• 한국전기전자재료학회논문지
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• 제23권11호
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• pp.854-858
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• 2010

In this study, we have investigated the effects of Cr dopant on the sintering and electrical properties of ZnO-$Sb_2O_3$ (ZS) ceramics for varistor application. Spinel phases including $\alpha-$ and $\beta$-type was formed at ZS system and $\alpha$-spinel was stabilized by Cr doping in ZS system. Densification of ZS and ZSCr system was retarded to $1000^{\circ}C$ by the formation of spinel at $800^{\circ}C$. The morphology and its distribution of spinel phases in ZS system was homogeneous but disturbed by Cr doping. In ZSCr the densification of ZnO compared with ZS system was more retarded by low concentration of Zn interstitial defects induced by Cr doping in addition to the effect of spinel phase formation. The defects in each system were identified as attractive coulombic center (ZS: 0.13 eV, ZSCr: 0.12 eV) and singly charged oxygen vacancy $V_0^{\cdot}$ (ZSCr: 0.33 eV). In all ZS and ZSCr system have week varistor behavior by the formation of double Schottky barrier at grain boundary but its stability of barrier was very sensitive to sintering temperature.

• 한국식생활문화학회지
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• 제18권5호
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• pp.475-482
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• 2003

오미자 추출물의 가열 및 저장에 의한 변색을 지연시킴으로써 식품 소재로써 오미자 추출물의 이용도를 증진시키고자 식품에 가장 광범위하게 이용되는 첨가물인 당과 색소 안정화제의 효과를 조사하였다. 단당류로써 glucose, fructose, 이당류로써 sucrose, maltose를 처리한 결과 단당류는 가열에 의한 변색을 촉진시켰고 이당류는 가열에 의한 변색을 억제시키는 효과가 있어 maltose를 10%처리하였을 때 40%정도 변색이 억제되었다. 색소 안정화제 로 각각 1%와 5%의 maltodextrin, ${\beta},\;{\gamma}-cyclodextrin$, ascorbic acid, phosphoric acid를 첨가하여 조사한 결과 ${\beta}-$ 및 ${\gamma}-cyclodextrin$과 maltodextrin 5% 처리구의 경우 DI값이 대조군보다 낮게 나타나 가열 변색에 대한 안정화 효과를 나타내었다. 복잡한 구성성분으로 인하여 matrix 효과를 나타내는 식품에의 적용효과를 조사하고자 오미자 색소 추출물을 첨가한 겔 시스템을 모델 식품으로 사용하여 $25^{\circ}C$ 및 $35^{\circ}C$에서 저장하면서 표면 색도의 변화를 측정하였다. 저장 온도 및 기간이 증가할수록 a값이 감소하는 경향을 나타내었으며 maltodextrin을 5.0% 첨가한 경우 a 값이 $15{\sim}20%$증가하여 matrix effect가 고려된 실제 식품에서도 색소안정화 효과가 확인되었다.

• 상하수도학회지
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• 제30권3호
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• pp.271-278
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• 2016

Recently, reverse osmosis (RO) is the most common process for seawater desalination. A common problem in both RO and thermal processes is the high energy requirements for seawater desalination. The one energy saving method when utilizing the osmotic power is utilizing pressure retarded osmosis (PRO) process. The PRO process can be used to operate hydro turbines for electrical power production or can be used directly to supplement the energy required for RO desalination system. This study was carried out to evaluate the performance of both single-stage PRO process and two-stage PRO process using RO concentrate for a draw solution and RO permeate for a feed solution. The major results, were found that increase of the draw and feed solution flowrate lead to increase of the production of power density and water permeate. Also, comparison between CDCF and CDDF configuration showed that the CDDF was better than CDCF for stable operation of PRO process. In addition, power density of two-stage PRO was lower than the one of single-stage. However, net power of two-stage PRO was higher than the one of single-stage PRO.

• 한국분무공학회지
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• 제15권1호
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• pp.1-7
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• 2010

As world attention has focused on global warming and air pollution, high efficiency diesel engines with low $CO_2$ emissions have become more attractive. Premixed diesel engines in particular have the potential to achieve the more homogeneous mixture in the cylinder which results in lower NOx and soot emission. Early studies have shown that the operation conditions such as the EGR, intake conditions, injection conditions and compression ratio are important to reduce emissions in a PCCI (Premixed Charge Compression Ignition) engine. In this study a modified cam was employed to reduce the effective compression ratio. While opening timing of the intake valve was fixed, closing timing of the intake valve was retarded $30^{\circ}$. Although Atkinson cycle with the retarded cam leads to a low in-cylinder pressure in the compression stroke, the engine work can still be increased by advanced injection timing. On that account, we investigated the effects of various injection parameters to reduce emission and fuel consumption; as a result, lower NOx emission levels and almost same levels of fuel consumption and PM compared with those of conventional diesel engine cam timing could be achieved with the LIVC system.

