• 한국진공학회:학술대회논문집
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• 한국진공학회 2009년도 제38회 동계학술대회 초록집
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• pp.438-438
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• 2010

The abnormal behavior of the argon metastable density during the E-H mode transition in argon ICP discharge was investigated. Lots of investigations including global models expected that during and after the mode transition of ICP discharge, the density of metastable increases with applied rf power (i.e. electron density). However, recent direct measurement of metastable density revealed that the metastable density of argon decreases with the applied power during and after the mode transition. This result may not be explained by the previous global model which is based on the assumption of the Maxwellian electron energy distribution function (EEDF). In this paper, to explain this abnormal behavior with simple manners, a simple global model taking account of the effect of the non-Maxwellian EEDFs incorporating into a set of coupled rate equations is proposed. The result showed that the calculated metastable density taking account of non-Maxwellian EEDF and its evolution during the transition has an abnormal behavior with electron density and is in good agreement with the previous measurement results, indicating the close coupling of electron kinetics and the behavior of metastable density. The proposed simple model is expected to provide qualitative kinetic insight to understand the behavior of the metastable density in various plasma discharges which typically exhibit non-Maxwellian distribution.

• KIEAE Journal
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• 제11권4호
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• pp.19-27
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• 2011

This study aims to find the determining factors for apartment rental prices by using Stepwise Multiple Regression Analysis. In the process, differences among the groups and multicollinearity and correlation between the variables are examined using analysis of variance(ANOVA), correlation analysis and factor analysis. The comprehensive analysis of reliability of the variable and comprehensivization ensure objectivity. For this analysis, the characteristics of the determining factors for apartment rental prices by sub-regions in Seoul are as follows : First, the housing supply rate appears center of the central and the southwest region is influenced by the cultural and ecological environment, convenience, the size of the complex and reputation of the developer. Second, the northeast region is generally influenced by the regional economy, housing size, the density of the complex, well-known construction companies and relevant variables of individual housing and the density of the complex, physical and social environment, reputation of the developer, local economy and housing size. Lastly, the southeast region appears to be influenced by the local economy, the density of the complex, housing size and the educational environment.

• Structural Engineering and Mechanics
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• 제75권6호
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• pp.771-784
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• 2020

Reliability analysis techniques combining with various surrogate models have attracted increasing attention because of their accuracy and great efficiency. However, they primarily focus on the structures with continuous response, while very rare researches on the reliability analysis for structures with discontinuous response are carried out. Furthermore, existing adaptive reliability analysis methods based on importance sampling (IS) still have some intractable defects when dealing with small failure probability, and there is no related research on reliability analysis for structures involving discontinuous response and small failure probability. Therefore, this paper proposes a novel reliability analysis method called AGPC-IS for such structures, which combines adaptive Gaussian process classification (GPC) and adaptive-kernel-density-estimation-based IS. In AGPC-IS, an efficient adaptive strategy for design of experiments (DoE), taking into consideration the classification uncertainty, the sampling uniformity and the regional classification accuracy improvement, is developed with the purpose of improving the accuracy of Gaussian process classifier. The adaptive kernel density estimation is introduced for constructing the quasi-optimal density function of IS. In addition, a novel and more precise stopping criterion is also developed from the perspective of the stability of failure probability estimation. The efficiency, superiority and practicability of AGPC-IS are verified by three examples.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2005년도 춘계학술대회 논문집
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• pp.607-610
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• 2005

A remeshing algorithm using tetrahedral elements has been developed, which is adapted to the mesh density map constructed by a posteriori error estimation. In the finite element analyses of metal forging processes, numerical error increases as deformation proceeds due to severe distortion of elements. In order to reduce the numerical error, the desired mesh sizes in each region of the workpiece are calculated by a posteriori error estimation and the density map is constructed. Piecewise density functions are then constructed with the radial basis function in order to interpolate the discrete data of the density map. The sample mesh is constructed based on the point insertion technique which is adapted to the density function and the mesh size is controlled by moving and deleting nodes to obtain optimal distribution according to the mesh density function and the quality optimization function as well. After finishing the redistribution process of nodes, a tetrahedral mesh is constructed with the redistributed nodes, which is adapted to the density map and resulting in good mesh quality. A goodness and adaptability of the constructed mesh is verified with a testing measure. The proposed remeshing technique is applied to the finite element analyses of forging processes.

• Membrane and Water Treatment
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• 제7권2호
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• pp.127-141
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• 2016

Electrodialysis (ED) is known to be a useful membrane process for desalination, concentration, separation, and purification in many fields. In this process, it is desirable to work at high current density in order to achieve fast desalination with the lowest possible effective membrane area. In practice, however, operating currents are restricted by the occurrence of concentration polarization phenomena. Many studies showed the occurrence of a limiting current density (LCD). The limiting current density in the electrodialysis process is an important parameter which determines the electrical resistance and the current utilization. Therefore, its reliable determination is required for designing an efficient electrodialysis plant. The purpose of this study is the development of a predictive model of the limiting current density in an electrodialysis process using response surface methodology (RSM). A two-factor central composite design (CCD) of RSM was used to analyze the effect of operation conditions (the initial salt concentration (C) and the linear flow velocity of solution to be treated (u)) on the limiting current density and to establish a regression model. All experiments were carried out on synthetic brackish water solutions using a laboratory scale electrodialysis cell. The limiting current density for each experiment was determined using the Cowan-Brown method. A suitable regression model for predicting LCD within the ranges of variables used was developed based on experimental results. The proposed mathematical quadratic model was simple. Its quality was evaluated by regression analysis and by the Analysis Of Variance, popularly known as the ANOVA.

