• 한국음향학회지
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• 제23권1호
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• pp.17-23
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• 2004

일반적으로 무선 이동 채널은 협대역 스펙트럼을 갖는 복소 랜덤 프로세스로 모델링된다. 본 논문에서는 TMS320C6414 DSP칩과 XC2VP30 FPGA칩을 사용한 페이딩 신호의 실시간발생에 대해 기술한다. 여기서 제시된 시뮬레이터는 플랫 페이딩 및 주파수 선택성 페이딩 채널의 일반적인 모델로 그 대상으로 하였으며 여러 다양한 채널 왜곡 현상을 모사할 수 있도록 설계되었다. 시뮬레이터는 다음 세가지 기본적인 채널 특성을 포함한다; 레일리 페이딩, log-normal shadowing, 주파수 선택성 페이딩. DSP의 연산부담을 최소로 하면서 이동 채널의 통계 특성을 재현하기 위해 multi-rate신호처리 기법이 사용되었다. 채널 파라미터 값을 변화시키면서 많은 실험을 행하였고, 시뮬레이터에서 실시간 출력된 채널 포락선들의 각 통계 특성이 이론치와 일치됨을 확인했다.

• 한국음향학회지
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• 제33권5호
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• pp.309-315
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• 2014

본 논문은 능동 소음 제어 시스템에 적합한 새로운 가변 수렴 상수 filtered-x gradient adaptive lattice(NVSS-FxGAL) 알고리즘을 제안한다. Gradient adaptive lattice(GAL) 알고리즘은 협대역 특성을 가지는 소음을 효과적으로 제어할 수 있다. GAL 알고리즘의 수렴 성능을 개선하기 위한 가변 격자 필터의 각 단계에 동일하게 적용하면 입력 신호의 특성 변화에 강인하게 대처하지 못한다. 제안 알고리즘은 격자 필터의 각 단계에 적합한 로컬 가변 수렴상수를 이용하여 안정적이고 일관성 있는 수렴 성능을 보장한다. 실험을 통해 제안 알고리즘은 빠른 수렴 속도와 낮은 정상 상태를 보임을 확인하였다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2016년도 제50회 동계 정기학술대회 초록집
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• pp.189-189
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• 2016

Recently, many researchers have shown an increased interest in colloidal quantum dots (QDs) due to their unique physical and optical properties of size control for energy band gap, narrow emission with small full width at half maxima (FWHM), broad spectral photo response from ultraviolet to infrared, and flexible solution processing. QDs can be widely used in the field of optoelectronic and biological applications and, in particular, colloidal QDs based light emitting diodes (QDLEDs) have attracted considerable attention as an emerging technology for next generation displays and solid state lighting. A few methods have been proposed to fabricate white color QDLEDs. However, the fabrication of white color QDLEDs using single QD is very challenging. Recently, hybrid nanocomposites consisting of CdTe/ZnO heterostructures were reported by Zhimin Yuan et al.[1] Here, we demonstrate a novel but facile technique for the synthesis of CdTe/ZnO/G.O(graphene oxide) quasi-core-shell-shell quantum dots that are applied in the white color LED devices. Our best device achieves a maximum luminance of 484.2 cd/m2 and CIE coordinates (0.35, 0.28).

• 한국세라믹학회지
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• 제53권4호
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• pp.400-405
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• 2016

Ferric oxide (${\alpha}-Fe_2O_3$, hematite) is an n-type semiconductor; due to its narrow band gap ($E_g=2.1eV$), it is a highly attractive and desirable material for use in solar hydrogenation by water oxidation. However, the actual conversion efficiency achieved with $Fe_2O_3$ is considerably lower than the theoretical values because the considerably short diffusion length (2-4 nm) of holes in $Fe_2O_3$ induces excessive charge recombination and low absorption. This is a significant hurdle that must be overcome in order to obtain high solar-to-hydrogen conversion efficiency. In consideration of this, it is thought that elemental doping, which may make it possible to enhance the charge transfer at the interface, will have a marked effect in terms of improving the photoactivities of ${\alpha}-Fe_2O_3$ photoanodes. Herein, we report on the synthesis by pulsed electrodeposition of ${\alpha}-Fe_2O_3$-based anodes; we also report on the resulting photoelectrochemical (PEC) properties. We attempted Ti-doping to enhance the PEC properties of ${\alpha}-Fe_2O_3$ anodes. It is revealed that the photocurrent density of a bare ${\alpha}-Fe_2O_3$ anode can be dramatically changed by controlling the condition of the electrodeposition and the concentration of $TiCl_3$. Under optimum conditions, a modified ${\alpha}-Fe_2O_3$ anode exhibits a maximum photocurrent density of $0.4mA/cm^2$ at 1.23 V vs. reversible hydrogen electrode (RHE) under 1.5 G simulated sunlight illumination; this photocurrent density value is about 3 times greater than that of unmodified ${\alpha}-Fe_2O_3$ anodes.

