• 한국정밀공학회지
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• 제27권10호
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• pp.29-33
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• 2010

UV laser micromachining of metallic materials has been used in microelectronic and other industries. This paper shows on experimental investigation of micromachining of copper using a 355nm UV laser with 50ns pulse duration. A finite element model with high strain rate effect is especially suggested to investigate the phenomena which are only dominated by mechanically pressure impact in disregard of thermally heat transfer. In order to consider the strain rate effect, Cowper-Symonds model was used. To analyze the dynamic deformation during a very short processing time, which is nearly about several tens nanoseconds, a commercial Finite Element Analysis (FEA) code, LS-DYNA 3D, was employed for the computational simulation of the UV laser micro machining behavior for thin copper material. From these computational results, depth of the dent (from one to six pulsed) were observed and compared with previous experimental results. This will help us to understand interaction between UV laser beam and material.

• 한국정밀공학회지
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• 제28권5호
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• pp.537-542
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• 2011

The thermo-mechanical interaction between brake block and wheel tread during braking has been found to cause thermal crack on the wheel tread. Due to thermal expansion of the rim material, the thermal cracks will protrude from the wheel tread and be more exposed to wear during the wheel/block contact than the rest of the tread surface. The wheel rim is in residual compression stress when is new. After service running, the region in the tread has reversed to tension. This condition can lead to the formation and growth of thermal cracks in the rim which can ultimately lead to premature failure of wheel. In the present paper, the thermal cracks of railway wheel, one of severe damages on the wheel tread, were evaluated to understand the safety of railway wheel in running condition. The residual stresses for damaged wheel which are applied to tread brake are investigated. Mainly X-ray diffusion method is used. Under the condition of concurrent loading of continuous rolling contact with rails and cyclic frictional heat from brake blocks, the reduction of residual stress is found to correlate well with the thermal crack initiation.

• 동의생리병리학회지
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• 제24권6호
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• pp.911-920
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• 2010

The basic principles in the "Spleen-stomach theory(脾胃論)" sets up the phases and roles of spleen-stomach (脾胃) by establishing Earth(地 坤 土) and exposing the reality of spleen-stomach(脾胃) of human body which has its own shape and form with Heaven's reality exhibited. The meaning of Earth is based on the constant meaning of Earth in 'Earth Original-Earth as extended and stable ground(坤元一正之土)' giving form and shape, and Earth's movement with circulation, then exposes itself as 'Earth as plowing land(耕種之土)' concerning both the application of Five Phases and the physical characteristics of Earth. The Yin-Yang recognition on Earth is revealed as Yin Earth(陰土)-Yang Earth(陽土). Spleen(脾) was established as Yin Earth(陰土) and Stomach(胃) as Yang Earth(陽土). The seasonal assignment of Earth is Indian Summer(長夏), which is divided from Summer, and becomes Heat(熱), and the Yin-Yang recognition of Earth comes to be the meaning of the center and border. According to the Five Phasic recognition, it becomes Earth(土) and gets to be Dampness(濕) in accordance with Six Qi(六氣). 'Extreme Yin(至陰)' indicates Qi's status exposing the fundamental meaning regarding the role of creating, changing, and propelling Spleen-Stomach(脾胃) as a characteristic Yin Earth. Earth comprehends 'Four Courses(四維)' meaning, recognizes them as four parts of the 12 Earth's Branches(辰戌丑未) and the terminals of four seasons(四季之末), and has the meaning of the president of the change in four seasons. The theory of principle in the "Spleen-stomach theory(脾胃論)" stands on the basis of the 'Form Qi theory(形氣論)' and that of 'Upbearing, Downbearing, Floating, and Sinking theory(升降浮沈論)'. It manifests the theory of movement in the interaction between Form(形) and Qi(氣), and 'Qi Interior Form Exterior(氣裏形表)' indicates that Qi(氣) moves interiorly and Form(形) exteriorly.

• 한국자동차공학회논문집
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• 제19권5호
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• pp.134-142
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• 2011

Although combustion is essential in most energy generation processes, it is one of the major causes of air pollution. Exhaust pipes with circular fin were designed to study the effect of cooling the recirculated exhaust gases (EGR) of Diesel engines on the chemical composition of the exhaust gases and the reduction in the percentages of pollutant emissions. The gases examined in this study were oxides of nitrogen (NOx), carbon dioxide ($CO_2$) and carbon monoxide (CO). In addition, $O_2$ concentration in the exhaust was measured. The designs adopted in this study were about exhaust pipes with solid and hollow fins around them direct surface force measurement in water using a nano size colloidal probe technique. The direct force measurement between colloidal surfaces has been an essential topic in both theories and applications of surface chemistry. As particle size is decreased from micron size down to true Carbon nano Colloid size (<10 nm), surface forces are increasingly important. Nano particles at close proximity or high solids loading are expected to show a different behavior than what can be estimated from continuum and mean field theories. The current tools for directly measuring interaction forces such as a surface force apparatus or atomic force microscopy (AFM) are limited to particles much larger than nano size. This paper use Water and CNC fluid at normal cooling system of EGR. Experimental result showed all good agreement at Re=$2.54{\times}10^4$ by free convection and Re=$3.36{\times}10^4$ by forced air furnace.

