• Title/Summary/Keyword: coefficient-based method

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Effect of Annealing Temperature on Microstructure and Properties of the Pressureless-Sintered $SiC-TiB_2$ Electroconductive Ceramic Composites (상압소결(常壓燒結)한 $SiC-TiB_2$ 전도성(電導性) 복합체(複合體)의 미세구조(微細構造)와 특성(特性)에 미치는 Annealing 온도(溫度)의 영향(影響))

  • Shin, Yong-Deok;Ju, Jin-Young
    • The Transactions of the Korean Institute of Electrical Engineers C
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    • v.55 no.10
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    • pp.467-474
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    • 2006
  • The effect of pressureless-sintered temperature on the densification behavior, mechanical and electrical properties of the $SiC-TiB_2$ electroconductive ceramic composites was investigated. The $SiC-TiB_2$ electroconductive ceramic composites were pressureless-sintered for 2 hours at temperatures in the range of $1,750{\sim}1,900[^{\circ}C]$, with an addition of 12[wt%] $Al_2O_3+Y_2O_3(6:4\;mixture\;of\;Al_2O_3\;and\;Y_2O_3)$ as a sintering aid. The relative density, flexural strength, vicker's hardness and fracture toughness showed the highest value of 84.92[%], 140[MPa], 4.07[GPa] and $3.13[MPa{\cdot}m^{1/2}]$ for $SiC-TiB_2$ composites of $1,900[^{\circ}C]$ sintering temperature at room temperature respectively. The electrical resistivity was measured by the Pauw method in the temperature ranges from $25[^{\circ}C]\;to\;700[^{\circ}C]$. The electrical resistivity showed the value of $5.51{\times}10^{-4},\;2.11{\times}10^{-3},\;7.91{\times}10^{-4}\;and\;6.91{\times}10^{-4}[\Omega{\cdot}cm]$ for ST1750, ST1800, ST1850 and ST1900 respectively at room temperature. The electrical resistivity of the composites was all PTCR(Positive Temperature Coefficient Resistivity). The resistance temperature coefficient showed the value of $3.116{\times}10^{-3},\;2.717{\times}10^{-3},\;2.939{\times}10^{-3},\;3.342{\times}10^{-3}/[^{\circ}C]$ for ST1750, ST1800, ST1850 and ST1900 respectively in the temperature ranges from $25[^{\circ}C]\;to\;700[^{\circ}C]$. It is assumed that because polycrystallines, such as recrystallized $SiC-TiB_2$ electroconductive ceramic composites, contain of porosity and In Situ $YAG(Al_5Y_3O_{12})$ crystal grain boundaries, their electrical conduction mechanism are complicated. In addition, because the condition of such grain boundaries due to $Al_2O_3+Y_2O_3$ additives widely varies with sintering temperature, electrical resistivity of the $SiC-TiB_2$ electroconductive ceramic composites with sintering temperature also varies with sintering condition. It is convinced that ${\beta}-SiC$ based electroconductive ceramic composites for heaters or ignitors can be manufactured by pressureless sintering.

The homogenization analysis for permeability coefficients by fracture aperture variations (균질화 해석법을 이용한 단열 간극변화에 따른 투수계수 해석)

  • 채병곤
    • The Journal of Engineering Geology
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    • v.14 no.1
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    • pp.47-60
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    • 2004
  • The permeability coefficients were calculated by the homogenization analysis method with sufficient consideration of fracture geometry dependent on aperture change. According to the results of aperture measurements using a confocal laser scanning microscope, apertures on each measuring point display different magnitudes, indicating that fracture walls can not be assumed as parallel feature. After construction of fracture model based on the aperture values measured on each pressure level, the homogenization analysis was conducted to compute permeability coefficients. The calculated permeability coefficients distribute in the ranges of $10^{-1}~10^{-3}cm/sec$. Most of the specimens show decreasing permeability coefficients with the increase of the applied pressure. However, the decreasing rates of permeability coefficients do not show a constant trend on each pressure level. This phenomenon is well matched to the observation results of Chae et al. (2003). It proves that aperture change strongly influences on permeability characteristics. Three sections of each specimen have all different values of permeability coefficient. It suggests that the variation of permeability coefficient depends sensitively on aperture magnitudes and characteristics of fracture geometry. It is very important to consider accurate fracture geometries for analysis of permeability characteristics in rock fractures bearing different aperture distribution. Therefore, it needs to consider sufficiently the fracture geometries for calculating the permeability coefficients of fractures.

