• Bulletin of the Korean Chemical Society
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• 제7권3호
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• pp.224-228
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• 1986

A nonlinear theory is presented for the fluctuations of intermediates in the Brusselator near the critical point caused by diffusion. The method used is the two time scaling method different from the conventional method in the sense that a slight nonlinear effect is included in the initial time region where the linear approximation is conventionally valid. The result obtained by the nonlinear theory shows that fluctuations close to the critical point approach the value of a stable steady state or deviate infinitely from an unstable steady state, as time goes to infinity, while the linear theory gives approximately time-independent fluctuations. A brief discussion is given for the correlation at a time between fluctuating intermediates when the system approaches a stable steady state.

• International Journal of Naval Architecture and Ocean Engineering
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• 제13권1호
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• pp.367-378
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• 2021

This paper develops a dynamic regression model to quantify the contribution of key external factors to operational energy efficiency of ships. On this basis, kernel density estimation is applied to explore distribution patterns of fluctuations in operational performance. An empirical analysis based on these methods show that distribution of fluctuations in Energy Efficiency Operational Indicator (EEOI) is leptokurtic and fat tailed, rather than a normal one. Around 85% of fluctuations in EEOI can be jointly explained by capacity utilization and sailing speed, while the rest depend on other external factors largely beyond control. The variations in capacity utilization and sailing speed cannot be fully passed on to the energy efficiency performance of ships, due to complex interactions between various external factors. The application of the methods is demonstrated, showing a potential approach to develop a rating mechanism for use in the legally binding framework on operational energy efficiency of ships.

• 국제학술발표논문집
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• The 1th International Conference on Construction Engineering and Project Management
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• pp.908-912
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• 2005

Construction Cost Indices are values for measuring fluctuations in direct construction costs which include material costs, labor costs, and equipment costs for construction operations. In Korea, Korea Institute of Construction Technology (KICT) has been assessing and announcing these indices since January, 2004. The main goals of this paper are to look over the calculation process for those indices and then present the trend in construction costs according to the types of facilities with the past construction cost index data. Also, this paper traces the origin of the occurrence of significant changes on those indices through the further analysis of the trend. In addition, this paper shows the practicality of the indices and the way how to put them to practical use. An alternative estimate method using the indices is suggested for compensating the changes of construction costs caused by price fluctuations.

• Korean Chemical Engineering Research
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• 제46권4호
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• pp.707-713
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• 2008

직경이 0.102 m이고 높이가 2.0 m인 annular 유동층에서 최소유동화 속도 및 압력 요동 특성을 고찰하였다. 기체유속($U_G$), 고체 입자의 크기($d_p$) 그리고 유동층 온도가 최소유동화 속도 및 압력 요동 특성에 미치는 영향을 검토하였다. 본 연구 결과, annular 유동층 내의 압력 요동 자료로부터 구한 상관차원을 유동층 내부의 기체 및 유동 입자의 복합적인 거동을 정량적으로 나타내는 파라미터로 쓸 수 있었으며, 이 상관차원의 값은 기체의 유속, 유동 입자의 크기 그리고 반응기의 온도가 증가함에 따라 증가하였다. 유동층에서 유동입자의 최소유동화 속도를 유동층에서 압력 강하 및 압력 요동자료의 표준 편차를 사용하는 방법뿐만 아니라 압력 요동 자료의 상관차원을 이용하여서도 구할 수 있었으며 이들 각기 다른 방법으로 구한 최소 유동화 속도 값은 서로 매우 유사하였다. Annular 유동층에서 유동 입자의 최소유동화 속도는 유동 입자의 크기가 증가할수록 증가하였으나 유동층의 온도가 증가함에 따라 감소하였다. 본 연구의 범위내에서 annular 유동층에서 최소 유동화 속도를 압력 요동 자료의 상관 차원과 무차원군의 함수로 나타낼 수 있었다.

• 한국초전도학회:학술대회논문집
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• 한국초전도학회 1999년도 High Temperature Superconductivity Vol.IX
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• pp.22-25
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• 1999

We apply the nonperturbative parquet approximation method, which was previously used to study the effect of thermal fluctuations in two-dimensional vortex systems, to vortices in a layered superconductor. We set up the parquet equations for the Lawrence-Doniach model and present two different numerical methods to solve them. The results for a superconductor consisting of two and four layers are also discussed in connection with an observed first order transition line in the vortex liquid regime.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2003년도 제20회 춘계학술대회 논문집
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• pp.240-243
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• 2003

Combustion instability phenomena have been observed in various different combustion systems. For each specific combustion system, pressure fluctuations measured during high frequency combustion instability presented many different characteristics. High frequency instability occurring in a lean premixed gas turbine combustor mar be dominantly affected by a nonlinear relation between pressure oscillations and heat release rate fluctuations, and gas dynamics plays a crucial role in determining an amplitude of a limit cycle for a liquid rocket thrust chamber. Combustion instability phenomena manifest their inherent nonlinear characteristics. One is a limit cycle and the other bifurcation described by nonlinear time series analysis.

