• 한국세라믹학회지
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• 제31권9호
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• pp.989-994
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• 1994

This study aims at finding the closest packings of regular shape particles such as sphere, circle rod and hexagonal rod type. As the ratio of particle size to container lowered to less than 1/10, the wall effect decreased gradually. The tap density of spherical particles with almost orthorhombic arrangement was 59.5%, while those of circle rod and hexagonal rod type particles were 63.5% and 63.0% respectively. And it was decreased with increasing the aspect ratio of regular particles. The tap density of binary mixtures was larger than that corresponding to the monosized particles packing by about 15%. The tap density of ternary mixtures was larger than that of corresponding to the packing of binary mixtures by about 9%. This work employed the binary mixture of 60% coarse particles and 40% fine particles with size ratio of 1.0 to 1/10 and the ternary mixture of 60% coarse particles, 20% medium and 20% fine particles with size ratio of 1:1/10:1/400 respectively.

• 한국연소학회지
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• 제15권4호
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• pp.15-21
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• 2010

The transported probability density function(PDF) model has been applied to simulate the turbulent nonpremixed piloted jet flame. To realistically account for the mixture fraction PDF informations on the turbulent non-premixed jet flame, the present Lagrangian PDF transport approach is based on the joint velocity-composition-turbulence frequency PDF formulation. The fluctuating velocity of stochastic fields is modeled by simplified Langevin model(SLM), turbulence frequency of stochastic fields is modeled by Jayesh-Pope model and effects of molecular diffusion are represented by the interaction by exchange with the mean (IEM) mixing model. To validate the present approach, the numerical results obtained by the joint velocity-composition-turbulence frequency PDF model are compared with experimental data in terms of the unconditional and conditional means of mixture fraction, temperature and species and PDFs.

• 항공우주기술
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• 제12권1호
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• pp.200-206
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• 2013

액체로켓엔진에서 추진제 밀도와 공급 압력 변화에 대한 성능 민감도를 분석하였다. 해석 프로그램은 터보펌프-가스발생기 연계시험 결과와 비교하여 1% 오차를 가지는 것으로 확인되었다. 연료 공급압력이 증가하면 혼합비 감소로 인해 엔진 연소압이 감소하였고 연료의 밀도가 증가하면 혼합비 감소에도 불구하고 추진제 유량이 증가하므로 엔진 연소압이 증가하는 것으로 예측되었다. 또한 산화제의 밀도가 증가되거나 공급압력이 증가하면 엔진의 연소압이 증가할 것으로 분석되었다.

• 폴리머
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• 제24권4호
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• pp.505-512
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• 2000

본 연구는 초임계 용매인 $CO_2$, CHF$_3$ 및 CHClF$_2$내에서 poly(lactide-co-glycolide) [PLGAI 용액과의 흔합물 밀도를 측정하였다. 초임계 용매와 Poly(lactic acid) [PLA] 및 PLGA간의 흔합물 밀도는 온도 27-10$0^{\circ}C$와 압력 3000 bar까지 실험하여 나타내었다 [PLGA$_{x}$의 X는 0~50 mo1% 범위에 대한 glycolide의 몰농도이다]. PLA-$CO_2$ 흔합물은 약 1430 bar 이내에서, PLA-CHF$_3$계는 700 bar 이하에서, PLA-CHClF$_2$계는 100bar 이하에서 각각 용해되었다. 이때 온도범위는 27~93$^{\circ}C$이며, 흔합물 밀도는 1.084~l.334g/$cm^3$ 범위에서 나타났다. PLGA$_{15}$ 공중합체-$CO_2$ 흔합물은 약 1900 bar 이하에서 용해되었으며, 이때 혼합물 밀도는 37~92$^{\circ}C$에서 1.158~l.247g/$cm^3$으로 나타났다. PLGA$_{25}$공중합체-$CO_2$계는 약 2390 bar이하에서, PLGA$_{25}$-CHF$_3$계에 대해서는 1470 bar이하에서, PLGA$_{25}$-CHClF$_2$계에 대해서는 118 bar 이하에서 각각 용해되었으며, 흔합물 밀도는 29~81$^{\circ}C$사이에서 1.154~1.535g/$cm^3$로 나타났다. PLGA$_{50}$-$CO_2$계는 24$0^{\circ}C$, 3000 bar내fl서는 용해되지 않았으며, 반면 PLGA$_{50}$과 CHClF$_2$의 흔합물은 오히려 5$0^{\circ}C$와 100 bar내에서 쉽게 용해되었다. 또한 PLGA와 CHClF$_2$계는 glycolide 농도가 증가함에 따라 흔합물 밀도가 증가하였다.다..다..다..

• 한국해양공학회:학술대회논문집
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• 한국해양공학회 2001년도 추계학술대회 논문집
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• pp.269-274
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• 2001

This paper describes the experimental results on direct selective laser sintering of WC-Co mixture. The experiments were carried out within an air, argon and nitrogen atmosphere. The main problem occurred during sintering within an air atmosphere was oxidation of WC-Co mixture. As the power of laser is increased and scanning speed is decreased, more severe oxidation takes place. Within an argon and nitrogen atmosphere the oxidation is reduced significantly. As the energy density is increased the thickness of the sintered layer is increased.

