• 대한전자공학회논문지
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• 제24권1호
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• pp.133-139
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• 1987

A phase-locked Channel-Substrate-Planar(CSP) laser arrays is described. Arrays of emitters with weak coupling are operated in a set of discrete modes determined by the number and spacing of the emitters. The interactions between emitters lead to a splitting of the wave-length and gain which are calculated from the coupling strength. Phase-locked arrays has exhibited to CW output-power as high as 80 m W and the highest order mode will have preferred oscillation. A strong hole burning is occurred at p=30m W. The most stable lasing mode is occurred at element spacing S=3.5\ulcornerm and there is no coupling at S>7 \ulcornerm.

• 한국광학회:학술대회논문집
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• 한국광학회 2000년도 제11회 정기총회 및 00년 동계학술발표회 논문집
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• pp.124-125
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• 2000

We introduce a scheme with a maximized efficiency of detecting atoms passing through an optical standing-wave mode cavity. Consider a standing-wave optical cavity illuminated by a weak probe beam through one of its mirrors where the transmission through the other mirror is monitored by a photodetector. If an atom is put in the cavity, the atom-cavity coupling shifts the resonance frequency of the system via the so-called normal mode splitting, and thereby the transmission power will drop. In fact, this type of atom detection scheme has been used in recent single atom trap experiments In practice, however, the field in a standing-wave mode will have a geometrical structure having nodes and antinodes that when the atom traverses the cavity through one of the nodes, there will be no such effect of atom-field interaction. (omitted)

• 대한기계학회논문집A
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• 제32권6호
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• pp.496-503
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• 2008

With the improvement of computer power and technology, fracture modelling by finite element methods has become a topic of extensive studies. However, fracture simulation much limited to an academic study of crack propagation with a fine mesh. Element deletion method is a useful tool for estimating damage due to accidental or extreme loads on structures, provided that an effective and realistic criterion is established for simulating the material failure and subsequent element deletion. In this study, ABAQUS/Explicit is used to simulate the material failure on the basis of experimental results by X. Huang et al. Through numerical experiments, we suggest a formulation to determine the failure strain associated with the size and thickness of removed elements.

• Journal of Magnetics
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• 제16권4호
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• pp.408-412
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• 2011

We investigated theoretically the magnetic field dependence of the quantum optical transition of qusi 2-Dimensional Landau splitting system, in GaN and ZnO. We apply the Quantum Transport theory (QTR) to the system in the confinement of electrons by square well confinement potential. We use the projected Liouville equation method with Equilibrium Average Projection Scheme (EAPS). Through the analysis of this work, we found the increasing properties of the optical Quantum Transition Line Shapes(QTLSs) which show the absorption power and the Quantum Transition Line Widths(QTLWs) with the magnetic-field in GaN and ZnO. We also found that QTLW, ${\gamma}(B)_{total}$ of GaN < ${\gamma}(B)_{total}$ of ZnO in the magnetic field region B < 25 Tesla.

• ETRI Journal
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• 제40권1호
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• pp.61-71
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• 2018

In this study, we developed hybrid control algorithms in smart base stations (SBSs) along with devised communication, caching, and computing techniques. In the proposed scheme, SBSs are equipped with computing power and data storage to collectively offload the computation from mobile user equipment and to cache the data from clouds. To combine in a refined manner the communication, caching, and computing algorithms, game theory is adopted to characterize competitive and cooperative interactions. The main contribution of our proposed scheme is to illuminate the ultimate synergy behind a fully integrated approach, while providing excellent adaptability and flexibility to satisfy the different performance requirements. Simulation results demonstrate that the proposed approach can outperform existing schemes by approximately 5% to 15% in terms of bandwidth utilization, access delay, and system throughput.

• Applied Science and Convergence Technology
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• 제27권5호
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• pp.105-108
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• 2018

Transparent $TiO_2$ nanotube arrays are successfully prepared by a two-step approach involving electrochemical anodization and RF magnetron sputtering. First, a Ti film is deposited on an FTO substrate by RF magnetron sputtering at room temperature. The morphologies of the Ti film are controlled by the working distance, Ar flow, and DC power. Second, an anodization treatment is electrochemically performed for the formation of nanotube arrays from the deposited Ti film, followed by post-annealing treatment in air for the formation of $TiO_2$ crystallization. The back side of the crystallized $TiO_2$ nanotube arrays is illuminated with solar light to characterize the photoelectrochemical reaction, and their photoelectrochemical properties are investigated. This work provides information on application of a thin film deposited by RF sputtering in the field of photoelectrochemical water splitting.

