• 한국연소학회:학술대회논문집
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• 한국연소학회 2006년도 제33회 KOSCO SYMPOSIUM 논문집
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• pp.276-281
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• 2006

Although fireside corrosion of heat transfer surfaces in coal fired steam generators has been a problem to some extent for a number of tears, with the advent of low NOx firing systems these surfaces can be exposed to conditions that will exacerbate wastage rates. Numerous reports of waterwall wastage in coal fired boilers have appeared in the literature. It is believed that wastage results both from gaseous phase attack of metal surfaces and from deposition of ash and unburned fuel. Gaseous phase attack is known to occur in the presence of reducing sulfur species such as $H_2S$ and in the presence of fuel chlorine. The highest wastage rates are thought to be due to deposition of unoxidized material and the presence of fuel chlorine. Localized wall and near wall conditions that may exacerbate wastage include reducing conditions, high temperatures, high heat fluxes, and a high fraction of unoxidized material deposited. So, this study is directed at developing an advanced corrosion model in coal-fired utility boilers.

• Molecules and Cells
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• 제23권2호
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• pp.239-245
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• 2007

DnaK is a major antigen in Streptococcus pneumoniae, and is induced by a minor shift in temperature (30 to $37^{\circ}C$) but not by ethanol shock. Although HrcA in the presence of $Ca^{{+}{+}}$ represses the expression of both groEL and hrcA, the control of transcription of the dnaK operon is not completely understood. In this study, the dnaK operon of S. pneumoniae (5' hrcA-grpE-dnaK-dnaJ) was cloned and analyzed. It contains large intergenic regions in grpE/dnaK and dnaK/dnaJ. Pulse labeling with [$^{35}S$]-methionine and immunoblot analyses revealed the presence of higher levels of DnaK than of HrcA even in the presence of $Ca^{{+}{+}}$ after heat shock suggesting that $Ca^{{+}{+}}$ differentially regulates the heat shock responses of hrcA and dnaK. By blocking de novo mRNA synthesis with rifampin it was shown that neither the hrcA nor the groEL transcripts were stabilized by heat shock even though dnaK transcripts were stabilized. We conclude that S. pneumoniae uses fine regulation of the transcription of the individual genes of the tetracistronic dnaK operon to cope with the various stresses experienced during infections.

• 대한금속재료학회지
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• 제56권11호
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• pp.796-804
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• 2018

The Charpy impact toughness of the heat affected zone (HAZ) of electro gas welded 390 MPa yield strength grade steel, manufactured by a thermo mechanically controlled process, was investigated. The effects of added Nb on the toughness of the steel and the factors influencing scatter in toughness are discussed in the present work. It was observed that adding Nb to the steel led to the deterioration of HAZ toughness. The presence of soluble Nb in the HAZ increased its hardenability and resulted in a larger amount of low toughness bainitic microstructure. Microstructural observations in the notch root area revealed the significant role of different microstructures in the area. In the presence of a larger amount of bainitic microstructures, the HAZ exhibited a lower Charpy toughness with a larger scatter in toughness. A softened zone with a lower hardness than the base metal was formed in the HAZ. However, theoretical analysis revealed that the presence of the zone might not be a problem in a real welded joint because of the plastic restraint effect enforced by surrounding materials.

• Nuclear Engineering and Technology
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• 제47권5호
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• pp.567-578
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• 2015

In a nuclear reactor containment, wall condensation forms with noncondensable gases and their accumulation near the condensate film leads to a significant reduction in heat transfer. In the framework of nuclear reactor safety, the film condensation in the presence of noncondensable gases is of high relevance with regards to safety concerns as it is closely associated with peak pressure predictions for containment integrity and the performance of components installed for containment cooling in accident conditions. In the present study, CUPID code, which has been developed by KAERI for the analysis of transient two-phase flows in nuclear reactor components, is improved for simulating film condensation in the presence of noncondensable gases. In order to evaluate the condensate heat transfer accurately in a large system using the two-fluid model, a mass diffusion model, a liquid film model, and a wall film condensation model were implemented into CUPID. For the condensation simulation, a wall function approach with a heat/mass transfer analogy was applied in order to save computational time without considerable refinement for the boundary layer. This paper presents the implemented wall film condensation model, and then introduces the simulation result using the improved CUPID for a conceptual condensation problem in a large system.

• Wind and Structures
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• 제29권1호
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• pp.65-75
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• 2019

A heated square cylinder (with height $A^*$) is kept parallel to the cold wall at a fixed gap height $0.5A^*$ from the wall. Another adiabatic rectangular cylinder (of same height $A^*$ and width $0.5A^*$) is placed upstream in an inline tandem arrangement. The spacing between the two cylinders is fixed at $3.0A^*$. The inlet flow is taken as Couette-Poiseuille flow based non-linear velocity profile. The conventional fluid (also known as base fluid) is chosen as water (W) whereas the nanoparticle material is selected as $Al_2O_3$. Numerical simulations are performed by using SIMPLE algorithm based Finite Volume approach with staggered grid arrangement. The dependencies of hydrodynamic and heat transfer characteristics of the cylinder on non-dimensional parameters governing the nanofluids and the fluid flow are explored here. A critical discussion is made on the mechanism of improvement/reduction (due to the presence of the upstream cylinder) of heat transfer and drag coefficient, in comparison to those of an isolated cylinder. It is observed that the heat transfer increases with the increase in the non-linearity in the incident velocity profile at the inlet. For the present range studied, particle concentration has a negligible effect on heat transfer.

