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인지 라디오 네트워크에서 우선 사용자 출현 확률을 고려한 하향링크 스케줄링 알고리즘
허대철(Daecheol Heo),김정종(Jungjong Kim),이정원(Jungwon Lee),황준호(Junho Hwang),이원철(Woncheol Lee),신요안(Yoan Shin),유명식(Myungsik Yoo) 한국통신학회 2009 韓國通信學會論文誌 Vol.34 No.2b
인지 라디오 (Cognitive Radio: CR)란 할당된 주파수 대역 중에 우선 사용자가 사용하지 않는 유휴 주파수를 사용하여 주파수의 효율을 극대화 시킬 수 있는 기술이다. 그러나 CR 환경에서는 우선 사용자에 대한 간섭이 없는 상태에서만 자원을 공유하는 매우 엄격한 제한을 가지고 있다. 더욱이 유휴 주파수 자원은 시간, 주파수 별로 변화하기 때문에 이를 효율적으로 사용하기 위한 스케줄링 알고리즘이 필수적이다. 그러나 기존의 우선 사용자들만 존재하는 무선 통신 환경에서 적용되던 스케줄링 알고리즘은 CR 환경에 대한 제약 조건이 반영되지 않아 유휴 주파수 자원 사용의 효율성 문제가 발생한다. 이에 본 논문에서는 무선 채널 상태와 우선 사용자 출현 확률을 고려하는 하향링크 스케줄링 알고리즘을 제안한다. 제안 스케줄링 알고리즘의 성능 평가를 위해 모의실험을 수행하였으며, 그 결과 제안 알고리즘이 우선 사용자 출현 확률을 고려하지 않는 하향링크 스케줄링 알고리즘에 비해 우수한 성능이 제공됨을 확인하였다. Cognitive radio (CR) technology is to maximize the spectrum utilization by allocating the unused spectrums to the unlicensed users. In CR environment, it is strictly required for the unlicensed users not to interference with the licensed users. Thus, it is essential to rely on the scheduling algorithm to avoid the interference when utilizing spectrum holes that are changing in time and frequency. However, the existing scheduling algorithms that are applied for the wireless communication environment considering the licensed users only is not appropriate for CR environment. In this paper, we propose downlink scheduling algorithm based on probability of incumbent user presence for cognitive radio networks. With computer simulations, it is shown that the proposed scheduling algorithm outperforms the conventional scheduling algorithm.
Haridas, Anupriya K.,Heo, Jungwon,Liu, Ying,Ahn, Hyo-Jun,Zhao, Xiaohui,Deng, Zhao,Agostini, Marco,Matic, Aleksandar,Cho, Kwon-Koo,Ahn, Jou-Hyeon American Chemical Society 2019 ACS APPLIED MATERIALS & INTERFACES Vol.11 No.33
<P>In order to satisfy the escalating energy demands, it is inevitable to improve the energy density of current Li-ion batteries. As the development of high-capacity cathode materials is of paramount significance compared to anode materials, here we have designed for the first time a unique synergistic hybrid cathode material with enhanced specific capacity, incorporating cost-effective iron sulfide (FeS) nanoparticles in a sulfurized polyacrylonitrile (SPAN) nanofiber matrix through a rational in situ synthesis strategy. Previous reports on FeS cathodes are scarce and consist of an amorphous carbon matrix to accommodate the volume changes encountered during the cycling process. However, this inactive buffering matrix eventually increases the weight of the cell, reducing the overall energy density. By the rational design of this hybrid composite cathode, we ensure that the presence of covalently bonded sulfur in SPAN guarantees high sulfur utilization, while effectively buffering the volume changes in FeS. Meanwhile, FeS can compensate for the conductivity issues in the SPAN, thereby realizing a synergistically driven dual-active cathode material improving the overall energy density of the composite. Simultaneous in situ generation of FeS nanoparticles within the SPAN fiber matrix was carried out via electrospinning followed by a one-step heating procedure. The developed hybrid cathode material displays enhanced lithium-ion storage, retaining 688.6 mA h g<SUB>(FeS@SPAN composite)</SUB><SUP>-1</SUP> at the end of 500 cycles at 1 A g<SUP>-1</SUP> even within a narrow voltage range of 1-3.0 V. A high discharge energy density > 900 W h kg<SUB>(FeS@SPAN composite)</SUB><SUP>-1</SUP>, much higher than the theoretical energy density of the commercial LiCoO<SUB>2</SUB> cathode, was also achieved, revealing the promising prospects of this hybrid cathode material for high energy density applications.</P> [FIG OMISSION]</BR>
