Radiation from a Slotted Rectangular Waveguide Filled with Asymmetrically Biased Ferrite Slabs

Hwang, Keum Cheol,Eom, Hyo J. Taylor Francis 2009 ELECTROMAGNETICS Vol.29 No.6

<P> Radiation from a slotted rectangular waveguide filled with asymmetrically biased ferrites is investigated in this study. A theoretical model of slotted parallel plates is used for analysis. A boundary value problem is rigorously solved with the Fourier transform and mode matching method to obtain simultaneous equations. The radiation field is represented in a fast convergent series that is efficient for numerical calculation. The radiation behaviors are estimated in terms of ferrite configurations and bias fields. Maximum angular scanning of 90.2° is achieved when the DC magnetic bias field varies from 0 to 2,000 oe.</P>

X-Band 모노펄스 추적 레이더를 위한 광대역 도파관 Magic-T 최적화 설계

황금철(Keum Cheol Hwang) 한국전자파학회 2009 한국전자파학회논문지 Vol.20 No.10

본 논문에서는 광대역 X-Band 추적 레이더의 모노펄스 비교기(comparator)에 적용 가능한 도파관 magic-T 설계 및 최적화 문제에 대해서 고찰하였다. 다층으로 구성된 도체 실린더(cylinder)를 이용하여 기존의 X-Band magic-T에 비해 광대역의 임피던스 정합을 구현하였다. 최적화된 파라미터 도출을 위해 유전 알고리즘과 particle swarm optimization을 결합한 하이브리드 최적화 알고리즘을 설계에 적용하였으며, 최적 설계된 도파관 magic-T는 모든 도파관 포트에 대해, 최소 12 % 이상의 대역폭에서 -20 ㏈ 이하의 반사 특성을 나타내었다. 전력 분배손실은 0.2 ㏈ 이하이며 전력 분배 편차 또한 0.1 ㏈ 이하로 우수한 특성을 보여주었다. 또한 측정된 결과는 시뮬레이션 결과와 잘 일치하는 것을 확인하였다. 마지막으로, 적층 실린더의 차수를 증가시켜 5단 및 7단 적층된 구조에 대한 대역폭 성능도 분석하였다. Design and optimization of a broadband waveguide magic-T was performed for X-Band tracking radars. A multistepped conducting cylinder was used to enhance the bandwidth performance of the conventional waveguide magic-Ts. Particles swarm optimization in conjunction with genetic algorithm was employed to obtain the optimized geometrical parameters. The optimized design exhibits low reflection coefficient below -20 ㏈ at all waveguide ports with frequency bandwidth of 12 %. The transmission loss and difference are within 0.2 ㏈ and 0.1 ㏈, respectively. Measured results are also shown to be in good agreement with the simulated results. Finally, the bandwidth performances for five and seven-stepped conducting cylinders are also investigated.

Hybrid Particle Swarm Optimization 기법을 적용한 X-대역 광대역 편파 변환기 설계

황금철(Keum Cheol Hwang) 한국전자파학회 2009 한국전자파학회논문지 Vol.20 No.4

본 논문에서는 미앤더 스트립라인을 이용한 X-대역 광대역 편파 변환기 설계 및 최적화 문제에 대해서 고찰하였다. 편파 변환기에 입사되는 편파를 수직, 수평 성분으로 분리하고 각 편파별로 등가 전송선 모델(transmission line model)을 사용하여 교차 편파 억제율과 편파 변환율을 계산하였다. 또한, 최적화된 파라미터 도출을 위해 유전 알고리즘과 particle swarm optimization에 기반한 하이브리드 알고리즘의 성능을 평가하고 설계에 적용하였다. 최적화된 편파 변환기는 X-대역(8.45~11.38 ㎓)에서 -25 ㏈ 이하의 편파 억제 성능을 보여주고 있으며, 편파 변환 손실은 0.2 ㏈ 이하로 계산되었다. 또한, 이 결과를 상용 시뮬레이션 수치와 비교 분석하였다. Design and optimization of a broadband meander-line twist reflector was performed for X-band application. Based on the equivalent transmission line model, the polarization twist performance was evaluated. Genetic analysis, particles swarm, and hybrid swarm optimizations were employed to obtain the optimized geometrical parameters. The optimized design exhibits low cross-polarization level below -25 ㏈ between 8.45 and 11.38 ㎓. The polarization twist loss was below 0.2 ㏈. Comparison between computed and simulated results was also discussed.