• 센서학회지
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• 제15권6호
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• pp.379-385
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• 2006

Single crystal of p-$CdIn_{2}Te_{4}$ was grown in a three-stage vertical electric furnace by using Bridgman method. The quality of the grown crystal has been investigated by x-ray diffraction and photoluminescence measurements. From the photoluminescence spectra of the as-grown $CdIn_{2}Te_{4}$ crystal and the various heat-treated crystals, the ($D^{o}$, X) emission was found to be the dominant intensity in the photoluminescence spectrum of the $CdIn_{2}Te_{4}$:Cd, while the ($A^{o}$, X) emission completely disappeared in the $CdIn_{2}Te_{4}$:Cd. However, the ($A^{o}$, X) emission in the photoluminescence spectrum of the $CdIn_{2}Te_{4}$:Te was the dominant intensity like in the as-grown $CdIn_{2}Te_{4}$ crystal. These results indicated that the ($D^{o}$, X) is associated with $V_{Te}$ which acted as donor and that the ($A^{o}$, X) emission is related to $V_{Cd}$ which acted as acceptor, respectively. The p-$CdIn_{2}Te_{4}$ crystal was obviously found to be converted into n-type after annealing in Cd atmosphere. The origin of ($D^{o},{\;}A^{o}$) emission and its to phonon replicas is related to the interaction between donors such as $V_{Te}$ or $Cd_{int}$, and acceptors such as $V_{Cd}$ or $Te_{int}$. Also, the In in the $CdIn_{2}Te_{4}$ was confirmed not to form the native defects because it existed in a stable bonding form.

• 한국세라믹학회지
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• 제34권6호
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• pp.652-658
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• 1997

The phase stability in the interface of Sr-doped LaMnO3(LSM)/Gd-doped CeO2(CGO) was examined in this study in order to check the feasibility of using LSM as the cathode material in a low-temperature SOFC(solid oxide fuel cell) using CGO as the electrolyte. For the purpose, CGO powders of Ce0.82Gd0.18O0.91 and two LSM powders having different compositions, La0.9Sr0.1MnO3(LSM10) and La0.5Sr0.5MnO3(LSM50), were synthesized using Pechini method. Then, specimens having the LSM/CGO interface were prepared, heat-treated at 130$0^{\circ}C$ for up to 3 days, and analyzed by XRD and STEM/EDX. Face-centered cubic CGO powders of less than 10 nm size were obtained by calcination of polymeric precursor formed in the process at 45$0^{\circ}C$. Higher calcination temperature of $700^{\circ}C$ was necessary for monoclinic LSM10 and cubic LSM50 powders. LSM powders were coarser than CGO and observed to be in the range of 50~100 nm. No trace of LSM-CGO interaction product was found in the XRD pattern. Also it was known from the concentration profile in the vicinity of the interface that interdiffusion was occurred over only a small penetration depth of ~100 nm order.

• Nuclear Engineering and Technology
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• 제47권1호
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• pp.11-25
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• 2015

The accident at Japan's Fukushima Daiichi nuclear power plant in March 2011, caused by an earthquake and a subsequent tsunami, resulted in a failure of the power systems that are needed to cool the reactors at the plant. The accident progression in the absence of heat removal systems caused Units 1-3 to undergo fuel melting. Containment pressurization and hydrogen explosions ultimately resulted in the escape of radioactivity from reactor containments into the atmosphere and ocean. Problems in containment venting operation, leakage from primary containment boundary to the reactor building, improper functioning of standby gas treatment system (SGTS), unmitigated hydrogen accumulation in the reactor building were identified as some of the reasons those added-up in the severity of the accident. The Fukushima accident not only initiated worldwide demand for installation of adequate control and mitigation measures to minimize the potential source term to the environment but also advocated assessment of the existing mitigation systems performance behavior under a wide range of postulated accident scenarios. The uncertainty in estimating the released fraction of the radionuclides due to the Fukushima accident also underlined the need for comprehensive understanding of fission product behavior as a function of the thermal hydraulic conditions and the type of gaseous, aqueous, and solid materials available for interaction, e.g., gas components, decontamination paint, aerosols, and water pools. In the light of the Fukushima accident, additional experimental needs identified for hydrogen and fission product issues need to be investigated in an integrated and optimized way. Additionally, as more and more passive safety systems, such as passive autocatalytic recombiners and filtered containment venting systems are being retrofitted in current reactors and also planned for future reactors, identified hydrogen and fission product issues will need to be coupled with the operation of passive safety systems in phenomena oriented and coupled effects experiments. In the present paper, potential hydrogen and fission product issues raised by the Fukushima accident are discussed. The discussion focuses on hydrogen and fission product behavior inside nuclear power plant containments under severe accident conditions. The relevant experimental investigations conducted in the technical scale containment THAI (thermal hydraulics, hydrogen, aerosols, and iodine) test facility (9.2 m high, 3.2 m in diameter, and $60m^3$ volume) are discussed in the light of the Fukushima accident.

