• 한국통신학회논문지
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• 제28권7A호
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• pp.557-562
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• 2003

An output multiplexer of manifold type is widely used in a recent satellite transponder for its mass and volume reduction. For correct operation, the filters of such a multiplexer must be singly terminated. In this paper, a simple synthesis method of a 6-pole dual-mode singly-terminated filter is described. From the transfer function of the filter, network parameters such as in/output terminations and coupling coefficients are obtained easily without complicated matrix algebra such as orthogonal projection and similarity transformation. Two different-structure filters are taken into consideration and the network parameters of each filter have been extracted from the same transfer function. It is shown that the responses of two filters are same to each other since their network parameters are obtained from the same transfer function. The method described in this paper can be applied to the other degree singly terminated filter.

• 한국항공우주학회지
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• 제32권10호
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• pp.102-111
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• 2004

본 논문에서는 와류분사기를 가진 액체로켓엔진용 축소형 연소기의 설계/제작/시험에 대해 기술하였다. 와류분사기는 내부에 액체산소 외부에 케로신을 공급하여 노즐 외부에서 혼합하는 구조를 가지고 있다. 축소형 연소기는 분사기 헤드, 삭마 냉각방식의 내열재 연소실 그리고 물냉각 노즐로 구성되어 있다. 분사기 헤드는 18 개의 주 분사기, 하나의 중앙 분사기, 연료 메니폴드, 산화제 메니폴드 그리고 추진제 분배기 등으로 구성되어 있다. 축소형 연소기 제작 후 수류시험 및 점화시험을 거쳐 설계점 및 탈설계점에서의 연소시험을 성공적으로 수행하였다. 연소시험결과 분사기 차압은 수류시험시의 값과 비슷하였고 연소효율은 목표치보다 높게 나왔으며, 정상연소시 동압의 진폭은 규격조건을 만족하였고 고주파 연소 불안정은 발생하지 않았다.

• 한국추진공학회지
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• 제11권5호
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• pp.72-77
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• 2007

액체로켓엔진용으로 내부혼합 동축 와류형 분사기를 장착한 축소형 연소기에 대한 설계 및 연소시험결과를 기술하였다. 추진제는 액체산소 및 케로신이며 연소기는 분사기 헤드, 삭마냉각방식의 연소실 그리고 물냉각 노즐부로 구성되어 있다. 분사기 헤드는 액체산소 매니폴드, 연료 매니폴드, 중앙 분사기 그리고 내부혼합 형태의 18개 분사기로 이루어졌다. 축소형 연소기 연소시험은 성공적으로 이루어졌으며, 분사기의 손상이 발생하지 않았고 연소특성속도는 설계점에서 1756 m/sec을 나타내었다. 고주파 연소불안정은 나타나지 않았지만 탈설계점에서 압력의 저주파 섭동이 기준치를 넘는 결과를 보여주었다.

• 한국가스학회지
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• 제16권3호
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• pp.48-53
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• 2012

이 논문의 목적은 LPG 자동차의 액상 분사시스템에 관련된 고장사례를 연구하는 것이다. LPi 분사시스템인 인젝터를 점검한 결과, 인젝터에 카본이 누적되어 운전 중에 간헐적으로 연료를 분사하는 인젝터의 미세한 홀을 막아 연비를 5% 정도 떨어뜨리는 것으로 확인되었다. 엔진의 공회전을 조절하는 시스템인 공회전 조절장치 부품과 엔진에 공기를 공급하는 시스템인 스로틀 보디에 카본이 퇴적되어 공기의 흐름을 간섭함으로써 연비가 7% 악화된 것을 확인되었다. 엔진의 흡기 매니폴드 개스킷의 일부가 찢어져, 실린더 헤드와 실린더 블록의 밀착성이 약화되어 흡기행정에서 외부의 공기가 이 틈새로 간헐적으로 유입되면서 증가된 공기량만큼 연료량의 증가를 가져와 엔진의 회전수가 증가하여 부조화 현상이 발생되어 정상적인 상태보다 연비가 3% 정도 악화된 것으로 확인되었다. 이러한 고장사례는 운전중에 엔진의 출력 성능을 떨어뜨리고, 자동차의 연비를 악화시키는 요인이 된다. 따라서 품질확보에 철저하게 대처하여 고장현상을 최소화 하여야 할 것으로 판단된다.

