• 천문학회지
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• 제40권4호
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• pp.91-97
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• 2007

The Fokker-Planck (FP) model is one of the commonly used methods for studies of the dynamical evolution of dense spherical stellar systems such as globular clusters and galactic nuclei. The FP model is numerically stable in most cases, but we find that it encounters numerical difficulties rather often when the effects of tidal shocks are included in two-dimensional (energy and angular momentum space) version of the FP model or when the initial condition is extreme (e.g., a very large cluster mass and a small cluster radius). To avoid such a problem, we have developed a new integration scheme for a two-dimensional FP equation by adopting an Alternating Direction Implicit (ADI) method given in the Douglas-Rachford split form. We find that our ADI method reduces the computing time by a factor of ${\sim}2$ compared to the fully implicit method, and resolves problems of numerical instability.

• 한국자동차공학회논문집
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• 제8권1호
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• pp.72-84
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• 2000

To analyze the correlation between drivetrain systems and to optimize the vehicle design with satisfying of the initial design objects, the performance sensitivity analysis through the iterative design procedure must be carried out. In this study, effects of the design parameters for the main components of the parallel type hybrid drivetrain system are analyzed by using the developed method of the vehicle performance simulation, and the basis of the optimal selection of the design parameters from the relation of design constraints and required performances is suggested. In driving control of the parallel hybrid vehicle, power split ratio is the most important factor, and the improved drivetrain system can be constructed through the only change of the algorithm for determination of the power spilt ratio, which is strongly applicable to the driving patterns and the environments. Therefore, Various techniques, such as the change of the weighting factors and the range extended algorithm, are suggested and evaluated in this paper.

• 전기학회논문지P
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• 제63권4호
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• pp.345-350
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• 2014

DC electrolytic capacitor is widely used in the power converter including PWM inverter, switching power supply and PFC Boost converter system because of its large capacitance, small size and low cost. In this paper, basic characteristics of DC electrolytic capacitor vs. frequency is presented and the real-time estimation scheme of ESR and capacitance based on the bandpass filtering is adopted to the single phase boost converter of uninterruptible power supply to diagnose its split dc-link capacitors. The feasibility of this real-time failure prediction monitoring system is verified by the computer simulation of the 5[kW] singe phase PFC half-bridge boost converter.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 춘계학술대회
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• pp.551-556
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• 2004

We propose a 2D 'crack' element for the simulation of propagating crack with minimal remeshing. A regular finite element containing the crack tip is replaced with this novel crack element, while the elements which the crack has passed are split into two transition elements. Singular elements can easily be implemented into this crack element to represent the crack-tip singularity without enrichment. Both crack element and transition element proposed in our formulation are mapped from corresponding master elements which are commonly built using the moving least-square (MLS) approximation only in the natural coordinate. In numerical examples, the accuracy of stress intensity factor $K_I$ is demonstrated and the crack propagation in a plate is simulated.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2000년도 춘계학술대회 논문집
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• pp.537-542
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• 2000

When visual intrusion Is an Important factor, it is desirable to find alternative methods of Improving the insertion loss of a noise barrier without Increasing the height. Therefore, the primary object of the work attenuate the noise due to railway by small interference device installed at noise barrier edge. In this paper the performance of noise barriers with attached interference device, in terms of shape, absorptive material and split panel, we examined using the boundary element approach. Also, the scale models are mounted in an anechoic chamber and the frequency of the sound sources are appropriately scaled to simulate full scale site conditions. Lastly, experimental measurements of the designs are executed for a range of frequencies and receiver positions, and are compared with the results of numerical modeling.

• 대한전기학회논문지:전력기술부문A
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• 제54권1호
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• pp.43-50
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• 2005

The presence of transmission congestion may reduce the market size and split the bulk power system into smaller systems. Consequently, this can be a key factor to the increase in market price. This paper analyzes the effect of exercising local market power on the market price, and derives a range of indices which quantify the degree and incentive of local market power through statistical analysis in an electricity market with uniform pricing scheme. The applicability and effectiveness of the derived indices on competitive electricity markets are demonstrated on the Korea electricity market.

• Journal of Mechanical Science and Technology
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• 제20권6호
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• pp.896-904
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• 2006

In a liquid rocket engine, the role of gas-liquid scheme injector as an acoustic resonator or absorber is studied experimentally for combustion stability by adopting linear acoustic test. The acoustic-pressure signals or responses from the chamber are monitored by acoustic amplitude. Acoustic behavior in a rocket combustor with a single injector is investigated and the acoustic-damping effect of the injector is evaluated for cold condition by the quantitative parameter of damping factor as a function of injector length. From the experimental data, it is found that the injector can play a significant role in acoustic damping when it is tuned finely. The optimum tuning-length of the injector to maximize the damping capacity is near half of a full wavelength of the first longitudinal overtone mode traveling in the injector with the acoustic frequency intended for damping in the chamber. When the injector has large diameter, the phenomenon of the mode split is observed near the optimum injector length and thereby, the acoustic-damping effect of the tuned injectors can be degraded.

