물과 R-113에서의 와이어붙이관의 풀 비등 성능 ( Pool Boiling Performance of Wire-wrapped Tubes )

김정식,김내현 대한기계학회 1993 대한기계학회 춘추학술대회 Vol.- No.-

염을 이용한 Sr 페라이트의 분말합성과 그의 자성특성

김정식,김시동,Kim, Jung-Sik,Kim, Si-Dong 한국세라믹학회 2005 한국세라믹학회지 Vol.42 No.10

In this study we prepared the Sr-ferrite powders and magnet by a molten salt method using the (NaCl+KCl) salt mixture. Starting materials of $Fe_{2}$$O_{3}$ and Sr$Co_{3}$ were mixed as the molar ratio of 5.70:1, and 0.08 mol$ \% $ $Al_{2}$$O_{3}$, 0.10 mo1$ \% $ Si$O_{2}$ and 0.12 mo1$ \% $ CaO were added as additives. Sr-ferrite powders synthesized at the reaction temperatures of 800$\∼$1200$ ^{\circ}C $ showed the typical M-type hexagonal ferrite phase, and hexagonal plate-like morphology with uniform distribution of 1$\∼$3 $\mu$m particle size. The bulk density of the sintered Sr-ferrite magnet prepared with powders by the molten salt method showed the maximum density of 4.82 g/$cm^{3}$ at the sintering temperature of 1200$^{\circ}C $. The maxima of remanent flux density (Br, 45 emu/g) and coercive force (iHc, 3.75 kOe) occurred at the sintering temperatures of 1150$ ^{\circ}C$ and 1200$^{\circ}C $.

경내경정맥 간내문맥간정맥 단락술

이창수,김홍,김정식 啓明大學校 醫科大學 1998 계명의대학술지 Vol.17 No.1

TIPS는 문맥 고혈압을 효과적으로 감압시킬 수 있는 비교적 안전한 시술법이며 내시경 치료에 실패한 위식도 정맥류의 출혈등 적절한 적응증에 사용될 경우 생명 유지 시술로 유용하며 궁극적인 간이식수술을 고려할 경우 적절한 장기를 구할 때까지 환자가 출혈에 의해 사망하지 않도록 시간 여유를 가질 수 있게 하나 장기 추적시 TIPS후 간성 뇌변증의 빈도가 증가하고 협착이나 폐색에 의한 재출혈의 가능성이 있으므로 정기적인 추적검사가 필요하다.

귀금속 첨가에 의한 나노 (Ni, Zn)-페라이트의 $CO_2$분해 향상

김정식,안정률,강계명,Kim, Jeong-Sik,An, Jeong-Ryul,Gang, Gye-Myeong 한국재료학회 2001 한국재료학회지 Vol.11 No.10

In the present study, nano-size powders of ternary ferrites, $Ni_{0.5}Zn_{0.5}Fe_2O_4$, as the potential catalysts of $CO_2$decomposition, were prepared by the wet processing of hydrothermal synthesis and coprecipitation method, and the catalyzing effects of impregnation of the noble metals, Pt and Pd, onto $Ni_{0.5}Zn_{0.5}Fe_2O_4$for the $CO_2$decomposition were investigated. XRD results of the synthesized ferrites showed a typical spinel structure of ferrite and the particle size was very small as about 6~10 nm. BET surface area of the ternary ferrites was not affected by the impregnation of Pt and Pd. The reactivity of the $CO_2$decomposition to carbon was improved by the impregnation of the noble metals of Pd and Pt. The effect of Pd-impregnation on the $CO_2$decomposition rate was higher than Pt-impregnation.

DCT계수의 재배열을 통한 웨이브렛 변환 형식의 정지 영상 부호화

김정식,김응성,이근영,Kim, Jeong-Sik,Kim, Eung-Seong,Lee, Geun-Yeong 대한전자공학회 2001 電子工學會論文誌-SP (Signal processing) Vol.42 No.3

DCT(Discrete Cosine Transform)는 공간 영역과 주파수 영역을 균등하게 분할함으로써 인간의 시각특성을 제대로 반영하지 못하는 단점이 있다. DCT의 영역 분할에 대한 단점을 극복할 수 있는 알고리듬으로 웨이브렛 변환을 이용하여 영상을 부호화하는 여러 가지 기법들이 있지만, 본 논문에서는 DCT와 웨이브렛 변환의 장점을 결합한 새로운 알고리듬을 제안한다. 제안 방법은 DCT의 DC 계수에 에너지 집중도가 좋은 장점을 효과적으로 이용함과 더불어 이들 계수들을 웨이브렛 변환 형식에 적용한다. 웨이브렛 상의 대역간 상관 관계와 대역내 상관 관계를 동시에 효율적으로 이용하고 각 대역 특성별로 양자화를 수행하며, 부호화 방법에 대해서도 중요 계수 정보·지 양자화 계수들은 대칭적인 분포를 나타내며 절대값이 커질수록 발생확률이 감소하는 특징을 이용하여 알고리듬이 간단하고 복호화 시간이 빠른 장점을 가지는 대칭적 양방향 트리 구조의 새로운 방법을 제시한 전지 영상 압축 부호화 알고리듬을 제안하였다. JPEG 알고리듬과 제안 알고리듬을 비교하였을 때, 동일한 비트율에서 제안 알고리듬이 객관적 화질뿐만 아니라 주관적으로도 높은 화질의 영상을 얻을 수 있었다. Since DCT algorithm divides an image into blocks uniformly in both the spatial domain and the frequency domain, it has a weak point that it can not reflect HVS(Human Visual System) efficiently To avoid this problem, we propose a new algorithm, which combines only the merits of DCT and wavelet transform. The proposed algorithm uses the high compaction efficiency of DCT, and applies wavelet transform mode to DCT coefficients, so that the algorithm can utilize interband and intraband correlations of wavelet simultaneously After that, the proposed algorithm quantizes each coefficient based on the characteristic of each coefficient's band. In terms of coding method, the quantized coefficients of important DCT coefficients have symmetrical distribution, the bigger that value Is, the smaller occurrence probability is. Using the characteristic, we propose a new still image coding algorithm of symmetric and bidirectional tree structure with simple algorithm and fast decoding time. Comparing the proposed method with JPEG, the proposed method yields better image quality both objectively and subjectively at the same bit rate.

