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Ultrafast Graphene Light Emitters
Kim, Young Duck,Gao, Yuanda,Shiue, Ren-Jye,Wang, Lei,Aslan, Ozgur Burak,Bae, Myung-Ho,Kim, Hyungsik,Seo, Dongjea,Choi, Heon-Jin,Kim, Suk Hyun,Nemilentsau, Andrei,Low, Tony,Tan, Cheng,Efetov, Dmitri K. American Chemical Society 2018 Nano letters Vol.18 No.2
<P>Ultrafast electrically driven nanoscale light sources are critical components in nanophotonics. Compound semiconductor-based light sources for the nanophotonic platforms have been extensively investigated over the past decades. However, monolithic ultrafast light sources with a small footprint remain a challenge. Here, we demonstrate electrically driven ultrafast graphene light emitters that achieve light pulse generation with up to 10 GHz bandwidth across a broad spectral range from the visible to the near-infrared. The fast response results from ultrafast charge-carrier dynamics in graphene and weak electron-acoustic phonon-mediated coupling between the electronic and, lattice degrees of freedom. We also find that encapsulating graphene with hexagonal boron nitride (hBN) layers strongly modifies the emission spectrum by changing the local optical density of states, thus providing up to 460% enhancement compared to the gray-body thermal radiation for a broad peak centered at 720 run. Furthermore, the hBN encapsulation layers permit stable and bright visible thermal radiation with electronic temperatures up to 2000 K under ambient conditions as well as efficient ultrafast electronic cooling via near-field coupling to hybrid polaritonic modes under electrical excitation. These high-speed graphene light emitters provide a promising path for on-chip light sources for optical communications and other optoelectronic applications.</P>
김형식(Hyungsik Kim),박진모(Jinmo Park),한자령(Jaryoung Han),이영철(Youngchul Lee) 한국가스학회 2018 한국가스학회지 Vol.22 No.2
메탄을 주성분으로 하는 일반적인 합성천연가스의 열량은 9,300 kcal/㎥ 이하이며, 이러한 합성천연가스를 국내에서 도시가스로 사용하기 위해서는 10,200 kcal/㎥로의 증열이 필요하다. 일반적으로, 합성천연가스의 열량조절에는 프로판가스를 상용하나, 가격의 변동폭이 크고 대체로 합성천연가스의 제조원가보다 비싸왔다. 그러므로 프로판을 통한 증열 대신 고열량의 합성천연가스를 직접 생산할 수 있다면, 합성천연가스의 생산가격을 상당히 감소시킬 수 있다. 본 논문에서는 미국 NETL 분석 자료를 기반으로, 메탄이 주성분인 합성천연가스의 제조 및 증열과 고열량 합성천연가스의 직접 제조 시의 원가를 비교분석하였다. The calorific value of general synthetic natural gas(SNG) mainly composed of methane is 9,300kcal/㎥ or less. In order to use such synthetic natural gas as city gas in Korea, it is necessary to heat up to 10,200 kcal/㎥. Generally, propane gas is commonly used to control the calorific value of SNG. However, the price of propane gas has fluctuated widely and has been higher than the cost of producing SNG. So if the high-calorie SNG can be produced directly instead of the calorie control by propane mixing, the production price of SNG can be significantly reduced. In this paper, based on the US NETL analysis, we compare the cost of methane based SNG production and the cost of high-calorie SNG direct production.
Mobile Widget based Advertisement System using Push Message Control
YoungSuk Kim,DongGi Yang,HyungSik Kim,ByoungCheol Choi 대한전자공학회 2008 ICEIC:International Conference on Electronics, Inf Vol.1 No.1
In this paper, we present mobile widget based advertisement system(MWAS) using push message control algorithm. Data push technology is an effective advertising scheme to synchronize or deliver information in serverdriven manner. For efficient delivery of push message, we propose push message control algorithm considering QoS class and the effectiveness of advertisement content to be delivered. We model advertising effectiveness of content with the most proper time and range of effectiveness. MWAS select and control push message using the proposed control algorithm. To protect user from the undesired advertising information, we also present mobile widget application to enable user to select the pushed advertising information. In experiment, we show simulation results of push control algorithm applying 4 different advertisement contents with 3 QoS classes and implemented widget application containing choice functionality for advertisement content.
An Enhanced QAM-FBMC Scheme With Interference Mitigation
Han, Hyungsik,Kim, Heesu,Kim, Namshik,Park, Hyuncheol IEEE 2016 IEEE communications letters Vol.20 No.11
<P>Cyclic prefixed orthogonal frequency division multiplexing (CP-OFDM) has been used as a waveform for mobile communications, but CP-OFDM has weaknesses in an asynchronous heterogeneous network scenario. To overcome the disadvantage of CP-OFDM, a quadrature amplitude modulation (QAM)-filter-bank-based multi-carrier (FBMC) system is proposed to achieve superior spectrum confinement and better spectral efficiency. However, QAM-FBMC has inevitable performance degradation because of interferences from non-orthogonal filters. In this letter, we propose a decision feedback equalization (DFE)-based interference mitigation scheme for the QAM-FBMC system to cancel a residual interference. The interference from the filters of QAM-FBMC influences to other subcarriers and symbols, and it is modeled as an end-to-end system transfer function with para-Hermitian polynomial matrix form, equivalently. By spectral factorization of the system transfer function, the system response is transformed into causal, and the receiver detects the symbols successively. This letter describes the spectral factorization method and formulates the feed-forward and feedback filter of the DFE structure with the spectral factor of transfer function. Simulation results show the superiority of the proposed scheme to the conventional QAM-FBMC receiver scheme.</P>