• 천문학논총
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• 제19권1호
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• pp.1-10
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• 2004

On the framework of a linearly perturbed Friedmann-Robertson-Walker spacetime, we derive an expression for the cosmological angular diameter distance affected by scalar and tensor perturbations. Our expression is applicable in linear order to distances in general FRW models. We study the effect of a stocastic gravitaional wave background on the two-point correlation function of the angular diameter distance fluctuations and, on the basis of this we also derive an expression for the power spectrum of the angular diameter distance fluctuations.

• 한국콘텐츠학회논문지
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• 제17권9호
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• pp.300-309
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• 2017

건설경기 국면에 대한 정확한 판단은 경제활동에 참여하는 주체들의 의사결정에 있어 매우 중요하다. 본 연구에서는 건설경기의 대표적인 변수인 건설수주와 건설투자에 대해 HP 필터와 함께 그간 연구에서 다루지 않은 밴드패스 필터 및 베버리지-넬슨 분해의 방법론을 이용하여 순환변동 분석을 실시하였다. 아울러 GDP 변동과의 관계 비교를 하였다. 의미 있는 분석결과는 다음과 같다. 1976년 1분기부터 2017년 1분기까지 건설수주는 약 7회의 순환변동이 발생한 것으로 분석되었다. 순환변동 상 건설수주는 2015년 2분기에 정점을 기록한 후 하향추세로 전환한 것으로 나타났다. 반면에 건설투자는 같은 기간 약 6회의 순환변동이 발생하였으며, 현재 2012년 3분기 저점 이후 지속적으로 상승하고 있는 것으로 나타났다. 이를 통해 건설수주가 건설투자를 선행한다는 일반적인 속성이 적용되고 있음을 확인할 수 있었다. 또한 건설수주, 건설투자, GDP의 진폭을 비교한 결과, GDP의 진폭이 가장 작고 안정적인 것으로 나타났으며, 건설수주는 그 진폭의 변동성이 가장 큰 것으로 나타났다. 따라서 건설수주는 상대적으로 변동성에 따른 리스크가 큰 변수로 경기 국면에 맞게 정부정책 등으로 조절되어야 할 필요성이 큰 것으로 판단된다.

• IEIE Transactions on Smart Processing and Computing
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• 제1권3호
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• pp.152-160
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• 2012

This paper proposes a frame-level rate control algorithm for low delay video applications to reduce the fluctuations in the bitrate. The proposed algorithm minimizes the bitrate fluctuations in two ways with minimal coding loss. First, the proposed rate control applies R-Q model to all frames including the first frame of every group of pictures (GOP) except for the first one of a sequence. Conventional rate control algorithms do not use any R-Q models for the first frame of each GOP and do not estimate the generated-bit. An unexpected output rate result from the first frame affects the remainder of the pictures in the rate control. Second, a rate-distortion (R-D) cost is calculated regardless of the hierarchical coding structure for low bitrate fluctuations because the hierarchical coding structure controls the output bitrate in rate distortion optimization (RDO) process. The experimental results show that the average variance of per-frame bits with the proposed algorithm can reduce by approximately 33.8% with a delta peak signal-to-noise ratio (PSNR) degradation of 1.4dB for a "low-delay B" coding structure and by approximately 35.7% with a delta-PSNR degradation of 1.3dB for a "low-delay P" coding structure, compared to HM 8.0 rate control.

• Wind and Structures
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• 제16권1호
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• pp.47-60
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• 2013

A dominant opening in a windward wall, which generates large internal pressures in a building, is a critical structural design criterion. The internal pressure fluctuations are a function of the dominant opening area size, internal volume size and external pressure at the opening. In addition, many buildings have background leakage, which can attenuate internal pressure fluctuations. This study examines internal pressure in buildings for a range of dominant opening areas, internal volume sizes and background porosities. The effects of background porosity are incorporated into the governing equation. The ratio of the background leakage area $A_L$ to dominant opening area $A_W$ is presented in a non-dimensional format through a parameter, ${\phi}_6-A_L/A_W$. Background porosity was found to attenuate the internal pressure fluctuations when ${\phi}_6$ is larger than 0.2. The dominant opening discharge coefficient, ${\kappa}$ was estimated to lie between 0.05 to 0.40 and the effective background porosity discharge coefficient ${\kappa}^{\prime}_L$, was estimated to be between 0.05 to 0.50.