• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.279-279
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• 2010

한국형 헬륨 냉각 고체형 증식(Helium Cooled Solid Breeder : HCSB) 시험 블랑켓(Test Blanket Module : TBM)은 삼중수소 증식을 위해서 $Li_2TiO_3$ 및 $Li_4SiO_4$ 페블을 고려하고 있으며, 중성자 반사 재료로는 SiC가 코팅된 흑연 페블을 사용할 예정이다. $Li_2TiO_3$ 및 $Li_4SiO_4$ 페블을 제조하기 위해서는 먼저 각각의 분말 제조가 선행되어야 한다. $Li_2TiO_3$ 분말을 합성하기 위해서는 먼저 Lithium 금속염과 Isopropoxide를 용매 및 폴리머 캐리어로서의 두 가지 기능을 하는 에틸렌글리콜에 첨가한 후 가열하여 완전히 용해시킨 후 혼합 용액을 건조시켜 겔형의 전구체를 제조한다. 이를 하소한 후 결정화시켜 Titanate 분말을 얻는데 이때의 건조, 하소 및 결정화 온도의 조건에 따른 분말의 크기 및 특성이 각각 다르다. 즉 하소 온도가 $600^{\circ}C$ 미만이면 열분해된 폴리머로부터 잔유 탄소가 남게 되고, $700^{\circ}C$를 초과하면 결정화가 시작된다. 이렇게 얻어진 Titanate분말은 지르코니아 볼을 이용하여 약 24 시간 동안 볼 밀링 과정을 통해 입도분포가 좁은 미세한 Titanate 분말로 만들었다. $Li_2TiO_3$ 페블은 위의 과정에서 얻어진 미세분말에 바인더를 이용하여 페블화 시킨 후 $1200^{\circ}C$의 전기로에서 최종 소결한 것이다. 중성자 반사 재료인 흑연페블은 강도가 약하기 때문에 표면에 SiC를 수 ${\mu}m$ 코팅해서 사용할 예정이다. 선행실험으로 건식법을 이용하여 SiC 코팅을 실시했으며, 그 결과를 소개할 것이다.

• Korean Journal of Materials Research
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• v.31 no.5
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• pp.286-295
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• 2021

This study attempts to find optimal conditions of the friction coefficient using a discrete element method (DEM) simulation with various friction coefficient conditions and three different grinding media with various ball sizes in a traditional ball mill (TBM). Using ball motion of the DEM simulation are obtained using the optimal friction coefficient compared with actual motion; photographs are taken by the digital camera and the snapshot images are analyzed. In the simulation, the rotation speed of the mill, the materials and velocity of the grinding media, and the friction coefficient between the balls and the wall of the pot are fixed as the actual experimental conditions. We observe the velocity according to the friction coefficient from the DEM simulation. The friction coefficient is found to increase with the velocity. Milling experiments using a traditional ball mill with the same experimental conditions as those of the DEM simulation are conducted to verify the simulated results. In addition, particle morphology change of copper powder is investigated and analyzed using scanning electron microscopy (SEM) for the milling experiment.

• Tunnel and Underground Space
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• v.29 no.2
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• pp.124-134
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• 2019

Subcritical crack growth in rock material can occur under monotonic and cyclic loading. Subcritical crack growth plays an important role in evaluating the long-term stability of structures in rocks. This paper presents the results of studies conducted to determine subcritical crack growth parameters under monotonic and cyclic loading in rock-like material. The constant stress rate method was employed for monotonic loading. The subcritical crack growth parameter of n under cyclic loading was determined by the relation between the rate of crack growth per cycle and stress intensity factor range. The specimens contained pre-existing flaws with 45 and 60 degrees of inclination angle and flaws spacing and continuity were varied to arrange crack growth in shear or tensile manner. The results show that the parameter of n is almost constant regardless of the applied load conditions such as monotonic and cyclic or shear and tension.

