• Nuclear Engineering and Technology
• /
• 제56권1호
• /
• pp.1-8
• /
• 2024

In this study, the influence of thermal aging on structural integrity is investigated for Gr. 91 steel. A commercial grade Gr. 91 steel is used for the virgin material, and service-exposed Gr. 91 steel is sampled from a steam pipe of a super critical plant. Time versus creep strain curves are obtained through creep tests with various stress levels at 600 ℃ for the virgin and service-exposed Gr. 91 steels, respectively. Based on the creep test results, the improved Omega model is characterized for describing the total creep strain curve for both Gr. 91 steels. The proposed parameters for creep deformation model are used for predicting the steady-state creep strain rate, creep rupture curve, and stress relaxation. Creep-fatigue damage is evaluated for the intermediate heat exchanger (IHX) in a large-scale sodium test facility of STELLA-2 by using creep deformation model with proposed creep parameters and creep rupture curve for both Gr. 91 steels. Based on the comparison results of creep fatigue damage for the virgin and service-exposed Gr. 91 steels, the thermal aging effect has been shown to be significant.

• 한국자동차공학회논문집
• /
• 제7권8호
• /
• pp.24-33
• /
• 1999

This paper investigate the effects of the variations of engine operation condition in the flame kernel formation and developmnet . A model for calculating the initial kernel development in spark ignition engines is formualted. It considered input of electrical energy, combustion energy release and heat transfer to the spark plyg, cylinder head, and unburned mixture. The model also takes into accounts strain rate of initial kernel and residual gas fraction. The breakdown process and the subsequent electrical power input initially control the kernel growth while intermediate growth is mainly dominated by diffusion or conduction. Then, the flame propagates by the chemical energy and turbulent flame expansion. Flame kernel development also influenced by engine operating conditions, for example, EGR rate, air-fuel ration and intake manifold pressure.

• Composites Research
• /
• 제36권3호
• /
• pp.199-204
• /
• 2023

저온 분사된 입자와 섬유강화 복합재료 사이의 접착력을 향상시키기 위해 금속 메쉬와 금속 입자/에폭시 접착제가 조합된 중간층이 도입되었다. 저온 분사 입자 및 금속 메쉬 그리고 금속 입자에는 모두 알루미늄을 활용하였다. 높은 변형률 속도에서 중간 층의 응력을 예측하기 위해서는 접착제 물성의 측정 또는 계산이 필요하다. 따라서, 본 연구에서는 금속 입자/에폭시 접착제의 물성을 계산하기 위해 혼합법칙(Rule of mixture)을 활용한 균질화 기법의 연구를 진행하였다. 균질화 기법의 검증을 위해 금속 메쉬/접착제로 구성된 중간층에 알루미늄 입자를 활용한 저온 분사를 진행하여, 실험으로 측정된 입자의 침투 깊이를 유한요소 해석에서 계산된 입자의 침투 깊이와 비교하였다. 시험과 해석에서 저온 분사 입자 혹은 중간층에 도입된 입자 하나 수준 크기의 침투 결과를 확인하였고, 이를 통해 높은 변형률 속도를 갖는 입자강화 복합재료 층의 물성 예측에 있어 균질화 기법이 적용될 수 있는 가능성을 확인하였다.

• 화약ㆍ발파
• /
• 제35권3호
• /
• pp.15-20
• /
• 2017

발파 하중에 대한 암석의 동적 응답 특성을 획득하기 위해서는, 내충격 고감도의 충격하중센서가 필요하다. 이러한 충격 하중 센서는 석영(quartz) 하중셀, 압전소자(piezoelectric element), 변형률 게이지를 적용하여 제작되고 있으나, 석영 및 압전소자의 경우 고가이기 때문에, 충격하중가압시험과 같이 압력 센서의 손상이 빈번한 경우에는 제약이 따르게 된다. 본 연구에서는 원통형 압축셀에 변형률 게이지 측정원리를 적용한 내충격 고감도 하중센서를 개발하였다. 개발된 하중 센서는 Nonex Rock Cracker (NRC) 구동 고속충격 하중 장치를 이용한 화강암 동적 압열 인장 실험에 적용하여 동적하중이력의 측정에 적용되었다. 그 결과, NRC 구동 고속충격하중장치는 암석 강도의 중간 변형률 속도 의존성 연구에 적용 가능한 것으로 파악되었다.