• 한국통신학회논문지
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• 제28권10C호
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• pp.936-941
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• 2003

최근에 소개된 density evolution 기법은 sum-product 알고리즘에서 LDPC 부호가 갖는 성능의 한계를 분석하였다[1]. 또한. Iterative decoding 알고리즘에서 전달되는 정보가 Gaussian 확률분포를 갖는 점을 이용하여 기존의 density evolution 기법을 단순화 시킨 연구결과가 소개되었다[2]. 한편. LDPC 부호의 한계 성능을 sum-product가 아닌 min-sum 알고리즘에서 분석한 결과가 최근에 발표되었다[3]. 본 논문에서는 이러한 일련의 연구 결과를 바탕으로 min-sum 알고리즘을 이용하면서 Gaussian 확률 분포 특성을 이용한 density evolution 기법을 소개한다. 제안된 density evolution 기법은 기존의 방법보다 적은 계산으로 정확한 threshold를 구할 수 있으며. 그 결과가 numerical simulation 결과와 잘 일치함을 나타내었다.

• 대한교통학회지
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• 제24권5호
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• pp.135-142
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• 2006

교통류 이론에서 fundamental diagram이라고 불리는 교통량-밀도 관계는 stationary 상태에서의 교통량과 밀도사이의 평형관계 (equilibrium relation)를 나타낸다 본 연구에서는 개별차량 데이터를 이용하여 교통량-밀도 관계의 전제조건인 stationary 조건을 만족하는 데이터를 추출하는 방법을 제시하였고, stationary 조건을 만족하는 데이터를 교통량-밀도 평면에 도시하였다. 개별차량의 흐름이 자유교통류상태와 혼잡교통류상태에서 상이하며 지점에서 관측된 데이터가 서로 다른 특성의 시계열특성을 보인다는 점에 근거하여 두 가지 상태에 따라 서로 다른 stationary조건을 제시하였다. 본 논문에서 제시된 stationary 조건을 실제로 관측된 데이터에 적용한 결과 자유교통류상태의 stationary조건을 만족하는 데이터는 현재까지 알려진 바와 같이 교통류-밀도 관계의 왼쪽가지에 위치하고. 혼잡교통류상태의 stationary조건을 만족하는 데이터는 교통류-밀도관계의 오른쪽 가지에 위치한다. 또한 본 연구에서 제시된 방법론에 따라 교통류-밀도관계의 전범위에 걸쳐 stationary조건을 만족하는 데이터를 구별하여 교통류-밀도평면에 도시한 결과 교통류의 거의 전영역에 걸쳐 재현 가능한 관계가 나타나는 것을 확인할 수 있었다.

• 농촌의학ㆍ지역보건
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• 제48권4호
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• pp.275-284
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• 2023

Objectives: This study aimed to assess hand grip strength and femoral neck bone mineral density levels among Korean fishery workers and investigate their association. Methods: Hand grip strength and femoral neck bone mineral density were measured in a survey and health examination conducted in 2021 among fishery workers in a southern region of South Korea. Covariates including gender, age, education level, income level, smoking behavior, drinking behavior, family history of hip fractures, use of calcium and vitamin D supplements, hypertension, diabetes, regular exercise, and body mass index were investigated. Multiple regression analysis was employed to assess the association between hand grip strength and femoral neck bone mineral density. Results: Among 147 fishery workers, 8.16% exhibited low hand grip strength levels indicative of possible sarcopenia, and a significant association was found between low hand grip strength and decreased femoral neck bone mineral density (β = -89.14, 95% CI = -160.50, -17.78). Additionally, factors such as women gender, advanced age, family history of hip fractures, and a body mass index below 25 kg/m² were associated with decreased femoral neck bone mineral density. In the subgroup analysis by gender, a correlation between low hand grip strength and decreased femoral neck bone mineral density was observed only in men. Conclusions: Further research is needed to explore various determinants and intervention strategies to prevent musculoskeletal disorders among fishery workers, ultimately enhancing their quality of life and well-being.

• 농업과학연구
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• 제50권4호
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• pp.841-860
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• 2023

The present study was conducted to evaluate the effects of dietary mangosteen peel extract (MPE) on growth performance, serum biochemistry, jejunum morphology, and cytokine levels in growing pigs raised at a high stocking density. A total of 120 male growing pigs (43.68 ± 0.48 kg) were randomly arranged in a 2 × 2 factorial design with stocking density (high; HD, 0.55 m²/pig and normal; ND, 0.82 m²/pig) and dietary MPE (0 or 5 g/kg) as factors. Each treatment had six replicates with four or six pigs per treatment. Feed and water were provided ad libitum for 6 weeks. The HD group exhibited lower final body weight, average daily gain, and average daily feed than the ND group (p < 0.05). None of the factors affected villus height to crypt depth ratio. Dietary MPE, but not stocking density, increased IL-10 levels in the serum com-pared to the non-supplemented control diet (p < 0.05). In the microbiome analysis, alpha diversity analysis showed significant reductions in the MPE-treated group only under normal density conditions. High density stress induced gut microbiome changes and these response was differ between normal and MPE diet fed pigs. Overall, each group exhibited different major microbial composition in the gut. In conclusion, there were significant changes in the major microbial composition in response to high-density stress, and this variation was influenced by dietary treatment.

• 한국분말재료학회지
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• 제4권2호
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• pp.83-89
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• 1997

A finite element analysis to solve the coupled thermomechanical problem in the plane strain upsetting of the porous metals was performed. The analysis was formulated using the yield function advanced by Lee and kim and developed using the thermo-elasto-plastic time integration procedure. The density and temperature dependent thermal and mechanical properties of porous metals were considered. The internal heat generation by the plastic deformation and the changing thermal boundary conditions corresponding to the geometry were incorporated in the program. The distributions of the stress, strain, pressure, density and temperature were predicted during the free resting period, deformation period and dwelling period of the forging process.