• 천문학회보
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• 제44권2호
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• pp.48.4-48.4
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• 2019

We studied the metal-distribution of isolated Milky-way mass galaxy using various hydrodynamic solvers and investigated the difference of the result between AMR and SPH codes. In particle-based codes, physical quantities like mass or metallicity defined in each particle are conserved unless being injected explicitly by the effect of the supernova, whereas in the Eulerian codes the diffusion is simply accomplished by hydro-equation. Therefore, without including explicit physics of diffusion on the SPH- codes, the metal mixing in the galaxy or CGM only can be accomplished by the direct motion of the particles, however, the standard-SPH codes depress the instability of the turbulent fluid mixing. In this work, we simulated under common initial conditions, common gas-physics like cooling-heating models, and star-formation feedback using ENZO(AMR) GIZMO and GADGET-2 codes. We additionally included a metal-diffusion algorithm on the SPH-codes, which follows the subgrid-turbulent mixing model investigated by Shen et al. (2010) and compared the effect of the metal-outflow on the halo region of the galaxy in different hydro-solvers. We also found that for the implementation of the diffusion scheme in the SPH-codes, the existence of a sufficient number of the gas-particles, which is the carrier of the metals, is necessary. So we tested a new initial condition for proper implementation of the diffusion scheme on the SPH simulations. By comparing the metal-contamination of the circumgalactic medium with different hydrodynamics models, we quantify the diffusion strength of AMR codes using diffusion parameterization of the SPH codes and also suggest the calibration solutions in the different behavior of codes in metal-outflow.

• 한국시스템다이내믹스학회:학술대회논문집
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• 한국시스템다이내믹스학회 2002년도 추계학술대회발표논문집
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• pp.103-122
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• 2002

Construct ion sector government policies are targeted towards regulation than facilitation and management. This approach often fails to integrate different segments of the public and private and seems to be inadequate in encouraging the private sector to achieve better quality construction. This situation suggests a need for a better and systematic approach for construct ion policy making. This paper suggests a model-based approach to public policy making using system dynamics approach. Singapore government's policy making efforts to encourage the use of prefabrication are discussed as an application example. This paper presents system models which discuss strengths and weaknesses of the current construction system in Singapore using casual loops, and highlights the feedback processes that would be useful in decision making for the government. Based on these system dynamics models, this paper identifies four major potential policy interventions policy interventions.

• 한국소음진동공학회논문집
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• 제17권12호
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• pp.1223-1229
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• 2007

Flow traveling over a cavity opening forms a vortex due to unstable shear layer and induces an aerodynamic pressure excitation from the diffusion of the vortex convecting out of the trailing edge of the opening. The interaction between the excitation force and the cavity response sustains resonance in the resonator(cavity) and locked-in vortex shedding at the leading edge of the opening. The aerodynamic excitation force can be described from the diffusion of the vortex over the trailing edge and the level of its diffusivity is related to the strength of vorticity seeded at the leading edge. In this study, the control scheme of the internal pressure oscillation was proposed from regulating the vorticity at the leading edge by use of an oscillating spoiler. It was found that the relative motion between the spoiler and the air mass at the cavity opening influenced vorticity strength and the control was achieved by direct feedback of the cavity pressure fluctuation to the actuator.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2005년도 추계학술대회논문집
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• pp.196-199
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• 2005

Flow traveling over a cavity opening forms a vortex due to unstable shear layer and induces an aerodynamic pressure excitation from the diffusion of the vortex convecting out of the trailing edge of the opening. The interaction between the excitation force and the cavity response sustains resonance in the resonator(cavity) and locked-in vortex shedding at the leading edge of the opening. The aerodynamic excitation force can be described from the diffusion of the vortex over the trailing edge and the level of its diffusivity is related to the strength of vorticity seeded at the loading edge. In this study, the control scheme of the internal pressure oscillation was proposed from regulating the vorticity at the leading edge by use of an oscillating spoiler. It was found that the relative motion between the spoiler and the air mass at the cavity opening influenced vorticity strength and the control was achieved by direct feedback of the cavity pressure fluctuation to the actuator.

• 전기의세계
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• 제29권4호
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• pp.256-259
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• 1980

A singular pertubation theory is applied to obtain an approximate solution for suboptimal control of nuclear reactors with spatially distributed parameters. The inverse of the neutron velocity is regarded as a small perturbing parameter, and the model, adopted for simplicity, is a cylindrically symmetrical reactor whose dynamics are described by the one group diffusion equation with one delayed neutron group. The Helmholtz mode expansion is used for the application of the optimal theory for lumped parameter systems to the spatially distributed parameter systems. An asymptotic expansion of the feedback gain matrix is obtained with construction of the boundary layer correction up to the first order.

• 한국콘텐츠학회:학술대회논문집
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• 한국콘텐츠학회 2008년도 춘계 종합학술대회 논문집
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• pp.87-91
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• 2008

네트워크 분야에서 데이터 압축은 네트워크 트래픽을 줄이기 위한 전통적이고, 효과적인 방법 중 하나이다. 센서 네트워크의 데이터는 시 공간적인 연관성을 가지고 있으며, 이러한 특성을 이용한 데이터 압축 기법들이 많이 연구되고 있다. 센서 노드는 통신 범위의 제약을 가지고 있기 때문에 공간적인 특성을 이용한 압축시 데이터의 범위로 제한된 정보를 사용한다. 하지만, 때때로 전역적인 데이터 분포와 특성은 데이터 압축 기법의 효율을 증가시킬 수 있는 기회를 제공하기도 한다. 본 논문에서는 이러한 기회를 활용하기 위한 새로운 접근의 데이터 압축기법을 제안한다. 제안하는 기법은 기지국 혹은 슈퍼 노드에 의해 수집된 데이터를 통해 압축을 위한 정보, 즉, 피드백 정보를 생성하고 배포함으로써 네트워크 전체의 데이터 압축을 용이하게 한다. 본 논문의 우수성을 보이기 위해서 시뮬레이션을 통해 성능 평가를 수행하였으며 그 결과 네트워크의 수명이 약 30% 증가하였다.

