• 소성∙가공
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• 제9권1호
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• pp.72-79
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• 2000

Dynamic recrystallization (DRX), which may occur during hot deformation, is important for the microsturctural evolution of 304 stainless steel. Especially, the current interest in modelling hot rolling demands quantitative relationships among the thermomechanical process variables, such as strain, temperature, strain rate, and etc. Thus, this paper individually presents the relationships for flow stress and volume fraction of DRX as a function of processing variables using torsion tests. The hot torsion tests of 304 stainless steel were performed at the temperature range of 900~110$0^{\circ}C$ and the strain rate range of 5x10-2~5s-1 to study the high temperature softening behavior. For the exact prediction of flow stress, the equation was divided into two regions, the work hardening (WH) and dynamic recovery (DRV) region and the DRX region. Especially, The flow stress of DRX region could be expressed by using the volume fraction of DRX (XDRX). Since XDRX was consisted of the critical strain($\varepsilon$c) for initiation of dynamic recrystallization (DRX) and the strain for maximum softening rate ($\varepsilon$*), that were related with the evolution of microstructure. The calculated results predicted the flow stress and the microstructure of the alloy at any deformation conditions well.

• KSBB Journal
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• 제5권1호
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• pp.25-35
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• 1990

In the Xanthan gum fermentation by Xanthomonas campestris there are problems of the large energy consumption by long fermentation time, the mass transfer of oxygen and nutrients by high viscous fermentation broth. In this study, the media optimization and the fed batch fermentation were carried out to decrease fermentation time and increase Xanthan gum yield. The $O_2$ uptake rate (OUR) and $CO_2$ evolution rate(CER) which were obtained from the analysis of fermentation exit gas using a gas chromatograph were investigated. As a result, the fermentation time decreased at optimal assimilable nitrogen concentration but increased at poor or rich assimilable nitrogen concentration, the Xanthan gum biosynthesis was stimulated under the limited condition of assimilable nitrogen source and the optimum fermentation medium was obtained as follow; Glucose=30g / l, Peptone=8.0g / l, $K_2HPO_4=2.0g/l$, $MgS0_47H_2O=10g/l$, Sodium acetate=20g/l, Sodium pyruvate=0.5g/1. As the agitation speed and nitrogen concentration increased, the $O_2$ uptake rate and $CO_2$ evolution rate increased. The OUR and CER were 37.3mmol $O_2/\;l$ hr and 20.2 mmol $CO_2/\;L$ hr at peptone 11g / l and agitation speed 990RPM, respectively. In fed batch fermentation, the final concentration of Xanthan gum was enhanced up to 29g / l.

• 대한금속재료학회지
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• 제46권5호
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• pp.283-288
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• 2008

We observed the in-situ stress behavior of Cu and Ag thin films during deposition using a thermal evaporation method. Multi-beam curvature measurement system was used to monitor the evolution of in-situ stress in Cu and Ag thin films on 100 Si(100) substrates. The measured curvature was converted to film stress using Stoney formula. To investigate the effects of the deposition rates on the stress evolution in Cu and Ag thin films, Cu and Ag films were deposited at rates ranging from 0.1 to $3.0{\AA}/s$ for Cu and from 0.5 to $4.0{\AA}/s$ for Ag. Both Cu and Ag films showed a unique three stress stages, such as 'initial compressive', 'a tensile maximum' and followed by 'incremental compressive' stress. For both Cu and Ag films, there is no remarkable effect of deposition rate on the thickness and average stress at the tensile maximum. There is, however, a definite decrease in the incremental compressive stress with increasing deposition rate.

• 한국과학교육학회지
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• 제35권4호
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• pp.691-707
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• 2015

이 연구는 생명과학교사들의 진화개념 향상을 위한 논변활동 프로그램을 개발하고 이를 교사교육에 적용하여 진화개념에 대한 논변활동 특성을 분석함으로써 효과를 알아보고자 하는 것이었다. 이를 위해 먼저 진화를 이해하는데 필요한 주요 개념들을 문헌 조사를 통해 추출하여 '변이', '변이의 유전', '경쟁', '자연선택과 적응', '차등적 생식력', '개체군 내 개체분포의 변화', '대진화'를 주요개념으로 선정하였고, 각각의 개념에 대한 논변활동 질문지를 개발하였다. ADI모형을 변형한 7단계로 이루어진 순환적 논변활동 학습모형도 개발하였다. 총 7회에 대학원 교과교육 수업에 적용하였다. 현직 생명과학교사 4명과 예비 생명과학교사 2명을 대상으로 남, 여 3명씩 두 개의 소집단으로 구성하여 논변활동을 진행하였다. 프로그램이 진행되는 동안 녹음을 통한 담화와 논변글쓰기의 자료를 수집하여 분석하였다. 논변글쓰기는 '설명의 충분성', '설명의 개념적 수준', '증거의 수준', '정당화의 적절성'의 4가지 범주를 기준으로 논변의 질 수준을 분석하여 사전사후에 진화개념의 변화 정도를 확인하였고, 담화분석을 통해 진화주요개념에 대한 논변활동 특성을 분석하였다. 논변글쓰기와 담화를 분석한 결과 개발된 논변활동 모형과 프로그램은 생명과학교사들의 진화개념 이해 향상에 효과적이었다. 이 연구는 논변활동을 통한 교수학습 전략이 생명과학교사교육을 위한 효과적인 진화개념학습 전략이될 수 있음을 보여주었다.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2008년도 추계학술대회 논문집
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• pp.95-98
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• 2008

