• Composites Research
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• 제12권1호
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• pp.68-75
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• 1999

본 연구에서는 저속 충격에서 충격 속도에 따른 금속복합재료의 동적 거동을 연구하였다. 시험에 사용된 재료는 모재로 AC8A와 보강재로 알루미나($Al_2O_3$)와 탄소를 사용하였으며 용탕 주조법을 이용하여 금속복합재료를 제조하였다. 금속복합재료에는 15%의 부피분율을 가진 알루미나 예비성형체와 알루미나와 탄소를 각각 12%와 3% 사용한 혼합 에비성형체가 사용되었다. 제조된 금속복합재료는 인장 시험과 진동 시험을 통해 인장 강도와 탄성계수를 구하였으며, 저주파 여파기(low pass filter)와 계장화 충격 시험기를 이용하여 충격 속도에 따른 금속복합재료의 충격 거동을 연구하였다. 저주파 여파기를 이용함으로써 충격 속도에 관계없이 안정적인 실험치를 확보할 수 있었다. 충격 속도의 증가에 따라 모재와 금속복합재료의 충격에너지는 증가하였으나, 동적인성치는 일정한 값을 보였다. 충격 속도가 증가할수록 충격에너지 중 균열전파에너지의 향상이 두드러졌으며, 재료의 변형량이 증가하였다. 충격에너지 중 균열개시에너지와 동적파괴인성치의 관계를 설명하기 위하여 변형율 에너지와 노치에서의 응력 분포를 이용하여 간단한 모델을 제시하였으며, 이로부터 균열개시에너지는 동적 파괴 인성치의 자승에 비례하고 탄성계수에 반비례하는 것을 보였다.

• International Journal of Advanced Culture Technology
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• 제9권4호
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• pp.409-416
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• 2021

We are invented the movement composition technique that is to check the food adjacent-package status of the wireless-management movement monitoring level (WMMML) on the movement monitoring communication system. The movement monitoring level condition by the movement monitoring communication system is formatted with the adjacent-package system. As to inspection a wireless RFID of the wireless RFID, we are found of the movement value with wireless RFID by the adjacent upper take form. The concept of movement monitoring level is formatted the reference of wireless-management level for composition signal by the movement package communication system. Further symbolizing a food composition of the WMMML of the medium-minimum in terms of the adjacent-package communication system, and the movement wireless RFID package that was the movement value of the far composition of the Mo-MMCS-FA-_φMED-MIN with 5.80±1.20 units, that was the movement value of the convenient composition of the Mo-MMCS-CO-_φMED-MIN with 4.06±(-0.04) units, that was the movement value of the flank composition of the Mo-MMCS-MO-_φMED-MIN with 0.91±0.07 units, that was the movement value of the vicinage composition of the Mo-MMCS-VI-_φMED-MIN with 0.18±(-0.03) units. The adjacent package will be to look into at the food ability of the adjacent-package communication system with wireless RFID by the movement monitoring level on the WMMML that is supply the wireless communication by the movement monitoring level system. We will be possible to make effort of a communication system by the management signal and to put to use of the delivery data of RFID level by the delivery system.

• 한국어병학회지
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• 제8권2호
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• pp.119-134
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• 1995

