• 한국진공학회:학술대회논문집
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• 한국진공학회 2015년도 제49회 하계 정기학술대회 초록집
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• pp.76.1-76.1
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• 2015

Optical resonances of metallic or dielectric nanoantennas enable to effectively convert free-propagating electromagnetic waves to localized electromagnetic fields and vice versa. Plasmonic resonances of metal nanoantennas extremely modify the local density of optical states beyond the optical diffraction limit and thus facilitate highly-efficient light-emitting, nonlinear signal conversion, photovoltaics, and optical trapping. The leaky-mode resonances, or termed Mie resonances, allow dielectric nanoantennas to have a compact size even less than the wavelength scale. The dielectric nanoantennas exhibiting low optical losses and supporting both electric and magnetic resonances provide an alternative to their metallic counterparts. To extend the utility of metal and dielectric nanoantennas in further applications, e.g. metasurfaces and metamaterials, it is required to understand and engineer their scattering characteristics. At first, we characterize resonant plasmonic antenna radiations of a single-crystalline Ag nanowire over a wide spectral range from visible to near infrared regions. Dark-field optical microscope and direct far-field scanning measurements successfully identify the FP resonances and mode matching conditions of the antenna radiation, and reveal the mutual relation between the SPP dispersion and the far-field antenna radiation. Secondly, we perform a systematical study on resonant scattering properties of high-refractive-index dielectric nanoantennas. In this research, we examined Si nanoblock and electron-beam induced deposition (EBID) carbonaceous nanorod structures. Scattering spectra of the transverse-electric (TE) and transverse-magnetic (TM) leaky-mode resonances are measured by dark-field microscope spectroscopy. The leaky-mode resonances result a large scattering cross section approaching the theoretical single-channel scattering limit, and their wide tuning ranges enable vivid structural color generation over the full visible spectrum range from blue to green, yellow, and red. In particular, the lowest-order TM01 mode overcomes the diffraction limit. The finite-difference time-domain method and modal dispersion model successfully reproduce the experimental results.

• Korea-Australia Rheology Journal
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• 제15권3호
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• pp.131-150
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• 2003

A new numerical algorithm of finite element methods is presented to solve high Deborah number flow problems with geometric singularities. The steady inertialess planar 4 : 1 contraction flow is chosen for its test. As a viscoelastic constitutive equation, we have applied the globally stable (dissipative and Hadamard stable) Leonov model that can also properly accommodate important nonlinear viscoelastic phenomena. The streamline upwinding method with discrete elastic-viscous stress splitting is incorporated. New interpolation functions classified as rational interpolation, an alternative formalism to enhance numerical convergence at high Deborah number, are implemented not for the whole set of finite elements but for a few elements attached to the entrance comer, where stress singularity seems to exist. The rational interpolation scheme contains one arbitrary parameter b that controls the singular behavior of the rational functions, and its value is specified to yield the best stabilization effect. The new interpolation method raises the limit of Deborah number by 2∼5 times. Therefore on average, we can obtain convergent solution up to the Deborah number of 200 for which the comer vortex size reaches 1.6 times of the half width of the upstream reservoir. Examining spatial violation of the positive definiteness of the elastic strain tensor, we conjecture that the stabilization effect results from the peculiar behavior of rational functions identified as steep gradient on one domain boundary and linear slope on the other. Whereas the rational interpolation of both elastic strain and velocity distorts solutions significantly, it is shown that the variation of solutions incurred by rational interpolation only of the elastic strain is almost negligible. It is also verified that the rational interpolation deteriorates speed of convergence with respect to mesh refinement.

• Steel and Composite Structures
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• 제19권4호
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• pp.861-876
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• 2015

Composite sections design consists on checking that the point defined by axial load and bending moment keeps included within the surface enclosed by the section interaction curve. Eurocode 4 suggests a method for tracing this diagram based on the plastic stress distribution method. However curves obtained according to this criterion overvalue concrete encased sections bearing capacity, especially when axial force comes with high bending moment values, so a correction factor is required. This article proposes a method for tracing this diagram based on the strain compatibility method. When stresses on the section are integrated by considering the Navier hypothesis, the use of the materials nonlinear constitutive equations provides curves much more adjusted to reality. This process requires the use of rather complex software which might reveal as too complex for practitioners. Preserving the same criteria of an elastic-plastic stress distribution, this article presents alternative expressions to obtain the failure internal forces in five significant points of the interaction diagram having considered five different positions of the neutral axis. These expressions are simply enough for their practical application. Concordance of curves traced strictly relying on these five points with those obtained by computer assisted stress integration considering the strain compatibility method and even with Eurocode 4 weighted curves will be presented for three different cross-sections and two different concrete strengths, revealing very good results.