로렌츠 다양체상에서 쟈코비안의 비교 정리

양기열,김삼태,김정식 順天大學校 1998 論文集 Vol.17 No.1

본 논문에서는 두 로렌츠 다양체 위에서 자코비안을 정의하고, 각 Ricci 곡률과 평균곡률의 조건이 주어질 때 두 자코비안의 크기를 비교하였으며 이 결과를 이용하여 [9]에서 증명한 Rauch 비교 정리도 간단히 증명 하였다. In this paper, we will define the Jacobian along the unit speed future directed timelike geodesic segment perpendicular to the spacelike submanifold N and present the comparison of Jacobians under assumption on the curvatures such as the extension of the Rauch comparison theorem for timelike geodesics[9].

제철소의 연소배가스 $CO_2$ 분해용 (Ni, Zn)-ferrite 미세분말 합성공정 연구

김정식,안정률 한국세라믹학회 2000 한국세라믹학회지 Vol.37 No.2

Flue gases in the iron foundry consist of 15~20% CO2 as an air pollution gas whose emission should be mitigated in order to protect the environment. In the present study, ultrafine powders of NixZn1-xFe2O4 as a potential catalyst for the CO2 decomposition were prepared by the coprecipitation methods. Oxygen deficient ferrites (MeFe2O4-$\delta$) can decompose CO2 as C and O2 at a low temperature of about 30$0^{\circ}C$. The XRD result of synthesized ferrites showed the spinel structure of ferrites and ICP-AES and EDS quantitative analyses showed the composition similar with initial molar ratios of the mixed solution prior to reaction. The BET surface area of the (Ni, Zn)-ferrites was about 77~89.5$m^2$/g and their particle size was observed about 10~20 nm. The CO2 decomposition efficiency of the oxygen deficient (Nix, Zn1-x)-ferrites was the highest at x=0.3, and the ternary (Ni, Zn)-ferrites was better than that of binary Ni-ferrites.

도시부 소형차 전용 지하도로 피난연결통로 간격에 관한 연구

김정식,임준범,김도훈,오미영 한국도로학회 2021 한국도로학회논문집 Vol.23 No.3

PURPOSES : This study aims to deduce the appropriate interval of cross passage for small vehicle exclusive roads within urban underground roads to ensure safety. METHODS : This study evaluated evacuation safety by fire and evacuation simulations. The simulation was applied to a passenger-caronly urban underground road, which was performed in the entry/exit section with a gradient of 6.0% and the mainline on level grade. The values of the variables for the simulations were determined to be close to the actual situation based on of the statistics and the results of previous studies. In the simulation scenario, the cross passage interval was visible. The evacuation safety was evaluated by comparing the “evacuation completion time” and the “smoke diffusion time.” Evacuation safety can be desirable when the evacuation completion time is shorter than the smoke diffusion time. RESULTS : According to the results of the simulation, the desirable cross passage interval is 180 m for the entry/exit sections with a 6% gradient in passenger-car-only tunnels. This criterion may be prolonged to an interval of 210 m and a width of 0.9 m for the construction reduction, based on the results of the statistical analysis. CONCLUSIONS : According to the results of this study, the risk indices of the “Small Vehicles Road Tunnel Fire Safety Facility Installation and Management Guidelines” may be supplemented by the tunnel class and the gradient of the entry/exit section. In addition, the guideline may provide an improved interval of evacuation cross passage and the width of the cross passage door by the safety index.

전력수요량 예측방법에 관한 연구

김정식 한국교통대학교 2016 한국교통대학교 논문집 Vol.51 No.-

Korea has been difficult of continuous electrical supply in recent years. It happened with the lack of energy supply, which is not meet the energy demand forecast. An importance of correct electrical power demand forecasting is emphasized than ever before. In this paper, we compared with three forecasting models. moving average, least square method, and exponential smoothing method. After that, we compared with these methods and suggested appropriate forecasting model of electric energy in local city.

On C-Bochner curvature tensor of a contact metric manifold

김정식,Mukut Mani Tripathi,최재동 대한수학회 2005 대한수학회보 Vol.42 No.4

We prove that a (kappa,mu)-manifold with vanishing E-Bochner curvature tensor is a Sasakian manifold. Several interesting corollaries of this result are drawn. Non-Sasakian (kappa,mu)-manifolds with C-Bochner curvature tensor B satisfying B(xi;X)S = 0, where S is the Ricci tensor, are classied. N (kappa)-contact metric manifolds M^{2n +1} , satisfyingB (xi,X)R = 0 or B (xi,X)B = 0 are classied and studied.