• 대한화학회지
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• 제55권5호
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• pp.896-899
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• 2011

• 통합자연과학논문집
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• 제2권1호
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• pp.18-23
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• 2009

This minireview provides the chosen examples of our recent discoveries in the polymerization of hydrosilanes, dihydrosilole, lactones, and vinyl derivatives using various catalysts. Hydrosilanes and lactones copolymerize to give poly(lactone-co-silane)s with $Cp_2MCl_2$/Red-Al (M = Ti, Zr, Hf) catalyst. Hydrosilanes (including dihydrosilole) reduce noble metal complexes (e.g., $AgNO_3$, $Ag_2SO_4$, $HAuCl_4$, $H_2PtCl_6$) to give nanoparticles along with silicon polymers such as polysilanes, polysilole, polysiloxanes (and silicas) depending on the reaction conditions. Interestingly, phenylsilane dehydrocoupled to polyphenylsilane in the inert nitrogen atmosphere while phenylsilane dehydrocoupled to silica in the ambient air atmosphere. $Cp_2M/CX_4$ (M = Fe, Co, Ni; X = Cl, Br, I) combination initiate the polymerization of vinyl monomers. In the photopolymerization of vinyl monomers using $Cp_2M/CCl_4$ (M = Fe, Co, Ni), the photopolymerization of MMA initiated by $Cp_2M/CCl_4$ (M = Fe, Co, Ni) shows while the polymerization yield decreases in the order $Cp_2Fe$ > $Cp_2Ni$ > $Cp_2Co$, the molecular weight decreases in the order $Cp_2Co$ > $Cp_2Ni$ > $Cp_2Fe$. For the photohomopolymerization and photocopolymerization of MA and AA, the similar trends were observed. The photopolymerizations are not living. Many exciting possibilities remain to be examined and some of them are demonstrated in the body of the minireview.

• 한국강구조학회 논문집
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• 제9권4호통권33호
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• pp.467-477
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• 1997

모달실험 기법의 강부재 손상발견 적용성에 대한 실험적 연구를 수행하였다. 단경간 및 2경간 강재보에 손상을 모사한 단계적인 절단을 가하면서 모달실험을 반복하고, 손상 정도에 따른 모달 파라미터의 변화를 관찰하였으며, 실험 결과를 검증할 목적으로 수치해석을 병행하였다. 고려한 모달 파라미터는 고유진동수(Frequency), 변위 모드형상(Displacement Mode Shape), 변형률 모드형상(Strain Mode Shape)이며, 이들 모달 파라미터를 구하기 위하여 가속도계와 변형률계를 사용한 모달실험을 실시하였다. 각각의 손상단계에서 손상에 의한 변위 모드형상과 변형률 모드형상의 변화를 위치에 대해 정량적으로 나타내기 위하여, CoMAC과 Modal Vector Error를 사용하였다. 고유진동수는 손상의 정도가 심해짐에 따라 감소하는 경향을 보였으며, 손상의 위치를 발견하는 데에 가장 효과적으로 사용될 수 있는 것은 변형률 모드형상이었다.

• 한국멀티미디어학회논문지
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• 제11권6호
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• pp.845-851
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• 2008

The ID/password method is the most classical method among authentication techniques on the internet, and is performed more easily and successfully than other methods. However, it is a vulnerable method against attacks such as eavesdropping or replay attack. To overcome this problem, OTP technique is used. The most popular OTP is HOTP algorithm, which is based on one-way hash function SHA-1. As recent researches show the weakness of the hash function, we need a new algorithm to replace HOTP. In this paper we propose a new OTP algorithm using the MAC(Message Authentication Code) based on AES. We also show that the new OTP outperforms HOTP experimentally.

• ETRI Journal
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• 제37권6호
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• pp.1096-1107
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• 2015

This paper presents a dynamic retry adaptation scheme for H.264 HD video, called DRAS.264, which dynamically adjusts the retry limits of frames at the medium access control (MAC) layer according to the impact those frames have on the streamed H.264 HD video. DRAS.264 is further improved with a bandwidth estimation technique, better prediction of packet delays, and expanded results covering multi-slice video. Our study is performed using the Open Evaluation Framework for Video Over Networks as a simulation environment for various congestion scenarios. Results show improvements in average peak signal-to-noise ratios of up to 4.45 dB for DRAS.264 in comparison to the default MAC layer operation. Furthermore, the ability of DRAS.264 to prioritize data of H.264 bitstreams reduces error propagation during video playback, leading to noticeable visual improvements.

