• v.34 no.8
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• pp.367-376
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• 2007

In this paper, we introduce an application-specific and adaptive power management technique for portable systems that support dynamic voltage scaling (DVS). We exploit both the idle time of multitasking systems running soft real-time tasks as well as memory- or CPU-bound code regions. Detailed power and execution time profiles guide an adaptive power manager (APM) that is linked to the operating system. A post-pass optimizer marks candidate regions for DVS by inserting calls to the APM. At runtime, the APM monitors the CPU's performance counters to dynamically determine the affinity of the each marked region. for each region, the APM computes the optimal voltage and frequency setting in terms of energy consumption and switches the CPU to that setting during the execution of the region. Idle time is exploited by monitoring system idle time and switching to the energy-wise most economical setting without prolonging execution. We show that our method is most effective for periodic workloads such as video or audio decoding. We have implemented our method in a multitasking operating system (Microsoft Windows CE) running on an Intel XScale-processor. We achieved up to 9% of total system power savings over the standard power management policy that puts the CPU in a low Power mode during idle periods.

• Journal of Energy Engineering
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• v.28 no.4
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• pp.103-110
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• 2019

The domestic innovative power reactor named iPOWER will employ the passive molten corium cooling system(PMCCS) to cool down and stabilize the core melt in the severe accident. The final design concept of the PMCCS is yet to be determined, but the in-vessel retention through external reactor vessel cooling has been also considered as a viable strategy to cope with the severe accident. In this study, the two-phase natural circulation flow established between the reactor vessel and the insulation was simulated using a thermal-hydraulic system code, MARS-KS. The flow path of cooling water was modeled with one-dimensional nodes, and the boundary condition of the heat load from the molten core was defined to estimate the naturally-driven flow rate. The evolution of major thermal-hydraulic parameters were also evaluated, including the temperature and the level of cooling water, the void fraction around the lower head of the reactor vessel, and the heat transfer mode on its external surface.

• Korean Journal of Materials Research
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• v.8 no.8
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• pp.693-698
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• 1998

The effects of $AI_{2}$$O_{3}$ and the ratio of $Na_2O/B_2O_3$ on the phase separation and optical properties of sodium borosilicate glass film fabricated by AFD(Aerosol Flame Deposition) were investigated. When AI,O, of 6wt% was added to $66SiO_2-27B_2O_3-7Na_2O$ the clear glass film without any crystallization was produced under air-quenching condition after consolidation. As the amount of $AI_{2}$$O_{3}$ increased from 1.5 to 6.0 wt% the refractive index linearly increased from 1.4610 to 1.4701, and the difference of TE and TM mode causing by residual stress in film increased gradually. However, the difference of TE and TM mode to reveal birefringence could be minimized by annealing below the glass transition temperature after consolidation and air quenching. On the other hand. as the ratio of $Na_2O/B_2O_3$ increased the refractive index and birefringence of glass film tended to increase, but the measurement of their values were not available at over the critical ratio of $Na_2O/B_2O_3$, because of the cloudiness due to crystallization. The phase separation was greatly accelerated with increasing the ratio of $Na_2O/B_2O_3$.