임파조혈조직내에 MMC가 과다축적될 경우 형태학적 또는 기능학적인 손상가능성의 유무를 알기 위하여, 틸라피아 복강내에 V. anguillarum FKC를 단독으로 투여하거나(제 1 MMC 유도군) 또는 이 세균입자항원과 함께 콜로이드 탄말액을 반복투여함으로써(제 2 MMC 유도군) 비장 및 두신내에 인위적으로 MMC 형성을 유도하였다. 제 1유도군에서는 대조군에 비하여 MMC 형성증가가 있었으나 현저하지 않았고, 제 2유도군에서는 MMC가 비장 및 두신의 대부분을 점유할 정도로 과다하게 형성되었다. 모든 실험군에서, 비장조직에서는 주로 동정맥벽내나 유초동맥에 밀접하여 형성되었고, 특히 제 2유도군에서는 동정맥벽내가 아닌 곳의 MMC는 그 중심 또는 변연에 유초동맥으로 인정되는 얇은 내피만 남은 내강이 자주 인정되었다. 두신에서토 임파구가 밀집한 임파구 영역내에 주로 형성되었으나 혈관벽과의 관계는 불분명하였다. 이러한 MMC의 밀집에도 불구하고 조혈조직실질의 조직학적 변성소견은 인정할 수 없었다. 한편, 방어기능손상의 유무를 알기 위하여 제 2유도군에 대하여 E. tarda 생균으로 공격하였으나 감염감수성의 증가는 없었으며 오히려 현저한 감소를 보였다. 또한 동 세균 FKC를 투여한 후 혈청항체가의 변동을 경시적으로 추적하였다. 그러나 항체생산능에 손상가능성은 전혀 없었을 뿐 아니라 두 MMC 형성유도군에서 모두 1주째부터 대조군에 비해 4배 내지 8배의 높은 항체가를 나타내었으며 이 경향은 4주째까지 지속되었다. 또한 조혈기능 손상여부와 관련하여 말초혈액내 혈구조성을 경시적으로 조사하였으나 유의한 변화가 인정되지 않았다. 따라서 틸라피아에서 MMC는 유초동맥을 포함한 혈관벽과 밀접하여 또는 이들 주위로 형성되나, 이들의 과다형성으로 임파조혈조직의 형태학적 및 기능적 손상을 야기하지 않으며, 균체항원의 주사 또는 탄말에 의한 MMC 형성량의 차이는 어체 방어계의 활성과 밀접한 관련성이 있는 것으로 사료되었다.

• Journal of Power Electronics
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• 제17권1호
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• pp.242-252
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• 2017

This paper deals with the blocking of DC-fault current during DC cable short-circuit conditions in HVDC (High-Voltage DC) transmission systems utilizing Modular Multilevel Converters (MMCs), where a new SubModule (SM) topology circuit for the MMC is proposed. In this SM circuit, an additional Insulated-Gate Bipolar Translator (IGBT) is required to be connected at the output terminal of a conventional SM with a half-bridge structure, hereafter referred to as HBSM, where the anti-parallel diodes of additional IGBTs are used to block current from the grid to the DC-link side. Compared with the existing MMCs based on full-bridge (FB) SMs, the hybrid topologies of HBSM and FBSM, and the clamp-double SMs, the proposed topology offers a lower cost and lower power loss while the fault current blocking capability in the DC short-circuit conditions is still provided. The effectiveness of the proposed topology has been validated by simulation results obtained from a 300-kV 300-MW HVDC transmission system and experimental results from a down-scaled HVDC system in the laboratory.

• 한국정밀공학회지
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• 제15권6호
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• pp.124-138
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• 1998

Particles reinforced MMCs have many advantages over monolithic metals including a higher specific modulus, higher specific strength, better properties at elevated temperatures and better wear resistance. SiC$_p$/A16061 composites have good results in its mechanical properties. This work investigates SiC$_p$/A16061 composites in the microscopic view and compares the analytical results with the experimental ones. The discrepancy of the material properties between the reinforced particle, SiC$_p$, and the matrix material, A16061 appears to be so significant. Especially the coefficient of thermal expansion(CTE) of A16061 is 5 times larger than that of SiC$_p$. Thermal residual stress in MMCs is induced at high temperatures. The shape of particle is various but the theoretical model is not able to consider the nonuniform shape. Particle distribution is not homogeneous in experimental specimen. However, it is assumed to be homogeneous in simulation model. The shapes of particles are assumed to be not only perfect global but hexahedral shapes. The types of particle distribution are two - simple cubic array(SC array) and face-centered cubic array(FCC array).

• 한국주조공학회지
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• 제29권4호
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• pp.176-180
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• 2009

Effect of matrix microstructure on creep behaviors of squeeze cast magnesium matrix composites was investigated. Aluminum borate whisker was used as reinforcement and AZ31, AS52 and Sr added AS52 Mg alloys were used for matrix alloys. The reinforcement was distributed homogeneously and defect-free composite was manufactured. Creep tests were carried out at the temperature of $150^{\circ}C$ under the applied stress of 50 and 100 MPa for Mg alloys and Mg MMCs, respectively. The creep resistance of Mg MMCs was in this order: AS52-Sr > AS52 AZ31 MMCs. Void initiation during creep mainly occurred at $Mg/Mg_{17}Al_{12}$ interface and propagation went along grain boundaries. On the other hand, $Mg_2Si$ phase was not attributed to the creep void initiation.