Self-Energy Recycling for RF Powered Multi-Antenna Relay Channels

Hwang, Duckdong,Hwang, Keum Cheol,Kim, Dong In,Lee, Tae-Jin INSTITUTE OF ELECTRICAL AND ELECTRONICS ENGINEERS 2017 IEEE Transactions on Wireless Communications Vol. No.

<P>We investigate self-energy recycling (S-ER)-based RF powered multi-antenna relay channels (RCs) for the coverage extension in sensor networks or small cells. In the S-ER-based RF powered RC, the power used at the relay station for data transmission depends only on the energy from the access point and the recycled energy from its own transmission. We propose an optimal beamforming scheme with associated protocols and study their behaviors for both cases of downlink only and joint up-down link. Strategies for the power allocation between data transmission and RF powering are provided and a comparison with the conventional RF powered RC is made. For the proposed power allocation strategies, the performance of the conventional RC is achieved by the proposed RF powered RC only when infinite RF power is available. A high value of S-ER helps the proposed systems to reach the performance of conventional relay systems. In the joint up-down link protocol, we show that the up-down rate region can simply be constructed with easy power allocation strategy.</P>

Pretreatment with paricalcitol attenuates inflammation in ischemia–reperfusion injury via the up-regulation of cyclooxygenase-2 and prostaglandin E2

Hwang, Hyeon Seok,Yang, Keum Jin,Park, Ki Cheol,Choi, Hyun Soo,Kim, So Hee,Hong, Sung Youp,Jeon, Byeong Hwa,Chang, Yoon Kyung,Park, Cheol Whee,Kim, Suk Young,Lee, Sang Ju,Yang, Chul Woo Oxford University Press 2013 Nephrology, dialysis, transplantation Vol.28 No.5

<P><B>Background</B></P><P>The effect of paricalcitol on renal ischemia–reperfusion injury (IRI) has not been investigated. We examined whether paricalcitol is effective in preventing inflammation in a mouse model of IRI, and evaluated the cyclooxygenase-2 (COX-2) and prostaglandin E2 (PGE2) pathways as a protective mechanism of paricalcitol.</P><P><B>Methods</B></P><P>Paricalcitol (0.3 μg/kg) was administered to male C57BL/6 mice 24 h before IRI. Bilateral kidneys were subjected to 23 min of ischemia, and mice were killed 72 h after IRI. The effects of paricalcitol on renal IRI were evaluated in terms of renal function, tubular necrosis, apoptotic cell death, inflammatory cell infiltration and inflammatory cytokines. The effects of paricalcitol on COX-2, PGE2 and its receptors were investigated.</P><P><B>Results</B></P><P>Paricalcitol pretreatment improved renal function (decreased blood urea nitrogen and serum creatinine levels), tubular necrosis and apoptotic cell death in IRI-mice kidneys. The infiltration of inflammatory cells (T cells and macrophages), and the production of proinflammatory cytokines (RANTES, tumor necrosis factor-α, interleukin-1β and interferon-γ) were reduced in paricalcitol-treated mice with IRI. Paricalcitol up-regulated COX-2 expression, PGE2 synthesis and mRNA expression of receptor subtype EP4 in post-ischemic renal tissue. The cotreatment of a selective COX-2 inhibitor with paricalcitol restored functional injury and tubular necrosis in paricalcitol-treated mice with IRI.</P><P><B>Conclusions</B></P><P>Our study demonstrates that paricalcitol pretreatment prevents renal IRI via the inhibition of renal inflammation, and the up-regulation of COX-2 and PGE2 is one of the protective mechanisms of paricalcitol in renal IRI.</P>

Tempering Behavior of TiC-Reinforced SKD11 Steel Matrix Composite

Hwang, Ji-In,Kim, Seong Hoon,Heo, Yoon-Uk,Kim, Dae Ha,Hwang, Keum-Cheol,Suh, Dong-Woo Springer-Verlag 2018 METALS AND MATERIALS International Vol.24 No.3