• Journal of Communications and Networks
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• 제13권5호
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• pp.421-427
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• 2011

Problems encountered in IEEE 802.11 medium access control (MAC) design are interferences from neighboring or hidden nodes and collision from simultaneous transmissions within the same contention floors. This paper presents the selective decoding schemes in MAC protocol for multiple input multiple output ad-hoc networks. It is able to mitigate interferences by using a developed minimum mean-squared error technique. This interference mitigation combined with the maximum likelihood decoding schemes for the Alamouti coding enables the receiver to decode and differentiate the desired data streams from co-channel data streams. As a result, it allows a pair of simultaneous transmissions to the same or different nodes which yields the network utilization increase. Moreover, the presented three decoding schemes and time line operations are optimally selected corresponding to the transmission demand of neighboring nodes to avoid collision. The selection is determined by the number of request to send (RTS) packets and the type of clear to send packets. Both theoretical channel capacity and simulation results show that the proposed selective decoding scheme MAC protocol outperforms the mitigation interference using multiple antennas and the parallel RTS processing protocols for the cases of (1) single data stream and (2) two independent data streams which are simultaneously transmitted by two independent transmitters.

• Tuberculosis and Respiratory Diseases
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• 제53권1호
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• pp.5-16
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• 2002

연구배경 : 말초혈액 단핵구와 폐포 대식세포가 림프구에 의하여 활성화된 후 탐식된 세포내 결핵균을 제거하는 최종 효과기로 작용하지만 결핵균은 이러한 세포 내에서조차 살아남아 증식한다. 본 연구에서는 인체 감염의 경우와 유사하도록 낮은 감염률(결핵균:포식세포 1:10)을 이용하여 MAC(Mycobacterium avium)과 Mycobaterium tuberculosis $H_{37}Ra$에 대한 단핵구와 폐포 대식세포의 림프구 의존적 결핵균 살해능의 정도를 측정하고자 하였다. 방 법 : 정상인과 폐결핵 환자의 말초혈액 단핵구를 Ficoll gradient 방법을 이용하여 분리하고, 정상인의 폐포 대식세포를 기판지폐포 세척액에서 분리 하여 96well plate에 $1{\times}10^5$ 씩 분주하고 결핵균주 MAC과 $H_{37}Ra$에 낮은 감염률(결핵균:단핵구 1:10)로 감염시켰다. 일부는 비부착세포(림프구)를 림프구:포식세포 10:1 비율로 첨가하여 $37^{\circ}C$, 5% $CO_2$ 배양기에 배양하였다. 1일, 4일, 및 7일째 각각 수확하여 middlebrook 7H10/OADC agar plate에 접종 후 집락이 형성될 때까지 $37^{\circ}C$, 5% $CO_2$ 배양기에 배양하였다. 결핵균의 수는 lysate의 $m{\ell}$(세포수 $10^6$)당 CFU로 표시하였고, 결핵균의 살해능은 log killing ratio[logKR=$log_{10}$(Final CFU/Initial CFU)]로 표시하였다. 배양 1일째 상층액에서 TNF-${\alpha}$, 배양 4일째 상층액에서 ${\gamma}$-IFN을 Elisa kit를 사용하여 측정하였다. 결 과 : 단핵구의 세포내 결핵균 살해능은 정상대조군에 비하여 결핵환자군에서 ${\Delta}logKR$가 MAC -0.4, $H_{37}Ra$ -0.2 정도로 유의하게 증가되어 있었다(p<0.05). 정상대조군에서 폐포 대식세포의 결핵균 살해능은 단핵구에 비하여 ${\Delta}$logKR가 MAC과 $H_{37}Ra$ 모두 -0.2정도로 증가된 경향을 보였다. 단핵구와 폐포 대식세포내 결핵균 살해능은 림프구 의존적으로 림프구 첨가시의 ${\Delta}logKR$는 MAC -0.4, $H_{37}Ra$ -0.5 정도로 포식세포 단독에 비하여 유의하게 증가되었다 (p<0.05). ${\gamma}$-IFN은 말초 단핵구와 폐포 대식세포 단독배양시 분비량이 경미하였으나 림프구 첨가시에는 유의한 분비의 증가를 보였다. 결 론 : 본 연구는 낮은 결핵균 감염률을 이용한 인체 포식세포의 세포내 결핵균 감염 모델이다. 결핵균 살해능은 림프구 의존적이며, 포식세포의 결핵균 탐식 후 7일까지의 배양에서 결핵환자의 단핵구와 PPD 양성 정상인의 폐포 대식세포에 림프구를 첨가한 경우에만 실질적인 균 증식의 제한을 볼 수 있었다.

