• International Journal of Fuzzy Logic and Intelligent Systems
• /
• v.13 no.3
• /
• pp.186-199
• /
• 2013

We pose pattern classification as a density estimation problem where we consider mixtures of generative models under partially labeled data setups. Unlike traditional approaches that estimate density everywhere in data space, we focus on the density along the decision boundary that can yield more discriminative models with superior classification performance. We extend our earlier work on the recursive estimation method for discriminative mixture models to semi-supervised learning setups where some of the data points lack class labels. Our model exploits the mixture structure in the functional gradient framework: it searches for the base mixture component model in a greedy fashion, maximizing the conditional class likelihoods for the labeled data and at the same time minimizing the uncertainty of class label prediction for unlabeled data points. The objective can be effectively imposed as individual mixture component learning on weighted data, hence our mixture learning typically becomes highly efficient for popular base generative models like Gaussians or hidden Markov models. Moreover, apart from the expectation-maximization algorithm, the proposed recursive estimation has several advantages including the lack of need for a pre-determined mixture order and robustness to the choice of initial parameters. We demonstrate the benefits of the proposed approach on a comprehensive set of evaluations consisting of diverse time-series classification problems in semi-supervised scenarios.

• Proceedings of the Korean Magnestics Society Conference
• /
• 2012.11a
• /
• pp.172-172
• /
• 2012

A Pt-skin $Pt_3Ni$(111) surface was reported to show high catalytic activity. In this study, we investigated the magnetic properties and electronic structures of the various oriented surfaces of bulk-terminated and Pt-segregated $Pt_3Ni$ by using a first-principles calculation method. The magnetic moments of Pt and Ni are appreciably enhanced at the bulk-terminated surfaces compared to the corresponding bulk values, whereas the magnetic moment of Pt on the Pt-segregated $Pt_3Ni$(111) surface is just slightly enhanced because of the reduced number of Ni neighboring atoms. Spin-decomposed density of states shows that the dz2 orbital plays a dominant role in determining the magnetic moments of Pt atoms in the different orientations. The lowering of the d-band center energy (-2.22 eV to -2.46 eV to -2.51 eV to -2.65 eV) in the sequence of bulk-terminated (100), (110), (111), and Pt-segregated (111) may explain the observed dependence of catalytic activity on surface orientation. Our d-band center calculation suggests that an observed enhanced catalytic activity of a $Pt_3Ni$(111) surface originates from the Pt-segregation.

• Bulletin of the Korean Chemical Society
• /
• v.35 no.3
• /
• pp.899-904
• /
• 2014

The atomic structures and electronic properties of six classical and nonclassical $H_2O$@$C_{24}$ fullerene regioisomers are systematically studied using the hybrid density functional B3LYP method and M06-2X method with empirical dispersion in conjunction with the 6-31G(d,p) basis sets. The charge transfer, frontier orbitals, dipole moment, energy gap between the HOMO and LUMO, and volume change of the $C_{24}$ cage are analyzed upon encapsulation of a $H_2O$ molecule in each $C_{24}$ regioisomer. All encapsulation processes are endothermic and the relative stabilities of six $C_{24}$ fullerene regioisomers change upon encapsulation of $H_2O$.

• Journal of the Korean Magnetics Society
• /
• v.25 no.4
• /
• pp.106-110
• /
• 2015

We have studied electronic and magnetic structure of 2 kinds of diiron molecules using OpenMX method based on density functional method. The calculated density of states of diiron-2 is similar with that of diiron-4 because of equal number of 6 ligand atoms. The calculated total energy with antiferromagnetic spin configuration is lower than those of ferromagnetic configurations for both of them. The exchange interaction J of diiiron-4 between $Fe^{+3}$ atoms is one order larger than that of diiron-2, and the calculated J matches well with the experimental one. That comes from the short distance of Fe-O and the high O 2p energy levels. It derives a strong super exchange interaction. The angle of diiron-4 between Fe atoms is bigger than that of diiron-2. It also derives a strong super exchange interaction because of the ${\sigma}$-bond between Fe and O atoms.

• Journal of Sensor Science and Technology
• /
• v.24 no.6
• /
• pp.385-391
• /
• 2015

In this paper, we propose a new method to infiltrate $Fe_3O_4$-nanoparticles into a porous silicon film and a monitoring technique to detect packing density of nanoparticles within the film. Recently, research to use porous silicon as a drug carrier or a new functional sensor material by infiltrating $Fe_3O_4$-nanoparticles has been extensively performed. However, it is still necessary to enhance the packing density and to develop a monitoring technique to detect the packing density in real time. In this light, we forcibly injected a nanoparticle solution into a rugate-structured free-standing porous silicon (FPS) film by applying a pressure difference between the two sides of the film. We found that the packing density by the pressure-infiltration method proposed in this paper is enhanced, relative to that by the previous diffusion method. Moreover, a continuous shift in wavelength of the rugate reflectance peak measured from the film surface was observed while the nanoparticle solution was being injected. By exploiting this phenomenon, we could qualitatively monitor the packing density of $Fe_3O_4$-nanoparticles within the FPS film with the injection volume of the nanoparticle solution.