Park, Cheolwoo,Park, Jeesu,Park, Jaehoon,Heo, Iljeong,Kim, Wooyul,Kim, Jungwon Elsevier 2019 CATALYSIS TODAY - Vol.335 No.-
<P><B>Abstract</B></P> <P>Most Ru(II) complex-sensitized TiO<SUB>2</SUB> systems for hydrogen (H<SUB>2</SUB>) production suffer from instability of the photosensitized system because the anchoring groups of Ru(II) dyes, which are required for their adsorption on TiO<SUB>2</SUB>, are intrinsically vulnerable to chemical and photochemical cleavage. In this study, a new method that enables the use of a Ru(II) dye without any anchoring groups (Ru(bpy)<SUB>3</SUB> <SUP>2+</SUP>) was developed and investigated. The stable photocatalytic efficiency in repeated H<SUB>2</SUB> production cycles under visible-light irradiation indicates that the Ru(II) dye without anchoring groups is highly stable during dye-sensitized H<SUB>2</SUB> production. The dye-sensitized H<SUB>2</SUB> production in the Ru(bpy)<SUB>3</SUB> <SUP>2+</SUP>-sensitized TiO<SUB>2</SUB> system comprising Ru(bpy)<SUB>3</SUB> <SUP>2+</SUP> as a photosensitizer, platinized TiO<SUB>2</SUB> (Pt-TiO<SUB>2</SUB>) as a cocatalyst-electron mediator, and ethylenediaminetetraacetic acid as an electron donor was negligible. However, the addition of phosphate (PO<SUB>4</SUB> <SUP>3–</SUP>) to the Ru(bpy)<SUB>3</SUB> <SUP>2+</SUP>-sensitized TiO<SUB>2</SUB> system enabled the production of H<SUB>2</SUB> via dye sensitization in the absence of any anchoring groups on the dye. The adsorption of PO<SUB>4</SUB> <SUP>3–</SUP> changed the surface charge of Pt-TiO<SUB>2</SUB> from positive to negative under acidic conditions, thereby inducing adsorption of cationic Ru(bpy)<SUB>3</SUB> <SUP>2+</SUP> on the surface of Pt-TiO<SUB>2</SUB> and facilitating electron transfer from excited Ru(bpy)<SUB>3</SUB> <SUP>2+</SUP> to the conduction band of TiO<SUB>2</SUB>. The PO<SUB>4</SUB> <SUP>3–</SUP> adsorption-induced change in the surface charge and the subsequent adsorption of Ru(bpy)<SUB>3</SUB> <SUP>2+</SUP> on the surface of PO<SUB>4</SUB> <SUP>3–</SUP>-adsorbed Pt-TiO<SUB>2</SUB> were confirmed by zeta potential measurements and Fourier transform infrared spectroscopy, respectively. In contrast with H<SUB>2</SUB> production, the presence of PO<SUB>4</SUB> <SUP>3–</SUP> had little effect on the kinetics of anionic chromate (CrO<SUB>4</SUB> <SUP>2–</SUP>) reduction in the Ru(bpy)<SUB>3</SUB> <SUP>2+</SUP>-sensitized TiO<SUB>2</SUB> system. This result indicates that electron transfer from Pt to the electron acceptor on PO<SUB>4</SUB> <SUP>3–</SUP>-adsorbed Pt-TiO<SUB>2</SUB> is highly dependent on the charge character of the electron acceptor (i.e., electron transfer to the cationic electron acceptor is more favored). The negative charge on the surface of Pt-TiO<SUB>2</SUB> induced by the adsorption of PO<SUB>4</SUB> <SUP>3–</SUP> attracts the positively charged protons to the surface, which