• 융합신호처리학회논문지
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• 제8권3호
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• pp.178-184
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• 2007

일반적으로 EEG 신호는 Alpha파, Beta파, Theta파, Delta파로 구분할 수 있다. Alpha파는 사람에게 있어서 가장 우세한 파형으로써 정신적으로 안정 시 잘 나타나는 뇌파이며, Beta파는 흥분 시 우세하게 나타난다. 본 연구에서는 EEG의 안정 상태를 정량적으로 나타내기 위해 웨이브렛 변환과 파워 스펙트럼 분석을 이용하였다. EEG신호를 웨이브렛 변환을 통해 Alpha파와 Beta파만 검출하여 고속 푸리에 변환을 이용 Alpha파와 Beta파의 파워 스펙트럼을 구하였다. 이후 Beta파의 파워 스펙트럼에 대한 Alpha파의 파워 스펙트럼 비율로 정의되는 상대적 안정상태비(Stable State Ratio)를 계산하였다. 그 결과 피험자가 정상적인 활동 상태에서 정신적으로 편안한 안정 상태에 이르기까지 5분 이내가 16%, $5{\sim}10$분 사이가 9%, 그리고 최소 10분 이상의 시간이 소요되는 피험자집단이 총 69%로 우세하게 나타났다.

• 전기전자학회논문지
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• 제12권4호
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• pp.204-210
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• 2008

EEG 신호 중, 알파파는 안정시에 우세하게 나타나며 베타파는 흥분시에 우세하게 나타나는 것으로 알려져 있다. 또한 동양의 한의학에서는 상대적으로 길고 고른 호흡일 때가 짧고 변화가 심한 호흡일 때 보다 안정된 상태를 나타낸다고 알려져 있다. 본 연구에서는 EEG의 안정상태를 정량적으로 나타내기 위한 뇌파의 정량화 지표와 호흡의 안정상태를 정량적으로 나타내기 위한 호흡 정량화 지표를 정의하여 안정상태에 있어서 EEG와 호흡의 연관성을 찾아내고자 하였다. 총 20명의 피험자에 대해 각각 20분간의 실험을 통해 본 연구의 유효성을 검증하였다.

• 한국지진공학회논문집
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• 제27권2호
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• pp.119-127
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• 2023

In this paper, seismic performance evaluation was carried out for eight circular reinforced concrete columns designed seismically by KRTA[1]and KCI[8]. Primary design parameters for such columns included many longitudinal reinforcements, yield strength of reinforcements, the vertical spacing of spirals, aspect ratio, and axial force ratio. The test results showed that all the columns exhibited stable hysteretic and inelastic responses. Based on the test results, drift ratios corresponding to each damage state, such as initial yielding, initial cover spalling, initial core concrete crushing, buckling, and fracture of longitudinal reinforcement and final spalled region, were evaluated. Then, those ratios were compared with widely accepted damage limit states. The comparison revealed that the existing damage states were considerably conservative. This implies that additional research is required for the damage limit states of such columns designed seismically by current Korean design codes.

• Journal of applied mathematics & informatics
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• 제31권3_4호
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• pp.385-398
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• 2013

In this paper, a turbidostat model with ratio-dependent growth rate and impulsive state feedback control is considered. We obtain sufficient conditions of the globally asymptotically stable of the system without impulsive state feedback control. We also obtain that the system with impulsive state feedback control has periodic solution of order one. Sufficient conditions for existence and stability of periodic solution of order one are given. In some cases, it is possible that the system exists periodic solution of order two. Our results show that the control measure is effective and reliable.

• 대한수학회보
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• 제50권6호
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• pp.1847-1854
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• 2013

The main concern of this paper is to study the dynamics of an n-dimensional ratio-dependent predator-prey system with diffusion. We study the dissipativeness, persistence of the system and it is shown that the unique positive constant steady state is globally asymptotically stable under some assumptions.

• 한국자동차공학회논문집
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• 제15권3호
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• pp.91-98
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• 2007

This paper presents the induced mathematical modeling equations for evaluating the operation stability with automatic transmission of heavy duty vehicle. This theoretical approach indicates that linearized governing equations of system can be converted into eigen-value problems. if the eigen-value has positive number, we can predict the engine operating point locates an unstable operating region. To be a stable state, the unstable operating point diverges toward a stable point which is able to maintain uniform velocity. Based on the previous theoretical analysis, we carry out dynamic simulation to show the behavior of engine operating point and torque converter in transient state. As a result of the dynamic simulation, the suggested theoretical method is found to be reasonable for evaluating the operation stability of a torque converter. In addition, the numerical results explain the engine stops and fluctuating phenomenon in reality.