• Geomechanics and Engineering
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• v.29 no.3
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• pp.311-320
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• 2022

TBM concrete segment requires a higher level of material properties compared to general concrete structures due to difficulties in maintenance and uncertainty in ground conditions. In this regard, recently, as one of the methods to achieve enhancement effect on concrete strength, many researchers have been focusing on adding CNTs to concrete mixture. However, even CNTs do not compensate the weakness that concrete exhibits brittle behavior after cracking. Separately, over the past few decades, a number of studies have been conducted on fiber reinforced concrete which exhibits ductile behavior due to fibers bridging cracks. However, only limited studies have been conducted to employ the advantages of the both materials together. In this study, an experimental program has been conducted to investigate the effect of CNTs on the workability and the compressive behavior of PVA-ECC which exhibits ductile tensile behavior with well-distributed cracks even without a conventional rebar. In addition to the compression test, SEM analysis has been also conducted for detailed investigation in the microstructure. The variable was the CNTs mix ratio, which were set to 0.00, 0.25, and 0.50 wt.% to the binding materials. It was observed though the test results that as the CNTs mix ratio increased, the workability considerably decreased with the reduced slump and slump flow. From the compression test results, it was also investigated that the compressive behavior was improved since the compressive strength, the strain corresponding to the compressive strength, and the modulus of elasticity increased with an increase of CNTs mix ratio. The contents of this paper will be useful for relevant research areas such as fiber reinforced concrete with CNTs which might be applied for high performance TMB concrete segments.

• Journal of the Korean Society of Systems Engineering
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• v.18 no.1
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• pp.1-13
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• 2022

The Yongin Light Rail train was manufactured by Bombardier Transportation in Canada in 2008 and is a privately invested railway line that has been operating in Yongin-si, Gyeonggi-do, since 2013. When the frequency of train failure increases due to aging, and there is a delay in the delivery period of imported parts used in the Bombardier manufactured trains, timely vehicle maintenance may not be performed due to lack of parts. To solve this problem, it is necessary to build a 'vehicle parts maintenance demand forecasting system' that analyzes the accurate and actual maintenance demand annual based on the condition of vehicle parts. The full scope of analysis in this paper analyzes failure data from various angles after opening of Yongin light rail vehicle to analyze failure patterns for each part and identify replacement cycles according to possible failures and consumption of parts. Based on this study, it is expected that Yongin Light Rail's maintenance system will change from the existing time-based replacement (TBM) concept to the condition-based maintenance (CBM) concept. It is expected that this study will improve the efficiency of the Yongin Light Rail maintenance system and increase vehicle availability. This paper is a fundamental for establishing of a system for predicting the replacement timing of vehicle parts for Yongin Light Rail. It reports the results of data analysis on some vehicle parts.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.46 no.2
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• pp.133-142
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• 2023

The large process plant is currently implementing predictive maintenance technology to transition from the traditional Time-Based Maintenance (TBM) approach to the Condition-Based Maintenance (CBM) approach in order to improve equipment maintenance and productivity. The traditional techniques for predictive maintenance involved managing upper/lower thresholds (Set-Point) of equipment signals or identifying anomalies through control charts. Recently, with the development of techniques for big analysis, machine learning-based AAKR (Auto-Associative Kernel Regression) and deep learning-based VAE (Variation Auto-Encoder) techniques are being actively applied for predictive maintenance. However, this predictive maintenance techniques is only effective during steady-state operation of plant equipment, and it is difficult to apply them during start-up and shutdown periods when rises or falls. In addition, unlike processes such as nuclear and thermal power plants, which operate for hundreds of days after a single start-up, because the pumped power plant involves repeated start-ups and shutdowns 4-5 times a day, it is needed the prediction and alarm algorithm suitable for its characteristics. In this study, we aim to propose an approach to apply the optimal predictive alarm algorithm that is suitable for the characteristics of Pumped Storage Power Plant(PSPP) facilities to the system by analyzing the predictive maintenance techniques used in existing nuclear and coal power plants.