<P>TiC-reinforced SKD11 steel matrix composite, fabricated by a pressure infiltration casting, undergoes monotonic decrease in hardness as tempering temperature increases. Element mappings by TEM-EDS and thermodynamic calculation indicate that remarkable redistribution of V between the reinforcement and the steel matrix occurs by partial dissolution and re-precipitation of MC carbides upon casting process. The absence of secondary hardening is led by the enrichment of V in the reinforcement that reduces the V content in the steel matrix; this reduction in V content makes the precipitation of fine VC sluggish during the tempering.</P>

유창성장애 치료 기법에 대한 언어재활사의 인식조사

류철민(Cheol Min Lyu),정석연(Seok Yeon Jeong),조명희(Myoung Hee Jo),강호곤(Ho Gon Kang),황현주(Hyun Ju Hwang),이일금(Il Keum Lee),김효정(Hyo Jung Kim) 한국언어치료학회 2020 한국언어치료학회 학술발표대회 논문집 Vol.2020 No.11

광대역 원형편파 스피드론 프랙탈 유전체 공진기 시퀀셜 로테이션 배열 안테나

황동휘(Hwang Dong Hyee),임홍준(Lim Hong Jun),황금철(Hwang Keum Cheol) 한국통신학회 2021 한국통신학회 학술대회논문집 Vol.2021 No.2

본 논문은 새로운 형상의 광대역 원형편파 스피드론 프랙탈 유전체 공진기 시퀀셜 로테이션 배열 안테나를 제안한다. 원형편파 특성을 갖는 단일 스피드론 프랙탈 유전체 공진기 안테나와 시퀀셜 로테이션 급전 네트워크를 각각 설계하고 결합하여 광대역 원형편파 스피드론 프랙탈 유전체 공진기 시퀀셜 로테이션 배열 안테나를 설계 및 제작하였다. 제안된 안테나의 3 dB 축비 대역폭은 29.18%(2.02-2.71 GHz)로 넓은 대역폭 특성을 갖고 있고, 3 dB 축비 대역폭 내에서 최대 이득은 12.66 dBic 로 고이득 특성을 보였다.

Scale-up and optimization of HfO₂-ZrO₂ solid solution thin films for the electrostatic supercapacitors

Kim, Keum Do,Lee, Young Hwan,Gwon, Taehong,Kim, Yu Jin,Kim, Han Joon,Moon, Taehwan,Hyun, Seung Dam,Park, Hyeon Woo,Park, Min Hyuk,Hwang, Cheol Seong unknown 2017 Nano energy Vol.39 No.-

<P><B>Abstract</B></P> <P>To date, the high energy storage performances observed in the field-induced ferroelectric HfO<SUB>2</SUB>- or ZrO<SUB>2</SUB>-based films have had an obstacle to scale-up due to the involvement of low-k monoclinic phase at the large thickness (> ~ 10nm). Considering that the monoclinic phase formation is closely related with the in-situ (partial) crystallization during the atomic layer deposition (ALD) process, in this work, the ALD temperature of Hf<SUB>0.5</SUB>Zr<SUB>0.5</SUB>O<SUB>2</SUB> thin films was lowered, and its influence on the energy storage performances was systematically examined. Carbon and nitrogen dopants incorporated at a low deposition temperature in combination with grain size decrease change the polymorphism of Hf<SUB>0.5</SUB>Zr<SUB>0.5</SUB>O<SUB>2</SUB> thin film from the genuine ferroelectric to field-induced (incipient) ferroelectric crystal structure. The Hf<SUB>0.5</SUB>Zr<SUB>0.5</SUB>O<SUB>2</SUB> thin film deposited at 210°C shows improved resistance to degradation by monoclinic phase involvement up to ~ 40nm compared to the previously-reported Hf<SUB>0.3</SUB>Zr<SUB>0.7</SUB>O<SUB>2</SUB> thin films. By investigating Hf<SUB>0.5</SUB>Zr<SUB>0.5</SUB>O<SUB>2</SUB> thin films with wide ALD temperature and thickness ranges, energy storage density of ~ 55Jcm<SUP>−3</SUP> with an efficiency of ~ 57% can be achieved at the ~ 7.1nm Hf<SUB>0.5</SUB>Zr<SUB>0.5</SUB>O<SUB>2</SUB> thin films deposited at 215°C. The performance can be retained even after 10<SUP>10</SUP> bipolar switching cycles, and the film endures thermal stress up to 175°C without severe degradation, demonstrating notable reliability.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The field-induced ferroelectricity was acquired from the Hf<SUB>0.5</SUB>Zr<SUB>0.5</SUB>O<SUB>2</SUB> thin film. </LI> <LI> Chemical/structural changes by the decreased deposition temperature were elucidated. </LI> <LI> The crystallization in the as-deposited state was minimized by controlling Zr content and T<SUB>dep</SUB>. </LI> <LI> The electrostatic HfO<SUB>2</SUB>-ZrO<SUB>2</SUB> capacitor were scaled-up for the large energy storage. </LI> <LI> The FFE Hf<SUB>0.5</SUB>Zr<SUB>0.5</SUB>O<SUB>2</SUB> capacitor does not degrade even after 10<SUP>10</SUP> switching cycles and up to 175°C. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>The crystallization in the as-deposited state and the resulting low-k monoclinic phase evolution were suppressed by changing the Zr content and the deposition temperature of the electrostatic supercapacitors based on the HfO<SUB>2</SUB>-ZrO<SUB>2</SUB> solid solution. While the energy storage density of the Hf<SUB>0.3</SUB>Zr<SUB>0.7</SUB>O<SUB>2</SUB> thin films deposited at 280°C drastically decreased at the large thickness due to the monoclinic phase formation (upper panel), the Hf<SUB>0.5</SUB>Zr<SUB>0.5</SUB>O<SUB>2</SUB> thin films deposited at 210°C retained the large energy storage density even up to 40nm (bottom panel), enabling the scaling-up pathway of the HfO<SUB>2</SUB>-ZrO<SUB>2</SUB> solid solution.</P> <P>[DISPLAY OMISSION]</P>