• Journal of Nuclear Fuel Cycle and Waste Technology
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• 제1권1호
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• pp.65-73
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• 2013

Temperature-dependent hydrolysis behaviors of aqueous U(VI) species were investigated with time-resolved laser fluorescence spectroscopy (TRLFS) in the temperature range from 15 to $75^{\circ}C$. The formation of four different U(VI) hydrolysis species was measured at pHs from 1 to 7. The predominant presence of $UO{_2}^{2+}$, $(UO_2)_2(OH){_2}^{2+}$, $(UO_2)_3(OH){_5}^+$, and $(UO_2)_3(OH){_7}^-$ species were identified based on the spectroscopic properties such as fluorescence wavelengths and fluorescence lifetimes. With an increasing temperature, a remarkable decrement in the fluorescence lifetime for all U(VI) hydrolysis species was observed, representing the dynamic quenching behavior. Furthermore, the increase in the fluorescence intensity of the further hydrolyzed U(VI) species was clearly observed at an elevated temperature, showing stronger hydrolysis reactions with increasing temperatures. The formation constants of the U(VI) hydrolysis species were calculated to be $log\;K{^0}_{2,2}=-4.0{\pm}0.6$ for $(UO_2)_2(OH){_2}^{2+}$, $log\;K{^0}_{3,5}=-15.0{\pm}0.3$ for $(UO_2)_3(OH){_5}^+$, and $log\;K{^0}_{3,7}=-27.7{\pm}0.7$ for $(UO_2)_3(OH){_7}^-$ at $25^{\circ}C$ and I = 0 M. The specific ion interaction theory (SIT) was applied for the extrapolation of the formation constants to infinitely diluted solution. The results of temperature-dependent hydrolysis behavior in terms of the U(VI) fluorescence were compared and validated with those obtained using computational methods (DQUANT and constant enthalpy equation). Both results matched well with each other. The reaction enthalpies and entropies that are vital for the computational methods were determined by a combination of the van't Hoff equation and the Gibbs free energy equation. The temperature-dependent hydrolysis reaction of the U(VI) species indicates the transition of a major U(VI) species by means of geothermal gradient and decay heat from the radioactive isotopes, representing the necessity of deeper consideration in the safety assessment of geologic repository.

• International Journal of Concrete Structures and Materials
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• 제11권2호
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• pp.199-213
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• 2017

Chloride penetration is among the main causes of corrosion initiation in reinforced concrete (RC) structures producing premature degradations. Weather and exposure conditions directly affect chloride ingress mechanisms and therefore the operational service life and safety of RC structures. Consequently, comprehensive chloride ingress models are useful tools to estimate corrosion initiation risks and minimize maintenance costs for RC structures placed under chloride-contaminated environments. This paper first presents a coupled thermo-hydro-chemical model for predicting chloride penetration into concrete that accounts for realistic weather conditions. This complete numerical model takes into account multiple factors affecting chloride ingress such as diffusion, convection, chloride binding, ionic interaction, and concrete aging. Since the complete model could be computationally expensive for long-term assessment, this study also proposes model simplifications in order to reduce the computational cost. Long-term chloride assessments of complete and reduced models are compared for three locations in France (Brest, Strasbourg and Nice) characterized by different weather and exposure conditions (tidal zone, de-icing salts and salt spray). The comparative study indicates that the reduced model is computationally efficient and accurate for long-term chloride ingress modeling in comparison to the complete one. Given that long-term assessment requires larger climate databases, this research also studies how climate models may affect chloride ingress assessment. The results indicate that the selection of climate models as well as the considered training periods introduce significant errors for mid- and long- term chloride ingress assessment.

• Korean Chemical Engineering Research
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• 제46권5호
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• pp.903-914
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• 2008

본 연구는 ethylene oxide로부터 monoethylene glycol을 주제품으로 생산하는 상용화된 실제 공정의 생산 능력 증가시에 필요한 공정 모사와 에너지 절감을 위한 최적화 연구로서, 공정에 관여하는 다성분계의 기/액 상평형 거동을 NRTL-RK식으로 나타내고, 필요한 총 91개의 2성분계쌍의 상호작용 파라미터 값들로는 8개의 2성분계쌍에 대해서는 Aspen $Plus^{TM}$ 상용 모사기(Ver. 2006)에 내장된 값, 28개의 쌍에 대해서는 상평형 데이터를 문헌에서 조사하여 회귀분석하고 나머지 2성분계에 대해서는 모사기 내의 추산 기능을 이용하여 구한 값을 사용하였으며, 공정 모사 결과와 실제 공정 데이터와의 비교를 통해 상평형 계산의 정확성을 확인한 후, 모사기에 내장된 민감도 분석 기능을 사용하여 전체 에너지 소모량에 대한 각 장치의 민감도를 조사하여 적절한 조절변수를 선정하고 모사기 내에 내장되어 있는 순차적 2차 계획법에 의한 최적화 기능을 이용하여 공정 전체의 에너지 절약을 위한 최적화 작업을 수행하였다.