• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 1999년도 유체기계 연구개발 발표회 논문집
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• pp.179-186
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• 1999

Three-dimensional flow analysis is implemented to investigate the flow through transonic axial-flow compressor rotor(NASA R67), and to evaluate the performances of k-$\epsilon$ and Baldwin-Lomax turbulence models. A finite volume method is used for spatial discretization. And, the equations are solved implicitly in time with the use of approximate factorization. Upwind difference scheme is used for inviscid terms, but viscous terms are centrally differenced. The flux-difference-splitting of Roe is used to obtain fluxes at the cell faces. Numerical analysis is performed near peak efficiency and near stall. And, the results are compared with the experimental data for NASA R67 rotor. Blade-to-Blade Mach number distributions are compared to confirm the accuracy of the code. From the results, we conclude that k-$\epsilon$ model is better for the calculation of flow rate and efficiency than Baldwin-Lomax model. But, the predictions for Mach number and shock structure are almost same.

• Nuclear Engineering and Technology
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• 제50권6호
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• pp.849-853
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• 2018

Mechanistic calculations for wet scrubbing of aerosol/vapor from gas bubble rising in liquid pool are essential to safety of sodium-cooled fast reactor. Hence, scrubbing of volatile fission product from mixed gas bubble rising in sodium pool is presented in this study. To understand this phenomenon, a theoretical model has been setup based on classical theories of aerosol/vapor removal from bubble rising through liquid pools. The model simulates pool scrubbing of sodium iodide aerosol and cesium vapor from a rising mixed gas bubble containing xenon as the inert species. The scrubbing of aerosol and vapor are modeled based on deposition mechanisms and Fick's law of diffusion, respectively. Studies were performed to determine the effect of various key parameters on wet scrubbing. It is observed that for higher vapor diffusion coefficient in gas bubble, the scrubbing efficiency is higher. For aerosols, the cut-off size above which the scrubbing efficiency becomes significant was also determined. The study evaluates the retention capability of liquid sodium used in sodium-cooled fast reactor for its safe operation.

• 융복합기술연구소 논문집
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• 제1권1호
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• pp.41-47
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• 2011

With the world-wide demand on the emission minimization, the needs on the diesel aftertreatment devices with high efficiency are also increasing. In order to effectively develop or design a high-performance diesel particulate filter, a clear understanding on the deposition and regeneration mechanism is required. In the present study, a theory on the lumped parameter model for wall-flow type diesel particulate filters is described focusing on the deposition efficiency, pressure drop inside the filter. The fourth order explicit Runge-Kutta method is utilized for the mass flow rate computation. Engine operation modes with controlled and uncontrolled regeneration options are selected. The computational lumped parameter model is validated by comparing the computed results with the measured data.

• Advances in nano research
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• 제16권5호
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• pp.521-529
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• 2024

The integration of nanoparticles into various industries has spurred interest in understanding their impact on logistics and transportation systems. In this study, we investigate the effect of nanoparticles on the economic aspects of railway logistics transport using a mathematical model. By incorporating factors such as transportation costs, time efficiency, and environmental considerations, we aim to assess the overall economic feasibility of integrating nanoparticles into railway logistics operations. Through mathematical modeling and analysis, we explore how the introduction of nanoparticles affects cost-benefit analyses, resource allocation, and decision-making processes within railway logistics. Our findings provide valuable insights into the economic implications of nanoparticle integration in railway transport, offering potential strategies for optimizing logistics operations and enhancing overall efficiency and sustainability.

• 유통과학연구
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• 제15권8호
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• pp.75-86
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• 2017