In the present work, cross-roil rolling was rallied out using a rolling mill in which the roll axes are tilted by $5^{\circ},\;7.5^{\circ},\;10^{\circ}$ towards the transverse direction of the roiled sample. The evolution of strain states during cross-roll rolling was investigated by three-dimensional finite element method (FEM) simulation. Parallel to cross-roll rolling, normal-rolling using a conventional rolling mill was also carried out in the same rolling condition for clarifying the effect of cross-roll rolling. It turned out that three shear rate components were all introduced to the rolled sample by the cross-roll rolling process, while only one shear rate component operated during normal-rolling.

• 한국세라믹학회지
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• 제31권11호
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• pp.1299-1306
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• 1994

Effect of MgO content on microstructural evolution and microwave dielectric properties of Ba(Mg1/3Ta2/3)O3 system was investigated. MgO content was varied from 10 mol% deficiency to 10 mol% excess of stoichiometric composition, respectively. It was found that MgO-deficient specimen showed faster grain growth rate than stoichometric and MgO excess BMT system. Besides, sandwich type precipitates of Ba5Ta4O15 which was formed within the BMT grain, might lead to the anisotropic grain growth of BMT grain. On the contrary, in MgO excess specimen, BMT grain growth rate was retarded by precipitations of MgO phase in grain boundary. Besides, the Q values of MgO-deficient showed lower than MgO-excess due to precipitations of Ba5Ta4O15 within BMT grain.

• 한국수소및신에너지학회논문집
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• 제4권2호
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• pp.5-15
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• 1993

Hydrogen production in visible light with the following semiconductor systems, $CdS-WO_3$, $CdS-TiO_2$, have been investigated in the presence of redox catalyst (Pt, $RuO_2$). MeOH, EtOH, isopropanol, sulfide/sulfite mixture, lactic acid were used as sacrifical reagents. The optimal condition for $H_2$ evolution was found to be in qgueous lactic acid media for $CdS-WO_3/RuO_2$. The photochemical efficiency for this system was 1.05 % and the $H_2$ evolution rate was 26.5ml/min. at $6.07{\times}10^{-5}$ einstein/sec photon rate

• 한국농공학회지
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• 제40권5호
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• pp.100-108
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• 1998

Compost stability represents the state of microbiological activity and measurements of respiration either through $CO_2$ evolution or $O_2$ uptake should provide the best indication of this state. Hog manure amended with sawdust was composted in a pilot-scale reactor vessels using continuous and intermittent aeration for 3 weeks. In this study we evaluated the $CO_2$ respiration rate effect of aeration method on the reduction of $CO_2$ evolution, and investigated the stability of fresh and finished compost for plant growth. The intermittently aerated composting is a practical proposition for a very stable compost making. The $CO_2$ respiration rate in the fresh and finished compost during intermittently aerated composting was maintained from 0.3 to 1.4 and was good for use in horticulture, while the continuously aerated composting was 7 to 23 and needed more time for compost curing.

• Environmental Engineering Research
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• 제17권2호
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• pp.69-75
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• 2012

Composting of water hyacinth, mixed with cattle manure, rice husk and sawdust in four different proportions, was performed in a pilot scale rotary drum composter. The physico-chemical characteristics, i.e., temperature, moisture content, pH, electrical conductivity, total organic matter (OM), nitrogen dynamics and nutrients were evaluated during the 20 days composting process. The stabilities of the composts were also investigated with respirometric analysis, i.e., $CO_2$ evolution rates and oxygen uptake rate (OUR). Among all trials, trial 1 (6 water hyacinth, 3 cattle manure, 1 rice husk) indicated the best composting mix, as shown by the highest temperature profile and OM loss, and lowest $CO_2$ evolution rate and OUR.

• 한국정보통신학회:학술대회논문집
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• 한국해양정보통신학회 2008년도 지능정보 및 응용 학술대회
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• pp.149-150
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• 2008

일반적으로, 소나 표적의 식별을 위한 PSR(Propeller Shaft Rate) 추정 알고리즘은 다음의 문제점들을 가지고 있다. 즉, 주파수 스펙트럼으로부터 하모닉군을 구별하는 것은 필수적이면서도 어렵기 때문에 정확하고 효율적인 구별법을 요구한다. 나아가, 구조와 파라메터에 있어서 용이한 설계 절차를 요구한다. 이 문제들을 해결하기 위해서 전문가 지식 및 진화 전략(ES : Evolution Strategy)을 이용하는 진화적인 PSR 추정기가 제안되었다. 시뮬레이션 결과는 제안된 알고리즘이 그 문제점들을 효과적으로 해결할 수 있음을 보여준다.