• 한국진공학회:학술대회논문집
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• 한국진공학회 2014년도 제46회 동계 정기학술대회 초록집
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• pp.432.2-432.2
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• 2014

Recently, colloidal core/shell type quantum dots lighting-emitting diodes (QDLEDs) have been extensively studied and developed for the future of optoelectronic applications. In the work, we fabricate an inverted CdSe/ZnS quantum dot (QD) based light-emitting diodes (QDLED)[1]. In order to reduce work function of indium tin oxide (ITO) electrode for inverted structure, a very thin (<10 nm) polyethylenimine ethoxylated (PEIE) is used as surface modifier[2] instead of conventional metal oxide electron injection layer. The PEIE layer substantially reduces the work function of ITO electrodes which is estimated to be 3.08 eV by ultraviolet photoemission spectroscopy (UPS). From transmission electron microscopy (TEM) study, CdSe/ZnS QDs are uniformly distributed and formed by a monolayer on PEIE layer. In this inverted QD LED, two kinds of hybrid organic materials, [poly (9,9-di-n-octyl-fluorene-alt-benzothiadiazolo)(F8BT) + poly(N,N'-bis (4-butylphenyl)-N,N'-bis(phenyl)benzidine (poly-TPD)] and [4,4'-N,N'-dicarbazole-biphenyl (CBP) + poly-TPD], were adopted as hole transport layer having high highest occupied molecular orbital (HOMO) level for improving hole transport ability. At a low-operating voltage of 8 V, the device emits orange and red spectral radiation with high brightness up to 2450 and 1420 cd/m2, and luminance efficacy of 1.4 cd/A and 0.89 cd/A, respectively, at 7 V applied bias. Also, the carrier transport mechanisms for the QD LEDs are described by using several models to fit the experimental I-V data.

• 한국통신학회논문지
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• 제31권9A호
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• pp.837-843
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• 2006

WPAN환경에서 고속 저속 네트워크를 위한 표준 IEEE 802.15.3과 IEEE 802.15.4이 설계되었다. 현재 WPAN 표준에서 제시하는 MAC 프로토콜의 다중 접근 방식은 CSMA방식과 TDMA방식을 분리하여 결합한 방식이다. TDMA부분에서는 PNC(Piconet Coordinator)에 의해 가변적인 길이의 timeslot이 각 station에 할당된다. 그리고 각 timeslot내에는 여러 개의 데이터 패킷이 전송 가능한 multi-frame TDMA구조를 이루고 있다. 하지만 표준에서 정의하는 다중 접근 방식은 VBR (Variable Bit Rate)과 같이 데이터 전송률의 변화가 빈번한 데이터 서비스를 효율적으로 지원하기 어렵다. 이러한 특성의 데이터 트래픽에서는 superframe 내에 많은 수의 idle timeslot을 발생시키므로 시스템의 throughput을 감소시키고 delay를 증가시키게 된다. 본 논문에서는 가상 슬롯 기반의 다중 접근 방식인 VSMA(Virtual Slot Multiple Access)를 제안한다. 제안하는 기법은 multi-frame TDMA의 환경에서 성능을 향상시킬 수 있는 기법으로서 가상 슬롯을 할당 받은 station은 높은 접근 우선 순위를 갖고 그 밖의 station은 낮은 접근 우선 순위를 갖게 하여 채널을 효과적으로 사용할 수 있는 기법이다. 다양한 환경에서의 시뮬레이션을 통해 본 논문에서 제안한 기법이 효율적인 채널 사용을 통해서 향상된 성능을 보인다는 것을 증명하였다.

• 한국통신학회논문지
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• 제36권8A호
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• pp.712-722
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• 2011

Wireless body area network (WBAN)은 인체 주변 영역에서의 통신서비스를 제공한다. WBAN 서비스는 인체 내부에 이식된 의료 응용을 위한 MICS 주파수 대역과 의료 응용과 consumer electronics (CE) 응용 분야 모두를 제공할 수 있는 ISM 주파수 대역에서의 서비스로 이루어지기 때문에 WBAN을 위한 MAC 프로토콜은 의료 응용과 CE 응용간의 상이한 특징과 유연성 (flexibility)을 고려하여 설계되어야 한다. 본 논문에서는 WBAN MAC 프로토콜의 요구사항을 확인하고, WBAN의 요구사항을 만족하는 WBAN MAC 프로토콜을 제안한다. WBAN의 다양한 응용을 위한 전송 유연성을 제공하기 위해서 동적 CFP(Contention Free Period) 할당(Dynamic CFP Allocation)을 제안한다. 또한, 경쟁 기반의 긴급 의료 데이터를 발생하는 의료 응용과 때때로 대량의 데이터를 발생하는 CE 응용을 지원하기 위해서 OCDP(opportunistic contention decision period) 구간과 4-mode Opportunity period를 제안하고, 제안한 방안을 이용하여 Inactive period와 Opportunity period를 일시적으로 전환하여 사용할 수 있는 기법을 제안한다. 다양한 시뮬레이션 결과 IEEE 802.15.4 MAC 프로토콜과 제안하는 WBAN MAC 프로토콜을 비교하였을 때, WBAN 환경에서의 전송 처리량, CFP 이용율, 전송지연 측면에서 증가된 성능 결과를 얻을 수 있었다.