• Journal of Microbiology and Biotechnology
• /
• 제10권6호
• /
• pp.789-796
• /
• 2000

In order to analyze the effects of tktA, $aroF^{FBR}$, and aroL expression in a tryptophan-producing Escherichia coli, a series of plasmids carrying the genes were constructed. Introduction of tktA, $aroF^{FBR}$, and aroL into the E. coli strain resulted in approximately 10-20 fold increase in the activities of transketolase, the feedback inhibition-resistant 3-deoxy-D-arabinoheptulsonate-7-phosphate synthase, and shikimate kinase. Expression of $aroF^{FBR}$ in the aroB mutant strain of E. coli resulted in the accumulation of 10 mM of 3-deoxy-D-arabinoheptulsonate-7-phosphate (DAHP) in the medium. Simultaneous expression of tktA and $aroF^{FBR}$ in the strain further increased the amount of excreted DAHP to 20 mM. In contrast, the mutant strain which has no gene introduced accumulated 0.5 mM of DAHP. However, the expression of tktA and $aroF^{FBR}$ in a tryptophan-producing E. coli strain did not lead to the increased production of tryptophan, but instead, a significant amount of shikimate, which is an intermediate in the tryptophan biosynthetic pathway, was excreted to the growth medium. Despite the fact that additional expression of shikimate kinase in the strain could possibly remove 90% of excreted shikimate to 0.1 mM, the amount of tryptophan produced was still unchanged. Removing shikimate using a cloned aroL gene caused the excretion of glutamate, which suggests disturbed central carbon metabolism. However, when cultivated in a complex medium, the strain expressing tktA, $aroF^{FBR}$, and aroL produced more tryptophan than the parental strain. These data indicate that additional rate-limiting steps are present in the tryptophan biosynthetic pathway, and the carbon flow to the terminal pathway is strictly regulated. Expressing tktA in E. coli cells appeared to impose a great metabolic burden to the cells as evidenced by retarded cell growth in the defined medium. Recombinant E. coli strains harboring plasmids which carry the tktA gene showed a tendency to segregate their plasmids almost completely within 24h.

• 한국응용과학기술학회지
• /
• 제8권1호
• /
• pp.59-67
• /
• 1991

The reactions of semicarbazide hydrochloride with aliphatic and alicyclic ketones were studied kinetically at 15, 25, 35 and 45$^{\circ}C$ in 20% ethanol solution buffered at pH 2.9. The rate of cyclohexanone semicarbazone formation is 5.5 times as fast as that of cyclopentanone semicarbazone, while 3-pentanone semicarbazone is 4.7 times as slow as that of 2-pentanone, The activation energy of cyclohexanone, 2-pentanone, 2 hexanone, cyclopentanone, 4-methyl-2-pentanone and 3-pentanone semicarbazone formation are calculated 5.08, 7.52, 8.79, 9.59, 9.49, 11.59, respectively. It is concluded from the effect of ionic strength that the reaction is affected by not ion but neutral molecules being progressed hydrogen bond between oxygen atom of carbonyl group and hydrogen atom of acid-catalyst and concerted nucleophilic attack of free base on the carbonly compound. Dependence on pH of the rate of 2-pentanone semicarbozone formation is linear relationship below pH 4.60 and above pH 5.60. As a result of studing citric acid catalysis, second order constants increase linearly with citric acid concentration. As the catalyst concentration is varied from 0.025 to 0.10 mol/1 at pH 2.90, the rate constants increase 1.4 times, but slight increase is observed at pH 5.60. Conclusively, the rate-determining step is formation of tetrahedral interemediate below pH 4.65 and dehydration between pH 5.60 and pH 7.11. It is concluded that the formation reaction of cyclohexanone semicarbazone is faster than cyclopentanone semicarbazone due to the steric strain in the process of forming tetrahedral intermediate.

• 한국지반공학회:학술대회논문집
• /
• 한국지반공학회 2009년도 춘계 학술발표회
• /
• pp.195-198
• /
• 2009

Rammed Aggregate Pier method is intermediate foundation of deep and shallow foundation, it has been built on world wide. But the investigation and research in domestic is not accomplished. In this paper, examined details of different spacing of piles, bearing capacities, respectively, conclude with recommendations on how RAP can be used in future needs. This documentation further provides comparisons of the laboratory test results which were obtained from differenciate the spacing of piles, namely installed rammed aggregate pier. Strain control test was conducted to determine the bearing capacities of the piers; 20mm, 30mm and 40mm diameter drilling equipment to drill holes were installed in sand at initial relative densities of 40%. By comparing different spacing of piles, in this experiment, piles are spaced structually span, form a ring shape, narrowing the distance of each other, to the center. the result shows that as diameter of pier is bigger in diameter, bearing capacity also dramatically increased due to raised stiffness. Also, the space between each piers narrowed, settlement rate of soil was decreased significantly. From the test results, as the space between each piles were getting closer, allows greater chances to have resistance to deformation, shows improved stability of structures.