Purpose - The online-to-offline (O2O) business model has brought considerable changes to the traditional Chinese business model. The main difference between O2O and pure online consumption is that O2O offers a richer experience and word-of-mouth. it is easier to trigger online word-of-mouth. However, few scholars have been concerned about the impact of experiential value on customer satisfaction and online word-of-mouth (e-WOM) in the study of O2O. This study takes the O2O business model in China's catering industry as its research object and uses structural equation modelling to analyze the impact of online and offline experiential values on customer satisfaction and e-WOM. Research design, data, and methodology - According to previous researches, consumer experiential value is mainly divided into return on investment (economy and efficiency), service excellence, playfulness and aesthetics. According to the characteristics of O2O in China's catering industry, this study divides the online experience value into efficiency and economy (return on investment). The offline part is divided into return on investment (economy and efficiency), service excellence, playfulness and aesthetics. Using a web-based survey, we collected 303 valid samples. Structural equation modelling was used to create the research model. Results - The results show that efficiency (online) and service excellence (offline) have a significant effect on customer satisfaction. Economics (online) and playfulness (offline) have a positive impact on customers' e-WOM. In addition, the higher the customer satisfaction, the greater the positive impact on the spread by word of mouth. However, aesthetic(offline) and return on investment(offline) have no significant impact to customer satisfaction and e-WOM. Conclusions - The study findings show that the key to boost customer satisfaction in the catering industry is to improve product quality and service. Although traditional competitive strategies such as online discount have been questioned by many scholars about their decreasing effectiveness, they are indispensable means to attract online traffic and trigger e-WOM. The traditional enterprises can reconstruct traditional business processes through the O2O model to effectively improve customer satisfaction and word of mouth by improving the experiential value of economy and efficiency. Additionally, it can be used as the natural advantages of online communication to induce customers to engage in word of mouth and attract more potential customers.

• 생물환경조절학회지
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• 제13권4호
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• pp.209-216
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• 2004

본 연구에서는 폐쇄형 식물 생산시스템 내에서 생체정보에 의한 최적 환경제어와 식물의 환경스트레스 판단을 위하여 엽록소형광 분석법으로 광합성효율 모델을 만들었으며, 광합성효율 모델에 유전알고리즘을 적용하여 재배환경 최적화 프로그램의 응용성을 평가하였다. 6가지 미기상 요인 중 5가지는 고정하고 1가지씩만 변화시켜 가며 측정한 Fv'/Fm'이 최대가 되는 환경조건은 기온 $21^{\circ}C,\;CO_2$농도 $1,200\~1,400ppm$, 상대습도 $68\%$, 기류속도 $1.4m{\cdot}s^{-1}$, 배양액온도 $20^{\circ}C$이었으며 PPF가 $140{\mu}mol{\cdot}m^{-2}{\cdot}s^{-1}$ 보다 증가할수록 광합성 효율은 감소하였다. 광합성효율모델의 오차는 평균 $2.5\%$였다. 재배환경 최적화 프로그램으로부터 계산된 밀폐형식물 생산시스템내에서 상추의 최적재배환경조건은 기온 $22^{\circ}C$, 배양액온도 $19^{\circ}C,\;CO_2$농도 1,400ppm, 기류속도 $1.0m{\cdot}s^{-1}$, PPF $430{\mu}mol{\cdot}m^{-2}{\cdot}s^{-1}$, 상대습도 $65\%$이다. 이상의 연구 결과로부터 광합성 효율 모델을 이용하여 식물 생산시설의 환경모니터링 시스템과 식물 생체정보에 의한 최적제어시스템의 개발이 가능함을 확인하였다.

• 한국항만경제학회지
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• 제38권3호
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• pp.29-51
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• 2022

본 연구의 목적은 국제해사기구(IMO)의 배출규제해역(ECA) 시행에 따른 환경규제가 페리 선사들의 재무지표로 구성된 효율성에 어떠한 영향을 미쳤는지 실증적으로 분석하는데 있다. 이에 따라 본 연구에서는 2004년부터 2017년 까지 북유럽, 지중해, 북미 지역의 8개 페리선사의 재무데이터를 수집하여, ECA가 페리선사의 재무성과에 미친 영향을 효율성의 관점에서 지역별로 추정하였다. 방법론적 측면에서 본 연구의 학술적 기여는 다음과 같다. DEA의 자의적인 변수 선정 문제를 완화하기 위하여 Dyson et al.(2001)이 제시한 변수 선정 기준을 적용했으며, Network SBM DEA 모형을 통하여 기업의 규모를 고려하는 동시에 기업의 수익 창출 과정을 단계별로 구분하여 재무성과를 보다 세밀하게 측정하였다. 또한 BTR 모형을 적용하여 편의(Bias)를 최소화한 결과를 도출하였다. 연구 결과 가장 강한 규제를 받았던 북유럽 선사의 경우 오히려 효율성의 꾸준한 증가가 관측되었다. 북미지역 선사들의 경우 정부지원금이 효율성에 큰 영향을 미친 것으로 드러났으며, 상대적으로 ECA와 유가에 의한 영향은 적었던 것으로 관측되었다. 반면 지중해 지역의 경우 가장 낮은 수준의 규제를 받았음에도 불구하고, 규제 이후로 효율성 값이 낮아지는 모습이 관측되었다. 본 연구는 향후 ECA가 확대될 예정인 아시아의 페리선사와 정책당국에 의사결정의 참고자료로서 기능할 수 있을 것으로 생각된다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제7권1호
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• pp.81-98
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• 2013

