• 대한전기학회논문지:시스템및제어부문D
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• 제54권6호
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• pp.390-395
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• 2005

Sunspots are dark areas that grow and decay on the lowest level of the sun that is visible from the Earth. Shot-term predictions of solar activity are essential to help plan missions and to design satellites that will survive for their useful lifetimes. This paper presents a parallel-structure fuzzy system(PSFS) for prediction of sunspot number time series. The PSFS consists of a multiple number of component fuzzy systems connected in parallel. Each component fuzzy system in the PSFS predicts future data independently based on its past time series data with different embedding dimension and time delay. An embedding dimension determines the number of inputs of each component fuzzy system and a time delay decides the interval of inputs of the time series. According to the embedding dimension and the time delay, the component fuzzy system takes various input-output pairs. The PSFS determines the final predicted value as an average of all the outputs of the component fuzzy systems in order to reduce error accumulation effect.

• Kyungpook Mathematical Journal
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• 제57권2호
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• pp.265-285
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• 2017

In this article, a mathematical model is proposed and analyzed to study the delayed dynamics of a system having a predator and two preys with distinct growth rates and functional responses. The equilibrium points of proposed system are determined and the local stability at each of the possible equilibrium points is investigated by its corresponding characteristic equation. The boundedness of the system is established in the absence of delay and the condition for existence of persistence in the system is determined. The discrete type gestational delay of predator is also incorporated on the system. Further it is proved that the system undergoes Hopf bifurcation using delay as bifurcation parameter. This study refers that time delay may have an impact on the stability of the system. Finally Computer simulations illustrate the dynamics of the system.

• 보건행정학회지
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• 제13권4호
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• pp.115-130
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• 2003

Reperfusion delay in patients with acute myocardial infarction leads to increased morbidity and mortality. We sought to measure the rates of reperfusion delay and to identify factors associated with reperfusion delay after arrival to hospitals. We included 360 patients who had acute myocardial infarction with ST-elevation or left bundle branch block on electrocardiogram and received reperfusion therapy from the three participating academic medical centers from 1997 to 2000. Through retrospective chart review, we collected data about time to reperfusion therapy, patient and hospital factors potentially associated with reperfusion delay. Factors independently associated with reperfusion delay were determined by logistic regression analysis. Median door­to­needle time was 60.0 minutes, and median door­to­balloon time was 102.5 minutes. According to recommendation of the American College of Cardiology/American Heart Association Guidelines, 226 out of 264(85.6％) of thrombolytic patients and 43 out of 96(44.8％) percutaneous transluminal coronary angioplasty(PTCA) patients experienced reperfusion delay. The significant factors associated with delay were type of reperfusion therapy, patient factors including hypertension and delayed symptom onset to presentation(>4 hours), and hospital factors including nocturnal presentation(6pm∼8am), weekend, and an individual hospital. A significant proportion of patients experienced reperfusion delay. The identified predictors of reperfusion delay may help design a hospital system to reduce the delay in reperfusion therapy

• 조명전기설비학회논문지
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• 제19권7호
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• pp.15-19
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• 2005

시간지연이 존재하는 시스템의 제어기 설계에 많이 사용되는 Smith Predictor는 플랜트와 모델이 완전히 일치해야만 특성방정식에서 시간지연을 제거 할 수 있기 때문에 실제 공정에서는 적용하기가 매우 어렵다. 본 논문에서는 Smith Predictor의 모델을 플랜트와 일치한 식이 아닌 시간지연을 포함한 2차식 형태로 제안하여 큰 시간지연에서의 응답특성을 향상 시켰다. PI 제어기의 적분상수의 범위를 제안하였다.

• Transactions on Control, Automation and Systems Engineering
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• 제2권3호
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• pp.149-156
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• 2000

Time delay observer (TDO), thanks to the time delay control (TDC) concept, requires little knowledge of a plant model, and hence is easy to design, robust to parameter variation and computationally efficient, yet can reconstruct states rather reliable for nonlinear plant. In this paper, we propose an improved version of TDO that solves two problems inherent in TDO as follows: TDO displays large reconstruction errors due to low-frequency uncertainty and has some restrictions on selecting its gains. By introducing a low pass filter and a state associated with it, we obtain an enhanced time delay observer (ETDO). This observer turns out to have smaller reconstruction errors than those of TDO and not to have any restriction on selecting its gains, thereby solving the problems. Through performance comparison by transfer function and simulation, we validate the analysis results of two observers (TDO and ETDO) and evaluate the performances. Finally, through experiments on BLDC motor system, the analysis results are clearly conformed.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2005년도 ICCAS
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• pp.1955-1959
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• 2005

This paper presents a systematic analysis and a simple design of a robust adaptive control law for a class of non linear systems with modeling errors and a time-delay input. The theory for designing a robust adaptive control law based on input- output feedback linearization of non linear systems with uncertainties and a time-delay in the manipulated input by the approach of parameterized state feedback control is presented. The main advantage of this method is that the parameterized state feedback control law can effectively suppress the effect of the most parts of nonlinearities, including system uncertainties and time-delay input in the pp-coupling perturbation form and the relative order of non linear systems is not limited.

