• Geomechanics and Engineering
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• 제25권2호
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• pp.89-98
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• 2021

The paper presents an experimental study on the strength behaviour of a coral gravelly sand from Vietnam subjected to monotonic and cyclic loading. A series of direct shear tests were carried out to investigate the shear strength behaviour and the factors affecting the shear strength of the sand such as relative density, cyclic load, amplitude of the cyclic load and loading rate. The study results indicate that the shear strength parameters of the coral gravelly sand include not only internal friction angle but also apparent cohesion. These parameters vary with the relative density, cyclic load, the amplitude of the cyclic load and loading rate. The shear strength increases with the increase of the relative density. The shear strength increases after subjecting to cyclic loading. The amplitude of the cyclic load affects the shear strength of coral gravelly sand, the shear strength increases as the amplitude of the cyclic load increases. The loading rate has insignificantly effect on the shear strength of the coral gravelly sand.

• 대한토목학회논문집
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• 제41권6호
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• pp.637-644
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• 2021

대부분 동적 성능 평가는 반복 가력 실험을 수행함으로써 구조물의 동적 응답을 평가할 수 있다. 일반적으로 강재는 재하속도 의존성 재료로 알려져 있으며 기둥 부재의 횡방향인 수평방향 가력 시 기둥 부재의 축력인 수직하중이 작용하면 부재의 응답에 영향을 미친다. 하지만, 강재 기둥 구조물의 실험 시 수평 및 수직하중을 동시에 제어하는 것이 어려워 관련 연구는 부족한 실정이다. 본 연구에서는 기둥 부재를 ATS Compensator와 FLB 시스템을 이용하여 수평 및 수직하중을 고속으로 제어하였다. 실험은 H-형 구조용 압연강재인 SS275을 이용하여 수직 하중을 제어하면서 여러 속도로 단조 및 반복 가력 실험을 수행하고 부재의 항복 하중을 비교하였다. 또한, 유한요소해석 시 재하속도에 따라 새로운 항복 응력을 제안하고 수치해석을 통해 비교하였다.

• ETRI Journal
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• 제32권5호
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• pp.657-664
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• 2010

Many embedded multimedia systems employ special hardware blocks to co-process with the main processor. Even though an efficient handling of such hardware blocks is critical on the overall performance of real-time multimedia systems, traditional real-time scheduling techniques cannot afford to guarantee a high quality of multimedia playbacks with neither delay nor jerking. This paper presents a hardware-aware rate monotonic scheduling (HA-RMS) algorithm to manage hardware tasks efficiently and handle special hardware blocks in the embedded multimedia system. The HA-RMS prioritizes the hardware tasks over software tasks not only to increase the hardware utilization of the system but also to reduce the output jitter of multimedia applications, which results in reducing the overall response time.

• 전기학회논문지
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• 제60권1호
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• pp.193-200
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• 2011

This paper presents an optimal checkpoint strategy for fault-tolerance in real-time systems. In our environment, multiple real-time tasks with arbitrary periods are scheduled in the system by Rate Monotonic (RM) algorithm, and checkpoints are inserted at a constant interval in each task while the width of interval is different with respect to the task. We propose a method to determine the optimal checkpoint interval for each task so that the probability of completing all the tasks is maximized. Whenever a fault occurs to a checkpoint interval of a task, the execution time of the task would be prolonged by rollback and re-execution of checkpoints. Our scheme includes the schedulability test to examine whether a task can be completed with an extended execution time. A numerical experiment is conducted to demonstrate the applicability of the proposed scheme.

• 전기학회논문지
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• 제61권1호
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• pp.148-154
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• 2012

For a successful checkpointing strategy, we should place checkpoints so as to optimize fault-tolerance capability of real-time systems. This paper presents a novel scheme of checkpoint placement for real-time systems with periodic multi-tasks. Under the influence of transient faults, multi-tasks are scheduled by the Rate Monotonic (RM) algorithm. The optimal checkpoint intervals are derived to maximize the probability of task completion. In particular, this paper is concerned about the general case that the deadline of a task is longer than the period. Compared with the special condition that the deadline is equal to or less than the period, this general case causes a more complicate test procedure for schedulability of the RM algorithm with respect to a given set of checkpoint re-execution vectors. The probability of task completion is also derived in a more complex form. A case study is given to show the applicability of the proposed scheme.

• Geomechanics and Engineering
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• 제22권6호
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• pp.475-488
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• 2020

The recent increase in the use of Expanded Polystyrene (EPS) geofoam in construction and geotechnical projects has driven researchers to investigate its behavior, more deeply. In this paper, a series of experimental tests to investigate the stress-strain behavior and the mechanical properties of EPS blocks, under monotonic axial loading are presented. Four different densities of cylindrically shaped EPS with different dimensions are used to investigate the effects of loading rate, height and diameter, as well as the influence of the density of EPS on the stress-strain response. The results show that increasing the height of the EPS samples leads to instability of the sample and consequent lower resistance to the applied pressure. Large EPS samples show higher Young's modulus and compressive resistance due to some boundary effects. An increase in the rate of loading can increase the elastic moduli and compressive resistance of the EPS geofoam samples, which also varies depending on the density of the samples. It was also determined that the elastic modulus of EPS increases with increasing EPS density. By implementing an efficient numerical procedure, the stress-strain response of EPS geofoam samples can be reproduced with great accuracy. The numerical analysis based on the proposed method can used to evaluate the effect of different factors on the behavior of EPS geofoam.