• 대한조선학회논문집
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• 제43권3호
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• pp.285-293
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• 2006

Three-dimensional and time-dependent solution for the fluid flow and heat transfer past a circular cylinder with fins is obtained using accurate and efficient spectral methods. A Fourier expansion with a corresponding uniform grid is used along the circumferential direction. A spectral multi-domain method with a corresponding Chebyshev collocation is used along r-z plane to handle fins attached to the surface of a circular cylinder. At the Reynolds number of 300 based on a cylinder diameter, results with fins are compared with those without fins in order to see the effects of the presence of fins on three-dimensional and unsteady fluid flow and heat transfer past a bluff body. The detail structures of fluid flow and temperature field are obtained as a function of time to investigate how the presence of fins changes heat transfer mechanism related to the vortical structure in the wake region.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2010년도 춘계 학술대회 제22권1호
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• pp.445-446
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• 2010

본 연구는 최근 보편적으로 이루어지고 있는 한중콘크리트 시공에서 이중버블시트를 이용한 한중콘크리트 단열보온양생공법의 효용성 검증의 일환으로 이중버블시트에 물이 침투하였을 경우에 콘크리트의 온도이력과 강도특성을 분석하고자 하였다. 그 결과 시트내의 함수율 증가에 따른 영향은 거의 없는 것으로 분석되었다.

• 한국동물학회지
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• 제32권2호
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• pp.134-141
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• 1989

본 연구는 온열처리에 의한 세포치사의 mechqnism을 밝히기 위해서 heat sensitizer인 low pH와 heat protector인 glycerol을 이용하여 cell lethlity와 단백질의 분해 kinetics를 검토한 것이다. 41-45도씨의 온열처리 중에서 41도씨를 제외한 전 온도범위에서 sensitizer와 protector의 효과가 뚜렷이 나타났으며, protector이 효과는 cell lethality와 단백질분해 모두에서 sensitizer의 효과에 비해서 현저히 나타나서 sensitizer와 protector의 작용기작은 서로 다를 것으로 생각되었다. 즉, 43-44도씨에서 cell inactivation energy는 정상, low pH, glycerol 상태에서 각각 239, 190, 317 kcal/mole의 값을 보였다. 단백질분해 kinetics의 경우에도 대체적인 경향성은 cell inactivation kinetics와 유사하였으나, 직접적인 연관성은 발견할 수 없었다. 이와 같은 결과로 미루어 볼 때, cell lethality와 단백질 분해의 mechanism 사이에 직접적인 관계는 없고, 주로 막단백질로 추정되는 단백질의 inactivation에 의한 세포내 환경의 변화에 의해서 2차적으로 세포치사가 일어나는 것으로 추정할 수 있으며, 정확한 mechanism을 밝히기 위해서는 DNA polymerase를 비롯한 몇가지 가능한 표적에 대한 연구가 이루어져야 할 것으로 사료된다.

• Asian-Australasian Journal of Animal Sciences
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• 제21권4호
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• pp.596-602
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• 2008

Ovotransferrin (OTf) was phosphorylated by dry-heating in the presence of pyrophosphate at pH 4.0 and $85^{\circ}C$ for 1 and 5 d, and the functional properties of phosphorylated OTf (PP-OTf) were investigated. The phosphorus content of OTf increased to 0.91% as a result of phosphorylation and the electrophoretic mobility of PP-OTf also increased. Although the solubility of dry-heated OTf slightly decreased, the decrease was reduced by phosphorylation. The stability against heat-induced insolubilization of OTf was somewhat improved by phosphorylation, but more than 70% of PP-OTf was insolubilized when it was heated at $70^{\circ}C$ for 10 min at pH 7.0. However, heat-induced insolubilization of PP-OTf was reduced when it was heated in the presence of phosphorylated ovalbumin. This may explain the excellent stability of phosphorylated egg white protein against heat-induced insolubilization which was reported previously. The emulsifying property of OTf was also somewhat improved by phosphorylation. The calcium phosphate-solubilizing ability of PP-OTf was enhanced. Although the degree of phosphorylation of OTf by dry-heating in the presence of pyrophosphate was similar to that of ovalbumin, the improvement of properties of PP-OTf was considerably different from those of phosphorylated ovalbumin.

• 에너지공학
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• 제1권1호
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• pp.66-75
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• 1992

이중창의 열전달 성능을 수치해석과 실험적 방법을 통하여 조사하였다. 이중창 사이의 간격이 0.5cm에서 10cm사이의 실제적인 범위에서 이중창 사이의 간격이 작을 때에는 전도에 의한 열전달이 두드러졌으며 이중창 사이의 간격이 넓어지고 Rayleigh 수가 높은 영역에서는 대류에 의한 열전달이 크게 나타나 이중창 간격이 넓어진 이점을 크게 상쇄시켰다. 이와 같은 이중창 단열문제에 대한 보완책으로 이중창 중앙에 하나의 유리창을 더 설치한 3중창 경우에 대해 대류열전달 감소효과와 복사열차폐(radiation shield) 효과를 검토하였으며 또한 이중창 중간 높이에 스페이서(spacer)를 설치하여 대류유동 강도를 줄이는 방안 등에 대한 분석이 이루어졌다. 3중창을 사용한 경우에는 이중창에 비해 30-50%, 이중창에 스페이서를 설치한 경우에는 l0% 정도의 에너지 절약 효과를 기대할 수 있다.