• 정보보호학회논문지
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• 제26권2호
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• pp.335-344
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• 2016

부채널 분석 중 전력 분석 공격은 가장 실용적이며 강력한 기법으로 알려져 있다. 전력 분석 공격 중 단일 파형공격은 단 하나의 파형을 이용하여 공개키 암호 시스템의 비밀정보를 복원하는 강력한 분석기법으로 최근에 활발히 연구되고 있다. 가장 최근에 Sim 등은 이러한 공격에 높은 안전성을 갖는 새로운 지수승 알고리즘을 소개하였다. 본 논문에서 Sim 등이 제안한 단일 파형 공격에 높은 공격 복잡도를 갖는 알고리즘의 취약점을 분석한다. 메시지 블라인딩과 지수 분할 기법에 윈도우 기법을 적용해 높은 공격 복잡도를 갖는 알고리즘을 제안하였지만 사전 연산과정에서 발생하는 정보를 이용하여 비밀정보를 복원할 수 있음을 확인하였다. 또한 취약점을 보완하여 단일파형 공격에 높은 공격 복잡도를 갖는 지수승 알고리즘을 새롭게 제안하였다. 설계된 알고리즘은 사전 연산 과정에서 실제지수 연산에 사용되는 값들의 재사용을 최소화 하여 충돌 공격에 대해 높은 안전성를 보장한다.

• Journal of Communications and Networks
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• 제13권6호
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• pp.664-677
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• 2011

In order to control interference and improve spectrum efficiency in the femtocell and macrocell overlaid system (FMOS), we propose a joint frequency bandwidth dynamic division, clustering and power control algorithm (JFCPA) for orthogonal-frequency-division-multiple access-based downlink FMOS. The overall system bandwidth is divided into three bands, and the macro-cellular coverage is divided into two areas according to the intensity of the interference from the macro base station to the femtocells, which are dynamically determined by using the JFCPA. A cluster is taken as the unit for frequency reuse among femtocells. We map the problem of clustering to the MAX k-CUT problem with the aim of eliminating the inter-femtocell collision interference, which is solved by a graph-based heuristic algorithm. Frequency bandwidth sharing or splitting between the femtocell tier and the macrocell tier is determined by a step-migration-algorithm-based power control. Simulations conducted to demonstrate the effectiveness of our proposed algorithm showed the frequency-reuse probability of the FMOS reuse band above 97.6% and at least 70% of the frequency bandwidth available for the macrocell tier, which means that the co-tier and the cross-tier interference were effectively controlled. Thus, high spectrum efficiency was achieved. The simulation results also clarified that the planning of frequency resource allocation in FMOS should take into account both the spatial density of femtocells and the interference suffered by them. Statistical results from our simulations also provide guidelines for actual FMOS planning.

• 한국인터넷방송통신학회논문지
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• 제19권5호
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• pp.55-62
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• 2019

본 논문에서는 K 사용자 MIMO 간섭 채널을 고려하였으며, 정보와 전력을 동시에 전송하는 SWIPT 시스템을 위한 송수신기 설계 방법에 대해서 다룬다. 그리고, 정보 수신 장치와 전력 수확 장치가 같은 수신기에 존재하는 SWIPT 시스템을 고려한다. 제안하는 방식에서는 신호대 누수 잡음비 (SLNR)를 비용 함수로 사용하고, 수확 전력에 대한 임계값을 만족하도록 송수신기를 설계한다. 즉, 수확 전력에 대한 제약 조건 하에서, SLNR을 최대화시키도록 송신단 프리코딩 벡터, 수신단 검파기 벡터, 전력 분배 상수를 동시에 설계한다. 컴퓨터 모의실험을 통하여, 제안하는 기법과 기존 기법의 신호 대 간섭 잡음비 (SINR) 성능을 비교하였다. 사용자 수, 송신 안테나 개수, 수신 안테나 개수 간의 특별한 제약 조건을 만족하는 경우, 제안하는 기법은 낮은 SNR에서 기존 기법보다 우수한 SINR 성능을 나타낸다는 것을 보였다. 또한, 특별한 제약 조건을 만족하지 못하는 경우에는, 제안 기법이 모든 SNR 범위에 대해서 기존 기법보다 더 우수한 성능을 나타낸다는 것을 보였다.

• 한국항행학회논문지
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• 제23권4호
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• pp.309-315
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• 2019

본 논문은 1:3과 1:4 분배 비율을 갖는 비대칭 분배기를 CPW와 offset 결합 전송선로를 이용하여 다단 구조로 구현한 것이다. 이 분배기는 다단 구조의 전송선로와 캐패시터와 저항이 병렬로 연결된 회로로 구성되어 있다. 다단 전송선로는 임의의 임피던스로 종단된 ${\lambda}/4$ 단일 전송선로를 분해하여 그것을 $90^{\circ}$ 전기적 길이보다 짧은 다단 전송선로로 정합시키는 방법으로 구현하였고, RC 병렬회로는 출력 포트의 반사계수와 출력 포트 사이의 고립 특성을 얻기 위해서 전송선로 사이에 연결하였다. 이러한 방법으로 2 GHz에서 설계된 전력분배기는 각 단의 전송선로는 ${\lambda}/4$보다 짧게 구현되어 기존 것 보다 최소 27% 작게 구현하였고, 광 대역 특성을 얻을 수 있음을 확인하였다.