• 한국동물위생학회지
• /
• 제35권2호
• /
• pp.91-97
• /
• 2012

The strategy for infectious bursal disease (IBD) control and its success rate under field conditions depends on hygiene management, IBD field pressure, level, and variation in maternally derived IBD antibodies. This study investigated the level of IBD-specific antibody by ELISA and the prevalence of IBD virus by PCR in broilers, white-semi broilers, and Korean native chickens raised in Jeongeup, Jeonbuk. IBD-specific maternally derived antibodies were measured from 698 chickens and the mean titers of maternal antibodies were $3,572{\pm}1,402$ in broilers, $1,262{\pm}762$ in white-semi broilers, and $1,932{\pm}912$ in Korean native chickens. At 2 weeks after vaccination, the geometric mean antibody titers of broiler, white-semi broiler, and Korean native chicken were $582{\pm}427$, $3255{\pm}1,080$, and $1,023{\pm}499$, respectively. According to sequence analysis of the variable virion protein 2 gene, 4 isolates were found to be very virulent IBDV, 9 isolates classical virulent, and 2 isolates intermediate plus vaccine strain.

• 한국연소학회지
• /
• 제10권4호
• /
• pp.33-40
• /
• 2005

The propagation rates of advancing and retreating non-premixed edge flames in a slot-jet counterflow were measured as a function of strain rate for varying jet spacing, mixture strength, stoichiometric mixture fractions $(Z_{st})$ and Lewis numbers (Le). Methane and propane fuels were tested and nitrogen and carbon dioxide were used as inerts. As results, we could identify igniting fronts, retreating fronts, two total extinction limits, and short-length edge flames. A burner separation affected to a low extinction limit only. Regimes for advancing and retreating edges together with total extinction were mapped in terms of normalized flame thickness and heat loss factor for $CH_4/O_2/N_2$ mixtures. Edge flames for $Z_{st}$ > 0.5 behaved like a stronger mixture while for $Z_{st}$ < 0.5 showed deteriorated feature, because of relative locations of a non-premixed flame and intermediate species such as CO and $H_2$. Furthermore, due to the relative importance of heat loss, propagating speeds of edge flames were significantly enhanced in $CH_4/O_2/CO_2$ mixtures (Le < 1) demonstrating increasing stability limits. However $C_3H_8/O_2/N_2$ mixtures (Le > 1) showed opposite result.

• 한국도로학회논문집
• /
• 제5권3호
• /
• pp.31-42
• /
• 2003

국내의 포장 재료와 교통 및 기후조건이 반영되는 포장설계법 개발을 위한 연구가 진행중에 있으며, 이를 위해 실제 교통량 및 기후조건이 반영되고 이에 따른 포장의 거동을 모니터링 할 수 있는 대규모의 현장시험시설로 시험도로를 건설하였다. 시험도로 아스팔트 포장구간은 15개의 다양한 두께 및 재료를 가진 단면들로 구성되어 있다. 이러한 단면들을 평가하기 위해 포장체 내에 다양한 계측기들이 매설되어 있다. 계측기 매설에 있어서 핵심 요소는 매설 위치의 정확성과 장기적인 생존율 및 내구성이다. 외국의 시험사례를 보면, 이런 정확성과 내구성은 매설 방법에 크게 영향을 받는다. 이에 본 연구에서는 2000년도부터 3년여 동안 일반적인 계측기 매설 방법인 마운드, 블록아웃. 트렌치컷에 대해 시험시공을 수행하였으며 시험시공 결과를 분석하여 시험도로에 적용하였다. 위치의 정확성, 생존의 안전성, 시공성, 재료의 균질성 측면에서 시험시공 결과를 평가한 결과 블록아웃이 가장 효율적인 방법으로 나타났다. 그러나, 표층의 경우 블록아웃에 부적절한 층두께 등의 특성을 감안하여 마운드 방법을 사용하는 것으로 결정하였다. 아스팔트 기층과 중간층의 매설에는 블록아웃을, 표층의 매설에는 마운드를 사용하는 것으로 결정했다. 2003년 9월 3일부터 11월 18일까지 2달 여에 걸쳐 총 374개의 아스팔트 포장 변형률계를 시험도로에 매설하였다. 계측값 분석 결과, 마운드의 경우 6.3%, 블록아웃은 2.5%의 계측기가 매설 전후의 계측값 변화가 일반적인 계측기 사양 범위를 초과하는 것으로 나타났다. 생존율의 경우 매설후 손실된 계측기는 2개로 99.5%의 높은 생존율을 나타났다.