• Smart Structures and Systems
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• 제8권5호
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• pp.449-470
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• 2011

During the last thirty years many structural control concepts have been proposed for the reduction of the structural response caused by earthquake excitations. Their research and implementation in practice have shown that seismic control of structures has a lot of potential but also many limitations. In this paper the importance of two practical issues, time delay and saturation effect, on the performance of controlled structures, is discussed. Their influence, both separately and in interaction, on the response of structures controlled by a modified pole placement algorithm is investigated. Characteristic buildings controlled by this algorithm and subjected to dynamic loads, such as harmonic signals and actual seismic events, are analyzed for a range of levels of time delay and saturation capacity of the control devices. The response reduction surfaces for the combined influence of time delay and force saturation of the controlled buildings are obtained. Conclusions regarding the choice of the control system and the desired properties of the control devices are drawn.

• 산업경영시스템학회지
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• 제28권4호
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• pp.14-19
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• 2005

In general, cell transmission delay is more sensitive for real time video service rather than cell losses in a wireless ATM network. Existing handoff schemes, which are emphasizing the prevention of cell losses, have limitations in cell transmission delay to satisfy QoS. In this paper, we propose a scheme to minimize transmission delay generated during the handoff and to maintain the sequence of cells. Transmission delay can be reduced by transmitting ATM cells with low CLP(i.e., CLP=0) prior to others and by discarding cells with high CLP(i.e., CLP= 1). The simulation results show that the proposed scheme is suitable for delay sensitive real time VBR service as well as fast handoff by giving high CLP to less meaningful MPEG frames.

• 한국항행학회논문지
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• 제22권6호
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• pp.630-635
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• 2018

본 논문에서는 시변 지연이 있는 선형 이산 시스템에 비구조화된 불확실성이 존재하는 경우에 대하여 시스템의 안정성을 다룬다. 고려된 시스템은 지연 없는 상태변수와 지연 상태 변수에 대한 시스템 행렬들은 시불변이나 지연시간이 구간범위에서 시변으로 변동하고, 크기에 대한 정보만을 얻을 수 있는 비구조화된 비선형 불확실성이 있는 시스템이다. 기존의 많은 결과들은 시변지연과 비구조화된 불확실성을 동시에 고려하지 못하고 한 가지 요소만 고려하여 연구되었다. 본 논문에서는 이 두 가지 요소를 모두 고려하여 새로운 안정조건을 도출하였고, 한 가지 요소만 고려한 기존 연구 결과와 비교하였다. 새로운 안정조건은 기존의 결과를 포함하는 매우 효과적인 수식으로 제안되며, 이는 복잡한 선형행렬부등식 혹은 리아프노프 방정식 등과 같은 복잡한 수치계산을 요구하지 않는 간단한 부등식이다. 수치예제를 통하여 제안된 안정조건이 기존의 결과들을 포함할 수 있음을 보이고 확장성과 효용성이 우수함을 확인한다.

• Journal of Welding and Joining
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• 제17권5호
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• pp.61-68
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• 1999

For the last two decades, waveform control techniques have been successively developed and applied for the inverter welding machines resulting in the substantial reduction of spatter generated in CO₂ welding. One of the constituents commonly involved in those techniques is to delay the instant of current increase to some extent after the initiation of short-circuiting. Although this technique has been known to be quite effective in reducing the spatter generation through the suppression of is instantaneous short circuiting, the delay time necessary for minimum spatter has not been clearly understood. In this study, the control system for varying the delay time was constructed so that the spatter generation rates could be measured over a wide range of delay time, 0.29-2.0 msec. As a result of this study, it was demonstrated that spatter generation rate(SGR) sharply decreased at delay time of 0.6 msec and longer accompanied with the change in characteristics of short circuit mode from the instantaneous short-circuiting(ISC) dominant to normal short-circuiting(NSC) dominant. Another feature that have been found in current waveform of over 0.6msec was the creation of current pulse right after the arc reignition stage. Because of this current pulses weld pool oscillated in wave-like fashion and it looks like to play an important role in developing short circuiting between electrode and weld pool.