• 한국항행학회논문지
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• 제22권6호
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• pp.648-653
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• 2018

영상 신호의 특정 파장대역에 대한 분석은 오래된 연구 분야다. 그러나 특정 파장대의 특성을 갖는 신호에 대한 분석이나 샘플의 생성에 관한 연구는 최근에도 활발하게 이루어지고 있다. 특히 블루 노이즈 특성을 갖는 샘플링 방법에 관한 연구들이 다양하게 이루어지고 있으며 본 논문에서는 디지털 하프토닝 영상에 대한 신호를 분석한다. 하프토닝을 신호의 관점에서 해석한 것은 Ulichney에 의해 처음 이루어졌다. 하프토닝에 사용되는 픽셀간의 신호 특성을 블루 노이즈일 경우 보기에 좋은 결과를 낸다는 관점으로 접근하였다. Lau는 출력의존피드백을 오차확산법에 활용하여 그린 노이즈 특성을 보이는 하프토닝 방법을 개발하였다. Jho는 반응확산 모델을 이용하여 하프토닝 영상을 만들어 내는 방법을 개발하였다. 본 연구에서는 반응확산 하프토닝을 신호의 관점에서 분석하여 그린 노이즈를 나타냄을 보이고 기존의 그린 노이즈 하프토닝과 비교하고자 한다.

• Nuclear Engineering and Technology
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• 제55권11호
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• pp.4048-4056
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• 2023

The feasibility of using the Monte Carlo code MCS to generate multigroup cross sections for nodal diffusion simulations RAST-F of liquid metal fast reactors is investigated in this paper. The performance of the MCS/RAST-F code system is assessed using steady-state simulations of the ANTS-100e core. The results show good agreement between MCS/RAST-F and MCS reference solutions, with a keff difference of less than 77 pcm and root-mean-square differences in radial and axial power of less than 0.5% and 0.25%, respectively. Furthermore, the MCS/RAST-F reactivity feedback coefficients are within three standard deviations of the MCS coefficients. To validate the internal thermal-hydraulic (TH) feedback capability in RAST-F code, the coupled neutronic/TH1D simulation of ANTS-100e is performed using the case matrix obtained from MCS branch calculations. The results are compared to those obtained using the MARS-LBE system code and show good agreement with relative temperature differences in fuel and coolant of less than 0.8%. This study demonstrates that the MCS/RAST-F code system can produce accurate results for core steady-state neutronic calculations and for coupled neutronic/TH simulations.

• Management Science and Financial Engineering
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• 제8권1호
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• pp.21-38
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• 2002

Rapid advances in information technology(IT) and telecommunication systems impact the number and quality of decision-making in organizations. Specifically, middle mangers must posses or develop the creativity necessary for survival in a constantly changing and volatile business environment. While tradition and conventional wisdom tell us that a middle managers role centers on control and monitoring, todays competitive arena has spun out a new managerial requirement developing and maintaining an innovative attitude. Problematically, most previous research has focused on the issue of changing decision authority (i. e. centralization/decentralization). Moreover, much previous research has also largely ignored environmental changes exposing new roles that middle managers have assumed. This study explores the means of identifying middle managerial roles, managerial possibilities involving the growing popularity of open systems through electronic brainstorming, and an adaptation and development of Diffusion Theory and attempt to counter criticism leveled at the theory's inability to provide an adequate explanation for diffusion of complex organizational technology. This paper develops three ideas: 1) Introducing the 'Chasing Curve' as a theoretical background. 2) Suggesting a new methodology using electronic brainstorming for analyzing the gap between Knowing (the perceived importance of middle managers' roles) and Doing (the degree of current status of middle managers' roles), which we term the 'Spiral Gap Analysis Model'. 3) Identifying a feedback system for minimizing the Knowing - Doing gap, aimed at development of IT strategic priority decision support, which we call this the 'Star Process'.

• 대한전기학회논문지:전기기기및에너지변환시스템부문B
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• 제51권1호
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• pp.34-39
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• 2002

Most X-ray generator had been used do rectifier type transformer high tension generator which is supplied in a clinical diagnosis. But it is difficult to miniaturize and become light weight. Also, because the ripple rate of tube voltage is high, X-ray generating efficiency is very low. Therefore, it is supplied gradually from abroad being developed high tension generator for inverter type X-ray generator which use semi-conductor switching element for electric power that have high speed switching ability to solved these problem. But, semi-conductor element of big capacity are used by X-ray tube's big consumption power and diffusion is difficult in the small size hospital because production cost is ascending by doing digital control through DSP and product price becomes expensive. Therefore, in this paper, design and manufactured CR type voltage divider for feedback control of tube voltage of high frequency resonance type inverter and high tension transformer for high frequency to apply economical diffusion type X-ray generator which have wide output voltage and load extent. It is Proved do X-ray generator and stability of X-ray tube's output characteristics through an experiment.