• 한국안전학회지
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• 제14권2호
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• pp.83-89
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• 1999

The electrical properties due to mixture ratio of linear low density polyethylene(LLDPE) and ethylene vinyl acetate(EVA) films are studied. An experimental specimen is selected as LLDPE/EVA of thickness 200${\mu}{\textrm}{m}$ produced by mixture ratio of 50 : 50, 60 : 40, 70 : 30 and 80 : 2 wt%. In temperature range from $25^{\circ}C$ to 12$0^{\circ}C$, the measurement of volume resistivity using a highmegohm meter is performed within 10 minutes since each voltage of DC 100 V, 250 V, 500 V and 1000 V is applied, according to the step voltage method. From FT-IR spectrum for an analysis of physical properties, it can be confirmed that LLDPE blended with EVA shows an absence of carbonyl groups(1735 $cm^{-1}$, C=0) and ether groups(1242 $cm^{-1}$, C-O). The peak of LLDPE and EVA made of mixture ratio of 70 : 30 at 2$\theta$ =21.4$^{\circ}$ in the results of XRD is higher than the others. In the experiment for volume resistivity characteristics in order to investigate the electrical properties of specimen, it is confirmed that volume resistivity is decreased with the increase of the molecular motion and temperature.

• Advances in concrete construction
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• 제10권2호
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• pp.127-140
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• 2020

This study explores the feasibility of granite waste aggregate (GWA) as a partial replacement of natural fine aggregate (NFA) in binary blend self-compacting concrete (SCC) prepared with fly ash. Total of nine SCC mixtures were prepared wherein one was Ordinary Portland cement (OPC) based control SCC mixture and remaining were fly ash based binary blend SCC mixtures which included the various percentages of GWA. Fresh properties tests such as slump flow, T₅₀₀, V-funnel, J-ring, L-box, U-box, segregation resistance, bleeding, fresh density, and loss of slump flow (with time) were conducted. Compressive strength and percentage of permeable voids were evaluated in the hardened state. All the SCC mixtures exhibited sufficient flowability, passing ability, and resistance to segregation. Besides, all the binary blend SCC mixtures exhibited lower fresh density and bleeding, and better residual slump (up to 50% of GWA) compared to the OPC based control SCC mixture. Binary blend SCC mixture incorporating up to 40% GWA provided higher compressive strength than binary blend control SCC mixture. The findings of this study encourage the utilization of GWA in the development of binary blend SCC mixtures with satisfactory workability characteristics as a replacement of NFA.

• 한국병원경영학회지
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• 제10권4호
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• pp.75-97
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• 2005

The research objective is to empirically investigate the compensation packages maximizing the utilities of internal customers by applying the market segmentation theory. Data was collected from four Korean hospitals in Seoul, Busan and Gyunggi-do. The research is designed to seek the compensation package maximizing the utility of doctors by mixture regression model, which has been applied as latent structure and other type of finite mixture models from various academic fields since early 1980s. The mixture regression model shows the optimal segments number and fuzzy classification for each observation by EM(expectation-maximization algorism). The finite mixture regression model is to unmix the sample, to identify the groups, and to estimate the parameters of the density function underlying the observed data within each group. The doctors were segmented into 5 groups by their preference for the compensation package. The results of this study imply that the utility of doctors increases with differentiated compensation package segmented by their preference.

• 응용통계연구
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• 제24권2호
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• pp.425-433
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• 2011

Reject inference in credit scoring is a statistical approach to adjust for nonrandom sample bias due to rejected applicants. Function estimation approaches are based on the assumption that rejected applicants are not necessary to be included in the estimation, when the missing data mechanism is missing at random. On the other hand, the density estimation approach by using mixture models indicates that reject inference should include rejected applicants in the model. When mixture models are chosen for reject inference, it is often assumed that data follow a normal distribution. If data include missing values, an application of the normal mixture model to fully observed cases may cause another sample bias due to missing values. We extend reject inference by a multivariate normal mixture model to handle incomplete characteristic variables. A simulation study shows that inclusion of incomplete characteristic variables outperforms the function estimation approaches.

• 보건행정학회지
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• 제12권2호
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• pp.1-22
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• 2002

Since the early 1980s scholars have applied latent structure and other type of finite mixture models from various academic fields. Although the merits of finite mixture model are well documented, the attempt to apply the mixture model to medical service has been relatively rare. The researchers aim to try to fill this gap by introducing finite mixture model and segmenting inpatients DB from one general hospital. In section 2 finite mixture models are compared with clustering, chi-square analysis, and discriminant analysis based on Wedel and Kamakura(2000)'s segmentation methodology schemata. The mixture model shows the optimal segments number and fuzzy classification for each observation by EM(expectation-maximization algorism). The finite mixture model is to unfix the sample, to Identify the groups, and to estimate the parameters of the density function underlying the observed data within each group. In section 3 and 4 we illustrate results of segmenting 4510 patients data including menial and ratio scales. And then, we show AHP can be identify the attractiveness of each segment, in which the decision maker can select the best target segment.