• 한국재료학회지
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• 제31권8호
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• pp.471-479
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• 2021

The electrochemical reaction between lead borate glass frit doped with Sn metal filler and Ni-Cr wire of a J-type resistor during a term of Joule heating is investigated. The fusing behavior in which the Ni-Cr wire is melted is not observed for the control group but measured for the Sn-doped specimen under 30 V and 500 mA. The Sn-doped lead borate glass frit shows a fusing property compared with other metal-doped specimens. Meanwhile, the redox reaction significantly contributes to the fusing behavior due to the release of free electrons of the metal toward the glass. The electrons derived from the glass, which used Joule heat to reach the melting point of Ni-Cr wire, increase with increasing corrosion rate at interface of metal/glass. Finally, the confidence interval is 95 ± 1.95₉ %, and the adjusted regression coefficient, R in the optimal linear graph, is 0.93, reflecting 93% of the data and providing great potential for fusible resistor applications.

• 한국지열·수열에너지학회논문집
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• 제17권2호
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• pp.1-10
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• 2021

Lithium-ion batteries with high energy density, long cycle life and other advantages, have been widely used to energy storage systems(ESS). But as ESS fires frequently occur, the safety concern has become the main obstacle that hinders the large-scale applications of lithium-ion batteries. Especially, thermal runaway is the key scientific problem in battery safety research. Therefore, in this study, we performed a numerical analysis on the thermal runaway phenomenon of NCM111, NCM523 and NCM622 batteries using a two-dimensional analysis model. The results show that the two-dimensional simulation results are generally matched with three-dimensional simulation. Also, In the case of NCM111 with a low Ni content in the temperature range used in this study, thermal runaway phenomenon does occurred very slowly, but as the Ni content is increased, the thermal runaway phenomenon occurs rapidly and the thermal stability tends to be decreased. And, in NCM523 and NCM622 batteries, chain reactions occur almost simultaneously, but in the case of NCM111 battery, it is found that after the SEI(Solid Electrolyte Interface) layer decomposition reaction, the cathode-electrolyte reaction is appeared sequentially. After that, the anodic decomposition reaction is increased and leads to the thermal runaway reaction.

• Structural Engineering and Mechanics
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• 제83권1호
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• pp.79-92
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• 2022

In this paper, the impact of a vernacular pozzolanic kaolinite mine on concrete alkali-silica reaction and strength has been evaluated. For making the samples, kaolinite powder with various levels has been used in the quality specification test of aggregates based on the ASTM C1260 standard in order to investigate the effect of kaolinite particles on reducing the reaction of the mortar bars. The compressive strength, X-Ray Diffraction (XRD) and Scanning Electron Microscope (SEM) experiments have been performed on concrete specimens. The obtained results show that addition of kaolinite powder to concrete will cause a pozzolanic reaction and decrease the permeability of concrete samples comparing to the reference concrete specimen. Further, various machine learning methods have been used to predict ASR-induced expansion per different amounts of kaolinite. In the process of modeling methods, optimal method is considered to have the lowest mean square error (MSE) simultaneous to having the highest correlation coefficient (R). Therefore, to evaluate the efficiency of the proposed model, the results of the support vector machine (SVM) method were compared with the decision tree method, regression analysis and neural network algorithm. The results of comparison of forecasting tools showed that support vector machines have outperformed the results of other methods. Therefore, the support vector machine method can be mentioned as an effective approach to predict ASR-induced expansion.

• 한국항공우주학회지
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• 제33권11호
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• pp.65-73
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• 2005

천음속 미교란 모델과 1단계 1차 Arrhenius 화학반응식을 이용하여 반응유체의 압축성 유동에 대하여 연구하였다. 유체 유동은 적은 열방출을 수반하는 희박 예혼합 반응에 국한시켰다. 천음속 연소에 끼치는 채널형상과 채널입구 마하수의 영향 등을 수치해석을 이용하여 조사하였다. 수치결과에서 채널확대는 주어진 채널길이 내에서 화학반응을 증가시키고 있음에 반하여 채널수축은 출구 근처에서 화학반응을 억제시키고 있음을 보여주고 있다. 확대형 채널 내에서 입구유동 마하수 증가는 고정된 반응속도에서 유동을 가속시켰으며 불활성 유체 경우에는 나타나지 않는 약한 충격파가 나타났다. 또한 확대형 채널 출구 근처의 압력과 온도를 증가시키고 주어진 채널길이 내에서 반응체의 소비를 도와준다.

