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신혜경,정용식,박병기,이효진,김의화,Shin, Hye-Kyoung,Chung, Yong-Sik,Park, Pyong-Ki,Lee, Hyo-Jin,Kim, Eui-Hwa 한국섬유공학회 2006 한국섬유공학회지 Vol.43 No.6
Chitosan is the second abundant natural polymer after cellulose and shows a lot of potential functional advantages such as biodegradability, biocompatibility, antimicrobial properties etc. Cotton knit/chitosan sponge composite structures were prepared by coating chitosan solutions ($CH_3COOH$, HCI) onto the cotton knit fabrics, freezing at $-80^{\circ}C$, and Iyophilizing. Chitosan in two kinds of salts solutions was crosslinked with glutaraldehyde and citric acid prior to coating. Knit/chitosan sponge structures were transformed into the hydrogel structure when they absorbed water. 2% chitosan acetate composite crosslinked with citric acid absorbed water about 23 times of its dry weight. Weak physical properties of Iyophilized chitosan sponge were improved by forming knit/chitosan composite structure.
이정훈,정용식,소준호,김준연,장원,Lee Jung-Hoon,Chung Young-Seek,So Joon-Ho,Kim Junyeon,Jang Won 한국전자파학회 2006 한국전자파학회논문지 Vol.17 No.2
본 논문에서는 시간 영역 유한차분법(FDTD: Finite-Difference Time-Domain Method)과 설계 민감도법(design sensitivity analysis)을 이용하여 미지의 유전체 산란체(dielectric scatterer) 복원을 위한 역산란 문제(inverse scattering)의 새로운 해석 기법을 제안하였다. 본 연구에서는 빠른 수렴을 위하여 목적 함수의 도함수를 이용한 설계 민감도법을 도입하였고, 시간 영역 유한차분법으로부터 직접 설계 민감도 수식을 도출하였다. 해석의 효율성을 위하여 보조 변수법(adjoint variable method)을 도입하여 보조 변수 방정식을 도출하고 최적화 알고리듬으로 최대 경사도법을 이용하여 반복적인 추정을 통하여 미지의 유전체를 복원하였다. 본 연구의 타당성의 보이기 위하여 2차원 $TM^z$에서의 유전체 복원 사례를 제시한다. In this paper, we proposed a new algorithm of the inverse scattering for the reconstruction of unknown dielectric scatterers using the finite-difference time-domain method and the design sensitivity analysis. We introduced the design sensitivity analysis based on the gradient information for the fast convergence of the reconstruction. By introducing the adjoint variable method for the efficient calculation, we derived the adjoint variable equation. As an optimal algorithm, we used the steepest descent method and reconstructed the dielectric targets using the iterative estimation. To verify our algorithm, we will show the numerical examples for the two-dimensional $TM^2$ cases.
Laguerre 다항식을 이용한 전송 선로의 시간 영역 BLT 방정식 해석
이윤주,정용식,소준호,신진우,천창율,이병제,Lee, Youn-Ju,Chung, Young-Seek,So, Joon-Ho,Shin, Jin-Wo,Cheon, Chang-Yul,Lee, Byung-Je 한국전자파학회 2007 한국전자파학회논문지 Vol.18 No.9
본 논문은 Laguerre 다항식을 이용하여 BLT 방정식을 시간 영역에서 해석하는 방법을 제안한다. 본 논문은 Laguerre 다항식의 재귀적 성질과 미분 및 적분 등의 특성을 이용하여 시간 영역에서의 전송 선로의 BLT 방정식해를 구하였다. 위의 해석 방법을 저항과 커패시터가 부하로 있는 2선 전송 선로에 적용하여, 외부에서 평면파펄스가 인가되었을 때의 각 전송 선로 종단에서의 전압의 파형을 주파수 영역의 BLT 결과를 IFFT한 값과 비교함으로 정확성을 확인하였다. In this paper, we propose the method to solve the BLT equations using Laguerre polynomials in time domain. The solution of BLT equations is obtained by recursive, differential and integral properties of Laguerre polynomials. The verification of the proposed method is tested by applying it to the two-wired transmission line with resistors and capacitors, which is illuminated by the electromagnetic plane wave pulse. And the result is compared with the corresponding transient responses obtained from inverse fast Fourier transform(IFFT) of the frequency domain solutions of BLT equations.
그래핀 산화물/알지네이트 기반 그라파이트 섬유의 제조 및 특성
임나영,심진태,정용식,Lim, Na-Young,Shim, Jin-Tae,Chung, Yong-Sik 한국섬유공학회 2018 한국섬유공학회지 Vol.55 No.6
Graphene oxide can be prepared from graphene by introducing hydrophilic functional groups to facilitate dispersion in water. This process has attracted significant attention for production of fillers for polymer composite materials. Alginate is a natural polymer that can be used as a composite fiber matrix that is industrially applicable and is currently being studied for the development of novel materials. Graphene oxide/alginate composite fibers were prepared with various graphene oxide contents by wet spinning in a calcium chloride coagulation solution. To improve thermal and electrical properties, the graphene oxide/alginate fibers were reduced using hydrogen iodide and acetic acid. After low temperature carbonization over a graphite nickel catalyst, the yield of the carbonized alginate precursor increased from 20.3% to 36.1% upon addition of graphene oxide. After reduction and carbonization, XRD analysis showed the presence of a $2{\theta}=26.4^{\circ}$ peak arising from the (002) plane of the graphite structure. In addition, electrical conductivity increased from 225 to 13575 S/m, indicating that the composite fibers successfully incorporated graphite.
박제기,김동환,정용식,김환철,Park, Jac-Ky,Kim, Dong-Hwan,Chung, Yong-Sik,Kim, Hwan-Chul 한국섬유공학회 2009 한국섬유공학회지 Vol.46 No.4
PVA/collagen blend fibers were produced by air-gap spinning method, and were successfully spun to blend fiber. Maximum collagen content to produce the fiber was 30%, above which the fiber was found to be broken in the drawing process. Thermal and mechanical properties of the fibers were investigated by changing blend ratios of the PVA to collagen. Melting point of PVA was decreased with the increase of the amount of collagen. The strength and the elongation of the fiber were also decreased due to the inhomogeneous structure of the blend fiber. Hot water resistance was endowed by the heat treatment after drawing process, and when the fiber was treated at $230^{\circ}C$ for 10 minutes, it was neither swelled nor broken in boiling water.