• 한국콘텐츠학회논문지
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• 제4권2호
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• pp.50-60
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• 2004

오늘날 대부분의 내장형 시스템은 목적상 많은 기능뿐만 아니라 실시간성도 함께 요구하고 있다. 특히, 경성 실시간 시스템에서는 주기 태스크들의 엄격한 마감시간 보장이 시스템의 성능을 좌우한다. 본 논문에서는 CPU 이용률이 놓아 비율단조 기법으로는 마감시간을 보장 할 수 없는 주기 태스크 셋을 위한 비율단조 기반의 스케줄러를 설계하고 구현한다. 이 스케줄러는 확장된 스케줄 가능성 검사를 실시하여, 태스크 셋의 수행 전태스크들의 공통주기를 찾아 마감시간 우선 기법을 기반으로 마감시간 보장 수행패턴을 생성한다. 이렇게 생성된 수행패턴을 참조하여 결정된 우선순위에 따라 태스크 셋을 실행하게 된다. 마감시간 우선 기법을 기반으로 생성된 패턴은 그 특성에 따라 CPU 이용률을 100% 까지 가능하게 하며, 수행패턴을 참조하여 수행함으로써 동적 우선순위 할당 기법의 단점인 실행시간 스케줄링 오버헤드를 없앨 수 있다.

• Transactions on Electrical and Electronic Materials
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• 제8권6호
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• pp.229-233
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• 2007

In this study, we carried out an investigation of the etching characteristics(etch rate, selectivity) of $HfO_2$ thin films in the $CH_4/Ar$ inductively coupled plasma. It was found that variations of input power and negative dc-bias voltage are investigated by the monotonic changes of the $HfO_2$ etch rate as it generally expected from the corresponding variations of plasma parameters. At the same time, a change in either gas pressure or in gas mixing ratio result in non-monotonic etch rate that reaches a maximum at 2 Pa and for $CH_4(20%)/Ar(80%)$ gas mixture, respectively. The X-ray photoelectron spectroscopy analysis showed an efficient destruction of the oxide bonds by the ion bombardment as well as showed an accumulation of low volatile reaction products on the etched surface. Based on these data, the ion-assisted chemical reaction was proposed as the main etch mechanism for the $CH_4-containing$ plasmas.

• 응용통계연구
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• 제22권3호
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• pp.541-551
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• 2009

Generalized processor sharing(GPS) service policy is a scheduling algorithm to allocate the bandwidth of a queueing system with multi-class input traffic. In a queueing system with single-class traffic, the stationary queue length becomes larger stochastically when the bandwidth (i.e. the service rate) of the system decreases. For a given GPS server, we consider the similar problem to this. We define the monotonicity for the head of the line processor sharing(HLPS) servers in which the units in the heads of the queues are served simultaneously and the bandwidth allocated to each queue are determined by the numbers of units in the queues. GPS is a type of monotonic HLPS. We obtain the HLPS server whose queue length of a class stochastically bounds upper that of corresponding class in the given monotonic HLPS server for all classes. The queue lengths process of all classes in the obtained HLPS server has the stationary distribution of product form. When the given monotonic HLPS server is GPS server, we obtain the explicit form of the stationary queue lengths distribution of the bounding HLPS server. Numerical result shows how tight the stochastic bound is.

• 한국컴퓨터정보학회논문지
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• 제10권6호
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• pp.27-36
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• 2005

유한고장 속성을 가진 비동질적인 포아송 과정에 기초한 모형들에서 잔존 결함 1개당 고장 발생률은 일반적으로 상수, 흑은 단조증가 및 단조 감소 추세를 가지고 있다. 본 논문에서는 잔존 결함 1개당 고장 발생률이 단조증가(혹은, 단조감소) 속성을 가진 일반화 감마분포를 이용한 신뢰성 모형을 제안하였다. 일반화 감마분포를 이용한 유한 속성 비동질적 모형에 대한 모수추정은 고장 간격시간으로 구성된 실측자료를 이용하여 모수 추정을 수행하였다. 일반적 감마분포 형상모수의 제안을 위하여 특수한 형태를 적용하였다. 본 논문에서는 기존 모형의 분포를 적용하고 추가적인 소프트웨어 고장 해석을 위하여 감마 및 와이블 분포를 이용하였다. 일반화 감마 분포모형의 고장자료분석을 위하여 산술적 및 라플라스 검정, 적합도 검정, 편의 검정 등을 이용하였다.