• 콘크리트학회논문집
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• 제16권2호
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• pp.229-240
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• 2004

불균형 휨모멘트를 재하받는 플랫플레이트-기둥 접합부의 편심전단강도와 모멘트강도를 규명하기 위해 그동안 많은 실험연구가 수행되어 왔다. 기존 실험들은 서로 다른 실험방식을 사용하고 있는데, 접합부의 전단강도는 실험방식에 따라 차이가 있는 것으로 나타났다. 따라서 기존 실험에 근거하여 개발된 현행 설계기준들은 플랫플레이트의 강도를 정확히 설명하고 있지 못한 실정이다. 선행 연구에서는 연속 플랫플레이트에 대한 비선형 유한요소해석에 근거하여, 슬래브-기둥 접합부에 패한 새로운 설계방법을 개발하였다. 그러나 제안된 설계방법에서는 휨모멘트 강도산정에 필요한 접합부 편심강도를 경험식에 의존하여 산정하고 있다. 본 연구에서는, 접합부 파괴 메카니즘을 분석하기 위해서, Rankine 재료파괴기준을 이용하는 이론적인 접근법을 채택하였다. 분석결과에 근거하여 개선된 편심전단강도모델이 개발되었고, 기존 실험과의 비교를 통해 검증되었다. 개발된 강도식을 이용하여, 선행연구에서 개발된 설계방법을 재검증하였다.

• 대한전자공학회논문지SP
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• 제47권5호
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• pp.18-24
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• 2010

본 논문에서는 돌비 프로로직 II/IIx를 대체하기 위한 가상 음원 위치 정보 기반의 새로운 메트릭스 디코더 시스템을 제안하고자 한다. 제안하는 신규 메트릭스 디코더는 역행렬 계산을 통해 얻어지는 수동 메트릭스 디코딩부와 수동 메트릭스 디코딩을 통해서 얻은 신호들을 멀티채널 신호의 채널간 이미지 특성에 따라서 적응적으로 가변시키는 능동 메트릭스 디코딩부로 구성된다. 멀티채널 환경에서 채널 간에 형성되는 다수의 이미지는 실제 청각 시스템에 의해서 인지되어 만들어지는 가상의 사운드 이벤트와 연결이 되어 있다. 따라서 이 이미지의 위치와 크기에 기반하여 멀티채널 신호를 적응적으로 가변시키면, 인지적인 관점에서 우수한 성능의 메트릭스 디코더를 설계할 수 있다. 더불어 채널간 분리도를 향상시키기 위해서 비선형 삼각함수의 조합을 사용하였다.

• Earthquakes and Structures
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• 제7권4호
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• pp.587-607
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• 2014

Progressive collapse, which is referred to as the collapse of the entire building under local damages, is a common failure mode happened by earthquakes. The collapse process highly depends on the whole structural system. Since, asymmetry of the building plan leads to the local damage concentration; it may intensify the progressive collapse mechanism of asymmetric buildings. In this research the progressive collapse of regular and irregular 6-story RC ordinary moment resisting frame buildings are studied in the presence of the earthquake loads. Collapse process and collapse propagation are investigated using nonlinear time history analyses (NLTHA) in buildings with 5%, 15% and 25% mass asymmetry with respect to the number of collapsed hinges and story drifts criteria. Results show that increasing the value of mass eccentricity makes the asymmetric buildings become unstable earlier and in the early stages with lower number of the collapsed hinges. So, with increasing the mass eccentricity in building, instability and collapse of the entire building occurs earlier, with lower potential of the progressive collapse. It is also demonstrated that with increasing the mass asymmetry the decreasing trend of the number of collapsed beam and column hinges is approximately similar to the decreasing trend in the average story drifts of the mass centers and stiff edges. So, as an alternative to a much difficult-to-calculate local response parameter of the number of collapsed hinges, the story drift, as a global response parameter, measures the potential of progressive collapse more easily.