• 한국환경과학회지
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• 제25권12호
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• pp.1717-1726
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• 2016

In this study, the reductive decolorization of three acid and basic dyes using modified zero-valent iron (i.e., acid-washed iron (Aw/Fe) and palladium coated iron (Pd/Fe)) at various pH conditions (pH 3~5) was experimentally investigated and the decolorization characteristics were evaluated by analyzing the absorbance spectra and reaction kinetics. In the case of acid dyes such as methyl orange and eriochrome black T, color removal efficiencies increased as initial pH of the dye solution decreased. However, the color removal of methylene blue, a basic dye, was not affected much by the initial pH and more than 70% of color was removed within 10 min. During the decolorization reaction, the absorbance of methyl orange (${\lambda}_{max}=464nm$) and eriochrome black T (${\lambda}_{max}=528nm$) decreased in the visible range but increased in the UV range. The absorbance of methylene blue (${\lambda}_{max}=664nm$) also decreased gradually in the visible range. Pseudo-zero order, pseudo-first order, and pseudo-second order kinetic models were used to analyze the reaction kinetics. The pseudo-second order kinetic model was found to be the best with good correlation. The decolorization reaction rate constants ($k_2$) of methylene blue were relatively higher than those of methyl orange and eriochrome black T. The reaction rate constants of methyl orange and eriochrome black T increased with a decrease in the initial pH.

• 펄프종이기술
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• 제43권3호
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• pp.52-58
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• 2011

Proton-NMR spectroscopic method was applied to kinetic study of concentrated sulfuric acid hydrolysis reaction, especially focused on 2nd step of acid hydrolysis with deferent reaction time and temperature as main variables. Commercial xylan extracted from beech wood was used as model compound. In concentrated acid hydrolysis, xylan was converted to xylose, which is unstable in 2nd hydrolysis condition, which decomposed to furfural or other reaction products. Without neutralization steps, proton-NMR spectroscopic analysis method was valid for analysis of not only monosaccharide (xylose) but also other reaction products (furfural and formic acid) in acid hydrolyzates from concentrated acid hydrolysis of xylan, which was the main advantages of this analytical method. Higher temperature and longer reaction time at 2nd step acid hydrolysis led to less xylose concentration in xylan acid hydrolyzate, especially at $120^{\circ}C$ and 120 min, which meant hydrolyzed xylose was converted to furfural or other reaction products. Loss of xylose was not match with furfural formation, which meant part of furfural was degraded to other undetected compounds. Formation of formic acid was unexpected from acidic dehydration of pentose, which might come from the glucuronic acid at the side chain of xylan.

• 한국식품과학회지
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• 제20권3호
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• pp.453-458
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• 1988

식품의 가공, 저장 및 조리중 있어서 Maillard 반응으로 용이 하게 생성되는 Maillard 반응생성물과 비투석성 melanoidin의 아질산염 소거작용에 관하여 검토하였는데 그 결과를 요약하면 다음과 같다. 1. Maillard 반응생성물과 비투석성 melanoidin의 아질산염 소거능은 우수한 것으로 나타났다. 2. 반응용액의 pH변화에 따른 아질산염 소거능은 pH1.2에서 가장 켰으며 pH가 증가 할수록 아질산염 소거능은 감소하였다. 3. 환원능을 소실시키고 난 후의 아질산염 소거능은 pH1.2에서 1/2이하로 감소하였다. 4. Maillard반응생성물이 나타내는 아질산염 소거작용에는 melanoidin이 크게 관여하는 것으로 나타났다.