• Current Research on Agriculture and Life Sciences
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• 제31권1호
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• pp.18-24
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• 2013

This work attempted to fabricate organic/inorganic nanocomposite by combining organic cellulose nanofibrils (CNFs), isolated by 2,2,6,6-tetramethylpiperidine-1-oxy radical (TEMPO)-mediated oxidation of native cellulose with inorganic nanoclay. The morphology and dimension of CNFs, and tensile properties and thermal stability of CNF/clay nanocomposites were characterized by transmission electron microscope (TEM), tensile test, and thermogravimetry (TG), respectively. TEM observation showed that CNFs were fibrillated structure with a diameter of about $4.86{\pm}1.341nm$. Tensile strength and modulus of the hybrid nanocomposite decreased as the clay content of the nanocomposite increased, indicating a poor dispersion of CNFs or inefficient stress transfer between the CNFs and clay. The elongation at break increased at 1% clay level and then continuously decreased as the clay content increased, suggesting increased brittleness. Analysis of TG and derivative thermogravimetry (DTG) curves of the nanocomposites identified two thermal degradation peak temperatures ($T_{p1}$ and $T_{p2}$), which suggested thermal decomposition of the nanocomposites to be a two steps-process. We think that $T_{p1}$ values from $219.6^{\circ}C$ to $235^{\circ}C$ resulted from the sodium carboxylate groups in the CNFs, and that $T_{p2}$ values from $267^{\circ}C$ to $273.5^{\circ}C$ were mainly responsible for the thermal decomposition of crystalline cellulose in the nanocomposite. An increase in the clay level of the CNF/clay nanocomposite predominately affected $T_{p2}$ values, which continuously increased as the clay content increased. These results indicate that the addition of clay improved thermal stability of the CNF/clay nanocomposite but at the expense of nanocomposite's tensile properties.

• 대한토목학회논문집
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• 제40권2호
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• pp.177-182
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• 2020

본 연구에서는 시멘트 페이스트에 혼합된 나노 섬유가 경화된 시멘트페이스트의 압축강도와 인장강도에 미치는 영향을 연구하였다. 2종류의 나노 섬유를 사용하였다. 나일론 66 나노 섬유와 카본 나노 튜브로 보강된 나일론 66 나노 섬유를 전기방사로 제작하여 시멘트 파우더에 각각 혼합하였다. 물-시멘트비 0.5의 시멘트 페이스트 시편을 제작하고 28일간 양생하였다. 실험 결과, 나노섬유의 혼합이 시멘트 페이스트 시편의 압축강도와 인장강도를 증가시킴을 확인하였다. 나노 섬유의 보강 매카니즘을 확인하기 위해 주사전자현미경(SEM) 분석, 전계방사 투과전자 현미경(FE-TEM) 분석 및 열 중량 분석(TGA)을 수행하여 나노섬유를 포함한 시멘트 페이스트의 미세 구조를 분석하였다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2011년도 제40회 동계학술대회 초록집
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• pp.118-118
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• 2011

The Nano-Floating Gate Memory(NFGM) devices with ZnO:Cu thin film embedded in Al2O3 and AlOx-SAOL were fabricated and the electrical characteristics were evaluated. To further improve the scaling and to increase the program/erase speed, the high-k dielectric with a large barrier height such as Al2O3 can also act alternatively as a blocking layer for high-speed flash memory device application. The Al2O3 layer and AlOx-SAOL were deposited by MLD system and ZnO:Cu films were deposited by ALD system. The tunneling layer which is consisted of AlOx-SAOL were sequentially deposited at $100^{\circ}C$. The floating gate is consisted of ZnO films, which are doped with copper. The floating gate of ZnO:Cu films was used for charge trap. The same as tunneling layer, floating gate were sequentially deposited at $100^{\circ}C$. By using ALD process, we could control the proportion of Cu doping in charge trap layer and observe the memory characteristic of Cu doping ratio. Also, we could control and observe the memory property which is followed by tunneling layer thickness. The thickness of ZnO:Cu films was measured by Transmission Electron Microscopy. XPS analysis was performed to determine the composition of the ZnO:Cu film deposited by ALD process. A significant threshold voltage shift of fabricated floating gate memory devices was obtained due to the charging effects of ZnO:Cu films and the memory windows was about 13V. The feasibility of ZnO:Cu films deposited between Al2O3 and AlOx-SAOL for NFGM device application was also showed. We applied our ZnO:Cu memory to thin film transistor and evaluate the electrical property. The structure of our memory thin film transistor is consisted of all organic-inorganic hybrid structure. Then, we expect that our film could be applied to high-performance flexible device.----못찾겠음......