• Asian-Australasian Journal of Animal Sciences
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• 제13권5호
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• pp.641-644
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• 2000

In vitro true digestibility of cup-plant (Silphium perfoliatum L.) is higher than other alternative forages and comparative to alfalfa (Medicago sativa L.) even at the high neutral detergent fiber (NDF) concentration. This study was conducted to determine whether the digestion kinetic parameters of cup-plant could explain high in vitro true digestibility of cup-plant at the several NDF levels. Cup-plant and alfalfa were both collected in Arlington and Lancaster, Wisconsin to meet the NDF content within 40 to 50% range. The collected samples were incubated with rumen juice to investigate the digestion kinetics at 3, 6, 9, 14, 20, 28, 36, 48, and 72 h. Kinetics was estimated by the model $R=D_0\;e-k(t-L)+U$ where R is residue remaining at time t, and $D_0$ is digestible fraction, k is digestion rate constant, L is discrete lag time, and U is indigestible fraction. Parameters of the model were estimated by the direct nonlinear least squares (DNLS) method. Digestion rate and potential extent of digestion were not statistically different in either forage. However, alfalfa had shorter lag time (p<0.05). The indigestible fraction increased with maturation in alfalfa and in cup-plant (p<0.05). The ratio of indigestible fraction to acid detergent lignin (ADL) was higher in cup-plant than in alfalfa (p<0.05). From the results, alfalfa is probably digested more rapidly than cup-plant, however, cup-plant maintains higher digestibility with maturation due to a relatively slower increase of indigestible fraction in NDF.

• International Journal of Concrete Structures and Materials
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• 제8권3호
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• pp.213-228
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• 2014

Alkali-activated binder (AAB) is recently being considered as a sustainable alternative to portland cement (PC) due to its low carbon dioxide emission and diversion of industrial wastes and by-products such as fly ash and slag from landfills. In order to comprehend the behavior of AAB, detailed knowledge on relations between microstructure and mechanical properties are important. To address the issue, a new approach to characterize hardened pastes of AAB containing fly ash as well as those containing fly ash and slag was adopted using scanning electron microscopy (SEM) and energy dispersive X-ray spectra microanalyses. The volume stoichiometries of the alkali activation reactions were used to estimate the quantities of the sodium aluminosilicate (N-A-S-H) and calcium silicate hydrate (CSH) produced by these reactions. The 3D plots of Si/Al, Na/Al and Ca/Si atom ratios given by the microanalyses were compared with the estimated quantities of CSH(S) to successfully determine the unique chemical compositions of the N-A-S-H and CSH(S) for ten different AAB at three different curing temperatures using a constrained nonlinear least squares optimization formulation by general algebraic modeling system. The results show that the theoretical and experimental quantities of N-A-S-H and CSH(S) were in close agreement with each other. The $R^2$ values were 0.99 for both alkali-activated fly ash and alkali-activated slag binders.

• 전산구조공학
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• 제7권2호
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• pp.89-99
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• 1994

본 연구는 국도및 고속도로상에 설치되어 있는 철제 오성방호책인 가아드레일의 동력학적 거동분석을 4개의 설계변수, 즉 보와 지주의 단면형상 충돌시의 차량속도, 충돌각도 및 차량중량에 따라 BARRIER VII프로그램을 사용하여 수행하였다. 컴퓨터 모의해석 프로그램인 BARRIER VII은 비교적 정교한 것으로 실제의 실물충돌시험 결과와 근접한 결과를 보여줄 뿐 아니라 경제적인 이유로 차량과 방호책의 상호작용을 해석하는데 실물충동시험 대신에 많이 사용된다. 본 연구의 주된 관심은 구조적 적합성, 탑승자 위험도와 차량의 궤적이라 할 수 있다. 이 목적을 위해 최대처짐 및 최대충격력이 계신되어 안전노변대 설계와 충격완화 효과를 분석하는데 사용된다. 본 연구의 결과로부터 도로상의 대형참사를 예방하기 위해서는 가아드레일의 설계기순을 보다 강화할 필요가 있다고 판단된다.

• Journal of the Korean Data and Information Science Society
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• 제21권2호
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• pp.211-218
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• 2010

다구찌는 파라미터 설계에서 설계인자의 최적조건을 구하는데 필요한 수행측도로서 신호대 잡음비를 이용하여 자료 분석을 하였다. 다구찌 품질공학은 품질을 개선하는데 있어서 큰 기여를 하였으나 자료 분석하는데 있어서 망목특성에서의 신호대 잡음비의 사용은 많은 문제점이 지적되었고 여러 학자들에 의하여 대체방안 연구되었다. 제품의 설계단계에서 품질특성과 여러 개의 설계인자와의 관계는 복잡한 비선형 형태를 가지는 경우가 대부분이다. 신경망은 유연한 모형 선택과 학습능력은 알수 없는 복잡한 비선형 형태를 파악하는데 아주 유용한 도구이다. 본 논문은 파라미터 설계에서 설계인자의 최적조건을 찾는데 있어서 문제가 되는 신호대 잡음비을 사용하지 않고 신경망을 이용한 최적화 방안을 제안하고자 한다. 아울러 예제를 들어 기존의 다구찌 방법과 새로이 제안한 대체방안을 비교하고자 한다.