• Nuclear Engineering and Technology
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• 제54권3호
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• pp.803-810
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• 2022

The small modular liquid-metal fast reactor (SMFR) is an important component of advanced nuclear systems. SMFRs exhibit relatively low breeding capability and constraint space for control rod installation. Consequently, control rods are deeply inserted at beginning and are withdrawn gradually to compensate for large burnup reactivity loss in a long lifetime. This paper is committed to investigating the impact of control rod compensation operation on core neutronics characteristics. This paper presents a whole core fine depletion model of long lifetime SMFR using OpenMC and the influence of depletion chains is verified. Three control rod position schemes to simulate the compensation process are compared. The results show that the fine simulation of the control rod compensation process impacts significantly the fuel burnup distribution and absorber consumption. A control rod equivalent position scheme proposed in this work is an optimal option in the trade-off between computation time and accuracy. The control position is crucial for accurate power distribution and void feedback coefficients in SMFRs. The results in this paper also show that the pin level power distribution is important due to the heterogeneous distribution in SMFRs. The fuel burnup distribution at the end of core life impacts the worth of control rods.

• 한국경영과학회지
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• 제29권3호
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• pp.1-7
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• 2004

We demonstrate in this paper that the level crossing technique can be applied to such a system that not only the state vector is two-dimensional but Its two components are heterogeneous. As an example system, we use the GI-G/c/K queue whose state vector consists of the number of customers in the system and the total unfinished work.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2003년도 신호처리소사이어티 추계학술대회 논문집
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• pp.509-512
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• 2003

On-going convergence between broadcasting and communication is currently bringing in lots of drastic changes to multimedia services to the home. The FTTH-based home networks will be the interface among the digital home appliances for broadcast digital contents as weil as for broadband data connection. In this paper, we discuss several design issues for home gateway architecture that effectively distributes realtime broadcasting contents (from either the headend in the access network or the satellite/terrestrial broadcasts) to heterogeneous devices in the home network.

• Macromolecular Research
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• 제17권5호
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• pp.296-300
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• 2009

Ethylene-1-butene copolymers were prepared with $SiO_2$-supported $TiCl_4$ catalyst by changing of 1-butene/ethylene molar ratio in feed, and the resulting copolymers were analyzed using temperature rising elution fractionation (TREF) and crystallization fractionation (Crystaf) methods to investigated the influence of $C_4/C_2$ molar ratio in feed on chemical compositional distribution and other parameters such as molecular weight and its distribution. TREF analysis showed that the copolymers had a broad and bimodal chemical compositional distribution (CCD) regardless of the content of 1-butene in the copolymer. The chemical composition was in the range of 5 to 55 branches per 1,000 carbons for all copolymers prepared in the study. Furthermore, the broader CCD was revealed for the copolymers having the higher content of 1-butene. Crystaf analysis did not showed a bimodal CCD for the copolymers having the 1-butene content of less than 5.1 wt%. The lower crytalline part having 1-butene content in Crystaf analysis was less than of TREF analysis.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회B
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• pp.1996-2000
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• 2008

In autothermal reforming reaction, oxygen to carbon ratio (OCR) and steam to carbon ratio (SCR) are significant factors, which control temperature and carbon deposition into the reactor. The OCR is more sensitive than the SCR to affect the temperature distribution and reforming efficiency. In conventional operation, hydrocarbon fuel, steam, and oxygen was homogeneously mixed and injected into the reactor in order to get hydrogen-rich gas. The temperature was abruptly raised due to fast oxidation reaction in the former part of the reactor. Deactivation of packed catalysts can be accelerated there. In the present study, therefore, the effect of the oxygen distribution is introduced and investigated to suppress the carbon deposition and to maintain the reactor in the mild operating temperature (e.g., $700{\sim}800^{\circ}C$). In order to investigate the effect numerically, the following models are adopted; heterogeneous reaction model and two-medium model for heat balance.

• 한국통신학회논문지
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• 제24권6B호
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• pp.1098-1107
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• 1999

멀티미디어 응용에서 송신자는 일반적으로 다중 스트림을 생성하게 된다. 이질형 멀티미디어 멀티 캐스트에서는 송신자가 생성한 다중 스트림을 수신자가 모두 수신할 필요 없이 일부만을 수신할 수 있다. 수신자는 수신하기를 원하는 스트림에 대하여 입찰하고 연결이 성립되면 동일한 양을 송신자는 이익으로 갖게 된다. 송신자의 이익을 최대로 하는 이질형 멀티 캐스트를 위한 스트림 분배 문제는 NP-complete로 알려진 0-1 정수 문제로 유도된다. 본 논문에서는 멀티캐스트 트리상의 임의 링크의 용량이 그 자손 링크의 용량보다 작지 않다는 제약조건을 가지는 제약된 모델과 제약되지 않은 모델을 모두 고려하여, 기존에 제시된 알고리즘에 비하여 시간 복잡도와 공간 복잡도 면에서 우수한 알고리즘들을 제안한다. 이 알고리즘은 또한 분산화 되어 구현되기 쉬우며, 이는 대규모 네트워크에서 매우 중요한 장점이 된다.