• Journal of TMJ Balancing Medicine
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• v.12 no.1
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• pp.1-6
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• 2022

Objectives: For the deviation phenomenon occurring during the treatment process in temporo-mandibular balancing medicine (TBM), hypotheses were established regarding the cause and mechanism of formation from the perspective of neuro-science and material mechanics, and a verification method was proposed. Methods: The deviation phenomenon was theoretically analyzed based on the structure theories of material mechanics of the joint and the neurological pain mechanism. Results: Deviation occurs due to temporary yield by the accumulation of heterogeneous stress in the temporo-mandibular joint and the affected joint. Because the joint structures are corresponding with material mechanics showing compressive and tensile properties. The size of the deviation is expressed in terms of strain. The occlusal surface of the teeth is level with the axial joint. Since the magnitude of the deviation has a proportional relationship with the degree of abnormality of the temporo-mandibular joint, the magnitude of the deviation calculated by the balance measurement can be replaced by the strain. The major variables involved in the occurrence of deviations are the strength of joint structures and neurological conditions. Therefore plastic deformation and adaptation occur as a long-term depression of neural circuits is strengthened in different ways at different locations each time in various clinical situations. This is the reason why the sequence of the restoration process while correcting deviations is following reverse order of the accumulation in many layers in the muscular nervous system. Conclusions: From the above results, it can be inferred that the occurrence and correction of the deviations are corresponding with the plastic deformation and neuro-plasticity.

• Journal of Embryo Transfer
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• v.19 no.2
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• pp.173-183
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• 2004

This study was carried out to examine the effects of epidermal growth factor (EGF) and the number of cumulus-oocyte complexes (COCs) on in vitro maturation (IVM) of porcine immature oocytes, and on subsequent in vitro fertilization (IVF) and development (IVD). COCs were collected from antral follicles of porcine ovaries collected from abattoir, and were maturated in modified NCSU-23 (mNCSU-23) with 10% pFF, 0.6 mM cysteine, 50 ${\mu}mM{\beta}-mercaptoethanol$, 1 mM dbcAMP, 10 IU/mL PMSG and 10 IU/mL hCG, which was supplemented with or without 10 ng/mL EGF and into which 50 or 15 COCs per droplet was put. Oocytes matured in vitro, were fertilized in vitro in modified Tris-buffered medium (mTBM) with the final motile sperm concentration of 1${\times}$105 sperm/mL, and subsequently putative embryos were developed in vitro in NCSU- 23. The results are as follows. 1.In the result of IVM, 10 ng/mL EGF supplement duplicated the percentage of C4 group of COCs(41% vs 81%). But the rate of germinal vesicle breakdown (GVBD) and of nuclear maturation were not significantly different between control and EGF supplemented, or between the number of COCs per culture droplet, and there was not a significant interaction between the two factors, either. 2. In the result of IVF, there was not significantly different between control and EGF supplemented, or between the number of COCs per culture droplet, or was not a significant interaction between the two factors, in the rate of sperm penetration, in the percentage of oocytes with male pronucleus (MPN), and in the rate of polyspermy. 3. In the result of IVD, there was not significantly different between control and EGF supplemented, or between the number of COCs per culture droplet in the percentage of cleaved oocytes. There was not significantly different between the number of COCs per culture droplet, but between control and EGF supplemented (p<0.01) in the percentage of blastocysts, the number of inner cell mass (ICM), trophectoderm (TC) and total cells. There was no significant interaction between the two factors anywhere. These results suggested that 10 ng/mL EGF supplement into mNCSU-23 for IVM was effective in the production of more as well as better blastocysts during IVD through increasing the number of cells in those.