A Study on Influence Factors for Tunnel Collapse Risk Analysis using Delphi Method (델파이 기법을 활용한 터널 붕괴 위험도 분석을 위한 영향인자 도출에 관한 연구)

  • Kim, Jeong Heum;Kim, Chang Yong;Lee, Seung Soo;Lee, Jun Hwan
    • The Journal of Engineering Geology
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    • v.27 no.2
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    • pp.165-172
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    • 2017
  • This research aims to define influence factors to perform an optimized section design and evaluate tunnel collapse risk during construction using Delphi technique. A total of five upper classification systems were constructed through literature review, pervious research analysis, and brainstorming of expert group for establishing influence factors. The $1^{st}$, $2^{nd}$, and $3^{rd}$ Delphi survey process was proceeded by panel group which is consisted 21 experts to prevent errors and bias in the expert judgement process. In Delphi $1^{st}$ survey, a total of 22 influence factors candidates were derived through open-ended questionnaire. In Delphi $2^{nd}$ survey, questionnaire was proceeded based on 7-point Likert scale method. In order to verify the validity, CVR (Content Validity Ration) analysis was performed to exclude inappropriate candidates. In the $3^{rd}$ survey, verification of influence factors was proceeded once more with the result of $2^{nd}$ survey, and lastly, a total of 14 influence factors was derived by CVR and COV (Content Validity Ration) analysis for response of experts.

Examples of NCS-based Learning Assessment: For the College of Radiotechnology (NCS 기반 학습평가 사례: 전문대학 방사선과 학생들을 대상으로)

  • Park, Jeongkyu
    • Journal of the Korean Society of Radiology
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    • v.13 no.3
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    • pp.407-414
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    • 2019
  • Recently, after the reorganization as the basis of NCS education, various learning methods are being sought for improving the basic occupational ability and job ability required by NCS, and the evaluation method accordingly is urgently needed. The purpose of this study was to evaluate the applicability of meta-cognitive learning and Havruta learning as evaluation cases in order to improve the job skills and basic skills required in the NCS curriculum. As a result, the meta-cognitive learning response sample statistic showed an average of 2.6883 when the pre-meta-cognitive learning questionnaire was a 5-point scale, and an average of 4.2468 after the meta-cognitive learning questionnaire. The correlation coefficient was 0.782 and the significance probability was 0.045. In the case of the Havruta learning correspondence sample statistic, the average of 3.1515 when the preliminary Havruta learning questionnaire was a 5 point scale and the average of the post-Havruta learning questionnaire was 4.3853, which was improved by 1.23 points. The correlation coefficient was 0.631 and the significance probability was 0.049. Meta-cognitive learning and Havruta learning were found to be correlated. The mean of meta cognition was 3.4675 and the mean of Havruta was 3.7684. Metacognitive learning and Havruta learning were -0.042 And there was no statistically significant difference. Therefore, the learning method to improve the job ability should be applied considering the characteristics of the subject.

A Study on Comparison of Density Test Methods for Quality Control of Cement and Mineral Admixture (시멘트 및 혼화재의 품질관리를 위한 밀도 시험방법 비교 연구)

  • Jae-Seung, Lee;Sang-Kyun, Noh;Cheol, Park;Hong-Chul, Shin
    • Journal of the Korean Recycled Construction Resources Institute
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    • v.10 no.4
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    • pp.435-442
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    • 2022
  • In this study, the density of KS L 5110 was compared with that of gas pycnometer and electronic densimeter for efficient density management of cement, blast furnace slag powder and fly ash. Correlation and usability according to the test method were reviewed, and based on the results of the experiment, the availability of alternative test methods was analyzed. As a result of the density test according to test methods, the density of cement, blast furnace slag powder and fly ash tended to decrease in the order of gas pycnometer, KS L 5110 and electronic densimeter. Because the volume range of the sample to be evaluated is different depending on test methods. The coefficient of determination R2 was in the range of 0.71 to 0.93, and the correlation according to test methods showed a relatively good correlation. If correction is applied through correlation, it is analyzed that alternative test methods can be used. As a result of the usability review considering the test procedure, measurement time and coefficient of variation, the gas pycnometer had the simplest test procedure and good reliability. In addition, it is expected that the reproducibility between the testers is relatively high because the skill is not greatly required.