• 한국운동역학회지
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• 제32권3호
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• pp.87-93
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• 2022

Objective: The purpose of this research was to investigate the age-related changes in whole-body motor variability during sit-to-stand (STS) task. It has been reported that children perform motor tasks less accurately with greater variability as compared to adults. However, it is still unknown how they utilize the abundant degrees of freedom and accomplish voluntary actions. Uncontrolled manifold (UCM) analysis has been used to partition motor variabilities into two independent variability components, task-relevant variability (V_ORT) and task-irrelevant variability (V_UCM). We investigated what differences exist between children and adults with respect to these two motor variability components in relation to motor development stages. Method: Ten 6-year-old children (height: 116.2 ± 4.3 cm, weight: 23.1 ± 3.9 kg, motor development assessment percentile score: 77.5 ± 18.6%), ten 10-year-old children (height: 138.7 ± 7.2 cm, weight: 35.8 ± 10.3 kg, motor development assessment percentile score: 73.9 ± 12.7%), and ten young adults (age: 23 ± 1.6 year-old, height: 164.3 ± 11.4 cm, weight: 60.8 ± 12.0 kg) participated in this study. Each participant performed STS ten times, and a motion capture system was used to capture the whole-body kinematics. Each segment centers of mass and the whole-body center of mass were calculated, and UCM analysis was used to quantify motor variabilities, V_ORT and V_UCM. One-way ANOVA was used for statistical analysis. Results: We found that children produced more motor variabilities in V_ORT and V_UCM in all three dimensions, anterior-posterior, medial-lateral, and vertical. As age increased, both, V_ORT and V_UCM significantly decreased (p<.05). Conclusion: The greater V_ORT found in children compared to adults indicates that the repeatability over repetitions improves through development, while the greater V_UCM found in children suggests that children better utilize the abundant degrees of freedom during STS compared to adults.

• 대한수학회지
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• 제48권6호
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• pp.1225-1248
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• 2011

The present paper is concerned with a two-competitor/oneprey population system with Holling type-II functional response and two discrete delays. By linearizing the system at the positive equilibrium and analyzing the associated characteristic equation, the asymptotic stability of the positive equilibrium and existence of local Hopf bifurcations are investigated. Particularly, by applying the normal form theory and the center manifold reduction for functional differential equations (FDEs) explicit formulae determining the direction of bifurcations and the stability of bifurcating periodic solutions are derived. Finally, to verify our theoretical predictions, some numerical simulations are also included at the end of this paper.

• 대한수학회보
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• 제50권2호
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• pp.353-373
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• 2013

In this paper, a class of delayed predator-prey models of prey migration and predator switching is considered. By analyzing the associated characteristic transcendental equation, its linear stability is investigated and Hopf bifurcation is demonstrated. Some explicit formulae for determining the stability and the direction of the Hopf bifurcation periodic solutions bifurcating from Hopf bifurcations are obtained by using the normal form theory and center manifold theory. Some numerical simulations for justifying the theoretical analysis are also provided. Finally, biological explanations and main conclusions are given.

• 대한수학회지
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• 제55권1호
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• pp.43-58
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• 2018

In this paper, we study a delayed predator-prey system with Holling type IV functional response incorporating the effect of habitat complexity. The results show that there exist stability switches and Hopf bifurcation occurs while the delay crosses a set of critical values. The explicit formulas which determine the direction and stability of Hopf bifurcation are obtained by the normal form theory and the center manifold theorem.

• Journal of applied mathematics & informatics
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• 제29권3_4호
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• pp.781-802
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• 2011

Of concern in the paper is a Holling-Tanner predator-prey model with modified version of the Leslie-Gower functional response. Dynamical behaviours such as stability, permanence and Hopf bifurcation have been carried out deterministically. Using the normal form theory and center manifold theorem, the explicit formulae determining the stability and direction of Hopf bifurcation have been derived. The deterministic model is extended to a stochastic one by perturbing the growth equation of prey and predator by white and colored noises and finally the mean square stability of the stochastic model systems is investigated analytically. An extensive quantitative analysis has been performed based on numerical computation so as to validate the applicability of the proposed mathematical model.

• Kyungpook Mathematical Journal
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• 제49권4호
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• pp.605-618
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• 2009

A stage-structured predator-prey system with time delay and Beddington-DeAngelis functional response is considered. By analyzing the corresponding characteristic equation, the local stability of a positive equilibrium is investigated. The existence of Hopf bifurcations is established. Formulae are derived to determine the direction of bifurcations and the stability of bifurcating periodic solutions by using the normal form theory and center manifold theorem. Numerical simulations are carried out to illustrate the theoretical results.