• 한국멀티미디어학회논문지
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• 제14권11호
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• pp.1438-1449
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• 2011

수중센서네트워크 응용은 적용 대상 및 지역적 범위에 따라 효과적인 모델링이 필요하고 이러한 특정화된 응용 모델 기반에서 에너지 효율적인 데이터통합 방법이 필요하다. 본 논문에서는 수중에 고정된 닻으로 좌우 움직임이 가능한 센서노드들로 구성된 3차원 육각기둥 벌집모델에 기초하여 오염 및 침투 감시용 응용 모델링 및 이를 기초로 한다. 이 모델에서는 층별 구성 셀들의 이벤트 감지 데이터와 해당 층 위치 데이터를 수면기지국까지 효율적으로 전송하면 그 목적이 달성된다. 여기서 기존의 데이터통합 방법을 적용하면 최소 경로나 멀티캐스트 트리에 기반된 관계로 과정이 복잡하여 에너지 비효율적이다. 본 논문에서는 층별 셀들에서 발생되는 이벤트 데이터를 해당 층 헤드노드로 효과적으로 전달하기위한 클러스터 내부에서 클러스터 기반의 에너지 효율적인 세 가지 가능한 데이터통합 방법을 제시한다. 그리고 층별 클러스터 헤드노드에서 수집된 데이터를 기지국까지 효율적으로 전달하기위한 클러스터 간 세 가지 데이터통합 방법도 제시한다. 제시된 데이터통합 방법들은 주어진 영역 침투 감시등과 같은 특정화된 응용 대상으로 동작의 단순성과 에너지 효율화 측면이 주된 고려 요소이다. 마지막으로 시뮬레이션과 성능 비교분석을 통해 제시된 클러스터 층별 및 층간 데이터통합 방법의 조합 중 가장 우수한 에너지 효율적인 데이터통합 방법을 도출한다.

• Journal of Photoscience
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• 제9권2호
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• pp.110-113
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• 2002

We demonstrate here a dynamic structure of bacteriorhodopsin (bR) as revealed by $^{13}$ C NMR studies on [3_$^{13}$ C]_,[1-$^{13}$ C]Ala- and/or Val-labeled wild type and a variety of site-directed mutants at ambient temperature. For this purpose, well-resolved (up to twelve) I$^{13}$ C NMR peaks were assigned with reference to the displacement of peaks due to the conformation-dependent I$^{13}$ C chemical shifts and reduced peak-intensities due to site-directed mutations. Revealed bR structure was not rigid as anticipated from 2D crystals of hexagonal array but a dynamically heterogeneous, undergoing a variety of local fluctuations depending upon specific site with frequency range of 10$^2$ -10$^{8}$ Hz. In particular, dynamics- dependent suppression of peaks turned out to be very sensitive to the motion of 10$^{-4}$ s and 10$^{-5}$ s interfered with frequency of magic angle spinning and proton decoupling, respectively. It is also noteworthy that such dynamic feature is strongly dependent upon the manner of 2D crystalline packing: $^{13}$ C NMR peaks of monomeric bR yielded either highly broadened or completely suppressed signals, depending upon the type of $^{13}$ C-labeled amino-acid residues.

• Composites Research
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• 제33권1호
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• pp.30-37
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• 2020