• 한국유체기계학회 논문집
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• 제18권3호
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• pp.60-65
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• 2015

This paper deals with performance characteristics and efficiencies of Pelton turbine can be applied as one of ERDs (Energy Recovery Devices) of PRO (Pressure Retarded Osmosis) system for desalination. The objective of this study is experimentally estimating the performance of micro-scale Pelton turbine for PRO pilot plant. Especially the performance characteristics with variations of jet nozzle diameter of Pelton turbine are discussed in detail. In order to do this, lab scale test rig of Pelton turbine was made for performance test, which includes water tank, Pelton wheel with buckets, jet nozzle and torque brake and so on. The parameter effects related on Pelton turbine's efficiency were investigated and discussed on the influence of the variations of load and speed ratio.

• 멤브레인
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• 제22권5호
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• pp.352-358
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• 2012

본 연구는 pressure retarded osmosis (PRO) 분리막의 구조적 특성이 미치는 영향에 대하여 수행되었다. 이를 위해, 유사 분자구조를 가지며 자유부피는 차이가 나는 BPS-XX, BisA-XX가 선택되었다. BPS-XX와 BisA-XX는 축중합 반응을 통해 합성되었으며, 또한 더 세분화된 결과를 위해서 20~60 mol.%로 술폰화되었다. 자유부피의 변화에 따른 분리막의 특성을 입증하기 위해서 몇 가지 특성평가가 진행되었다. 연구 결과에서 동일 분자구조에서 자유부피가 증가하면 막의 투과도가 증가하였고, 선택도는 감소하였다. 본 연구의 투과도-선택도 결과에서, 분자의 기본 구조와 자유부피 조절에 따라서, 고 투과도와 선택도를 가진 막을 제조 가능함을 알 수 있었다.

• 전기의세계
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• 제31권3호
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• pp.209-217
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• 1982

This paper considers a finite spectrum assignment Problem for a functional retarded linear differential system with delays in control only. In this problem, by generalizing from an abstract linear system characterized by Semigroups on a Hilbert space to a finite dimensional linear system, we unify the relationship between a control-delayed system and its non-delayed system, and then by using the spectrum of the generator-decomposition of Semigroup, we try to get a feedback law which yields a finite spectrum of the closed-loop system, located at an arbitrarily preassigned sets of n points in the complex plane. The comparative examinations between the standard spectrum assignment method and the method of spectral projection for the feedback law which consists of proportional and finite interval terms over present and past values of control variables are also considered. The analysis is carry down to the elementary spectral projection level because, in spite of all the research efforts, so far there has been no significant attempt to obtain the feedback implementation directly from the abstract representation forms in the case of multivariables.

• 대한치과의사협회지
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• 제13권10호
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• pp.929-933
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• 1975

A girl aged 15 years 6 months, had a class Ⅲ malocclusion characterized by severe maxillary anterior crowding and a retarded maxilla. Molar relationship was class Ⅲ on both sides, incisor overjet was - 2.9mm. and incisor overbite was 5.5mm. The patient underwent extraction of four first premolars and was trested with a multi-banded light force system. After 13 months, the patient gained a normal verbite-overjet relationship of anterior teeth and a class 1 molar relationship. Superimposition of pretreatment and posttreatment cephalograms upon the line SN registered at S showed backward downward rotation of the mandible.

• 충청수학회지
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• 제34권4호
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• pp.355-368
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• 2021

In this paper, we investigate necessary and sufficient conditions for the approximate controllability for semilinear stochastic functional differential equations with delays in Hilbert spaces without the strict range condition on the controller even though the equations contain unbounded principal operators, delay terms and local Lipschitz continuity of the nonlinear term.

• 한국세라믹학회지
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• 제26권4호
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• pp.514-520
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• 1989

The early hydration characteristics according to the C3S/C3A ratio and presence of gypsum, in order to establish the hydration mechanism of the system C3S-C3A, have been studied. The rate of C3S dissolution in the system C3S-Gypsum was higher than that in the system C3S. Consequently, the induction period was reduced and the rate of Ca(OH)2 formation in the accleration period was increased. The hydration of C3S in the system C3S-C3A was retarded because Al3+ in the liquid phase originating from the hydration of C3A was incorporated into calcium hydrosilicates formed. The retardation phenomenon of C3S hydration was not appeared in the system C3S-C3A-gypsum because the reaction of monosulfate formation became the rate-determining step.