• 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.

• East Asian Economic Review
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• 제24권4호
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• pp.417-440
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• 2020

The coronavirus pandemic of 2019-20 confronted fiscally dominant regimes around the world with the question of whether the large deficits caused by the health crisis should be monetized or financed by issuing debt. The unpleasant monetarist arithmetic of Sargent and Wallace (1981) states that in a fiscally dominant regime tighter money now can cause higher inflation in the future. In spite of the qualifier 'unpleasant,' this result is positive in nature, and, therefore, void of normative content. I analyze conditions under which it is optimal in a welfare sense for the central bank to delay inflation by issuing debt to finance part of the fiscal deficit. The analysis is conducted in the context of a model in which the aforementioned monetarist arithmetic holds, in the sense that if the government finds it optimal to delay inflation, it does so knowing that it would result in higher inflation in the future. The central result of the paper is that delaying inflation is optimal when the fiscal deficit is expected to decline over time.

• 전자공학회논문지A
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• 제31A권7호
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• pp.1-16
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• 1994

In this paper, we propose a new multiple access scheme for VSAT(Very Small Aperture Terminal) data communications. The proposed scheme has better performance in terms of delay throughput than Controlled Multiaccess Scheme which has excellent performance. The proposed scheme use the spare reservation method, adaptation method to offered load, and fixed bandwidth reservation method. In this paper, we analyze the performance using simple queueing model and present the simulation results. When network traffic is very low, the new scheme and the controlled multiaccess scheme have almost the same access delay characteristic. As the network load becomes higher, the new scheme's access delay gain becomes larger. Futhermore, even when the network traffic is very high it is possible to access satellite link within the delay similar to one round-trip delay. In addition to access delay performance enhancement, the new scheme has facility that supports fixed bandwidth reservation. So it shows more enhanced performance in the environment that stream traffic is dominant such as in VSAT communication environment.

• 한국건설관리학회논문집
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• 제16권3호
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• pp.165-176
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• 2015

국내 건설산업의 침체가 장기화됨에 따라 대형 건설업체를 중심으로 국내사업 비중이 줄고 상대적으로 해외사업의 비중이 증가되고 있으며, 중견 건설업체 및 특수기술을 가지고 있는 전문건설업체의 해외프로젝트 수행이 확대되고 있다. 이러한 해외건설공사 수행의 중요성이 부각되고 있는 최근 상황에서 해외 대형건설공사에서 일반적으로 발생되고 있는 공기지연에 대한 적극적 대응이 성공적 프로젝트관리의 중요한 이슈로 제기되고 있다. 본 연구에서는 해외 대형프로젝트의 공기지연 클레임의 공기연장기간을 입증하는데 활용되는 기존 공기연장기간 분석방법의 실무적 적용상의 문제점을 제기하였다. 제시된 문제점을 해결하기 위한 개선방법으로 1)클레임의 명확성을 확보하기 위해 지연영향력 분석이전에 주요지연(dominant delay)를 선정하는 절차를 갖는 개선개념과 2)Time Impact Analysis을 시행을 위한 분석구간의 설정방법에 대한 개선개념을 제시하였다. 본 연구에서 제시한 공기연장기간 분석방법을 실제 해외 대형건설공사의 공기지연 클레임 사례에 적용함으로써, 제안한 개선안의 실무적용에 대한 유효성을 입증하였다. 국내의 해외 대형공사 공기지연 클레임을 담당하고 있는 기술자들이 본 연구에서 제안한 방법들을 공기지연 클레임 추진 및 관련자 협상 등과 같은 실무 추진에 참고하고 활용함을 통해, 공기연장기간 입증관련 클레임의 협상실패로 인한 리스크와 후속적인 분쟁 및 회사의 경영손실 리스크를 최소화 하는데 도움이 될 것이라고 사료된다.

• International Journal of Control, Automation, and Systems
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• 제3권4호
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• pp.640-645
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• 2005

Closed-loop model-free optimization of positive feedback time delay controllers for dominant time delay systems is presented. Iterative feedback tuning (IFT) is applied to the tuning of positive feedback time delay controller. Three experiments are carried out to perform the model-free gradient descent optimization. The initial controller parameters and duration in specifying the cost function are suggested. The effects of step size, filter function and time weighting function on the performance of the optimized controlled are given. Simulation and experimental studies are included to demonstrate the effectiveness of the tuning scheme.