단방향 연속 섬유 강화 복합소재에 대하여 섬유 배열에 따른 응력 분포 양상을 연구하기 위해 단면 형상을 대표하는 체적 요소를 생성하였다. 대표 체적 요소에 횡방향 하중을 가하였을 때, 섬유와 기지재 강성의 차이로 인해 섬유 둘레에서 응력 집중 현상이 발생하며, 섬유 간 좁은 간격 때문에 집중된 응력이 중첩되며 섬유 주변에서 높은 응력이 구해질 것이라 쉽게 예측할 수 있다. 본 연구에서는 섬유 둘레 응력 증감이 단순히 섬유 간 간격 뿐 아니라 섬유의 상대적 위치가 하중 방향과 이루는 각도에 의해서도 결정됨을 보여준다. 정규 육각 구조를 가지는 대표 체적 요소의 중앙에 위치한 섬유를 다양한 방향으로 이동시키며 횡방향 하중을 가하여, 섬유 주변 응력이 증가하거나 감소하는 양상을 유한요소해석 기법을 이용해 측정하였다. 섬유 간 거리가 최소이면서 두 섬유의 중심을 잇는 선분의 방향이 하중 방향과 일치할 때 응력이 최대로 증가하였으며, 섬유 간 거리가 최소라 하더라도 하중 방향에 수직일 때 최대 응력은 오히려 감소한다는 것을 보여준다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2012년도 제42회 동계 정기 학술대회 초록집
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• pp.135-136
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• 2012

Carbon atoms near the surface of W(110) induce reconstructions such as $R(15{\times}12)$ -C/W(110) which consists of two characteristic parts, one square shaped and bright protrusion and two smaller ones. In the atomic resolution STM image, the bigger protrusion shows the periodicities of clean W(110), indicating that it is almost carbon poor region. The smaller protrusion contains hexagonal carbide surface layer of ${\alpha}$-W2C on W(110). Employing this carburized W(110) as templates, we grow Co and Fe clusters of less than ten atoms. Due to the selectivity of bonding sites, growth of larger cluster is highly unfavorable for Co and the size of clusters is very uniform. Since Co atoms prefer to sit on the bigger protrusion rather than smaller one, Co cluster can be arranged one-dimensionally in $R(15{\times}12)$-C/W(110) with quite uniform size distribution. However, Fe clusters sit on both sites without favored site, but still with uniform size distribution. On the other hand, Fe clusters can be grown with quasi one-dimensional order in $R(15{\times}3)$-C/W(110), which consists of only smaller protrusions. We investigate the magnetic properties of the ordered nano-sized clusters. Experiments using XMCD reveals little magnetic moment of Co cluster on $R(15{\times}12)$-C/W(110). This observation is consistent with the predictions of our first principles calculations that small Co clusters can be nonmagnetic or antiferromagnetic with low mean magnetic moment per atom.

• 천문학회보
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• 제39권1호
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• pp.51.1-51.1
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• 2014

DOTIFS is a new multi-object Integral Field Spectrograph (IFS) being designed and fabricated by the Inter-University Center for Astronomy and Astrophysics, Pune, India, (IUCAA) for the Cassegrain side port of the 3.6m Devasthal Optical Telescope (DOT). The telescope is constructed by the Aryabhatta Research Institute of Observational Sciences, Nainital (ARIES). Its main scientific objectives are the physics and kinematics of the ionized gas, star formation and H II regions in nearby galaxies. It is a novel instrument in terms of multi-IFU, built in deployment system, and high throughput. It consists of one magnifier, 16 integral field units (IFUs), and 8 spectrographs. Each IFU is comprised of a microlens array and 144 optical fibers, and has $7.4^{\prime\prime}{\times}8.7^{\prime\prime}$ field of view with 144 spaxel elements with a sampling of 0.8" hexagonal aperture. The IFUs can be deployed on the telescope side port over an 8' diameter focal plane by x-y actuators. 8 Identical, all refractive, dedicated fiber spectrographs will produce 2,304 R~1800 spectra over 370-740nm wavelength range with single exposure. Currently, conceptual and baseline design review had been done, and is in the critical design phase with a review planned for later this year. Some of the components have already arrived. The instrument will see its first light in 2015.