• 대한화학회지
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• 제53권5호
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• pp.499-504
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• 2009

금속은 생명현상에 필수적인 효소반응에서 핵심적인 역할을 수행한다. 따라서 금속효소 안에서 일어나는 반응에 대한 구체적인 메커니즘은 많은 과학자의 오랜 관심사였다. Methane MonoOxygenase (MMO)는 메탄을 메탄올로 산화시키는 반응을 일으키는 효소이며 최근 Tolman등은 MMO의 모델로서 Bis(μ-oxo)dicopper Complexes의 Hydroxide Transfer 반응에 대한 몇 가지 가능한 메커니즘을 제시하였다. 이후 Hydrogen Transfer와 Hydroxide Rebound의 2단계로 이루어지는 메커니즘이 이론적으로 제시 되었다. 본 연구에서는 Bis($\mu$-oxo)dicopper Complexes 의 반응단계 중 첫 번째 단계인 Hydrogen Transfer 반응과정의 반응물과 전이상태, 생성물의 구조를 최근에 개발된 M06계열의 M06, M06L, M06-2X를 비롯한 여러 가지 DFT방법을 이용하여 계산하였다. M06/6-31G(d,p)/LANL2DZ방법을 사용하여 계산된 반응물의 구조가 실험에서 얻은 XRD구조와 가장 잘 일치했으며 기저함수의 크기에 따라 전이상태의 구조, 활성화 에너지 및 반응에너지에 큰 차이를 보였다.

• 한국지진공학회논문집
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• 제19권1호
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• pp.37-43
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• 2015

This paper presents a detailed procedure for a nonlinear soil-structure interaction of a seismically isolated NPP(Nuclear Power Plant) structure using the boundary reaction method (BRM). The BRM offers a two-step method as follows: (1) the calculation of boundary reaction forces in the frequency domain on an interface of linear and nonlinear regions, (2) solving the wave radiation problem subjected to the boundary reaction forces in the time domain. For the purpose of calculating the boundary reaction forces at the base of the isolator, the KIESSI-3D program is employed in this study to solve soil-foundation interaction problem subjected to vertically incident seismic waves. Wave radiation analysis is also employed, in which the nonlinear structure and the linear soil region are modeled by finite elements and energy absorbing elements on the outer model boundary using a general purpose nonlinear FE program. In this study, the MIDAS/Civil program is employed for modeling the wave radiation problem. In order to absorb the outgoing elastic waves to the unbounded soil region, spring and viscous-damper elements are used at the outer FE boundary. The BRM technique utilizing KIESSI-3D and MIDAS/Civil programs is verified using a linear soil-structure analysis problem. Finally the method is applied to nonlinear seismic analysis of a base-isolated NPP structure. The results show that BRM can effectively be applied to nonlinear soil-structure interaction problems.

• 대한의용생체공학회:의공학회지
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• 제21권3호
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• pp.285-293
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• 2000

나이에 의한 외부의 환경조건의 변화는 이에 적응하려는 척추의 구조적인 변화를 가져온다. 이러한 구조적인 변화는 척추의 biomechanical 거동에 영향을 미칠 것이다. 이러한 구조적인 변화의 효과를 연구하기 위하여, 나이에 의한 척추의 재료 및 기계적인 물성의 변화는 제외되었다. 유한요소법 (finite element method)에 의한 lumbar spine model (L3-L4)에 있어서, Annulus 의 유한요소 모델은 laminate composite elements로서 16개의 layer와 6개의 물성으로 구성되어있다. Spinal stiffness 와 facet reaction은 나이가 들수록 증가했다. 나이가 들수록 inner annulus의 fiber/layer tensile strains, cancellous bone stress 및 end-Plate stress는 감소했다. Fiber/layer compressive strains, facet reaction, ligament reaction and end-plate rigidity는 나이에 의한 척추의 구조적인 변화에 의하여 증가했다. 따라서 나이에 의한 척추의 정상적인 쇠퇴과정에 있어서 척추의 구조적인 변화는 spinal stiffness를 증가 시켜서 척추 및 disc의 지나친 변형을 감소시킬 것이다.