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머신러닝 알고리즘을 결합한 협업필터링 개인화 추천시스템 응용연구
김재식,김범수 한국경영과학회 2024 經營 科學 Vol.41 No.1
This study proposes a new personalized recommendation system by combining collaborative filtering model with machine learning algorithms from the Random Forest and K-means clustering methods. It presents a solution to the traditional issues of collaborative filtering such as data sparsity, cold start problem, increased computational complexity, and difficulties in applying big data. We reduce the dimension of the data-matrix greatly, by first utilizing methods from the Random Forest model to predict user preferences for product categories, and in turn using these predictions as a basis for forming groups of users with similar preferences through k-means clustering. We demonstrate the practical applicability and effectiveness of the recommendation system with real-world big data from an actual e-commerce company. With our proposed method we were able to create a user specific recommendation system based on the entire dataset of over 7 million transactions with 214,638 unique items, all the while greatly improving computational efficiency by only using 221MB of memory. The results of our study suggest that our proposed collaborative filtering approach combined with machine learning algorithms offers a different perspective in the development of collaborative filtering based recommendation systems, providing new groundwork for future research.
소결온도에 따른 (1-x)Mg4Ta2O9-xTiO2(x=0, 0.3, 0.4) 세라믹스의 마이크로파 유전특성
김재식,최의선,이문기,이영희 대한전기학회 2004 전기학회논문지C Vol.53 No.2(C)
The microwave dielectric properties and microstructure of the (1-x)Mg4Ta2O9-xTiO2(x=0, 0.3, 0.4) ceramic were investigated. The specimens were prepared by the conventional mixed oxide method with sintering temperature of 1350℃~1425℃. According to the XRD patterns, the (1-x)Mg4Ta2O9-xTiO2(x=0, 0.3, 0.4) ceramics have the Mg4Ta2O9 phase(hexagonal). The dielectric constant(εr) and density increased with sintering temperature and mole fraction of x. To improve the quality factor and the temperature coefficient of resonant frequency, TiO2(εr = 100, Q×fr = 40,000GHz, τf = +450 ppm/℃) was added in Mg4Ta2O9 ceramics. In the case of the 0.7Mg4Ta2O9-0.3TiO2 and the 0.6Mg4Ta2O9-0.4TiO2 ceramics sintered at 1400℃ for 5hr., the microwave dielectric properties were εr = 11.72, Q×fr = 126,419GHz, τf = -31.82 ppm/℃ and εr = 12.19, Q×fr = 109,411GHz, τf = -17.21 ppm/℃, respectively.
김재식,최재호,임성수,이은규 전력전자학회 1999 전력전자학회 논문지 Vol.4 No.4
본 논문에서는 철도차량용 보조전원장치에 순시전압제어기법을 적용할 때 발생하는 문제들의 해결방안을 제시한다. 비선형부하나 과도상태에서 빠른 응답특성을 얻기 위해 순시전압제어기법을 사용할 때 LC 필터의 공진문제와 존재하는 정상상태 오차가 더욱 심각해진다. 인버터 출력측 LC 필터에 기인하는 공진현상을 억제하기 위해 전압전달함수의 제동비를 증가시키기 위한 방안으로 필터 커패시터 궤환제어기가 고려되었다. 그리고 교류전압 순시제어시 존재하는 정상상태 오차를 제거하기 위하여 고이득 전달함수를 기존의 PI 제어기에 첨가하였다. 이론적인 분석이 시뮬레이션 결과와 함께 잘 설명되어져 있다. 제안된 기법의 타당성을 5kVA급 시제품에 대한 시뮬레이션과 실험을 통하여 입증하였다. This paper presents an instantaneous voltage control scheme of au킹liary power supply system for the electric railway v vehicles, The resonance problem of the LC filter and the existing steady state error are more serious as the use of l instantaneous voltage control techniques for the fast transient response at the nonlinear load, A filter capacitor current f feedback loop is considered to increase the damping ratio of the voltage transfer function for the suppression of the resonance problem of the LC inverter output filter. To eliminate the steady state en‘or existing in case of the AC l instantaneous voltage control. the high gain transfer function is added to the conventional PI controller. The theoretical a analysis is well described with the simulation results. The validity of the proposed schemes is well verified through the s simulation and expelimental results for the 5 kVA prototype.
김재식,최의선,이문기,배선기,이영희,Kim, Jae-Sik,Choi, Eui-Sun,Lee, Moon-Kee,Bae, Sun-Gi,Lee, Young-Hie 한국전기전자재료학회 2005 전기전자재료학회논문지 Vol.18 No.1
The microwave dielectric properties of 0.6TiTe$_3$O$_{8}$-0.4MgTiO$_3$ ceramics with H$_3$BO$_3$-SnO were investigated to improve the sintering condition for the LTCC. According to the X-ray diffraction patterns, 0.6TiTe$_3$O$_{8}$-0.4MgTiO$_3$ ceramics with H$_3$BO$_3$-SnO had the columbite structure of TiTe$_3$O$_{8}$ phase and the ilmenite structure of MgTiO$_3$ phase and there were no second phase. Increasing the addition of H$_3$BO$_3$-SnO, the density and dielectric constant of the 0.6TiTe$_3$O$_{8}$-0.4MgTiO$_3$ ceramics were increased but the quality factor was decreased. The temperature coefficient of resonant frequency was shifted to the negative(-) direction with addition of H$_3$BO$_3$-SnO.EX>-SnO.