• Advances in materials Research
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• 제3권3호
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• pp.139-149
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• 2014

Surface enhanced Raman Scattering (SERS) has attracted attention because the technique enables detection of various chemicals, even down to single molecular scale. Among the diverse candidates for SERS substrates, Au nanoparticles are considered promising due to their fine optical properties, chemical stability and ease of surface modification. Therefore, the fabrication and optical characterization of gold particles on solid supports is highly desirable. Such structures have potential as SERS substrates because the localized surface plasmon resonance of gold nanoparticles is very sensitive to combined molecules and environments. In addition, it is well-known that the properties of Au nanoparticles are strongly dependent on their shape. In this work, arrays of shape-controlled Au nanoparticles were fabricated to exploit their enhanced and reproducible optical properties. First, shape-controlled Au nanoparticles were prepared via seed mediated solution-phase synthesis, including spheres, octahedra, and rhombic dodecahedra. Then, these shape-controlled Au nanoparticles were arranged on a PDMS substrate, which was nanopatterned using soft lithography of poly styrene particles. The Au nanoparticles were selectively located in a pattern of hexagonal spheres. In addition, the shape-controlled Au nanoparticles were arranged in various sizes of PDMS nanopatterns, which can be easily controlled by manipulating the size of polystyrene particles. Finally, the optical properties of the fabricated Au nanoparticle arrays were characterized by measuring surface enhanced Raman spectra with 4-nitrobenezenethiol.

• 방사선산업학회지
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• 제5권4호
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• pp.325-330
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• 2011

To predict the details of flow in industrial process unit, single photon emission computed tomography (SPECT) is a promising technique. Recently, industrial SPECT based on medical system has developed by researchers of the Korea Atomic Energy Research Institute (KAERI) and Hanyang University. In the present study, to confirm the effect of the number of detectors on image quality, and determine the optimal number of detectors in industrial SPECT, industrial SPECT system with various geometries were evaluated by the Monte Carlo simulation. CsI(Tl) detectors ($12mm{\times}12mm{\times}20mm$) with collimators (the geometric resolution of collimator $R_g$ was 4 cm at the center of the 30 cm diameter cylindrical vessel object) were modeled in a hexagonal array, and the point sources of $^{99m}Tc$, $^{68}Ga$, and $^{137}Cs$ were simulated at the center of the cylindrical vessel object using the MCNPX code. Then, the reconstruction images of each geometry were reconstructed using the expectation maximization (EM) algorithm. In this study, the reciprocity theorem was used to improve computation time required for system matrix of the EM algorithm. The result shows that the resolution of the reconstructed image was significantly improved by increasing the number of detectors in industrial SPECT system and more than 60 detectors will be required for the resolution of the reconstructed image.

• 전기전자학회논문지
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• 제23권3호
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• pp.1112-1115
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• 2019

본 논문에서는 정찰포탄의 활공날개에 적용할 수 있는 새로운 평판형 무지향성 마이크로스트립 안테나를 제안하였다. 제안한 안테나는 무지향성 방사패턴을 얻기 위하여 얇은 기판에 7개의 정육각형 공진기를 준원형을 배열한 구조를 가지고 있다. 안테나 기판의 하단부에 그물망 형태로 이루어진 접지선 구조를 적용하여, 안테나의 공진주파수와 임피던스 대역폭에 관한 연구를 수행하였다. 그물망 형태의 접지선 구조의 유효성을 검증하기 위하여, 접지선의 선폭을 이론적으로 분석하여 상대 대역폭, Q-factor 및 안테나 이득을 만족시키기 위한 최적화 기법을 수행하였다. 제안한 안테나는 모의실험결과와 유사한 측정결과를 보임으로써, 무지향성 방사패턴이 잘 형성됨을 시연하였다. 마지막으로 제작한 안테나 시제품은 5.77 GHz를 중심으로 약 5.65%의 상대대역폭에 해당하는 326 MHz의 동작대역폭을 확인하였으며, 공진주파수 5.84 GHz에서 5.49 dBi의 안테나 이득을 확인하였다.