Poster Session:PS 0497 ; Nephrology : Paricalcitol Pretreatment Attenuates Apoptosis and Infl ammation in Renal Ischemia-Reperfusion Injury via Prostaglandin E2 Receptor Ep4

( Hyeon Seok Hwang ),( Keum Jin Yang ),( Sung Eun Kim ),( Ki Cheol Park ),( Hyun Soo Choi ),( Jeong Min Oh ),( Yoon Kyung Chang ),( Cheol Whee Park ),( Chul Woo Yang ),( Suk Young Kim ) 대한내과학회 2014 대한내과학회 추계학술대회 Vol.2014 No.1

Background: Paricalcitol has protective effects against renal ischemia-reperfusion (IR) injury, but the mechanism by which this occurs remains unclear. We investigated whether paricalcitol attenuates apoptosis and infi ammation in renal IR injury through the prostaglandin E2 (PGE2) receptor EP4. Methods: Human proximal tubular cell line (HK-2) was exposed to LPS and ischemia by mineral oil monolayer. Male C57BL/6 mice were subjected to 23 min of bilateral kidney ischemia and 24 h reperfusion. The effects paricalcitol pretreatment with or without antagonist was investigated in both in vitro and in vivo models. Results: Paricalcitol treatment upregulated the signaling pathway of cyclooxygenase (COX)-2 and PGE2, and it increased the expression of EP4 in HK-2 cells. Paricalcitol pretreatment prevented the HK-2 cell death induced by IR and LPS exposure, and the cotreatment of EP4-specifi c antagonist offset the cell protective effects of paricalcitol. The phosphorylation of Akt and cAMP-responsive element binding protein was increased after paricalcitol pretreatment in IR-exposed cells. EP4 antagonist blunted the phosphorylation of these cell survival signals. EP4 antagonist also reversed the inhibitory effects of paricalcitol on p65 NF-κB phosphorylation and nuclear translocation in LPS-exposed cell. In mice kidneys with IR injury, EP4 blockade restored serum creatinine levels and tubular necrosis, which was reduced by paricalcitol pretreatment. Decreased TUNEL-positive cells, decreased Bax levels and increased Bcl-2 expression were observed in paricalcitol-treated mice kidney with IR injury. These apoptotic effects of paricalcitol were abolished by EP4 antagonist. Paricalcitol attenuated the infiltration of infiammatory cells (T-cells and macrophages) and the production of proinfi ammatory cytokines (RANTES, tumor necrosis factor-a, interleukin-1ß and interferon- γ, MIP-1a). The cotreatment with EP4 antagonist reversed the infi ammatory cells infi ltration and proinfi ammatory cytokines expressions. Conclusions: Paricalcitol attenuates apoptosis and infi ammation through the EP4 dependent pathway in renal IR injury.