• 한국초전도ㆍ저온공학회논문지
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• 제16권4호
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• pp.66-70
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• 2014

The superconducting fault current limiter (SFCL) is an electrical power system device that detects the fault current automatically and limits the magnitude of the current below a certain safety level. The SFCL module does not have any electrical resistance below the critical temperature, which facilitates lossless power transmission in the electric power system. Once given the fault current, however, the superconducting conductor exhibits extremely high electrical resistance, and the magnitude of the current is accordingly limited to a low value. Therefore, SFCL should be maintained at a temperature below the critical temperature, which justifies the cryogenic cooling system as a mandatory component. This report is a study which reported on the cooling system for the 154 kV-class hybrid SFCL owned by Korea Electric Power Corporation (KEPCO). Using the cryocooler, the temperature of liquid nitrogen (LN2) was lowered to 71 K. The cryostat was pressurized to 5 bars to improve the dielectric strength of nitrogen and suppress nitrogen bubble foaming during operation of SFCL. The SFCL module was immersed in the liquid nitrogen of the cryostat to maintain the superconducting state. The performance test results of the key components such as cryocooler, LN2 circulation pump, cold box, and pressure builder are shown in this paper.

• Journal of Communications and Networks
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• 제11권5호
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• pp.433-444
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• 2009

The bi-directional relay channel is the natural extension of a three-terminal relay channel where node a transmits to node b with the help of a relay r to allow for two-way communication between nodes a and b. That is, in a bi-directional relay channel, a and b wish to exchange independent messages over a shared channel with the help of a relay r. The rates at which this communication may reliably take place depend on the assumptions made on the relay processing abilities. We overview information theoretic limits of the bi-directional relay channel under a variety of conditions, before focusing on half-duplex nodes in which communication takes place in a number of temporal phases (resulting in protocols), and nodes may forward messages in four manners. The relay-forwarding considered are: Amplify and forward (AF), decode and forward (DF), compress and forward (CF), and mixed forward. The last scheme is a combination of CF in one direction and DF in the other. We derive inner and outer bounds to the capacity region of the bi-directional relay channel for three temporal protocols under these four relaying schemes. The first protocol is a two phase protocol where a and b simultaneously transmit during the first phase and the relay r alone transmits during the second. The second protocol considers sequential transmissions from a and b followed by a transmission from the relay while the third protocol is a hybrid of the first two protocols and has four phases. We provide a comprehensive treatment of protocols in Gaussian noise, obtaining their respective achievable rate regions, outer bounds, and their relative performance under different SNR and relay geometries.

• 디지털융복합연구
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• 제13권3호
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• pp.201-208
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• 2015

최근 IT 제품의 활용 분야가 다양화 되면서 소프트웨어의 활용 분야가 컴퓨터, 스마트폰, 의료기기 등 다양한 환경에서 이용되고 있다. 이처럼 소프트웨어의 활용분야가 다양해짐에 따라 소프트웨어 보안 취약점을 악용하는 공격사례가 증가하고 있으며 이에 따라 다양한 시큐어코딩 프로그램이 출시되었지만 이력관리, 업데이트, API 모듈 등의 취약점이 존재하고 있다. 본 논문에서는 안전한 소프트웨어 개발을 위해 송신모듈에 형상관리를 연동하는 시스템과, 콘텐츠 단위로 소스코드의 취약점을 점검할 수 있는 CMS 연동 시스템을 구현하고, 프로그램의 기능을 세분화하여 국내외 시큐어코딩 관련 표준을 분석 및 적용함으로서 효율적인 시큐어코딩 시스템 방법을 구현하였다.

• Macromolecular Research
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• 제16권1호
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• pp.6-14
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• 2008

Polypropylene (PP)-layered silicate nanocomposites were developed using a new processing method involving a supercritical carbon dioxide ($scCO_2$)-assisted co-rotating twin-screw extrusion process. The nanocomposites were prepared through two step extrusion processes. In the first step, the PP/clay mixture was extruded with $CO_2$ injected into the barrel of the extruder and the resulting foamed extrudate was cooled and pelletized. In the second step, the foamed extrudate was extruded with venting to produce the final PP/clay nanocomposites without $CO_2$. In this study, organophilic-clay and polypropylene matrix were used. Maleic anhydride grafted polypropylene (PP-g-MA) was used as a compatibilizer. This study focused on the effect of $scCO_2$ on the dispersion characteristics of the clays into a PP matrix and the rheological properties of the layered silicate based PP nanocomposites. The dispersion properties of clays in the nanocomposites as well as the rheological properties of the nanocomposites were examined as a function of the PP-g-MA concentration. The degree of dispersion of the clays in the nanocomposites was analyzed by X-ray diffraction and transmission electron microscope. Various rheological properties of the nanocomposites were measured using a rotational rheometer. In the experimental results, the $scCO_2$ assisted continuous manufacturing extrusion system was used to successfully produce the organophilic-clay filled PP nanocomposites. It was found that $scCO_2$ had a measurable effect on the clay dispersion in the polymer matrix and the melt intercalation of a polymer into clay layers.