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안광준 한국물리학회 2017 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.71 No.10
We theoretically investigate resonance fluorescence of a ladder- and a triangular-type three-level atomic system in the full quantization regime. By solving Heisenberg’s quantum kinetic equations of motion of an electron interacting with photons and two coherent laser fields, we obtain the firstorder electric field correlation function, which corresponds to photoluminescence spectrum. When the single electrons in both systems are resonantly excited by two strong cw-laser fields, in contrast to the ladder-type atomic systems emitting mainly incoherent photons, the triangular-type system shows that continuous coherent photons can be selectively generated from three optical transitions by trapping electronic population inversions and manipulated by changing the transition rates.
Graphene Plasmon Modes on Slab Waveguides at Telecom Wavelengths
안광준 한국물리학회 2015 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.67 No.12
In this study, the transversal magnetic (TM) and electric (TE) modes of graphene plasmon in a homogeneous environment and three-layered systems were theoretically investigated. The dispersion relations of the graphene plasmon modes were derived in the framework of classical electrodynamics with plane wave modes and Neumann-Dirichlet boundary conditions. The graphene plasmon modes in the three-layer system reproduced exactly the same dispersion relations as freestanding graphene (Phys. Rev. Lett. 99, 016803 (2007)), as all layers had the same refractive index. The impulse matching condition between the graphene plasmon and guided photons and the propagation decay length of graphene plasmon were investigated by numerically solving the dispersion relations for different values of the Fermi-energy and the refractive index of the upper layer. The TE-mode graphene plasmon has potential for applications of graphene as a polarization-selective modulator due to its convenient impulse matching with guided photons in the region of telecom wavelengths, despite its low propagation decay rates.
Enhanced Photon Absorption of Organic Solar Cells by Three-dimensional Metallic Structures
안광준 한국물리학회 2015 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.67 No.12
The photon absorption enhancement of thin organic solar cells with periodic three-dimensional (3D) metal structures in a photoactive medium is theoretically investigated in this study. The suggested metal structures have a match form, a gold sphere on a thin cylindrical post. With a finite difference time method tool, the optimized sizes and positions of the metal structure are obtained in the scattered radiation pattern of the incident light, and the photon absorption spectra are calculated and analyzed. The organic solar cell equipped with the 3D metal structures shows approximately a 10% enhanced photon absorption compared to the value obtained by same solar cells without the 3D metal structures. The reason for the enhanced absorption can be understood based on the electric field distributions and is attributed to the fact that the 3D metal structure can lead to improved absorption at long wavelengths region where almost negligible absorption occurs in the same solar cells without the metal structures.
안광준,윤우진,송재용 한국인사조직학회 2009 한국인사ㆍ조직학회 발표논문집 Vol.2009 No.2
본 연구는 네트워크 이론을 기반으로 인수합병 전 피인수기업의 네트워크 포지션이인수합병 후 인수기업의 혁신창출에 미치는 영향력을 관찰하였다. 보다 구체적으로네트워크 이론의 관점에서 도출한 변수들인 피인수 기업의 기술적 지위와 중개위치 수준이인수합병 후 인수기업의 혁신창출의 정도에 미치는 영향을 파악해 보고자 하였다. 한편이러한 피인수기업의 인수합병 전 네트워크 포지션의 효과가 인수기업의 기술적경로의존성의 정도에 따라 변화하는지 역시 살펴보고자 하였다. 이를 위해 본 연구에서는대표적인 지식집약적 산업 중의 하나인 화학/제약 (chemical/pharmaceutical) 산업에서지난 1994년부터 1998년까지 행해진 인수합병 사례를 표본으로 하여 실증분석을수행하였다. 실증분석에서는 인수합병 후 인수기업에서 출원한 특허 건수를 사용하여인수기업의 혁신 창출 정도를 측정하고 이를 음이항 회귀분석 (negative binomialregression)의 종속변수로 삼아 분석하였다. 분석 결과 피인수기업의 기술적 지위와중개위치 수준은 인수합병 후 인수기업의 혁신 창출에 긍정적 영향을 미치는 것으로나타났으며, 피인수기업의 기술적 지위의 긍정적 효과는 인수기업의 기술적 경로의존성이강할 경우 약화되는 것으로 밝혀졌다. The purpose of this paper is to examine the impact of status and brokerage of the acquired firm on the subsequent innovation performance of the acquiring firm in technological acquisitions. We draw upon the network theory to develop a theoretical model and a network-based mapping of the technological positions of the acquired firms in an industry. Specifically, we focus on two dimensions of the acquired firm: status and brokerage. This study further examines how path-dependency of the acquiring firm moderates the positive effect of status and brokerage of the acquired firm on the subsequent innovation performance of the former. To empirically examine hypotheses, we indentify 135 sample firms whose acquisition announcements were completed in chemical/ pharmaceutical industry of high-tech industries during 1994-1998, using the SDC (Securities Data Corporation) database. Following Podolny and Stuart (1995), we configure the patent data in a binary, patent-to-patent citation matrix to compute measures of technological positioning. The results of the study generally support our theoretical predictions. Status and brokerage of the acquired firm have positive and significant effects on subsequent innovation output of the acquiring firm. Path-dependency of the acquiring firm has a negatively moderating effect between status and innovation output.
성근 바인 코풀라 모형을 이용한 고차원 금융 자료의 VaR 추정
안광준,백창룡 한국통계학회 2021 응용통계연구 Vol.34 No.6
Value at Risk (VaR) is the most popular measure for market risk. In this paper, we consider the VaR estimation of portfolio consisting of a variety of assets based on multivariate copula model known as vine copula. In particular, sparse vine copula which penalizes too many parameters is considered. We show in the simulation study that sparsity indeed improves out-of-sample forecasting of VaR. Empirical analysis on 60 KOSPI stocks during the last 5 years also demonstrates that sparse vine copula outperforms regular copula model. 최대예상손실액(VaR)은 위험관리수단으로 금융에서 시장위험을 측정하는 대표적인 값이다. 본 논문에서는 다양한 자산으로 이루어진 고차원 금융자료에서 자산들 간의 의존성 구조를 잘 설명할 수 있는 성근 바인 코풀라를 이용한 VaR 추정에 대해서 논의한다. 성근 바인 코풀라는 정규 바인 코풀라 모형에 벌점화를 적용한 방법으로 추정하는 모수의 개수를 벌점화를 통해 축소하는 방법이다. 모의 실험 결과 성근 바인 코풀라를 이용한 VaR 추정이 더 작은 표본 외 예측오차를 줌을 살펴볼수 있었다. 또한 최근 5년간의 코스피 60개 종목을 바탕으로 실시한 실증 자료 분석에서도 성근 바인 코풀라 모형이 더 좋은 예측 성능을 보임을 확인할 수 있었다.