• 한국자동차공학회논문집
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• 제7권5호
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• pp.66-72
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• 1999

It is necessary to discuss lightening engine parts and reducing the friction of sliding parts to improve fuel consumption and combustion stability at idling condition. Lean best torque combustion which produce maximum power at a lean air-fuel ratio is effective for the reduction of exhaust gas emission and the improvement of fuel consumption. Accordingly, this study deals with the expansion of lean combustible limitation, the combustion stability and the reduction of idle speed through the analysis of combustion characteristics on the base of the control technique of precise air-fuel ratio because it does not need to maximum power at idling condition. The idle speed is increased proportional to ISC(Idle Speed Control) duty ratio. On the other hand the idle speed decreased by lean air-fuel ratio. The COV in engine speed is stable within maximum two percent up to 17.6 mixture ratio by the control of ISC duty ratio.

• Wind and Structures
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• 제36권2호
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• pp.91-103
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• 2023

Tuned liquid dampers (TLDs) are increasingly being used as efficient dynamic vibration absorbers to mitigate wind-induced vibration in super high-rise buildings. However, the damping characteristics of screens and the control effectiveness of actual structures must be investigated to improve the reliability of TLDs in engineering applications. In this study, a numerical TLD model is developed using computational fluid dynamics (CFD) and a simulation method for achieving the coupled vibration of the structure and TLD is proposed. The numerical results are verified using shaking table tests, and the effects of the solidity ratio and screen position on the TLD damping ratios are investigated. The TLD control effectiveness is obtained by simulating the wind-induced vibration response of a full-scale structure-TLD system to determine the optimal screen solidity ratio. The effects of the structural frequency, damping ratio, and wind load amplitude on the TLD performance are further analyzed. The TLD damping ratio increases nonlinearly with the solidity ratio, and it increases with the screens towards the tank center and then decreases slightly owing to the hydrodynamic interaction between screens. Full-scale coupled simulations demonstrated that the optimal TLD control effectiveness was achieved when the solidity ratio was 0.46. In addition, structural frequency shifts can significantly weaken the TLD performance. The control effectiveness decreases with an increase in the structural damping ratio, and is insensitive to the wind load amplitude within a certain range, implying that the TLD has a stable damping performance over a range of wind speed variations.

• Food Science and Biotechnology
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• 제14권3호
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• pp.305-310
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• 2005

Flaxseed is outstanding for lignans and oil rich in ${\alpha}$-linolenic acid which protect against several major illnesses. Better understanding of processing and storage characteristics of flaxseed will increase options for food use. Lignans and oil are found in the hull and embryo, respectively. Comparison of pearling and impact-dehulling processes for separation of lignan and oil-rich fractions showed the impact process was less effective, but easier to scale-up. Screw-pressing embryo reduced oil yield compared to whole seed, but doubled productivity and sharply reduced frictional heating of the oil. Flaxseed hull and embryo, also whole, ground and steamed-ground samples, were stable up to 30 weeks in closed containers at $23^{\circ}C$. Steamed-ground samples in open trays at $40^{\circ}C$ deteriorated markedly (peroxide value > 100 by 22 weeks); yet, whole seed remained stable. Incorporation of 18% flaxseed embryo into yellow perch feed increased ${\alpha}$-linolenic acid to 13 to l4% of muscle and liver lipids, compared to 0.5 to 0.7% in the no-embryo control. Feed conversion ratio, weight gain, and survival were similar. These studies are helping to establish the technological base for processing and utilizing flaxseed and flaxseed fractions to improve human diets.

• Ocean Science Journal
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• 제42권4호
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• pp.223-230
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• 2007

To understand the origin and biogeochemistry of the organic matter in surface sediments of Lake Shihwa and Lake Hwaong, organic nitrogen, inorganic nitrogen, labile organic carbon, and residual organic carbon contents as well as stable isotope ratios for carbon and nitrogen were determined by KOBr-KOH treatment. Ratios of organic carbon to organic nitrogen $(C_{org}/N_{org})$ (mean = 24) were much higher than ratios of organic carbon to total nitrogen $(C_{org}/N_{tot})$ (mean= 12), indicating the presence of significant amounts of inorganic nitrogen in the surface sediments of both lakes. Stable isotope ratios for organic nitrogen were, on average, $5.2\%_{\circ}$ heavier than ratios of inorganic nitrogen in Lake Shihwa, but those same ratios were comparable in Lake Hwaong. This might be due to differences in the origin or the degree of degradation of sedimentary organic matter between the two lakes. In addition, stable isotope ratios for labile organic carbon were, on average, $1.4\%_{\circ}$ heavier than those for residual organic carbon, reflecting the preferential oxidation of $^{13}C$-enriched organic matter. The present study demonstrates that KOBr-KOH treatment of sedimentary organic matter can provide valuable information for understanding the origin and degradation state of organic matter in marine and brackish sediments. This also suggests that the ratio of $(C_{org}/N_{org})$ and stable isotope ratios for organic nitrogen can be used as indexes of the degree of degradation of organic matter.