• Korea-Australia Rheology Journal
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• 제17권1호
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• pp.1-7
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• 2005

Acrylonitrile-Butadiene-Styrene (ABS), polycarbonate (PC) and their alloys are an important class of engineering thermoplastics that are widely used for automotive industry, computer and equipment housings. For the process of recycling mixtures of ABS and PC, it is desirable to know how sensitive the blend properties are to changes in compositions. It was for this reason that blends of virgin ABS and virgin PC at five different compositions, namely, $15\%,\;30\%,\;50\%,\;70%$ and $85\%$ by weight of ABS were prepared and characterised by rheological and mechanical measurements. Rheological properties of these blends in steady, oscillatory and transient step shear and mechanical properties, namely, tensile strength, elongation-at-break and Izod impact strength are reported. The results show that PC behaves in a relatively Newtonian manner, but ABS exhibits significant shear thinning. The ABS-rich blends show a trend that is similar to that of ABS, while PC-rich blends, namely $0\%$ and $15\%$, exhibit a nearly Newtonian behaviour. However, at a fixed shear rate or frequency, the steady shear or the dynamic viscosity varied respectively in a non-mono-tonic manner with composition. Except for $15\%$ blend, the viscosities of other blends fall into a narrow band indicating a wide-operation window of varying blend ratio. The blends exhibited a lower viscosity than either of the two pure components. The other noticeable feature was that the blends at $70\%$ and $85\%$ ABS content had a higher G' than pure ABS, indicating an enhancement of elastic effect. The tensile yield strength of the blends followed the 'rule of mixtures' showing a decreasing value with the increase of ABS content in PC. However, the elongation-at-break and the impact strength did not appear to obey this 'rule of mixtures,' which suggests that morphology of the blends also plays a significant role in determining the properties. Indeed, scanning electron micrographs of the fracture surfaces of the different blends validate this hypothesis, and the $15\%$ blend is seen to have the most distinct morphology and correspondingly different behaviour and properties.

• 대한소아치과학회지
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• 제30권3호
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• pp.453-458
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• 2003

유전치의 인접면 수복에는 흔히 celluloid strip과 wedge를 이용하는 방법 또는 기성품으로 시판되는 celluloid strip crown form을 이용한 방법이 사용된다. 그러나, 이와 같은 방법은 하악에서는 유치의 치관이 작고 치아사이의 발육 공간이 있어 matrix의 견고한 고정이 어려우며, matrix의 강직성으로 인해 풍융한 인접면 형태 및 변연부를 적절히 형성하기 어렵다. 또한 구강이 좁은 소아 환자에서는 술자의 손가락으로 matrix를 지지하기가 불편하다. 이에 저자는 유전치의 인접면을 충전하기 위하여 시중에서 쉽게 구할 수 있는 빨대를 이용하여 편리하면서도 변연부 적합성을 높일 수 있는 변형된 방법을 고안하였다. 이 방법은 증례에 따라 적절히 사용한다면 유전치 수복에 있어 간편하고 효율적인 방법 이 될 것으로 사료된다.

• 한국ITS학회 논문지
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• 제6권2호
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• pp.95-106
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• 2007

본 논문은 음악 정보검색에 사용되는 효과적인 템포 특징 추출방식을 제안한다. 제안된 템포 정보는 협소 밴드상의 일시적인 변조 성분에 의해 형성된다. 이러한 변조 성분은 시간 축 상의 음악 신호로부터 스펙트럼을 구한 후, 각 스펙트럼 성분에 대한 주파수 영역 분석을 통해 획득된 변조 스펙트럼으로 구성된다. 실제 구현에 있어서는 MP3 음악파일로부터 부분 디코딩에 의해 출력된 변형된 이산 코사인 변환 계수에 퓨리에 변환을 취하여 변조스펙트럼을 구하였다. 획득된 변조 스펙트럼의 진폭으로부터 고속으로 추출된 음악 템포 특징값은 다양한 음악 정보 검색에 적용되었다. 음악 무드 및 장르 분류에서는 로그 변조 주파수 계수를 적용하여 분류 성능을 개선시켰으며, 적응 변조 스펙트럼에서 유도된 비트 벡터는 오디오 핑거프린팅에 적용되어 잡음환경 하에서도 검색 성능을 크게 향상시켰다.

