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Choi, Heechae,Khan, Sovann,Choi, Junghyun,Dinh, Duong T.T.,Lee, Seung Yong,Paik, Ungyu,Cho, So-Hye,Kim, Seungchul Elsevier 2017 Applied Catalysis B Vol.210 No.-
<P><B>Abstract</B></P> <P>Impurity doping and synthesizing polymorphic particles are the common strategies to improve activity of TiO<SUB>2</SUB> photocatalyst by lowering the band gap and enhancing electron-hole separation rate. However, these two approaches have side effects. Doping of impurities make space charge region (SCR) thinner near the surface, which requires smaller sized particles than undoped TiO<SUB>2</SUB> for the optimal performance. Polymorphic TiO<SUB>2</SUB> particles, in which rutile and anatase phases coexist in a particle, are usually large due to energetic unstability of the rutile phase in a fine particle. For this contradiction that one needs small size while the other needs large size, two effects are not easy to be combined. In this study, we suggest a <I>dual-doping</I> strategy to solve the contradictory problem of SCR reduction by donor doping and inevitable size growth in polymorphic particles. We successfully dope W, a band gap narrower, into fine size of polymorphic particles by Sn-codoping, a promoter of the anatase-to-rutile transformation (ART), and demonstrate greatly improved photocatalytic activity. The accelerated ART by Sn-doping could keep the size of polymorph junctioned TiO<SUB>2</SUB> small (∼10nm) as lower temperature annealing become able to induce the ART. The concept of dual doping with a band gap narrower and an ART promoter provides a way to synthesize highly active photocatalysts by overcoming the drawback from shortened SCR length.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Band gap narrowing by W-doping into TiO<SUB>2</SUB>. </LI> <LI> Electron-hole separation at rutile-anatase boundary of Sn-doped TiO<SUB>2</SUB>. </LI> <LI> Separately controllable band gap and phase boundary in TiO<SUB>2</SUB> nano-particles by co-doping. </LI> <LI> W-doping in ∼10nm polymorphic TiO<SUB>2</SUB> nano-particles at lowered temperature. </LI> <LI> Simultaneously enhanced photo-absorption rate and electron-hole separation rate. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
LTCC bandpass filter using 3D coupled helical inductors
Choi, SeungChul,Youm, JungEun,Heo, Keun,Lim, JuHwan,Park, ChulSoon,Hwang, SungWoo Wiley Subscription Services, Inc., A Wiley Company 2007 MICROWAVE AND OPTICAL TECHNOLOGY LETTERS Vol.49 No.5
<P>A new low-temperature co-fired ceramic (LTCC) bandpass filter using three-dimensionally coupled helical inductors is presented. The resonator is a via-connected multilayer helical inductor and the filter uses mixed coupling between face-to-face inductors. The fabricated filter exhibits the center frequency of 5.8 GHz, 3-dB bandwidth of 800 MHz, and the insertion loss of 1.9 dB. The size of the active region is 1.7 × 2.3 × 0.8 mm<SUP>3</SUP>. The measured results are consistent with the three-dimensional electromagnetic simulation and the equivalent circuit modeling. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1146–1147, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI.10.1002/mop.22366</P>
OSI 계층 구조에서 엔티티와 그들간 인터페이스에 관한 모델링
박승철(Seungchul Park),최선완(Sunwan Choi),최양희(Yanghee Choi) 한국정보과학회 1987 한국정보과학회 학술발표논문집 Vol.14 No.2
본 논문은 OSI 참조 모델의 각 계층에서 정의되는 엔티티 상호간 통신 구조를 모델링한 것이다. 한 계층에서 정의된 엔티티 같은 시스템내의 인접한 상 · 하위 계층에서 정의되는 엔티티와 통신하게 되며, 일정한 프로토콜에 맞게 다른 시스템의 같은 계층에서 정의된 엔티티(peer entity)와 통신한다. 여기서는 이 두 종류의 통신이 어떤 구조를 통해서 어떻게 이루어지는가를 구체적으로 보여주는 모델을 제시하고 있다.