• Bulletin of the Korean Chemical Society
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• 제35권2호
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• pp.377-382
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• 2014

Micro-/macroporous carbons (MMCs) were prepared using a hollow mesoporous silica capsule (HMSC) as a sacrificial hard template. The carbonization process after the infiltration of furfuryl alcohol into the template-free HMSC material afforded MMC materials in high yield. The hard template HMSC could be removed by HF etching without deteriorating the structure of MMC. The MMC materials were fully characterized by SEM, TEM, PXRD, XPS, and Raman spectroscopy. The replication processes were so successful that MMCs exhibited a hollow capsular structure with multimodal microporosity. Detailed textural properties of MMC materials were investigated by volumetric $N_2$ adsorption-desorption analysis at 77 K. To explore the gas sorption abilities of MMCs for other gases, $H_2$ and $CO_2$ sorption analyses were also performed at various temperatures. The multimodal MMC materials were found to be good sorbents for both $H_2$ and $CO_2$ at low pressure.

• Composites Research
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• 제13권4호
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• pp.1-10
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• 2000

SiC가 강화된 금속복합재료는 기존의 금속재료에 비하여 비탄성계수와 비강도가 높기 때문에 자동차 및 항공산업에 많은 응용이 기대되고 있다. 금속복합재료의 파손기구는 적용된 하중에 의한 미시적 손상의 축적에 의해 많은 영향을 받기 때문에 금속복합재료의 광범위한 응용을 위해서는 금속복합재료가 반복 하중을 받을 때 미시적 파손기구를 이해하는 것이 대단히 중요하다. 따라서 본 연구에서는 SiCp/A356 금속복합재료의 미시적 손상 축적을 모니터링 하기 위하여 초음파와 음향방출기법을 적용하였다. 반복하중의 증가에 따라 초음파의 속도와 감쇠의 변화는 각 미시적 손상기구에 따라 3영역으로 나눌 수 있었다. 또한 각 영역에서 발생하는 AE 신호의 특징은 초음파의 속도 및 감쇠 변화와 비교, 분석되었다.

• 한국재료학회지
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• 제15권1호
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• pp.61-65
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• 2005

The titanium $diboride(TiB_2)$ has high strength(750MPa), high melting point $(3225^{\circ}C)\;and\;10\%$ IACS electrical conductivity. On this account, the dispersion hardening $Cu-TiB_2$ composites(MMCs) are a promising candidate for applications as electrical contact materials. MMCs for electrical contact materials can reduce material cost and resource consumption caused by wear, due to its good mechanical and electrical property. In this study, we attempt to prepare MMCs with various volume fraction and particle size of $TiB_2$ by means of hot extruded and cold drawn process. Dry sliding wear tests were performed on a pin-on-disk type wear tester, sliding against SM45C under the different applied loads. After wear testing, the microstructures of the worn surfaces were observed by SEM and the microhardnesses of the subsurface zone were measured.

• The Korean Journal of Physiology and Pharmacology
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• 제27권6호
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• pp.513-520
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• 2023

Cornuside is a secoiridoid glucoside compound extracted from the fruits of Cornus officinalis. Cornuside has immunomodulatory and anti-inflammatory properties; however, its potential therapeutic effects on diabetic nephropathy (DN) have not been completely explored. In this study, we established an in vitro model of DN through treating mesangial cells (MMCs) with glucose. MMCs were then treated with different concentrations of cornuside (0, 5, 10, and 30 μM). Cell viability was determined using cell counting kit-8 and 5-ethynyl-2'-deoxyuridine assays. Levels of proinflammatory cytokines, including interleukin (IL)-6, tumor necrosis factor-α, and IL-1β were examined using enzyme-linked immunosorbent assay. Reverse transcription quantitative real-time polymerase chain reaction and Western blotting were performed to detect the expression of AKT and nuclear factor-kappa B (NF-κB)-associated genes. We found that cornuside treatment significantly reduced glucose-induced increase in MMC viability and expression of pro-inflammatory cytokines. Moreover, cornuside inhibited glucose-induced phosphorylation of AKT and NF-κB inhibitor alpha, decreased the expression of proliferating cell nuclear antigen and cyclin D1, and increased the expression of p21. Our study indicates that the anti-inflammatory properties of cornuside in DN are due to AKT and NF-κB inactivation in MMCs.