• Proceedings of the Korean Magnestics Society Conference
• /
• 2004.12a
• /
• pp.219-220
• /
• 2004

Superparamagnetic regions and magnetic anisotropic properties in randomly orientated Co nano dots(NDs) were investigated as a function of dot diameter, spacing, and density. The Co NDs were fabricated by intentionally exposing a laser source on ultra thin film. Various dot sizes are ultimately realized by changing laser power, scan condition, and intial film thickness. Magnetic hysteresis loops, angle-dependent magnetization, and temperature dependence magnetization of the Co NDs were measured with a superconducting quantum interference device. The analysis of magnetization and hysteresis loops was effectively used to determine superparamagnetic regions of the Co NDs. Up to now, the experimentally observed results repeal that room temperature superparamagnetic limit of our Co NDs was about 30 nm in diameter, with the confirmation of high resolution transmission electron microscope.

• Proceedings of the Korean Magnestics Society Conference
• /
• 2011.06a
• /
• pp.129-129
• /
• 2011

The limited understanding of the surface properties of $Pt_3Ni$ for the oxygen reduction reaction (ORR) in polymer electrolyte membrane fuel cell (PEMFC) has motivated the study of properties and electronic structures of seven layered $Pt_3Ni$ (001), (110), and (111) surfaces. The first principle method based on density functional theory (DFT) is carried out. It is found that the bulk $Pt_3Ni$ has a ferromagnetic ground state with the ordered fcc type L12 structure, which is in good agreement with other results. Non magnetic Pt has the induced magnetic moment due to the strong hybridization between 3d Ni and 5d Pt. The magnetic moment of Pt and Ni enhanced on the surface of each due to surface effect however the magnetic moment of surface Pt in the Pt-segregated Pt3Ni (111) decreased and the magnetic moment of Ni in Ni rich subsurface increased significantly. The calculated d band centers of Pt explain the possibilities for oxygen absorption and play the important roles in altering the catalytic properties. The spin polarized densities of states are presented in order to understand physical properties of Pt in different surfaces in detail.

• Proceedings of the Korean Magnestics Society Conference
• /
• 2011.12a
• /
• pp.14-14
• /
• 2011

Limited understanding of the surface properties of $Pt_3Ni$ for the oxygen reduction reaction (ORR) in polymer electrolyte membrane fuel cell (PEMFC) has motivated the study of magnetic properties and electronic structures of Pt segregated $Pt_3Ni$ (111) surface during adsorption of oxygen molecule on it. The first principle method based on density functional theory (DFT) is carried out. Nonmagnetic Pt has induced magnetic moment due to strong hybridization between Ni 3d and Pt 5d. It is found that an oxygen molecule prefers bridge site with Pt rich subsurface environment for adsorption on the surface of Pt segregated $Pt_3Ni$ (111). It is seen that there is very small charge transfer from $O_2$ to Pt. The curve of energy versus magnetic moment of the oxygen explains the magnetic moments in transition states. We found the dissociation barrier of 1.07eV significantly higher than dissociation barrier 0.77eV on Pt (111) suggesting that the dissociation is more difficult on Pt segregated $Pt_3Ni$ (111) surface. The spin polarized densities of states are presented in order to understand electronic structures of Pt and $O_2$ during the adsorption in detail.

• Journal of the Korean Vacuum Society
• /
• v.4 no.S2
• /
• pp.75-78
• /
• 1995

Gas source molecular beam epitaxy have been used in the growth of InAlAsAnGaAs MSM-PD structure, in which InAlAs ultra thin layer was used as Schottky barrier enhancement material. High performance MSM-PDs have been constructed on the grown wafer. High breakdown voltage of >30V, low dark current density of $3pA/\mu \textrm{cm}^2$ at 10V bias and fast transient response of <20ps rise time / <40ps FWHM have been measured, which confirm the results that GSMBE is a superior method for the growth of materials with high layer and interfacial quality, especially for InP based InAIAdInGaAs system.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2013.08a
• /
• pp.137-137
• /
• 2013

The most stable adsorption structures and their corresponding energies of 4-pyridone, 4-hydroxypyridine, 2-pyridone and 2-hydroxypyridine have been investigated by Density Functional Theory (DFT) calculation method and high-resolution photoemission spectroscopy (HRPES). We confirmed that between the two reaction centers of 4- and 2-pyridone, only O atom of carbonyl functional group can act as a Lewis base and thus, O dative bonding structure is the most stable. On the other hand, we clarified that both the two reaction centers (the cyclic N atom and the O atom of hydroxyl functional group) of 4- and 2-hydroxypyridine (tautomers of 4- and 2-pyridone) can successfully function as a Lewis base. Through the interpretation of the N 1s and O 1s core level spectra obtained using HRPES, we could confirm the electronic structures and bonding configurations of these molecules with a coverage dependence on the Ge(100) surface.