• 한국분무공학회지
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• 제25권3호
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• pp.119-125
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• 2020

In this paper, we used Helmholtz solver based on 3D finite element method to quantitatively analyze the effects of change of gain, time delay and time delay spread, which are the main variables of flame transfer function, on combustion instability in gas turbine combustor. The effects of the variable of flame transfer function on the frequency and growth rate, which are the main results of combustion instability, were analyzed by applying the conventional heat release fluctuation model and modified one considering the time spread. The analysis results showed that the change of gain and time delay in the same resonance mode affected the frequency of the given resonance modes as well as growth rate of the feedback instability, however, the effect of time delay spread was not relatively remarkable, compared with the dominant effect of time delay.

• 오토저널
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• 제11권5호
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• pp.55-64
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• 1989

The effect of discharge have been investigated for condition of spark in a multiple spark ignition engine, as the spark duration, capacitive and inductive discharge energy were calculated for condition of spark by ignition wave and energy formula. The useful portion of spark discharge is divided into capacitance portion and inductance portion. It was found that capacitive discharge energy and spark duration were increased according to increasing number of spark, and inductive discharge energy was increased according to increasing spark interval. Therefore engine torque was increase and lean misfire limit was extended comparing with the standard ignition system. It found that spark energy was discharged within ignition delay period availability acted on the formation and growth of flame kernel, and total spark energy was increased according to increasing number of spark times, but discharged spark energy after ignition delay became unavailable energy. And the capacitive discharge energy has the dominant effect for stoichiomeric or not very rich air-fuel mixture but inductive discharge energy has the dominant effect for lean air-fuel mixture.

• 터널과지하공간
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• 제16권4호
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• pp.326-333
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• 2006

본 연구에서는 측정된 진동파형을 토대로 다른 발파공들로부터 간섭을 받지 않은 단일공의 진동파형을 분리 하였고 이를 FFT 주파수 분석을 통하여 우세 주파수를 분석하였다. 또한 진동의 지속시간과 발파공수가 PPV에 미치는 영향을 검토하기 위해 분리된 진동파형을 $2{\sim}15$공으로 발파공수를 조절하면서 $1{\sim}80ms$까지 1 ms의 간격으로 지연시차에 변화를 주며 발파진동에 중첩 모델링을 실시하였다. 그 결과 진동의 지속시간이 길어질수록 다른 발파공들로부터 간섭받지 않기 위한 지연시차 또한 길어졌고 동일 지연시차 내에서의 발파공 수에 관한 영향은 크게 나타나지 않았다.

• 한국시스템다이내믹스연구
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• 제5권1호
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• pp.127-142
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• 2004

Feedback loop dominance is a key concept to understand structural driving forces of system behavior. In this paper, we propose two kinds of shifts in dominant feedback loops: continuous shifts (CS) and discrete shifts (DS). With the help of questionnaires, we verified three hypotheses regarding cognitive biases in perceiving the shifts in dominant feedback loops: 1) failure in perceiving continuous shifts, 2) tendency of decision making based on discrete shifts, and 3) different perception on the dominant feedback loops between level variables and rate variables. We discussed the implication of these cognitive biases on time delay and timing strategy in decision-making processes.

• 대한전자공학회논문지SD
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• 제41권6호
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• pp.81-90
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• 2004

집적회로 시스템이 고집적화 됨에 따라, 연결선은 회로 전체 성능을 결정하는 중요한 요소가 되었다. 버퍼 삽입은 연결선의 성능 향상의 효과적인 방법이다. 하나의 신호선이 허용 범위를 넘는 전달지연시간을 가질 때, 우리는 하나 또는 그 이상의 버퍼를 삽입하여 지연시간을 줄일 수 있다. 이제까지 많은 연구들에서 하나의 신호선에 대해 버퍼를 삽입하는 방법을 개발하였으나, 우리는 여러 신호선에 동시에 버퍼 위치를 찾아 버퍼를 삽입하는 방법을 연구하였다 이 방법은 여러 개의 신호선에 버퍼를 삽입하는 위치를 찾는 어려움을 효과적인 방법을 이용하여 그 위치를 결정한다. 또한 본 연구에서는 fan-out이 여럿인critical path에 대해서도 버퍼 삽입으로 지연시간을 최적화하는 기술을 개발하였다. 이 방법은 Elmore Delay 모델을 이용하여 지연시간을 계산하고 각 신호선에 지연시간을 최적화 할 수 있는 버퍼를 결정한다.