• Current Optics and Photonics
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• 제5권3호
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• pp.250-260
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• 2021

A tapered As₂S₃ photonic crystal fiber (PCF) with four layers of air holes in a hexagonal array around the core is designed in this paper. Numerical simulation shows that the dispersion D decreases and the nonlinearity coefficient γ increases from the thick to the thin end along the tapered PCF. We simulate the midinfrared pulse compression in the tapered As₂S₃ PCF using the adaptive split-step Fourier method. Initial Gaussian pulses of 4.4 ps and a central wavelength of 2.5 ㎛ propagating in the tapered PCF are located in the anomalous dispersion region. With an average power of assumed input pulses at 3 mW and a repetition frequency of 81.0 MHz, we theoretically obtain a pulse duration of 56 fs and a compression factor of 78 when the pulse propagates from the thick end to the thin end of the tapered PCF. When confinement loss in the tapered PCF is included in the simulation, the minimum pulse duration reaches 72 fs; correspondingly, the maximum compression factor reaches 61. The results show that in the anomalous-dispersion region, midinfrared pulses can be efficiently compressed in a dispersion-decreasing and nonlinearity-increasing tapered As₂S₃ PCF. Due to confinement loss in the tapered fiber, the efficiency of pulse compression is suppressed.

• 한국정보디스플레이학회:학술대회논문집
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• 한국정보디스플레이학회 2008년도 International Meeting on Information Display
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• pp.993-994
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• 2008

Electrochromic (EC) devices are capable of reversibly changing their optical properties upon charge injection and extraction induced by the external voltage. The characteristics of the EC device, such as low power consumption, high coloration efficiency, and memory effects under open circuit status, make them suitable for use in a variety of applications including smart windows and electronic papers. Coloration due to reduction or oxidation of redox chromophores can be used for EC devices (e-paper), but the switching time is slow (second level). Recently, with increasing demand for the low cost, lightweight flat panel display with paper-like readability (electronic paper), an EC display technology based on dye-modified $TiO_2$ nanoparticle electrode was developed. A well known organic dye molecule, viologen, was adsorbed on the surface of a mesoporous $TiO_2$ nanoparticle film to form the EC electrode. On the other hand, ZnO is a wide bandgap II-VI semiconductor which has been applied in many fields such as UV lasers, field effect transistors and transparent conductors. The bandgap of the bulk ZnO is about 3.37 eV, which is close to that of the $TiO_2$ (3.4 eV). As a traditional transparent conductor, ZnO has excellent electron transport properties, even in ZnO nanoparticle films. In the past few years, one-dimension (1D) nanostructures of ZnO have attracted extensive research interest. In particular, 1D ZnO nanowires renders much better electron transportation capability by providing a direct conduction path for electron transport and greatly reducing the number of grain boundaries. These unique advantages make ZnO nanowires a promising matrix electrode for EC dye molecule loading. ZnO nanowires grow vertically from the substrate and form a dense array (Fig. 1). The ZnO nanowires show regular hexagonal cross section and the average diameter of the ZnO nanowires is about 100 nm. The cross-section image of the ZnO nanowires array (Fig. 1) indicates that the length of the ZnO nanowires is about $6\;{\mu}m$. From one on/off cycle of the ZnO EC cell (Fig. 2). We can see that, the switching time of a ZnO nanowire electrode EC cell with an active area of $1\;{\times}\;1\;cm^2$ is 170 ms and 142 ms for coloration and bleaching, respectively. The coloration and bleaching time is faster compared to the $TiO_2$ mesoporous EC devices with both coloration and bleaching time of about 250 ms for a device with an active area of $2.5\;cm^2$. With further optimization, it is possible that the response time can reach ten(s) of millisecond, i.e. capable of displaying video. Fig. 3 shows a prototype with two different transmittance states. It can be seen that good contrast was obtained. The retention was at least a few hours for these prototypes. Being an oxide, ZnO is oxidation resistant, i.e. it is more durable for field emission cathode. ZnO nanotetropods were also applied to realize the first prototype triode field emission device, making use of scattered surface-conduction electrons for field emission (Fig. 4). The device has a high efficiency (field emitted electron to total electron ratio) of about 60%. With this high efficiency, we were able to fabricate some prototype displays (Fig. 5 showing some alphanumerical symbols). ZnO tetrapods have four legs, which guarantees that there is one leg always pointing upward, even using screen printing method to fabricate the cathode.