• Communications for Statistical Applications and Methods
• /
• v.31 no.5
• /
• pp.557-569
• /
• 2024

Based on the investigation of logistic regression models utilizing sparse triangulation within a compact domain in ℝ², this study addresses the limited research extending the triogram model to logistic regression. A primary challenge arises from the potential instability induced by a large number of vertices, hindering the effective modeling of complex relationships. To mitigate this challenge, we propose introducing sparsity to boundary vertices of the triangulation based on the Ramer-Douglas-Peucker algorithm and employing the K-means algorithm for adaptive vertex initialization. A second order coordinate-wise descent algorithm is adopted to implement the proposed method. Validation of the proposed algorithm's stability and performance assessment are conducted using synthetic and handwritten digit data (LeCun et al., 1989). Results demonstrate the advantages of our method over existing methodologies, particularly when dealing with non-rectangular data domains.

• Journal of the Korean Mathematical Society
• /
• v.38 no.5
• /
• pp.955-970
• /
• 2001

Two compact Riemannian manifolds are said to be isospectral if the associated Laplace-Beltrami operators have the same eigenvalue spectrum. We describe a method, based on the used of Riemannian submersions, for constructing isospectral manifolds with different local geometry and survey examples constructed through this method.

• Honam Mathematical Journal
• /
• v.27 no.2
• /
• pp.273-285
• /
• 2005

In this paper, when N is a compact Riemannian manifold, we discuss the method of using warped products to construct Lorentzian metrics on $M=[a,\;b){\times}_f\;N$ with specific scalar curvatures.

• Bulletin of the Korean Mathematical Society
• /
• v.37 no.2
• /
• pp.317-336
• /
• 2000

In this paper, when N is a compact Riemannian manifold, we discuss the method of using warped products to construct timelike or null future (or past) complete Lorentzian metrics on $M=(-{\infty},{\;}\infty){\;}{\times}f^N$ with specific scalar curvatures.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 2011.06a
• /
• pp.919-920
• /
• 2011

• Journal of the Korean Society for Industrial and Applied Mathematics
• /
• v.7 no.2
• /
• pp.75-81
• /
• 2003

Compact schemes are shown to be effective for a class of problems including convection-diffusion equations when combined with multigrid algorithms [7, 8] and V-cycle convergence is proved[5]. We apply the multigrid algorithm for an semianalytic finite difference scheme, which is desinged to preserve high order accuracy despite of singularities.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.13 no.7
• /
• pp.3140-3145
• /
• 2012

In this paper, a design method for a compact slot antenna fed by a coplanar waveguide (CPW) is studied. A T-shaped tuning stub is inserted inside a narrow rectangular slot and the slot is impedance matched to the CPW feedline by adjusting the width, length, and position of the stub. The resonance frequency is adjustable by the slot length and the antenna size can be reduced by bending the slot. The resonance frequency and impedance matching property of the compact slot antenna are similar to those of the half-wavelength slot antenna, which enables one to design compact antenna of this type with ease. A compact slot antenna for 2.45-GHz ISM band is designed, fabricated on an FR4 substrate (dielectric constant of 4.4 and thickness of 0.8 mm), and experimentally tested. The measured results agree well with the simulations, which confirms the validity of this study. The fabricated compact slot antenna shows an impedance bandwidth of 200 MHz(2.32-2.52 GHz) for a VSWR < 2, which is suitable for 2.45-GHz ISM band (2.4-2.48 GHz). The measured radiation patterns show ${\infty}$-shaped directional pattern in the E-plane and nearly omni-directional pattern in the H-plane with a peak gain of 2.0 dBi, which are similar to those of a monopole antenna. The proposed antenna is expected to be suitable for the applications as antennas for WLAN, RFID, and mobile handset.

• The Journal of the Acoustical Society of Korea
• /
• v.37 no.4
• /
• pp.248-255
• /
• 2018

It is known that the road noise on the rear seat of a hatchback type car is worse than that of a sedan type car because of the weakness on sealing structure. Therefore, a sound sealing system and sufficient absorption/insulation performance are required. In the case of a compact segment car, however, the application of the sufficient absorption and insulation materials is limited, because of the restriction on the production cost and weight of the car. In this study, we estimate the noise transmission path on the vehicle's body structure from tires and ground using the PBNR (Power Based Noise Reduction) method which is useful in quantitative measurement. Based on these results, we suggest an alternative absorption/insulation method for the better performance of rear seat road noise reduction in a compact hatchback car.

• Journal of the Korean Ceramic Society
• /
• v.34 no.1
• /
• pp.95-101
• /
• 1997

Using aluminum powder with average particle size of 22.1 $\mu$m, aluminum compact made by Pressureless Powder Packing Method showed 52% green density. The activation energy of aluminum oxidation was cal-culated from the weight change of TG, and it was varied in the range of 16~64 kJ/mol. It was found from the variation of the activation energy and the observation of the microstructure that oxidation was de-pendent on the destruction of oxide film and the melt-out of aluminum. Aluminum compact was reaction-bonded at 1000~140$0^{\circ}C$ for 4~60hrs, and oxidation was dependent on temperature rather than time. Reac-tion-bonded aluminum oxide at 140$0^{\circ}C$ for 60hrs showed 92% oxidation percent. It was sintered at 1$600^{\circ}C$ for 15hrs and the sintered body showed 62% relative density.

• Journal of the Korean Solar Energy Society
• /
• v.31 no.4
• /
• pp.9-18
• /
• 2011

This study assessed the performance of a compact heat exchanger with staggered tube banks for recuperation of high temperature exhaust thermal energy for SOFC fuel cell system. The compact heat exchanger in this study is two pass system which consists of $315{\times}202.5{\times}48.5mm^3$ and 132 tubes of $6.0mm{\Phi}$ for each heat exchanger. From experiments of the 2 pass heat exchanger system, air temperature was increased from $60{\sim}85^{\circ}C$ to $402{\sim}482^{\circ}C$ while gas temperature was decreased from $600^{\circ}C$ to $305{\sim}402^{\circ}C$ according to mass flow rates of 3.9~7.8 g/s. The experimental heat transfer rates of the heat exchanger were compared with CFD numerical solutions with the conventional ${\xi}-NTU$ method. From the comparisons, the following conclusions were obtained. For the heat exchanger system, the relative errors of heat transfer rate by CFD solution were from 7.1 to 27%, and those by ${\xi}-NTU$ method were from 0.6% to 21% compared with experimental data. From the comparisons, it can be said that both of CFD and ${\xi}-NTU$ method almost simulated to experimental data except specific conditions. Pressure drops through air tubes and gas passages were calculated with both of the CFD computation and head loss equations. The differences between them were from 14 to 22%.