Since Probabilistic Latent Semantic Analysis (PLSA) and Latent Dirichlet Allocation (LDA) were introduced, many revised or extended topic models have appeared. Due to the intractable likelihood of these models, training any topic model requires to use some approximation algorithm such as variational approximation, Laplace approximation, or Markov chain Monte Carlo (MCMC). Although these approximation algorithms perform well, training a topic model is still computationally expensive given the large amount of data it requires. In this paper, we propose a new method, called non-simultaneous sampling deactivation, for efficient approximation of parameters in a topic model. While each random variable is normally sampled or obtained by a single predefined burn-in period in the traditional approximation algorithms, our new method is based on the observation that the random variable nodes in one topic model have all different periods of convergence. During the iterative approximation process, the proposed method allows each random variable node to be terminated or deactivated when it is converged. Therefore, compared to the traditional approximation ways in which usually every node is deactivated concurrently, the proposed method achieves the inference efficiency in terms of time and memory. We do not propose a new approximation algorithm, but a new process applicable to the existing approximation algorithms. Through experiments, we show the time and memory efficiency of the method, and discuss about the tradeoff between the efficiency of the approximation process and the parameter consistency.

• 대한산업공학회지
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• 제37권4호
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• pp.358-366
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• 2011

Multi-criteria ABC inventory classification, which aims to classify inventory items by considering more than one criterion, is one of the most widely employed techniques for inventory control. The weighted linear optimization (WLO) model proposed by Ramanathan (2006) solves the problem of multi-criteria ABC inventory classification by generating a set of criterion weights for each inventory item and assigning a normalized score to the item for ABC analysis. However, the WLO model has some limitations. First, many inventory items can share the same optimal score, which can hinder a precise classification of inventory items. Second, the model allows too much flexibility in weighting multiple criteria; each item is allowed to choose its own weights so that it can maximize its score. As a result, if an item dominates the others in terms of a certain criterion, it may be classified into a higher class regardless of other criteria by assigning an overwhelming weight to the criterion. Consequently, an item with a high value in an unimportant criterion and low values in others may be inappropriately classified as class A, leading to an inaccurate classification of inventory items. To overcome these shortcomings, we extend the WLO model by using the cross-efficiency method in data envelopment analysis. We claim that the proposed model can provide a more reasonable and accurate classification of inventory items by mitigating the adverse effect of flexibility in the choice of weights and yielding a unique ordering of inventory items.

• 한국농공학회논문집
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• 제50권1호
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• pp.25-37
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• 2008

When livestock facilities in Korea have been changed larger and denser, rearing conditions have been getting worse and the productivity of animal production have been decreased. Especially in the cold season, the minimized ventilation has generally been operated to save energy cost in Korea resulting in very poor environmental condition and high mortality. While the stability, suitability, and uniformity of the rearing condition are the most important for high productivity, the ventilation configuration is the most important to improve the rearing condition seasonally. But, it is so difficult to analyze the internal air flow and the environmental factors by conducting only field experiment because the weather condition is very unpredictable and unstable as well as the structural specification can not be easily changed by the researchers considering cost and labor. Accordingly, an aerodynamic computer simulation was adopted to this study to overcome the weakness of conducting field experiment and study the aerodynamic itself. It has been supposed that the airflow is the main mechanism of heat, mass, and momentum transfers. To make the simulation model accurately and actually, simplified pig models were also developed. The accuracy of the CFD simulation model was enhanced by 4.4 % of errors compared with the data collected from field experiments. In this paper, using the verified CFD model, the CFD computed internal rearing condition of the mechanically ventilated pig house were analyzed quantitatively as well as qualitatively. Later, this developed model will be computed time-dependently to effectively analyze the seasonal ventilation efficiency more practically and extensively with tracer gas decay theory.