Experimental Study on Reduction of Nitrogen-Containing Compounds Contained in Crude Methylnaphthalene Oil by Solvent Extraction (I): Reduction of Nitrogen-Containing Compounds Contained in Model Crude Methylnaphthalene Oil of 5 Components System (용매 추출에 의한 조제 메틸나프탈렌유에 함유된 함 질소화합물의 저감에 관한 실험적 연구(I): 5성분계 모델 조제 메틸나프탈렌유에 함유된 함 질소화합물의 저감)

  • Kang, Ho-Cheol;Kim, Su Jin
    • Applied Chemistry for Engineering
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    • v.33 no.4
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    • pp.431-435
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    • 2022
  • The reduction of nitrogen-containing compounds (NC) containing the model crude methylnaphthalene oil (CMNO) of 5 compounds system was experimentally studied by solvent extraction. The model CMNO consisting of 3 kinds of NC including quinolone (QU), iso-quinoline (IQU), indole(IN) and 2 kinds of bicyclic aromatic compounds such as 1-methylnaphthalene (1MNA), 2-methylnaphthalene (2MNA) as raw materials, as well as the aqueous solution of formamide as a solvent, were used. The increase in the volume fraction of water to the solvent at the initial state (yw,0) sharply decreased, but the distribution coefficient and the yield of NC conversely increased the selectivity of NC based on 2MNA, and an increase in the volume fraction of solvent to feed (S/F) simultaneously increased the distribution coefficient, yield and selectivity of NC. The yields of QU, IQU and IN under constant conditions (yw,0 = 0.1, S/F = 1, equilibrium temperature 303 K) were 30%, 31% and 10%, respectively, and selectivity was 15, 15 and 20, respectively. From the excellent yield and selectivity of NC, the formamide extraction method of this study was expected as a method for reducing the NC contained in the model CMNO.

A Study on Improvement of Air Quality Dispersion Model Application Method in Environmental Impact Assessment (II) - Focusing on AERMOD Model Application Method - (환경영향평가에서의 대기질 확산모델 적용방법 개선 연구(II) - AERMOD 모델 적용방법을 중심으로 -)

  • Suhyang Kim;Sunhwan Park;Hyunsoo Joo;Minseop So;Naehyun Lee
    • Journal of Environmental Impact Assessment
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    • v.32 no.4
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    • pp.203-213
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    • 2023
  • The AERMOD model was the most used, accounting for 89.0%, based on the analysis of the environmental impact assessment reports published in the Environmental Impact Assessment Information Support System (EIASS) between 2021 and 2022. The mismatch of versions between AERMET and AERMOD was found to be 25.3%. There was the operational time discrepancy of 50.6% from industrial complexes, urban development projects between used in the model and applied in estimating pollutant emissions. The results of applying various versions of the AERMET and AERMOD models to both area sources and point sources in both simple and complex terrain in the Gunsan area showed similar values after AERMOD version 12 (15181). Emissions are assessed as 24-hour operation, and the predicted concentration in both simple and complex terrain when using the variable emission coefficient option that applies an 8-hour daytime operation in the model is lowered by 37.42% ~ 74.27% for area sources and by 32.06% ~ 54.45% for point sources. Therefore, to prevent the error in using the variable emission coefficient, it is required to clearly present the emission calculation process and provide a detailed explanation of the composition of modeling input data in the environmental impact assessment reports. Also, thorough reviews by special institutions are essential.

LOCA Analysis and Development of a Simple Computer Code for Refill-Phase Analysis (냉각재 상실사고 분석 및 재충진 단계해석용 전산코드 개발)