• Current Optics and Photonics
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• 제5권2호
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• pp.191-197
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• 2021

The anomalous propagation characteristics of a single Airy beam in nonlocal nonlinear medium are investigated by utilizing the split-step Fourier-transform method. We show that besides the normal straight propagation trajectory, the breathing solitons formed by the interaction between Airy beam and nonlocal nonlinear medium can propagate along the sinusoidal trajectory, and the anomalous trajectory can be modulated arbitrarily by altering the initial amplitude and the nonlocal nonlinear coefficient. In addition, the initial amplitude and the nonlocal nonlinear coefficient can have inverse impacts on the formation and transformation of the equilibrium state of spatial solitons, when the two parameters are larger than certain values. Therefore, the reversible transformation of the evolution dynamics of two soliton states can be realized by adjusting those two parameters properly. Finally, it is shown that the propagation properties of the solitons formed by the interaction between Airy beam and nonlocal nonlinear medium can be controlled arbitrarily, by adjusting the distribution factor and nonlocal coefficient.

• 정신신체의학
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• 제6권2호
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• pp.155-175
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• 1998

The purpose of this study was to test a reliability and validity of the Korean version of Eating Attitudes Test-26(KEAT-26). Using multi-stage sampling, we finally got 3,496 subjects(1422 males and 2074 females) who were available for analysis from target 4,400 Korean adults over 18 in the nationwide areas of9 kus, 10 middle or small cities, and 17 kuns. We tried to make T score norm of the KEAT-26 as a cutoff score and STEN score norm as a index of severity for disordered eating behaviors. For the male group, Cronhach's internal consistency was .83 and Spearman-Brown split half correlation coefficiency was .75. For the female group, each of them was .81 and .75, and .81, .75 for the grand total group respectively. Validity test was performed by construct validation analysis. By a iterated principal axis factoring, 4 factors were extracted. There were some differences in the factors of the KEAT-26 by sex. In the male group, factor I was 'self-control of eating and bulimic symptom', factor II was 'food preoccupation and dieting', factor III was 'preoccupation with being thinner', factor N was 'avoidance of sweet foods'. In contrast with the male group, factor I was 'self-control of eating and bulimic symptom', factor II was 'preoccupation with being thinner', factor III was 'food preoccupation' and factor N was 'dieting' in the female group. We used T score 65 as a cutoff score. T score 65 corresponded to raw score 19 in the male group, 22 in the female group and 21 in the grand total group. Severity of disordered eating behaviors was measured by a STEN score. In the male group, each of the score range of 0-10, 11-14, 15-18, 19-22 and over 23 represented the degree of none, subclinical, manifest, moderate and severe severity respectively. Each of the score range of 0-13, 14-17, 18-21, 22-26 and over 27 in the female group, and the score range of 0-12, 13-16, 17-20, 21-25 and over 26 in the grand total group also represented the same degree of severity as like in the male group. These results support that KEAT-26 is a reliable and valid scale for evaluating disordered eating behaviors and eating problems.

• 한국노년학
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• 제41권1호
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• pp.149-168
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• 2021

본 연구는 만성질환 노인의 약물이행을 측정하기 위한 도구(Medication Adherence Scale in Elderly, MAS-E)를 개발하고 신뢰도와 타당도를 검증하는 방법론적 연구이다. MAS-E는 혼종모형을 이용한 내용 분석에 의해 개념적 기틀을 구성하고 이를 기반으로 문항을 구성하고 내용타당도를 검증하여 예비문항을 구성하였고 문항을 검토한 후 예비 조사를 실시하여 총 26문항을 최종 확정하여 본 조사를 실시하였다. 설문조사 자료는 일대일 인터뷰를 통해 지역사회에 거주하는 만성질환 노인 345 명으로부터 수집되었다. 도구평가를 위해 신뢰도와 타당도를 검증하고 검증결과를 기반으로 최종 문항을 확정하여 만성질환 노인의 약물이행 도구(MAS-E)를 개발하였다. 타당도 검증에서 문항분석, 요인분석, 총점-요인 간 상관관계를 통해 4개 요인과 18문항이 도출되었으며-약물사용 기억하기(2문항), 약물효과에 대한 기대(5문항), 처방과 지시에 따른 약물사용 실천(8문항), 의료인과의 소통(3문항), 전체 18문항은 분산의 69.7 %를 설명하는 것으로 나타났다. 최종 도구의 총점-요인 간 상관관계는 모두 유의한 상관관계를 나타냈다. 준거타당도 검증 결과, 개발된 도구는 Morisky Medication Adherence Scale (MMAS-8)과 유의하게 양의 상관관계(r = .72, p <.001)를 나타냈다. 신뢰도 검증에서 문항내적 일관성 신뢰도 Cronbach'α는 .906, Guttman 반분검사 신뢰도는 .804, 검사-재검사 신뢰도는 .912로 나타나 개발된 도구는 안정적이고 일관성을 확보하였다. 본 연구를 통해 개발된 MAS-E는 타당도와 신뢰도가 모두 검증된 도구로서 만성질환 노인의 약물이행 정도를 평가하고 약물이행 개선을 위한 중재연구의 효과 평가에 활용될 수 있을 것이다