• Journal of Embryo Transfer
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• v.19 no.3
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• pp.245-255
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• 2004

In recent years, an increasing number of studies on pig in vitro maturation(IVM) and in vitro fertilization(IVF) have been separated. the wide range of new technologies, including that in applied molecular genetics, has increased this interest. the production of viable porcine embryos in vitro is a prerequisites for the successful production of transgenic pigs to date. The efficiency of IVM/IVF techniques in the porcine is lower than that obtained in other species such as cattle and mouse. The several problems are generally thought to be the cause of poor results: the low rate of MPN formation derived from inadequate IVM of oocytes, the high incidence of polyspermy after IVF and cell blocking at 4 cell during embryos culture. For there reasons overcoming, many studies have been conducted to improve in vitro embryo-genic competence of oocytes. In the last several years, many maturation culture media have been evaluated and various exogenous factors such as hormones and grows factors have been tested to improve the efficiency of porcine in vitro system. In the study several antioxidants have been examined to improve in vitro fertilization and development of porcine oocytes. In this study, several antioxidants were examined to determine the effects on the development of oocytes to the cleavage, morula and blastocyst stage when added at the maturation(IVM) or in vitro fertilization(IVF) or in vitro culture(IVC) of porcine embryos. Porcine oocytes were matured, fertilized and embryos were cultured in defind conditioned medium in vitro with or without supplementation with the antioxidents of cysteine, catalase and glutathione. 1. Significant improvement of blastocyst rate (27.2％ versus 15.4％, p<0.05) were achieved when catalase(500U/$m\ell$) were added to TCM-199 medium and morula rate(72.0％ versus 53.9％, p<0.05) were significantly higher when glutathione(1.0mM/$m\ell$) were added to TCM-199 medium than those of control. 2. In mTBM medium for oocytes fertilization, the addition of cysteine, catalase and glutathione had no positive effect on embryonic development. glutathione had no positive effect on embryonic development. In conclusion, this study shows that addition of catalase, gluththione during IVM improved the rate of porcine embryo development.

• Journal of Embryo Transfer
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• v.21 no.3
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• pp.255-262
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• 2006

The purpose of this study is to investigate the effects of vitrification in open pulled straws (OPS) methods on in vitro survival ability of porcine embryos. For in vitro maturation of immature oocytes, the porcine ovaries were collected from local slaughter-house. The cumulus-oocytes complexes were aspirated from 2 to 6 mm follicles. The collected oocytes were cultured for in vitro maturation in NCSU-23 medium with 5 mM hypotaurine, 0.57 mM cysteine, 10% porcine follicle fluid, 10 IU/ml PMSG and 10 IU/ml hCG for $21{\sim}22$ hrs. Then, the oocytes were more cultured $21{\sim}22$ hrs in vitro maturation in medium removed hormones. The frozen-thawed spermatozoa were washed by centrifugation 2 times for 10 min at 1,500 rpm in D-PBS with 5.56 mM glucose, 0.33 mM Na-pyruvate, 100 IU/ml penicillin, $100 {\mu}g/ml$ streptomycin and 4 mg/ml BSA. The fertilization medium used mTBM with 2 mM caffeine and 2 mg/ml BSA and adjusted to a pH of 7.2 to 7.4. The final concentration of spermatozoa was adjusted to $2.5{\times}10^6$cells/ml motile sperm during fertilization in vitro. At 8 hrs after insemination, the oocytes were transferred into NCSU-23 medium with 5.0 mM hypotaurine, 4 mg/ml BSA and 10 ng/ml EGF and cultured for 7 days. When the blastocysts of different stages were frozen-thawed by OPS methods, the proportions of embryos with normal morphology were significantly (p<0.05) higher in embryos frozen-thawed at expanded blastocyst stage (38.9%) than in early blastocyst stage (28.3%). On the other hand, the proportions of embryos damaged after frozen-thawing were significantly (p<0.05) higher in embryos frozen at early blastocyst stages than in expanded blastocyst stage. In another experiment, the normal embryos morphology after frozen- thawing were further cultured for 48 hrs. After culture, the proportions of embryos hatched were 6.7, 20.0 and 33.3% for embryos frozen-thawed at early blastocyst, mid-blastocyst and expanded blastocyst stages. These finding indicate the possible broader application for OPS methods, as frozen-thawed embryos may be accompanied by developmental stage according to requirements of the survival ability after freezing of blastocyst stage in the pig.