kinetically enhanced electron transfer from Pt to the protons. The (photo)electrochemical data demonstrate that PO<SUB>4</SUB> <SUP>3–</SUP> adsorbed on Pt-TiO<SUB>2</SUB> facilitates the interfacial electron transfer processes by enhancing the adsorption of Ru(bpy)<SUB>3</SUB> <SUP>2+</SUP> and attracting protons to the surface. The positive effect of PO<SUB>4</SUB> <SUP>3–</SUP> on H<SUB>2</SUB> production increased with increasing PO<SUB>4</SUB> <SUP>3–</SUP> concentration and decreasing pH, where the conditions are more favorable for PO<SUB>4</SUB> <SUP>3–</SUP> and proton adsorption on the surface of Pt-TiO<SUB>2</SUB>. Among the five anions evaluated in this study (PO<SUB>4</SUB> <SUP>3–</SUP>, AsO<SUB>4</SUB> <SUP>3–</SUP>, F<SUP>–</SUP>, NO<SUB>3</SUB> <SUP>–</SUP>, and SO<SUB>4</SUB> <SUP>2–</SUP>), PO<SUB>4</SUB> <SUP>3–</SUP> was most efficient and facilitated stable H<SUB>2</SUB> production.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Adsorption of PO<SUB>4</SUB> <SUP>3–</SUP> changes the surface charge of TiO<SUB>2</SUB> from positive to negative. </LI> <LI> PO<SUB>4</SUB> <SUP>3
정재윤(Jae Yoon Jeong),이동준(Dong Jun Lee),허정원(Jungwon Heo),임두현(Du-Hyun Lim),서양곤(Yang-Gon Seo),안주현(Jou-Hyeon Ahn),최창호(Chang-Ho Choi) 한국청정기술학회 2020 청정기술 Vol.26 No.2
기존의 석유계부산물 기반 음극재의 대체물질을 개발하고자, 친환경적이며 가격이 저렴한 대나무 기반 1차 탄화숯을 저온 흑연화 공정을 통해 흑연으로 전환 후 음극재로 활용하였다. 저온 흑연화 공정을 위해 탄화철을 촉매로 사용하였으며, 첨가된 탄화철의 양에 따라 흑연화 정도를 X선 회절기(x-ray diffraction, XRD), 라만 분광기(raman spectroscopy), TEM (transmission electron microscopy)을 사용하여 분석 한 후 탄화철의 최적 양을 결정하였다. 가스흡착법 (brunauer-emmett-teller, BET)를 사용하여 흑연화 숯의 기공특성도 분석하였다. 분석 결과 촉매 표면을 중심으로 비정질의 탄소가 흑연으로 전환되었으며, 흑연화 공정 후 촉매를 제거하기 위해 산 처리를 하는 동안 기존의 1차 탄화숯보다 크기가 큰 기공이 형성되어 상대적으로 표면적이 줄어들었다. 최적 양의 촉매를 사용하여 제조된 흑연화 숯을 음극재로 활용하여 전지성능을 분석한 결과 1차 탄화숯과 비교하여 방전용량과 충방전 효율이 증가하였다. 이는 흑연화 공정으로 비정질의 탄소가 흑연으로 전환되었기 때문으로 추정되며, 전지성능을 더욱 향상시키기 위해서는 탄화철 촉매의 크기를 최대한 작게 조절하고, 흑연화 숯의 입자크기를 균일화 하는 연구가 필요할 것으로 사료된다. Biomass bamboo charcoal is utilized as anode for lithium-ion battery in an effort to find an alternative to conventional resources such as cokes and petroleum pitches. The amorphous phase of the bamboo charcoal is partially converted to graphite through a low temperature graphitization process with iron oxide nanoparticle catalyst impregnated into the bamboo charcoal. An optimum catalysis amount for the graphitization is determined based on the characterization results of TEM, Raman spectroscopy, and XRD. It is found that the graphitization occurs surrounding the surface of the catalysis, and large pores are formed after the removal of the catalysis. The formation of the large pores increases the pore volume and, as a result, reduces the surface area of the graphitized bamboo charcoal. The partial graphitization of the pristine bamboo charcoal improves the discharge capacity and coulombic efficiency compared to the pristine counterpart. However, the discharge capacity of the graphitized charcoal at elevated current density is decreased due to the reduced surface area. These results indicate that the size of the catalysis formed in in-situ graphitization is a critical parameter to determine the battery performance and thus should be tuned as small as one of the pristine charcoal to retain the surface area and eventually improve the discharge capacity at high current density.