• Asian-Australasian Journal of Animal Sciences
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• 제33권6호
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• pp.1012-1022
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• 2020

Objective: Caseins and fatty acids of milk are synthesized and secreted by the epithelial cells of the mammary gland. All-trans retinoic acid (ATRA), an active metabolite of vitamin A, has been shown to promote mammary development. This study was conducted to determine the effect of ATRA on casein synthesis and fatty acid composition in MAC-T cells. Methods: MAC-T cells were allowed to differentiate for 4 d, treated with ATRA (0, 1.0, 1.5, and 2.0 μM), and incubated for 3 d. We analyzed the fatty acid composition, the mRNA expression of casein and fatty acid synthesis-related genes, and the phosphorylation of casein synthesis-related proteins of MAC-T cells by gas chromatography, quantitative polymerase chain reaction, and western blotting, respectively. Results: In MAC-T cells, ATRA increased the mRNA levels of α_S1-casein and β-casein, janus kinase 2 (JAK2) and E74-like factor 5 of the signal transducer and activator of transcription 5 β (STAT5-β) pathway, ribosomal protein S6 kinase beta-1 (S6K1) and eukaryotic translation initiation factor 4E binding protein 1 of the mammalian target of rapamycin (mTOR) pathway, inhibited the mRNA expression of phosphoinositide 3-kinase and eukaryotic initiation factor 4E of the mTOR pathway, and promoted the phosphorylation of STAT5-β and S6K1 proteins. Additionally, ATRA increased the de novo synthesis of fatty acids, reduced the content of long-chain fatty acids, the ratio of monounsaturated fatty acids to saturated fatty acids (SFA), the ratio of polyunsaturated fatty acids (PUFA) to SFA, and the ratio of ω-6 to ω-3 PUFA. The mRNA levels of acetyl-CoA carboxylase 1, fatty acid synthase, lipoprotein lipase, stearoyl-CoA desaturase, peroxisome proliferator-activated receptor gamma, and sterol regulatory element-binding protein 1 (SREBP1) were enhanced by ATRA. Conclusion: ATRA promotes the synthesis of casein by regulating JAK2/STAT5 pathway and downstream mTOR signaling pathway, and it improves the fatty acid composition of MAC-T cells by regulating SREBP1-related genes.

• 한국전자파학회논문지
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• 제25권1호
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• pp.76-82
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• 2014

이기종 비면허 기기들이 동일한 주파수 대역을 공동 사용하기 위해서는 주파수 간섭 회피 기법이 필요하다. 본 논문에서는 이기종 비면허 대역 공동 사용의 대표적인 예로서 2.4 GHz ISM 대역에서 동작하는 WLAN과 WPAN 간의 주파수 간섭을 MAC 계층에서 분석하였다. 분석 결과, WPAN의 성능이 WLAN의 간섭으로 인하여 크게 저하되는 것을 시뮬레이션과 실험을 통해 확인하였다. 이러한 주파수 간섭을 회피하기 위한 방법으로 WPAN 시스템을 위한 채널 변경 기법을 새롭게 제안하였다. 실험을 통하여 제안한 채널 변경 기법이 고정된 채널을 사용하는 기존의 방법에 비하여 주파수 간섭의 영향을 회피할 수 있음을 확인하였다.

• Journal of Magnetics
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• 제13권1호
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• pp.1-6
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• 2008

MacDonald and co-workers recently predicted that high current densities could affect the magnetic order of antiferromagnetic (AFM) multilayers, in ways similar to those that occur in ferromagnetic (F) multilayers, and that changes in AFM magnetic order can produce an antiferromagnetic Giant Magnetoresistance (AGMR). Four groups have now studied current-driven effects on exchange bias at F/AFM interfaces. In this paper, we first briefly review the main predictions by MacDonald and co-workers, and then the results of experiments on exchange bias that these predictions stimulated.