• 천문학회보
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• 제40권2호
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• pp.28.3-29
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• 2015

$Ly{\alpha}$ nebulae, or "$Ly{\alpha}$ blobs", are extended (~100 kpc), bright (L[$Ly{\alpha}$] ~ 1044 erg/s) clouds of $Ly{\alpha}$-emitting gas. The origin of the $Ly{\alpha}$ emission remains unknown, but recent theoretical work suggests that measuring the polarization could discriminate among powering mechanisms. we will discuss current status of $Ly{\alpha}$ polarization observations at high-redshift and our on-going survey program. We will present the first narrow-band, imaging polarimetry of a $Ly{\alpha}$ blob, B3 J2330+3927 at z=3.09, with an embedded, radio-loud AGN (C. You et al. in prep.). The AGN lies near the blob's $Ly{\alpha}$ emission peak and its radio lobes align roughly with the blob's semi-major axis. With the SPOL polarimeter on the MMT telescope, we map the polarization in a grid of circular apertures of radius 0.6" (4.4 kpc), detecting a significant (>$2{\sigma}$) polarization fraction P% in 10 apertures and achieving strong upper-limits (as low as 2%) elsewhere. The degree of the polarization map increases from P% ~ 5% at ~5 kpc from the blob center to ~20% at the outer part (~30 kpc). The detections are distributed asymmetrically, roughly along the blob's major axis. The polarization angles (${\Theta}$) are mostly perpendicular to this axis. These results are consistent with the picture that $Ly{\alpha}$ photons produced at the AGN (or the host galaxy) are resonantly scattered away from the center. Higher polarization fraction on the radio jet suggests that the gas is more optically thin along the jet than the off-axis region.

• 천문학회보
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• 제40권2호
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• pp.41.4-42
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• 2015

Outflows and jets from young stellar objects (YSOs) are prominent observational phenomena in star formation process. Indicating currently ongoing star formation and directly tracing mass accretion, they provide clues about the accretion processes and accretion history of YSOs. While outflows of low-mass YSOs are commonly observed and well studied, such studies for high-mass YSOs have been so far rather limited owing to their large distances and high visual extinction. Recently, we have found a number of molecular hydrogen (H2 1-0 S(1) at 2.12 micron) outflows in the long, filamentary infrared dark cloud (IRDC) G53.2 located at 1.7 kpc from UWISH2, the unbiased, narrow-band imaging survey centered at 2.12 micron using WFCAM/UKIRT. In IRDC G53.2 which is an active star-forming region with ~300 YSOs, H2 outflows are ubiquitously distributed around YSOs along dark filaments. In this study, we present the most prominent H2 outflow among them identified in one of the IRDC cores MSXDC G53.11+00.05. The outflow shows a remarkable bipolar morphology and has complex structures with several flows and knots. The outflow size of ~1 pc and H2 luminosity about ~1.2 Lsol as well as spectral energy distributions of the Class I YSOs at the center suggest that the outflow is likely associated with a high-mass YSO. We report the physical properties of H2 outflow and characteristics of central YSOs that show variability between several years using the H2 and [Fe II] images obtained from UWISH2, UWIFE and Subaru/IRCS+AO188 observations. Based on the results, we discuss the possible origin of the outflow and accretion processes in terms of massive star formation occurring in IRDC core.

• Journal of electromagnetic engineering and science
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• 제10권3호
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• pp.158-165
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• 2010

This study reviewed terahertz technologies of time domain spectroscopy, T-ray imaging, and high rate wireless data transfer. The main topics of the terahertz research area were investigation of materials and package modules for terahertz wave generation and detection, and setup of the terahertz system for time domain spectroscopy(TDS), T-ray imaging and sub-THz wireless communication. In addition to Poly-GaAs film as a photoconductive switching antenna material, a table-top scale for the THz-TDS/imaging system and terahertz continuous wave(CW) generation systems for sub-THz data transfer and narrow band T-ray imaging were designed. Dielectric properties of ferroelectric BSTO($Ba_xSr_{1-x}TiO_3$) films and chalcogenide glass systems were characterized with the THz-TDS system at the THz frequency range. Package modules for terahertz wave transmitter/receiver(Tx/Rx) photoconductive antenna were developed.