  • Ree, Hee-Do;Park, Goon-Cherl;Kim, Hyo-Jung;Kim, Jin-Soo
    • Nuclear Engineering and Technology
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    • v.18 no.3
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    • pp.200-208
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    • 1986
  • The loss of coolant accident based on a double-ended cold leg break is analyzed with the discharge coefficient (Ca) of 0.4. This analysis covers the whole transient period from the start of depressurization to the complete refilling of the core by using RELAP4/MOD6-EM and RELAP4/ MOD6-HOT CHANNEL for the system thermal-hydraulics and the fuel performance during the blowdown phase respectively, and RELAP4/MOD6-FLOOD and TOODEE2 during the reflood phase. A simple analytical method has been developed to account for the lower plenum filling by approximating steam-water countercurrent flows and superheated wall effects at the downcomer during the refill period. Based on the informations. at the time of EOB (end-of-bypass), the refill duration time and the initial reflooding temperature were estimated and compared with the results from the RELAP4/MOD6, resulting in a good agreement. In addition, some parametric studies on the EOB were performed. The form loss coefficient between upper head and upper downcomer was found to be sensitive to the occurrence of the spurious EOB. Appropriate form loss coefficients should be taken into account to avoid the flow oscillations at the downcomer. The analyses with the six and three volume core nodalizations, respectively, show much similar trends in the system thermal-hydraulic performance, but the former case is recommended to obtain good results.

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Development of a Meso-Scale Distributed Continuous Hydrologic Model and Application for Climate Change Impact Assessment to Han River Basin (분포형 광역 수문모델 개발 및 한강유역 미래 기후변화 수문영향평가)

  • Kim, Seong-Joon;Park, Geun-Ae;Lee, Yong-Gwan;Ahn, So-Ra
    • Journal of the Korean Association of Geographic Information Studies
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    • v.17 no.3
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    • pp.160-174
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    • 2014
  • The purpose of this paper is to develop a meso-scale grid-based continuous hydrological model and apply to assess the future watershed hydrology by climate change. The model divides the watershed into rectangular cells, and the cell profile is divided into three layered flow components: a surface layer, a subsurface unsaturated layer, and a saturated layer. Soil water balance is calculated for each grid cell of the watershed, and updated daily time step. Evapotranspiration(ET) is calculated by Penman-Monteith method and the surface and subsurface flow adopts lag coefficients for multiple days contribution and recession curve slope for stream discharge. The model was calibrated and verified using 9 years(2001-2009) dam inflow data of two watersheds(Chungju Dam and Soyanggang Dam) with 1km spatial resolution. The average Nash-Sutcliffe model efficiency was 0.57 and 0.71, and the average determination coefficient was 0.65 and 0.72 respectively. For the whole Han river basin, the model was applied to assess the future climate change impact on the river bsain. Five IPCC SRES A1B scenarios of CSIRO MK3, GFDL CM2_1, CONS ECHO-G, MRI CGCM2_3_2, UKMO HADGEMI) showed the results of 7.0%~27.1 increase of runoff and the increase of evapotranspiration with both integrated and distributed model outputs.

The Economic Impact of Government Purchases on the Price Volatility of Korean Dried Red Pepper (건고추 정부수매의 가격안정화효과에 대한 사후영향평가분석)

  • Park, Su-Yeon;Kim, In-Seck
    • The Journal of Industrial Distribution & Business
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    • v.9 no.10
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    • pp.73-82
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    • 2018
  • Purpose - Unstable vegetable prices have been one of the major concerns in Korean agricultural and food marketing system. The Korean government has implemented a number of policy instruments, including government purchasing programs in order to alleviate fluctuations in vegetable prices. The economic impact of policy instruments has been assessed based on the average monthly price change rate before and after the implementation of the policy. However, this approach failed to provide a net impact of policy measures on price stabilization in the vegetable markets, as policy impacts could not be successfully distinguished from other effects on price changes in the vegetable market. The purpose of this study is to evaluate the net impact of the government purchasing program on the price volatility of dried red pepper which is considered one of the major vegetables in Korea. Research design, data, and methodology - This study develops a monthly dynamic partial equilibrium model of Korean dried red pepper market. Behavioral equations in the model were estimated by OLS and synthetic method based on the annual and monthly time series data from 1993 to 2015. The model is first simulated to yield actual dried red pepper market conditions in 2015 as a baseline and then compared it to the scenario assuming that there were no government purchases of dried red pepper in 2015. Results - According to the ex-post scenario analysis using the developed model, without the government procurements in 2015, the average monthly price change rate and the value of coefficient of variation of dried red pepper in 2015 would be respectably 7.9 percent and 0.10. It is relatively higher than the actual average monthly price change rate and the value of coefficient of variation of dried red pepper in 2015 which were respectively 1.7 percent and 0.06. Conclusions - The ex-post simulation results in this study shows that if there were no government purchases of dried red pepper in 2015, the dried red pepper market would have had much higher volatile price movements. The results of this study would provide useful information for future price stabilization policy of vegetable markets in Korea.