• Nuclear Engineering and Technology
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• 제55권6호
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• pp.2112-2124
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• 2023

With the rise of economic and safety standards for nuclear reactors, new concepts of Gen-IV reactors and modular reactors showed more complex designs that challenge current tools for reactor physics analysis. A Monte Carlo (MC) two-step method was proposed in this work. This calculation scheme uses the continuous-energy MC method to generate multi-group cross-sections from heterogeneous models. The multi-group MC method, which can adapt locally-heterogeneous models, is used in the core calculation step. This calculation scheme is verified using a Gen-IV modular lead-based fast reactor (LFR) benchmark case. The influence of homogenized patterns, scatter approximations, flux separable approximation, and local heterogeneity in core calculation on simulation results are investigated. Results showed that the cross-sections generated using the 3D assembly model with a locally heterogeneous representation of control rods lead to an accurate estimation with less than 270 pcm bias in core reactivity, 0.5% bias in control rod worth, and 1.5% bias on power distribution. The study verified the applicability of multi-group cross-sections generated with the MC method for LFR analysis. The study also proved the feasibility of multi-group MC in core calculation with local heterogeneity, which saves 85% time compared to the continuous-energy MC.

• 기술혁신학회지
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• 제21권2호
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• pp.860-874
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• 2018

본 연구는 신 국제무역이론(Melitz, 2012, 2014, 2015)에 대한 실증분석을 목적으로 한다. 신 국제무역이론은 기업기술역량에 대한 이질적 기업분포가 무역효과에 미치는 영향을 중심으로 전개되고 있으며, 기업기술역량분포형태가 무역효과를 결정한다는 중요한 가정에서 출발한다. 본 연구는 실증적으로 우리나라 제조업에 기업기술역량분포를 추정하였다. 이 연구목적을 위하여 우리나라 총 기업기술역량분포를 기술혁신과 기술모방분포로 분리하였으며, 분포형태의 적합성에 대하여 통계적으로 검증하고, 신 국제무역이론기반에 대한 적정성을 평가하였다. 연구시사점으로 본 분석결과를 바탕으로 기술정책 및 산업정책 방향을 간단하게 제언하였다.

• Investigative Magnetic Resonance Imaging
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• 제24권3호
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• pp.95-122
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• 2020

In this article, we evaluated the performance of radiofrequency (RF) coils in terms of the signal-to-noise ratio (S/N) and homogeneity of magnetic resonance images when used for ultrahigh-frequency (UHF) 7T magnetic resonance imaging (MRI). High-quality MRI can be obtained when these two basic requirements are met. However, because of the dielectric effect, 7T magnetic resonance imaging still produces essentially a non-uniform magnetic flux (|B₁|) density distribution. In general, heterogeneous and homogeneous RF coils may be designed using electromagnetic (EM) modeling. Heterogeneous coils, which are surface coils, are used in consideration of scalability in the |B₁| region with a high S/N as multichannel loop coils rather than selecting a single loop. Loop coils are considered state of the art for their simplicity yet effective |B₁|-field distribution and intensity. In addition, combining multiple loop coils allows phase arrays (PA). PA coils have gained great interest for use in receiving signals because of parallel imaging (PI) techniques, such as sensitivity encoding (SENSE) and generalized autocalibrating partial parallel acquisition (GRAPPA), which drastically reduce the acquisition time. With the introduction of a parallel transmit coil (pTx) system, a form of transceiver loop arrays has also been proposed. In this article, we discussed the applications and proposed designs of loop coils. RF homogeneous coils for volume imaging include Alderman-Grant resonators, birdcage coils, saddle coils, traveling wave coils, transmission line arrays, composite right-/left-handed arrays, and fusion coils. In this article, we also discussed the basic operation, design, and applications of these coils.

• Communications for Statistical Applications and Methods
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• 제18권2호
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• pp.219-227
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• 2011

본 연구에서는 두 반응변수의 이질적 산포를 허용하는 좀 더 일반적인 형태의 이변량 음이항 회귀모형을 삼각소거법(trivariate reduction technique)을 이용하여 제안하였다. 이 분포에서 산포의 동일성에 대한 스코어 검정과 LR 검정을 유도하고 모의실험을 통하여 각 검정법의 효율성을 비교하였다. 모의실험 결과 스코어 검정과 LR 검정 모두 명목유의수준을 제대로 유지하고 검정력도 높게 나타나 산포의 동일성을 검정하는데 효율적인 검정법으로 나타났다. 하지만 스코어 검정은 LR 검정에 비하여 계산이 간편하다는 장점이 존재하고 모의실험을 통하여 스코어 검정이 LR 검정보다 약간 나은 효율을 보였으므로 산포의 동일성에 대한 검정에서 스코어 검정의 사용을 제안하고자 한다. 더불어 실제 사례에 두 검정법을 적용하고 그 결과를 제시하였다.