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Sungmin Cho,Wanjin Chung 한국자동차공학회 2019 International journal of automotive technology Vol.20 No.Supp
Surface deflection is a phenomenon that causes fine wrinkles on the outer surfaces of sheet metal and deteriorates product external appearance. It is quantitatively defined as the difference between the section curve of the sheet and the ideal curve. In this study, using neural networks, a prediction model for surface deflection according to material properties was constructed and combined with a genetic algorithm; the combination of the material properties was studied to predict the minimum surface deflection. Because of the limited number of simulation data, neural networks were developed using several sampling methods such as central composite design, Latin hypercube sampling, and random sampling. In the training of the neural networks, the optimal hyper-parameter of the neural network was found automatically using Latin hypercube sampling. In conclusion, for prediction of surface deflection in rectangular embossing, neural networks made by central composite design showed the best performance. In addition, it was confirmed that the procedure of combining automatic training of a neural network and the genetic algorithm accurately predicted the set of material properties that generates the minimum surface deflection. Also, the quantity of surface deflection predicted by the neural network was very close to that predicted by finite element analysis.
Model Predictive Control with Cross-Product Term between State and Input
Sungmin Cho,Masatsugu Otsuki,Takashi Kubota 제어로봇시스템학회 2018 제어로봇시스템학회 국제학술대회 논문집 Vol.2018 No.10
Model Predictive Control (MPC) is one of control methods for the discrete time system. The optimum input is calculated by using Linear Quadratic Regulator (LQR). In MPC, the cross-product term is generally omitted in the evaluation function for LQR. However, the effectiveness of the cross-product term for LQR is confirmed by various researches. Therefore, this paper addresses the expanded form of cross-product term applied to MPC. Simulation of zero momentum spacecraft shows that the cross-product term is effective for consideration of performance to MPC.
Acid ceramidase, an emerging target for anti-cancer and anti-angiogenesis
Sungmin CHO,Ho Jeong Kwon 대한약학회 2019 Archives of Pharmacal Research Vol.42 No.3
Sphingolipid metabolism plays an important role in determining the fate of a cell. Among several sphingolipid metabolites, ceramide is a key player in intracellular signal transduction. Ceramide is usually converted to various metabolites such as sphingomyelin, sphingosine, ceramide-1-phosphate, and glucosylceramide. If ceramide is accumulated in the cell, it induces apoptosis. On the other hand, its metabolite sphingosine is converted to sphingosine-1-phosphate (S1P), which promotes angiogenesis via G protein coupled receptor signaling. Therefore, the equilibrium in ceramide and S1P levels in cells plays an important role in angiogenesis as well as cell death. Acid ceramidase (AC) is a promising target protein in the development of multi-targeted anticancer drugs as its inhibition can simultaneously inhibit angiogenesis via the Akt and ERK 1/2 pathway and limit cancer growth through ceramide-induced apoptosis. Although some inhibitors of AC have been reported, they have not been proven effective for human therapy. Recent advancement in the elucidation of AC structure will facilitate the development of better inhibitors for treating human diseases.
The Chinese Perspectives of the Korean Unification: Evidence from the Chinese Academic Publications
Sungmin Cho 한국학술연구원 2020 Korea Observer Vol.51 No.4
What a re the Chinese p erspectives on Korean unification, and what a re the concerns and expectations? The English-language literature on this subject lacks citations from primary sources to claim a wide survey of Chinese perspectives. Based upon the 62 Chinese journal articles and 29 expert commentaries in Chinese, I infer a broad spectrum of Chinese thinking on the Korea unification. I find that the Chinese analysts have contemplated a relatively more moderate approach to managing the Korean unification process with the US than often assumed outside China. In this context, I argue that there is a room for negotiation to enhance the crisis-management mechanism with China on the affairs of Korean unification. This article contributes to broadening the extant body of knowledge on the China-Korean Peninsula relations by identifying the breadth of the Chinese views on the Korean unification.
Sungmin Cho,Dongkyu Kim,Yeongkyu Yun,Jeongyeon Lee,Taeshik Earmme,SungYong Seo,Choongik Kim 한국공업화학회 2020 Journal of Industrial and Engineering Chemistry Vol.92 No.-
Solid polymer electrolyte gate dielectric based on cross-linked poly(ethylene oxide) (CPEO) was developed and employed for organic thin-film transistors (OTFTs). Mechanical stability, high areal capacitance, and amorphous morphology of CPEO were achieved via the use of polyhedral oligomeric silsesquioxane (POSS) as cross-linker, dissolved ion [EMIM][TFSI] as electrolyte, and PEO with low molecular weight as polymer matrix, respectively. The resulting solid polymer electrolyte showed excellent insulating properties with low leakage current density (1.8 × 10−7 A cm−2 at 1 V) and high capacitance per area (∼ 1 μF cm−2 at 100 Hz). Furthermore, dielectric properties of the developed polymer electrolytes including ionic conductivity as well as segmental relaxation time were investigated. The polyelectrolyte dielectric was employed for bottom-gate/top-contact organic thin-film transistors and the resulting devices showed decent electrical performance with a carrier mobility of 0.12 (±0.03) cm2 V−1 s−1 and a current on/off ratio of 103 at low operating voltage of 5 V.
A Study on Optimization of Tooth Micro-geometry for Wind Turbine High Speed Stage Helical Gear Pair
Sungmin Cho(조성민),Do-Young Lee(이도영),Laesung Kim(김래성),Sangpil Cho(조상필),Sung-ki Lyu(류성기) 한국기계가공학회 2014 한국기계가공학회지 Vol.13 No.5
The wind industry grew in the first decade of the 21st century at rates consistently above 20% a year. For wind turbine, gearbox failure can be extremely costly in terms of repair costs, replacement parts, and in lost power production due to downtime. In this paper, gear tooth micro-modification for the high speed stage was used to compensate for the deformation of the teeth due to load and to ensure a proper meshing to achieve an optimized tooth contact pattern. The gearbox was firstly modeled in a software, and then the various combined tooth modification were presented, and the prediction of transmission under the loaded torque for the helical gear pair was investigated, the normal load distribution and root stress were also obtained and compared before and after tooth modification under one torque. The simulation results showed that the transmission error and normal load distribution under the load can be minimized by the appropriate tooth modification. It is a good approach where the simulated result is used to improve the design before the prototype is available for the test.
NUMERICAL DISCRETIZATION OF A POPULATION DIFFUSION EQUATION
SUNGMIN CHO,DONGHO KIM,MI-YOUNG KIM,EUN-JAE PARK 한국산업응용수학회 2010 Journal of the Korean Society for Industrial and A Vol.14 No.3
A numerical method is proposed and analyzed to approximate a mathematical model of age-dependent population dynamics with spatial diffusion. The model takes a form of nonlinear and nonlocal system of integro-differential equations. A finite difference method along the characteristic age-time direction is considered and primal mixed finite elements are used in the spatial variable. A priori error estimates are derived for the relevant variables.
A NONCONFORMING PRIMAL MIXED FINITE ELEMENT METHOD FOR THE STOKES EQUATIONS
Cho, Sungmin,Park, Eun-Jae Korean Mathematical Society 2014 대한수학회보 Vol.51 No.6
In this article, we propose and analyze a new nonconforming primal mixed finite element method for the stationary Stokes equations. The approximation is based on the pseudostress-velocity formulation. The incompressibility condition is used to eliminate the pressure variable in terms of trace-free pseudostress. The pressure is then computed from a simple post-processing technique. Unique solvability and optimal convergence are proved. Numerical examples are given to illustrate the performance of the method.